Kinetics of the CO+N(2)Oreaction over noble metals I. Pt/Al2O3

The kinetics of the CO + N2O reaction on Pt/Al2O3 have been studied between 260 and 320 degrees C with partial pressures ranging from 1 x 10(-3) to 8 x 10(-3) atm for N2O and 4 x 10(-3) to 14 x 10(-3) atm for CO. A mechanism has been selected from those suggested in the literature, It involves molec ular adsorptions of N2O and CO and a dissociation step of adsorbed N2O on a nearest neighbor vacant site which is assumed to be rate limiting. A rate expression has been derived which led to the estimation of the rate constan t of N2O dissociation and of the equilibrium adsorption constants of N2O an d CO. Enthalpies of adsorption of N2O and CO, Delta H-ads,H-CO and Delta H- ads,H-N2O, and the energy of activation for adsorbed N2O dissociation, E, h ave been estimated in order to model temperature-programmed experiments. A divergence between experimental and calculated conversion vs temperature ha s been observed mainly at high conversion. Such a discrepancy has been main ly assigned to changes in the adsorption enthalpy of CO and NO with the ads orbate surface coverage. Such an effect has been tentatively quantified. (C ) 1999 Academic Press.