Solid-state interactions, adsorption sites and functionality of Cu-ZnO/ZrO2

Structure, adsorption properties and surface reactivity of Cu-ZnO/ZrO2 catalysts (ZrO2 loading, 43 wt%; Zn/Cu (at/at), 0.0-2.8) have been probed by BET, XRD, TPR, N2O-titration, FTIR and TPD measurements of H2, CO and CO2. Characterization data indicate that ZnO promotes the dispersion and reactivity of metal copper to oxygen, while both ZnO and ZrO2 support markedly enhance the surface CO2 adsorption. A synergism of metal Cu hydrogenation and oxide basic sites discloses the primary role of the metal/oxide interface on the functionality of Cu-ZnO/ZrO2 catalysts in the CO2 to CH3OH hydrogenation reaction. The extent of the oxide/metal interface, probed both by Cud+/Cu0 and oxide-to-metal surface area (OSA/MSA) ratios, provides a normalization of the Cu site specific activity (TOF) in a wide range (3-60%) of metal dispersion proving the dual-site nature and, then, the formal structure-insensitive character of the title reaction.