METHOD OF SUPPORTED METAL CATALYST PRODUCTION

Abstract: The invention is directed to a method for preparing a supported metal catalyst comprising adding a soluble metal salt to a substrate and then reducing the metal salt to the metal by heating in the presence of a gaseous or liquid hydrocarbon which polymerises on heating.

Description: METHOD OF SUPPORTED METAL CATALYST PRODUCTION TECHNICAL FIELD The invention relates to a method for preparing supported metal catalysts and to supported metal catalysts prepared thereby. The method comprises adding a metal salt to a substrate and then reducing the metal salt by heating in the presence of a hydrocarbon which polymerises on heating. BACKGROUND Catalysts containing metals such as platinum supported on a high surface area substrate are used for a wide range of chemical processes. As a result, there is a large body of knowledge on their preparation and characterisation. It is generally found that the most active catalysts are those with highly dispersed small metal particles. The method used to prepare these catalysts determines the size of the resultant metal particles and their distribution on the substrate and is therefore crucial to the catalyst activity. Both zeolites and alumina are commonly used as catalyst supports, but zeolites have the advantage that they are crystalline materials. This means that a particular zeolite can be selected to give the required reactant/product selectivity and the aluminium concentration can be chosen to control active site distribution and hydrophobicity of the catalyst. The final distribution of metal sites is more homogeneous, as ion exchange of the metal salt results in each metal cation being associated with a zeolite anionic (Al) site. In general, with reference to the preparation of a supported platinum catalyst, a platinum salt is added to the support either by impregnation (where the added solution is evaporated so that all the metal salt remains on the sample) or ion exchange (where after allowing time for exchange to occur, the sample is washed so that only the bound metal salt remains). After washing and drying, the platinum cations are reduced to platinum metal. During this process some of the platinum is mobile and tends to agglomerate forming larger particles. If the platinum salt in the substrate is reduced by heating in hydrogen, large platinum particles are formed in the substrate. An initial calcination in air, before reduction, results in a more active catalyst with smaller platinum particles however, as described by Lei et al (J. Catal. 140, 601), to be effective this calcination must be carried out in an extremely high flow of dry air (200 cm 3 /min/g), with a heating rate of 0.5°C/min. When platinum tetramine salt is used, it is thought that this calcination causes the ammonia ligands to be removed to give bare Pt 2+ cations bound to zeolite anion sites. These bare Pt 2+ are later reduced by hydrogen. Without an extremely high air flow during calcination or during direct reduction in hydrogen, partial reduction of platinum by the departing ammonia ligands occurs. This results in a mobile platinum species being formed which will tend to agglomerate to form large particles thus detrimentally affecting the distribution and size of the platinum particles on the substrate. As a result the activity of the catalyst produced is detrimentally affected. A liquid phase reducing treatment using sodium borohydride is also known but is not used on a large scale. Platinum catalysts produced by industry are simply reduced in hydrogen. Specialised methods have also been used in connection with the reduction of other metal containing compounds to the metal, for example reduction of Fe by CO gas and Ag by decomposition of neo-acids (as reported in USP 4,555,501). Other techniques widely used include electrolysis in Al production for example. USP 4,555,501 to the Halcon SD Group Ine, discloses a method for the oxidation of ethylene to ethylene oxide with molecular oxygen, using a supported Ag catalyst. The preparation of the supported Ag catalyst is disclosed in detail in columns 5 and 6 of USP 4,555,501. The catalysts are stated as being prepared by impregnating a support with a water-free hydrocarbon solution of a silver neo-acid salt. Impregnation is achieved by immersing the support in the silver salt/hydrocarbon solution. The catalyst is then activated by heating the impregnated support to remove the solvent and decompose the neo-acid salt to the elemental silver. The hydrocarbon solvent employed includes hydrocarbons such as toluene, cyclohexane, xylene, ethylene, benzene or cumene. The hydrocarbon solvent used must be such that it is able to be removed by heating prior to the decomposition of the Ag neo-acid salt. JP 59049844 to Cataler Kogyo KK describes a catalyst production method which involves attaching