MXPA06001578A - Method for preparing catalysts and the catalysts produced thereby - Google Patents

Abstract

Processes for preparing mixed metal oxide catalysts suitable for partial oxidation of alkanes, alkenes and mixtures thereof, where in the processes comprise the steps of:providing an aqueous aerosol of one or more metal oxide catalyst precursors;and irradiating the aqueous aerosol of one or more metal oxide catalyst precursors with microwave energy. Optionally, the catalyst may be further modified using one or more chemical treatments, one or more physical treatments and one or more combinations of chemical and physical treatments, to further improve catalyst performance characteristics.

Description

METHOD FOR PREPARING CATALYSTS, AND THE CATALYSTS PRODUCED BY THIS METHOD The present invention relates to methods for producing mixed metal oxide catalysts, useful for catalytically converting alkanes, alkenes and their mixtures, to their corresponding oxygenates, including unsaturated carboxylic acids and their ethers, by the oxidation of vapor phase . In particular, the present invention relates to methods for preparing mixed metal oxide catalysts, which involve the irradiation of the mixed metal oxide precursors with a microwave energy at the frequencies of these microwaves. Partial catalytic oxidations of alkanes and alkenes to unsaturated carboxylic acids and their corresponding esters are important commercial processes. However, efforts to improve the selectivity and efficiency of these processes are in progress and sometimes focus on the optimization of the mixed metal oxide catalysts used in these processes, as well as the methods to obtain them.

International Publication No.99 / 00326 describes the initiation of a redox reaction between a plurality of metal salts in an aqueous solution, which requires at least one strong oxidizing agent and at least one strong reducing agent, using microwave energy, in which the product of the metal oxide is produced by establishing a redox couple. However, the publication fails to describe any method for controlling the particle size of the material that is irradiated with microwave energy. Also, this publication fails to describe or suggest the use of microwave energy for the successful synthesis of mixed metal oxide catalysts, which are suitable for the partial oxidation of alkanes, alkenes and their mixtures. The present invention provides a process for preparing one or more mixed metal oxide catalysts, suitable for the partial oxidation of alkanes, alkenes and their mixtures, this process comprises the steps of: a) generating one or more aerosols from one or more solutions, comprising at least one precursor of a metal oxide catalyst; and b) irradiating said one or more aqueous aerosols of said one or more mixed metal oxide precursors, with microwave energy, having one or more microwave frequencies. These aerosols of oxide precursors Mixed metals can be generated using an ultrasonic nozzle. The present invention also provides a catalyst prepared by the aforementioned process. The catalyst may comprise a compound, which has the empirical formula: MoV.NbbXcZdO, wherein X is at least one element, selected from the group consisting of Te and Sb, Z is at least one element, selected from the group consisting of W, Cr, T a, Ti, Zr, Hf, Mn, Re, Fe , Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Pb, P.B, And, Rare earth elements and alkaline earth elements, 0-1 < a < 1.0, 0.01 £ b £ 1.0, 0.01 < _ c 1.0, 0 £ d £ l.0 and n was determined by the oxidation states of the other elements. The calcination of the aforementioned compound can be carried out after the irradiation step, or during the microwave irradiation of one or more aerosols of mixed metal oxide precursors. The process of the present invention may comprise the further step of further modifying this one or more metal oxide catalysts, using one or more chemical treatments, one or more physical treatments and one or more combinations of chemical and physical treatments. The present invention also provides a process for the partial oxidation of an alkane, alkene or a mixture of an alkane and an alkene, in the presence of a catalyst, produced by the above process, in which this process produces one or more oxidation products. partial, selected from the group consisting of an unsaturated carboxylic acid and an unsaturated nitrile. The present invention provides a process for preparing mixed metal oxide catalysts, by generating an aerosol of one or more solutions, comprising precursors of mixed metal oxides and irradiating this aerosol with microwave energy, having one or more microwave frequencies. More particularly, the precursor solutions can be sprayed through one or more ultrasonic devices (or any other comparable mechanical device, which allows control of the droplet size of the solution) and inside the microwave chamber, which already contains a solution of the additional precursor. In the latter case, the precipitation / formation of gel, in the addition of one or more solutions of sprayed precursors. The frequency, dimensions and power level (constant, degree of oscillation, maximum instantaneous shape, etc.) of the microwave device can be varied to optimize the physical characteristics of the catalyst, crystallinity and the like. Both inorganic and organic models can be used to control and direct the morphology of the catalyst precursor and the final catalyst. The aerosol can be fed into the microwave chamber, under turbulent flow conditions, where it can be irradiated with microwave energy, at atmospheric temperature and / or pressure, or, alternatively, at a high temperature and / or pressure. Without intending to be limited by theory, it is believed that, by controlling the size of the aerosol droplets, under a turbulent flow, the resulting metal oxide catalyst will have well-defined and uniform particle sizes, improved particle morphology, and preferably , improved catalytic phases. In particular, it is believed that the use of an ultrasonic spray or similar device allows control of the droplet sizes of one or more precursor solutions. A) Yes, in turn, allows one to control the particle size, morphology and potential plane of crystallites, exposure AND surface area / porosity of the resulting mixed metal oxides precursor solid, The mixed metal oxide catalysts, produced by this method, are useful in converting alkanes, alkenes and their mixtures, to their corresponding oxygenates, which include unsaturated carboxylic acids and unsaturated nitriles. Likewise, the resulting mixed metal oxide catalysts can also be improved by subjecting them to further chemical, physical treatments and combinations of these chemical and physical treatments (referred to as "subsequent treatments" of the prepared catalysts). Such methods and subsequent treatments have resulted in unexpected improvements in the efficiency and selectivity of the catalysts, as well as unexpected changes in the catalytic properties, including the structure, density and surface area of the catalysts. The inventors have further discovered, for example, that the mixed metal oxide catalysts, prepared by the method of the present invention, provide, unexpectedly, selectivities and improved oxygenate yields, including carboxylic acids unsaturated, of their corresponding alkanes, with a constant conversion of these alkanes. According to one embodiment, the mixed metal oxide, prepared by the method of the present invention, has the empirical formula: MoV_NbbXcZdO, wherein X is at least one element, selected from the group consisting of Te and Sb, Z is at least one element, selected from the group consisting of, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru , Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Pb, P. B, Y, rare earth elements and alkaline earth elements, 0-1 £ to £ 1.0 , 0.01 b £ l.'O, 0.01 c £ 1.0,? £ d £ l.O and n was determined by the oxidation states of the other elements. The performance of the mixed metal oxides catalyst, based on Mo-V-Nb-Te can, for example, be optimized by increasing its surface area, porosity, maximizing the exposure of the plane [001] and minimizing the aspect ratio, which they can be achieved by the process of the present invention, in which the aerosol containing the precursor is irradiated with microwave energy.

