We have investigated the ultraviolet (UV) photon-stimulated reactions of CO, acetone and oxygen adsorbed on TiO2(110). The O2 photochemistry depends on the coverage. For small coverages, only ~14% desorbs while the rest either dissociates during UV irradiation, or remains molecularly adsorbed on the surface. For the maximum coverage of chemisorbed oxygen, the fraction of O2 that photodesorbs is ~45%.  While photo-generated holes are responsible for the O2 photodesorption, photo-generated electrons are responsible for the photo-induced O2 dissociation.  When CO is co-adsorbed with O2, CO2 is produced during UV irradiation. The CO2 preferentially desorbs in the plane perpendicular to the bridge-bonded oxygen (BBO) rows at an angle of 45�. Furthermore, the production rate of CO2 is zero when the UV irradiation starts and reaches a maximum value at intermediate times before decaying at longer times. The results demonstrate that the photooxidation of CO is a multi-step reaction that proceeds through a metastable intermediate state that is oriented perpendicular to the BBO rows. This state is consistent with an O-O-C-O state found via density functional theory. For acetone co-adsorbed with oxygen, previous research suggests that a thermal reaction between acetone and adsorbed oxygen to form an acetone diolate precedes the photochemistry. During UV irradiation, a methyl radical is ejected leaving acetate on the surface. Using infrared reflection absorption spectroscopy (IRAS), we have identified the acetone diolate. We have also measured the angular distribution of the photodesorbing methyl radicals. Consistent with its ejection from acetone diolate, we observe a peak in the distribution at ~45� in the plane perpendicular to the BBO rows. However, a second photodesorption peak normal to the surface indicates that a second reaction channel is available. In general, these studies provide new insights into mechanisms responsible for the photochemistry of small molecules on TiO2.

Photochemistry of CO, acetone and O<sub>2</sub> on reduced rutile TiO<sub>2</sub>(110)

248th National Meeting (2014)

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Photochemistry of CO, acetone and O2 on reduced rutile TiO2(110)

Photochemistry of CO, acetone and O₂ on reduced rutile TiO₂(110)