HYDROCARBON CONVERSION WITH A TRIMETALLIC CATALYST

Abstract: A novel trimetallic catalyst composite comprises a refractory support having a nominal diameter of at least 650 microns, deposited on which is a uniformly-dispersed platinum component, a uniformly-dispersed tin component, a halogen component, and a surface-impregnated metal component selected from rhodium, ruthenium, cobalt, nickel, and iridium. When this catalyst composite is used in the conversion of hydrocarbons, and particularly in the reforming of hydrocarbons at low pressures, there are significant improvements in activity stability compared to catalysts of the prior art.

Description: The subject of the present invention is a novel trimetallic catalyst composite, which has exceptional activity and resistance to deactivation when employed in a hydrocarbon conversion process that requires a catalyst having both a hydrogenation-dehydrogenation function and a cracking function. More precisely, the present invention provides a novel dual-function trimetallic catalyst composite which, quite surprisingly, permits substantial improvements in hydrocarbon conversion processes that have traditionally used a dual-function catalyst. In another embodiment, the present invention provides improved hydrocarbon conversion processes using the novel catalyst composite, more specifically, an improved reforming process which employs the novel catalyst exhibiting improved activity, selectivity, and stability characteristics. Catalyst composites having a hydrogenation-dehydrogenation function and a cracking function are widely used today in many industries, such as the petroleum and petrochemical industry, to accelerate a wide variety of hydrocarbon conversion reactions. Generally, the cracking function is thought to be associated with an acid-acting material of the porous, adsorptive, refractory oxide type, which is typically used as the support or carrier for a heavy metal component, such as the metals or compounds of metals of Groups V to VIII of the Periodic Table, which are generally considered to provide the hydrogenation-dehydrogenation function. These catalyst composites are used to accelerate a wide variety of hydrocarbon conversion reactions, such as hydrocracking, isomerization, dehydrogenation, hydrogenation, desulphurization, cyclization, alkylation, polymerization, cracking, hydroisomerization, etc. In many instances, the commercial applications of these catalysts are in processes where more than one of these reactions proceeds simultaneously. An example of this type of process is reforming, wherein a hydrocarbon feed stream containing paraffins and naphthenes is subjected to conditions which promote dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to aromatics, isomerization of paraffins and naphthenes, hydrocracking of naphthenes and paraffins, and other reactions to produce an octane-rich or aromatic-rich product stream. Another example is a hydrocracking process, wherein catalysts of this type are employed to effect selective hydrogenation and cracking of high molecular weight unsaturated materials, selective hydrocracking of high molecular weight materials, and other like reactions, to produce a generally lower boiling, more valuable output stream. Yet another example is an isomerization process, wherein a hydrocarbon fraction, which is relatively rich in straight-chain paraffin compounds, is contacted with a dual-function catalyst to produce an output stream rich in isoparaffin compounds. Regardless of the reaction involved, or the particular process involved, it is of critical importance that the dual-function catalyst should be able not only initially to perform its specified functions, but also that it should be able to perform them satisfactorily for prolonged periods. The analytical terms used in the art to measure how well a particular catalyst performs its intended functions in a particular hydrocarbon reaction environment, are activity, selectivity and stability. For purposes of discussion herein, these terms are conveniently defined for a given charge stock as follows: (1) "activity" is a measure of the ability of the catalyst to convert hydrocarbon reactants into products at a specified severity level, where "severity level" means the specific reaction conditions, e.g. the temperature, pressure, contact time, and the presence of diluents such as hydrogen; (2) "selectivity" refers to the amount of desired product of products obtained relative to the amount of reactants charged or converted; (3) "stability" refers to the rate of change with time of the activity and selectivity parameters. Obviously, smaller rates imply a more stable catalyst. In a reforming process, for example, activity commonly refers to the amount of conversion that takes place for a given charge stock at a specified severity level, and is typically measured by octane number of the C₅⁺ product stream; selectivity refers to the amount of C₅⁺ yield that is obtained at a particular activity level; and stability is typically equated to the rate of change of activity with time , as measured by octane number of C₅⁺ product, and of selectivity, as measured by C₅⁺ yield. Actually, the last statement is not strictly accurate in practice, because generally a continuous reforming process is run to produce a constant octane C₅⁺ product, with severity level being continuously adjusted to attain this result; and, furthermore, the severity level is for this process usually varied by adjusting the conversion temperature in the reaction zone so that, in point of fact, the rate of change of activity finds response in the rate of change of conversion temperature and changes in this last parameter are customarily taken as indicative of activity stability. As is well known to those skilled in the art, the principal cause of observed deactivation or instability of a dual-function catalyst, when it is used in a hydrocarbon conversion reaction, is associated with the fact that coke forms on the surface of the catalyst during the course of the reaction. More specifically, the conditions employed in these hydrocarbon conversion processes, typically result in the formation of heavy, high molecular weight, black, solid or semi-solid, carbonaceous material, which coats the surface of the catalyst and reduces its activity by shielding its active sites from the reactants. In other words, the performance of this dual-function catalyst is sensitive to the presence of carbonaceous deposits on the surface of the catalyst. Accordingly, the major problem facing workers in this area of the art is the development of more active and selective catalysts that are not as sensitive to the presence of these carbonaceous materials, and/or have the capability to suppress the rate of formation of these carbonaceous materials on the catalyst surface. This sensitivity to formation of carbonaceous materials becomes more important as practitioners of the art reduce pressure and increase the severity of processing units in an attempt to extract the maximum octane yield from a given feedstock. Viewed in terms of performance parameters, the problem is to develop a dual-function catalyst having superior activity, selectivity and stability while operating at low pressures, typically less than 125 psig (962 kpa). Accordingly, the present invention is concerned with the problems of providing an improved catalyst for the reforming of hydrocarbons, means of preparing the improved catalyst, and an improved catalytic reforming process for improving the anti-knock properties of a gasoline fraction. Accordingly, in a broad embodiment the present invention provides a catalyst composite for the conversion of hydrocarbons comprising a combination of a uniformly-dispersed platinum component, a uniformly-dispersed tin component, a halogen component, and a surface-impregnated metal compound selected