Kinetics of the CO+O2 reaction over three-way Pt-Rh catalysts Original Research Article

The kinetics of the reaction between CO and O2 over bimetallic Pt-Rh/Al2O3 catalysts was studied with a differential fixed bed flow reactor running under reducing conditions (CO/O2>5). Temperature, CO and O2 partial pressures were in the range 25–500°C, 5×10−3 to 9×10−3 and 0.25×10−3 to 2×10−3 atm, respectively. Kinetic results have been interpreted in the light of various mechanisms proposed in the literature. The best agreement is obtained with a mechanism scheme involving a bimolecular reaction between adsorbed CO and adsorbed O2 molecules as determining step. A rate expression has been derived as a function of adsorption equilibrium constants of O2 and CO, λO and λCO, and of the rate constant of the limiting step k respectively. These parameters have been estimated at 215°C, then the influence of temperature on λi and k has been investigated. Finally, the effect of NO addition to the feed upon the reaction rate has been studied. It is shown that CO is adsorbed much more strongly than O2 under our experimental conditions.