Oxidation of CO on a Pt/Al2O3 catalyst : From the surface elementary steps to light-off tests. I. Kinetic study of the oxidation of the linear CO species

摘要: Abstract The adsorption of CO (1% CO/He mixture) at 300 K on a 2.9% Pt/Al2O3 catalyst leads to the detection strong IR band 2075 cm−1 associated with weak and broad ≈1850 ascribed linear (denoted by L) multibound (Bridged 3-fold coordinated) species, respectively. Due high heat adsorption, L species does not desorb in helium temperature lower than 350 K. This allows us study rate oxidation using several x% O2/He mixtures (x range 0.5–100) five reaction temperatures (range 298–350 K). It is shown that oxidized into CO2 according elementary step S3): + Oads → (rate constant k3) involving dissociatively adsorbed oxygen species. change disappearance (determined evolution its coverage θL) O2 partial pressure (PO2) indicates proceeds (a) without any competition between species; (b) an apparent ka which varies linearly P0.5O2. weakly θo) given Langmuir's model for dissociative chemisorption: θo=(KO2PO2)0.5 (KO2PO2)0.5⪡1. S3 determined activation energy Ea=E3-(EO2/2)=65±3 kJ/mol (where E3 EO2 oxygen). preexponential factor agreement value expected from statistical thermodynamics considering immobile Moreover, when one considers even PO2=105 Pa, it must be