platinum and rhodium to an activated alumina carrier which is then impregnated with a solution of water soluble carbohydrates and then baked. Before baking the water must be removed. There is thus a water removal step needed. The carbohydrates used are high oxygen containing compounds such as sucrose. It is therefore an object of the invention to provide a method for producing catalysts with a metal dispersed on the substrate. Summary of the Invention The invention comprises a method for preparing a supported metal catalyst comprising adding a soluble metal salt to a substrate and then reducing the metal salt to the metal by heating in the presence of a gaseous or liquid hydrocarbon which polymerises on heating. Preferably the metal is a transition metal. Preferably the metal is Pd, Rh, Re, Au, Ag, Cu, Co, Sn, Sb or Pb. Preferably the metal is Pt. Preferably the metal is Pt, Pd, Rh or Au. Preferably the hydrocarbon polymerises on heating in air and the reduction of the metal salt to the metal occurs on heating in air. Preferably the substrate plus the added metal salt is dried without decomposing the metal salt prior to heating in the presence of the gaseous or liquid hydrocarbon. Preferably the metal salt is a tetramine, chloride, nitrate, acetate or carbonate. Preferably the gaseous or liquid hydrocarbon contains no oxygen in its elemental makeup or contains oxygen only in carboxylic groups. Preferably the gaseous or liquid hydrocarbon contains no oxygen in its elemental makeup. Preferably the liquid hydrocarbon polymerises before volatilising. Preferably the liquid hydrocarbon is an oil in which the substrate plus metal salt is soaked before heating. Preferably the oil is an unsaturated vegetable oil or a mineral oil. Preferably the oil is linseed, olive or cedar oil. Preferably the gaseous hydrocarbon is an unsaturated hydrocarbon. Preferably the gaseous hydrocarbon is ethylene, propene or butene. Preferably the gaseous or liquid hydrocarbon flows through the substrate plus platinum salt while it is heated. Preferably the substrate is alumina, silica, a zeolite, a zeotype, or a mesostructure. Preferably the substrate plus metal salt plus organic material is heated to a temperature or range of temperatures, between about 300°C and about 1000°C, more preferably about 450°C. Preferably the substrate plus metal salt plus gaseous or liquid hydrocarbon is held at temperature for a time between about 1 and about 100 hours. Preferably the soluble metal salt is added to a substrate, the combination is then dried without decomposing the metal salt, and then the metal salt is reduced to the metal by heating in air and in the presence of a gaseous or liquid hydrocarbon which contains no elemental oxygen, or contains oxygen only in carboxylic groups, and which polymerises on heating in air. Preferably the combination is dried by heating to a temperature, or range of temperatures, between about 80°C and about 120°C, more preferably about 100°C. Preferably the metal salt is a platinum salt. Preferably the platinum salt is platinum tetramine associated with the chloride or nitrate. Preferably the platinum salt is chloroplatinic acid. The invention in a more limited aspect comprises: (a) adding a soluble metal salt to a substrate; (b) heating the combination of substrate plus soluble metal salt to a temperature sufficient to dry the combination but low enough to avoid decomposition of the soluble metal salt; (c) adding a gaseous or liquid hydrocarbon to the combination; and (d) reducing the soluble metal salt to the metal by heating the substrate plus soluble metal salt plus hydrocarbon to a temperature at which the hydrocarbon is pyrolysed. Preferablv the soluble metal salt is a chloride or nitrate. Preferablv the substrate is a zeolite or alumina. Preferably the hydrocarbon is a liquid hydrocarbon which pyrolyses before it volatilises. Preferably the metal is Pd, Rh, Re, Au, Ag, Cu, Co, Sn, Sb or Pb. Preferably the metal is Pt. Preferably the non-volatile hydrocarbon is ethylene, propene, or butene. Preferably the non-volatile hydrocarbon is a vegetable or mineral oil such as pump oil, linseed oil, olive oil or cedar oil. Preferably the temperature at which the combination of substrate plus soluble metal salt is dried is between about 80°C and 120°C, or any temperature or range of temperatures therein. Preferably the temperature at which the non-volatile hydrocarbon is pyrolysed is between about 300°C and about 1000°C or any temperature or range of temperatures therein. Detailed Description of the Invention The invention is directed to a method by which supported metal catalysts may be prepared. The metal is supported by a substrate as will be known in the art and the catalyst is prepared by adding a soluble metal salt to the substrate and then heating the combination in the presence of a gaseous or a liquid