Sequence of Ni/SiO2 and Cu/SiO2 in dual catalyst bed significantly impacts coke properties in glycerol steam reforming

Abstract

Coke formation is a major challenge in steam reforming reactions. In addition to development of robust catalyst for tackling coking, in this study we explored the approach of using dual catalyst bed with the catalyst on top as the guard or sacrifice catalyst while with the bottom catalyst to catalyze the steam reforming. The rationale is that some oxygen-containing reactants are prone to polymerize on heating, and the polymeric coke could directly fall on surface of catalyst and leads to the rapid deactivation. Hence, glycerol was selected as the reactant for steam reforming in the catalyst bed with the Cu/SiO2 placed on the top of Ni/SiO2 catalyst. Our results demonstrate that first contact of glycerol to Cu/SiO2 on top changed abundance/type of small intermediates and the π-conjugated oligomers reached the Ni/SiO2 catalyst, rendering the Ni catalyst with a higher resistivity towards coking and deactivation. In addition, the carbon nanotube form of coke over Ni/SiO2 was thinner in wall thickness and larger in inner diameter of the cavity due to the impact of D-Cu/SiO2. Substantial polymeric coke with amorphous structure and low thermal stability formed over Cu/SiO2 via polymerisation of reaction intermediates. The characterization (in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)) for the glycerol steam reforming indicated that the Cu/SiO2 and Ni/SiO2 catalyst induced the formation of the very different functionalities of the reaction intermediates.