CN1333871A - Method and apparatus for screening catalyst libraries - Google Patents

Abstract

Rapid screening for activities and selectivities of catalyst libraries having addressable test sites is achieved by contacting potential catalysts at the test sites with reactant streams forming product plumes at the addressable test sites. The product plumes are screened by translating a sample probe and/or the library to a position that one addressable site is in proximity to the sampling probe sample orifice and passing a portion of the reaction products through the sampling orifice forming a free jet expanded volume in at least one vacuum stage and passing a portion of the cooled and reduced pressure jet stream through an inlet orifice of a mass spectrometer for analysis. The mass spectrometric analysis may be combined with resonance enhanced multiphoton ionization methods of detection for very rapid library evaluation. Suitable reactors, microreactors, and product transfer sample microprobes for product transfer to a mass spectrometer are disclosed.

Description

Method and device for screening catalyst libraries

The present invention relates to a method for rapid screening of heterogeneous and homogeneous catalyst library activity and selectivity using a mass spectrometer. The present invention provides a method for rapid screening of gaseous, liquid or solid products from all catalyst sites in a catalyst library by combining them with selective Resonance Enhanced Multiple Photon Ionization (REMPI) using a mass spectrometer.

Solid and liquid catalysts are used in the production of large quantities of chemicals and fuels, in such a way that they can contribute significantly to economy and high living standards. The National research Committee, "catalysis of Future prospects (games to the Future)", National academy Press, Washington, D.C., 1992. Catalysts also have important environmental benefits, such as in the context of catalytic converters for internal combustion engines. However, despite their significant advantages and widespread use, the development of new and improved catalysts remains a difficult and relatively unpredictable trial and error approach. Traditionally, a single catalyst was prepared using a number of tedious and time consuming methods, and the catalytic activity was determined and evaluated, modified, re-determined and evaluated until no further modification was made. This process, despite being time consuming, has successfully found a large number of solid catalysts, Heinemann, h., "industrial catalyst history", Catalysis: science and Technology, Anderson, j.r.andboudart, m.eds., Chapter 1, Springer-Verlag, Berlin, 1981, and homogeneous liquid catalysts, Montreus, a.and Petit, f., "industrial applications of industrial catalysts" Kluwer Publishing, New York, 1988.

Combinatorial chemistry, where a large number of chemical variants are rapidly prepared, and the resulting chemical libraries are then screened for desired properties using appropriate techniques, is a particularly attractive method for finding new catalysts. Chem. eng. news, 12 feb.1996. combinatorial synthesis methods were used initially to synthesize large libraries of biological oligomers, such as peptides and nucleotides, but the creation of small molecule libraries useful for drug testing is increasing. Nielsen, j., Chem.&Indus, 902, 21 Nov.1994. Recently, the Combinatorial diversity synthesis Approach has been expanded to solid-state compounds for superconduction, Xiang, X-d, Sun, X, bridno, g, Lou, y, Wang, K-a, Chang, h, Wallace-Freedman, w.g., Chen, S-w.and Schultz, p.g., "a Combinatorial Approach to Materials Discovery" (science, 268, 1738, 1995, magneto-resistive effect, bridno, g., Chang, h, Sun, X, h.Schultz, P.G. and Xiaoing, X-D., "a Class of Cobalt Oxide magnetoresistive Materials found using Combinatorial synthesis methods (A Class of Cobalt Oxide magnetoresistive Materials Discovered using Combinatorial synthesis methods) (scientific, 270, 273, 1995 and luminescence, Wang, J., Yoo, Y., Takeuchi, I, SunX-D., Chang, H, Xiang, X-D.and Schultz, P.G.," Identification of blue fluorescent Composite Materials from Combinatorial Libraries "(Identification of blue fluorescent Composite library)," scientific (Science)279, 1712, 1998, Danielson, E.G., gold, J.H., Composite Materials from Combinatorial library, "family of blue fluorescent library," 1997, optimal for lighting, scientific and Optimization of phosphor Materials, "natural Optimization of phosphor Materials," scientific and Optimization of phosphor Materials, "scientific" 279, 1712, 1998, Danielson, E.H.944, and Optimization of phosphor, scientific, and combination of phosphor, emission of natural, emission Optimization of C.D.D., "natural Optimization of phosphor, emission of combinations of phosphor, emission, luminescence, emission of C.D.D.D. and combinations of phosphor, luminescence, emission Optimization of natural emission of phosphor, luminescence, and luminescence of luminescence, and luminescence of plants, and luminescence of the family of the ", App.Phy.Lett., 70, 3353, 1997 and Sun, X-D., Wang, K.A., Yoo, Y.Wallace-Freedman, W.G., Gao, C, Xiang, X-D, and Schultz, P.G., "Solution-Phase Synthesis of luminescent material Libraries", adv.Mater, 9, 1046, 1997. Microprobe sampling, Kassem, M., Qum, M, and Senkan, S.M. "enriched 1, 2-C bound to mass spectra₂H₄Cl₂/CH₄/O₂Chemical structure of/Ar flame fuel: the effect of microprobe cooling on chlorinated hydrocarbon flame sampling ", combus. sci. tech., 67, 147, 1989, and in situ IR, mootes, f.c., Somani, m., Annamalai, j, Richardson, j.t., Luss, d.and Wilson, r.c." Infrared temperature differential Screening methods for Heterogeneous catalyst combinatorial libraries of Heterogeneous Catalysts "," ind. eng. chem.res, 35, 4801, 1996, have been proposed, but suffer from serious deficiencies, do not have sufficient sensitivity, selectivity, spatial resolution or high throughput to screen catalyst libraries, and lack the ability to simultaneously evaluate the activity of hundreds or thousands of compounds. Service, R.F. "High Speed Materials designDesign), ", Science, 277, 474, 1997. Microprobe mass spectrometry requires sampling and transferring very small quantities of gas containing low concentrations of product species from each site, which makes this method impractical for rapid sieving. The in situ red line technique does not provide information about product selectivity, which is very important for the identification of the catalyst.

Mass spectrometry is a well-established and widely used method for determining the mass of gaseous species. This technique involves the ionization of gaseous molecules by a variety of methods, such as, by way of example, electron impact or photoionization followed by ion separation using techniques such as quadrupole mass spectrometry or time-of-flight mass spectrometry and detection of selected ions using a suitable detector. Capillary probe sampling mass spectrometry has recently been reported for screening of catalyst libraries, Cong, P.; giaquinta, d.; guan, s.; McFarland, e.; self, k.; turner, h.; and Weinberg, w.h., "a combinatorial Chemistry Approach to oxidation Catalyst Discovery and Optimization" (process ministration selection, 2nd intl.conf.micro technol., March 9-12, 1998, New orans, La., pg.118.con et al, teach that introducing a reactant gas through the annular space around the capillaries to individual library sites from which product gas flows via the capillaries to the mass spectrometry ionization zone. Cong. et al report that the measurement of 144 pool sites was completed in about 2 hours. The sample transfer rate using the capillary in the Cong, et al method is limited by the pump pressure rate allowed in the mass spectrometry chamber. Another disadvantage of capillary probe sampling is that the relatively long transfer tubing surface can cause possible adsorption and catalysis. There are a large number of unexplored binary, ternary, quaternary and higher solid state materials, organometallic species and other complex metal compounds that may all have excellent catalytic properties. The prior conventional methods have not been sufficient to rapidly synthesize and screen these large quantities of catalytic compounds. Development or more efficient and systematic methods for preparing heterogeneous and homogeneous state libraries and screening for desired catalytic performance are highly desirable. Combinatorial solid state synthesis techniques have not been used to discover new and/or improved catalysts. One important obstacle is the lack of broad applicability, sensitivity, selectivity and high throughput measurement techniques (which can be used to rapidly screen large libraries of catalysts). Catalyst screening requires the unambiguous detection of the presence of a particular product molecule in close proximity to a very small catalyst site on a large library, unlike superconducting or magnetoimpedance effects, both of which can be readily detected using conventional contact probes, or alternatively, light emission, unlike luminescence.

The present invention provides a high throughput method for rapidly screening the activity and selectivity of homogeneous and heterogeneous catalyst libraries generated by combinatorial synthesis methods. Solid and liquid catalyst libraries can be created by employing a variety of techniques, and they can contain a large number of combinations of chemical elements and compounds.

In one embodiment, the library of catalysts may be screened for activity and selectivity by high throughput screening using mass spectrometry. According to the present invention, the microreactors of the catalyst library and the direct transfer of reaction products into the mass spectrum for analysis provide a rapid screening method for the catalyst library. The technique and apparatus of the present invention, which employs a catalyst library with microreactors arranged in a monolithic structure with a free jet sampling probe to deliver reaction products to the mass spectrometer, makes it possible to screen each site for a period of about 1-5 seconds, a significant improvement over the method taught by Cong et al, above, while eliminating the possible wall effect inherent to capillary microprobe sampling.

In another embodiment, mass spectrometry can also be used in conjunction with resonance enhanced ionization of the product gas and microelectrode sieving. In the case where both screening methods are available, radiation activation can also be used to rapidly identify promising sites, and mass spectrometry can then be used to quantify yield and selectivity in more detail. Identification of a resonance enhanced multi-photon ionization signal unique to the reaction product in the radiation frequency range may not be applicable, in which case mass spectrometry methods can be used to rapidly screen catalyst libraries.

In situ detection in a reactor is by resonance enhanced multiple photon ionization with high sensitivity, specificity and real time characteristics, REMPI, in which a pulsed and tunable ionizing light source is used to selectively photoionize the desired reaction product rather than the ionized reactant and/or other background species. Photoions or photoelectrons formed by the tunable light beam in the reaction product stream resulting from the contact of the reactants with a particular catalyst reservoir site are detected by a series of microelectrodes positioned near the reservoir site. Although the present invention is described with respect to a tunable ionizing beam, any radiation beam having any energy level that promotes generation of specific photo-ions and photo-electrons may be used. If the reaction product is a solid or liquid, it may be ablated by a pulsed laser beam, followed by selective photo-ionization of the product by a suitable UV laser. By detecting several reaction product species, the method of the present invention can provide information about catalyst selectivity. The method of the present invention can be accomplished by using different light frequencies to sequentially form specific ions of different products, which REMPI signal is then converted to absolute concentration using calibration standards.

Internal calibration standards introduced with existing reaction feeds can be used to meter the reaction products, as will be readily understood by those skilled in the art. The method of the invention has wide applicability and can be used for screening the whole catalyst library simultaneously. The method of the present invention can also be used to study operating life, poison resistance, regeneration and catalyst loss in a test or during production in a chemical plant.

The method for rapidly screening the catalytic performance of a potential catalyst library of the present invention broadly comprises: forming a pool of latent catalysts having latent catalysts at a plurality of addressable sites, passing a reactant gas through the plurality of addressable sites into contact with the latent catalysts, and sieving a plume of gas of reaction products from the addressable sites, the sieving comprising translating at least one addressable site to a position proximate to an aperture of a sampling probe, and subsequently passing the reaction products through a free jet sampling probe into a mass spectrometer for analysis and by an energy level a radiation beam that promotes the formation of specific ions and electrons in the product stream, e.g., a laser beam at a frequency that promotes the formation of specific photo-ions or photoelectrons, and collecting and detecting the formed photo-ions or photoelectrons in situ in the immediate vicinity of the addressable sites by microelectrodes.

