The role of CO2 in methanol synthesis on Cu$z.sbnd;Zn oxide: An isotope labeling study

Methanol synthesis using H2, CO, and 18O-labeled CO2 was studied over a Cu-Zn oxide catalyst at 220 °C and 17 atm in a batch reactor. In the absence of gaseous water, the rate of production of C 18O was rapid. The rate of production of 18O-labeled methanol was about 50% of that of 16O-labeled methanol. The presence of gaseous water suppressed the production of [18O]methanol, but not C 18O or [16O]methanol. The results indicated that there are at least four parallel reactions on the catalyst: CO-CO2 exchange, CO hydrogenation, CO2 hydrogenation, and water-gas shift. Exchange of lattice oxygen with oxygen in CO2 also took place. There was no evidence for the production of methanol from the reaction of CO and water.