A detailed understanding of the interactions among the active components in gallium promoted Cu/ZnO catalysts, depending on the speciation of the gallium, are reported using in situ/operando spectroscopic studies, and their effect in the CO hydrogenation to methanol unraveled. In this contribution, the promoting effect of Ga-doped in the wurtzite ZnO lattice of a Cu/ZnO/GaO catalyst is compared to that of a zinc gallate (ZnGaO) phase. Remarkably, a strong inhibition of CO formation, together with an enhanced methanol formation, are observed in the Ga-doped ZnO sample, specifically at conditions where the competitive reverse water gas shift reaction predominates. The catalytic performance has been correlated with the microstructure of the catalyst where a surface enrichment with reduced ZnO species, together with the stabilization of positive charged copper species and an increase in the amount of surface basic sites for CO adsorption are observed on the most selective sample.
The research leading to these results has received funding from the Spanish Ministry of Science, Innovation and Universities through “Severo Ochoa” Excellence Programme (SEV-2016-0683) and through RTI2018-099668-B-C21 project. The authors thank the Microscopy Service of UPV for kind help on measurements. J.C. thanks the Spanish Government (MINECO) for a “Severo Ochoa” grant (BES-2015-075748). C.W.L. (Science without Borders-Process no. 13191/13-6) thanks CAPES for a predoctoral fellowship. Authors from UV acknowledge the Spanish Ministry of Science, Innovation and Universities through the project MAT2017-84118-C2-1-R. Authors thank to the support of HZB/Bessy II (ISISS beamline) and ALBA Synchrotron (BL22-CLÆSS) staff for the successful performance of the measurements.