A temperature-programmed and transient kinetic study of CO2 activation and methanation over CeO2 supported noble metals

The interaction of CO2 with noble metals deposited on ceria surfaces have been studied by temperature-programmed techniques. A transient kinetic study of CO2 activation and methanation over M/CeO2 has also been conducted. The mechanism of interaction between M/CeO2 and CO2 and its activation in the presence of Hz to CH4 is strongly influenced by the reduction temperature, regardless of the metal employed. It is suggested that, by increasing the reduction temperature, a progressive reduction of bulk CeO2 takes place, which is not promoted by the presence of the metal. The interaction mechanism suggested involves activation of CO2 on a surface Ce3+ site with formation of CO followed by oxidation of Ce3+ to Ce4+. The presence of oxygen bulk vacancies will create the additional driving force for the reduction of CO2 to CO and/or surface carbonaceous species which then rapidly hydrogenate to CH4 over the supported metal. (C) 1997 Academic Press.