TOTAL OXIDATION OF CARBON-MONOXIDE AND METHANE OVER TRANSITION METAL-FLUORITE OXIDE COMPOSITE CATALYSTS .2. CATALYST CHARACTERIZATION AND REACTION-KINETICS

Cu-Ce-O and Au-Ce-O catalysts were characterized by XRD, XPS, and STEM. Copper in small amounts showed a strong tendency to associate with cerium oxide, When the cerium oxide surface was saturated with copper, excess copper formed bulk copper oxide particles. The cuprous(+1) oxidation state was identified by XPS for the copper clusters distributed in cerium oxide, while gold in the Au-Ce-O catalyst was in the form of metallic particles distributed in the cerium oxide matrix. The reaction kinetics of CO and methane oxidation over the Cu-Ce-O catalysts were measured at a partial pressure of CO or oxygen from 0.001 to 0.06 bar, at a partial pressure of methane from 0.001 to 0.03 bar, and at temperatures ranging from 40 to 200 degrees C for CO oxidation and from 400 to 550 degrees C for methane oxidation. The oxidation rates of CO and methane over the Cu-Ce-O catalysts were expressed as kK(R)P(R)P(O)(n)/(1 + KRPR), where P-R denotes the partial pressure of CO or methane and Po is the partial pressure of oxygen. CO oxidation kinetics over the Au-Ce-O catalyst were described by kP(CO)(0.3)P(O)(0.18). The kinetic results were interpreted with the Langmuir-Hinshelwood mechanism and in terms of a synergistic effect resulting from the interaction of the two kinds of materials. (C) 1995 Academic Press, Inc.