Crystallization of faujasite Y from seeds dispersed on mesoporous materials

An original procedure to obtain a solid which combines the microporosity of a Y zeolite with a broad distribution of mesoporosity is described. The starting gel is composed of a mixture of Y zeolite and a source of silica, such as mesoporous FSM-16 or rice hull ash (RHA). Seeds of the crystalline fraction are obtained by depolymerizing the crystalline frameworks of Y zeolite in glycerol, heated at 200 °C for 3–5 h. An amorphous polysilanol alkoxide gel is produced by this reaction. The hydrolysis of this gel is carried out with 0.05 N tetra-methyl ammonium hydroxide (TMAOH) aqueous solution. After aging in an autoclave, a well-crystallized Y zeolite supported on a mesoporous material is obtained. The final calcined solid exhibits high surface area (>400 m2/g) and large pore volume (≈0.4 cc/g) in the mesoporous domain. The Y zeolite lattice and the mesoporous support provide both Brønsted and Lewis acidity. Furthermore, this procedure reduces the sodium content in the final material.