Effects of α- and γ-cyclodextrin-modified impregnation method on physicochemical properties of Ni/SBA-15 and its catalytic performance in CO2 reforming of methane

Abstract

Organic compounds containing multiple hydroxyl groups, namely α-cyclodextrin and γ-cyclodextrin, were used as additives for promoting Ni dispersion on supported Ni/SBA-15 catalysts. Catalysts prepared using modified and unmodified impregnation methods were characterized using N2 adsorption-desorption isotherms, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, and thermogravimetric analysis, and their catalytic performance in the CO2 reforming of methane (CRM) to syngas was evaluated. The results show that compared with Ni/SBA-15 prepared using a conventional impregnation method, the cyclodextrin-modified catalysts had smaller NiO particles. They also exhibited higher catalytic activity and had stronger ability to resist carbon deposition in the CRM. Mechanistic studies showed that for the unmodified catalysts, Ni2+ could migrate into the channels of SBA-15 as a result of concentration differences, and the Ni species were sintered during the following thermal treatment processes, and could not be well dispersed. In contrast, various types of complex were formed between Ni(NO3)2 and the cyclodextrins, and this would be favorable for Ni2+ being taken into the channels of the SBA-15. The presence of cyclodextrins was beneficial to the mutual isolation of Ni species, and finally resulted in better dispersion of Ni species.