Synthesis, Characterization And Catalytic Prorerties Of Aluminosilicate Porous Materials With Enhanced Acidity And High Hydrothermal Stability

Zeolites are widely used in industrial applications because they have many desirable properties, such as high surface area, adjustable pore size, acidity and high thermal and hydrothermal stability. However, the main drawback of zeolites is their small pore channels which make large sized reactants and products to and from the active sites of catalysts difficult. Mesoporous molecular sieves with pore diameters of 2–50 nm can overcome the pore size constraint of microporous zeolites and allow the diffusion of lager molecules. However, mesoporous materials have low acidity and hydrothermal stability because of their amorphous nature of frameworks, which limit their use as catalysts in industrial processes. Recently, much effort has been devoted to prepare new molecular sieves which combine the advantages of micro- and mesoporous materials.In the chapter three, Beta/MCM-41 micro/mesoporous composite materials have been prepared through assembly of zeolite Beta nanoclusters and their decomposed products by NaOH solution in the presence of CTAB under static or stirred conditions. The composite materials exhibit stronger acidity and higher hydrothermal stability than traditional mesoporous MCM-41. In the alkylation reaction of phenol with tert-butanol, composite materials display higher catalytic activities than that of Al-MCM-41.In the chapter four, micro/mesoporous composite materials have been prepared by using zeolite Beta nanoclusters and their decomposed products by NaOH solution as silica and aluminus source in the presence of P123 under strong or weak acidic condition. When it is synthesized under strong acidic condition, the resulting material exhibit highly ordered hexagonally arranged mesochannels similar to that of SBA-15. However, the acidity of the material is largely weakened by dealumination under strong acidic condition. The material synthesized under weak acidic condition shows disordered worm-like mesoporous channels. In the alkylation reaction of phenol with tert-butanol, the material syntheszed under weak acidic condition exhibits higher conversion of phenol and selectivity for 2,4-di-tert-butyl phenol (2,4-DTBP) than the material synthesized under strong acidic condition.In the chapter five, mesoporous molecular sieves with strong acidity have been prepared through a simple one step synthesis procedure in the presence of tetralkylammonium hydroxide. The resulting materials exhibit stronger acidity than conventional mesoporous MCM-41. All materials show high conversion of phenol and selectivity for 2,4-di-tert-butyl phenol (2,4-DTBP) in alkylation of phenol with tert-butanol.