from rhodium, ruthenium, cobalt, nickel, iridium, and mixtures thereof, with a refractory porous support having a uniform composition and a nominal diameter of at least 650 µm. In another embodiment, the invention provides a method of preparing the catalyst composite by forming said refractory support having said tin component uniformly dispersed through it, uniformly dispersing said platinum component through said support, performing a halogenstripping step, surface-impregnating said support with said metal component, and adding said halogen component. In yet another embodiment, the invention provides a process for the catalytic reforming of a gasoline fraction naphtha to produce a high-octane reformate comprising contacting the gasoline fraction naphtha and hydrogen at reforming conditions with the above-defined catalyst composite. These, as well as other aspects and embodiments, will become apparent upon review of the more detailed description of the invention set forth below. Several catalyst composites relevant to the composition of the present invention are disclosed in the art, but no reference or combination of references discloses the unique combination of components of this invention. US-A-3651167 discloses a catalyst composition for the selective hydrogenation of C₄-acetylenes using a catalyst comprising a Group VIII noble metal, preferably palladium, deposited on a refractory inorganic oxide carrier material, wherein said Group VIII noble metal is surface-impregnated. US-A-3651167 is totally silent however, as to the advantageous use of a surface-impregnated metal in combination with uniformly-dispersed platinum and tin. Further, the catalyst is preferably non-acidic, which is in contradistinction to the present invention wherein it is essential that a halogen component should be included in the catalyst composition. US-A-3840471 discloses a catalyst composition containing platinum, rhodium, and a base metal composited on an inert material, wherein tin may be chosen as one of a possible 25 base metals disclosed. The intended use of this catalyst is for the oxidation of organic compounds, specifically the oxidation of engine or combustion exhausts. Further, US-A-3840471 does not even remotely suggest the beneficial effect of surface-impregnated rhodium. Of particular interest is the catalyst disclosed in US-A-3898154, which discloses a catalyst composite comprising platinum, rhodium, tin, and a halogen on a porous carrier material. It is essential, however, that the rhodium component is incorporated by any means known to result in a uniform dispersion thereof in the carrier material. A similar reference, US-A-3909394 discloses a catalyst composite comprising platinum, ruthenium, and a halogen on a porous support. Additionally, it is disclosed that the catalyst may comprise a Group IVA metal component, tin being specifically disclosed as one of the possible metals. US-A-3909394, however, teaches that it is essential that the components thereof are uniformly distributed throughout the porous carrier material. In particular, it is taught that the ruthenium component may be incorporated by any means known to result in a uniform dispersion thereof in the carrier material. Accordingly, it can be seen that US-A-3909394 suggests the use of ruthenium, platinum, tin, and halogen with a porous support, however, only when the ruthenium is uniformly distributed. By way of contrast, it has been discovered in the present invention that an improved catalyst is obtained when a metal component selected from rhodium, ruthenium, cobalt, nickel, or iridium is non-uniformly dispersed, i.e., surface-impregnated. Further, as the surprising and unexpected results of the Examples presented hereinafter show, a catalyst with a surface-impregnated metal component demonstrates superior performance when compared to a prior art catalyst having the same metal uniformly dispersed. The catalyst composite of the present invention comprises a uniformly dispersed platinum component, a uniformly dispersed tin component, a halogen component and a surface-impregnated metal component selected from rhodium, ruthenium, cobalt, nickel, iridium and mixtures thereof on a refractory support having a nominal diameter of at least 650 microns. Accordingly, considering first the refractory support used in the present invention, it is preferred that the material be a porous, adsorptive, high-surface area support having a surface area of 25 to 500 m²/g. The porous carrier material should also be uniform in compositionand relatively refractory under the conditions employed in the hydrocarbon conversion process. The term "uniform in composition" means that the support should be unlayered, should have no concentration gradients of the species inherent to its composition, and should be completely homogenous in composition. Thus, if the support is a mixture of two or more refractory materials, the relative amounts of these materials should be constant and uniform throughout the entire support. It is intended to include within the scope of the present invention carrier materials which have traditionally been utilized in dual-function hydrocarbon conversion catalysts such as: (1) activated carbon, coke, or charcoal; (2) silica or silica gel, silicon carbide, clays and silicates, including those synthetically prepared and naturally occurring, which may or may not be acid-treated, for example, attapulgus clay, diatomaceous earth, fuller's earth, kaolin, kieselguhr, etc.: (3) ceramics, porcelain, or bauxite; (4) refractory inorganic oxides such as alumina, titanium dioxide, zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria, boria, silica-alumina, silica-magnesia, chromia-alumina, alumina-boria, silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates, such as naturally occurring or synthetically prepared mordenite and/or faujasite, either in the hydrogen form or in a form which has been treated with multivalent cations: and, (6) combinations of one or more materials from one or more of these groups. The preferred porous carrier materials of use in the present invention are refractory inorganic oxides, with best results obtained with alumina. Suitable alumina materials are the crystalline aluminas known as gamma-, eta-, and theta-alumina, with gamma-alumina giving best results. In addition, in some embodiments, the alumina may contain minor proportions of other well known refractory inorganic oxides such as silica, zirconia, magnesia, etc.; the preferred support is, however, substantially pure gamma-alumina. Preferred carrier materials have an apparent bulk density of 0.3 to 0.7 g/cm³, surface area characteristics such that the average pore diameter is 2 to 30 nm, and the pore volume is 0.1 to 1 cm³/g. In general, excellent results are typically obtained with gamma-alumina which is used in the form of spherical particles having a relatively small diameter (i.e., typically about 1.6 mm or 1/16 inch), an apparent bulk density of about 0.5 g/cm³, a pore volume of about 0.4 cm³/g, and a surface area of about 175 m²/g. The preferred alumina carrier material is uniform in composition and may be prepared in any suitable manner and may be synthetically prepared or naturally-occurring. Whatever type of alumina is employed, it may be activated before use by one or more treatments, including drying, calcination, steaming, etc., and it may be in a form known as activated alumina, activated alumina of commerce, porous alumina, alumina gel, etc. For example, the alumina may be prepared by adding a suitable alkaline reagent, such as ammonium hydroxide, to a salt of aluminium, such as aluminium chloride, aluminium nitrate, etc., in any amount to form an aluminium hydroxide gel which, upon drying and calcining, is converted into alumina. The refractory support may be formed in any desired shape, such as