Preparation of hierarchical β and Y zeolite-containing mesoporous silica–aluminas and their properties for catalytic cracking of n-dodecane

Hierarchical β and Y zeolite-containing mesoporous silica–aluminas were prepared by one pot sol–gel method. β and Y zeolite crystal structures were maintained and hierarchical structures with microporous zeolite in center and mesoporous silica–alumina in outer shell were constructed. β zeolite-containing catalysts exhibited much higher activity than Y zeolite-containing ones. The yield of gasoline fraction for each prepared catalyst was higher than that of single zeolite because overcracking was inhibited. The presence of larger pores than in the zeolite and the control of the amount of acid sites effectively increased the selectivity for single- and multi-branched products, which have higher octane numbers. Further, the yields of gasoline and branched products linearly increased with respect to the conversion of dodecane regardless of the kinds of zeolite used. The results show that the cracking and the isomerization to branched products occurred simultaneously and that the isomerization of carbenium ions proceeded very rapidly at zero-order reaction.