CO₂ Methanation on Cu-Cluster Decorated Zirconia Supports with Different Morphology: A Combined Experimental In Situ GIXANES/GISAXS, Ex Situ XPS and Theoretical DFT Study

Subnanometer copper tetramer–zirconia catalysts turn out to be highly efficient for CO₂ hydrogenation and its conversion to methane. The cluster size and substrate morphology are controlled to optimize the catalytic performance. The two types of zirconia supports investigated are prepared by atomic layer deposition (∼3 nm thick film) and supersonic cluster beam deposition (nanostructured film, ∼100 nm thick). The substrate plays a crucial role in determining the activity of the catalyst as well as its cyclability over repeated thermal ramps. A temperature-programmed reaction combined with in situ X-ray characterization reveals the correlation between the evolution in the oxidation state and catalytic activity. Ex situ photoelectron spectroscopy indicates Cu clusters with stronger interactions with the nanostructured film, which can be the cause for the higher activity of this catalyst. Density functional theory calculations based on the Cu₄O₂ cluster supported on a ZrOx subunit reveal low activation barriers and provide mechanism for CO₂ hydrogenation and its conversion to methane. Altogether, the results show a new way to tune the catalytic activity of CO₂ hydrogenation catalysts through controlling the morphology of the support at the nanoscale.