The above advantages and other features of the present invention may be better understood by reading the detailed description of the invention with reference to the drawings, in which:

FIG. 1 is a schematic diagram illustrating the principle of REMPI microelectrode detection of a product species;

FIG. 2 is a schematic diagram of a REMPI microelectrode detection illustrating the product formed by contacting a reactant with a catalyst reservoir with physical masking;

FIG. 3 is a schematic diagram of the REMPI microelectrode detection of products formed by contacting reactants with a catalyst reservoir through a dedicated reactant feed tube;

FIG. 4 is a schematic view similar to FIG. 3 with a tilted test site;

FIG. 5 is a schematic diagram of the detection of a REMPI microelectrode illustrating the product formed by the contact of the reactant stream with the catalyst reservoir via the porous site;

FIG. 6 is a schematic diagram illustrating the detection of a REMPI microelectrode of the product formed by contacting the reactant with a catalyst reservoir having a catalyst coated on a monolith structure;

FIG. 7 is a schematic of a monolithic catalyst library illustrating expansion cooling of the product for REMPI microelectrode detection;

FIG. 8 is a schematic diagram illustrating a reactor with a flat-plate solid catalyst library with row REMPI microelectrode detection;

FIG. 9 is a schematic diagram illustrating a reactor with a flat-plate solid catalyst reservoir in which reactants flow through a multi-well site with row REMPI microelectrode detection;

FIG. 10 is a top view of the reactor showing simultaneous detection of the REMPI microelectrode at all sites of FIG. 9;

FIG. 11 is a schematic diagram illustrating a reactor with an integrated solid catalyst library through which a reactant passes with REMPI microelectrode detection;

FIG. 12 is a schematic diagram illustrating a reactor with a monolithic catalyst library in which all sites are simultaneously tested for REMPI;

FIG. 13 is a schematic of a catalyst library illustrating the contact of reactants with homogeneous catalyst sites and with microelectrode detection of product REMPI;

FIG. 14 is a schematic diagram illustrating a reactor with a homogeneous catalyst library, with reactants passing through and product carrying REMPI microelectrode detection;

FIG. 15 is a schematic of a catalyst library illustrating the use of solid catalyst particles for gas distribution and catalyst contact, with product REMPI microelectrode detection;

FIG. 16 is a schematic diagram illustrating a heterogeneous catalyst library in which reactants flow through and the product is cooled by expansion for REMPI microelectrode detection;

FIG. 17 is a schematic of a catalyst library illustrating the use of an ablative laser to vaporize solid and/or liquid products for remPI microelectrode detection of the products;

FIG. 18 is a molecular beam REMPI spectrum of benzene and cyclohexane obtained by TOF-MS;

FIG. 19 is a microelectrode REMPI spectrum of benzene and cyclohexane;

FIG. 20 is a microelectrode REMPI signal obtained from site activity screening of a benzene-producing catalyst library;

FIG. 21 is a schematic representation of one embodiment of a single microreactor system of the present invention;

FIG. 22 is a schematic representation of another embodiment of a single microreactor system suitable for solution deposition in accordance with the present invention;

FIG. 23 is a schematic representation of an arrangement of microreactors in a single body;

FIG. 24 is a schematic representation of another embodiment of an arrangement of microreactors in a unitary body with a cover sheet;

FIG. 25 is a schematic illustration of a catalyst library of microreactors in a vertically stacked arrangement as shown in FIG. 24;

FIG. 26 is a schematic view of an arrangement of microreactors as shown in FIG. 24 mounted in a frame;

FIG. 27 is a schematic diagram of a block-in-frame microreactor arrangement as shown in FIG. 26 arranged in a side-by-side configuration;

FIGS. 28A and 28B schematically illustrate a schematic of combinatorial catalyst library preparation and screening according to one embodiment of the present invention;

FIG. 29 is a cross-sectional view illustrating a sampling probe having a tapered orifice for use in a sampling mode to move reaction products from a site of a catalyst library in a microreactor arrangement to a mass spectrometer for analysis;

FIG. 30 is a schematic view similar to FIG. 29 of a sampling probe having a capillary orifice and being translated;

FIG. 31 is a perspective view of a microreactor arrangement with a sampling probe single-dimensionally translated on a translation stage by the sampling probe to move portions of reaction products to a mass spectrometer combined with an activating energy beam for REMPI measurements; and

fig. 32 is a perspective view of a microreactor horizontal stack arrangement translated in two dimensions on a translation stage to measure reaction products from a catalyst library using combined mass spectrometry and REMPI.

Creation of combinatorial solid state libraries for superconducting measurements has been achieved by physical masking spray, Xiang, et al, 1995, supra, magneto resistive effect, briceono, et al, 1995, supra, and luminescence, Wang, et al, 1998, supra and Sun, et al, 1997, supra, other thin film deposition techniques are well known in the art, e.g., electron beam evaporation, Danielson, et al, 1997, supra, thermal, Miyao, t, Shishikura, i, Matsuoka, m.and Nagai, m.a. "CVD Synthesis of aluminum Supported molybdenum carbide catalysts (CVD Synthesis of aluminum Supported molybdenum carbide catalysts"), chem.lett, 121, 561, 1996, and Plasma, Kiz1, m.b.ras, s.g. "Preparation of Catalytic catalysts by Plasma orientation, reaction of Plasma orientation, c.a", Plasma orientation of Catalyst deposition techniques, e.g. deposition of pure Fe, reaction of Catalyst, reaction of carbon and deposition, etc. (for chemical vapor deposition of particles by Plasma, reaction of Catalyst, reaction of ion beam, reaction of ion, c. 1, c. 3, reaction of pure Fe, reaction of Catalyst, reaction of ion beam, reaction of carbon, reaction, c. 1, c. 2₂O₃(0001) And Fe₃O₄(001) Selective Growth and Characterization of membranes (Selective Growth and Characterization of pure epicial α -Fe₂O₃(0001)and Fe₃O₄(001) Films by plasma-Assisted Molecular Beam Epitaxy), surf.sci., 371, 358, 1997, and pulsed laser deposition, gorbouov, a.a., Pompe, w., Sewing, a.a., Gapanov, s.v., Akhsakhalyan, a.d., zaborodin, i.g., Kaskov, i.a., Klyenkov, e.b., Mozorov, a.p., salashenko, n.n., Dietsch,r., Mai, H, and Vollmar, S., "Ultrathin Film Deposition by Laser ablation with cross-beam Pulsed LaserAbslation Using cross Beams), "App. surf. Sci., 96-98, 649, 1996 and Russo, R.E., Mao, X.L., and Perry, D.L.," preparation of Catalytic Coatings by Pulsed Laser Deposition "(Make Catalytic Coatings by Pulsed-Laser Deposition)," Chemtech, 12, 14, 1994, can be used to create large libraries of solid-state catalysts. These techniques provide excellent surface chemistry control and are ideally suited to forming a broad spectrum of solid materials. Other established preparative techniques, such as coprecipitation and impregnation techniques, may also be used to generate the catalyst library. Satterfield, c.n., "Heterogeneous Catalysts in Practice", "2 nd ed.," chap.4, 87, McGraw Hill, New York, 1991. for example, a wide variety of coprecipitates can be synthesized in parallel and the resulting slurry/paste can be applied to a suitable substrate, for example, using a multi-channel pipette or solenoid jet valve, to form spatially addressable sites. Lemmo, a.v., Fisher, j.t., Geysen, h.m., and Rose, d.j, "characterization of an injection Chemical microdispenser for combinatorial library Synthesis (characterisationoff an Inkjet Chemical Micro disperpenser for combinatorial library Synthesis"), anal.chem., 69, 543, 1997. Catalyst libraries may also be prepared by impregnation of a suitable support material, such as, by way of example, porous silica or alumina, which have previously been coated onto addressable sites on a substrate using a suitable liquid solution containing the catalyst. The slurry/paste and impregnating solution applied to the substrate may then be dried and processed to prepare a suitable catalyst material. Porous catalyst libraries can also be prepared by applying a thin film of catalytic material to a porous support, such as silica or alumina, using various thin film deposition techniques as described above. An important aspect of this method is the prevention of excessive deposition to prevent the micropores from being blocked by the catalytic material. Contact of the reactants with the porous reservoir may be achieved by passing the reactants through or over the catalyst sites.

However, in evaluating catalysis, chemical composition is not the only factor determining activity. The physical properties of the surface, such as edges, corners, defects, and pore size, all contribute to determining activity. Satterfield, C.N., 1991, supra and Smith, J.M. "Chemical Engineering Kinetics", Chap.8,327-358, McGraw Hill, New York, 1981. these properties are largely determined by the procedure for preparing the catalyst. Thus, the library of film assemblies may be processed in a number of different ways to produce suitable catalytic materials, e.g., oxidation, reduction, calcination, leaching, subsequent addition of dopants and other processing methods known in the art. These different preparation methods also increase mainly the number of combinations of catalyst constituents which have to be tested to obtain the best catalyst.

Heterogeneous catalyst libraries can also be prepared using monolithic, or honeycomb structures. These materials provide parallel, uniform, straight and unconnected channels, providing an advantageous matrix for creating large catalyst libraries. Cell densities in the range of about 10 to 500 cells per square inch can be made with catalyst library sites in a variety of cell shapes and sizes. However, various cell densities outside and within the above range as desired by the customer may also be prepared. The monolithic structures may be prepared from metal or they may be formed from an inorganic dough such as magnesia-alumina silicate extruded through a die and then dried and calcined. The catalyst library may also be prepared by coating a metal monolith with an inorganic matrix, wherein the metal inlay acts as a barrier to prevent diffusion of species between cells. Which may then be followed by introduction of a catalyst into the library matrix using any of the known methods described above. The monolithic structure can also be fabricated according to the placement of the optical access and microelectrodes.

Homogeneous Catalyst libraries containing, as an example, organometallic and inorganic metal compounds and other complex molecules such as enzymes can likewise be prepared by using multichannel pipette and solenoid jet valve methods, "New catalysts and Conditions for C-H insertion reactions determined by High Throughput Catalyst Screening methods (New Catalyst and Conditions for a C-H insertion reaction identification by High Throughput Catalyst Screening)," New Catalyst and Conditions for C-H insertion reactions, "angle. These libraries may have an array of microtubes bundled together through which the reaction gas is bubbled. The homogeneous liquid catalyst may also be held or immobilized within the pores of a porous support, either in particulate form or coated on the walls of a monolithic structure. Since the sieving method of the present invention is convenient for miniaturization, the physical size of the catalyst sites that determine the density of the library is mainly based on the properties of the liquid or solid phase of the catalyst, the preparation method of the library, the diffusive mixing of the gas in the library, the thermal conductivity through the matrix of the library, the goal of the sieving process, and other relevant factors. For example, if the goal of screening is to evaluate catalytic materials for gas phase reactions using flat catalytic sites, the library density can be defined by gas phase diffusion, since at high library densities, diffusion between sites can cause signal overlap between sites. Nevertheless, evaluation of the catalyst operating temperature window requires the fabrication of a library in which each site is adiabatic to maintain a different temperature. In this case, the library density will be defined by the thermal conductivity of the substrate sheet. For liquid phase homogeneous catalysts, surface tension and viscosity play an important role in the diffusion of gases and thus determine the minimum size of the library sites and the library density.

