Process for preparing a spherical material with a hierarchical porosity comprising metallic particles trapped in a mesostructured matrix

Abstract

A process is described for the preparation of an inorganic material with a hierarchical porosity in the micropore and mesopore domains. The material has at least two elementary spherical particles having a maximum diameter of 200 microns. The process comprises: a) preparing a solution containing zeolitic nanocrystals with a maximum nanometric dimension equal to 60 nm based on silicon and/or precursor elements of proto-zeolitic entities based on silicon; b) mixing, in solution, metallic particles or at least one metallic precursor of metallic particles, a surfactant and the solution obtained in accordance with a) such that the ratio of the volumes of inorganic and organic materials, V.sub.inorganic/V.sub.organic, is 0.29 to 0.50; c) aerosol atomization of the solution obtained in b) resulting in formation of spherical particles; d) drying the particles; g) eliminating any remaining precursor elements of proto-zeolitic entities based on silicon and the surfactant.

Claims

1. A process for the preparation of an inorganic material with a hierarchical porosity in the micropore and mesopore domains, said material being constituted by at least two elementary spherical particles having a maximum diameter of 200 microns, each of said spherical particles comprising metallic particles containing at least one or more metals selected from vanadium, niobium, tantalum, molybdenum, tungsten, iron, copper, zinc, cobalt and nickel, said metallic particles being present within a matrix, which is mesostructured, based on silicon oxide, having microporous walls with a thickness in the range 1 to 60 nm, said process comprising at least the following steps: a) preparing a solution containing zeolitic nanocrystals with a maximum nanometric dimension equal to 60 nm based on silicon and/or precursor elements of proto-zeolitic entities based on silicon; b) mixing, in solution, said metallic particles or at least one metallic precursor of said metallic particles, at least one surfactant and at least said solution obtained in accordance with a) such that the ratio of the volumes of inorganic and organic materials, V.sub.inorganic/V.sub.organic, is in the range 0.29 to 0.50; c) aerosol atomization of said solution obtained in step b) in order to result in the formation of spherical particles; d) drying said particles; g) eliminating any remaining precursor elements of proto-zeolitic entities based on silicon and at least said surfactant; h) regenerating said metallic particles to the form of a polyoxometallate which have decomposed during step g); and i) drying the regenerated particles; wherein said metallic particles are in the form of a polyoxometallate with formula (X.sub.xM.sub.mO.sub.yH.sub.h).sup.q where H is a hydrogen atom, 0 is an oxygen atom, X is an element selected from phosphorus, silicon, boron, nickel and cobalt and M is one or more elements selected from vanadium, niobium, tantalum, molybdenum, tungsten, iron, copper, zinc, cobalt and nickel, x being equal to 0, 1, 2, or 4, m being equal to 5, 6, 7, 8, 9, 10, 11, 12 or 18, y being in the range 17 to 72, h being in the range 0 to 12 and q being in the range 1 to 20 and y, h and q being whole numbers.

2. A preparation process according to claim 1, wherein following said step d), a step e) is carried out consisting of autoclaving the particles obtained from said step d) then carrying out a step f) consisting of drying said particles obtained at the end of said step e).

3. A preparation process according to claim 2, in which said zeolitic nanocrystals comprise at least one zeolite selected from zeolites with structure type MFI, BEA, FAU and LTA and/or said proto-zeolitic entities comprise at least one species for initiating at least one zeolite selected from zeolites with structure type MFI, BEA, FAU and LTA.

4. A preparation process according to claim 1, in which said metallic particles have at least one band with a wave number in the range 750 to 1050 cm.sup.1 in Raman spectroscopy.

5. A preparation process according to claim 4, in which said metallic particles are oxide nanoparticles comprising at least one metal selected from molybdenum, tungsten and a mixture of these two metals.

6. A preparation process according to claim 5, in which at least one first monometallic precursor based on a metal selected from vanadium, niobium, tantalum, molybdenum and tungsten and at least one second monometallic precursor based on a metal from group VIII are dissolved to provide a solution prior to carrying out said step b), said solution then being introduced into the mixture in accordance with said step b).

7. A preparation process according to claim 1, in which said metallic particles are heteropolyanions with formula P.sub.2Mo.sub.5O.sub.23H.sub.h.sup.(6h), in which h=0, 1 or 2.