hydrocarbon, which polymerises on heating. The metal is preferably selected from Pt, Pd, Cu, Rh, Co, Sn, Au, Ag, Re, Sb, or Pb or the transition metals generally. Platinum and Palladium are most preferred. Mixtures of these metals can also be used. The metal salt is added to the catalyst substrate using known methods such as ion exchange or impregnation. Preferably the metal salt is the metal chloride or nitrate. If platinum is used the preferred platinum salt is platinum tetramine associated with any anion, for example chloride or nitrate. Other salts of use include metal acetates and carbonates. These would cause less hydrolysis of the substrate framework than can occur with the chlorides for example. Any other suitable metal salt or substrate as is known in the art may be used. The substrate may be alumina (in powder or pellet form) or a zeolite (as a powder or in pellet form with alumina) or silica (as a powder or pellet form) or a zeotype (powder or pellet form) or a mesoporous molecular sieve (powder or pellet form). If the liquid hydrocarbon is an oil the substrate plus metal salt is soaked in the oil prior to heating. If a gaseous hydrocarbon is used, the gas is allowed to flow through the substrate while it is heated. As specialised equipment is required to heat the substrate in the presence of a gas, the use of oil is preferred. Oil also results in a simple process which avoids the use of hazardous gases and the requirement for sophisticated atmosphere control. The substrate does not need to be saturated with oil. As seen in Examples 50-52 there is little difference between the "light off temperatures of samples prepared with 26, 50, and 125wt% oil added to the substrate. It appears that as the temperature rises, the oil flows into the pore structure of the substrate, thereby accessing all metal sites. Liquid hydrocarbons which do not volatilise on heating prior to polymerisation are preferred as the hydrocarbon will then not evaporate out of the substrate, and will therefore be retained. Thus substantially non-volatile hydrocarbons are preferred. Volatile compounds could be used but similar problems as for gaseous hydrocarbons occur and specialised equipment as discussed below, with necessary adaptions, may need to be used. As a result such liquid hydrocarbons are best avoided. When using gaseous hydrocarbons, specialised high temperature and gas handling apparatus will be required as known in the art. An example would be gas drying pressure vessels with heating or gas preheating capabilities and gas exhausting. These apparatus are generally constructed from high quality stainless steel, but in the given high temperature reducing conditions, may be required to be made from special steel or glass lined vessels which can be expensive and difficult to engineer for use at temperatures above 250°C. The gas is preferably ethylene and the oil is preferably a mineral oil or linseed, cedar or olive oil. Other oils or gases such as pump oil (eg santovac 5), or propene and butene may also be used as will be known in the art. It is preferred to use hydrocarbons that contain little or no oxygen. As will be known in the art vegetable oils are mixtures of fatty acids and as such contain terminal COOH groups. These oils can be used in the process of the invention due to the minimal amount of oxygen contained. Vegetable oils such as cedar, coconut, corn, cottonseed, groundnut, olive, palm, palm kernel, rapeseed, soybean, sunflower, sesame, sunflower, linseed or castor (or mixtures of these) may be used. The substrate should have a high surface area and allow for good diffusion of a gaseous or liquid hydrocarbon into the substrate framework. With reference to the use of a platinum metal, platinum tetramine, after the salt has been added to the catalyst substrate, it is preferable to dry the combination at a temperature low enough to prevent decomposition of the platinum tetramine complex. As will be readily apparent to a skilled person, this temperature will vary with the particular material salt and substrate used, however any individual temperature or range of temperatures between about 80°C and about 120°C are generally considered suitable with about 100°C being preferred. Following this, the gaseous or liquid non-volatile hydrocarbon, is added. The sample is then heated in air, preferably in a covered container, to a temperature at which the hydrocarbon is pyrolysed. This temperature is preferably any temperature or range of temperatures between 300°C to 1000°C, more preferably between 300°C and 800°C, and is most preferably about 450°C. If necessary, the cover of the container is removed and the sample further heated in air to completely remove the black char which is deposited. The thermal decomposition of the hydrocarbon results in a reducing atmosphere being created around the metal cations, causing their