Pd-promoted Cu/Zno catalyst systems for methanol synthesis from CO2/H2

Cu/ZnO-based catalysts are widely used for methanol production from CO/CO2/H-2. In recent years there has been growing interest in methanol synthesis from CO2/H-2. Cu/ ZnO catalysts are less active for methanol production in CO2-rich feed gas, but the activity appears to be promoted by the addition of Pd to the catalyst. This paper presents a brief chronological overview of kinetic results in these catalyst systems including the work done by the author. Experiments at controlled levels of conversion, including microreactor studies, have provided an insight into the role of products in the kinetics of methanol synthesis. In particular, it has been shown that the product water inhibits CO2 hydrogenation to methanol. Under these conditions, Pd appears to promote the activity, but in fact it plays a role in counteracting the inhibition by water. This could possibly be explained by hydrogen spillover which moderates the [Cu(metal) + H2O=Cu-O(ads) + H-2] redox. The paper goes on to discuss the mechanistic effect of water on Cu/ZnO-catalyst systems under CO2-rich and CO-rich atmospheres.