What role does Al3+ play in the methanol synthesis from CO2 hydrogenation using Cu/ZnO/Al catalysts?

[Display omitted] •Al replaces Zn in the ZnO lattice, favoring the formation of oxygen vacancies (Vo);•The maximum methanol formation rate occurs when the number of Vo is at its maximum;•Beyond Al solubility limit in ZnO, other phases are formed, hindering catalysis;•CO2 adsorption occurs on the Cu and the mixed oxide interface;•One of the O atoms of CO2 replenishes the Vo and the other interacts with Cu. Cu, Zn, and Al-based catalysts were prepared, characterized, and tested in order to describe the role of Al in the CO2 hydrogenation to methanol. This work shows that Al3+ replaces Zn2+ in the ZnO lattice, promoting the generation of oxygen vacancies (Vo) on the oxide surface. When the Al and Vo concentration increases, the rate of methanol formation also increases. Once Al3+ solubility in ZnO is reached this rate decreases. An Al-based compound is formed which occludes a portion of the catalyst’s surface, changing the behavior of the catalyst. DFT calculations highlight the role of Al in methanol formation by lowering the energy required for the formation of Vo. This species promotes the adsorption of CO2 on the interface between ZnO and Cu0. Thus, both Al and Vo show a pivotal role in the catalytic behavior of Cu/ZnO/Al.