Theoretical insight into the mechanism of CO2 and H2O formation from CO and OH over stepped Ni and Fe/Ni bimetallic surfaces

Abstract

During CO methanation on Ni-based catalysts, H2O and a small quantity of CO2 may be produced. Periodic density functional theory computations are used to explore the formation of CO2 and H2O on stepped Ni (211), Ni (111), Ni3Fe (111), and Ni3Fe (211) surfaces. The results show that concerted hydrogenation of OH is energetically favorable for H2O generation on both the step surface and the close-packed surface of Ni and Ni3Fe catalysts. The carboxyl mechanism is the main mechanism of CO2 formation, in which the conversion of the carboxyl group from cis to trans isomer is a key step. What’s more, compared with Ni (211), Ni3Fe (211)-AB can effectively inhibit the formation of CO2 and is expected to improve the selectivity of the target product CH4.