Molecular-Beam Infrared Chemiluminescence Study of the Dynamics of Catalytic Reactions

Decomposition and Oxidation of Methanol and Formic Acid and Partial Oxidation of Butane on Pd Surface

Abstract

The infrared chemiluminescence technique was applied to catalytic oxidation of CH₃OH, HCOOH and i-C₄H₁₀ on a Pd surface, and the reaction dynamics and mechanism were discussed in terms of internal energy states of nascent product CO₂ and CO molecules. The vibrational and rotational states of CO₂ produced by CH₃OH oxidation were quite similar to those of CO₂ produced by CO oxidation, indicating that the final step of the CO₂ formation in the CH₃OH oxidation involved a bimolecular process (i.e., CO_ad+O_ad). On the contrary, the intensity of IR emission of CO₂ produced by HCOOH oxidation was very weak, suggesting that most of CO₂ was not so vibrationally excited and that CO₂ was formed via decomposition of HCOO_ad (unimolecular decomposition of formate). The selective production of CO and H₂O was observed by the partial oxidation of i-C₄H₁₀ on Pd, and the vibrational state of product CO was very different between the Pd and Pt surfaces. These differences in internal energy states of the CO and CO₂ products can provide us with new information on the dynamics and mechanism of catalytic reactions.