Multiple Nonthermal Reaction Steps for the Photooxidation of CO to CO2 on Reduced TiO2(110).
The photooxidation of CO on reduced, rutile TiO2(110) is studied on a millisecond time scale. For CO coadsorbed with a saturation coverage of chemisorbed O2 (θsat), the CO2 photon-stimulated desorption (PSD) signal is initially zero, increases to a maximum after several tens of milliseconds, and then decreases at longer times. The initial CO2 PSD signal increases ∼5 times more quickly for an oxygen coverage of 0.5θsat. The initial rate of increase of the CO2 PSD signal is proportional to the flux of UV photons. The results show that two or more nonthermal reaction steps are required to photooxidize CO adsorbed on TiO2(110). The intermediate species involved in the reactions is stable for at least 100 s at 30 K. Previous models had suggested that CO photooxidation required only one nonthermal reaction. The likely initial and final charge states of the system suggest that an electron-mediated reaction and a hole-mediated reaction are needed for the complete photooxidation reaction.
Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, MSIN K8-88, P.O. Box 999, Richland, Washington 99352, United States.
Nikolay G
NG
Petrik
Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, MSIN K8-88, P.O. Box 999, Richland, Washington 99352, United States.
Greg A
GA
Kimmel
catalysis; heterogeneous catalysis; photocatalysis; photochemistry; titania