In the present invention, the catalyst sites must be separated from each other so that the product formed at each site and its unambiguous determination can be obtained. Monolithic or honeycomb structures have the advantage of providing well-defined physically separate library sites. These and other catalyst library design factors will be discussed further in the description of the screening method. The well-defined and rapid sieving of solid catalyst sites with a size of 0.5cm by 0.5cm has been demonstrated using the present invention. These site sizes provide a catalyst library with a density of 10 sites per square inch, which allows more than 900 sites to be created on a size substrate (size of one letter) of 8.5 inches by 11 inches. Higher library density is very practical to operate with either smaller site size or by using monolithic structures. The pattern of these sites should be designed to speed up the formation and screening of the library with rows of catalyst sites, which has significant advantages for the formation and screening of these sites. Any method of preparing chemical libraries having the characteristic sites described above is suitable for preparing catalyst libraries for use in the rapid screening method for catalyst evaluation of the present invention.

In one embodiment of the invention, sampling of the reaction product from each site in the library is accomplished by passing the reaction product through a small orifice (which is located adjacent to the reaction product source) to a chamber of relatively large cross-section for delivery to a measurement device such as a mass spectrometer. A catalyst library having various locations disposed within a microreactor is shown in fig. 29, which will be further described below. Briefly, inert microreactor body 100 has a reactant feed channel 102 leading to an enlarged catalyst zone with a catalyst bed 101. The reactant gas enters the reactant gas distribution chamber 104 via the reactant gas feed channel 103 for distribution into the reactant feed channel 102. The reaction product exits the microreactor via a reaction product outlet channel 105 and exits the reactor housing 106, or alternatively, a portion may flow from a single library site to an assay device via a microsampling probe. The reactor jacket may be pressurized to provide the desired reaction pressure. Alternatively, each microreactor may be individually pressurized, the catalyst evaluated at a different pressure, or each bank of microreactors may be individually pressurized. As shown in FIG. 29, the catalyst library is fixedly mounted on a translation table 107 so that a sampling probe 108 is placed over a single library site to assay for reaction products from that site. Translation stage 107 is movable in the x-y-z direction using a computer controlled stepper motor, as is well known to those skilled in the art, to rapidly move a single library site to a position for sampling from a single site using a sampling probe 108 fixedly mounted in reactor casing 106. It is also possible to translate the sampling probe and assay system while keeping the library stationary, or the library and sampling probe may be moved simultaneously by a translator. As shown in fig. 29, a single library site has been moved to a sampling position adjacent to sampling probe 108 so that a portion of the reaction product gas flows through the sampling probe into mass spectrum 109. Reactants may flow through all of the library sites, may be operated simultaneously, and product gases from other library sites may be removed from the reactor jacket 106. After analysis of the product gas at one particular library site, the library can be translated to a position for evaluation of another catalyst site. Since many or all of the sites in a library may be simultaneously under reaction conditions, analysis of the reaction products may also be performed immediately after the library site is determined, without waiting for equilibrium conditions and without encountering delays caused by the transfer tube when using a capillary sampling probe, as described by Cong et al.

The tip of the sampling probe 108 must be made of a material that is processable and able to withstand the pressure and temperature of the reaction chamber, and also required to be inert to the reactants and reaction products if the reactor jacket 106 is pressurized. As shown in fig. 29, reactor wall 106 has a sampling cone 110 which may be integral with the reactor wall or attached to the reactor wall with a suitable seal. The sampling cone can be attached directly to the mass spectrum if the interior of the microreactor in the reactor arrangement is pressurized and the product is vented to the atmosphere. As shown, sampling cone 110 has a sampling probe extension 111 to minimize disturbance of the reaction product stream and to allow the stationary sampling probe to be positioned in close proximity to the catalyst reaction site without interfering with product gas venting. The sampling cone 110 should have a half cone angle of about 15-45 degrees so that the gas sample can be freely jet expanded into the vacuum chamber, while the sampling probe extension 111 may have a smaller cone angle. Free jet expansion in the sampling probe will allow substantial cooling and quenching of all possible homogeneous and heterogeneous reactions and molecular flow to the mass spectrometer mounted downstream of the sampling cone. The sampling cone orifice 112, which is located at the smallest end of the cone, is sized so that the reaction chamber pressure and vacuum pump capacity are compatible for all stages. Suitable sampling cone orifices have a diameter of about 1 to 200 microns, and if a moderately sized vacuum pump is used, typically about 5 to 50 microns. The expanded reaction product sample from the sampling cone flows through the first vacuum section 113 and the skimmer cone 114 to ensure that only the central portion of the reaction product sample jet can enter the mass spectrometry chamber to eliminate all surface-induced reactions that may occur within the samplingprobe. The angle and diameter of the opening of the defoaming cone tip must be adapted to meet the requirements of reaction chamber pressure and sampling probe pumping rate, which can be easily determined by one skilled in the art. The reaction product sample jet flows through the skimmer cone, then through the second vacuum section 115, and is directly input into the mass spectrometer via mass spectrometer inlet orifice 116. The mass spectrometer may be a quadrupole mass spectrometer, orA time of flight spectrometer with fast electrons to collect and process data is well known to those skilled in the art. Electron collision or radiation may be used to ionize the species. Tunable lasers may also be used to selectively ionize the reaction products under REMPI conditions. If the catalyst library is screened at atmospheric pressure, or if the microreactor arrangement is internally pressurized and the product is vented to atmosphere, then only one evacuated section may be required to prepare the sample for use under mass pressure conditions, while a catalyst library screened at high pressure may require more than two evacuated sections, as is well known to those skilled in the art. The staged vacuum process quickly reduces the reaction product from a high pressure (in some applications about 20-50 atmospheres) to a small fraction of one atmosphere so that a sample of the reaction product can be introduced directly into the mass spectrometer (the mass spectrometer pressure is typically maintained at about 10 a)^-5-10^-6Torr). If the interior of the microreactors in the arrangement is pressurized and vented to the atmosphere, this creates an evacuated section. The pressure in the final vacuum section, second section in FIG. 29, and the mass spectrometer inlet orifice diameter must be matched to the vacuumThe pressure that is limited by the evacuation rate that can be achieved by the evacuation system is matched. Typically, the pressure in the first and second sections, respectively, in a two-section system should be maintained at about 760-10 f^-2And 10^-2-10^-5And (5) Torr. The pressure in all stages should be kept the same during calibration and sieving to quantify the results of the catalyst evaluation.

The distance from the sampling probe orifice to the mass spectrum should be as short as possible to maximize detection sensitivity, since the gas concentration is 1/r when expanded into vacuum²And decreases where r is the distance from the sampling probe tip. However, too short a distance of the sampling probe aperture from the mass spectrum can reduce the evacuation rate provided by the vacuum pump, which can adversely affect the free jet sampling process. In view of these conflicting results, the distance between the sampling probe aperture and the mass spectrum depends on the need for balanced signal detection and vacuum pumping speed. Typically, the distance between the sampling probe orifice and the mass spectrum is about 7.5-25 cm. Within this definition, the performance of the sampling system is close to the molecular beam sampling conditions, disclosed in Chang, w.d.; karra, s.b.; and Senkan, S.M., molecular Beam Mass Spectroscopy Study of Trichloroethylene Flames, environ.Sci.Technol., 20, 12, 1243, (1986), wherein the expanding sample jet velocity in the first stage reaches ultrasonic levels and the jet entering the Mass spectrum is a directed molecular beam.

Another embodiment of the present invention is shown in FIG. 30, wherein the microreactor-arranged catalyst library is retracted in a translational manner (translation mode) from the sampling position shown in FIG. 29, and the sampling orifice 117 is a short capillary tube which is inert to the reactants and reaction products, has a diameter of about 1-500 microns, typically about 5-100 microns, and a length of about 1 micron to about 20 cm, typically about 5-100 microns. The capillary apertures used in the present invention are significantly shorter than those employed by kastem, m., Qum, m., and Senkan, s.m., and by Cong, p., Giaquinta, d., Guan, s., McFarland, e., Self, k., Turner, h., and Weinberg, w.h., et al, supra. To maximize the product sample signal and minimize the vacuum pumping speed requirements, the capillary diameter is about 5-20 microns and the capillary length is about 50-100 microns, which is compatible with small commercial vacuum pumps. The capillary orifice described in this embodiment flows directly into the first vacuum section 113 of the sampling microprojection 108. In other respects, the apparatus and method shown in FIG. 30 is similar to that described above in connection with FIG. 29.

In the configuration of the sampling probe shown in fig. 29 and 30, the time required to transfer the product from the reaction zone of the microreactor into the mass spectrum may be on the level of between several microseconds to tens of milliseconds. The acquisition of mass spectral data can be done on a time scale of hundreds of milliseconds, particularly if monitoring is performed on ions of a particular mass. Thus, the time-defining step in the sieving process is to mechanically determine the time from each site in the library to a sampling position located adjacent to the sampling aperture of the sampling probe, the mechanical positioning being performed using a stepper motor driven translation device. All microreactor sites in the catalyst library can be operated simultaneously to form reaction products simultaneously. In this manner, product streams from any one site in the library can be sampled at any time without waiting for steady state operating conditions to be established at each site. Alternatively, the flow of reactant to each site of a particular library may be controlled separately by flow controllers in each reactant feed channel, so that the flow of reactant to a particular library may be turned on in advance of the screening at another site to meet the need to establish steady state operating conditions, and turned off when the screening process at that site is complete, as will be explained in more detail below. This mode of operation is essential if it is important to screen library sites under the same online time conditions.

The catalyst library shown in fig. 29 and fig. 30 represents a cross-section of a packed bed microreactor arrangement in a highly thermally conductive metal microreactor body. Catalyst powders, pellets or any other shaped solid catalyst may be placed in a cylindrical or other shaped cartridge that is insertable into the catalyst zone of the microreactor body. Other methods of microreactor catalyst loading are also possible, as will be described in more detail below. Embedded within microreactor body 100 is reactor heating element 118, which provides uniform temperature control throughout the library. The individual library sites may also be spaced apart from one another, each with a respective controlled heating element to provide different temperature control for each site. In a similar manner, each site may be configured with a separate flow control regulator, providing different residence times for each site. A similar reactant preheating zone, indicated by reactant preheating element 119, may also be provided in the reactant feed zone to heat the reactant gases to the desired temperature prior to contact with the catalyst. These microreactor configurations are described in more detail below. The entire library is attached in fixed relation to translation stage 107 to provide precise x-y-z three-dimensional movement, as indicated by translation arrow 120. The two-dimensional translation in the x and y axes moves the library to a sampling site-specific location, while the movement in the third dimension, the z axis, determines the proximity of the reaction product outlet channel 121 to the sampling cone-shaped aperture 112 of the sampling microprobe 108.

The mass spectrometry methods described above can be used for other catalyst library designs, such as those described herein, as well as other types of libraries, which can include homogeneous catalyst libraries, fluidized bed (gas and liquid) libraries, and combinations thereof. The mass spectrometry method, which can be used in conjunction with the resonance enhanced multiphoton ionization method REMPI, has been described in greater detail herein. The REMPI method for screening catalyst libraries has been described in Senkan, s.m.; a High Throughput Screening method for solid-State Catalyst Libraries (High-Throughput Screening of solid-State Catalyst Libraries), Nature, 394, 350, 23 July 1998. As mentioned above, the mass spectrometry method in combination with a microreactor arrangement as shown and described in FIG. 24 is disclosed in FIG. 31. As shown in FIG. 31, the microreactor arrangement 122 has a beam 77 of activating radiation which passes through the flow of reaction products from sites having microelectrodes 87 located in their vicinity, and has internal circuitry 88 for powering each electrode and delivering detection signals from each electrode to a detection means. In the manner described in fig. 29, a sampling cone-shaped tip 111 having a sampling aperture is placed in proximity to the reaction product stream of the respective microreactor outlet by movement of the microreactor arrangement on the translation stage 107 in the x-axis direction and in the sampling position by movement of the microreactor arrangement in the z-axis direction, as indicated by the translation arrow 120.