spheres, pills, cakes, extrudates, powders, granules, etc. It is a feature of the invention that the support should be of sufficient size that it has a nominal diameter of at least 650 µm. "Nominal diameter" means the narrowest characteristic dimension. Thus, if the shape of the support is a sphere, its diameter must be at least 650 µm. Alternatively, if the shape is an extruded cylinder, the diameter of the circular face must be at least 650 µm and the length of the cylinder must be at least 650 µm. Likewise, if the shape is a cube, the length of each side must be at least 650 µm. Typically, the preferred nominal diameter is from 650 to 3200 µm. Best results are obtained when the support has a diameter of about 1500 µm. For purposes of the present invention, a particularly preferred form of alumina is the sphere; and alumina spheres may be continuously manufactured by the well known oil-drop method which comprises: forming an alumina hydrosol by any of the techniques taught in the art, and preferably by reacting aluminium metal with hydrochloric acid; combining the resulting hydrosol with a suitable gelling agent; and dropping the resultant mixture into an oil bath maintained at an elevated temperature. The droplets of the mixture remain in the oil bath until they set and form hydrogel spheres. The spheres are then continuously withdrawn from the oil bath and typically subjected to specific ageing and drying treatments in oil and an ammoniacal solution to improve further their physical characteristics. The resulting aged and gelled particles are then washed, dried at a relatively low temperature of 149° to 204°C, and subjected to a calcination procedure at a temperature of 454° to 704°C for a period of 1 to 20 hours. This treatment effects conversion of the alumina hydrogel into the corresponding crystalline gamma-alumina, (see the teachings of US-A-2620314 for additional details). One essential ingredient of the catalyst according to this invention is the uniformly-dispersed platinum compound. This platinum component may exist within the final catalyst composite as a compound, such as an oxide, sulphide, halide, oxyhalide, etc., in chemical combination with one or more of the other ingredients of the composite, or as an elemental metal. Best results are obtained when substantially all of this component is present in the elemental state. Generally this component may be present in the final catalyst composite in any amount which is catalytically effective, but relatively small amounts are preferred. In fact the platinum component generally will comprise 0.01 to 2 wt. % of the final catalyst composite, calculated on an elemental basis. Excellent results are obtained when the catalyst contains 0.05 to 1 wt. % of platinum. This platinum component may be incorporated in the catalyst composite in any suitable manner, such as coprecipitation or cogelation, ion-exchange, or impregnation, provided that a uniform dispersion of the platinum component within the carrier material is obtained. The preferred method of preparing the catalyst involves use of a soluble, decomposable compound of platinum to impregnate the carrier material. For example, this component may be added to the support by commingling the latter with an aqueous solution of chloroplatinic acid. Other water-soluble compounds of platinum may be employed in impregnation solutions, and include ammonium chloroplatinate, bromoplatinic acid, platinum dichloride, platinum tetrachloride hydrate, platinum dichlorocarbonyl dichloride, dinitrodiaminoplatinum, etc. The use of a platinum/chlorine compound, such as chloroplatinic acid, is preferred since it facilitates the incorporation of both the platinum component and at least a minor quantity of the halogen compound in a single step. Best results are obtained in the preferred impregnation step, if the platinum compound yields complex anions containing platinum in acidic aqueous solution. Hydrogen chloride or the like acid is also generally added to the impregnation solution in order to facilitate further the incorporation of the halogen component and the distribution of the metal compound. In addition, it is generally preferred to impregnate thecarrier material after it has been calcined, in order to minimize the risk of washing away the valuable platinum compounds. In some instances, however, it may be advantageous to impregnate the carrier material when it is in a gelled state. Yet another essential ingredient of the catalyst of the present invention is the uniformly-dispersed tin component. This may be present as the elemental metal, as a chemical compound, such as the oxide, sulphide, halide, oxychloride, etc., or as a physical or chemical combination with the porous carrier material and/or other components of the catalyst composite. The tin component is preferably employed in an amount sufficient to result in a final catalyst composite containing 0.01 to 5 wt. percent of tin, calculated on an elemental basis, with best results obtained at a level of 0.1 to 2 wt. percent. The tin component may be incorporated in the catalyst composite in any suitable manner to achieve a uniform dispersion, such as by coprecipitation or cogelation with the porous carrier material, ion-exchange with the carrier material, or impregnation of the carrier material at any stage in its preparation. It is to be noted that it is intended to include within the scope of the present invention all conventional methods for incorporating a metal component in a catalyst composite. One preferred method of incorporating the tin component into the catalyst composite involves coprecipitating the tin component during the preparation of the preferred refractory oxide carrier material. In the preferred method, this involves the addition of suitable soluble tin compounds, such as stannous or stannic halide, to the alumina hydrosol, and then combining the hydrosol with a suitable gelling agent and dropping the resulting mixture into an oil bath, etc., as explained in detail hereinbefore. Following the calcination step, there is obtained a carrier material having a uniform dispersion of stannic oxide in an intimate combination with alumina. Another preferred method of incorporating the tin component into the catalyst composite, involves using a soluble, decomposable compound of tin to impregnate and uniformly disperse the tin throughout the porous carrier material. Thus, the tin component may be added to the carrier material by commingling the latter with an aqueous solution of a suitable tin salt or other water-soluble compound of tin, such as stannous bromide, stannous chloride, stannic chloride, stannic chloride pentahydrate, stannicchloride tetrahydrate, stannic chloride trihydrate, stannic chloride diamine, stannic trichloride bromide, stannic chromate, stannous fluoride, stannic fluoride, stannic iodide, stannic sulphate, stannic tartrate, and the like compounds. The use of a tin chloride compound, such as stannous or stannic chloride, is particularly preferred since it facilitates the incorporation of both the tin component and at least a minor amount of the preferred halogen component in a single step. In general, the tin component can be impregnated either before, simultaneously with, or after the other components are added to the carrier material. Yet another essential feature of the present invention is a surface-impregnated metal component selected from rhodium, ruthenium, cobalt, nickel, iridium and mixtures thereof. As heretofore noted, while the prior art has recognized that a platinum-tin reforming catalyst may advantageously contain a third metal component, it was believed essential that this metal component should be uniformly distributed throughout the catalyst to achieve beneficial results. By way of contrast it has now been determined that improved performance may be achieved by incorporating a surface-impregnated metal component into a reforming catalyst composite containing uniformly dispersed platinum and tin, as opposed to the uniformly distributed metal component of the art. It is to be understood that the term "surface-impregnated" as employed herein, means that at least 80% of the surface-impregnated component is located in the exterior surface of the catalyst particle. The "exterior surface" is defined as the outermost layer of the catalyst, preferably that which comprises the exterior 50% of the catalyst volume. Expressed in an alternative way, the "exterior surface" is defined as the exterior 0.2r layer when the catalyst is spherical in shape and 0.3r when the catalyst in cylindrical in shape and the length to diameter ratio of the cylinder is greater than or equal to 2:1. In both of these formulae, "r" is defined as the nominal radius of the support. When the shape of the catalyst is such that the word "radius" could have no clear meaning, (e.g., a cloverleaf shape), the "exterior surface" is defined as the outermost layer of the catalyst comprising the exterior 50% of the catalyst volume. By "layer" is meant a stratum of substantially uniform thickness. A metal component is considered to be surface-impregnated whenits average concentration in the exterior surface of the catalyst is at least 4 times the average concentration of the same metal component in the remaining interior portion of the catalyst. Alternatively, a metal component is said to be surface-impregnated when the average atomic ratio of the metal component to the uniformly dispersed platinum component is at least 4 times greater in the exterior surface of the catalyst than it is the remaining interior portion. As previously stated, the surface-impregnated metal is rhodium, ruthenium, cobalt, nickel or iridium. The surface-impregnated metal component may be present in the composite as an elemental metal or in chemical combination with one or more of the other ingredients of the composite, or as a chemical compound of the metal, such as the oxide, oxyhalide, sulphide, halide, and the like. The metal component may be employed in any amount which is cataiytically effective, with the preferred amount being 0.01 to 2 wt. %, calculated on an elemental metal basis. Typically, best results are obtained with 0.05 to 1 wt.% of surface-impregnated metal. Additionally, it is within the scope of the present invention that beneficial results may be obtained by having more than one of the above-named metals surface-impregnated on the catalyst. The surface-impregnated metal component may be incorporated into the catalyst composite in any suitable manner which results in the metal component being concentrated in the exterior surface of the catalyst support. In addition, it may be added at any stage of the preparation of the composite, either during preparation of the carrier material or thereafter, and the precise method of incorporation is not deemed to be critical, so long as the resulting metal component is surface-impregnated as the term is used herein. A preferred way of incorporating this component is an impregnation step, wherein the porous carrier material containing uniformly-dispersed tin and platinum is impregnated with a suitable metal-containing aqueous solution. It is also preferred that no "additional" acid compounds are to be added to the impregnation solution. In a particularly preferred method of preparation, the carrier material, containing tin and platinum, is subjected to oxidation and halogen-stripping procedures, as explained hereinafter, before the impregnation of the surface-impregnated metal components. Aqueous solutions of water soluble, decomposable surface-impregnated metal compounds are preferred, including hexamminerhodium chloride, rhodiumcarbonylchloride, rhodium trichloride hydrate, ammonium pentachloroaquoruthenate, ruthenium trichloride, nickel chloride, nickel nitrate, cobaltous chloride, cobaltous nitrate, iridium trichloride, iridium tetrachloride, and the like. The catalyst composite of the present-invention is considered to be an acidic catalyst. Accordingly, it is essential that the catalyst should contain a halogen component which imparts the necessary acidic function to the composite. The carrier material containing platinum and tin should be subjected to halogen-stripping, and preferably to oxidation procedures before addition of the surface-impregnated metal component. The presence of excessive amounts of halogen or halide, for example, chloride, on the carrier before the addition of the surface-impregnated metal, will prevent attainment of the novel surface deposition feature of the instant invention. The oxidation can be carried out at temperatures from 93°C (200°F) to 593°C (1100°F) in an air atmosphere for a period of 0.5 to 10 hours in order to convert the metal components substantially into the oxide form. The stripping procedure is conducted at a temperature of from 371°C (700°F) to 593°C (1100°F) in a flowing air/stream atmosphere for a period of from 1 to 10 hours. Following addition of the surface-impregnated metal component, the halogen is then added to the carrier material under oxidative conditions. Although the precise chemistry of the association of the halogen component with the carrier material is not entirely known, it is customary in the art to refer to the halogen component as being combined with the carrier material, or with the other ingredients of the catalyst, in the form of the halide (e.g., as the chloride). This combined halogen may be fluoride, chloride, iodide, bromide, or mixtures thereof. Of these, fluoride and, particularly, chloride are preferred for the purposes of the present invention. The halogen may be added to the carrier material in any suitable manner after the addition of the surface-impregnated metal component. For example, the halogen may be added as an aqueous solution of a suitable decomposable halogen-containing compound, such as hydrogen fluoride, hydrogen chloride, hydrogen bromide, ammonium chloride, etc. For reforming, the halogen will be typically combined with the carrier material in an amount sufficient to result in a final composite that contains 0.1 to 3.5 wt. %, and preferably 0.5 to 1.5 wt. %, of halogen, calculated on an elemental basis. Another significant parameter for the present catalyst is the "total metals content" which is defined as the sum of the platinum component, tin component and the surface-impregnated metal component, calculated on an elemental basis. Good results are ordinarily obtained when this parameter is fixed at a value of 0.2 to 6 wt. %, with best results ordinarily achieved at a metals loading of 0.3 to 2 wt. % Regardless of the details of how the components of the catalyst are combined with the porous carrier material, the final catalyst generally will be dried at a temperature of 93°C (200°F) to 316°C (600°F) for a period of from 2 to 24 hours, or even longer, and finally calcined or oxidized at a temperature of 371°C (700°F) to 593°C (1100°F) in an air atmosphere, for a period of 0.5 to 10 hours, in order to convert the metal components substantially into the oxide form. Best results are generally obtained when the halogen content of the catalyst is adjusted during the calcination step, by including water and a halogen or a decomposable halogen-containing compound in the air atmosphere utilized. In particular, when the halogen component of the catalyst is chlorine, it is preferred to use a mole ratio H₂O to HCl of 5:1 to 100:1 during at least a portion of the calcination step, in order to adjust the final chlorine content of the catalyst to a range of 0.5 to 1.5 wt. %. It is preferred that the resultant calcined catalyst composite be subjected to a substantially water-free reduction step before its use in the conversion of hydrocarbons. This step is designed to ensure a uniform and finely divided dispersion of