Insight into the mechanism of CO2 and CO methanation over Cu(100) and Co-modified Cu(100) surfaces: A DFT study

Abstract

Density functional theory calculations were carried out to investigate the mechanism of CO2 and CO methanation over pure Cu(100) and CoCu bimetallic catalysts. The most favorable pathways for the CO2 and CO hydrogenation were obtained. For the Cu(100) surface, the barriers of the rate-limiting step for the HCOO* and CO* hydrogenation were 122.52 kJ/mol and 106.14 kJ/mol. Because the barrier (77.34 kJ/mol) for the H2CO* hydrogenation is more than the desorption energy of 54.80 kJ/mol, H2CO gas was the main product from the hydrogenation of CO2 and CO on a pure Cu(100) surface. For the Co4/Cu(100) surface, the optimal pathways for the CO2 and CO methanation were the same as those on the Cu(100) surface. The rate-limiting step for CO2 and CO methanation is the H2COO* (barrier of 103.57 kJ/mol) and H2CO* hydrogenation (barrier of 107.80 kJ/mol). Compared to the mechanism of CO2 and CO over Cu(100), the Co dopant can modify the rate-limiting step and decrease the activation barrier. Particularly, the barrier for the H2COH decomposition was changed from 100.96 kJ/mol to 69.81 kJ/mol (CO2 pathway) and 61.26 kJ/mol (CO pathway). Furthermore, the co-adsorbed OH* group affects the hydrogenation pathway of some intermediates rather than electronic structures.