8. A preparation process according to claim 1, in which said step a) consists of preparing a solution containing precursor elements of proto-zeolitic entities based on silicon and aluminium.

9. A preparation process according to claim 1, in which said metallic particles are prepared by dissolving, prior to said step b), the metallic precursor(s) necessary for obtaining them in a solvent to provide a solution, said solution then being introduced into the mixture in accordance with said step b).

10. A preparation process according to claim 1, in which at least one sulphur-containing compound is introduced into the mixture said step b) or when carrying out said step g).

11. A process for the transformation of a hydrocarbon feed, comprising 1) bringing an inorganic material obtained in accordance with the preparation process according to claim 1 into contact with a feed comprising at least one sulphur-containing compound, then 2) bringing said material obtained from said step 1) into contact with said hydrocarbon feed.

Description

EXAMPLES

(1) In the examples below, the aerosol technique used was that described above in the disclosure of the invention: a model 9306A generator with a 6 jet atomizer supplied by TSI was used. The dispersive Raman spectrometer used was a commercial LabRAM Aramis apparatus supplied by Horiba Jobin-Yvon. The laser used had an excitation wavelength of 532 nm. The operation of this spectrograph in the execution of the examples 1 to 5 below was described above.

(2) For each of Examples 1 to 5 below, the ratio V.sub.inorganic/V.sub.organic of the mixture obtained from step b) containing the metallic particles or their precursors, the precursors of the (proto) zeolitic entities and the surfactant (P123 or F127) was calculated. This ratio is defined as follows: V.sub.inorganic/V.sub.organic=.sub.i(m.sub.inorg i/.sub.inorg i)/.sub.j(m.sub.org j/.sub.org j), where i is from 1 to the total number of inorganic precursors and j is from 1 to the total number of surfactants and templates and where m.sub.inorg i is the mass of oxide associated with the inorganic precursor i condensed in the solid elementary particle obtained by atomization, m.sub.org j is the mass of the surfactant or the non-volatile template j in the solid elementary particle obtained by atomization and .sub.org j and .sub.inorg i are the respective densities associated with each of the non-volatile organic j and inorganic i compounds. The density of the oxide associated with the inorganic precursor i is equal to the density of the corresponding crystalline oxide reduced by 15%. For the examples below, .sub.i(m.sub.inorg i/.sub.inorg i) generally corresponds to the sum of the ratios of the masses of the oxides MoO.sub.3, CoO, NiO and/or P.sub.2O.sub.5 added to the masses of SiO.sub.2 and Al.sub.2O.sub.3 over their respective density. Similarly, .sub.j(m.sub.org j/.sub.org j) generally corresponds to the sum of the weight ratios of the template, i.e. TPAOH, in Examples 1 to 5, supplemented by the mass of surfactant, i.e. the surfactant P123 or F127, in Examples 1 to 5, over their respective density. The polar solvent, ethanol in Examples 1 to 5, as well as the water are not taken into account in the calculation of said ratio V.sub.inorganic/V.sub.organic.

Example 1 (Invention)

(3) Preparation of a material with HPAs of the Strandberg type H.sub.2P.sub.2Mo.sub.5O.sub.23.sup.4.2Co.sup.2+, with 10% by weight of MoO.sub.3, 2.08% by weight of CoO and 1.97% by weight of P.sub.2O.sub.5 with respect to the final material. The oxide matrix has a hierarchical porosity in the micropore and mesopore domains which is organized in the mesopore domain, with amorphous microporous walls constituted by aluminosilicate proto-zeolitic entities of the type ZSM-5 (MFI) such that the molar ratio Si/Al=12.

(4) An aqueous solution containing 3.61 mole/L of MoO.sub.3, 1.44 mole/L of H.sub.3PO.sub.4, 1.44 mole/L of Co(OH).sub.2 was prepared, with stirring, at ambient temperature. Raman analysis carried out on the final material revealed the presence of Strandberg HPA H.sub.2P.sub.2Mo.sub.5O.sub.23.sup.4.2Co.sup.2+, as the major species.

