The Partial Oxidation of CH3OH to CO2 and H2 Over a Cu/ZnO/Al2O3 Catalyst

The partial oxidation of CH3OH to CO2 and H2 over a Cu/ZnO/Al2O3 catalyst has been studied by temperature-programmed oxidation (TPO) using N2O and O2 as the oxidant. Post-reaction analysis of the adsorbate composition of the surface of the catalyst was determined by temperature-programmed desorption (TPD). The temperature dependence of the composition of the mixture of products formed by TPO was shown to depend critically on the partial pressure of the oxidant, with the highest partial pressure of oxygen used (10% O2 in He, 101 kPa—the CH3OH partial pressure was 17% throughout), producing marked non-Arrhenius fluctuations on temperature programming. Unsurprisingly, therefore, the adsorbate composition of the catalyst revealed by post-reaction TPD was also found to be determined by the partial pressure of the oxidant. Using high partial pressures of oxidant (5% and 10% O2 in He, 101 kPa), the only adsorbate detected was the bidentate formate species adsorbed on Cu. Lowering the oxygen partial pressure to 2% in He (101 kPa) revealed a catalyst surface on which the bidentate formate on Cu was the dominant intermediate with the formate on Al2O3 also being present. A further lowering of the partial pressure of the oxidant, obtained by using N2O as the oxidant (2% N2O in He, 101 kPa), resulted in a surface on which the formate adsorbed on ZnO was the dominant adsorbate with only a small coverage of the Cu by the bidentate formate.