Comparative study of CO2 formation in CO oxidation by O2, NO and N2O on Pd(1 1 0) surface using infrared chemiluminescence

The infrared (IR) chemiluminescence spectra of CO2 were measured during steady-state CO oxidation by O2, NO and N2O over Pd(1 1 0) surface. Kinetics of these reactions were studied using a molecular-beam reaction system, and the order of the activity was as follows: CO + O2 > CO + NO > CO + N2O. From the analysis of the IR emission spectra, it is found that the antisymmetric vibrational mode of CO2 was more excited in the case of the CO + O2 and CO + N2O reactions, in contrast, the bending vibrational mode was more excited in the case of the CO + NO reaction. These results suggest that the activated complex of CO2 in the CO + NO reaction has more bent structure than those in the CO + O2 and CO + N2O reactions. The reason of this different behavior of the CO + NO reaction is discussed based on higher structure-sensitivity of the CO + NO reaction than the CO + O2 and CO + N2O reactions.