THE SYNTHESIS OF METHANOL AND THE REVERSE WATER-GAS SHIFT REACTION OVER ZN-DEPOSITED CU(100) AND CU(110) SURFACES - COMPARISON WITH ZN CU(111)/

The catalytic activity of Zn vapor-deposited Cut (100) and Cu (110) su rfaces for methanol synthesis by the hydrogenation of CO2 and thr reve rse water-gas shift reaction were studied using an XPS apparatus combi ned with a high-pressure flow reactor (18 atm). At a reaction temperat ure of 523 K. no promotional effect of Zn was observed for the methano l synthesis on both Zn/Cu(100) and Zn/Cu(110). The results were quite different from those for Zn/Cu(111). on which a significant promotion of methanol synthesis activity appeared to br due to the deposition of Zn, indicating that the promotional effect of Zn was sensitive to the surface structure of Cu. However, hysteresis was observed in the cata lytic activity for methanol synthesis over the Zn/Cu(110) surface upon heating above 543 K in the reaction mixture. The activity became twic e that measured before heating. which was close to the methanol synthe sis activity of Zn/Cu(111) at the same Zn coverage. On the other hand, no such hysteresis was observed for the reverse water-gas shift react ion on Zn/Cu(110). indicating that the active site for methanol synthe sis was not identical to that for the reverse water-gas shift reaction . In the post-reaction surface analysis, formate species was detected on both Zn/Cu(100) and Zn/Cu(110). whose coverage increased with incre asing Zn coverage at 0<Theta(Zn)<0.2. No correlation between the forma te coverage and the methanol synthesis activity was obtained, which wa s in contrast to the results for Zn/Cu(111). Thus, the structure sensi tivity observed in the catalytic activity of methanol synthesis over Z n-deposited Cu surfaces is ascribed to the significant difference in t he reactivity of the formate intermediate. (C) 1998 Elsevier Science B .V.