The Cu-ZnO synergy in methanol synthesis Part 3: Impact of the composition of a selective Cu@ZnOx core-shell catalyst on methanol rate explained by experimental studies and a concentric spheres model

Highly selective catalysts for methanol synthesis from CO2 and H-2 are required for increasing the process efficiency that actually produces large amounts of CO. The understanding of the Cu-ZnO synergy allowed the possibility to design core-shell catalysts of the type Cu@ZnOx with enhanced selectivity for methanol. This type of core-shell structure was synthesized with variable compositions and the catalytic efficiency as well as the physicochemical properties were scrutinized in order to build structure-reactivity relationships. Zn migration is responsible for the formation of the CuxZn(1-x)Oy active phase. The experimental results were compared with theoretical calculations based on a geometrical model taking into account the amount of Zn migrated. A direct correlation was found between theory and experiment. Finally, a linear correlation of catalyst activity versus Zn migrated is shown for three different catalyst designs, thus confirming that a high Zn migration is needed for obtaining an efficient methanol synthesis catalyst. (C) 2016 Elsevier Inc. All rights reserved.