Kinetics of the CO+N2Oreaction over noble metals -: II.: Rh/Al2O3 and Pt-Rh/Al2O3

The subsequent reduction of N2O by CO is an important subreaction in the overall CO + NO reaction. This study reports a kinetic investigation of the single CO + N2O reaction on Rh/Al2O3, and on Pt-Rh/Al2O3, between 264 and 310 degreesC with inlet partial pressures in the range 3.4-13.8 x 10(-3) and 1.5-5.9 x 10(-3) atm respectively for CO and N2O. Our mechanism proposal differs from those proposed earlier in the literature mainly by the dissociation step of chemisorbed N2O Species involving a nearest neighbor vacant site. The difference in the selectivity behavior toward the transformation of NO into N2O on Pt and Rh has been related to competitive adsorptions between NO and N2O. A comparison of the values of the equilibrium constant for the adsorption of N2O with those earlier calculated for NO from the kinetic study of the CO + NO reaction on similar catalysts [J. Catal. 175 (1998) 194] shows that, on Pt. this competition is in favor of N2O, which can readsorb and dissociate at low temperatures and low NO conversions. In contrast, the strongest NO adsorption on Rh inhibits the subsequent CO + N2O reaction. In the second part of this study, the selected mechanism has been tentatively validated in a wider range of temperatures and conversions. The adsorbate coverage dependencies of the strength of the metal-adsorbate bond has been accounted for to model temperature-programmed conversion curves. (C) 2004 Elsevier Inc. All rights reserved.