MXPA03004763A - Improved process for the obtention of pt-sn bimetallic catalysts and product obtained therefrom. - Google Patents

Abstract

The present invention relates to a novel and simple process for the obtention of a plurality of aluminate-type supports by means of precipitation and the sol-gel method, with the addition of platinum (PT) and tin (Sn) to said supports in predetermined compositions. A further property gained by the platinum catalyst supported in magnesium aluminate with the addition of tin is that the same is functional in different reaction media, even in the presence of water steam. Some prototypes have been prepared for obtaining Pt:Sn catalysts with different ratios by means of impregnation and co-precipitation, in order to present the substantial differences with respect to the sol-gel method since the latter have more resistance under severe conditions of reaction.

Description

IMPROVED PROCEDURE FOR OBTAINING BIMETALLIC CATALYSTS Pt-Sn AND RESULTING PRODUCT DESCRIPTION TECHNICAL FIELD OF THE INVENTION The present invention relates to a novel and simple procedure for obtaining via sol-gel via a series of supports aluminates type (magnesium spinels), which have been platinum (Pt) and tin (Sn) in compositions previously deposited established. A property that acquires the platinum catalyst supported in magnesium aluminate with the addition of tin is able to operate in different reaction media, even in the presence of water vapor.

As for the Pt-Sn catalysts, prototypes with different Pt-Sn ratios were prepared, by impregnation and coprecipitation, in order to present considerable differences with respect to the sol-gel route, since the latter have greater resistance under severe conditions of reaction. A combination of physical methods were selected: X-ray diffraction (XRD), N2 physisorption and ammonia-based TPD (Programmed Temperature Desorption) analysis, in order to more fully investigate the optimal composition and associated changes during treatment thermal.

BACKGROUND OF THE INVENTION The magnesium spinel (MgAI204) is widely used in various processes, for example as a support for dehydrogenation reactions of paraffins, methane combustion, such as optical ceramics, as a material for ultrafiltration membranes; In addition, metallic aluminates of zinc, magnesium and copper are the most used as supports for catalysts.

Regarding the preparation of the support, the literature reports works where different studies are carried out about the preparation of metallic alumina splints, varying the cation published in [a) .- Zaleta Pérez, A .; Master's Thesis, Technological Institute of Ciudad Madero, Tamaulipas, (1992). b) .- Lynn, K .; Kurihara and Steven, L; Chem. Matier, 5, 609-613, (1993) and c) .- Guilhaume, B. and Prímet, M .; Chemical society Faraday transport., 11, 1541-1545, (1994)], where the characteristics of the magnesium aluminate spinel are reported, which make it attractive to be used as a support for catalysts above other spinels. In other works, the preparation of magnesium aluminate is highlighted by coprecipitation at constant and variable pH, published by Tinoco Ramírez, G .; Bachelor Thesis, ESIQIE - IPN, Mexico, D. F., chapter 5, p. 86-87, (1996).

The synthesis stage of the catalysts is very important, since the physical and chemical properties such as the surface area, pore size, particle size and the structure itself have an influence on the activity, these properties being largely determined by the procedures of preparation published in Smith JM, Chemical kinetics engineering, Second Edition, Editorial CECSA, Chapter 8, p. 364-367 (1980). Therefore, in the preparation of catalysts, care should be taken to evaporate the solvents from the precipitate, gel or support, because this affects the structure of the material formed by Leach. B. L; in Applied Industrial Catalysis Academic Press, Volume II, (1983).

Regarding the Pt-Sn catalysts, numerous works have been published in the last years about the physicochemical characterization by means of diverse techniques, evidencing metal-metal and metal-support interactions; . { Bettcher F., Chaunette P., Didillon B. and Clause O., Science and Technology in Catalysis, 131-136, (1994). Balakrishnan K. and Gonzalez R. D., Langmuir, 10, 2487-2490, (1994). Gómez R., Bertin V., Bosh P., Lopez T., Del Angel P., and Schifter I., Catalysis Letters, 21, (1993). Vértes Cs., Tálas E., Czakó-Nagy I., Ryczkowski J., Góbólos S., Vértes A. and argitalfvi, Applied Catalysis, 68, 149-159, (1991). Paál, Z .; Gyóry, A .; Uszkurat, l .; Olivier, S .; Guérin, M .; Kappenstein, C; Journal of catalysis, 168, 164-175, (1997). Barias O. A., Holmen A. and Blekkan E.A., Journal of Catalysis, 158, 1-12, (1996). Valenzuela Zapata M., Doctoral Thesis, Chemistry, UAM, chapter 6, p. 74-87, Mexico D. F., (1994)} however, in most of these works supports of the alumina or silica type are used, little is known when using ceramic supports, published by Rennard R. J .; Freel J. Journal of catalysis, 98, 235-244, (1986). of the type of MgAI204.

