Ceria-supported Ni catalyst with high catalytic activity, selectivity and stability for CO2 conversion to CH4 by hydrogenation reaction investigated by X-ray absorption spectroscopy

Abstract

x%Ni/CeO2 (x = 3, 6, 9, 12 and 18 wt%) catalysts were synthesized for CO2 methanation reaction. The catalysts were prepared via sol-gel method with co-adding of citric acid to improve Ni dispersion. 18 wt%Ni/CeO2 exhibited the highest catalytic performance. An in-situ experiment during CO2 methanation for monitoring the oxidation state changes of Ni and Ce was conducted by TRXAS. The oxidation states of Ni2+ and Ce4+ were reduced upon increasing the reduction temperature. Moreover, Nio and Ce3+ remained unchanged during reaction. The operando XAS experiment was performed to investigate the electronic state changes of Ni species during fluctuating conditions. The state of Nio remained unchanged upon H2 dropout and re-purging, which indicated that Ni species were completely re-reduced after H2 was added into the feed stream again. The completely reduced behavior of Ni active species was caused by highly dispersed Ni by the addition of citric acid.