THE REACTIONS OF CARBON-DIOXIDE WITH THE COPPER METAL-SURFACE IN A CU/ZNO/AL2O3 CATALYST

Recent XPS studies of the reactions of CO2 on a polycrystalline copper metal surface cast new light on earlier results from the reactions of CO2 with the copper metal surface in a commercial Cu/ZnO/Al2O3 catalyst. The catalytic results are now re-interpreted in terms of the formation of two types of surface carbonate, both of which decompose above about 350 K in the absence of CO2 to leave O(a) on the Cu surface. The enthalpy change in the interconversion of the carbonates is about 18 kJ mol(-1). From the limits on adsorption it is estimated that one form of adsorbed carbonate occupies 1 (or possibly 2) Cu metal surface atoms whereas the other form occupies more than 5 Cu metal surface atoms. These results are used to show that a recent interpretation of the observed high coverages of O(a) after methanol synthesis on Cu/ZnO/Al2O3 catalysts is not valid.