Kinetics of the CO+O-2 reaction over three-way Pt-Rh catalysts

The kinetics of the reaction between CO and O-2 Over bimetallic Pt-Rh/Al2O3 catalysts was studied with a differential fixed bed flow reactor running u nder reducing conditions (CO/O-2 > 5). Temperature, CO and O-2 partial pres sures were in the range 25-500 degreesC, 5 x 10(-3) to 9 x 10(-3) and 0.25 x 10(-3) to 2 x 10(-3) atm, respectively. Kinetic results have been interpr eted in the light of various mechanisms proposed in the literature. The bes t agreement is obtained with a mechanism scheme involving a bimolecular rea ction between adsorbed CO and adsorbed O-2 molecules as determining step. A rate expression has been derived as a function of adsorption equilibrium c onstants Of O-2 and CO, lambda (O) and lambda (CO), and of the rate constan t of the limiting step k respectively. These parameters have been estimated at 215 degreesC, then the influence of temperature lambda (i) and k has be en investigated. Finally, the effect of NO addition to the feed upon the re action rate has been studied. It is shown that CO is adsorbed much more str ongly than O-2 under our experimental conditions. (C) 2001 Elsevier Science B.V. All rights reserved.