Kinetics and isotope effects for the C-O bond dissociation in the hydrogenation of CO on Pd/Al2O3 catalyst were investigated by using pulse surface reaction rate analysis (PSRA). The rate-determining step was found to be the C-O bond dissociation of the adsorbed CO species. The rate constant for the C-O bond dissociation process per adsorbed CO molecule was determined at various temperatures and Arrhenius parameters of the rate constant were obtained. The rate constant in flowing D2 (kD) was considerably larger than that in flowing H2 (kH), indicating an inverse isotope effect. The average value of kH/kD was 0.61. The extent of the inverse isotope effect for Pd was more significant than that for Ni (kH/kD = 0.75). The preexponential factor for kH on Pd (1.6 × 104 s-1) was much smaller than that on Ni (5.4 × 106 s-1). It was concluded that adsorbed CO is not directly dissociated to surface carbon and oxygen atoms but hydrogen atoms play an important role in the C-O bond dissociation. Further details of the mechanism for the C-O bond dissociation were discussed from the observed kinetics and isotope effects.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry