Interplay between carbon dioxide enrichment and zinc oxide promotion of copper catalysts in methanol synthesis

Abstract Methanol synthesis over Cu/ZnO/Al2O3 is a key industrial reaction. Typically, a ZnOx promoter and CO2 enrichment of the feed are applied to maximize the syngas conversion. However, understanding the effects of these additives on the performance of the Cu catalysts is obscured by the strong interaction between the ZnOx promoter and oxidic supports. Here, we use Cu nanoparticles on graphitic support to study the interplay between CO2 concentration and ZnOx promotion. CO2 enrichment enhanced the activity with an optimum at 3 vol% in the feed, but only if the ZnOx promoter was present, demonstrating the intricate interaction between the two. Interestingly, not only the activity but also the methanol selectivity was enhanced by CO2 enrichment, and even further by the addition of ZnOx. Understanding not only the role of the individual components, but also the interaction between them, is important to design catalysts for processes with more flexible feed compositions.