reduction. It is hypothesized that the less oxygen present around the metal cations there is, the more active the resulting catalyst will tend to be. It is thought that the hydrocarbon used polymerises around the metal cations on heating creating a barrier between the cation and the oxygen in the air in which the polymerisation of the hydrocarbons preferably takes place. Thus the hydrocarbon used should contain a minimum amount of oxygen in its component makeup however hydrocarbons containing oxygen may also work, although not so efficiently. The hydrocarbons used in the examples herein generally do not contain oxygen as part of their elemental makeup although the vegetable oils used will contain oxygen in their terminal COOH groups. A highly active catalyst can thus be formed because the hydrocarbon polymerises, ultimately forming a char, inside the pores and cavities of the substrate. In addition to the creation of the reducing atmosphere, this restricts the movement of metal cations during the reduction process and inhibits agglomeration to large particles. Thus, following reduction, the individual particles of metal are deposited uniformly through the catalyst substrate. No further treatment of the catalyst is required. EXAMPLES Catalyst Testing A standard test using the oxidation of ethylene was developed to rank the catalytic activity of each sample. About 11 mg of the sample was loaded into a glass reactor tube through which a gas stream containing 1% ethylene in air flowed at 1 ml/min. The ethylene concentration at the outlet of the reactor was measured by a total hydrocarbon detector. The reactor temperature was stepped to determine the temperature at which the ethylene became completely oxidised and this temperature (the "light off temperature) was used to rank the catalysts. Example 1 This example gives the preparation method for pelletised zeolite Y (LZY 52 from UOP) exchanged with platinum tetramine chloride and reduced by addition of linseed oil. Pelletised zeolite NaY (9.5 g) was washed with water to remove excess alkali and powdered material, and dried. A solution (30 ml) containing 0.058 wt% of platinum tetramine chloride (Pt(NH 3 ) 4 Cl 2 )(0.0098 g Pt) and 7% ammonia was added, well mixed, then exchanged at room temperature for 45 h. The sample was filtered, rinsed three times with distilled water and dried at 100°C overnight (Sample 1). The exchange and washing solutions were retained, evaporated down to 30 ml and analysed by AA. The result showed that less than 1.7xl0 "8 g Pt remained in solution. Therefore the sample contained 0.1 wt % Pt. To reduce the platinum salt, 1.8g of linseed oil was added to 3.5g of the platinum- exchanged zeolite, mixed well, then heated slowly in a covered crucible to 450°C and held at this temperature for 65h. Breaking a catalyst pellet revealed a white inner region (no char remaining) and a light grey outer region (showing a higher concentration of platinum in the outer shell of the pellet). Example 2 In this example, 0.5g of Sample 1 was reduced by heating in ethylene/air, followed by further reduction in hydrogen. The sample was heated in 1% ethylene in air (100 ml/min) at 0.5°C/min to 300°C and held for 1 h. The gas was changed to hydrogen and the temperature held at 300°C for another hour before cooling. The activity of the catalysts prepared in these examples for the oxidation of ethylene is shown in Table 1. Reduction by heating in oil produced the most active catalyst (light off at 140°C). The light-off temperature was 10°C higher for the catalyst treated by heating in ethylene/air then hydrogen, which was another 10°C higher than the catalyst treated with slow oxidation then reduction (160°C). Immersion in a solution of sodium borohydride also produced a catalyst with a light-off temperature of 160°C. The least active catalyst was produced by reduction in hydrogen alone (light off at 190°C). Example 3 In this example, 0.5g of Sample 1 was reduced by calcining in oxygen then reduction in hydrogen as described by Ahm et al (J Catal. 133, 191, 1992). The sample was slowly heated (at 0.5°C/min) in a high flow of oxygen (100 ml/min) from room temperature to 300°C and held for 2 h. The gas stream was changed to deoxygenated nitrogen (100 ml/min) and purged at 300°C for 2 h, then cooled. The gas stream was changed to hydrogen (100 ml/min) and the sample heated to 300°C at 0.5°C/min, held for 2 h and cooled in hydrogen. Example 4 In this example, 0.5 g of Sample 1 was reduced by immersion in a solution of sodium borohydride. The sample was immersed in an alkaline solution of BH 4 Na (1%) overnight. Fizzing was observed as the reduction occurred. The sample was rinsed and dried at 100°C. Example 5 In this example, 0.5g of Sample 1 was reduced by heating in hydrogen. The sample was slowly heated from room temperature to 300°C (at 0.5°C/min), held for 2 h, then