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

Abstract

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 liquid-phase transalkylation of diethylbenzene (DEB) with benzene (Bz). The beta zeolite catalyst prepared with an 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 °C, 4.0 MPa, WHSV (diethylbenzene) of 2.0 h⁻¹, W(benzene)/W(diethylbenzene) of 3/1, time on stream of 5 h. Then, to elucidate the catalytic roles of acid sites with different strengths, 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 the Brønsted 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 Brønsted acid sites of beta-IMD_0.5 were the active sites for the liquid-phase transalkylation of DEB with Bz and their utilization rate showed a trend of increasing first and then decreasing. Significantly, 31% of the external Brønsted acid sites of beta-IMD_0.5 contributed 81% of DEB conversion. The external acid sites had more contribution to the reaction due to the short diffusion path and fine accessibility.