Tuning reverse water gas shift and methanation reactions during CO2 reduction on Ni catalysts via surface modification by MoOx

Catalytic reduction of CO2 to CO via reverse water gas shift (RWGS) reaction provides a feasible approach to utilize CO2, since CO can be further converted to various versatile products through the syngas routes. Ni-based catalysts are low cost and have a high activity for CO2 reduction but are nonselective for RWGS due to competition from methanation. In this work, we demonstrated that surface modification of Ni by MoOx can be tailored to tune the reactions of RWGS and methanation. The addition of MoOx improves Ni dispersion through strong interactions whereas partially reduced MoOx modifies the surface of Ni particles through both geometric coverage and electronic modification. No CO adsorption was observed at room temperature on the NiMo catalyst with a Mo/Ni ratio of 1, confirmed by density functional theory calculation. Tracking product evolution showed that CO2 is first reduced to CO through RWGS on the Ni catalysts and methane is a product of CO hydrogenation. Apparent activation energy analysis indicates that the overall reaction is controlled by CO desorption. Addition of a small amount of Mo (Mo/Ni ratio of 0.1) shifts the reaction further to methanation selective with ∼100% CH4 selectivity as MoOx aids in the activation of both CO2 and CO. In contrast, the addition of a large amount of Mo (Mo/Ni ratio of 1) shifts the reaction to RWGS selective with a CO selectivity > 94%. This is attributed to the enhanced CO desorption from the surface as a result of MoOx modification.