In the WO 0072967 A1 of December 7, 2000, an invention for pretreating a catalyst based on Pt-Sn is presented. This invention relates to the search for optimal activity by subjecting the catalytic bed to the following stages: 1) Reduction by the use of hydrogen at elevated temperatures, 2) Dehydrogenation of alkanes at elevated temperatures, 3) Oxidation-regeneration by use of oxygen at high temperatures.

In the US patent US 2002 W27 number 6414209 of September 25, 2000 called "catalysts for converting paraffinic to olefinic hydrocarbons", the invention of the dehydrogenation process is presented in which the catalyst is constituted by: a) 0.2 to 2.0% of at least one of the elements of the platinum and iridium groups, and a combination of promoter elements, such as: b) 0.2 to 5.0% Ge, Sn, Pb, Ga, In, TI; c) 0.1 to 5.0% of at least one of the following elements: Li, Na, K, Rb, Cs, Fr; d) 0.2 to 5.0% of at least one of the following elements Fe, Co, Ni, Pd; e) 1.0 to 5.0% P; f) 0.2 to 5.0% of Be, Mg, Ca, Sr, Ba, Ra and lanthanides and g) 0.1 to 2.0% of Cl.

In the European patent EP 01 0702 A2 of June 13, 1984, in the European patent EP 0110702 A3 of December 27, 1985, and in the European patent EP 83307243 of November 28, 1983, the use of the preparation is presented of spinels containing an alkaline earth metal and aluminum, which combined at a selected pH form a precipitate, which when calcined forms the spinel structure. The product formed is capable of reducing the sulfur oxides emitted in the catalytic cracking reaction.

In the Mexican patent application MX 89018270 of November 8, 1989, entitled: "Process for the dehydrogenation of light alkanes", refers to a process for the dehydrogenation of light alkanes, characterized in that it comprises: a) contacting a current of feed comprising at least one alkane having from 2 to 5 carbon atoms per molecule, in a steam reactor and a catalyst composition comprising (i) at least one aluminate spinel selected from the group consisting of aluminates of a metal of the group HA and aluminates of a metal of group IIB (ii) at least one metal selected from the group consisting of nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, and (iii) at least one compound of a metal selected from the group consisting of germanium, tin and lead, under such dehydrogenation conditions as to at least partially convert at least one alkane to at least one a lqueno In the Mexican patent MX 185246 of the date of application, June 25, 1993 and the cession date of July 7, 1997, the invention is presented in reference to an improved catalytic process for the dehydrogenation of light paraffins in order to obtain olefins. of up to 4 carbon atoms, from a stream composed of hydrocarbons to be dehydrogenated and a reaction medium which may be hydrogen and / or water vapor, in the presence of a catalyst, characterized by the following steps: preparation of the stream of feed formed by the hydrocarbon to be dehydrogenated mixed in equal parts with a reaction medium which can be hydrogen and / or water vapor, at the time of mixing the feed is preheated from 20 to 400 ° C; feeding the mixed stream to a tubular reactor to bring it into contact with a catalyst based on platinum and tin supported on a ceramic material, carrying out the dehydrogenation reaction of the hydrocarbon fed at a temperature of 100 to 600 ° C and a pressure of 0.25 to 1.25 kg / cm2, with a space velocity (GHSV) of 0.5 to 20 s "1 and a reaction period of 1 to 200 hours, to cool and compress the effluent of the reaction until forming two phases, to separate the liquid phase , from which the olefin is obtained, from the gas phase integrated by light hydrocarbons and hydrogen, finally, an oxidative regeneration of the catalyst is carried out, to continue with the activation with hydrogen.

Considerable research has been done on platinum-tin catalysts, so far the nature of the tin species on the surface and the mechanisms of tin promotion have not been satisfactorily explained.

Despite this, some researchers J. Salmons, JA Wang, JA Galicia, G. Aguilar-Ríos, Journal of Molecular Catalysis A: Chemical 184 (2002) 203-213 have reported that the Pt-Sn catalyst when supported on aluminates of divalent metals, such as MgAI204, improves the stability and selectivity of the catalyst in relation to alumina as support.

