Catalytic synthesis of methanol from CO/H2I. Phase composition, electronic properties, and activities of the Cu/ZnO/M2O3 catalysts

The low pressure methanol synthesis catalysts CuZnO, Cu/ZnO/Al2O3, and Cu/ZnO/Cr2O3 were found to contain a new compound identified as a CuI solution in ZnO, which is also an active component of the above catalysts. Combined X-ray diffraction, optical, and XPS—Auger studies are presented that describe the formation, electronic structure, and surface composition of these catalysts. In particular, the surface of the working catalyst is free of carbon, both in the presence and absence of CO2 in the feed gas. A synthesis mechanism is proposed whereby the CuI centers nondissociatively chemisorb and activate carbon monoxide and the ZnO surface activates hydrogen. Catalyst deactivation in COH2 mixture is explained as the reduction of CuI to inactive copper metal, while the rate enhancing effect of O2, H2O, and CO2 is due to the maintenance of an oxidation potential high enough to keep the copper in the active CuI state. No special pore distribution or presence of crystalline phases such as spinels is necessary for selectivity of the CuZnO catalyst to the formation of methanol.