As used herein, the mixed metal oxide catalyst refers to a catalyst comprising more than one metal oxide. The term "catalytic system" refers to two or more catalysts. For example, the platinum metal and the indium oxide impregnated on an alumina support define both a catalyst system and a mixed metal oxide catalyst. Still another example of the system, is made of palladium metal, vanadium oxide and magnesium oxide, impregnated on silica. The new approach of the synthesis is useful for the optimization of known mixed metal oxide compositions (MM0s) 3 such as, without limitation, mixed metal oxide catalysts based on Mo-V-Te-Nb, as well as three components MMOs (for example, Me-V-Te-Ox). It is also useful for the synthesis of new MMOs, which can serve as selective oxidation catalysts (for example, the conversion of propane to acrylic acid). The process of the present invention can be conducted so that the catalyst precursors are dried and converted to the active calcined catalyst, controlling a number of experimental parameters, which include the type of energy, frequency, power level, pulse type of energy , dimensions of the reactor, time of residence, gas environment, flow rate, temperature, gas charge additives, and the like. The in-situ drying and calcination conduction has a number of advantages including improving the economics of the process, providing catalyst particles of a more preferred configuration, surface morphology, particle size range, crystalline phases, surface area, porosity, surface composition , and similar. According to one embodiment of the invention, the catalysts, prepared according to the process of the present invention, are one or more mixed metal oxide catalysts, having a catalyst having the empirical formula: MoV.NtOcZdOn wherein X is at least one element, selected from the group consisting of Te and Sb, Z is at least one element, selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Pb, P.B, And, Rare earth elements and alkaline earth elements, 0-1 < to 1.0, 0.01 < b < 1.0, 0.01 < c £ 1.0, 0 < d £ 1.0 and n was determined by the oxidation states of the other elements. The preparation of mixed metal oxide (MMO) catalysts is described in U.S. Patent Nos. 6,383,978; 6,541,996; 6,518,216; 5,403,525; 6,407,031; 6,407,280 and 6,589,907; US Application for Publication No. 20030004379; Provisional Requests Nos. Series: 60 / 235,979; 60 / 235,981; 60 / 235,084; 60 / 235,983; 60 / 226,000; 60 / 236,073; 60 / 236,129; 60 / 236,243; 60 / 236,605; 60 / 236,250; 60 / 236,260; 60 / 236,262; 60 / 236,263; 60 / 283,245 and 60 / 237,218; and European patents Nos. EP 1 080 784; EP 1 102 982; EP 1 192 983; EP 1 102 984; EP 1 102 986; EP 1 192 987; EP 1 192 988; EP 1 192 982; EP 1 249 274 and EP 1 270 068. It will be noted that the promoted mixed metal oxides, which have the empirical formulas of M? JVmTenNbuZx0o and WjVmTenNbyZz0o, in which Z, j, m, n, y, zyo are as defined above , are particularly suitable for use in connection with the present invention. Further suitable modalities are any of the empirical formulas, in which Z is Pd. Suitable solvents for the precursor solution include water, alcohols comprising, but not limited to methanol, ethanol, propanol and diols, etc .; as well as polar solvents known in the art. Water is generally preferred. This water is any water suitable for use in chemical synthesis, including, without limitation, distilled water and deionized water. The sanity of the water present is preferably an amount sufficient to keep the elements substantially in solution for a prolonged period, sufficient to keep the elements substantially in solution for a sufficient time to avoid or minimize the segregation of the composition and / or phase during the preparation steps. . Therefore, the amount of water will vary according to the amounts and solubilities of the combined materials. Preferably, although lower concentrations of water are possible to form an aqueous paste, as noted above, the amount of water is sufficient to ensure the formation of an aqueous solution, at the time of mixing. According to a separate embodiment of the invention, mixed metal oxide catalysts, prepared in accordance with the process of the present invention, can be one or more catalysts of promoted metal oxides, which have the empirical formula: JjMmNnYyZ? where J is at least one element selected from the group consisting of Mo and V, M are at least one element selected from the group consisting of V and Ce, N is at least one element selected from the group consisting of Te, Sb and Se , And is at least one element selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, Ace, Ge , Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb. P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selected from the group consisting of Ni, Pd, Cu, Ag and Au; and in that, when j = 1, m = 0.01 to 1.0, n = 0.01 to 1.0, y = 0.01 to 1.0, z = 0.01 to 0.1 and o is dependent on the oxidation state of the other elements. The preparation of mixed metal catalysts is described in U.S. Patent Nos. 6,383,978; 6,641,996; 6,518,216; 6,403,525; 6,407,031; 6,407,280 and 6,589,907; US Provisional Applications, Nos. Series 60 / 236,977; 60 / 235,979; 60 / 235,981; 60,235,984; 60 / 236,000; 60,236,073; 60 / 236,129; 60,235 / 143; 50 / 236,605; 60 / 236,250; 60,236,260; 50 / 236,262; 60 / 236,263; 60 / 283,245 and 50 / 236,218; and European Patents Nos. EP 1 080 784; EP 1 192 982; EP 1 192 983; EP 1 192 984; EP 1 192 986; EP 1 192 987; EP 1 192 988; EP 1 192 982 and EP 1 249 274.