In the European Patent EP 1013603 A1 of June 28, 2000, entitled "Process for Catalytic Reform of Hydrocarbons", the process for the reformation is shown by the use of a nickel catalyst supported on a magnesium-aluminum spinel, which It has been obtained by calcination at 400 ° C.

Finally, the present invention presents considerable differences with respect to the previous technologies due to the fact that it is related to a novel and simple procedure for the obtaining by sol-gel route of a series of supports aluminates type (spiroles of MgAbC), which have been deposited platinum (Pt) and tin (Sn) in previously established compositions. A property that acquires the platinum catalyst supported in magnesium aluminate with the addition of tin is able to operate in different reaction media, even in the presence of water vapor.

Therefore, one of the objects of the present invention is to provide a simple method for the synthesis of mesoporous materials of the aluminates type, in order to obtain supports with high surface area and high thermal stability.

Another object of the present invention is to provide a highly reproducible method for obtaining catalytic precursor aluminates, in powder form, with a high homogeneity and controlled composition, as well as contributing to the knowledge of the effect of the preparation method of the aluminate support. of magnesium and its physicochemical properties.

Still another object of the present invention is to provide a method capable of obtaining magnesium aluminate type supports / catalysts from the sol-gel method of prototype platinum (Pt) and tin catalysts (Sn).

Still another object of the present invention is to perform the surface and volumetric characterization of said aluminates, by: N2 adsorption (BET), X-ray diffraction (XRD) and desorption at programmed temperature (TPD).

BRIEF DETAILED DESCRIPTION OF THE DRAWINGS In order to have an understanding of the improved process for obtaining Pt-Sn bimetallic catalysts and resulting product, objects of the present invention, reference will be made to the accompanying figures: Figure 1 shows the scheme of the synthesis process of the Pt-Sn / MgAI204 catalyst by means of the impregnation method.

Figure 2 presents the scheme of the synthesis process of the Pt-Sn / MgAI204 catalyst by the coprecipitation method.

Figure 3 refers to a scheme of the synthesis process of the Pt-Sn / MgAI20 catalyst by the Sol-Gel method.

Figure 4 indicates the X-ray diffraction patterns of the Pt-Sn / MgAI204 catalysts calcined at 600 to 900 ° C, corresponding to the impregnated and coprecipitated samples, where: | indicates the formation of the spinel of gA C, ? specifies the formation of PtO and A specifies the formation of MgO.

Figure 5 refers to the graph of the adsorption-desorption isotherms of the catalyst prepared by coprecipitation, of composition: 5a) 0.5Pt-0.3Sn and 5b) 0.5Pt-0.6Sn.

Figure 6 shows the graph of the pore diameter distribution of the catalysts synthesized by coprecipitation, of composition: 6a) 0.5Pt-0.3Sn and 6b) 0.5Pt-0.6Sn.

Figure 7 shows the graphs of the adsorption-desorption isotherms of the catalysts prepared by impregnation, of composition: 7a) 0.5Pt-0.3Sn and 7b) 0.5Pt-0.6Sn.

Figure 8 presents the graph of the pore diameter distribution of the catalysts synthesized by impregnation, of composition: a) 0.5Pt-0.3Sn and b) 0.5Pt-0.6Sn.

Figure 9 refers to the graph of isotherms of adsorption-desorption of the catalysts synthesized by sol-gel, of composition: a) 0.5Pt-0.3Sn and b) 0.5Pt-0.6Sn.

Figure 10 illustrates the graph of pore diameter distribution of the catalysts synthesized by sol-gel, of composition: a) 0.5Pt-0.3Sn and b) 0.5Pt-0.3Sn.

In Figure 11 the graph TPD-NH3 of the synthesized Pt-Sn / MgAI204 catalysts is represented, where: | represents Pt0.3Sn by coprecipitation, · indicates Pt0.6Sn by coprecipitation, A refers toPt0.3Sn by impregnation,? points Pt0.3S by the sol-gel method and? shows Pt0.6Sn by the sol-gel method.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel and simple procedure for obtaining via sol-gel via a series of supports type aluminates (spinels of MgAbO-j), which have been platinum (Pt) and tin (Sn) in previously established compositions. A property that acquires the platinum catalyst supported in magnesium aluminate with the addition of tin is able to operate in different reaction media, even in the presence of water vapor.