A microreactor stack arrangement for a combined mass spectrometry and REMPI sieving method can be formed using a multi-microreactor arrangement, as shown in fig. 25. As in the case of the reactor arrangements in fig. 29 and 30, heating elements may be embedded between the heat-conducting walls between the individual microreactors. Inthe same manner as described in fig. 31, REMPI measurement and/or mass spectrometry can be performed by placing the array in a single site position for mass spectrometry sampling by moving the translation stage along the x-y-z axis as indicated by translation arrow 120. Fiber optics may conveniently mount the laser source on the translation stage 107 to provide the laser beam 77 simultaneously for all library sites for rapid REMPI microelectrode screening. For the case where both screening methods are feasible, radiation activation can be used to quickly identify promising sites, and mass spectrometry can be used to quantify yield and activity more accurately.

It will be apparent to those skilled in the art from this disclosure that any of the microreactor configurations, microreactor arrangements, and microreactor stacking arrangements disclosed for the REMPI microelectrode screening method can be readily adapted for mass spectrometry screening methods, including mounting the microreactors on a suitable translation stage and providing a free jet expansion sampling probe to the mass spectrometer.

The screening of large libraries for desired catalytic activity according to the present invention is based on the fact that the ionization cross section of a gaseous molecule is significantly improved when the laser frequency is tuned to the true electronic intermediate state of the molecule. This method is a resonance enhanced multiphoton ionization method, or REMPI. The probability of photo-ionization is very small if the laser wavelength is not tuned to the true electronic state. Therefore, the ionization cross section reflects the absorption-excitation spectrum of the intermediate electronic state of the molecule. With REMPI, specific catalytic reaction products can be selectively ionized efficiently by using appropriate laser frequencies, while avoiding simultaneous photoionization of reactants and/or background gases. Although the preferred embodiment of the present invention is described using a laser beam, other energy levels and radiation beams suitable for promoting the formation of specific ions and electrons from reaction products may be used, thereby allowing the detection of the formed ions and/or electrons using microelectrode collection located in downstream proximity to the radiation beam.

In the case where the catalytic reaction product cannot readily generate REMPI photoions, the method of the present invention can be used for detection of directly related products. For example, the reaction product molecules may be fragmented into smaller daughter products by a suitable energy source, such as a pulsed laser beam or by plasma arc. The fragments may be stable molecular, radical or ionic species. After the catalytic reaction product molecule is split into daughter products, which can be uniquely assigned to the catalytic reaction product molecule to be detected, the daughter products can be selectively photoionized using the REMPI method and detected using the microelectrodes described herein. Quantification of the reaction products by detection of their cleavage products requires additional calibration to account for the efficiency of the cleavage.

It is quite possible that when reaction products are irradiated with a particular light frequency, the reaction products, or their cleavage products, may emit radiation of a unique characteristic, including, for example, luminescence, fluorescence, or phosphorescence. These radiations can then be used to rapidly screen catalyst libraries, for example, by using a monochromator and diode array and a Charge Coupled Device (CCD) detector.

As an example, as ethylene (C)₂H₄) And (O)₂) Ethylene oxide (C) as a result of the reaction₂H₄O) and acetaldehyde (CH)₃CHO), can be performed on cleavage products, which can be illustrated by the following equation:

for acetaldehyde, the cleavage can be carried out in the following manner:

although it is also possible to detect the catalytic product molecules directly using their REMPI ions, information about their presence in the reactant-product mixture can also be obtained by measuring the REMPI properties of their cleavage products. Thus, cleavage of the product CH₂O、CH₂、C₂H₃O and OH can be singly attributed to ethylene oxide and CH₃And CHO formation may be attributed solely to acetaldehyde. In this manner, selective detection of any one cleavage product can indicate the level of the parent ethylene oxide and/or acetaldehyde in the mixture of chemicals, except for the presence of ethylene in significant amounts as a reactant.

Another example, if acrylonitrile (C)₂H₃CN) is by propane (C)₃H₈) Ammonia (NH)₃) Obtained by reaction with oxygen, which can be obtained by cleavage reaction C₂H₃CN＋hν→C₂H₂The + CN is detected by detection of any product which gives a single indication of the acrylonitrile level in the product mixture.

There are various methods for initiating REMPI, the most common method being the resonant 2-photon ionization method, R2PI, in which one photon, hv₁Giving the molecule energy to reach an excited electronic state, a second photon, h v₂Ionizing said molecule. Lubman, D.M. "laser and Mass Spectrometry", Oxford Univ.Press, New York, 1990, Chap.16, Lubman, D.M. and Li, L. "in the desorption of volatile compounds using pulsed laserResonance Two-Photon Ionization Spectroscopy (resonance Two-Photon Ionization Spectroscopy of biological Molecules in Supersonic jet emitted, 353). However, depending on the circumstances, the absorption of two or more photons in each step may also be used in the REMPI method. If (h nu)₁＋hν₂) If the ion is larger than IP, ionization will occur, wherein IP is ionization potential. The two photons used may have the same energy or different energies, and they may be obtained from the same or different lasersAnd (5) obtaining the product. Higher energy UV photons can also be used in a single photon approach to photo-ionize species. The two-photon REMPI process can be described for selective photoionization of product P according to the following equation: p + h v₁＝P^*And P^*＋hν₂＝P⁺+ e wherein P is said product, P^*Is the true electron excited state of the product, P⁺Is the product's photo-ion and e is a photo-electron. By varying the photon energy, which can be achieved by using a tunable laser, the ionization spectrum of the target molecule P can be mapped to determine the appropriate laser frequency that can be used specifically for ionization of that molecule without simultaneously ionizing other molecules in the mixture. Since the REMPI method involves two or more photons, the laser wavelength used must take this into account. As a rough approximation, in a successful REMPI, each photon must have an energy of about R for a single laser beam ₂1/2 for IP in PI method. Similarly, if a single laser beam is used, the energy per photon must be approximately 1/3 for IP in the 2 + 1 method, 1/4 for IP in the 2 + 2 method, and so on. If two or more laser beams are used, each photon energy can be independentlyselected to optimize the resulting REMPI signal. Laser wavelengths ranging from deep ultraviolet, UV such as 150 nm, to visible light such as 700 nm, can be used to induce REMPI using various multiphoton methods.

REMPI itself is a high resolution technique in which the ion absorption characteristics of any molecule can be determined with high precision. Furthermore, the molecules are ionized from the vibrational level of one electronically excited state, allowing specific photoionization of only the target molecule. This can be used to distinguish isomers, such as dichlorotoluene, because they have different electronic structures. Zimmerman, r., Lerner, Ch., Schramm, k.w., Kettrup, a. and Boesl, u., "three-dimensional tracer analysis: methods for combining Gas Chromatography, ultrasonic Beam UV spectroscopy and Time-of-Flight Mass Spectrometry (combinatorial of Gas Chromatography, Supersonic Beam UVSpectroscopy and Time-of-Flight Mass Spectrometry)', Euro. Mass Spectrum, 1, 341, 1995. The REMPI method can be used to sequentially detect different products by using different laser frequencies and, therefore, can also be used to determine the selectivity of the catalyst. REMPI is a highly sensitive technique that can detect low parts per billion units of species in Real Time, Gittins, c.m., Castaldi, m.j., Senkan, s.m., and Rohlfing, e.a, "Real-Time quantitative Analysis of Combustion by polycyclic aromatic Hydrocarbons using Resonance-Enhanced multiphoton ionization Time-of-Flight Mass spectrometry" of synthesized generalized polycyclic aromatic Hydrocarbons by Enhanced Resonance spectroscopy, "anal.chem., 69, 287, 1997, and high parts of parts per billion units have been demonstrated. Castaldi, m.j. and Senkan, s.m. "Real-Time ultrasensitive monitoring of Air poisons using Laser ionization Time-of-Flight mass spectrometry (Real-Time ultrasensitive monitoring of Air Toxics by Laser spectroscopy Time of Flight mass spectrometry), j.air and water mgmt.asoc., 48, 77, 1998.

FIG. 1 is a generalized schematic illustration of a REMPI method for selectively detecting gaseous products formed by contacting catalytic sites with reactants. According to the present invention, gaseous reaction products form plumes 22 when the catalyst 21 mounted on the substrate 20 comes into contact with the reactants. The gaseous product being photo-ionized by a pulsed UV laser beam 23 formed by a tunable laser source 24And/or a second tunable laser source 25 directed through the central portion of the gaseous product plume 22 via a mirror 26 to form photoions P +, and photoelectrons e^-As shown in fig. 1. The micro-electrode 27 is positioned a few millimeters above the laser beam 23 to collect the photoelectrons or photo-ions, which vary according to the bias voltage supplied by the dc power supply 30 to the cathode 28 and the anode 29. The electric signal collected by the micro-electrode 27 is then amplified and detected by a detector 31 such as a digital oscilloscope. If the measured electrical signal is higher than the reference site without catalyst, the site can be labeled as catalytically active. Otherwise, the site must be considered catalytically inactive. It is clear that the selection of a suitable laser frequency, or frequencies for detecting multiple products, is important to ensure that the electrical signal formed by the laser beam is a photoionization of only a particular product gas, and not from the reactant and/or background gas. Suitable laser frequencies for a particular substance may be determined by studies using laser photoionization mass spectrometry, and by way of example, tunable lasers and time-of-flight mass spectrometers may be used. Castaldi, m.j. and Senkan, s.m., 1997, supra and Gittins, c.m., Castaldi, m.j., Senkan, s.m., and Rohlfing e.a., 1998, supra. With this technique, a gas mixture containing the species of interest is introduced into a vacuum chamber using, for example, a pulsing valve. The jet of expanding gasis then intercepted by UV photons of a specific energy from the tunable laser generator. The resulting REMPI signal is then recorded by the time-of-flight mass spectrometer system. By scanning the UV laser frequency range, the photoionization spectra of the reactants, products, byproducts, and background gas can be determined. For molecular isomers, the photoionization spectrum of each isomer must be determined separately. After measurement of the photoionization spectra of all species of interest, a specific UV frequency can be determined, which can result in the REMPI ion specifically generating the particular product isomer desired to be evaluated.

It should be appreciated that the EMPI spectrum broadens at higher temperatures due to the overlapping transitions of a large number of electron resonance levels (rovibronic levels).However, due to the availability of widely tunable UV lasers, it is generally possible to determine the laser frequency at which a desired product can be selectively photo-ionized without interference from reactants, other products, and carrier gases. This identification method is rapid if the structure of the product gas is not the same as the reactant and background gases, e.g., in the preparation of benzene (an aromatic compound) from hexane (an aliphatic compound) in an Ar carrier gas, the only by-product is H₂. Potential problems associated with spectral stacking of the REMPI signal can be effectively addressed by using ultrasonic jet expansion. Parker, D.H. "Laser Ionization Spectrometry and Mass Spectrometry" is published in "Ultrasensitive Laser Spectroscopy" Kliger, D.S.Ed., Academic Press, New York, 1983 and Trembreul, R., Sin, C.H., Li, P, Pang, H.M. and Lubman, D.M. "the use of resonance two-photon Ionization in halogenated aromatics in ultrasonic Beam Mass Spectrometry" (applied of resonance Twoon Ionization in Supernic Beam Mass Spectrometry) and analytical chemistry, 57, 1185. Jet expansion, which can be achieved by expanding the product gas through a small orifice into a vacuum, induces transitional, rotational and vibrational cooling, resulting in a significant simplification of the REMPI spectrum. This approach allows selective detection of specific species in similar contexts.

