(616a) Effects of Support Composition on the Activity of Cu/Mxzr1-Xo2 (M = Ce, Pr, Mn) for Methanol Synthesis Via Co Hydrogenation

The effects of Ce, Pr, and Mn incorporation into ZrO2 on the catalytic performance of Cu/ZrO2 for the hydrogenation of CO were investigated. MxZr1-xO2 solid solutions were synthesized by forced hydrolysis at low pH and Cu was then deposited onto the surface of the calcined solid by deposition-precipitation. 3 wt% Cu/CexZr1-xO2 exhibited H2 consumption peaks at low temperature (< 500 K) during H2-TPR indicating a significant fraction of Ce4+ is reduced to Ce3+. The reducibility and the activity of 3 wt% Cu/CexZr1-xO2for CO hydrogenation go through the maximum with increased Ce content. 3 wt% Cu/Ce0.5Zr0.5O2 catalyst is 4 times more active for methanol synthesis than 3 wt% Cu/ZrO2 at 3.0 MPa at temperatures between 473 and 523 K and exhibits a higher selectivity to methanol. In-situ infrared spectroscopy shows that the primary surface species on Cu/CexZr1-xO2 during CO hydrogenation are formate and methoxide species. A shift in the band position of the bridged methoxide species with increased Ce content indicated that some of these groups were bonded to both Zr4+ and Ce3+ cations. The rate-limiting step for methanol synthesis is the reductive elimination of methoxide species regardless of the catalyst composition. The differences in methanol synthesis on Cu/CexZr1-xO2 was primarily due to a higher apparent rate constant, kapp, for methoxide hydrogenation, which is attributed to the higher surface concentration of H atoms on the surface of the catalysts with intermediate Ce content. The increased capacity of the Ce-containing catalysts is attributed to interactions of H atoms with Ce-O pairs present at the surface of the oxide phase. Very similar results were obtained with 3 wt% Cu/Pr0.3Zr0.7O2 and 3 wt% Cu/Mn0.3Zr0.7O2 catalysts. On the basis of methanol synthesis activity per unit of oxide surface area, the rate of methanol synthesis increased in the order 3 wt% Cu/Ce0.3Zr0.7O2 < 3 wt% Cu/Mn0.3Zr0.7O2 < 3 wt% Cu/Pr0.3Zr0.7O2.