IN-SITU FT-IR AND KINETIC-STUDY OF METHANOL SYNTHESIS FROM CO2 H-2 OVER ZNAL2O4 AND CU-ZNAL2O4 CATALYSTS/

The kinetics of the CO2/H-2 reaction over ZnAl2O4 and Cu-ZnAl2O4 catal ysts at 250 degrees C up to 0.3 MPa have been followed by in situ FT-I R spectroscopy, Both methanol and carbon monoxide formation were enhan ced in presence of copper. They were also produced by independent rout es through different adsorbed species. Formate (type I, I' and II), me thoxy and carbonate species were identified on the support and, in add ition, copper formate and copper carbonyl species when copper was pres ent, The hydrogenation of carbonate species to copper formate species was found rate determining in methanol synthesis over the Cu-ZnAl2O4 c atalyst whereas type I formate species were shown to be the active int ermediate for this reaction over the ZnAl2O4 support. Carbon monoxide resulted from the water gas shift reaction probably through the same s pecies as methanol formed over the Cu-ZnAl2O4 catalyst whereas it seem ed to stem from formate species of type II in the case of the ZnAl2O4 support. Type II formate species were shown inactive in presence of co pper whereas the methoxy species adsorbed on the support were found in active in presence and in absence of copper. The comparison of these r esults with those previously obtained with the CO/H-2, mixture showed that the nature and the role of the detected species strongly depended on the reactive atmosphere and on the presence or not of copper in th e catalyst composition. (C) 1998 Elsevier Science B,V. All rights rese rved.