Understanding the roles of different acid sites in beta zeolites with different particle sizes catalyzed liquid-phase transalkylation of diethylbenzene with benzene

A series of Beta zeolite catalysts with controllable particle sizes and similar Si/Al ratios were prepared by introducing imidazole (IMD) into the synthesis system and used for a liquid-phase transalkylation of diethylbenzene (DEB) with benzene (Bz). Beta zeolite catalyst prepared with IMD/SiO2 molar ratio of 0.5 possessed the smallest particle size (mean particle size of 119 nm) and the highest DEB conversion of 79.16%, under the reaction conditions: 260 oC, 4.0 MPa, WHSV (diethylbenzene) of 2.0 h-1, W(benzene)/W(diethylbenzene) of 3/1, time on stream of 5 h. Then, for the purpose of elucidating the catalytic roles of the acid sites with different strength, types and positions in Beta zeolite in the transalkylation reaction, we carried out Na+ loading on the prepared Beta zeolite to eliminate strong acid sites, and poisoned Bronsted acid sites and external acid sites by using 2,4-dimethylquinoline (2,4-DMQ) and triphenylphosphorus (TPP) as toxic reagents, respectively. The results suggested that the moderate and strong Bronsted acid sites of Beta-IMD0.5 were the active sites for the liquid-phase transalkylation of DEB with Bz and their utilization rate showed a trend of increased first and then decreased. Significantly, 31% of the external Bronsted acid sites of Beta-IMD0.5 contributed 81% of DEB conversion. The external acid sites had more contribution to the reaction, due to the short diffusion path and fine accessibility.