Any conventional equipment and methods used to generate an aerosol is usefully employed in accordance with the invention. According to one embodiment, the aerosol of precursors of mixed metal catalysts is generated under turbulent flow conditions. According to a separate embodiment, the aerosol is generated by an ultrasonic nozzle, which allows control of the size of the aerosol droplets. One of the problems encountered during the development of the spray drying method, during the production of mixed oxide catalysts of Mo, V, Nb, Sb and Te, was the sealing of the spray-drying nozzle. While this problem has been minimized by the delayed mixing and reaction of the starting conditions, by the cooling of the spray nozzle and by the use of large diameter spray nozzle tips, sealing remains an intermittent problem during our spray drying operations. Also, the use of spray nozzle tips, also results in gel precursor droplets, with large diameters which, in turn, require longer times to dry. In order to minimize the obturation problems associated with the production of precursors of mixed metal oxide catalysts of Mo, V, Nb, Sb and Te, as well as than to extend the range of sizes of the droplets of the precursor gel produced in the spray dryer in the micrometer range, we propose the use of ultrasonic atomizing nozzles. Ultrasonic atomizer nozzles have many convenient features for spray drying. They include a narrow droplet size distribution, low speed spraying, an ability to control droplet size, changing nozzle frequency, a nozzle that does not clog, short set times, ability to operate with sizes much smaller batch, multiple liquid feeding capacity and a high degree of flexibility. Some ultrasonic nozzles operate by converting a high-frequency electrical signal, powered by two electrodes sandwiched between two piezoelectric transducers, resulting in the mechanical expansion and contraction of these transducers. This causes vibrations to be sent down to the titanium horn of the nozzle, which vibrates ultrasonically at the spray tip of the nozzle. The liquid that emerges from the atomizing surface is broken in a spray by the ultrasonic energy concentrated there. The design of the mouthpiece Ultrasonic provides an atomized, easily controllable spray, which can not be obstructed due to the large flow loading orifice and ultrasonic self-cleaning vibration. The diameter of the droplets can be controlled, according to the frequency used in the nozzle, for example, a frequency of 25 kHz provides a droplet diameter of approximately 70 μ, a frequency of 48 Kz provides a droplet diameter of approximately 31 μg. μ, 60 kHz frequency provide a droplet diameter of approximately 31 μ, and 120 kHz frequency provide a droplet diameter of approximately 18 μ. The double feeding of liquid allows an even greater flexibility in the process, as two liquids can mix directly in the tip of the nozzle, during atomization. Such nozzles are commercially available from a source number, including the Sono-Tek Corporation, of Milton, New York, U.S.A. It is also possible for ultrasonic nozzles to use compressed are or gras to energize the nozzle; therefore, there is no piezoelectric effect or need electricity. A sonic field is created in the throat of the nozzle, as the compressed gas accelerates and reaches the speed of sound. High frequency waves, created by the cavity of the resonator, produce a cutting effect that interrupts the flow of liquid in a fine cloud, dispersed uniformly of extremely small droplets. These nozzles can produce droplet sizes significantly below conventional air atomizers, with average droplet diameters as small as 8 microns, are obtained when water is sprayed in certain nozzles. This makes these nozzles ideal for use in spray drying and other applications requiring extremely small droplets. Such nozzles are commercially available from a number of sources, including the Sono-Tek Corporation, of Milton, New York, U.S.A. The application of ultrasonic nozzles in the production of spray drying of combinations of 2, 3, 4 and 5 components of precursors of the mixed oxide catalysts, containing Mo, V, Nb, Sb and Te, with and without the addition of Support, such as silica, is expected to result in precursor particle sizes, such as, but not limited to, the concentration of the starting material solutions used in the process. Also, the primary spray-dried particles obtained by these methods are, in general, comprised of an agglomeration of minor particles and / or crystallites. Therefore, the use of Ultrasonic nozzles with standard spray drying conditions, it is expected to produce catalyst crystallites with sizes and configurations previously not available by standard spray drying.

