GB2544277A

GB2544277A - Catalysts

Info

Publication number: GB2544277A
Application number: GB1519799.9A
Authority: GB
Inventors: Michael Brown Christopher; Richard Ellis Peter
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2015-11-10
Filing date: 2015-11-10
Publication date: 2017-05-17
Also published as: GB201519799D0

Abstract

A process for the hydrogenation of an unsaturated organic compound to produce a more saturated compound (preferably the conversion of alkynes to alkenes) comprising the step of contacting a process feed stream comprising the unsaturated compound with hydrogen in the presence of a catalyst comprising at least two metals selected from the group consisting of platinum, palladium, gold, titanium and tin supported on a catalyst support material, wherein the catalyst is made by depositing the metals on the support by sputtering. Suitable catalyst supports include carbon, alumina, silica, kieselguhr, titania, zirconia, magnesia, iron oxide, a rare-earth oxide, a clay, cement, diatomaceous earth, zeolite and silicon carbide. Preferred sputtered hydrogenation catalysts are palladium-gold (Pd-Au) and palladium-titanium (Pd-Ti) on particulate alumina or titanium dioxide (TiO2). Preferably the catalyst is made by cluster beam sputtering methods. The hydrogenation of 3-hexyne-1-ol to 3-hexene-1-ol and 1-pentyne to 1-pentene are exemplified.

Description

Catalysts

The present invention concerns metallic catalysts, methods of manufacturing catalysts and use of catalysts in chemical reactions.

Metallic catalysts are very widely used to perform many types of reactions in the chemical industry. Traditional methods of catalyst preparation include precipitation of metal compounds from solution, optionally in the presence of a solid support material, and impregnation of porous solid support materials with solutions of compounds of catalytic metals, often followed by a calcination and/or reduction step. Deposition of charged or uncharged metal particles from the gas phase onto a support material is also known. For example, Palmer et al (J. Phys Chem. C 2012,116, 26295-26299) describe the synthesis of size-selected palladium nanoparticles by condensation of metal atoms and ions in the gas phase, followed by deposition on graphite powders and their use in the selective hydrogenation of 1-pentyne. Palmer et al (Phys. Chem. Chem. Phys. 2014 16 26631-26637) describe the effects of the same hydrogenation reaction on size-selected Au and Pd nanoclusters. There is a continuing need for improved catalysts and more efficient chemical reactions.

According to the invention, a process for the hydrogenation of an unsaturated organic compound to produce a more saturated compound comprises the step of contacting a process feed stream comprising said unsaturated compound with hydrogen in the presence of a catalyst comprising at least two metals selected from the group consisting of platinum, palladium, gold, titanium and tin supported on a catalyst support material, wherein said catalyst is made by depositing said metals on said support from the gas phase by sputtering.

By “more saturated compound” we mean that the amount of unsaturation in the unsaturated compound is reduced by the hydrogenation process of the invention. For example, an alkyne may be hydrogenated to an alkene, which is less unsaturated than an alkyne. The unsaturated organic compound may be an alkene or alkyne. The unsaturated organic compound may be multiply unsaturated, for example it may be a diene ortriene. The unsaturated organic compound may incorporate one or more functional groups in addition to the unsaturation, for example carbonyl groups (including carboxylic acid, ester, aldehyde, ketone, amide); hydroxyl, amine. In particular embodiments the unsaturated organic compound is an alkyne. The alkyne is preferably selectively hydrogenated to an alkene.

The process feed stream may contain compounds in addition to the unsaturated organic compound which is to be hydrogenated. Such additional compounds may be diluents or carrier compounds, such as other organic compounds or inert gases such as nitrogen. The unsaturated organic compound to be hydrogenated may be present as a minor component in the feed stream. For example, the unsaturated organic compound which is to be selectively hydrogenated may comprise an alkyne or a diene which is present as an impurity or byproduct in a feed stream comprising an alkene.

