Kinetics of the CO+N2Oreaction 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 molecular 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 constant of N2O dissociation and of the equilibrium adsorption constants of N2O and 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, have been estimated in order to model temperature-programmed experiments. A divergence between experimental and calculated conversion vs temperature has been observed mainly at high conversion. Such a discrepancy has been mainly assigned to changes in the adsorption enthalpy of CO and NO with the adsorbate surface coverage. Such an effect has been tentatively quantified. (C) 1999 Academic Press.