The mechanical simplicity of the aforementioned ultrasonic nozzles, the well-established simplicity and the low operating cost of standard spray drying, and the ability to use air, water and standard starting materials in the synthesis of nano-sized and micrometric particles, presents an economic advantage and operations on other methods that have been proposed in the past to achieve the same goal. For example, spray drying under supercritical conditions requires compression, high pressures to use and recycle C02, high ratios of an anti-solvent, such as alcohols, when using aqueous solutions, and the use of expensive starting materials and / or exotic, such as alkoxides, when non-aqueous solutions are preferred. Flame processes, such as the nGimat's NanoSpray ™ process, also require a more complex operational and experimental configuration, the use of fuels and elevated temperatures, limited control of the reduction potential of the environment, when forming the particles, as well as the use of starting materials and solutions that can be burned. Finally, the nanometer and micrometer scale precursor and the catalyst particles produced by the use of ultrasonic nozzles in conjunction with the standard spray drying are suitable for the further process, such as calcination or for direct use in bed reactors fluid. Ultrasonic nozzles are also ideal for use in other applications requiring extremely small droplets, such as, but not limited to, evaporative cooling and spray coating. The frequency, dimensions and power level (constant, degree of oscillation, maximum instantaneous shape, etc.) of the microwave device can vary to optimize the physical characteristics of the catalyst, crystallinity - of the composition and the like. Both inorganic and organic models can be used to control and direct the morphology of the catalytic precursors and the final catalyst. A catalyst of mixed metal oxides (promoted or not), thus obtained, exhibits excellent catalytic activities by itself. However, the mixed metal oxide catalyst can be converted to a modified catalyst that has major activities by one or more chemical, physical treatments and their chemical and physical combinations. As used herein, the term "modified catalysts" is equivalent to the term "subsequently treated catalysts" and both refer to any chemical or physical treatment or combinations thereof, modification or modification of one or more metal oxide catalysts, in comparison with the corresponding catalysts of a similar composition, which has not undergone such modification or modifications (also referred to as "known catalysts"). Modifications to the mixed metal oxide catalysts include, but are not limited to, any difference in the modified catalysts, as compared to the corresponding known catalysts. Suitable modifications to the catalysts include, for example, without limitation, structural changes, spectral changes (including the position and intensity of the characteristic X-ray diffraction lines, ridges and patterns), spectroscopic changes, chemical changes, physical changes, changes in composition, changes in physical properties, changes in catalytic properties, changes in characteristics of performance in conversions of organic molecules, changes in the yields of the organic products of the corresponding reagents, changes in the activity of the catalyst, changes in the selectivity of the catalyst and its combinations. These include one or more chemical modification agents (e.g., a reducing agent, such as an amine), one or more physical processes (e.g. mechanical crushing at cryogenic temperatures, also referred to as "cryo-grinding") and combinations of one or more chemical modifying agents and one or more physical processes. The term "cryo" versus any term of treatment, refers to any treatment that occurs with cooling, under freezing temperatures, at cryogenic temperatures and any use of cryogenic fluids. Suitable cryogenic fluids include, but are not limited to, for example, any conventional cryogenic agent and other chillers, such as chilled water, ice, compressible organic solvents, such as brakes, liquid carbon dioxide, liquid nitrogen, liquid helium, and their combinations. The modification, chemical or physical, of the catalysts, prepared according to the process of the present invention, may result in unexpected improvements in the efficiency of the modified catalyst and the selectivity in the alkane, alkene or in the oxidations of alkanes and alkenes, in comparison with the known corresponding catalysts, and improved yields of the oxygenated products. The known catalysts can be obtained from commercial sources, conventional preparation methods or by any of the methods of the present invention. The term "modified catalysts" does not refer to or includes regenerated, reconditioned and / or recycled catalysts. The term "conditioning" refers to the conventional heating of prepared metal oxide catalysts, with gases including hydrogen, nitrogen, oxygen and their selected combinations. As used herein, the term "cumulatively convert" refers to producing a desired product stream of one or more specific reagents, using one or more modified catalysts and modified catalyst systems of the invention, under specific reaction conditions. As an illustrative embodiment, the cumulative conversion of an alkane to its corresponding unsaturated carboxylic acid means that the modified catalysts used, they will produce a product stream comprising the unsaturated carboxylic acid corresponding to the added alkane, when acting in a charge stream, comprising the alkane and the molecular oxygen, under the assigned reaction conditions. According to a separate embodiment, the present invention also provides a process for optimizing the conversion of the recycled alkanes, alkenes, alkanes and specific alkenes and their corresponding oxygenated products. Optionally, the catalysts of modified metal oxides are obtained by the chemical, physical treatment and combinations of chemical and physical treatments of suitable prepared metal oxide oxidizers. Optionally, the modified catalysts are further modified by conventional process techniques, well known to those skilled in the art. The chemical treatments, which result in the modified catalysts, include one or more chemical modifying agents. Physical treatments, which result in modified catalysts include one or more physical processes. According to a separate embodiment, the modified catalysts include one or more chemical and / or physical treatments of the already modified catalysts.

Once obtained, the resulting precursor of the modified catalyst is used as modified or further modified by conventional processes, well known in the art, including further grinding and calcination. According to one embodiment, the calcination can be conducted in an atmosphere containing oxygen or in the substantial absence of oxygen, for example in an inert atmosphere or under vacuum. This inert atmosphere can be of any material that is substantially inert, ie does not react or interact with the catalytic precursor. Suitable examples include, without limitation, nitrogen, argon, xenon, helium or their mixtures. Preferably, the inert atmosphere is argon or nitrogen. The inert atmosphere can flow on the surface of the catalyst or can not flow on it (a static environment). When the inert atmosphere does not flow on the surface of the catalyst precursor, the deluxe regime can vary over a wide range, for example at a space velocity of 1 to 500 hr "1 The calcination of the MMO catalysts, such as those described above, they are usually carried out at temperatures of 350 to 850 ° C, preferably 400 to 700 ° C, more preferably 500 to 640 ° C. for a suitable amount of time to form the aforementioned catalyst. Typically, calcination is carried out for 0.5 to 30 hours, preferably 1 to 25 hours, more preferably 1 to 15 hours, to obtain the desired mixed metal oxide promoted. According to one embodiment, the catalyst is calcined in two stages. In the first step, the catalyst precursor is calcined in an oxidizing environment (for example air) at a temperature of 200 to 400 ° C, preferably 275 to 325 ° C, for 15 minutes to 8 hours, preferably 1 to 3 hours. In the second step, the material of the first stage is calcined in an oxidizing environment (for example in an inert atmosphere) at a temperature of 500 ° C 700 ° C, preferably at 550 ° C up to 650 ° C, for 15 minutes until 8 hours, preferably from 1 to 3 hours. Optionally, a reducing gas, such as, for example, ammonia or hydrogen, can be added during the second calcination stage. The MMO catalyst (promoted or not), obtained by the aforementioned method, can be used as a final catalyst, but can also be subjected to one or more additional chemical, physical and combinations of these treatments. According to one modality, the MMO catalysts produced according to the process of the present invention are further modified using a heat treatment. As an exemplary embodiment, the heat treatment is usually carried out at a temperature of 200 ° C to 700 ° C for 0.1 to 10 hours. The resulting mixed metal oxide (promoted or not) can be used by itself as a solid catalyst. The modified catalysts can be combined with one or more suitable carriers, such as, without limitation, silica, alumina, titania, aluminosilicate, diatomaceous earth or zirconia, according to the techniques described in the art. In addition, it can be processed to a suitable configuration or particle size, using the techniques described in the art, depending on the scale or system of the reactor. Alternatively, the metal components of the modified catalysts are supported on materials, such as alumina, silica, silica-alumina, zirconia, titania, etc., by conventional incipient wet techniques. In a typical method, the solutions containing the metals are brought into contact with the dry support, so that the support is moistened, then the resulting moistened material is dried, for example at a temperature from room temperature to 200 ° C, followed by calcination, as described above.

