Transition-Metal-Doped CeO for the Reverse Water-Gas Shift Reaction: An Experimental and Theoretical Study on CO Adsorption and Surface Vacancy Effects.

Transition metal-doped ceria (M-CeO) catalysts (M=Fe, Co, Ni and Cu) with multiple loadings were experimentally investigated for reverse water gas shift (RWGS) reaction. Density functional theory (DFT) calculations were performed to benchmark the properties that impact catalytic activity of CO reduction. Temperature-programmed desorption (TPD) was conducted to study the CO binding strength on doped CeO surfaces; the trend of the energy along increasing metal loading agrees with the DFT calculations. Notably, CO dissociative adsorption energy and oxygen vacancy (OV) formation energy are key descriptors obtained from both DFT and experiments, which can be used to evaluate catalytic performance. Results show the effectiveness of transition metal doping in enhancing CO adsorption and reducibility of the surfaces, with Fe showing particularly promising results, i. e., CO conversion higher than 56 % at 600 °C and 100 % selectivity to CO. Cu exhibits 100 % selectivity to CO but low CO conversion, while Co and Ni showed notable ability of methanation, particularly at high loadings. This study finds that an effective CeO based RWGS catalyst corresponds to OV sites that have low OV formation energies for surface reduction, and moderate CO adsorption energies for strong interaction with the surface to promote C-O bond scission.