Infrared chemiluminescence study of the dynamics of catalytic oxidation of CO and HCOOH on Pd(111) and polycrystalline Pd surfaces

The infrared chemiluminescence technique was applied to CO oxidation, HCOOH decomposition and HCOOH + O-2 reaction on Pd(111) single crystal and polycrystalline Pd surfaces for the study of the dynamics of the catalytic reactions. The vibrational temperature (T-V) of CO2 formed by CO oxidation on Pd(111) was much higher than that on polycrystalline Pd foil, indicating that the dynamics of CO oxidation are structure-sensitive. The vibrational temperature (T-V) and the rotational temperature (T-R) of CO2 formed by CO oxidation on Pd(111) increased with increasing the surface temperature, but this may not be due to the oxygen coverage effect because little change in T-V was observed by changing the O-2/CO ratio. In the case of HCOOH oxidation, the rate of CO2 formation was much more enhanced in the presence of O-2 than decomposition of HCOOH without O-2. However, the intensities of IR emission of CO2 produced by the HCOOH decomposition and oxidation on both Pd surfaces were very weak, suggesting that the product CO2 was not so excited vibrationally and that the internal energy distribution of the product CO2 was quite different from that of CO2 formed by CO oxidation (bimolecular reaction between CO(ad) and O(ad)).