cooled to room temperature. The hydrogen flow rate was 100 ml/min. RESULTS - EXAMPLES 1-5 The results of the examples 1-5 are presented in Table 1. Table 1 Reduction Method Example No Sample 1 Zeolite LZY52, light-off temperature (°C) 0.1% Pt 1 heated with linseed oil 140 2 heated in ethylene/air then 150 hydrogen 3 heated slowly in oxygen, 160 flushed with nitrogen, then heated in hydrogen 4 immersed in BH 4 Na solution 160 5 heated in hydrogen 190 Range of Platinum Concentration (examples 6-38) In this series of examples, the platinum concentration in the catalyst is varied from 2 wt% to 0 wt% to determine the Pt concentration required for observable catalytic activity. Zeolite Y (LZY52 (IJOP^ All the examples were prepared in the same manner as example 1, the only difference being the amount of platinum added. The Pt concentrations were 2%, 1%, 0.1%, 0.05%, 0.025%, 0.01%, 0.005%, 0.001% and 0 (examples 6 to 14 respectively). Zeolite ZSM-5 A commercial sample of HZSM-5 in palletised form was treated in the same manner as example 1, except that a different zeolite was used and the amount of platinum added was varied for each example. The resultant Pt concentrations were 2%, 1%, 0.5%, 0.1%, 0.05%, 0.025%, 0.01%, 0.005%, 0.001%) and 0 (examples 15 to 24 respectively). Zeolite H-Beta In the series of examples 25-31 a commercial sample of zeolite H-Beta in powder form was treated in the same manner as example 1, except that a different zeolite was used, a different oil was used, being olive oil, and the amount of platinum added was varied for each example. The resultant Pt concentrations were 1%, 0.5%, 0.1 %, 0.05%, 0.01%, 0.005%) and 0% (examples 25 to 31 respectively). Zeolite Na-Beta In the series of examples 32-34 a commercial sample of zeolite H-Beta in powder form was exchanged with excess 1.0 mol L "1 NaCl per gram zeolite at 100°C for 2h in order to form the Na exchanged analogue. The resultant Na-Beta was treated in the same manner as example 1, except that a different zeolite was used, a different oil was used, being olive oil, and the amount of platinum added was varied for each example. The resultant Pt concentrations were 1%, 0.5%, 0.1% (examples 32 to 34 respectively). v Alumina In these examples, platinum was added to a γ alumina catalyst (Harshaw A1-111-61-R Al- 3991R lot#PP01) to give platinum concentrations of 2%, 1%, 0.5% and 0 (examples 35 to 37 respectively). The resultant γ-alumina was treated in the same manner as example 1 except that a different substrate was used, a different oil was used, being olive oil, and the amount of Pt added was varied for each example (as shown in examples 35-38 respectively). RESULTS - EXAMPLES 6-38 The resultant catalytic activities of examples 6 to 38 are shown in Table 2. The highest catalytic activity (the lowest "light-off temperature) is obtained with the highest platinum concentration. For zeolite Y, a decrease in the platinum concentration twenty times from 2% to 0.1% results in a decrease in the light-off temperature of only 40°C. The sample containing a trace of platinum at 0.001% still shows a much lower light-off temperature (300°C) than the catalyst with zero platinum (420°C). This shows that a small amount of platinum is highly active and that increasing the platinum concentration (for example from 0.1% to 2%) results in a large portion of the platinum being deposited in a less active form. A similar trend of catalyst activity with platinum concentration is observed with ZSM-5 except that at around 0.1% Pt, zeolite Y is more active. The platinum on alumina catalysts show a slightly lower catalytic activity than the zeolite samples. However the zero platinum sample is more active for ethylene oxidation than the zero platinum zeolites. Table 2 Platinum Dilution series Example No Platinum concentration ( t%) Light-off temperature (°C) Zeolite LZY 52 6 2.0 100 7 1.0 120 8 0.1 140 9 0.05 180 10 0.025 200 11 0.01 200 12 0.005 290 13 0.001 300 14 0.0 420 Zeohte ZSM-5 15 2.0 100 16 1.0 120 17 0.5 130 Sample 2 0.4 120 18 0.1 170 19 0.05 180 20 0.025 220 21 0.01 230 22 0.005 260 23 0.001 330 24 0.0 400 Zeohte H-Beta 25 1.0 «100 26 0.5 -100 27 0.1 125 28 0.05 125 29 0.01 150 30 0.005 170 31 0.0 290 Zeohte Na-Beta 32 1.0 »100 33 0.5 -100 34 0.1 150 γ Alumina 35 2.0 120 36 1.0 130 37 0.5 140 38 0.0 320 Different Platinum Addition Methods Example 39 In this example, a 0.1% Pt zeolite Y catalyst was prepared by impregnation with platinum tetramine instead of ion exchange. 0.36 g of a solution containing 0.058 wt% of platinum tetramine chloride (Pt(NH 3 ) 4 Cl 2 ) and 7% ammonia was added, with shaking, to 1 g of dry NaY (LZY52). Most of the water was absorbed with the zeolite pellets appearing only slightly wet. The sample was allowed to air dry, then dried at 100°C overnight before reduction using linseed oil, as in example 1. Different Platinum Salts Example 40 In this example, chloroplatinic acid was added to NaY zeolite. H 2 PtCl 6 .6H 2 O (0.006 g) dissolved in 3 g water was added to 1 g of NaY (UOP LZY 52). The resultant solution pH was 4.6. After 24 h the sample was washed with distilled water, filtered and air dried. 