EFFECTS OF ZIRCONIA PROMOTION ON THE ACTIVITY OF CU SIO2 FOR METHANOLSYNTHESIS FROM CO/H-2 AND CO2/H-2/

The effect of zirconia promotion on Cu/SiO2 for the hydrogenation of C O and CO2 at 0.65 MPa has been investigated at temperatures between 47 3 and 573 K. With increasing zirconia loading, the rate of methanol sy nthesis is greatly enhanced for both CO and CO2 hydrogenation, but mor e significantly for CO hydrogenation. For example, at 533 K the methan ol synthesis activity of 30.5 wt% zirconia-promoted Cu/SiO2 is 84 and 25 times that of unpromoted Cu/SiO2 for CO and CO2 hydrogenation, resp ectively. For all catalysts, the rate of methanol synthesis from CO2/H -2 is higher than that from CO/H-2. The apparent activation energy for methanol synthesis from CO decreases from 22.5 to 17.5 kcal/mol with zirconia addition, suggesting that zirconia alters the reaction pathwa y. For CO2 hydrogenation, the apparent activation energies (similar to 12 kcal/mol) for methanol synthesis and the reverse water-gas shift ( RWGS) reaction are not significantly affected by zirconia addition. Wh ile zirconia addition greatly increases the methanol synthesis rate fo r CO2 hydrogenation, the effect on the RWGS reaction activity is compa ratively small. The observed effects of zirconia are interpreted in te rms of a mechanism, in which zirconia serves to adsorb either CO or CO 2, whereas Cu serves to adsorb H-2. It is proposed that methanol is fo rmed by the hydrogenation of the species adsorbed on zirconia.