A COMPARATIVE-STUDY OF METHANOL SYNTHESIS FROM CO2/H-2 AND CO/H-2 OVER A CU/ZNO/AL2O3 CATALYST

Methanol synthesis from CO2/H2 and CO/H2 has been compared over a Cu/ZnO/Al2O3 catalyst. Methanol synthesis was much faster with CO2/H2 than with CO/H2, particularly at low temperatures. A trace amount of CO2 improved the rates significantly. Thus it appeared that CO2 was the primary source of methanol with CO/CO2/H2 feed. When space velocities were varied, both of the previously conflicting observations on the effect of CO2/CO composition, i.e., monotonical increase in synthesis rate vs the presence of a maximum rate as CO2 concentration increased, were observed. The different conversion levels and consequent difference in surface oxygen coverage and/or water appeared to be responsible for the different effects. The more oxidized surface state of copper obtained for CO2/H2 was more active and stable in methanol synthesis than the overreduced surface obtained for the CO/H2 feed. Due to the promotional and inhibition effects of water for CO/H2 and CO2/H2 feeds, respectively, higher space velocities yielded higher synthesis rates for CO2/H2 and the opposite effect was observed for the CO/H2 feed. © 1993 by Academic Press, Inc.