The product photo-ions and photoelectrons generated at the catalyst sites can be collected using microelectrodes, which can be anodes or cathodes, or both anodes and cathodes. The substrate on which the catalyst reservoir is placed may also be used as a cathode or anode, or for this purpose, other microelectrodes may be placed in the substrate. The high temperature REMPI electrode method has previously been used to determine the concentration of gaseous species containing only a few atoms such as PO, NO, H and O. Smyth, K.C. and Mallard, W.G. "C₂H₂Two-photon Ionization method of PO in air flame (TwoPhoton Ionization Processes of PO in a C)₂H₂/air Flame)″，J.Chem.Phys.，77，1779，1982；Cool，T.A.，″Quantitative Measurement of NO density using Resonance Three-photon Ionization (Quantitative Measurement of NODensity by Resonance Three-photon Ionization), App. optics, 23, 10, 1559, 1984; goldsmith, J.E.M. "Resonant Multiphoton photoelectric Detection of atomic oxygen in flame (Resonant Multiphoton optoelectronic Detection ofAtomic Oxygen in membranes) ", j.chem.phys., 78(3), 1610, 1983; and Bjorklund, g.c., Freeman, r.r. and Storz, r.h. "Selective excitation of the reed primary level of Atomic Hydrogen using Three-photon absorption method" (Selective excitation of Rydberg Levels in Atomic Hydrogen by Three photon absorption), "Optics comm., 31(1), 47, 1979. These early studies addressed the problem of spectral stacking and broadening of the REMPI signal, suggesting that the REMPI-electrode approach cannot be employed if larger molecular species are involved. However, it has now been found that larger molecules can be measured using this technique to screen the catalyst. The noted significant broadening of the REMPI spectrum is allowable in catalyst screening because REMPI features of reactants and products are typically separated. If the REMPI spectra overlap, which should be rare for catalyst screening where reactants and products have different electronic structures, this problem can be solved by spray cooling the product, including expanding the product through small holes to a vacuum chamber.

The REMPI microelectrode technology can also be used to detect liquid and solid products. In these cases, the reaction product must first be vaporized using an ablative laser, e.g., pulsed CO₂Or other types of lasers. The vaporized product can then be photo-ionized according to the REMPI technique and detected using microelectrodes, as described above. The REMPI method can also be used to monitor reaction intermediates contained in the catalytic process, which cannot be detected by analyzing the product gas collected at the reactor outlet. This would be particularly helpful in exploring the reaction pathways associated with catalytic reactions, which could significantly accelerate the catalyst development process.

To the best of the inventors' knowledge, no literature has ever suggested the use of REMPI and microelectrodes for high-speed screening of heterogeneous and homogeneous catalyst libraries. There are many ways to rapidly screen large catalytically active libraries that may be followed, and the presently preferred methods described below are given as representative examples and should not be construed as limiting the invention.

For heterogeneous catalyst libraries, the solid catalyst may be placed on a flat plate in multiple rows of catalyst groups to speed up the screening process. In addition, monolithic or honeycomb structures with defined channels can also be used to generate suitable catalyst libraries. The catalyst sites may also be formed in porous or non-porous form, depending on the catalyst and method of preparation. Figure 2 shows a non-porous flat catalyst library with reactant and catalyst contact achieved by passing reactant gases through the library followed by cross-screening of the product plume. Like numbers refer to like meanings throughout the specification and drawings. The evaluation catalyst site 21 with the upstream catalyst site 21u and the downstream catalyst site 21d is shown as being located above the substrate 20, and the mask 32 shields the upstream catalyst site 21u from the reactant gas stream, as shown in the reactant velocity profile 33. After the product-containing gas is emitted from the site, it must be removed from the library to minimize product circulation in the reactor. In the configuration shown in fig. 2, the catalyst sites upstream of the evaluation catalyst site 21 must be masked to prevent the signals from different sites from overlapping. If upstream sites are not masked and a portion of these sites are catalytically active, the products formed at these sites are transported downstream and interfere with the in-line screening process. Masking may be accomplished by masking the upstream catalyst sites with a physical mask, as shown in fig. 2, or by introducing the reactant gas directly over the catalyst sites with a dedicated gas reactant feed (as shown at 34 in fig. 3). FIG. 4 shows angled catalyst evaluation sites 21t that promote product migration away from the catalyst surface. This configuration can improve signal detection of products from the site of evaluation.

When a reactant molecule flows through an evaluation site having catalytic properties, the product will be at that siteAnd (4) forming a surface. These products will then diffuse into the flowing gas stream and establish a product concentration boundary layer, or product plume 22, as shown in fig. 2-4. The thickness δ of the product concentration layer, assuming a constant product concentration at the catalyst surface_c(x)＝3.3(DxL/U₀)^1/3Where x is the distance from the edge of the catalyst site, as shown in FIGS. 2-4, D is the molecular diffusion factor of the product, U₀For a characteristic gas velocity, as shown in FIGS. 3-4, L is a characteristic dimension in the vertical direction, such as the reactor height or the diameter of the reactant feed tube, as shown at 2R in FIGS. 3-4.

To illustrate some of the design issues involved, assume a solid-state library of catalyst sites 5mm long and 5mm wide. Assuming a gas feed pipe diameter of 0.5cm, an average reactant gas velocity of 1.0cm/sec, and a diffusion factor of 0.1cm²This value is typical for most gases at 1atm, and the thickness of the concentration boundary layer at 5mm from the starting edge of the catalytic site can be estimated as follows:

δ_c(0.5)＝3.3[(0.1)(0.5)(0.25)/1.0)^1/30.767cm or 7.67mm

The boundary layer is thick enough to allow the laser beam to pass through and photo-ionize the product, if present. Diameter of gas feed pipe 2R, gas velocity U₀And catalyst site size x can be varied to further control the thickness of the concentration boundary layer. In addition, evaluation points 21t may be sloped during sieving, as shown in fig. 4, to promote product migration away from the catalyst surface.

If a porous catalyst library is created, the reactant gas may also pass through sites in the library, creating a product plume at the evaluation catalyst sites, as shown in FIG. 5. In this embodiment, the reactants pass through all catalyst sites, thereby making it possible to screen all sites in the library simultaneously. As shown in fig. 5, the reactants pass through the reactant plenum 36 and through the porous evaluation sites 21p to form product plumes 35, which can be measured using the same methods as described above.

The catalyst library can also be created using a monolithic structure 40, as shown in FIG. 6, where the reactant gas will also pass through channel 37, past catalyst coating 38 to form a product gas, which can pass through laser beam 23 and through microelectrodes 27. In this embodiment, simultaneous screening of the entire library is easily accomplished. Microelectrodes 27 can be inserted into channels 37, as shown in FIG. 6, to significantly reduce signal overlap between catalytic sites. The optical entry of the product gas in each channel must be provided with a small window 39 for the laser beam to pass through, as shown in figure 6. The monolithic structure provides a good framework for high throughput and allows for simultaneous screening of high density catalytic libraries due to the provision of good spatial resolution and site separation.

If the high temperature microelectrode REMPI spectra of the product molecules do not have distinguishing features, or the features show overlap, the product must be cooled to improve the REMPI spectra. This is facilitated by the expansion of a portion of the product gas plume 41 emanating from the library sites 33 through small holes 43 into a vacuum chamber 42, as shown in FIG. 7. A portion of the product gas introduced through the orifice 43 undergoes adiabatic expansion to form an ultrasonic jet in the vacuum chamber 42, thereby reducing the gas temperature and significantly simplifying the REMPI spectrum. Also, as shown in FIG. 7, a pre-cooling heat exchanger may be provided upstream of orifice 43 to reduce the temperature of the product gas before it flows through orifice 43. The gas flow into the vacuum chamber may also be pulsed to improve the vacuum requirements. For an ideal gas having a heat capacity ratio γ, where γ ═ C_p/C_vThe temperature of the gas is related to the pressure, and under adiabatic conditions, the following relationship exists: t is₂＝T₁(P₁/P₂)^(1-γ)γWherein T is₁、P₁And T₂、P₂The initial and final temperatures and pressures are indicated, respectively. For example, if γ is 1.4, and the initial temperature is 800K and the pressure is 760Torr, the adiabatic cooling gas is expanded to a pressure of 10^-3The temperature of the Torr vacuum was:

T₂＝800(10^-3/760)^{(1.4－1)/1.4}＝16.7K

this temperature is suitable for producing very good REMPI spectra. Castaldi, m.j. and Senkan, s.m., 1998, supra. Simultaneous product screening of the library is achieved by photo-ionization of the product using a laser beam 23, followed by detection of photoelectrons or photo-ions using a microelectrode 27 of a vacuum chamber 42 disposed adjacent to the expanded jet.

FIG. 8 shows a flat solid catalyst library containing 72 evaluation sites 21 arranged axially in 8 rows by 9 rows in reactor 45, which are sufficiently spaced apart to minimize diffusion of product gas between the sites. The contact of the reactants with the catalytic evaluation site is effected by the use of a reactant feed 34, as described with reference to fig. 3, which effectively masks the upstream catalyst site. At each evaluation site in the screened row there is a dedicated microelectrode 27 for the detection of product gas, 8 microelectrodes for screening being shown in the row in FIG. 8. Arranging the evaluation sites in rows speeds up the line-to-line screening with a single laser beam and enables simultaneous screening of 8 sites. Any row size can be adjusted using the present invention. However, each evaluation site has an arbitrary library pattern of specific addresses that can be moved by a two-dimensional translation device controlled by a computer to perform the screening.The minimum site size, with the highest library density, can be determined by the gas phase diffusion rate of the product gas between the evaluation sites. Thus, different products may allow for the generation and evaluation of different library densities. In the line screening method described, laser 23 passes through window 39 of reactor 45 and through the product gas above the evaluation point 21, in vertical relationship to the reactant gas flow from reactant feed line 34, and through product gas plumes at all points in the line, as shown by the dashed lines, and out of reactor 45 to laser unloading 46, as shown in fig. 8. Reactant feed 34 is supplied by a reactor gas supply manifold 48. In fig. 8, two lasers are shown, however, any number of lasers may be used for a given application. According to the numerical design example given above, positioning the laser beam about 5mm above the substrate surface should be sufficient to enable the laser beam to intercept product plume and generate photo-ions, if any, that are formed. The product gas exits the reactor 45 through gas outlet 49. However, the laser beam may be placed anywhere in the product plume to maximize the signal generated. It is clear that if the evaluation site is not catalytically active, no product is formed and therefore no photo-ionization takes place. The generated photo-ions and photo-electrons are collected by micro-electrodes 27 disposed at adjacent positions above the laser beam. According to the digital design example described above, the micro-electrode can be placed anywhere over 5mm above the surface of the evaluation site and adjacent to the laser beam to maximize signal intensity. However, microelectrodes may be placed at different positions above the evaluation site in order to maximize signal collection in combination with the local hydrodynamics of the product plume. As noted, the library substrate may also serve as a ground or cathode, or microelectrodes may be placed through a nonconductive substrate if desired, or the microelectrodes may include an anode and a cathode, as shown in FIG. 8. The microelectrodes may be powered by a DC power supply 30 via a multi-way switch, and the signal measured by each microelectrode is input to a detector 31. After evaluating a particular row, the library may be moved upstream or downstream using library translation stage 47 to determine the position of the next row of sites for catalytic screening.