(5) 0.44 g of aluminium tri-sec-butoxide was mixed with 2.17 g of an aqueous solution of TPAOH (40% by weight). After stirring for 10 minutes at ambient temperature, 22.4 g of deionized water was added. After homogenization, 4.43 g of TEOS was added then allowed to hydrolyze for 16 hours, with stirring at ambient temperature. Following hydrolysis, the solution was diluted with a solution containing 1.46 g of P123 (Sigma-Aldrich), 45.5 g of deionized water and 5.79 g of ethanol. A solution composed of 10.0 g of deionized water, 0.33 mL of the aqueous Strandberg solution H.sub.2P.sub.2Mo.sub.5O.sub.23.sup.4.2Co.sup.2+, containing 0.72 mole/L of HPA as well as 0.22 g of thiourea was prepared. After stirring for 5 min, this solution was added to the solution containing the P123. The ratio V.sub.inorganic/V.sub.organic of the mixture was equal to 0.32 and was calculated as described above. The mixture was stirred for 30 minutes then sent to the atomization chamber of the aerosol generator as described in the description above, and the solution was sprayed in the form of fine droplets under the action of a vector gas (dry air) introduced under pressure (P=1.5 bar). The droplets were dried in accordance with the protocol described in the disclosure of the invention above: they were channeled through PVC tubes by means of an O.sub.2/N.sub.2 mixture. They were then introduced into an oven adjusted to a fixed drying temperature of 350 C. The powder recovered was then dried for 18 hours at 95 C. The powder was then calcined in air for 5 hours at 550 C. The HPA was then regenerated by washing the solid with methanol for 4 hours using a Soxhlet. Finally, the material was dried at 80 C. for 24 hours. The solid was characterized by small angle XRD, by nitrogen volumetric analysis, by TEM, by SEM, by XRF and by Raman spectroscopy. The TEM analysis showed that the final material had an organized mesoporosity characterized by a vermicular structure. The nitrogen volumetric analysis combined with analysis using the .sub.s method produced a value for the microporous volume, V.sub.micro (N.sub.2), of 0.03 mL/g, a value for the mesoporous volume, V.sub.meso (N.sub.2), of 0.43 mL/g and a specific surface area of the final material of S=217 m.sup.2/g. The mesoporous diameter characteristic of the mesostructured matrix was 8.3 nm. The small angle XRD analysis produced a correlation peak at the angle 2=0.84. Bragg's law, 2d*sin(0.42)=1.5406, was used to calculate the correlation distance d between the organized mesopores of the material, i.e. d=10.5 nm. The thickness of the walls of the mesostructured material, defined by e=d, was thus e=2.2 nm. The Si/Al mole ratio obtained by XRF was 12. A SEM image of the spherical elementary particles obtained indicated that these particles have a dimension characterized by a diameter in the range 50 nm to 30 m, the size distribution of these particles being centred around 15 m. The Raman spectrum of the final material revealed the presence of Strandberg HPA, H.sub.2P.sub.2Mo.sub.5O.sub.23.sup.4, with a characteristic band of this heteropolyanion at 941 cm.sup.1 and secondary bands at 892, 394 and 369 cm.sup.1.

Example 2 (Invention)

(6) Preparation of a material with HPAs of the Strandberg type H.sub.2P.sub.2Mo.sub.5O.sub.23.sup.4.2Co.sup.2+, with 5% by weight of MoO.sub.3, 1.04% by weight of NiO and 0.99% by weight of P.sub.2O.sub.5 with respect to the final material. The oxide matrix has a hierarchical porosity in the micropore and mesopore domains which is organized in the mesopore domain, with amorphous microporous walls constituted by aluminosilicate proto-zeolitic entities of the type ZSM-5 (MFI) such that the molar ratio Si/Al=25.

(7) An aqueous solution containing 3.61 mole/L of MoO.sub.3, 1.44 mole/L of H.sub.3PO.sub.4, 1.44 mole/L of Ni(OH).sub.2 was prepared, with stirring, at ambient temperature. Raman analysis carried out on the final material revealed the presence of Strandberg HPA, H.sub.2P.sub.2Mo.sub.5O.sub.23.sup.4.2Co.sup.2+, as the major species.

