Cause of generation of para-selectivity of zeolites with MFI structure

The cause for generation of para-selectivity of modified zeolites and metallosilicates with MFI structure for alkylation of alkylbenzenes is distinct from that for disproportionation. In the alkylation of alkylbenzene, weaker acid sites on modified zeolites and metallosilicates with MFI structure provide higher para-selectivity, since in the narrow pores of the MFI structure, primary product is only p-dialkylbenzene and the secondary reaction, isomerization, is suppressed to some extent through 'restricted transition-state selectivity' and requires strong acid sites to take place, compared with alkylation. On the other hand, the para-selectivity for the disproportionation is related to tortuosity of the pore. In other words, the high para-selectivity for disproportionation is caused by 'product selectivity.'