A comparison of the dynamics of CO oxidation by oxygen atoms and molecules on Pt and Pd surfaces

The rovibrational excitation of desorbed CO2 produced from CO oxidation by adsorbed oxygen atoms and nascent oxygen atoms on a 600 K Pd foil and a 803 Pt foil under steady-state and quasi collision free conditions was probed by infrared emission using a Fourier transform infrared (FTIR) spectrometer operating at 0.012 cm(-1) resolution. For CO2 produced from CO oxidation by adsorbed oxygen atoms on the 600 K Pd foil, the apparent temperatures associated with each vibrational mode are T-antisymmetric(T-anti)=2200+/-200 K, T-bend=2200+/-200 K, and T-symmetric(T-sym)=2500+/-200 K. Whereas, T-anti=4000+/-1000 K, T-bend=3000+/-1000 K, and T-sym=8000+/-2000 K are found for CO2 produced from CO oxidation by nascent oxygen atoms on the 600 K Pd foil. For CO2 produced on the 803 K Pt foil, in the case of CO oxidation by adsorbed oxygen atoms, the apparent vibrational temperatures of CO2 are T-anti=1500+/-50 K, T-bend=2100+/-100 K, and T-sym=2000+/-100 K, while T-anti=3400+/-600 K, T-bend=6000+/-2000 K, and T-sym=3700+/-700 K were obtained for CO2 produced from CO oxidation by nascent oxygen atoms. Thus, it is clearly shown that, on both Pd and Pt, CO2 molecules produced from CO oxidation by nascent oxygen atoms are more excited than CO2 produced from CO oxidation by adsorbed oxygen atoms. The above result indicates that more energy flows into the system of CO oxidation by nascent oxygen atoms and suggests that the oxygen atoms sticking to the surface are not fully accommodated before they react with adsorbed CO. The fact that more energy flows into the system of CO oxidation by nascent oxygen atoms demonstrates that a different reaction mechanism is involved in CO oxidation by nascent oxygen atoms relative to CO oxidation by adsorbed oxygen atoms. (C) 1996 American Institute of Physics.