(8) 0.23 g of aluminium tri-sec-butoxide was mixed with 2.17 g of an aqueous solution of TPAOH (40% by weight). After stirring for 10 minutes at ambient temperature, 22.3 g of deionized water was added. After homogenization, 4.82 g of TEOS was added then allowed to hydrolyze for 16 hours, with stirring at ambient temperature. Following hydrolysis, the solution was diluted with a solution containing 1.45 g of P123 (Sigma-Aldrich), 45.4 g of deionized water and 5.78 g of ethanol. A solution composed of 10.0 g of deionized water and 0.15 mL of the aqueous solution of Strandberg HPA, H.sub.2P.sub.2Mo.sub.5O.sub.23.sup.4.2Co.sup.2+, with 0.72 mole/L of HPA was prepared. After stirring for 5 min, this solution was added to the preceding solution. The ratio V.sub.inorganic/V.sub.organic of the mixture was equal to 0.32 and was calculated as described above. The mixture was stirred for 30 minutes then sent to the atomization chamber of the aerosol generator as described in the description above, and the solution was sprayed in the form of fine droplets under the action of a vector gas (dry air) introduced under pressure (P=1.5 bar). The droplets were dried in accordance with the protocol described in the disclosure of the invention above: they were channeled through PVC tubes by means of an O.sub.2/N.sub.2 mixture. They were then introduced into an oven adjusted to a fixed drying temperature of 350 C. The powder recovered was then dried for 18 hours at 95 C. The powder was then calcined in air for 5 hours at 550 C. The HPA was then regenerated by washing the solid with methanol for 4 hours using a Soxhlet. Finally, the solid was dried at 80 C. for 24 hours. The solid was characterized by small angle XRD, by nitrogen volumetric analysis, by TEM, by SEM, by XRF and by Raman spectroscopy. The TEM analysis showed that the final material had an organized mesoporosity characterized by a vermicular structure. The nitrogen volumetric analysis combined with analysis using the .sub.s method produced a value for the microporous volume, V.sub.micro (N.sub.2), of 0.05 mL/g, a value for the mesoporous volume, V.sub.meso (N.sub.2), of 0.41 mL/g and a specific surface area of the final material of S=225 m.sup.2/g. The mesoporous diameter characteristic of the mesostructured matrix was 8.7 nm. The small angle XRD analysis produced a correlation peak at the angle 2=0.86. Bragg's law, 2 d*sin(0.43)=1.5406, was used to calculate the correlation distance d between the organized mesopores of the material, i.e. d=10.3 nm. The thickness of the walls of the mesostructured material, defined by e=d, was thus e=1.6 nm. The Si/Al mole ratio obtained by XRF was 25. A SEM image of the spherical elementary particles obtained indicated that these particles have a dimension characterized by a diameter in the range 50 nm to 30 m, the size distribution of these particles being centred around 15 m. The Raman spectrum of the final material revealed the presence of Strandberg HPA, H.sub.2P.sub.2Mo.sub.5O.sub.23.sup.4, with a characteristic band of this heteropolyanion at 943 cm.sup.1 and secondary bands at 894, 396 and 370 cm.sup.1.

Example 3 (Invention)

(9) Preparation of a material having oxide nanoparticles comprising molybdenum and cobalt with 5% by weight of MoO.sub.3 and 1.04% by weight of CoO with respect to the final material. The oxide matrix has a hierarchical porosity in the micropore and mesopore domains which is organized in the mesopore domain, with amorphous microporous walls constituted by aluminosilicate proto-zeolitic entities of the type ZSM-5 (MFI) such that the molar ratio Si/Al=12.

(10) An aqueous solution containing 0.11 mole/L of MoCl.sub.5 and 0.08 mole/L of Co(OH).sub.2 was prepared, with stirring, at ambient temperature.