0.001 g Pt remained in the washing solution, resulting in a catalyst containing 0.13 wt% Pt. After further drying at 100°C over night, the sample was reduced using linseed oil, as in example 1. Example 41 In this example, chloroplatinic acid was added to HZSM-5 zeolite. H 2 PtCl 6 .6H-,O (0.006 g) dissolved in 3 g water was added to 1 g of HZSM-5. The resultant solution pH was 3.8. After 24 h the sample was washed with distilled water, filtered and air dried. No significant Pt remained in the washing solution, resulting in a catalyst containing 0.23 wt% Pt. After further drying at 100°C over night, the sample was reduced using linseed oil, as in example 1. Example 42 In this example, zeolite NaY was exchanged with platinum tetramine hydroxide. 30 ml of a solution containing Pt(NH 3 ) 4 OH 2 (0.01 g Pt) and 7% NH 3 was added with stirring to 10 g NaY (UOP LZY52). After 24 h at room temperature the sample was filtered, rinsed three times and air dried. Analysis of the remaining solutions showed that less than 4 x 10 _;> g Pt remained in solution, and that the sample contained 0.1% Pt. After further drying at 100°C over night, the sample was reduced using linseed oil, as in example 1. Example 43 In this example, zeolite HZSM-5 was exchanged with platinum tetramine hydroxide. 30 ml of a solution containing Pt(NH 3 ) 4 OH 2 (0.0 lg Pt) and 7% NH 3 was added with stirring to 10 g HZSM-5. After 24 h at room temperature the sample was filtered, rinsed three times and air dried. Analysis of the remaining solutions showed that less than 4 x 10 g Pt remained in solution, and that the sample contained 0.1% Pt. After further drying at 100°C over-night, the sample was reduced using linseed oil, as in example 1. RESULTS - EXAMPLES 39-43 Table 3 shows the catalytic activity of examples 39 to 43 for ethylene oxidation. The light-off temperature of a sample of zeolite Y containing 0.1% Pt prepared by impregnation (example 39) was 20°C higher than the sample prepared by ion exchange (example 8). Examples 40 to 43 show that different Pt salts can be used with similar resultant activities to those prepared using platinum tetramine chloride. The largest difference was observed for the addition of chloroplatinic acid to zeolite Y (example 40). This catalyst had a light off temperature 20°C higher than example 8. Table 3 Example No Different Platinum Light-off Temperature (°C) Addition Methods 39 impregnation of NaY with 160 Pt(NH 3 ) 4 Cl, solution to give 0.1%) Pt Different Platinum Salts 40 Addition of H,PtCl 6 to NaY to 160 give 0.13% Pt~ 41 Addition of H,PtCl 6 to 140 HZSM-5 to give 0.23% Pt 42 Exchange of NaY with 140 Pt(NH 3 )OH 2 to give 0.1% Pt 43 Exchange of HZSM-5 with 180 Pt(NH 3 )OH 2 to give 0.1% Pt Different Oils as Reductants In this series of examples a range of oils are used to reduce a sample of platinum tetramine exchanged ZSM-5. Sample 2 was prepared from 12 g of a commercial sample of HZSM-5/alumina pellets. 20 ml of a Pt(NH 3 ) 4 Cl 2 / 7% NH 3 solution (0.056 g Pt) was added with stirring and left at room temperature for 100 h. This was decanted, rinsed three times, then 10 ml of fresh Pt(NH 3 ) 4 Cl 2 / 7% NH 3 solution (0.028 g Pt) added, stirred and left for 24 h. After rinsing three times and drying, the resultant zeolite contained 0.4% Pt. Example 44 In this example, Sample 2 was heated in air without any oil added. Sample 2 (0.2 g) was heated in air to 450°C and held at that temperature for 16 h. Example 45 In this example, cedar oil was added to Sample 2 before heating. 0.5 g cedar oil was added to 2 g sample 2. This was heated to 450°C and held for 20 h. Example 46 In this example, Santovac 5 diffusion pump oil was added to Sample 2 before heating. 0.1 g Santovac 5 was added to 0.2 g sample 2. This was heated to 450°C and held for 20 h. Example 47 In this example, linseed oil was added to Sample 2 before heating. 0.15g linseed oil was added to 0.52 g sample 2. This was heated to 450°C and held for 20 h. Example 48 In this example, olive oil was added to Sample 2 before heating. 0.2 g olive oil was added to 0.5 g sample 2. This was heated to 450°C and held for 20 h. Example 49 In this example mineral oil (Johnson's Baby Oil) was added to Sample 2 before heating. 0.25g mineral oil was added to 0.5g of sample 2. This was heated to 450°C and held for 20h. Example 50 In this example, 26% linseed oil was added to Sample 2 before heating. 0.15 g linseed oil was added to 0.52 g sample 2. This was heated to 450°C and held for 20 h. Example 51 In this example, 50% linseed oil was added to Sample 2 before heating. 