CO2 Hydrogenation on ZrO2/Cu(111) Surfaces: Production of Methane and Methanol

The conversion and utilization of carbon dioxide is a critical challenge for the reduction of greenhouse gas pollution and in the production of high value chemicals in C1 chemistry. ZrO2/Cu­(111) is an inverse oxide/metal catalyst that displays high activity and stability for the hydrogenation of CO2 into methanol at 500–600 K. At elevated temperatures, ZrO2 grows on a CuO x /Cu­(111) substrate forming islands of 10–12 nm in size and an average height of ∼3 Å. Reaction with H2 leads to the removal of the copper oxide producing ZrO2/Cu­(111) surfaces which are very active for the binding and dissociation of CO2 into CO and C. After exposing ZrO2/Cu­(111) to moderate or elevated pressures of a CO2/H2 mixture at 300 K, atomic C and minor amounts of CH x O and CO x are deposited on the catalyst surface. The adsorbed CH x O and CO x disappear upon heating above 400 K. The catalytic tests for CO2 hydrogenation give CO as the main reaction product and CH4 and CH3OH as secondary products. The relative yields of methane and methanol change with time and track the amount of atomic C deposited on the active ZrO2/Cu­(111) surface. The formation of methane stops once the catalyst surface is saturated with C. Under steady-state conditions, ZrO2/Cu­(111) is a much better catalyst for methanol synthesis than ZnO/Cu(111). This trend reflects variations in the size of the oxide islands and in the strength of oxide-metal interactions. The use of an inverse oxide/metal configuration is an important synthetic tool when preparing active, selective, and stable catalysts for CO2 hydrogenation.