As for the Pt-Sn catalysts, prototypes with different Pt / Sn ratios were prepared, by impregnation and coprecipitation, in order to present considerable differences with respect to the sol-gel route, object of the present invention, since the latter have greater resistance under severe reaction conditions. In all cases, concentrations of 0.5% Pt-0.3% Sn (Pt / Sn = 1.0) and 0.5% Pt-0.6% Sn (Pt / Sn = 0.5) were explored, which were calcined at 600 ° C in air flow. (0 ml / s).

The specific area of the synthesized materials was quantified by obtaining high specific surfaces for the Pt-Sn / MgAl204 catalysts by the sol-gel (SG) method. The specific area order was: impregnated aluminates < Coprecipitated aluminates < Aluminum sol-gel.

A combination of physical methods were selected: X-ray diffraction (XRD), N2 physisorption and ammonia-based TPD (Programmed Temperature Desorption) analysis, in order to more fully investigate the optimal composition and associated changes during treatment thermal.

EXAMPLES Below are some examples that support what is described in the present invention, which do not limit the scope thereof.

EXAMPLE 1 Method of impregnation.

The impregnation process consists in contacting a solid porous support with a solution containing the ions of the active metals. The solution penetrates the pores of the support and the ions adsorb on its surface. The impregnated support passes an activation process in order to obtain active metallic particles from the initially adsorbed ions. The process of synthesis by impregnation is graphically illustrated in Figure 1 and the actual content is tabulated in Table 1.

The synthesis of the Pt-Sn / MgAI204 catalysts by the impregnation method is described below. 1) Firstly, an optimum ratio Al / Mg = 3 is established, based on which: 2) The corresponding amounts of the respective nitrates (reactants) are weighed. 3) The solutions are precipitated keeping the pH constant. 4) The support prepared at pH 10 with (NH4) 2C03, with a surface area of 132 m2 / g, was impregnated with an alcohol solution of stannous chloride SnCl2, dried on a rotary evaporator, and calcined in an air flow at 600 ° C; and 5) It was impregnated with an alcoholic solution of H2PtCl6, generating a nominal 0.5 Pt / Sn composition. The heating program of the sample was 10 ° C / min, from room temperature until reaching the temperature at 600 ° C, keeping it for 10 hours.

EXAMPLE 2 The support was synthesized at pH 10 using NH 4 (CO) 3 as precipitant. It was impregnated with an alcoholic solution of SnCl2, dried on a rotary evaporator, calcined in an air flow at 600 ° C and impregnated with an alcoholic solution generating a nominal 0.5 Pt / Sn composition.

EXAMPLE 3 Coprecipitation Method The synthesis of MgAI204 was carried out following the technique of coprecipitation, with the variant of adding and co-precipitating the stoichiometric quantity of SnCl2 to obtain catalysts of 0.3% weight of Sn. The material thus obtained was washed repeatedly to remove impurities, dried at 110 ° C in vacuum and calcined at 600 ° C with air flow for 8 h; subsequently it was impregnated with 0.5% weight of Pt and calcined under the same conditions. The process of synthesis by coprecipitation is illustrated in Figure 2, and the actual content is tabulated in Table 1.

EXAMPLE 4 The synthesis of MgAI204 was carried out following the technique of coprecipitation, with the variant of adding and co-precipitating the stoichiometric amount of SnCl2 to obtain 0.6% Sn weight catalysts. The material thus obtained was washed repeatedly to remove impurities, dried at 110 ° C in vacuum and calcined at 600 ° C with air flow for 8 h; subsequently it was impregnated with 0.5% weight of Pt and calcined under the same conditions.

EXAMPLE 5. Sol-gel method.

Were weighed 2,331 grams of aluminum tri-secbutoxide dissolved in ethanol and reacted with 0.6858 grams of magnesium ethoxide, subjecting the reactant mixture to a stirring process for 2 hours. To the mixture of the aluminum and magnesium alkoxides, the SnCl2 was added in alcoholic ethanol solution; subsequently, the solution of? 2 was added? ¾ dissolved in ethanol. The mixture was left to react for 12 h.