(11) 0.45 g of aluminium tri-sec-butoxide was mixed with 2.16 g of an aqueous solution of TPAOH (40% by weight). After stirring for 10 minutes at ambient temperature, 22.3 g of deionized water was added. After homogenization, 4.59 g of TEOS was added then allowed to hydrolyze for 16 hours, with stirring at ambient temperature. At the end of hydrolysis, a solution composed of 1.58 g of F127 (Sigma-Aldrich), 45.3 g of deionized water and 5.77 g of ethanol was added to the solution containing the precursors of the proto-zeolitic entities. After homogenizing for 5 min, the solution containing the MoCl.sub.5 and the Co(OH).sub.2 was added dropwise. The ratio V.sub.inorganic/V.sub.organic of the mixture was equal to 0.30 and was calculated as described above. The mixture was stirred for 30 minutes then sent to the atomization chamber of the aerosol generator as described in the description above, and the solution was sprayed in the form of fine droplets under the action of a vector gas (dry air) introduced under pressure (P=1.5 bar). The droplets were dried in accordance with the protocol described in the disclosure of the invention above: they were channeled through PVC tubes by means of an O.sub.2/N.sub.2 mixture. They were then introduced into an oven adjusted to a fixed drying temperature of 350 C. The powder recovered was then dried for 18 hours at 95 C. The powder was then calcined in air for 5 hours at 550 C. Finally, the solid was dried at 80 C. for 24 hours. The solid was characterized by small angle XRD, by nitrogen volumetric analysis, by TEM, by SEM, by XRF and by Raman spectroscopy. The TEM analysis showed that the final material had an organized mesoporosity characterized by a vermicular structure. The nitrogen volumetric analysis combined with analysis using the .sub.s method produced a value for the microporous volume, V.sub.micro (N.sub.2), of 0.04 mL/g, a value for the mesoporous volume, V.sub.meso (N.sub.2), of 0.41 mL/g and a specific surface area of the final material of S=349 m.sup.2/g. The mesoporous diameter characteristic of the mesostructured matrix was 6.0 nm. The small angle XRD analysis produced a correlation peak at the angle 2=0.62. Bragg's law, 2 d*sin(0.31)=1.5406, was used to calculate the correlation distance d between the organized mesopores of the material, i.e. d=14.2 nm. The thickness of the walls of the mesostructured material, defined by e=d, was thus e=8.2 nm. The Si/Al mole ratio obtained by XRF was 12. A SEM image of the spherical elementary particles obtained indicated that these particles have a dimension characterized by a diameter in the range 50 nm to 30 m, the size distribution of these particles being centred around 15 m. The Raman spectrum of the final material revealed the presence of polymolybdate species interacting with the support with characteristic bands for these species at 950 and 887 cm.sup.1.

Example 4 (Invention)

(12) Preparation of a material having oxide nanoparticles comprising molybdenum and nickel with 5% by weight of MoO.sub.3 and 1.04% by weight of NiO with respect to the final material. The oxide matrix has a hierarchical porosity in the micropore and mesopore domains which is organized in the mesopore domain, with amorphous microporous walls constituted by aluminosilicate proto-zeolitic entities of the type ZSM-5 (MFI) such that the molar ratio Si/Al=12.

(13) An aqueous solution containing 0.11 mole/L of MoCl.sub.5 and 0.08 mole/L of Ni(OH).sub.2 was prepared, with stirring, at ambient temperature.

(14) 0.45 g of aluminium tri-sec-butoxide was mixed with 2.16 g of an aqueous solution of TPAOH (40% by weight). After stirring for 10 minutes at ambient temperature, 22.3 g of deionized water was added. After homogenization, 4.59 g of TEOS was added then allowed to hydrolyze for 16 hours, with stirring at ambient temperature. A step for maturing the solution was carried out at 80 C. for 24 h. At the end of the step, a solution composed of 1.58 g of F127 (Sigma-Aldrich), 45.3 g of deionized water and 5.77 g of ethanol was added to the solution containing the precursors of the proto-zeolitic entities. After homogenizing for 5 min, the solution containing the MoCl.sub.5 and the Ni(OH).sub.2 was added dropwise. The ratio V.sub.inorganic/V.sub.organic of the mixture was equal to 0.30 and was calculated as described above. The mixture was stirred for 30 minutes then sent to the atomization chamber of the aerosol generator as described in the description above, and the solution was sprayed in the form of fine droplets under the action of a vector gas (dry air) introduced under pressure (P=1.5 bar). The droplets were dried in accordance with the protocol described in the disclosure of the invention above: they were channeled through PVC tubes by means of an O.sub.2/N.sub.2 mixture. They were then introduced into an oven adjusted to a fixed drying temperature of 350 C. The powder recovered was then dried for 18 hours at 95 C. The powder was then calcined in air for 5 hours at 550 C. The solid was characterized by small angle XRD, by nitrogen volumetric analysis, by TEM, by SEM, by XRF and by Raman spectroscopy. The TEM analysis showed that the final material had an organized mesoporosity characterized by a vermicular structure. The nitrogen volumetric analysis combined with analysis using the .sub.s method produced a value for the microporous volume, V.sub.micro (N.sub.2), of 0.05 mL/g, a value for the mesoporous volume, V.sub.meso (N.sub.2), of 0.43 mL/g and a specific surface area of the final material of S=360 m.sup.2/g. The mesoporous diameter characteristic of the mesostructured matrix was 7.2 nm. The small angle XRD analysis produced a correlation peak at the angle 2=0.62. Bragg's law, 2 d*sin(0.31)=1.5406, was used to calculate the correlation distance d between the organized mesopores of the material, i.e. d=14.0 nm. The thickness of the walls of the mesostructured material, defined by e=d, was thus e=6.8 nm. The Si/Al mole ratio obtained by XRF was 12. A SEM image of the spherical elementary particles obtained indicated that these particles have a dimension characterized by a diameter in the range 50 nm to 30 m, the size distribution of these particles being centred around 15 m. The Raman spectrum of the final material revealed the presence of polymolybdate species interacting with the support with characteristic bands for these species at 951 and 886 cm.sup.1.

