JUNCTIONS BETWEEN CUOX AND ZNOY IN SENSORS FOR CO AND CATALYSTS FOR CO HYDROGENATION

Addition of CuOx to defective ZnOy (0.92. <y <1.00) yielded a disperse d catalyst that produced methanol at 523 K and 2 MPa with a selectivit y (relative to CH4) which was higher than that for a unit area of ZnOy or CuOx alone. Copper oxide-zinc oxide polycrystalline films (prepare d by ion beam sputter deposition) were as stoichiometric as the disper sed samples with junctions best represented as CuOx/ZnOy (with x close to 0.5 and y close to 1.0). Photo-STM reveals for the first time the width and nature of the n/p junction, although the gradient of the dep letion zone is shallower on the ZnO side of the junction (which is not expected from recent postulates). Responses to CO and H-2 were more r epresentative of CuOx than ZnOy. The properties of such junctions and their role in CO adsorption, catalysis and sensing is discussed, toget her with the relationship between catalytic and sensor science. Active sites at such junctions may have been detected as those binding CO2- with an IR band at 1557 cm(-1) which decompose to release CO2 or conve rt to formyl species (and then methanol) depending upon the prevailing conditions.