At the end of this period, deionized water is added and initially the product obtained is a sol; and finally with the continuous addition of deionized water the gel is formed. The catalyst thus synthesized had a Pt-Sn 1.0 ratio, was subjected to a drying step at 160 ° C in a mechanical vacuum of 1 to 4 hours, preferably 2 hours. Subsequently, it was subjected to a calcination stage at 600 ° C with air flow for a time of 1 to 6 hours, preferably 4 hours, thus obtaining the catalyst Pt-Sn / MgAI204. The process followed in this method is illustrated in Figure 3.

EXAMPLE 6 Following the methodology described in Example 5, object of the present invention, a catalyst prototype with a Pt-Sn 0.5 ratio was prepared, which was subjected to calcination with air flow in an oven, using a program of heating of 10 ° C / min, from room temperature until reaching the temperature of 600 ° C, keeping it for 4 hours.

Surface and volumetric characterization of the aluminates obtained in the examples described above. A combination of physical methods were selected: X-ray diffraction (XRD), N2 physisorption and ammonia-based TPD (Programmed Temperature Desorption) analysis, in order to more fully investigate the optimal composition and associated changes during treatment thermal.

Atomic Absorption The actual content of the metals in the catalysts was determined by atomic absorption spectroscopy. The results obtained are reported in table 1. The main variation in the Pt-Sn ratio is due to a higher concentration of tin in the catalysts, which even when the theoretical Pt / Sn ratio varies, is within the experimental error of The technique.

X-ray diffraction (XRD) The XRD results reveal the formation of the spinel structure in all the catalysts prepared via sol-gel (see figure 4). From the treatment at 600 ° C, the crystallographic structure of MgAl204 is more defined when the sol-gel synthesis is carried out; that when done by impregnation, or by coprecipitation. ' When the heat treatment is carried out at higher temperatures in the catalysts prepared by sol-gel, the metals tend to migrate to the surface of the support at temperatures higher than 750 ° C, as shown in Figure 4, the above can be seen from the presence of peaks that we associate to PtO in the catalyst, which do not appear at lower temperatures. That is, as the calcination temperature increases, it partially segregates from the spinel phase (MgAbC ^), magnesium oxide (MgO), so by using this diffraction technique, it is preferable to calcinate at T < 800 ° C.

Fisisorción of nitrogen The hysteresis cycles for nitrogen adsorption-desorption at -196 ° C on samples of zeolites were determined in a volumetric instrument ASAP 2100 of icrometrics Instrument Corp., as described by Greg, SJ Sing, KSW Adsorption Surface Area and Porosity , Academic Press (1982), 111-190. The exact determination of the pore form is intimately related to the adsorption-desorption isotherm and more particularly to the hysteresis classified by the International Union of Pure and Applied Chemistry (IUPAC).

The surface area of the catalysts was determined by the BET adsorption analysis method (Brunauer, Emmett and Teller method), the results are found in the corresponding table 2. It should be noted in this table that the catalysts obtained in examples 5 and 6, prepared by sol-gel, maintain their high surface area.

Figure 5 shows the adsorption and desorption isotherms of the catalysts synthesized by tin coprecipitation. { 5a) 0.3% Sn and 5b) 0.6% Sn} . The shape of the hysteresis curls of the catalyst with 0.6% weight of tin belong to type B and H3 according to the Boer classification, while the isotherm is similar to type II according to the classification of the Brunauer method, Demming , Demming and Teller (BDDT). { Thomas J. M., and Lambert R., Characterization of Catalysts, John Wiley & Sons, (1980). Gregg S. J., and Sing K. S. W., Adsorption, Surface Area and Porosity, Second Edition, Editorial Academic Press, (1982)} .

The catalyst with 0.3% Sn presents a form of hysteresis curls of type E and H2 according to the classification of Boer and IUPAC respectively, the isotherm belongs to type IV of the BDDT classification.

In Figure 6, the pore diameter distribution for the catalysts synthesized by the same method is shown. { 6a) 0.3% Sn and 6b) 0.6% Sn} , the 0.3% Sn catalyst shows a bimodal porous distribution, which we can classify as a mesoporous solid. In the 0.6% tin weight catalyst, the porous distribution is in the region of the mesopores with an average size of 200 A.

Figure 7 shows the adsorption-desorption isotherms of the catalysts prepared by impregnation. { 7a) 0.3% Sn and 7b) 0.6% Sn} , it is worth noting the similarity with the isotherms obtained from the coprecipitated catalysts; but apparently these are slightly more open in their hysteresis curl. The isotherms of the catalysts synthesized by this method are associated to type IV of the BDDT classification, and the curls to type E and H2 of the Boer and IUPAC classification.

