An in situ FT-IR study of adsorbed species on a Cu-ZnAl2O4 methanol catalyst under 1 MPa pressure and at 525 K: effect of the H2/CO/CO2 feed stream composition

An IR cell which can be used as a continuous flow reactor up to 1 MPa and 525 K is described. Application to the methanol synthesis from CO + CO2 + H2 reaction on a 15% Cu—ZnAl2O4 catalyst shows that two different mechanisms of CH3OC formation occur, depending on the gas feed composition. With no CO2, ZnAl2O4 plays an important role and ZnAl2O4 bidentate formate and methoxy species are intermediate. In the CO2 + H2 case, the reaction principally occurs on the copper sites, with copper formate species as intermediate. The maximum activity composition (H2: CO: CO2 = 67:30:3) does not correspond to a maximum in the number of adsorbed species, whatever their nature. In such a case, a mechanism close to that occurring with CO + H2 is suggested; the higher catalyst activity can possibly be related to the formation of a small amount of water, facilitating the desorption of ZnAl2O4 methoxy species by hydrolysis.