EFFECTS OF CARRIER DOPING ON KINETIC-PARAMETERS OF CO2 HYDROGENATION ON SUPPORTED RHODIUM CATALYSTS

A study of CO2 hydrogenation on Rh/TiO2 Catalysts and of the influence of doping the TiO2 carrier with W6+ cations on kinetic parameters has been conducted. It is found that while the reaction order with respect to H-2 and CO2 partial pressures does not significantly change, the specific activity of CO2 methanation is enhanced by up to 24 times upon doping the TiO2 support with less than 1 at.% W6+ cations. A reduction of the apparent activation energy by ca. 25-34 kJ/mol and improvement of the stability of the catalytic performance are also observed by carrier doping. The greatly increased activity caused by doping is found not to be related to the SMSI phenomenon but to enhanced hydrogen adsorption capacity and weakening of the Rh-CO bond, as revealed by H-2 chemisorption measurements and infrared spectroscopic studies. The rate of gaseous CO formation is also found to be affected by carrier doping to a significant extent, via the alteration of surface CO coverage and of the strength of the M-CO bond. The intrinsic reason for the dependence of catalytic parameters upon doping of the carrier is discussed with respect to alterations of the electronic structure of the support upon doping, and electronic interactions between rhodium crystallites and the doped carrier. (C) 1994 Academic Press, Inc.