the platinum component throughout the carrier material. Preferably, substantially pure and dry hydrogen (i.e., less than 20 vol. ppm H₂O) is used in the reducing agent in this step. The reducing agent is contacted with the calcined catalyst at a temperature of 427°C (800°F) to 649°C (1200°F) and for a period of 0.5 to 10 hours, or even longer, effective to reduce substantially all of the platinum component and the surface-impregnated metal component to the elemental state. When, however, the surface-impregnated metal component is nickel or cobalt, the surface-impregnated metal may be primarily in the oxide form after the reduction step. This reduction treatment may be performed in situ as part of a startup sequence if precautions are taken to predry the plant to a substantially water-free state and if substantially water-free hydrogen is used. The resulting reduced catalyst composite may, in some instances, be beneficially subjected to a presulphiding operation designed to incorporate in the catalyst composite from 0.05 to 0.50 wt. % of sulphur calculated on an elemental basis. Preferably, this presulphiding treatment takes place in the presence of hydrogen and a suitable sulphur-containing compound, such as hydrogen sulphide, lower molecular weight mercaptans, organic sulphides, etc. Typically, this procedure comprises treating the reduced catalyst with a sulphiding gas, such as a mixture of hydrogen and hydrogen sulphide having about 10 moles of hydrogen per mole of hydrogen sulphide, at conditions sufficient to effect the desired incorporation of sulphur, generally including a temperature of from 10°C (50°F) to 593°C (1100°F), or even higher. It is generally a good practice to perform this presulphiding step operation under substantially water-free conditions. According to the present invention, a hydrocarbon charge stock and hydrogen are contacted with the trimetallic catalyst described above in a hydrocarbon conversion zone. This contacting may be accomplished by using the catalyst in a fixed bed system, a moving bed system, a fluidized bed system, or in a batch type operation. In the fixed bed system, a hydrogen-rich gas and the charge stock are preheated by any suitable heating means to the desired reaction temperature, and then passed into a conversion zone containing a fixed bed of the catalyst. It is, of course, understood that the conversion zone may comprise one or more separate reactors with suitable means between them to ensure that the desired conversion temperature is maintained at the entrance to each reactor. It is also important to note that the reactants may be passed through the catalyst bed upwardly, downwardly, or in radial flow, with the latter being preferred. In addition, the reactants may be in the liquid phase, a mixed liquid-vapour phase, or a vapour phase, when they contact the catalyst, best results being obtained with the vapour phase. When the catalyst of the present invention is used in a reforming operation, the reforming system will comprise a reforming zone containing a fixed or moving bed of the catalyst. This reforming zone may comprise one or more separate reactors with suitable heating means between them to compensate for the endothermic nature of the reactions that take place in each catalyst bed. The hydrocarbon feed stream that is charged to this reforming system will comprise hydrocarbon fractions containing naphthenes and paraffins that boil within the gasoline range. The preferred charge stocks are naphthas, those consisting essentially of naphthenes and paraffins, although in many instances aromatics will also be present. This preferred class includes straight run gasolines, synthetic gasolines, and the like. On the other hand, it is frequently advantageous to charge thermally-or catalytically-cracked gasolines or higher boiling fractions thereof. Mixtures of straight run and cracked gasoline range naphthas can also be used to advantage. The gasoline range naphtha charge stock may be a full boiling gasoline having an initial boiling point of from 10°C (50°F) to 66°C (150°F) and an end boiling point of from 163°C (325°F) to 218°C (425°F), or may be a selected fraction thereof, which generally will be a higher boiling fraction commonly referred to as a heavy naphtha, for example, a naphtha boiling in the range of C₇ to 204°C (400°F). In some instances, it is also advantageous to charge pure hydrocarbons or mixtures of hydrocarbons that have been extracted from hydrocarbon distillates, for example, straight-chain paraffins, which are to be converted into aromatics. It is preferred that these charge stocks be treated by conventional catalytic Pretreatment methods such as hydrorefining, hydrotreating, hydrodesulphurization, etc., to remove substantially all sulphurous, nitrogenous and water-yielding contaminants, and to saturate any olefins that may be contained therein. In a reforming embodiment, it is generally a preferred practice to use the catalyst composite in a substantially water-free environment. Essential to the achievement of this condition in the reforming zone is the control of the amount of water and water-producing compounds in the charge stock and the hydrogen stream which are being charged to the zone. Best results are ordinarily obtained when the total amount of water entering the conversion zone from any source is held to a level substantially less than 50 ppm, and preferably less than 20 ppm, expressed as weight of equivalent water in the charge stock. In general, this can be accomplished by an appropriate pretreatment of the charge stock, coupled with careful control of the water present in the charge stock and in the hydrogen stream; the charge stock can be dried by using any suitable drying means known to the art, such as a conventional solid adsorbent having a high selectivity for water, for instance, sodium or calcium crystalline aluminosilicates, silica gel, activated alumina, molecular sieves, anhydrous calcium sulphate, high surface area sodium and the like adsorbents. Similarly, the water content of the charge stock may be adjusted by suitable stripping operations in a fractionation column or like device. In some instances, a combination of adsorbent drying and distillation drying may be used advantageously to effect almost complete removal of water from the charge stock. Preferably, the charge stock is dried to a level corresponding to less than 20 ppm of H₂O equivalent. In general, it is preferred to control the water content of the hydrogen stream entering the hydrocarbon conversion zone within a level of 5 to 20 vol. ppm of water or less. In the reforming embodiment, an effluent stream is withdrawn from the reforming zone and passed through a cooling means to a separation zone, typically maintained at -4°C (25°F) to 66°C (150°F), wherein a hydrogen-rich gas is separated from a high octane liquid product, commonly called an "unstabilized" reformate. When the water content of the hydrogen-rich gas is greater than desired, a portion of this hydrogen-rich gas is withdrawn from the separating zone and passed through an adsorption zone containing an adsorbent that is selective for water. The resultant substantially water-free hydrogen stream is then recycled through suitable compressing means back to the reforming zone. If the water content of the hydrogen-rich gas is within the range specified, a substantial portion of it can be directly recycled to the reforming zone. The liquid phase from the separating zone is typically withdrawn and commonly treated in a fractionating system in order to adjust the butane concentration, thereby controlling front-end volatility of the resulting reformate. The conditions used in the reforming embodiment of the present invention generally will include a pressure of 101 kPa (0 psig) to 6995 kPa (1000 psig), with the preferred pressure being 446 kPa (60 psig) to 2514 kPa (350 