BEA zeolite supported Ce-promoted nickel catalysts for CO2 methanation

Abstract

Two series of Ce-promoted nickel catalysts were prepared by co-impregnation method using unmodified and dealuminated Beta zeolites as supports, denoted Ni10Ce#-HAlBEA and Ni10Ce#-SiBEA, respectively. Transmission electron microscopy studies of the first group of catalysts evidenced the presence of nickel nanoparticles of various size (2–20 nm) and complex morphology, decorated with CeO2 nanoparticles, stemmed from the mutual diffusion of the corresponding species. An increase in Ce loading from 3 to 5 wt% facilitated direct interaction of metallic nickel crystallites with CeO2 nanoparticles, leading to a decrease in Ni crystallite size. In-situ DRIFTS studies indicated an improvement of the activation of CO2 and H2, formation of weakly adsorbed carbonyl groups, bicarbonate and carbonate intermediate species in the initial stages of the reaction, which increased the activity of catalysts in CO2 methanation reaction and their resistance towards sintering and poisoning with H2S. Raman and FTIR-PAS spectroscopy pointed out that strongly adsorbed sites produced upon dealumination and slight structural changes Beta zeolite influenced the way of formation of nickel crystallites and their morphology, dispersion of cerium oxide nanoparticles, acid-base and redox properties of catalysts. Thus, the second group of catalysts showed higher catalytic activity at low temperatures and higher sintering and poisoning resistance, which was attributed to the presence of small, regular nickel particles of the size ca. 2 nm, located in the close proximity to the dispersed cerium oxide phases. The CO2 methanation reaction proceeded mainly via formation of more strongly adsorbed intermediate surface carbonyl groups and carbonate species.