Computational exploration of sub-nano Zn and Cu species on Cu/ZrO2: Implications for Methanol synthesis

Ternary Cu/Zn/ZrO2 (CZZ) catalysts prepared recently using atomic layer deposition (ALD) have shown increased performance towards methanol synthesis. In the present computational study, we have investigated the structure, composition, and stability of various zinc and copper containing sub-nano size species on a zirconia support. Density functional theory calculations with minima hopping was used to sample the positioning and geometry of supported ZnxCuyOz structures up to 8 metal atoms in total. ZnO monomeric species were found to be energetically more favourable than small clusters, which could suggest a resistance to initial stage agglomeration. Ab-initio thermodynamics revealed that under typical methanol synthesis conditions the complete reduction of ZnO and mixed ZnO/Cu clusters is unfavourable. The investigated ZnO monomers and clusters are able to provide CO2 activation sites, with the Cu/ZnO/ZrO2 triple interface offering the best stabilization for the adsorbed CO2. All in all the findings suggest that small ZnO species generated by ALD could be stabilized by the zirconia component, while contact with copper species at the interface benefits CO2 activation.