psig), more preferably 446 to 962 kPa (50 to 125 psig). Particularly good results are obtained at low pressure, namely, a pressure of 446 kPa (50 psig) to 791 kPa (100 psig). In fact, it is a singular advantage of the present invention that it allows stable operation at lower pressures than have heretofore been successfully employed in so-called "continuous" reforming systems with a bimetallic catalyst (e.g. reforming of 0.5 to 5 or more barrels of charge per pound of catalyst (0.18 to 1.75 m³/Kg) without regeneration). In other words, the catalyst of the present invention allows the operation of a continuous reforming system to be conducted at lower pressure, e.g. about 446 kPa (50 psig) for about the same or better catalyst life before regeneration as has been heretofore realized with conventional bimetallic catalysts at higher pressures, e.g. 962 kPa (125 psig). Similarly, the temperature required for reforming with the catalyst of the present invention is generally lower than that required for a similar reforming operation using a high quality bimetallic platinum catalyst of the prior art. This significant and desirable feature of the present invention is a consequence of the selectivity of the catalyst of the present invention for the octane-upgrading reactions that are preferably induced in a typical reforming operation. Hence, reforming conditions include a temperature of from 427°C (800°F) to 593°C (1100°F), and preferably 482°C (900°F) to 566°C (1050°F). As is well known to those skilled in the continuous reforming art, the initial selection of the temperature within this broad range is made primarily as a function of the desired octane of the product reformate, considering the characteristics of the charge stock and the catalyst. Ordinarily, the temperature is thereafter slowly increased during the run to compensate for the inevitable deactivation that occurs and to provide a product of constant octane number. It is an advantage of the present invention that the rate at which the temperature is increased in order to maintain a product of constant octane number is substantially lower when using the novel catalyst. Moreover, the C₅⁺ yield loss for a given temperature increase is substantially lower than for a high quality bimetallic reforming catalyst of the prior art. In addition, hydrogen production is substantially higher. The reforming conditions of the present invention also include the use of sufficient hydrogen to provide an amount of l to 20 moles of hydrogen per mole of hydrocarbon entering the reforming zone, with excellent results being obtained when 5 to 10 moles of hydrogen are used per mole of hydrocarbon. The liquid hourly space velocity (LHSV) included in the reforming conditions employed in the invention is selected from the range of 0.1 to 10 hr.⁻¹, with a value of 1 to 5 hr.⁻¹ being preferred. In fact, the present invention allows operations to be conducted at a higher LHSV than normally can be stably achieved in a continuous reforming process with a high quality bimetallic platinum reforming catalyst of the prior art. This last feature is of immense economic significance, because it allows a continuous reforming process to operate at the same throughput level with a lower catalyst inventory than that heretofore used with conventional reforming catalysts, at no sacrifice in catalyst life before regeneration. The following working Examples are given to illustrate further the preparation of the catalyst composite of the present invention and the use thereof in the conversion of hydcarbons. It is understood that the Examples are intended to be illustrative rather than restrictive. These Examples make reference to the accompanying Drawings, in which: Figure 1 is a graphical depiction of metal distribution versus distance from edge of particle for Catalyst A, which is made in accordance with the invention, comparing the uniform distribution profiles of platinum and tin with the non-uniformly dispersed rhodium profile. Figure 2 is a graphical depiction of metal distribution of a particle of Catalyst B, which is not made according to the instant invention, showing the uniform distribution profiles of platinum, tin and rhodium. Figure 3 is a graphical depiction of catalyst selectivity as measured by the C₅⁺ reformate volume percent yield as a function of catalyst life, measured in barrels of charge stock processed per pound of catalyst. (1 barrel per pound = 0.35 m³ per Kg) performance data for both Catalyst A and Catalyst B are shown. Figure 4 is a graphical depiction of catalyst activity as measured by average reaction zone temperature necessary to provide a reformate of 102 research octane number, as a function of catalyst life measured in barrels of charge stock processed per pound of catalyst. (1 barrel per pound = 0.35 m³ per Kg) again, performance data for both Catalyst A and Catalyst B are shown. EXAMPLE 1 This Example sets forth a preferred method of preparing the catalyst composite of the present invention. Tin-containing alumina spheres were prepared by cogelling an alumina hydrosol containing a soluble tin compound by the oil-drop method. After oil-dropping and ageing, the cogelled spheres were dried and calcined. The resulting particles comprised uniformly distributed tin oxide and alumina in the shape of spheres having an approximate diameter of 1500 microns. An aqueous impregnation solution containing chloroplatinic acid and hydrogen chloride was then prepared. This solution contained hydrogen chloride in an amount corresponding to about 2 wt. % of the carrier material to be impregnated. The amount of hydrogen chloride in the impregnated solution was selected to ensure good dispersion of platinum throughout the catalyst particle. The amount of platinum in the impregnation solution used to make the catalyst of the present invention was sufficient to result in a finished catalyst composite containing 0.375 wt. % platinum. After impregnation, the catalyst was dried and calcined. After calcination, the catalyst was subjected to a chloride-stripping procedure, to remove any excess chloride ions that would have a deleterious effect on the subsequent rhodium impregnation. As heretofore mentioned, the presence of excess chloride ions would cause the rhodium to be uniformly distributed throughout the carrier material and not remain in the external 300 µm layer, as is essential in the present invention. The stripping procedure was conducted at a temperature of about 980°F (527°C) by passing a flowing air/stream mixture across the catalyst composite for approximately 2 hours. The resulting composite was next contacted with a rhodium-containing aqueous solution, prepared by adding rhodium trichloride hydrate to water in an amount sufficient to result in a composite containing 0.05 wt. % of rhodium. After the rhodium impregnation, the catalyst was again dried and calcined. After calcination, the catalyst was subjected to a chlorination step to add the halogen component. After chlorination the catalyst was reduced in a dry hydrogen stream for about 1 hour. The resulting catalyst particles were analyzed and found to contain, on an elemental basis, about 0.375 wt. % of platinum, about 0.05 wt. % of rhodium, about 0.3 wt. % of tin and about 1.05 wt. % of chlorine. This catalyst was designated Catalyst "A". In order to determine whether the rhodium component was surface-impregnated, Catalyst A was subjected to an electron microprobe distribution analysis. The results of this analysis are set forth in Figure 1. As can be noted, Figure 1 shows a normalized ratio of rhodium to aluminium as a function of the distance (in µm) from the sphere edge. The graph indicates that there is no substantial amount of rhodium beyond a depth of about 150 µm from the sphere edge. Accordingly, it can be seen that Catalyst A comprises a surface-impregnated rhodium component. EXAMPLE 