The porous distribution of the impregnated catalysts is very similar, it is associated with mesoporous materials (figures 8a and 8b), with average diameters of 250 A and bimodal porous distribution.

The 0.3% Sn catalyst synthesized by sol-gel (figure 9a), shows a type II adsorption isotherm according to the BDDT classification and hysteresis curls type A and H1 according to the Boer and IUPAC classification; the porous distribution (figure 10a) in this catalyst is unimodal mesoporosa with average diameter of 100 A. The isotherm of adsorption of the catalyst of 0.6% Sn (figure 9b), is assumed of type II according to the classification of BDDT, the curls of hysteresis belong to type E and H2 according to the classification of Boer and IUPAC; the porous distribution (figure 10b) in this catalyst is mesoporous unimodal with an average diameter of 70 Á.

Programmed thermodesorption-NH3.

To determine the acidity of the prepared catalysts, the Programmed Temperature Desorption (DTP) of ammonia was carried out, which implies that the greater the desorption of ammonia, the material under study will have greater acidity.

Figure 1 1 shows the desorption profiles obtained from the catalysts. The desorption of the ammonia is carried out in the range of 150 and 200 ° C, preferably at 180 ° C for all the catalysts, which indicates that the acid sites in the catalysts are weak. In the same figure it is clearly shown that the prototypes synthesized via sol-gel are the ones with the highest acidity.

Table 1.- Metallic content of the synthesized catalysts, determined atomic absorption.

Table 2.- Textural analysis of the Pt-Sn / MgAI204 catalysts.

Catalyst Specific area BET, held Pore diameter, Pore volume, or m2 / g Á cc / g in example 1 132 94 0.30 2 133 93 0.30 3 170 97 0.41 4 149 133 0.50 5 192 103 0.50 6 297 62 0.46

Claims (6)

NOVELTY OF THE INVENTION Having described the present invention, this is considered as a novelty and therefore the content in the following clauses is claimed as property:

1. - An improved process for obtaining Pt-Sn bimetallic catalysts supported on magnesium aluminates, comprising: a) mixing the aluminum and magnesium alkoxides, preferably aluminum trisecbutoxide and magnesium ethoxide at room temperature, maintaining a stoichiometric molar ratio Al / Mg = 3, preferably 2.8. b) adding an alcoholic solution of stannous chloride, such as ethanol; b) adding a solution of chloroplatinic acid (H2PtCI6) and an alcohol, such as ethanol; c) let the mixture react for 12 h; d) initially, by adding deionized water, obtain a sol as a product; d) finally, form a gel; e) drying the material obtained at 160 ° C under mechanical vacuum for 1 to 4 hours, preferably 2 hours; f) calcining the dry gel synthesized at 600 ° C with air flow for a time of 1 to 6 hours, preferably 4 to obtain the catalyst Pt-Sn / MgAI204.

2. - A Pt-Sn / MgAI204 catalyst according to clause 1, characterized in that it has: a Pt / Sn ratio of 0.5 to 1.0, a specific area of 190 to 300 m2 / g, a pore diameter of 55 to 105 A, and a pore volume with average values between 0.3 to 0.50 cc / g.

3. - A Pt-Sn / MgAl20 catalyst in accordance with clauses 1 and 2, characterized in that it has high specific areas of the synthesized materials in a range of 120 and 300 m2 / g, the order of the specific area being: impregnated aluminates < Coprecipitated aluminates < Aluminum sol-gel.

4. - A Pt-Sn / MgAbC catalyst according to clauses 1 to 3, characterized in that they show type II adsorption isotherms according to the BDDT classification and hysteresis curls of types A, H1 and E, H2 according to the Boer classification; a mesoporous unimodal porous distribution with an average diameter of 60 to 140 A.

5. - A Pt-Sn / MgAI20 catalyst according to clauses 1 to 4, characterized in that the crystallographic structure of the magnesium spinel (MgAI204) is defined by the migration of the metals to the surface of the support at temperatures in the range of 600 at 800 ° C of calcination in the angle range 2T = 34 ° and 2T = 47 ° of the X-ray diffraction pattern.

6. - A Pt-Sn / MgAbCu catalyst according to clauses 1 to 5, characterized in that the catalyst synthesized from platinum by the sol-gel method has the highest acidity, in the range of 150 and 200 ° C, preferably at 180 ° C .