Preparation of novel zeolite-containing hierarchical two-layered catalysts with large mesopores by gel skeletal reinforcement and their reactivities in catalytic cracking of n-dodecane

In order to crack hydrocarbons with a large molecular weight, it is necessary to diffuse those substrates deeply into the inside of a catalyst. Catalysts having the hierarchical structure including not only micropores of zeolites in the inner side but also large mesopores in the outer side could crack large molecules of hydrocarbons quite effectively. To prepare such hierarchical catalysts, in this study, ZSM-5, Y and beta zeolites were uniformly dispersed in silicas with large mesopores generated by the gel skeletal reinforcement (GSR) method. It was observed by XRD measurement that these catalysts maintained the framework of zeolite. Nitrogen adsorption and desorption measurement exhibited that the maximum pore volume and pore diameter of catalysts reached 5 cm(3)/g and 50 nm, respectively. These results indicated that silica having large mesopores would be present around the zeolite. When catalytic cracking of n-dodecane using these catalysts was performed, the ZSM-5-containing hierarchical catalysts exhibited 30% higher conversions than that of zeolite single. When catalysts containing beta- and Y-zeolites were used, the ratios of multi-branched hydrocarbons/single-branched hydrocarbons (m/s) and olefin/paraffin (O/P) ratios in the gasoline fraction were about 1.5-2 times higher than those of ZSM-5-containing catalysts. The O/P ratios and conversions increased as the mesoporous diameter increased while the iso-/n- ratio of the gasoline fraction tended to depend on the microporous sizes of the zeolites.