0.1 g linseed oil was added to 0.2g sample 2. This was heated to 450°C and held for 20 h. Example 52 In this example, 125% linseed oil was added to Sample 2 before heating. 0.45g linseed oil was added to 0.2g sample 2. This was heated to 450°C and held for 20 h. Different Amounts of Linseed Oil The zeolite pellets rapidly soak up the added oil. The sample with the least amount of linseed oil added (26% of the zeolite weight - example 50) appeared dry, the sample with 50% oil added (example 51) appeared slightly wet. For 125% linseed oil added (example 52), the sample was in a puddle of oil. Different firing conditions for a sample with linseed oil added: In this series of examples, the effect of different firing conditions on the resultant catalytic activity of Platinum ammine-exchanged HZSM-5 containing 50% linseed oil was investigated. Example 53 In this example, 50% linseed oil was added to 0.2g Sample 2 before heating to 570°C and holding for 10 h. Example 54 In this example, 50% linseed oil was added to 0.2g Sample 2 before heating to 450°C and holding for 10 h. Example 55 In this example, 50% linseed oil was added to 0.2g Sample 2 before heating to 400°C and holding for 20 h. Example 56 In this example, 50% linseed oil was added to 0.2g Sample 2 before heating in a closed container to 450°C and holding for 20 h. The lid was removed and the sample heated further at 450°C until no black char remained in the cores of the zeolite pellets. Example 57 In this example, 50% linseed oil was added to 0.2g Sample 2. This was fired rapidly by heating in an open crucible over a flame. This resulted in the flame burning over the catalyst. Different metals other than platinum: In the series of examples 58-62, a range of samples exchanged with different metals other than platinum were prepared. The metals were Pd, Cu, Rh, Co and Sn. A solution containing 1 wt % in metal of the desired metal chloride was added to 0.1 g of zeolite type Y (CKD-100) in the sodium exchanged powder form. Each sample was exchanged at 100°C for 2 h then overnight at room temperature. Each sample was filtered and washed three times with distilled water and dried at 100°C. Each sample was then reduced according to example 48. Platinum and one other metal for bimetallic catalysts In the series of examples 63-69, a range of bimetallic samples exchanged with platinum and one other metal were prepared using zeolites Na-Y and H-Beta. The other metals were Pd, Rh and Sn. A solution containing 0.5wt% (Pt(NH 3 ) 4 Cl 2 and 0.5wt% of the desired metal chloride was added to 0.5g of the desired zeolite. Each sample was exchanged at 100°C for 2h then overnight at room temperature. Each sample was filtered and washed 3 times with distilled water and dried at 100°C. Each sample was then treated according to example 48. Different Substrate In example 69, a sample was prepared in the same way as for example 25 except that the substrate was an [A1]-MCM-41 mesoporous molecular sieve. The MCM-41 sample was prepared using a standard S + X " I + assembly route from C 16 (Me) 3 N + Br template and tetraethyl orthosilicate SiO source. RESULTS - EXAMPLES 44-69 Table 4 shows the catalytic activities towards ethylene oxidation for Sample 2 treated with different oils. Heating in air with no oil (example 44) produced the least active catalyst). In all the materials tested, addition of an oil before heating increased the resultant activity of the catalyst. The best catalysts were produced using olive oil and mineral oil (examples 48 and 49). Varying the amount of linseed oil added (examples 54 to 56) resulted in no major differences in activity, with the sample prepared using 125% linseed oil having a light-off temperature only 10°C lower than the sample prepared using 26% linseed oil. The firing temperatures did appear to significantly affect the catalyst activity. A lower temperature of 400°C and a higher temperature of 570°C produced less active catalysts than heating to 450°C. Heating the sample in a closed container to 450°C produced the most active catalyst. This would have maintained the reducing conditions for longer. Rapid heating of the catalyst in a crucible over a flame gave a sample that was initially inactive towards ethylene in air at 120°C, but after 29 h at 120°C, reactivity increased to 100% and remained constant for the remainder of the experiment (36 h). Table 4 Example No Sample 2 heated with Different light-off temperature (°C) Oils 44 heat in air 450 C for 16 h 160 45 25% cedar oil added, heat in air 130 450 C, 20 h 46 50% Santovac 5 diffusion pump 120 oil added, heat in air 450 C, 20 h 66 l%Pt/Pd-Y 140 67 l%Pt/Rh-Y 160 68 l%)Pt/Sn-Y 160 Different substrate 69 l%Pt[Al]-MCM-41 < 100 The foregoing describes the invention including preferred forms thereof. Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated within the scope hereof as defined by the attached claims.

