CARBON-MONOXIDE OXIDATION OVER 3 DIFFERENT OXIDATION-STATES OF COPPER- METALLIC COPPER, COPPER (I) OXIDE, AND COPPER (II) OXIDE - A SURFACE SCIENCE AND KINETIC-STUDY

Reaction rates and activation energies were measured for carbon monoxi de oxidation over thin films of metallic copper, copper (I) oxide, and copper (II) oxide grown on graphite. The reactions were carried out i n the temperature range 200-350-degrees-C at total pressures of 100 To rr. Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectros copy (XPS) were used to characterize the growth and oxidation states o f the copper films before and after catalytic reactions. The stability of a given oxidation state of copper under reaction conditions was fo und to be a function of the oxidizing power of the CO/02 partial press ure ratio: metallic copper, Cu2O, and CuO were stable at 97/3, 90/10, and 66/33 ratios, respectively. The rate of reaction at 300-degrees-C decreased with increasing copper oxidation state (Cu > Cu2O > CuO) and the activation energy increased with increasing copper oxidation stat e (Cu 9 < Cu2O 14 < CuO 17 kcal/mol). The kinetic parameters for CO ox idation over platinum foil was tested at a 66/33 CO/02 ratio for compa rison. The reaction rate over platinum was approximately equal to that over metallic copper at 300-degrees-C and had a larger activation ene rgy (20 kcal/mol) than CuO. The possible mechanisms for CO oxidation o ver the different oxidation states of copper are discussed. (C) 1994 A cademic Press, Inc.