In another method, the metal solutions are contacted with the support, typically in bulk ratios greater than 3: 1 (metal solution: support) and the solution is stirred so that the metal ions are exchanged for ions in the support . The metal-containing support is then dried and calcined, as detailed above. According to a separate embodiment, the modified catalysts are also prepared using one or more monomers. The starting materials for the promoted mixed metal oxide are not limited to those described above. A wide range of materials includes, for example, oxides, nitrates, halides or oxyhalides, alkoxides, acetylacetonates and organometallic compounds, can be used. For example, the ammonium heptamolibdste can be used for the source of the molybdenum in the catalyst. However, compounds, such as Mo03 Mo02, MoCl2 MoOCl2, Mo (0C2H5) 2, molybdenum acetylacetonate, phosphomolybdic acid and silicomolybdic acid, can be used in place of ammonium heptamolybdate. Similiarly, the ammonium metavandate can be used for the vanadium source in the catalyst. However, compounds, such as V205, V203, V0C13, VCI3, V0 (0C2H5) 2, vanadium acetylacetonate, and vanadyl acetylacetonate, can be used, instead of ammonium tetravanadate. The source of tellurium can include telluric acid, TeCl, Te (OC2H5) 5, TeOCH (CH3) 2 and Te02. The source of niobium can include niobium-ammonium oxalate, Nb205, NbCl5, nbic acid Nb (OC2H5) 5, as well as the more conventional niobium oxalate. In addition, with reference to the promoter elements for the promoted catalyst, the nickel source may include nickel (II) acetate trihydrate, N (N03) 2, nickel (II) oxalate, NiO, Ni (OH) 2, NiCl2, NoBr2, nickel (II) acetylacetonate, nickel (II) sulfate, NiS or nickel metal. The palladium source may include Pd (N0) 2, palladium (II) acetate, palladium oxalate, PdO, Pd (0H) 2, PdCl 2, palladium acetylacetonate or palladium metal. The copper source can be copper acetate, copper acetate monohydrate, copper acetate hydrate, copper acetylacetonate, copper bromide, copper carbonate, copper chloride, copper chloride dihydrate, copper fluoride, hydrate of copper format, copper gluconate, copper hydroxide, copper iodide, copper methoxide, copper nitrate, copper nitrate hydrate, copper oxide, copper tartrate hydrate or a copper solution in an aqueous inorganic acid , for example the acid nitric. The silver source can be silver acetate, silver acetylacetonate, silver benzoate, silver bromide, silver carbonate, silver chloride, silver citrate hydrate, silver fluoride, silver iodide, silver lactate, silver nitrate, silver nitrite, silver oxide , silver phosphate or a silver solution in an aqueous inorganic acid, for example nitric acid. The gold source can be ammonium tetrachloroaurate, gold bromide, gold chloride, gold cyanide, gold hydroxide, gold iodide, gold oxide, gold trichloride acid and gold sulfide. The MMO catalysts, prepared according to the process of the present invention, have different chemical, physical and performance characteristics. in the catalytic reactions of carbon-based molecules, compared to the other catalysts. According to one embodiment of the modified catalyst, the changes that are exhibited in the X-ray diffraction lines, the peak positions and the intensity of each line and crests, as compared to the X-ray diffraction data for other corresponding catalysts . Such differences indicate structural differences between the catalysts known and the catalysts of the present invention and are evident from the activity and catalytic selectivity. The MMO catalysts, prepared according to the process of the present invention exhibit improved performance characteristics of the catalyst, selected from the group consisting of optimized catalyst properties of the oxygenates, including the unsaturated carboxylic acids of their alkanes, corresponding alkenes or combinations thereof, with a constant conversion of alkane / alkene, selectivity of the oxygenated products, including the unsaturated carboxylic acids, their alkanes, corresponding alkenes or corresponding alkane and alkene combinations, optimized charge conversion, cumulative yield of the desired oxidation product, optimized reagent / product recycling conversion, optimized product conversion, by recycling and their combination, compared to known catalysts. MMO catalysts, prepared according to the process of the present invention, have improved performance characteristics, compared to catalysts known in catalytic processes comprising any molecule containing carbon. From according to one embodiment of the invention, the modified catalysts have improved performance characteristics, compared to known catalysts in processes for preparing dehydrogenated products and oxygenated products from alkanes and oxygen, alkenes and oxygen and combinations of alkanes, alkene and oxygen . The reactions are typically carried out in conventional reactions with catalytically converted alkanes in conventional residence times (> 100 milliseconds) in conventional reactors. According to a separate embodiment, the reactions are carried out with short contact times (£ 100 milliseconds) in a short contact time reactor. Suitable alkanes include alkanes having straight or branched chains. Examples of suitable alkanes are C4-C25 alkanes. which include the C2-C8 alkanes, such as propane, butane, isobutane, pentane, isopentane, hexane and heptane. Particularly preferred alkanes are propane and isobutane. The MMO catalysts, prepared according to the process of the present invention, convert the alkanes, alkenes or alkanes and alkenes to their corresponding alkenes and oxygenates, which include the saturated carboxylic acids, unsaturated carboxylic acids, their esters and higher analog carboxylic acids and their esters. The catalytic and catalytic systems produced by the process of the present invention are designed to provide specific alkenes, oxygenates and combinations thereof. The alkenes are catalytically converted to one or more products in a single pass, which include the corresponding alkenes. Any alkane, alkene or unreacted intermediate is recycled to catalytically convert to its corresponding oxygenate. According to one embodiment, the alkenes produced from the dehydrogenation of the corresponding alkanes, which use the catalytic systems of the invention, are deliberately produced as intermediates of the chemical process and not isolated prior to partial selective oxidation to the oxygenated products. For example, when an alkane is catalytically converted to its corresponding ethylenically unsaturated carboxylic acid, any unreacted alkene produced is recovered or recycled to catalytically convert to its corresponding ethylenically unsaturated carboxylic acid product stream. The catalytic and catalytic systems produced by the process of the present invention also convert alkanes to their unsaturated carboxylic acids ethylenically, corresponding, and higher analogs, having straight or branched chains. Examples include ethylenically unsaturated C-C8 carboxylic acids, such as acrylic acid, methacrylic acid, butenoic acid, pentanoic acid, hexanoic acid, maleic acid and crotonic acid. The carboxylic acids, ethylenically unsaturated, higher analogues, are prepared from the corresponding alkanes and aldehydes. For example, methacrylic acid is prepared from propane and formaldehyde. According to a separate embodiment, the corresponding acid anhydrides are also produced when the ethylenically unsaturated carboxylic acids of their respective alkanes are prepared. The modified catalysts of the invention are usefully employed to convert propane to acrylic acid and its larger unsaturated carboxylic acids and to convert isobutane to methacrylic acid. The catalytic and catalytic systems produced by the process of the present invention are also advantageously used to convert the alkanes to their corresponding esters of unsaturated carboxylic acids and larger analogues. Specifically, its esters include, but are not limited to, butyl acrylate of butyl alcohol and propane, β-hydroxyethyl acrylate ethylene-glycol and propane, methyl methacrylate of methanol and isobutane, butyl methacrylate of butyl alcohol and isobutane, ß-hydroxyethyl methacrylate of ethylene glycol and isobutene, and methyl methacrylates of propane, formaldehyde and methanol. In addition to these esters, the ether esters are formed by this invention, varying the type of alcohol introduced into the reactor and / or the alkane, alkene or alkane and alkene introduced into the reactor. Suitable alcohols include the monohydric alcohols, dihydric alcohols and polyhydric alcohols. Of the monohydric alcohols reference may be made, without limitation, to the C?-C20 alco, preferably C3-C3, alcohols, more preferably C?-C4-alcohols. The monohydric alcohols may be aromatic, aliphatic or alicyclic, straight or branched chain, saturated or unsaturated and primary, secondary or tertiary. Particularly preferred monohydric alcohols include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol and tertiary butyl alcohol. From the dihydric alcohols reference may be made, without limitation, to the C2-C6 diols, preferably C2-C4 diols. Dihydric alcohols can be aliphatic or alicyclic, straight or branched chain, and primary, secondary or tertiary. Particularly preferred dihydric alcohols include ethylene glycol (1,2-ethanediol), propylene glycol (1,2-propanediol), trimethylene glycol (1,3-propanediol), 1,2-butanediol and 2,3- butanediol Of the polyhydric alcohols reference is made only to glycerol (1,2,3-propanetriol). The unsaturated carboxylic acid, which corresponds to the added alkane, is the α, β-unsaturated carboxylic acid having the same number of carbon atoms as the starting alkane and the same carbon chain structure, such as the starting alkane, For example, acrylic acid is the unsaturated carboxylic acid corresponding to propane and methacrylic acid is the unsaturated carboxylic acid corresponding to isobutane. The mixed metal oxide, thus obtained, is typically used by itself as a solid catalyst, but can be formed in a catalyst together with a suitable carrier, such as silica, alumina, titania, aluminosilicate, diatomaceous earth or zirconia. In addition, it can be routed in a suitable configuration and with a particle size that depends on the scale or system the reactor.

