Catalytic characteristics of a Ni–MgO/HZSM-5 catalyst for steam reforming of toluene

Steam reforming is a potential technology for the conversion of biomass pyrolysis tar into gaseous products. In this study, HZSM-5 was selected as the nickel-based catalyst support and toluene was chosen as the tar model compound. Ni was replaced with MgO to improve the coking resistance of the catalyst. The effects of Ni and MgO loading on toluene conversion and gaseous product generation rate were investigated. The low Ni-loading Ni/HZSM-5 catalyst exhibited poor catalytic activity, whereas a high Ni-loading catalyst displayed poor coking resistance. The addition of the MgO promoter enhanced the steam reforming performance of the Ni/HZSM-5 catalyst with a low loading of active metal Ni (3 wt%). The optimal MgO loading was found at 6 wt%. By characterizing the catalyst before and after the reaction, we found that MgO would enter the wall and pores of the support, resulting in increased pore size and decreased specific surface area. Ni and MgO were combined to form NiO–MgO solid solution active centers, which enhanced the catalytic reforming performance. Moreover, more MgO loading increased the alkaline strength of the catalytic surface, enhanced the adsorption of CO2, and improved the resistance to carbon deposition. This study revealed the feasibility of replacing Ni with MgO and the potential mechanism of maintaining similar catalytic performance. This study also laid the theoretical foundation for the industrial application of nickel-based catalysts.