Another embodiment of the present invention, illustrating the line screening method, is shown in FIG. 9. The embodiment shown in fig. 9 is similar to that of fig. 8, except that the porous catalyst reservoir having porous evaluation sites 21p is fed with reactant gas from a plenum located therebelow, which is fed with reactant gas through reactant gas feed inlet 50. The reactant gas flows through the porous evaluation sites 21p, simultaneously forming plumes over each evaluation site, as indicated by the arrows. The reactor can be rotated 180 ° along the x-axis, if desired, to improve product detection by altering the natural convection processes in the reactor vessel. As shown in fig. 9, the screening may be performed according to a similar row-by-row approach as described in fig. 8. Alternatively, simultaneous screening of all sites can be achieved by configuring each site with a dedicated microelectrode and passing the ionizing laser beam 23 through all sites simultaneously using a rotating mirror 26, as shown in the top view of FIG. 10. Optical fibers may also be used to direct the laser beam to all of the sites simultaneously. The signal from the microelectrodes can then be detected and recorded by a dedicated detector for each site on the catalyst library 51, or a computerized multiplexing system 65 can be used to detect the signal from each site rapidly and sequentially. It is clear that any catalyst library size and shape is recommended and that this simultaneous screening can be used, as long as the address of each site is individually addressable.

Another embodiment of the invention is shown in fig. 11, which illustrates a 16 x 16 or 256 site monolith 40, as described for fig. 7, forming a solid catalyst library. Any overall cell density may be used. Reactant gas is fed to the manifold below the reservoir through reactant gas feed inlet 50 and flows upwardly through the channels, over or through the catalyst, forming product plumes above the outlets of the channels shown in fig. 9, which may be measured in the channels shown in fig. 6, or subsequently cooled by ultrasonic spray into a vacuum chamber as shown in fig. 7. The catalyst screening can be performed by using a row-by-row approach as shown in fig. 11, or by using a method of screening all sites simultaneously as described for fig. 10.

Another embodiment of a monolith supported catalyst library screening structure in a reactor is shown in fig. 12, and generally employs a configuration as shown in fig. 6. As shown in fig. 12, a single catalyst library monolith 55 having 72 sites and a single catalyst screen monolith 56 form the catalyst screen structure within the reactor 45. A dedicated microelectrode 27 is mounted inside each global channel. Upstream of each microelectrode 27, the optical access for each channel is provided by a laser access window 39. Reactant gas is introduced using a reactant gas flow distributor and into each of the discrete library channels, as indicated by the arrows, to flow over the catalyst sites. Product is detected downstream in the screen stack 56. Laser light from the tunable laser sources 24 and/or 25 is directed into each row of the screened ensemble 56 via the beam splitter 52 and through the laser window 39, through the internal laser window shown through each channel in the row. This configuration allows screening of all sites in the library simultaneously. Different laser beams may be directed into different rows in the screening stack 56 to screen different products. This technique can also be used to screen other library configurations. Fiber optic line 53 may also be used to direct the laser beam to the library site. If product cooling is desired, this can be accomplished by adiabatically expanding the product gas plume through small holes into a vacuum chamber, as shown in FIG. 7.

In the above description of the catalyst screening apparatus and technique, the temperature at all catalyst sites is the same, which is suitable for screening new or improved catalysts. If possible, according to the invention, a library of catalysts can be created with discrete temperature control sites, where different sites should be kept at different temperatures, or their temperatures should be programmable according to a specific temperature-time program. Such different temperatures will yield information about the effect of the reaction temperature on the activity and selectivity of the catalyst. Discrete temperature control and programmable sites can be economically constructed using micro-machining techniques, as is done for thermal inkjet printer heads. It is clear that the amount of isolation provided by the matrix and the temperature programming requirements will affect the spacing between sites and the density of the catalyst library with temperature controlled sites.

It is also possible to operate in a batch mode to screen the entire catalyst library. In this batch mode, the entire catalyst library is first isolated from the reactant gases using a physical mask. The evaluation chamber was then purged and filled with fresh reactant gas. The contents of the chamber may be allowed to reach thermal equilibrium, which may be monitored using a thermocouple disposed in the evaluation chamber. The physical mask is then removed, exposing a particular portion or the entire catalyst library to the reactant gas. Since there is no forced convection, diffusion and natural convection are the main ways of gas migration in the evaluation chamber. The catalytically active sites then produce reaction products which are converted intoDiffuse into the bulk gas phase to form a product concentration plume. For a constant product concentration, the depth of penetration δ of the concentration_c(t) can be estimated according to the following relation: delta_c(t)＝(12D_t)^1/2Where D is the diffusivity and t is the time. The concentration penetration depth must be kept at a level below the site separation to prevent overlap of concentration plumes from adjacent sites from causing signal overlap. For the flat panel catalyst library, site spacing of 1cm, δ is assumed_c1 and a gas diffusivity of 0.1cm²Sec, then the entire library's REMPI measurement must be completed in about 1 second to prevent overlap of concentration boundary layers. Existing fast electronic devices can meet these requirements. Larger site sizes and/or physical barriers placed between sites can significantly reduce the diffusion-mixing rate between sites, thereby providing longer measurement times. In the case of monolithic structures, the presence of physical walls between sites effectively reduces diffusion between sites, allowingMicroelectrodes (which are used to detect photo-ions and/or photoelectrons generated by the laser beam) disposed adjacent to or within the channel acquire data over a longer period of time. One advantage of such a batch system is that it can be used to screen all sites in a solid catalyst library simultaneously.

FIG. 13 shows one embodiment of a homogeneous catalyst library that can be synthesized as described above and sized according to the method of the present invention, wherein a catalyst solution 57 is placed in a vessel 58 through which a reactant gas can be bubbled. Gas diffusion through the liquid catalyst may be carried out in any suitable manner as is well known to those skilled in the art, for example, pressurized reactant gas may be fed through a reactant plenum 36 and forced through a controlled porosity distribution plate located at the bottom of the sample site, as shown on the left side of fig. 13. Alternatively, the reactant gas from the reactant plenum 36 may be bubbled through a capillary bubbler 60 located at each sample site, as shown on the right in fig. 13. The formed gaseous product 22 leaves the liquid catalyst solution as indicated by the arrows in fig. 13, and detection of the product gas can be performed by any of the methods previously described. In determining the minimum diameter of the vessel 58 (which controls the library density), consideration must be given to the surface tension and viscosity of the catalyst solution 57, which can affect the degree of gas diffusion and liquid entrainment.

FIG. 14 is a schematic illustrating catalyst screening within reactor 45 using a homogeneous liquid catalyst library as described with respect to FIG. 13. REMPI catalyst screening may be on a row-by-row basis, as shown in fig. 14, or the entire catalyst library may be screened simultaneously using the method described with respect to fig. 10. The reactor system illustrated in fig. 14 may also be used to screen solid catalyst powders, which may be placed in a container, as will be described in further detail with reference to fig. 15.

Solid particles can be incorporated into the liquid catalyst library to obtain three-phase (gas-liquid-solid) operating conditions. Introduction of solid particles 60 into the liquid in vessel 58 can enhance dispersion of the gas, form smaller bubbles 61 to provide better gas-liquid contact and increase reactant conversion, thereby increasing the reservoir sieving rate, as shown in the left portion of fig. 15. The reaction bed may also be partially or fully fluidized under sieving conditions. Product gas 22, as indicated by the arrows, is emitted from vessel 58 and may be analyzed using any of the REMPI methods previously described. The solid particles employed may be catalytic in nature, providing the opportunity to screen heterogeneous catalytic reactions. In the system shown in fig. 15, a homogeneous liquid catalyst may also be placed in the porous particles, for example to immobilize a protein or a molten salt catalyst. Solid catalyst particles 62 may be introduced into vessel 58 in the absence of liquid to achieve gas-solid operating conditions, as shown in the right portion of fig. 15. The resulting catalyst powder, prepared using a number of different methods, can be placed in a vessel as shown in fig. 15 to form a bank of micro-packed bed reactors. Reactant gases may be introduced into the packed bed reactor via plenum 36 and the resulting product detected using the aforementioned REMPI microelectrode system.

FIG. 16 is a schematic diagram illustrating another catalyst screening process using catalyst particles in a monolith library. Catalyst particles or powders 62 prepared by a variety of different methods may be placed in the cells of the monolith 40. The reactant gas then passes through the packed bed of catalyst particles 62 and is discharged into the vacuum chamber 42 through the small channels/pores 43. The product jet is then cooled by expansion and passed through a laser beam 23 for the generation of photo-ions and photo-electrons. The photo-ions or photo-electrons generated are then detected by the micro-electrodes 27 as described previously.

The magnitude of the REMPI signal formed by photoionization of the product species is proportional to its concentration. In addition, the generated signal can also be affected by operating parameters such as the power of the UV laser used, the DC bias used to collect the light ions/photoelectrons, the separation distance between the anode and cathode, and the position of the microelectrodes relative to the laser beam. Once the optimization is achieved for the particular system to be used for catalyst library screening, the operating variables can be fixed so that the measured REMPI signal can be directly attributed to the product concentration produced at the catalyst site. Thus, in addition to qualitatively screening catalyst libraries for activity or inactivity, the REMPI microelectrode technology of the present invention can be used to quantitatively rank the activity and selectivity of catalysts. The more catalytically active sites will produce a higher product concentration in the product plume, resulting in a greater REMPI signal, and similarly, the less active catalyst sites will produce a lower product concentration, resulting in a lower REMPI signal. In the quantitative screening of the catalyst library, a gas mixture containing a known product gas concentration is first passed through the library in succession without reaction and the microelectrode response is recorded. Each site and microelectrode can be calibrated using microelectrode responses to known product concentrations. These calibration functions can then be used to determine the quantitative concentration of the product formed during the sieving of the active catalyst. If the catalyst loading is different at different library sites, this is also taken into account in the ranking of site catalytic activity. Alternatively, internal standards may be added to the reactant feed stream during the screening process to accelerate the quantification of catalyst site activity and selectivity.

The disclosed catalyst screening techniques can be used to obtain larger target spectra. Two or more laser beam energies can be used sequentially to monitor two or more reaction products in one product plume, which is important for determining catalyst selectivity and for discovering multifunctional catalysts. For example, the development of catalysts that maximize the formation of not only specific products but also minimize the formation of by-products or contaminants is an increasingly important goal in environmentally conscious manufacturing. In the practice of the present invention, a series of laser pulses, each pulse specifically photoionizing a selected molecule, can be used to sequentially monitor different products. Since laser photoionization and product detection are fast processes, with time scales in microseconds, multifunctional catalytic activity for rapid screening of large potential catalyst libraries can be achieved by sequentially detecting a large number of species.