The process feed stream may be liquid or gaseous. The process may be carried out as a batch reaction or continuously. The contact of the feed stream with hydrogen in the presence of a catalyst may be carried out at any suitable temperature and pressure. A typical process temperature may be in the range from room temperature up to 350 °C, for example from 100 - 300 °C. The temperature selected depends upon the nature of the organic unsaturated compound, the nature and concentration of the catalyst, the reaction pressure and other process parameters. The skilled person will select the most appropriate reaction temperature based on experience with similar reactions. A typical process pressure may be in the range from atmospheric pressure up to 120 bar, for example from 5-100 bar. The pressure selected depends upon the nature of the organic unsaturated compound, the nature and concentration of the catalyst, the reaction temperature and other process parameters. The skilled person will select the most appropriate reaction pressure based on experience with similar reactions.

The catalyst support material may be any known catalyst support. Typical catalyst supports include carbon, metal/metalloid oxide materials, clays, cements, diatomaceous earth and other minerals, zeolites, silicon carbide. Metal/metalloid oxide materials include alumina, particularly transition aluminas such as gamma, theta or delta alumina; silica, kieselguhr, titania, zirconia, magnesia, iron oxide and rare-earth oxides such as lanthana orceria. The supports may be in the form of powders, for example having a particle size of from about 10 nm to < 0.5mm. The catalyst may be in the form of powders or larger shaped particles, having a particle size of from 0.5mm to 10mm or larger. The shape of the shaped particles may be any of the shapes typically used in chemical processes, such as spheres, cylinders, granules, rings, saddles, etc. Such shapes may be formed by tabletting, extrusion, moulding, granulation or other methods. Such forming may take place after deposition of the metals onto the support. Alternatively a catalyst support in the form of such larger shaped particles may be used. The catalyst may be formed into a coating coated on a substrate such as a monolith or a surface of a reactor, such as the internal wall of a reaction tube.

The catalyst is made by depositing said metals on said support from the gas phase. This method of metal deposition is often referred to as sputtering. In particular the catalyst may be made by cluster beam sputtering methods, i.e. by generating clusters of metal atoms by magnetron sputtering metal atoms from a target, cooling and condensing the atoms into clusters. The cluster size may be monitored and selected using a mass selection chamber or mass filter. The metal clusters may be ionised. The clusters typically form a beam of particles which may be manipulated using “ion optics” to accelerate and direct the clusters into a deposition chamber. The support material is present in the deposition chamber. The support material is usually contained within a vessel provided with means to move or agitate the support material during deposition of the metal atoms or clusters so that the portion of surface of the support material which is exposed to the beam of atoms or clusters is continuously changed in order that the deposited metal atoms or clusters are deposited on a large proportion of the surface(s) of the support material or particles thereof. The vessel may be rotated, tilted or otherwise agitated in order to achieve movement of a support material contained therein.

The metals are present in the sputtering apparatus in the form of one or more solid sputtering targets. A target may be formed from the two or more metals comprising the catalyst of the invention. Alternatively more than one metal target may be used, e.g. a separate metal target may be used for each of the two or more metals comprising the catalyst of the invention.

Each metal target may be formed from a single metal. The metal targets(s) are installed into a magnetron mounted in a sputtering chamber. More than one magnetron may be present in the sputtering chamber. The use of more than one magnetron allows the sputtering conditions to be varied for each target. In this way, the relative cluster sizes, metal ratios and deposition patterns on the support may be varied.

The atom cluster sizes may be selected to be the same or different. The cluster sizes usually cover a range, usually distributed as a distribution curve when plotted as particle size vs number of particles of a particular particle size. The range of cluster sizes may vary from 1 to 20 nm. The peak of the particle size distribution curve may vary between 2-10 nm. The clusters are typically selected according to mass. The clusters may be selected to contain from about 50 to about 5000 atoms. The term “about” generally reflects the fact that the clusters normally contain a varied number of atoms. The number of atoms selected in a cluster size may be ± 10%. The clusters of atoms may contain a single metal or both or all of the at least two metals in the catalyst. The metal clusters may be deposited simultaneously or sequentially. The disposition of metals on the support may comprise a core-shell type of arrangement in which a first layer of metal on the support comprises predominantly a first metal or a first mixture of metals and then a second and optionally a subsequent layer of metal comprises predominantly a second metal or a second mixture of metals.

The catalyst contains at least two metals selected from the group consisting of platinum, palladium, gold, titanium and tin. Preferred catalysts contain palladium and/or gold.