Alternatively, the metal components of the modified catalysts can be supported on materials, such as alumina, silica, silica-alumina, zirconia, titania, etc. By conventional incipient moisture techniques. In a typical method, solutions, containing the metals, are brought into contact with the dry support, so that this support is moistened, then, the resulting moist material is dried, for example, at a temperature from the ambient to 200 °. C, followed by calcination, as described above. In another method, the metal solutions are contacted with the support, typically in bulk ratios greater than 3: 1 (metal solution: support) and the stirred solution so that the metal ions are exchanged on the support. The metal-containing support is then dried and calcined, as detailed above. When a catalyst system including two or more modified catalysts is used, this catalyst may be in the form of a physical mixture of several catalysts. Preferably, the concentration of the catalysts can vary so that the first component the catalyst has a tendency to be concentrated in the reactor inlet, while the subsequent catalysts they will have a tendency to be concentrated in areas in sequence, which extend to the exit of the reactor. More preferably, the catalysts will form a layer bed (also referred to as a mixed bed catalyst) with the first catalyst component forming the layer closest to the reactor inlet and the subsequent catalysts form layers in sequence at the outlet of the reactor. The layers abut one another or can be separated from each other by a layer of inert material or an empty space. The invention provides a process for producing an unsaturated carboxylic acid, which comprises subjecting an alkane, alkene or a mixture of alkanes and alkenes ("alkane / alkene") to a catalytic oxidation reaction in the vapor phase, in the presence of a catalyst containing the mixed metal oxide promoted above, to produce an unsaturated carboxylic acid. In the production of such unsaturated carboxylic acid, it is preferred to employ a gas of the starting material that contains water vapor. In such a case, as a gas of the starting material to be supplied to the reaction system, a gas mixture comprising an alkane containing steam or a mixture of gases containing an alkane containing steam in water, or a mixture of alkanes and Alkenes containing water vapor, and an oxygen containing gas, is generally used. However, the alkane containing water vapor or the mixture of alkanes and alkenes containing water vapor, and the oxygen-containing gas, can alternatively be supplied to the reaction system. The water vapor to be employed may be present in the form of the water vapor gas in the reaction system, and the manner of its introduction is not particularly limited. Also, as a gas in dilution, an inert gas, such as nitrogen, argon or helium, can be supplied. The molar ratio (alkane or mixture of alkane and alkene) (oxygen) (dilution gas): (H20) in the gas of the starting material is preferably (1): 0.1 to 10): (0 to 20): ( 0.2 to 70), more preferably of (1): (9 to 5.0): (0 to 10): (5 to 40). When the steam is supplied together with the alkane, or the mixture of alkanes and alkenes, as the gas of the starting material, the selectivity for an unsaturated carboxylic acid is distinctly improved, and the unsaturated carboxylic acid can be obtained from the alkane or the mixture of alkanes and alkenes, send performance, simply by contact in one stage. However, the Conventional technique uses a dilution gas, such as nitrogen, argon or helium for the purpose of diluting the starting material. As such, a dilution gas for adjusting the space velocity, the partial pressure of oxygen and the partial pressure of water vapor, an inert gas, such as nitrogen, argon or helium, can be used together with water vapor. As the alkane of the starting material, it is preferred to employ a C2_8 alkane, particularly propane, isobutane or n-butane, more preferably propane or isobutane, especially preferred, propane. According to the present invention, of this alkane, an unsaturated carboxylic acid, such as α, β-unsaturated carboxylic acid can be obtained in good yield. For example, when propane or isobutane is used as the alkane of the starting material, acrylic acid or methacrylic acid, respectively, can be obtained in good yield. This aspect of the present invention is described in even more detail with respect to a case where propane is used as the alkane of the starting material, and air is used as the source of oxygen. The reaction system may preferably be a fixed bed system. The proportion of the air to be supplied to the reaction system is important for the selectivity for the resulting acrylic acid, and is usually at most 25 moles, preferably 0.2 to 18 moles per mole of propane, so high selectivity can be obtained. The reaction can usually be conducted under atmospheric pressure, but can be conducted under slightly elevated pressure or slightly reduced pressure. With respect to other alkanes, such as isobutane, or mixtures of alkanes and alkenes, such as propane and propene, the composition of the charge gas can be selected according to the conditions for propane. Typical reaction conditions for the oxidation of propane or isobutane to acrylic acid or methacrylic acid can be used in the practice of the present invention. The process can be practiced in a single-pass mode (only a fresh charge is fed to the reactor) or in a recycling mode (at least a portion of the reactor effluent is returned to this reactor). The general conditions for the process of the present invention are as follows: the reaction temperature may vary from 200 ° C to 700 ° C, but is usually in the range of 200 ° C to 550 ° C, more preferably 250 ° C at 480 ° C, and especially preferred from 300 ° C to 400 ° C; speed Spatial gas, SV, in the vapor phase reaction, is usually within a range of 100 to 10,000 hr "1 preferably 300 to 6,000 hr" 1, more preferably 300 to 2,000 hr "1, the contact time average with the catalyst can be 0.01 to 10 seconds or more, but is usually in the range of 0.1 to 10 seconds, preferably 0.2 to 6 seconds, the pressure in the reaction zone usually ranges from 0 to 5.25 kg / cm2, but it is preferably no greater than 4.5 kg / cm.sup.2 In the one-pass mode process, it is preferred that the oxygen be supplied from an oxygen-containing gas, such as air.The process of the one-pass mode can be practiced with the addition of oxygen In the practice of the recycling mode process, the oxygen gas by itself is the preferred source, in order to avoid the accumulation of inert gases in the reaction zone The loading of hydrocarbons in the catalytic process it is dependent on the mode of operation tion (for example, a single pass, in batches, recycling, etc.) and varies from 2% by weight to 50% by weight. According to a separate mode, the catalytic process is a batch process. According to a separate process, the catalytic process is continuously operated. This catalytic process of conventional beds includes, but is not it limits to static fluid beds, fluidized beds, moving beds, transport beds, moving beds as the beds that rise and boil. Any catalytic process is carried out under stable state conditions or non-stable state conditions. The following illustrative examples are provided to further demonstrate the utility of the present invention and should not be construed in a limiting sense. Also, the examples provided are representative examples that make the claimed scope of the invention widely possible. In the following Examples, "propane conversion" is synonymous with "charge conversion" and was calculated according to the formulas provided hereinabove. Also, "AA yield" means the yield of acrylic acid and is synonymous with the "yield of the product" and was calculated according to the formulas provided herein above. Unless otherwise specified, all percentages mentioned in the following Examples are in volume, for the total volume of the load or product gas stream.