In some applications, the product formed by the catalytic reaction may be in a liquid or solid state, for example, a reaction catalyzed by an enzyme of a high molecular weight biomolecule, and thus, direct use of REMPI is not suitable for screening for catalytic activity and selectivity. However, if the reaction product has been previously vaporized, the REMPI process may be employed. This may be achieved by using a pulsed ablation laser, such as a pulsed CO₂Or excimer laser to rapidly vaporize product molecules from a liquid or solid surface. One embodiment using an ablative laser is shown in fig. 17, wherein an ablative laser source 63 generates an ablative laser beam 64 to rapidly vaporize product molecules from the surface of a liquid catalyst solution 57 into a gaseous product plume 22, which can be intercepted by an ionizing laser beam 23 and produce photo-ions and photoelectrons, which can be detected using any of the microelectrode methods previously described.

As is clear from the above disclosure, the reaction products as well as reaction intermediates can be monitored using the REMPI microelectrode method of the present invention. The ability to monitor the products as well as the reaction intermediates greatly increases the scope of application of the process of the invention. Furthermore, since the measurements according to the invention can be performed in real time without any delay, fast transient processes can also be monitored. This ability may then lead to a better understanding of the function of the catalyst and may thus facilitate the development of new and improved catalysts.

The following specific examples are intended to illustrate the invention in detail, and are not to be construed as limiting the invention in any way.

The catalyst screening method of the present invention is used in catalytic dehydrogenation of cyclohexane to prepare benzene in the reaction process of . This is a well established reaction catalyzed by transition and noble metals at temperatures ranging from 250 to 350 c. Rebhan, d.m. and Haensel, v., "kinetics and mechanism study of cyclohexane disproportionation: an Example of reversible hydrogen transfer (A Kinetic and mechanical Study of cyclic heterocyclic delivery: An Example of Irreversible hydrogenetic transfer), J.catalysis, 111, 397, 1988.

Supported Pt and Pd catalysts, 0.5% and 1.0% Pt and Pd on activated carbon, were obtained from precision Metals corp. These catalysts, along with several inert support materials, silica and alumina, were introduced into a row of 5mm x 5mm cells of the library matrix, similar to figure 5. The catalyst and inert support materials are addressed as: position 12345678: substance inertness 0.5%, inertness 1.0%, and inertness 0.5%

Pt Pd Pt Pd

The catalyst library was then placed in a reactor and heated to 300 ℃ in the presence of a stream of argon. After the steady state operating temperature is determined, which can be measured by a thermocouple within the reactor, a cyclohexane reactant stream is introduced into the reactor. The reactant stream composition contained 13% cyclohexane in argon, which was prepared by bubbling argon through a cyclohexane liquid at about 25c using a bubbler.

The library screening method requires accurate detection of benzene in cyclohexane, hydrogen and argon mixtures. A suitable UV laser wavelength for the selection of benzene REMPI ions has been determined in a separate evaluation using a laser photoion time of flight mass spectrometer (TOF-MS). Gas pulses of cyclohexane and benzene (each at a concentration of about 500ppm in argon) were expanded into the vacuum chamber of the TOF-MS using a pulse valve and the resulting jet/molecular beam was intersected with a pulsed UV laser beam in the 258-262nm range to produce their photoionization and mass spectra. The UV laser has about 100 μ J/pulse energy, obtained from a dye laser using coumarin 500 dye. These measurements lead to the conclusion that the REMPI ions generated by the 258-and 262nm UV laser were generated by photoionization of benzene (mass 78) only, and no photoionization was detected at a cyclohexane mass of 84 or an argon mass of 40 or a hydrogen mass of 2. No other peaks were detected except for the presence of the benzene precursor at mass 78. FIG. 18 shows the REMPI spectra of benzene and cyclohexane obtained by TOF-MS technique. As can be clearly seen from fig. 18, benzene has a major REMPI peak starting from 259.7nm with no contribution from cyclohexane.

The REMPI spectrum of benzene and cyclohexane can also be measured at 1atm and room temperature using the microelectrode method. Cyclohexane and benzene present in an argon carrier gas were photo-ionized by a 258-262nm pulsed UV laser beam at a probe tip of 1-2 mm. A dc bias of +500V from a power supply is applied to the anode to collect the photoelectrons. The resulting REMPI spectrum is shown in fig. 19, which is similar to the spectrum obtained in fig. 18 using the TOF-MS technique, with the expected spectral broadening observed at room temperature and 1atm pressure. This indicates that the presence of cyclohexane, argon and hydrogen in the reactor system with the 259.7 laser resulted in the formation of a specific and efficient benzene REMPI ion.

The reactor system shown in fig. 9 can be used to pass cyclohexane in an argon carrier gas through 8 library sites in a row as previously described. The 259.7nm laser beam passed through the product plume from the library site, the benzene REMPI signal detected at each of the 8 sites in the vicinity, as shown in fig. 20. These measurements correspond to data and signals obtained from one laser pass showing the pumping-decay time in microseconds. As is clear from fig. 20, significant benzene signals were received at positions 2, 4, 7 and 8, consistent with the presence of Pt and Pd catalysts at these positions. Although some REMPI signals were also detected at sites 1, 3, 5 and 6, they were very low, consistent with the absence of catalyst at these sites. It is clear that due to the low gas flow rate and the recirculation pattern within the reactor, there is a portion of benzene present in the bulk gas of the reactor, both of which slow the rapid removal of the reaction products from the reactor. Smaller reactor chambers, using monolithic structures or other library designs may reduce this problem. However, FIG. 19 shows that the method of the present invention can rapidly and accurately distinguish between active and inactive sites in a library. The reactor off-gas was also analyzed by TOF-MS using an 259.7nm laser beam during sieving to determine if species other than benzene might contribute to the measured microelectrode signal. No other photo-ions were detected except for these photo-ions of mass 78.

As shown in FIG. 20, the relative activity of the catalytic sites was shown to be 7>2>4>8, depending on the magnitude of the measured REMPI signal. These results are consistent with the relative loading of Pd and Pt commercial catalysts at these sites, and also indicate that Pt is a more active cyclohexane dehydrogenation catalyst than Pd. These findings are consistent with the results using conventional catalytic reactor systems. Rehbon, d.m. and Haensel, v., 1988, supra and Ahmed, k, and Chowdhury, h.m., "Dehydration of Cyclohexane and Cyclohexene over supported Nickel and Platinum Catalysts (Dehydration of Cyclohexane and Cyclohexene overlayed Nickel and Platinum Catalysts)", chem.eng.j., 50, 165, 1992.

It should be recognized that the conditions given in the foregoing description and examples are intended to illustrate the application of the catalyst screening technique of the present invention. From these descriptions and examples, one skilled in the art can deduce that the process of the present invention can be used to screen any catalyst for any reaction. The reaction conditions can be changedThe case of variable screening methods varies widely. For example, the reaction temperature can be readily varied from room temperature, e.g., 25 deg.C, to higher temperatures, e.g., 1000 deg.C. Likewise, the pressure may be varied from a vacuum such as 10^-4Torr, to a high pressure, e.g., 500 atm. The screening method is compatibleA wide range of reactant feed concentrations can be easily adjusted from 100% pure components to very dilute streams, such as hundreds of parts per million units, 100 ppm.

Combinatorial catalyst libraries can also be created using process microreactors, using integrated circuit fabrication steps such as thin film deposition, lithography, etching, plasma processing, etc. This technology has recently been used to fabricate reactors on a chip for Catalytic oxidation of ammonia, as disclosed in Srinivasan, r., Hsing, i.m., Berger, p.e., Jensen, k.f., Firebaugh, s.l., Schmidt, m.a., hard, m.p., Lerou, j.j.j., and Ryley, j.f., "microfabricated reactors for Catalytic Partial oxidation reactions" (micro-machined for Catalytic Partial oxidation reactions), "AIChE Journal, 43, 9-inch3069, 1997. In contrast to passive monolithic or honeycomb structures, the micromachined reactor may also incorporate flow and temperature sensors, heating elements, and tuning devices for operating condition control. In the present invention, a large number of microreactors are prepared in parallel using any suitable integrated circuit fabrication process. Each microreactor system includes channels for reactant feeds, catalytic reactions, product outlets, and radiation inlets. The channels may be fabricated by wet or dry etching an inert sheet substrate such as silicon oxide or aluminum oxide or a material having an inert film coated on its surface such as an inert material coated metal. The exit from each reaction zone should be large enough to accommodate the microelectrode used to detect the product REMPI ions. Sensors, flow and temperature controllers may also be embedded in the various reactor sites located on the sheets. Furthermore, circuitry may be embedded to electrochemically control the catalytic reaction. Different catalytic materials may be deposited into different reactor channels in the library using a variety of different techniques, such as sputtering, laser ablation, thermal or plasma enhanced chemical vapor deposition, and the like, using a mask. Another alternative is to deposit the catalyst into the reactor channels using solution techniques with the aid of micro-jet or droplet distributors. These distributors can also be used to deposit slurries containing catalyst particles. When a solution technique is employed, the reactor channels may be modified in the reaction zone to contain the necessary amount of liquid and/or slurry catalyst precursor. This improvement can be achieved by providing a reservoir in the central portion of the reactor channel to collect the liquid or slurry catalyst precursor mixture. These reservoirs can be of any shape and can also have intermediate partitions, regulating devices and sensors to better control the preparation of the catalyst and the operation of thereactor during the sieving process. These reservoirs can also be placed at various locations along the microreactor to control pressure drop, reactant preheating, and product quenching conditions. The liquid and/or slurry mixture of catalyst precursor may be introduced into the reservoir using a micro-jet or micro-drop dispenser and remote control techniques. After the liquid is added dropwise, agitation may be performed using, for example, mechanical vibration, microshifting, or sonication to ensure mixing of the liquid or slurry mixture. After the catalyst precursor is dispensed, the resulting mixture may be thermally and chemically treated to form a catalyst. These treatments may include drying, calcination, oxidation, reduction, and activation.

Fig. 21 and 22 are schematic illustrations of a single microreactor system base according to the present invention. Fig. 21 shows a microreactor suitable for a thin-film or solid-particle catalyst deposition process, and fig. 22 shows a microreactor also suitable for a solution-based catalyst deposition process. In the depicted figure, inert microreactor body 70 has reactant feed channels 71 leading to catalyst zones, designated as zones 72 in fig. 21 and enlarged reservoir catalyst zones 73 in fig. 22. As shown in fig. 22, a baffle structure 74 may be provided in the reservoir 73. This separator structure has a number of effects, such as providing additional exposed surfaces for the catalyst, and facilitating mixing to facilitate certain reactions. The product exits the reaction space via the outlet channel 75. Reactant feed and product effluent are shown by arrows. An activating radiation channel 76 having an optical entrance window for isolating the exit channel 75 for providing a passage of an activating radiation beam 77 through the exit channel 75 by the product stream. Fig. 21 shows the outer microelectrode 78 and fig. 22 shows the inner microelectrode, which is arranged in the exit channel 75 adjacent to the activating radiation beam 77 to collect photoelectrons or photo-ions for detection, as described earlier. Internal microelectrodes 84 are attached to microreactor body 70, e.g. embedded in the bottom, side walls and top wall of said product outlet channel, and thus are part of the microreactor body. These internal microelectrodes may be flush with the product outlet channel wall or may protrude from the channel wall. The internal microelectrode is provided with suitable circuitry to power the microelectrode and to transmit a test signal to a test measurement device. These lines and connections are embedded in the microreactor body during the manufacturing process using established microelectronic manufacturing techniques.