Preferred combinations of metals are Pd/Ti and Pd/Au. Bimetallic catalysts containing titanium deposited upon a support are difficult to make by traditional methods such as impregnation or precipitation. This is because titanium compounds are hydrolytically unstable so stable aqueous precursors of titanium are rare. The use of organic titanium compounds is, of course, feasible but the use of organic solvents in catalyst synthesis is economically and environmentally unfavourable. For example, we have been able to synthesize catalysts containing both palladium and titanium using THF as a solvent. THF is flammable, has mutagenic properties and can form explosive peroxides overtime when stored. This makes it poorly suited to manufacturing processes such as catalyst manufacturing. However, the paucity of water soluble titanium precursors means that an organic solvent is typically needed to make a PdTi catalyst. It is believed that the preparation of a supported palladium -titanium catalyst by deposition cluster beam magnetron sputtering is new and represents an inventive step over prior catalysts. Although the titanium deposited cluster beam magnetron sputtering may be oxidised in air to titanium oxides, the structure of such a catalyst is different from a palladium catalyst supported on titania. When titanium and palladium are deposited by sputtering, the Pd and Ti atoms are located in the same region of the catalyst and may be mixed together. When Pd is deposited onto a titania support material, the Ti atoms are part of the support, whist the Pd atoms are found on the surface of the support, or within pores. If Pd and Ti are co-impregnated from a solution, the Ti atoms are believed to migrate onto the support.

The catalyst may contain a mass ratio of each of the at least two metals to each other metal in the range 100- 1:1-100. The total amount of the at least two metals present in the catalyst may be in the range from 0.01 to 5%, especially 0.01 to 2%, particularly 0.01 - 1% by weight, based on the total mass of the catalytic metals plus the catalyst support.

The invention will be demonstrated in the following examples, which are not intended to limit the scope of the invention.

Example 1: Preparation of catalyst by cluster beam deposition of metals onto particulate catalyst support. A cluster beam magnetron sputtering apparatus was used which included a magnetron sputtering chamber, an ion optics chamber, mass selection chamber and a particle deposition chamber oriented 90 degrees from the main beam path in which a support container was loaded. When a bimetallic catalyst was made, the apparatus was operated using two magnetrons mounted in the magnetron sputtering chamber. A metal sputtering target of the required metal was installed in each magnetron. About 1 g of particulate support material was loaded into the support container and agitated. The vacuum system was pumped down to a base pressure of below 2.0 x 10-6 mbar and the condensation chamber was cooled using flowing liquid nitrogen. The system was allowed to reach thermal equilibrium (approximately 2 hours). A flow of about 80 seem (standard cubic centimetres per minute) argon and 20 seem helium into the condensation chamber was started. The pressure inside magnetron chamber was about 0.3 mbar, while the pressure outside in the vacuum chamber was about 0.001 mbar. Wth 5 Wto 10 W DC power applied to the magnetron, a plasma was ignited and sputtering process started. Metal clusters were generated and then voltages on the ion optics finely tuned to focus the beam into a mass filter chamber. The gas flow rates of Ar and He, the aggregation length and magnetron power were adjusted to adjust the size distribution of the metal clusters. Once the desired cluster size was generated, the cluster beam was deflected into the powder deposition chamber using an octosphere deflector. The deposition voltage was 1000V. The beam current was approximately! 0 nA, and the deposition took 10 hours. The catalysts made by this method are shown in Table 1.

The catalyst composition at the surface was analysed by X-ray photoelectron spectroscopy (XPS). These data are shown in Table 2.

Comparative Catalyst preparation X

Catalyst X was made by incipient wetness impregnation i.e. by pore-filling a porous support material with a solution of a metal salt, followed by drying and calcination in air or reduction with hydrogen. In a typical synthesis, the desired amount of palladium nitrate and tetrachloroauric acid (HAuCI4) was dissolved in the amount of water needed to fill the pores of the selected support completely, but with no excess solution left over. The impregnated solid was dried at 100°C and then reduced in flowing 5% H2/N2 mixture for two hours at 250°C.

Comparative Catalyst preparation Y

Catalyst Y was made by deposition-precipitation synthesis in which solutions of acidic metal precursors are hydrolysed by strong alkali metal bases in the presence of a suitable support. In a typical synthesis, a solution of mixed palladium nitrate and tetrchloroauric acid (HAuCI4) and a solution of sodium hydroxide were added simultaneously drop-wise to a slurry of the support in water at 60°C. The pH of the solution was maintained at 9 by addition of appropriate amounts of the two solutions. Once the addition was complete, the slurry was heated to boiling, then cooled to room temperature. The slurry was filtered and the solid washed with hot water. The product was dried at 100°C and then reduced in 5% H2/N2 at 250°C for two hours.