EXAMPLES Comparative Examples 1A-1G (synthesis with microwave irradiation) The ammonium heptahydrate, vanadate in ammonium and telluric acid were used to prepare Solution A, in the following amounts: M Mo, 0.3 M of V and 0.23 M of te. Niobium ammonium oxalate, oxalic acid dehydrate, palladium (II) nitrate hydrate and nitric acid were used to prepare Solution B, in the following amounts: 0.17 M Nb, 0.15 M oxalic acid, 0.24 M HN03 and 0.01 M of Pd. Alternative sources for V and Te include vanadyl sulfate hydrate and tellurium oxide. A catalyst of the nominal composition M ??. 0 V0.3 Te0.3 Nb0.? Pdo.oi 08, was prepared by mixing the mentioned solutions A and B within a reactor. The volume mixture was then irradiated with microwaves. The resulting gel was dried at room temperature. The dried sample was calcined under air at 25 ° C to 275 ° C at 10 ° C / minute and kept at 275 ° C for 1 hour, and then under argon at 275 ° C up to 600 ° C at 2 ° C / minute , and kept at 600 ° C for 2 hours. The catalyst, thus obtained, was pressed into a mole and then broken and sieved to 10-20 mesh granules. . 8 g of the above catalyst was packed in a stainless steel straight flow (SDF) tube reactor (inner diameter of 1.1 cm) for the gas phase oxidation of the propane. The SDF reactor was placed in an oven and fed with a mixture of propane, air and water vapor, which has a charge composition of 7% propane, 14.7% oxygen (in air) and 2% vapor in water The effluent from the reactor was condensed to a separate liquid phase and gas phase. The gas phase was analyzed by gas chromatography, to determine the conversion of propane. The liquid phase was also analyzed by gas chromatography for the supply of acrylic acid. The previous evaluation of the catalyst in the SDF reactor system was repeated four times. The results, together with residence time and reactor temperature, are shown in Table 1.

