Reaction intermediates in methyl alcohol decomposition on ZnO

Abstract

The decomposition of methyl alcohol on ZnO was studied using infra-red spectroscopy during the course of the reaction. The concentrations and reactivities of the chemisorbed and gas phase species were measured as well as the overall reaction rate under various non-stationary conditions. When CD₃OD vapour was introduced over ZnO, methoxide ion and formate ion were observed, and D₂, CO₂ and CO were evolved into the gas phase. When the CD₃OD in the ambient gas was removed by a dry ice-methyl alcohol trap during the course of the reaction, the evolution of D₂ and CO₂ stopped, while the evolution of CO continued unchanged. At 240°C, the decomposition rate of the surface formate ion was in reasonable agreement with the rate of production of carbon monoxide. On releasing the trapped methanol, the rates of formation of CO₂ and D₂ increased again, surface methoxide reappeared, and the concentration of the surface formate ion decreased correspondingly. These results lead to the conclusion that CO was produced mainly by the decomposition of formate ion, and D₂ and CO₂ came from the reaction between CD₃OD and DCOO(a).