Comparative Catalyst preparation Z

Catalyst Z was prepared by impregnation using tetrahydrofuran (THF) as a solvent. In a typical synthesis, the appropriate amounts of palladium (II) acetate and titanium tetraisopropoxide were dissolved in THF. The amount of THF used was chosen to completely fill the pores of the alumina pores but with no solution left over. One the addition was complete, the mixture was air-dried in a fume cupboard for two hours, then in a vacuum oven at40°C overnight. The resulting catalyst precursor was reduced in 5% H2/N2 at 250°C for two hours.

Table 1

*Ti02 support is Aeroxide® P25 fumed Ti02 from Evonik Industries ** alumina is Puralox® HP14/150 from Sasol

Table 2

Example 2: Use of catalyst for the liquid-phase hydrogenation of 3-hexyne-1-ol 3-hexyn-1-ol selective hydrogenation was carried out using a Chemscan reactor consisting of eight 8ml autoclaves which run in parallel with monitoring of hydrogen uptake. The pressure level is maintained throughout the reaction by adding more gas as it is consumed by the reaction. The autoclave was filled with catalyst (24.5mg) and 0.5M 3-hexyn-1-ol solution in ethanol (5ml) with 0.5M 1,4-dioxane as internal standard. The reactor was pressurised to 3 bar with hydrogen, and the reaction temperature increased to 30°C. The reaction time was 90 minutes, which was generally enough time to allow complete conversion to 3-hexen-1-ol. Analysis of products was by offline gas chromatography coupled to a flame ionisation detector (FID-GC) and reaction rates were calculated from the hydrogen uptake curves. The reaction rate R1 is the rate calculated for the hydrogenation of the alkyne triple bond to the alkene double bond. The reaction rate R2 is the rate calculated for the hydrogenation of the alkene double bond to an unsaturated product. R2/R1 may be used as a measure of selectivity where a low value indicates a high selectivity for the alkyne to alkene hydrogenation and a

low selectivity to the over-hydrogenation to the unsaturated product. Results are shown in Table 2:

Table 3

Example 3: Use of catalyst for the gas-phase hydrogenation of 1-pentyne

Pentyne selective hydrogenation testing was performed using a fixed bed reactor. 10mg of catalyst was held in a tube by two plugs of quartz wool. The gas feed consisted of 40% H2/He at 250ml min'1 and 1M pentyne solution in n-hexanewith 0.5M iso-hexane as internal standard at 0.06ml min'1. Once flushing was complete, the catalyst was heated to 230°C at 2°C min'1. Analysis was carried out by online gas chromatography. Conversion of pentyne and selectivity to pentene are shown in Table 3.

Table 4

Claims

1. A process for the hydrogenation of an unsaturated organic compound to produce a more saturated compound comprising the step of contacting a process feed stream comprising said unsaturated compound with hydrogen in the presence of a catalyst comprising at least two metals selected from the group consisting of platinum, palladium, gold, titanium and tin supported on a catalyst support material, wherein said catalyst is made by depositing said metals on said support by sputtering.

2. A process as claimed in claim 1, wherein the unsaturated organic compound is an alkene or alkyne.

3. A process as claimed in claim 2, wherein the unsaturated organic compound is an alkyne.

4. A process as claimed in any one of the preceding claims, wherein the catalyst supports is selected from the group consisting of carbon, alumina, silica, kieselguhr, titania, zirconia, magnesia, iron oxide a rare-earth oxide, a clay, cement, diatomaceous earth, zeolite or silicon carbide.

5. A process as claimed in any one of the preceding claims, wherein the catalyst contains palladium and/or gold.

6. A process as claimed in claim 5, wherein the catalyst contains either Pd and Ti or Pd and Au.

7. A process as claimed in any one of the preceding claims, wherein the catalyst is made by cluster beam sputtering methods.

8. A process as claimed in claim 7, wherein the support material is contained within a vessel provided with means to move or agitate the support material during deposition of the metal atoms or clusters.