Silica–Ceria sandwiched Ni core–shell catalyst for low temperature dry reforming of biogas: Coke resistance and mechanistic insights

Abstract In this paper, a novel sandwiched core–shell structured Ni-SiO 2 @CeO 2 catalyst, with nickel nanoparticles encapsulated between silica and ceria, was developed and applied for dry reforming of biogas (CH 4 / CO 2  = 3/2) under low temperature conditions to test its coke inhibition properties. Ni-phyllosilicate was used as the Ni precursor in order to produce highly dispersed Ni nanoparticles on SiO 2 . Cerium oxide was chosen as the shell due to its high redox potential and oxygen storage capacity, that can reduce coke formation under severe dry reforming conditions. The core shell Ni-SiO 2 @CeO 2 catalyst showed excellent coke inhibition property under low temperature (600 °C) reforming of biogas, with no coke detected after a 72 h catalytic run. Under the same conditions, Ni-SiO 2 catalyst deactivated within 22 h due to heavy coke formation and reactor blockage, while Ni-CeO 2 catalyst showed very low activity. The higher activity of the core–shell catalyst is attributed to its higher Ni dispersion and reducibility. TEM and XRD results show that the core–shell catalyst shows higher resistance to Ni particle sintering and agglomeration during the reaction than the Ni-SiO 2 and Ni-CeO 2 catalysts. In-situ DRIFTS on the Ni-SiO 2 @CeO 2 catalyst indicate a change in the reaction mechanism from a mono-functional pathway on the Ni-SiO 2 catalysts to a bi-functional route on the Ni-SiO 2 @CeO 2 catalyst with active participation of oxygen species from CeO 2 in carbon gasification. The confinement effect of the sandwich structure and the bifunctional mechanism of dry reforming are the primary reasons for the excellent coke resistance of the Ni-SiO 2 @CeO 2 catalyst.