Morphology and chemical behavior of model CsO_x/Cu₂O/Cu(111) nanocatalysts for methanol synthesis: Reaction with CO₂ and H₂

Cs is a promoter of Cu-based catalysts for the synthesis of alcohols from CO₂ hydrogenation. Scanning tunneling microscopy and ambient-pressure x-ray photoelectron spectroscopy were used to study the morphology and chemical properties of surfaces generated by the deposition of cesium on Cu₂O/Cu(111) and Cu(111) substrates. CsO_x nanostructures were formed after Cs metal was deposited on Cu₂O/Cu(111) at 300 K. The formed CsO_x protrude over the surface of copper oxide by 2–4 Å, with the dimension at the base of the nanostructures being in the range of 1–3 nm. Heating to elevated temperature induced significant changes in the size and dispersion of the CsO_x nanostructures, and there was a clear reconstruction of the copper oxide substrate, which then exhibited long range order with a hexagonally packed structure. The as-deposited and annealed surfaces of CsO_x/Cu₂O/Cu(111) were more reactive toward CO₂ than plain Cu₂O/Cu(111) or clean Cu(111). However, none of them were stable in the presence of H₂, which fully reduced the copper oxide at 400–450 K. In CsO_x/Cu(111), the CsO_x nanoclusters were dispersed all over the metallic copper in no particular order. The CsO_x species had an average width of 2 nm and ∼1 Å height. The CsO_x/Cu(111) systems exhibited the highest activity for the binding and dissociation of CO₂, suggesting that the CsO_x-copper interface plays a key role in alcohol synthesis.