Enhancement of catalytic activity for toluene disproportionation by loading Lewis acidic nickel species on ZSM-5 zeolite.

[Display omitted] • Nickel loaded on ZSM-5 exhibited higher catalytic performance than H-ZSM-5 zeolite in toluene disproportionation. • The Ni/ZSM-5 with Ni/Al = 0.6 showed high toluene conversion and lower benzene/xylene ratio closer to the stoichiometry. • The high catalytic performance for Ni-0.6 was supposed to be ascribed to the synergy effect of Brønsted acid sites and Lewis acid sites. Impregnation of various heteroelements on the ZSM-5 zeolite was applied to improvement of the catalytic activity in toluene disproportionation. Nickel loaded on ZSM-5 (Ni/ZSM-5) exhibited higher catalytic activity (toluene conversion) and lower benzene/xylene ratio (closer to the stoichiometry, meaning low rate of side reaction) than H-ZSM-5 zeolite. The Ni/ZSM-5 with Ni/Al = 0.6 showed the maximum in catalytic activity, and excess Ni loading caused decrease in the conversion and increase in the benzene/xylene ratio due to decrease of acid amount and acceleration of dealkylation, respectively. The detailed analysis of acidic property by means of ammonia IRMS-TPD method showed that the Ni loading generated Lewis acid sites on the zeolite. The synergy of Brønsted and Lewis acid sites, ascribed to Si-OH-Al and Ni species, respectively, is suggested to give the high activity of desired reaction. [ABSTRACT FROM AUTHOR]