TABLE 1 Examples 2A-2D (Synthesis for preparing precursor solutions comprising aerosol and irradiating with microwave energy). Ammonium heptahydrate, ammonium vanadate, and telluric acid were used to prepare Solution A, in the following amounts: 1M Mo, 0.3 M V, and 0. M Te. Niobium ammonium oxalate, oxalic acid dehydrate, palladium (II) nitrate hydrate, and nitric acid were used to prepare a solution B. In the following amounts: 0.17 M Nb, 0.155 M oxalic acid, 0.24 M of HN03 and 0.01 M of P.S. Alternative sources for V and Te include vanadyl sulfate hydrate and telluric oxide. A catalyst of the nominal composition: MOi.oVo.3Teo.23Nbo.17Pdo.01Ox was prepared in accordance with the process of the present invention, as follows: Solutions A and B were mixed in-itself by the passage through a Ultrasonic nozzle device, using two syringes, a connector on ¡T! And a syringe pump. The resulting mixture was injected into a tubular reactor into a microwave chamber, which uses a nozzle spray, which resulted in the formation of small droplets, which then formed a gel of the precursor mixture. The resulting gel was dried at room temperature. The dried sample was calcined under air at 25 ° C to 275 ° C at 10 ° C / minute and kept at 275 ° C for 1 hour, and then under argon at 275 ° C up to 600 ° C at 2 ° C / minute, and it was kept at 600 ° C for 2 hours. 5.8 g of the above catalyst were packed in a stainless steel straight flow (SDF) tube reactor (internal diameter of 1.1 cm) for the oxidation of propane gas. The SDF reactor was placed inside an oven and was fed with a mixture of propane, air and water vapor, which has a final composition of 6.9% propane, 14.7% oxygen (in the air) and 23% steam.

Water. The effluent from the reactor was condensed to a separate liquid phase and vapor phase. The gas phase was analyzed by gas chromatography, to determine the conversion of propane. The liquid phase was also analyzed by gas chromatography for the supply of acrylic acid. The previous evaluation of the catalyst in the SDF reactor system was repeated six times. The results, together with residence time and reactor temperature, are shown in Table 2.

TABLE2 The above examples demonstrate that the catalyst of Comparative Examples 1A-1G and Examples 2A-2F were both successful in the vapor phase oxidation of an alkane to partial oxidation products. However, the catalyst produced by the process in which the catalyst precursors are first mixed and atomized to an aerosol, using an ultrasonic nozzle, and then irradiated with microwave energy, ie, Examples 2A-2F, performed better in that higher yields of acrylic acid were achieved. It will be noted that the X-ray diffraction analysis (XRD) of the catalyst of Comparative Examples 1A-1G and Examples 2A-2F suggest the presence of the MI phase in both examples. The SEM analysis for both catalysts showed, respectively, a bar-type morphology. This bar-type morphology has been widely reported in the literature for this class of materials prepared by conventional hydrothermal methods. However, the particle dimensions of the materials prepared by Microwave, by both methods, were significantly lower. Both catalysts have particle sizes of about 0.2 nm to about 0.3 μm in diameter and about 1 μm in length. These dimensions were around 10 times smaller than hydrothermally prepared materials. In addition, the use of a nozzle spray in the catalyst preparation of Examples 2A-2F, in accordance with the process of the present invention, appeared to have a more uniform environment for the catalyst of Comparative Examples 1A-1G, for a process in volume and using microwave irradiation). It will be understood that the embodiments of the present invention, described above, are merely exemplary and that a person skilled in the art can make variations and modifications without departing from the spirit and scope of the invention. All these variations and modifications are intended to be included within the scope of the present invention.

Claims (8)

1. CLAIMS 1. A process to prepare one or more mixed metal oxide catalysts, suitable for the partial oxidation of alkanes, alkenes and their mixtures, this process comprises the steps of: a) generating one or more aerosols from one or more solve, comprising at least one precursor of a mixed metal oxide catalyst; and b) irradiating said one or more aqueous aerosols of one or more mixed metal oxide precursors, with microwave energy, having one or more microwave frequencies.
2. 2. The process, according to claim 1, wherein this one or more catalysts prepared from mixed metal oxides, comprises a compound having the empirical formula: MoV_NbbXcZdO, wherein X is at least one element, selected from the group consisting of Te and Sb, Z is at least one element, selected from the group consisting of , Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Pb, P. B , And, elements of rare earths and alkaline earth elements, 0-1 £ to £ 1.0, 0.01 £ b £ 1.0, 0. 01 c 1.0,? £ d £ l.O and n was determined by the oxidation states of the other elements.
3. 3. The process, according to claim 1, further comprising the step of calcining said one or more mixed metal oxide catalysts, after the irradiation step.
4. 4. The process, according to claim 1, wherein said one or more mixed metal oxide catalysts are calcined during the microwave irradiation of this one or more mixed metal oxide precursor aerosols.
5. 5. The process, according to claim 1, wherein said one or more mixed metal oxide precursor aerosols are generated using an ultrasonic nozzle.
6. 6. The process, according to claim 1, further comprising the step of further modifying this one or more metal oxide catalysts, using one or more chemical treatments, one or more physical treatments and one or more combinations of chemical and physical treatments. .
7. 7. A catalyst prepared by the process of claim 1.
8. 8. A process for the partial oxidation of an alkane, alkene or a mixture of an alkane and an alkene, in the presence of a catalyst, produced by the process of claim 1, wherein said process produces one or more oxidation products, selected of the group consisting of an unsaturated carboxylic acid and an unsaturated nitrile.