Enhancing Ni-SiO2 catalysts for the carbon dioxide reforming of methane: Reduction-oxidation-reduction pre-treatment

The work presented here evaluated the impact of reduction-oxidation-reduction (ROR) pre-treatment. on 5 and 10% Ni-SiO2 as an efficient and inexpensive manner of enhancing catalysts for the carbon dioxide reforming of methane. Samples were reduced, oxidised and subsequently re-reduced, with the Ni deposit characteristics being analysed at each step. It was demonstrated that ROR treatment decreased the average Ni deposit size and altered the interaction between the Ni and SiO2, which significantly enhanced catalytic performance. ROR pre-treatment resulted in an increase in CH4 conversion, most significantly for the 10% Ni-SiO2 samples (from 57% to 69% at 800 degrees C) with comparable carbon formation between the reduced and ROR pre-treated samples. During 600 degrees C stability tests the 10% reduced samples deactivated, due to carbon build-up, after 3-4 h reaction time. In contrast, at 600 degrees C the ROR sample maintained stable conversion after 6 h over a 12h time frame. Additionally, for all samples ROR pre-treatment resulted in a more stoichiometric H-2/CO ratio. The reduction in both Ni deposit size and crystallinity increased conversion and selectivity. This derived from a greater active metal surface area for conversion as well as a decrease in the prevalence of methane decomposition and the reverse water gas shift reaction by influencing the desorption of CO and lowering the occurrence of bulk NiO. Ultimately, ROR pre-treatment provides a simple and inexpensive means of improving dry reforming catalysts. (C) 2016 Elsevier B.V. All rights reserved.