2 (COMPARISON) In this Example, a catalyst was made in a fashion such that the rhodium component was uniformly dispersed throughout the catalyst particles. The resulting catalyst represents the catalyst compositions of the prior art. The important differences between the procedures used to make the prior art catalyst and Catalyst A, are that the prior art procedure utilizes a co-impregnation of platinum and rhodium, and does not employ a chloride-stripping procedure. Accordingly, the catalyst of this Example was prepared by starting with the same tin-containing alumina as in Catalyst A. A sulphur-free aqueous solution containing chloroplatinic acid, rhodium trichloride hydrate, and hydrogen chloride was then prepared. Similarly, this solution contained hydrogen chloride in an amount corresponding to about 2 wt. % of the carrier material to be impregnated. The amount of metal components in the impregnation solution used to make the catalyst was sufficient to result in a final composite containing 0.373 wt. % of platinum and 0.05 wt. % of rhodium. After impregnation, the catalyst was dried and calcined in the same manner as Catalyst A. After calcination, the catalyst was similarly subjected to a chlorination step to add the halogen component. After chlorination, the catalyst was reduced in a dry hydrogen stream for about 1 hour. The final catalyst composite comprised, on an elemental basis, about 0.375 wt. % of platinum, about 0.05 wt. % of rhodium, about 0.3 wt. % of tin, and about 1.05 wt. % of chlorine. This catalyst was designated Catalyst "B". In order to determine the rhodium distribution in Catalyst B, Catalyst B was subjected to an electron microprobe distribution analysis. The results of this analysis are set forth in Figure 2, which is a graph of the ratio of the counts of rhodium at a given distance from the sphere edge divided by the counts of aluminium detected by the microprobe scan. The data in Figure 2 clearly reveal that substantial amounts of rhodium are dispersed in the catalyst at a depth greater than 150 µm, and, in fact, rhodium is uniformly dispersed throughout the catalyst. Accordingly, the rhodium component of Catalyst B is not surface-impregnated. EXAMPLE 3 In order to compare Catalyst A, a composite made in accordance with the invention, with Catalyst B, a catalyst not having a surface-impregnated rhodium component, both catalysts were separately subjected to a high stress evaluation test designed to determine the relative activity and selectivity for the reforming of a gasoline charge stock. In all tests, the same charge stock was employed; its characteristics are given in Table 1 below. The tests were performed in a laboratory scale reforming plant comprising a reactor containing a catalyst undergoing evaluation, a hydrogen separating zone, a debutanizer column, suitable heating, pumping, and condensing means, etc. In this plant, a hydrogen recycle stream and a charge stock are commingled and heated to the desired conversion temperature. The resulting mixture is then passed downflow into a reactor containing a fixed bed of the catalyst under test. An effluent stream is withdrawn from the bottom of the reactor, cooled to about 0°C (32°F) and passed to the separating zone, wherein a hydrogen-rich gaseous phase separates from a liquid phase. The hydrogen-rich gaseous phase is then withdrawn from the separating zone and a portion of it is continually passed through a high surface area sodium scrubber. The resulting substantially water-free hydrogen stream is then recycled to the reactor in order to supply hydrogen for the reaction. The excess hydrogen over that needed for recycle is recovered as excess separator gas. Moreover, the liquid phase from the separating zone is withdrawn therefrom and passed to the debutanizer column, wherein light ends are taken overhead as debutanizer gas and a C₅⁺ reformate stream recovered as bottoms. The conditions employed in both tests were a reaction zone outlet pressure of about 50 psig (446 kPa), a 5.0 molar ratio of hydrogen-rich vapour to hydrocarbon charge stock, and a liquid hourly space velocity of 2.0. Reaction zone temperatures were selected to achieve a hydrocarbon product reformate having a research octane number of 102. The results of testing Catalysts A and B are set forth in Figures 3 and 4. Figure 3 is a graphical depiction of the C₅⁺ liquid volume percent yield, based on the volume of hydrocarbon charge stock, as a funtion of catalyst life, as measured by the barrels of charge stock processed per pound of catalyst, (and cubic metres of charge stock per kilogram of catalyst). Surprisingly and unexpectedly, Catalyst A, containing a surface-impregnated rhodium component consistently exhibits a higher C₅⁺ liquid volume percent yield of 102 research octane number reformate. Accordingly, Catalyst A exhibits improved selectivity for the production of 102 research octane number reformate relative to Catalyst B. Figure 4 is a graphical depiction of the average reactor inlet temperature necessary to achieve a reformate having a research octane number of 102 as a function of catalyst life defined as barrels of charge stock processed per pound of catalyst (1 bbl/lb = 0.35 m³/kg). Using the average inlet temperature as a measure of catalyst activity, it can be seen that, surprisingly and unexpectedly, Catalyst A, having a surface-impregnated rhodium component, exhibits a higher activity (lower average reactor inlet temperatures) than Catalyst B. More importantly, Catalyst A exhibits greater activity stability, as measured by the slope of the average reactor inlet temperature line. Thus, comparing the performance of the two catalysts at a given end-of-run temperature, for example, 990°F (532°C), shows that Catalyst A processed 124% more charge stock than did Catalyst B. In other words, Catalyst A was more than twice as stable as Catalyst B. Accordingly, Catalyst B showed much greater loss of activity as measured by the respective slopes of the lines obtained by plotting inlet temperature against catalyst life. EXAMPLE 4 The catalyst described in this Example represents another catalyst composite of the present invention. Oxidized, chloride-stripped spherical catalyst particles containing platinum and tin uniformly dispersed on an alumina support were prepared by following the procedure outlined in Example 1. An impregnation solution containing ammonium pentachloroaquoruthenate and water was contacted with the platinum-and tin-containing spherical particles in a manner to result in a composite containing 0.5 wt. % of surface-impregnated ruthenium. After the ruthenium impregnation, the catalyst was dried and calcined. After calcination, the composite was subjected to a chlorination step to add the halogen component. After chlorination, the catalyst was reduced in a dry hydrogen stream for about 1 hour. The resulting catalyst particles were found to contain, on an elemental basis, about 0.375 wt. % of uniformly dispersed platinum, about 0.5 wt. % of surface-impregnated ruthenium, about 0.3 wt. % of uniformly dispersed tin and about 1.05 wt. % of chlorine. This catalyst was designated as Catalyst "C". EXAMPLE 5 (COMPARISON) To illustrate clearly the benefits of surface-impregnated ruthenium, a catalyst composite with uniformly dispersed ruthenium was prepared for comparison. In making this uniformly dispersed ruthenium-containing catalyst, a uniformly dispersed tin-containing alumina support, identical to that used for preparing Catalyst "C", was contacted with an impregnation solution containing chloroplatinic acid, ruthenium trichloride, and 12 wt. % of hydrogen chloride, based on the weight of the carrier material. This high-acid solution was selected to ensure a uniform dispersion of both the platinum and ruthenium. The drying, calcining, and halogen addition steps were identical to those used for Catalyst "C". Accordingly, this catalyst was made in accordance with the teachings of US-A-3909394. The final catalyst composite comprised, on an elemental basis, about 0.375 wt. % of uniformly dispersed platinum, about 0.5 wt. % of uniformly dispersed ruthenium, about 0.3 wt. % of uniformly dispersed tin, and about 1.05 wt. % of chlorine. This catalyst was designated Catalyst "D". EXAMPLE 6 In order to compare Catalyst "C", a composite made in accordance with the invention, with Catalyst "D", a catalyst not having a surface-impregnated metal component, both catalysts were tested following the procedure outlined in Example 3. The performance results are presented in Table 2. It is observed that, at the completion of a 45°F (25°C) temperature cycle, Catalyst "C" produces slightly higher C₅⁺ liquid volume percent yield of 102 research octane number reformate than does the uniformly-dispersed ruthenium catalyst. More importantly, Catalyst "C", having surface-impregnated ruthenium, is much more activity-stable, as indicated by the lower deactivation rate shown in the first column of Table 2 for Catalyst "C" and is capable of processing about 30% more feed than Catalyst "B" for the same temperature cycle. In other words, the uniformly dispersed ruthenium catalyst, Catalyst "D", deactivated about 35% faster than the catalyst composite of the present invention. EXAMPLE 7 The catalyst described in this Example represents another catalyst composite of the present invention. Oxidized, chloride-stripped spherical catalyst particles containing platinum and tin uniformly dispersed on an alumina support were prepared following the procedure outlined in Example 1. An impregnation solution containing nickel nitrate and isopropanol was contacted with the platinum-and tin-containing spherical particles in a manner to result in a composite containing 0.36 wt. % of surface-impregnated nickel. After the nickel impregnation, the catalyst was dried and calcined. After calcination, the catalyst was subjected to a chlorination step to add the halogen component. After chlorination, the catalyst was reduced in a dry hydrogen stream for about 1 hour. The resulting catalyst particles were found to contain 0.387 wt. % of uniformly dispersed platinum, 0.36 wt. % of surface-impregnated nickel, 0.3 wt. % of uniformly dispersed tin and 1.05 wt. % of chlorine. This catalyst was designated as Catalyst "E". EXAMPLE 8 (COMPARISON) To illustrate the advantages of having surface-impregnated nickel, a catalyst composite was prepared for comparison wherein the nickel was uniformly dispersed throughout the catalyst composite. In preparation of the uniformly dispersed nickel-containing catalyst, a uniformly dispersed tin-containing alumina support, identical to that used for preparing Catalyst "E", was contacted with an impregnation solution containing chloroplatinic acid, nickel nitrate, and 2 wt. % of hydrogen chloride, based on the weight of the alumina carrier material. This hydrogen chloride level was selected to allow for uniform dispersion of both the platinum and nickel. The drying, calcining, and halogen-addition steps were identical to those used for Catalyst "E". The final catalyst composite comprised, on an elemental basis, 0.39 wt. % of uniformly dispersed platinum, 0.36 wt. % of uniformly dispersed nickel, 0.3 wt. % of uniformly dispersed tin, and 1.14 wt. % of chlorine. This catalyst was designated Catalyst "F". EXAMPLE 9 The catalyst described in this Example represents another catalyst composite of the present invention. Oxidized, chloride-stripped spherical catalyst particles containing platinum and tin uniformly dispersed on an alumina support were prepared following the procedure outlined in Example 1. An impregnation solution containing cobaltous chloride and isopropanol was contacted with the platinum-and tin-containing spherical particles in a manner to result in a composite containing 0.42 wt. % of surface-impregnated cobalt. After the cobalt impregnation, the catalyst was subjected to identical finishing conditions to those used in Example 7. The resulting catalyst particles were found to contain 0.384 wt. % of uniformly dispersed platinum, 0.42 wt. % of surface-impregnated cobalt, 0.3 wt. % of uniformly dispersed tin and 1.03 wt. % of chlorine. This catalyst was designated Catalyst "G". EXAMPLE 10 Catalysts "E", "F" and "G" were performance-tested in a manner identical to that set forth in Example 3. Table 3 presents the results. Comparing Catalyst "E" to Catalyst "F" shows that the surface-impregnated nickel catalyst surprisingly and unexpectedly exhibited an average C₅⁺ liquid yield of 102 research octane number reformate, 4.1 volume percent greater than Catalyst "F" having uniformly dispersed nickel. More importantly, the surface-impregnated catalyst deactivates at a much lower rate than the uniformly-dispersed nickel catalyst, resulting in an activity stability improvement of 48%. This stability improvement allows for 56% more feedstock to be processed in a given 30°F (16.7°C) temperature cycle by the catalyst of the present invention compared to the uniformly dispersed nickel containing catalyst. Test results for Catalyst "G" similarly illustrate exceptional performance, thus demonstrating the surprising benefit realized when surface-impregnated cobalt is employed with uniformly dispersed platinum and tin. In summary, it can be seen from these test results that, by incorporating a surface-impregnated metal component in accordance with the present invention, a superior and improved reforming catalyst is achieved.

Claims: A catalyst composite for hydrocarbon conversion comprising a platinum component, a tin component, a halogen component, a metal component selected from rhodium, ruthenium, cobalt, nickel, iridium, and mixtures thereof, and a refractory porous support having a uniform composition and a nominal diameter of at least 650 µm, characterized in that the platinum and tin components are uniformly dispersed and the metal component is surface impregnated on the support. A catalyst composite according to Claim 1 characterized in that it comprises, on an elemental basis, from 0.05 to 1 wt. % of platinum, from 0.05 to 1 wt. % of surface-impregnated metal, from 0.1 to 2 wt. of % tin, and from 0.5 to 1.5 wt. % of chlorine on a refractory porous support having a nominal diameter of 650 to 3200 µm. A catalyst composite according to Claim 1 or 2 characterized in that at least 80% of the Surface-impregnated metal component is deposited within the exterior 50% by volume of said refractory porous support. A method of preparing a catalyst composite according to any one of Claims 1 to 3 characterized by forming said refractory support having said tin component uniformly dispersed through it, uniformly dispersing said platinum component through said support, performing a halogen-stripping step, surface-impregnating said support with said metal component, and adding said halogen component. A method according to Claim 4 characterized in that the refractory support comprises alumina formed by gelation and in that the tin component is composited by means of a cogelation step during formation of the alumina support. A process for the catalytic reforming of naphtha charge stock by contacting the naphtha and hydrogen at reforming conditions with a catalyst, characterized in that the catalyst is a composite according to any one of Claims 1 to 3. A process according to Claim 6 characterized in that the sulphur content of the naphtha feedstock is less than 0.1 wt. ppm. A process according to Claim 6 or 7 characterized in that the reforming conditions include a pressure of from 446 to 962 kPa (50 to 125 psig).

Inventors: LAWSON, RANDY J., MOSER, MARK D.
Applicants: UOP (A NEW YORK GENERAL PARTNERSHIP)
Application year: 1987
Main classification: B01J23
IPC codes: B01J23, B01J35, B01J27, B01J37, C10G49, C10G11, C10G35, C10G45