Factors affecting primary and secondary pathways in CO2 hydrogenation to methanol over CuZnIn/MZrOx (La, Ti or Y)

Abstract

CO2 hydrogenation to methanol was investigated over CuZnIn/MZrOx (M = La, Y or Ti) catalysts at 20 bar and at 225 °C with the purpose to elucidate the effects of the metal oxide promoter for ZrO2 and InOx for CuZnOx on reaction scheme of product formation, catalyst activity and product selectivity. Although the additives do not affect the overall scheme of product formation, they are relevant for the rates of direct CO2 conversion into methanol or CO and of methanol decomposition to CO and H2. This is due to their influence on dispersion of CuOx and the strength of basic sites for CO2 adsorption. Highly dispersed CuOx species are essential for CO2 conversion but not for methanol selectivity. The selectivity is improved over polymerized CuOx with strong basicity. This catalyst property can be controlled through promoting of (i) ZrO2 with La2O3/Y2O3 or (ii) CuZnOx with InOx. The latter promoter is crucial for hindering the undesired methanol decomposition to carbon monoxide.