The role of CO₂ in methanol synthesis on CuZn 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.