SYNTHESIS OF METHANOL FROM A MIXTURE OF H2 AND CO2 ON CU(100)

The rate of methanol synthesis over a Cu(100) single crystal from a binary mixture of CO2 and H2 has been measured for total pressures of 1-4 bar, various gas compositions ranging from CO2:H2 ratios of 4:1 to 3: 17 and a temperature range of 483-563 K. At a pressure of 2 bar and a gas composition of CO2:H2 = 1:1, the apparent activation energy is determined to be 69 +/- 4 kJ mol-1 and at 543 K the turnover rate is 2.7 x 10(-4) site-1 s-1. The turnover rate is observed to scale with the total pressure as p2.36+/-0.14 and the turnover rate has a maximum for a mole fraction of H2 of roughly 60%. These results are found to be consistent with a simple model where hydrogenation of dioxomethylene or formaldehyde are the rate limiting step in the methanol synthesis.