Ni/γ-Al2O3 CATALYST FOR CO2 REFORMING OF BENZENE AS A MODEL COMPOUND OF BIOMASS GASIFICATION TAR: PROMOTIONAL EFFECT OF ULTRASONIC TREATMENT ON CATALYTIC PERFORMANCE

摘要

This paper aims to understand the promotional effect of ultrasonic treatment on catalytic performance of Ni/γ-Al2O3 catalyst for CO2 reforming of benzene as a model compound of tar derived from biomass gasification, and the catalytic cracking mechanism was also discussed. Firstly, three Ni/γ-Al2O3 catalysts were prepared by ultrasonic impregnation as the ultrasonic power variant at 0, 120 and 500W, and the physicochemical property of catalysts were characterized using N2-adsorption, SEM and XRD, etc. Then the catalytic performance of three catalysts for CO2 reforming of benzene was tested in a micro-reactor. The outlet gas was measured using a Micro-GC. Finally, the coking amount on the catalyst surface was measured by thermogravimetry (TG). The results showed that ultrasonic treatment significantly modified the pore size distribution of the catalysts especially in the pore size range of 10-50nm and also improved the capability of the coke resistance. It's beneficial to increase the lifetime of the catalyst. Meanwhile, lower ultrasonic power (120W) was more favorable to improve the coke resistance of the catalyst in the power range tested (120 and 500W). The main surface reactions over Ni/γ-Al2O3 catalysts included two steps: Firstly, benzene adsorbed on the catalyst surface, the metal active sites dehydrogenation took place, and the residual molecule fragments (coke precursor) would condense further which led to coke formation. Then, CO2 reacted with coke precursor and coke for coke elimination. The first step carried out very quickly, and the second step was the rate-determining step. To reduce the coke deposition on the catalyst surface, the performance of CO2 adsorption and activation and surface oxygen transmission capacity should be improved further.