Claims: CLAIMS 1. A method for preparing a supported metal catalyst comprising adding a soluble metal salt to a substrate and then reducing the metal salt to the metal by heating in the presence of a gaseous or liquid hydrocarbon which polymerises on heating. 2. The method of claim 1 wherein the metal is selected from Pd, Rh, Re, Au, Ag, Cu, Co, Su, Sb or Pb, or mixtures thereof. 3. The method of claim 1 wherein the metal is Pt. 4. The method of claim 1 wherein the metal is a transition metal. 5. The method of any one of claims 1-4 wherein the metal salt is a tetramine, chloride, nitrate, carbonate, or acetate. 6. The method of any one of the previous claims wherein the hydrocarbon is a liquid hydrocarbon which pyrolyses before volatilising. 7. The method of claim 6 wherein the hydrocarbon is an unsaturated vegetable or mineral oil. 8. The method of any one of claims 1 to 5 wherein the hydrocarbon is an unsaturated gaseous hydrocarbon. 9. The method of any one of the preceding claims wherein the metal salt is reduced to the metal by heating to a temperature of between about 300°C and about 1000°C. 10. A method for preparing a supported metal catalyst comprising the steps of: (a) adding a soluble metal salt to a substrate; (b) heating the combination of substrate plus soluble metal salt to a temperature sufficient to dry the combination but low enough to avoid decomposition of the soluble metal salt; (c) adding a gaseous or liquid hydrocarbon to the dry combination of substrate plus metal salt; and (d) reducing the metal salt to the metal by heating the substrate plus metal salt plus hydrocarbon to a temperature at which the hydrocarbon is pyrolysed. 11. The method of claim 10 wherein the metal is selected from Pd, Rh, Re, Au, Ag, Cu, Co, Su, Sb or Pb, or mixtures thereof. 12. The method of claim 10 wherein the metal is Pt. 13. The method of claim 10 wherein the metal salt is a tetramine, chloride, nitrate, carbonate, or acetate. 14. The method of claim 10 wherein the hydrocarbon is an unsaturated vegetable or mineral oil. 15. The method of claim 10 wherein the hydrocarbon is an unsaturated gaseous hydrocarbon. 16. The method of claim 10 wherein the metal salt is reduced to the metal by heating to a temperature of between about 300°C and about 1000°C. 17. The method of claim 10 wherein the substrate plus soluble metal salt are dried by heating to a temperature of between about 80°C and about 120°C. 18. A method for preparing a supported platinum metal catalyst comprising adding a soluble platinum salt to a substrate and then reducing the platinum salt to the platinum metal by heating in the presence of a gaseous or liquid hydrocarbon which polymerises on heating. 19. A method for preparing a supported platinum metal catalyst comprising the steps of: (a) adding a soluble platinum salt to a substrate; (b) heating the combination of substrate plus soluble platinum salt to a temperature sufficient to dry the combination but low enough to avoid decomposition of the soluble platinum salt; (c) adding a gaseous or liquid hydrocarbon to the dry combination of substrate plus platinum salt; and (d) reducing the platinum salt to the platinum metal by heating the substrate plus platinum salt plus hydrocarbon to a temperature at which the hydrocarbon is pyrolysed. 20. The method of claim 18 or 19 wherein the platinum salt is platinum tetramine associated with the chloride or nitrate. 21. The method of claim 18 or 19 wherein the platinum salt is chloroplatinic acid. 22. The method of claim 19 wherein the hydrocarbon is a liquid hydrocarbon which pyrolyses before volatilising. 23. The method of claim 18 or 19 wherein the hydrocarbon is an unsaturated vegetable or mineral oil. 24. The method of claim 18 or 19 wherein the hydrocarbon is an unsaturated gaseous hydrocarbon. 25. A process for the preparation of a supported metal catalyst substantially as herein described with reference to any one of the Examples. 26. A supported metal catalyst when prepared by the method of any one of preceding claims.

Inventors: BAGSHAW STEPHEN ALLAN, PARKER LINDA, PATTERSON JOHN EWEN, BAGSHAW, STEPHEN, ALLAN, PARKER, LINDA, PATTERSON, JOHN, EWEN
Applicants: BAGSHAW STEPHEN ALLAN, IND RES LTD, PARKER LINDA, PATTERSON JOHN EWEN, BAGSHAW, STEPHEN, ALLAN, INDUSTRIAL RESEARCH LIMITED, PARKER, LINDA, PATTERSON, JOHN, EWEN
Application year: 1997
Main classification: B01J
IPC codes: B01J23, B01J29, B01J37