Example 5 (Invention)

(15) Preparation of a material having oxide nanoparticles comprising molybdenum and nickel with 5% by weight of MoO.sub.3 and 1.04% by weight of NiO with respect to the final material. The oxide matrix has a hierarchical porosity which is organized in the micropore and mesopore domains, with microporous crystalline walls constituted by zeolitic aluminosilicate entities of the ZSM-5 (MFI) type such that the molar ratio Si/Al=59.

(16) An aqueous solution containing 0.11 mole/L of MoCl.sub.5 and 0.08 mole/L of Ni(OH).sub.2 was prepared, with stirring, at ambient temperature.

(17) 0.10 g of aluminium tri-sec-butoxide was mixed with 2.16 g of an aqueous solution of TPAOH (40% by weight). After stirring for 10 minutes at ambient temperature, 22.3 g of deionized water was added. After homogenization, 5.01 g of TEOS was added then allowed to hydrolyze for 16 hours, with stirring at ambient temperature. A step for maturing the solution was carried out at 80 C. for 24 h. At the end of this step, a solution composed of 1.58 g of F127 (Sigma-Aldrich), 45.3 g of deionized water and 5.77 g of ethanol was added to the solution containing the precursors of the zeolitic entities. After homogenizing for 5 min, the solution containing the MoCl.sub.5 and the Ni(OH).sub.2 was added dropwise. The ratio V.sub.inorganic/V.sub.organic of the mixture was equal to 0.30 and was calculated as described above. The mixture was stirred for 30 minutes then sent to the atomization chamber of the aerosol generator as described in the description above, and the solution was sprayed in the form of fine droplets under the action of a vector gas (dry air) introduced under pressure (P=1.5 bar). The droplets were dried in accordance with the protocol described in the disclosure of the invention above: they were channeled through PVC tubes by means of an O.sub.2/N.sub.2 mixture. They were then introduced into an oven adjusted to a fixed drying temperature of 350 C. The powder recovered was then dried for 18 hours at 95 C. 100 mg of this powder was placed in a 1 L autoclave in the presence of 0.6 mL of distilled water. The autoclave was heated to 95 C. for 48 hours. The powder recovered was then oven dried at 100 C. then calcined in air for 5 h at 550 C. The solid was characterized by small angle and wide angle XRD, by nitrogen volumetric analysis, by TEM, by SEM, by XRF and by Raman spectroscopy. The TEM analysis showed that the final material had an organized mesoporosity characterized by a vermicular structure. The nitrogen volumetric analysis combined with analysis using the .sub.s method produced a value for the microporous volume, V.sub.micro (N.sub.2), of 0.13 mL/g, a value for the mesoporous volume, V.sub.meso (N.sub.2), of 0.33 mL/g and a specific surface area of the final material of S=180 m.sup.2/g. The mesoporous diameter characteristic of the mesostructured matrix was 17 nm. The small angle XRD analysis produced a correlation peak at the angle 2=1.32. Bragg's law, 2d*sin()=1.5406, was used to calculate the correlation distance d between the organized mesopores of the material, i.e. d=67 nm. The thickness of the walls of the mesostructured material, defined by e=d, was thus e=50 nm. Wide angle XRD produced a correlation peak at angles 2=7.9 and 8.9, characterizing the crystalline MFI structure of the ZSM-5 zeolite. The Si/Al mole ratio obtained by XRF was 59. A SEM image of the spherical elementary particles obtained indicated that these particles have a dimension characterized by a diameter in the range 50 nm to 30 m, the size distribution of these particles being centred around 15 m. The Raman spectrum of the final material revealed the presence of polymolybdate species interacting with the support with characteristic bands for these species at 952 and 887 cm.sup.1.