| Sumario: | The catalytic properties of zeolites can be improved in principle by anchoring them to mesoporous aluminosilicate networks that should allow diffusion of the species of interest towards the active sites. In this work the formation of composites between commercial zeolites and a sol precursory of aluminosilicates was studied in order to obtain this type of material. The silica-alumina/zeolite composites were prepared at room temperature and basic pH by using the sol-gel method in combination with a coprecipitation process. Aluminum nitrate and tetraethylortosilicate were used as aluminum and silicon precursors and the biopolymer chitosan added to the solution was used as a templating agent. Finally between 5 and 10% in weight of the zeolite (ZSM-5) was added to this solution. When the resulting white and dense gel was dried, calcined at 550°C/12 h, composites with high surface area (400 m2/g) and pore diameter of around 30 A0 were obtained. The materials are mesoporous but they maintain the microporosity of the constituent zeolite. On the other hand, when dry material undergoes hydrothermal treatment before calcination, the surface area diminishes ca.100 m2/g, but the mean pore diameter increases to 150 A0 with a pore volume of 1,3 cm3/g. The total micropore volume remains constant indicating that the structure of zeolite was not affected with the treatment, which was also corroborated by XRD analysis. It was also demonstrated that the presence of Chitosan lead to a narrower distribution of the pore size. These results allowed us to conclude that the composites are conformed by zeolite supported on a mesoporous silica-alumina matrix where its porosity is modeled by the HT-treatment and by the presence of chitosan.The catalytic properties of zeolites can be improved in principle by anchoring them to mesoporous aluminosilicate networks that should allow diffusion of the species of interest towards the active sites. In this work the formation of composites between commercial zeolites and a sol precursory of aluminosilicates was studied in order to obtain this type of material. The silica-alumina/zeolite composites were prepared at room temperature and basic pH by using the sol-gel method in combination with a coprecipitation process. Aluminum nitrate and tetraethylortosilicate were used as aluminum and silicon precursors and the biopolymer chitosan added to the solution was used as a templating agent. Finally between 5 and 10% in weight of the zeolite (ZSM-5) was added to this solution. When the resulting white and dense gel was dried, calcined at 550°C/12 h, composites with high surface area (400 m2/g) and pore diameter of around 30 A0 were obtained. The materials are mesoporous but they maintain the microporosity of the constituent zeolite. On the other hand, when dry material undergoes hydrothermal treatment before calcination, the surface area diminishes ca.100 m2/g, but the mean pore diameter increases to 150 A0 with a pore volume of 1,3 cm3/g. The total micropore volume remains constant indicating that the structure of zeolite was not affected with the treatment, which was also corroborated by XRD analysis. It was also demonstrated that the presence of Chitosan lead to a narrower distribution of the pore size. These results allowed us to conclude that the composites are conformed by zeolite supported on a mesoporous silica-alumina matrix where its porosity is modeled by the HT-treatment and by the presence of chitosan.The catalytic properties of zeolites can be improved in principle by anchoring them to mesoporous aluminosilicate networks that should allow diffusion of the species of interest towards the active sites. In this work the formation of composites between commercial zeolites and a sol precursory of aluminosilicates was studied in order to obtain this type of material. The silica-alumina/zeolite composites were prepared at room temperature and basic pH by using the sol-gel method in combination with a coprecipitation process. Aluminum nitrate and tetraethylortosilicate were used as aluminum and silicon precursors and the biopolymer chitosan added to the solution was used as a templating agent. Finally between 5 and 10% in weight of the zeolite (ZSM-5) was added to this solution. When the resulting white and dense gel was dried, calcined at 550°C/12 h, composites with high surface area (400 m2/g) and pore diameter of around 30 A0 were obtained. The materials are mesoporous but they maintain the microporosity of the constituent zeolite. On the other hand, when dry material undergoes hydrothermal treatment before calcination, the surface area diminishes ca.100 m2/g, but the mean pore diameter increases to 150 A0 with a pore volume of 1,3 cm3/g. The total micropore volume remains constant indicating that the structure of zeolite was not affected with the treatment, which was also corroborated by XRD analysis. It was also demonstrated that the presence of Chitosan lead to a narrower distribution of the pore size. These results allowed us to conclude that the composites are conformed by zeolite supported on a mesoporous silica-alumina matrix where its porosity is modeled by the HT-treatment and by the presence of chitosan.The catalytic properties of zeolites can be improved in principle by anchoring them to mesoporous aluminosilicate networks that should allow diffusion of the species of interest towards the active sites. In this work the formation of composites between commercial zeolites and a sol precursory of aluminosilicates was studied in order to obtain this type of material. The silica-alumina/zeolite composites were prepared at room temperature and basic pH by using the sol-gel method in combination with a coprecipitation process. Aluminum nitrate and tetraethylortosilicate were used as aluminum and silicon precursors and the biopolymer chitosan added to the solution was used as a templating agent. Finally between 5 and 10% in weight of the zeolite (ZSM-5) was added to this solution. When the resulting white and dense gel was dried, calcined at 550°C/12 h, composites with high surface area (400 m2/g) and pore diameter of around 30 A0 were obtained. The materials are mesoporous but they maintain the microporosity of the constituent zeolite. On the other hand, when dry material undergoes hydrothermal treatment before calcination, the surface area diminishes ca.100 m2/g, but the mean pore diameter increases to 150 A0 with a pore volume of 1,3 cm3/g. The total micropore volume remains constant indicating that the structure of zeolite was not affected with the treatment, which was also corroborated by XRD analysis. It was also demonstrated that the presence of Chitosan lead to a narrower distribution of the pore size. These results allowed us to conclude that the composites are conformed by zeolite supported on a mesoporous silica-alumina matrix where its porosity is modeled by the HT-treatment and by the presence of chitosan.
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