FIG. 23, in which like numerals refer to like elements throughout, illustrates a microreactor arrangement within a single inert microreactor body 70. Any number of microreactors may be present in the arrangement, depending on the dimensions of the microreactors and the physical properties of the matrix sheet. Each microreactor 72 may be of any size, however, reaction channels at a level of about 0.1-2mm wide are best suited for fabrication and subsequent sieving processes. A reactant plenum 79 is in fluid communication with each reactant feed channel 72 for distributing reactants into each microreactor. Reactant plenum 79 is large enough to ensure that similar flow rates of fluids through each microreactor are achieved, provided that the pressure drop properties of the microreactors are similar. Alternatively, flow sensors and regulators may be fabricated in each microreactor to independently control the flow of fluid through each microreactor. A different catalyst may be placed in each microreactor using any of the described techniques. The physical form of these catalysts may be in the form of a thin film, as shown at 86, or in the form of a powder, as shown at 85. Fabrication of the microreactor arrangement from a single substrate sheet ensures good alignment of the activating radiation channels 76 with microelectrodes 84, thereby speeding up the sieving process. The internal electrodes 84 make it possible for internal wiring to supply electric power to the microelectrodes and to transmit detection signals to the detection measuring device. Alternatively, separate and distinct electrodes, one to the anode and one to the cathode, may be embedded in different walls of the reactor for power and signal detection. Suitable connectors may be provided on the outside of the array to facilitate connection of the entire array and to a power supply and detection measurement device via the selection switch. Reactant feed and product effluent are shown by arrows.

After fabrication of the microreactor base layer, an inert cover sheet 80 is bonded to inert microreactor base 70 to cover the microreactor arrangement, as shown in FIG. 24, to separate each microreactor system while allowing reactants to flow into and products to flow out of the microreactor arrangement. As shown in FIG. 24, the internal microelectrodes 87 are attached to or embedded in the cover sheet 80 in a similar manner as the internal microelectrodes 84 attached to the microreactor body 70, as described above. An internal wiring 88 connects each micro-electrode 87 to an external connector 89 for supplying power to each micro-electrode and transmitting a detection signal of each micro-electrode to the detection device. Alternatively, separate electrodes may be embedded in the substrate 70 to detect signals and/or provide power. Heating elements may be embedded in thermally conductive microreactor bodies 70 located between microreactor chambers 72 and/or in thermally conductive cover sheets 80 and/or in thermally conductive plates between stacked reaction arrangements to provide desired temperature control of the microreactors and/or reactant feed channels. As shown in fig. 25, individual flat-plate microreactor arrays, as shown in fig. 24, can be vertically stacked to obtaina multi-component flat-plate microreactor array having a three-dimensional structure, so that a large number of samples can be rapidly analyzed in a similar manner to that shown in fig. 12. The microreactor arrangement may be provided with suitable holders to maintain adjacent arrangements in a fixed relationship to each other. The microelectrodes are powered by a DC power supply, and the signal from each microelectrode is transmitted to a measuring device through a multichannel selector.

The microreactor arrangement 91 shown in FIG. 26, as shown in FIG. 24, may be provided in a microreactor arrangement block 92 to facilitate operation and connection of catalyst screening. The microreactor arrangement is mounted in an opening in the frame as indicated by the reversible arrow. The reactant feed is fed through the block into the reactant feed manifold of the microreactor arrangement as indicated by the arrow, and the product is discharged through the block as indicated by the arrow. The radiation channels 93 are provided for the entry and exit of the aligned radiation beam 77 through the frame 92 to pass through the radiation channels 76 in the microreactor body 70, as described above. The frame may also have internal circuitry 94 for connecting one end to the internal circuitry 88 of the microreactor arrangement and the other end to a power supply and a test measurement device. The internal circuitry of the multi-component microreactor array housing may be connected to external electrical wiring via a single connector. The block may also have a reactant feed manifold configured to provide reactants from a single feed source to the multiple microreactor array-block assembly. The frame may also provide temperature control for the microreactor arrangement via heating elements mounted in the frame. The microreaction array-frame may have any suitable elements for connecting adjacent microreactor array frame assemblies.

The multiple microreactor-frame assemblies may be combined together in a vertical fashion similar to that shown in fig. 25. In another embodiment, as shown in FIG. 27, the microreaction array-frame assemblies 95 can be joined horizontally in a side-by-side fashion. The alignment of the radiation channel 93 makes it possible to evaluate large catalyst libraries with only one radiation beam 77.

Sieving is accomplished by passing a known quantity of reactant gas through the microreactor arrangement to contact a latent catalyst to form a reaction product which can be activated by passing a suitable tunable radiation beam through activation irradiation channel 76 having an inlet window providing fluidic separation to form product REMPI ions in product outlet channel 75. These product REMPI ions were detected using a microelectrode located in the exit channel and measured using the methods described previously. The microreactor arrangement may be provided in a furnace for providing temperature control of the entire arrangement during the screening process, or the temperature of each microreactor may be independently controlled using sensors and heating elements installed in the microreactors during the microreactor manufacturing process. Alternatively, temperature control may be provided by the frame.

FIGS. 28A and 28B schematically illustrate another example of a combined catalyst library preparation and screening method using different microreactor arrangements and droplet/microjet techniques of the present invention. Step 1 shows the preparation of an inert matrix for the catalyst library using a plug to form the desired channels and retain the liquid during solution deposition. Step 2 shows the deposition of the catalyst precursor solution into the reservoir of the catalyst reaction zone. Step 3 shows the drying and calcination of the catalyst using methods well known in the art. Step 4 shows opening the product outlet channel byremoving the plug used to form the channel. Step 5 shows the formation and/or activation of a catalyst by passing a suitable gas through the microreactor arrangement. Step 6 shows the sizing of the catalyst within the microreactor arrangement by passing reactant gases through the catalyst within each microreactor, passing a beam of radiation of sufficient energy level to promote the formation of specific ions through each reaction product stream, and collecting to detect the formed ions or electrons using a microelectrode positioned adjacent to the beam of activated radiation.

While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the specific details described herein can be varied considerably without departing from the basic principles of the invention.

Claims (20)

1. A microreactor and sampling probe system for mass spectrometry screening of catalytic and potentially catalytic reaction products, said system comprising: a plurality of addressable microreactors, each microreactor comprising an inert matrix body, a reactor channel extending from a first opening on one side of said matrix body to a second opening on the other side of said matrix body, a reaction zone in a central portion of said reactor channel as a reaction zone for reactants to contact a catalyst located in said reaction zone, a reactant zone of said reactor channel extending from said reaction zone as a reactant feed channel, and a product zone of said reactor channel extending from said reaction zone to said second opening as a product outlet channel; a tubular sampling probe comprising a sampling orifice at one end forming a free jet expanded stream into a substantially expanded chamber of at least one vacuum stage and an open opposite end connectable to an inlet port of a mass spectrometer; and a means for translating capable of placing said sampling aperture in proximity to the product outlet channel of an addressable single microreactor as a sampling mode and capable of rapidly translating to position said sampling aperture in proximity to the product outlet channel of a second addressable single microreactor as a sampling mode for said second microreactor.

2. The system of claim 1, wherein the sampling orifice has a diameter of about 1 to 200 microns and is located at the top of the expansion cone with a half cone angle of about 15 to 45 °.

3. The system of claim 1, wherein the sampling orifice is a short capillary tube having a diameter of about 1 to 500 microns and a length of about 1 to 200 microns.

4. The system of claim 3, wherein the capillary has a diameter of about 5 to about 20 microns and a length of about 50 to about 100 microns.

5. A system as in any preceding claim, wherein the distance from the sampling orifice to the mass spectrometer inlet orifice is about 3-10 inches.

6. A system according to any preceding claim, wherein the expansion chamber comprises two vacuum sections with a defoaming orifice between the first vacuum section and the second vacuum section.

7. The system of any preceding claim, wherein the microreactor further comprises: a radiation beam passage extending through said substrate body generally perpendicular to and intersecting said product region, said radiation beam passage having a radiation beam entrance window providing a passage for a radiation beam and fluidly separating said radiation passage from said product region; and a microelectrode located in the product region adjacent to where the radiation beam channel intersects the product region.

8. The system of any one of the preceding claims, wherein said plurality of microreactors are an in-line array of microreactors fixedly mounted on a translation stage and rapidly movable along an x-axis to align said sampling orifice and said product outlet channel and along a z-axis to bring said sampling orifice and said product outlet channel into close proximity with each other.

9. The system of any one of the preceding claims, wherein said plurality of microreactors is a parallel stack of microreactors arranged in a row, fixedly mounted on a translation stage, rapidly movable along x-axis and y-axis to align said sampling orifice and said product outlet channel, and movable along z-axis to bring said sampling orifice and said product outlet channel into proximity with each other.

10. A system according to any of the preceding claims, wherein each of said microreactors comprises temperature and flow control elements for controlling the temperature and flow rate, respectively, in each microreactor.

11. A system according to any of the preceding claims, wherein each of said microreactors comprises a plug for loading catalyst into or removing catalyst from said reaction zone.

12. A method of rapidly screening potential catalyst library catalyticperformance comprising: forming a library of potential catalysts at a plurality of addressable test sites; contacting a reactant gas with a latent catalyst through at least one of the plurality of addressable sites; and screening the gaseous plume of reaction products from said addressable sites, said screening comprising translating at least one sampling probe and said reservoir to a position where an addressable site is adjacent to a sampling probe orifice, passing a portion of said reaction products from said addressable site through said sampling probe orifice, forming a free jet expanded stream within the substantially expanded space of at least one vacuum section, thereby cooling and reducing the pressure of said jet stream of reaction products to a pressure suitable for introduction into a mass spectrometer, and passing a portion of the jet stream of reaction products under reduced pressure through an inlet orifice into the mass spectrometer for analysis.

13. The method of claim 12, wherein said sampling orifice has a diameter of about 1 to 200 microns and is located at the top of the expansion cone with a half cone angle of about 15 to 45 °.

14. The method of claim 12, wherein said sampling probe orifice is a short capillary tube having a diameter of about 1 to 500 microns and a length of about 1 to 200 microns.

15. The method of claim 14, wherein the capillary has a diameter of about 5 to about 20 microns and a length of about 50 to about 100 microns.

16. A method as in any of claims 12-15, wherein the distance from the sampling probe orifice to the mass spectrometer inlet orifice is about 7.5-25 cm.

17. A method as claimed in any one of claims 12 to 16 wherein the expansion chamber comprises two vacuum sections with a defoaming orifice between the first vacuum section and the second vacuum section.

18. The method of any one of claims 12-17, further comprising: at least one energy level sufficient to facilitate the formation of a radiation beam comprising the excitation products of specific ions and electrons, to pass through said gas plume of reaction products, and to detect the formed ions or electrons in real time by microelectrode in situ collection at a location adjacent to said addressable site.

19. The method of claim 18, further comprising contacting said reaction product with at least one energy beam to form a cleaved sub-product, said screening and said detecting being performed on said cleaved sub-product.

20. The method of any one of claims 12-19, wherein said plurality of addressable evaluation sites comprises a plurality of microreactors in parallel stacked in rows of microreactors, fixedly mounted on a translation stage, rapidly movable along x-axis and y-axis to align said sampling wells and reaction product outlet channels from individual addressable microreactors, and movable along z-axis to bring said sampling wells and said product outlet channels into close proximity to each other.

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