Thermo-and photoreactivities of methoxy (CH 3 O(a)) and ethoxy groups (C 2 H 5 O(a)) bonded, via the oxygen atom, to one Ti ion (monodentate adsorption form) or to two Ti ions (bidentate adsorption form) on TiO 2 have been studied by Fourier transformed infrared spectroscopy. Regardless of the similar thermal stability for the two adsorption geometries of the adsorbed alkoxy groups, difference in photoreactivity is observed by monitoring the change of their integrated IR absorptions as a function of UV irradiation time. The monodentate photooxidation rate is ∼1.5 times that of bidentate for both methoxy and ethoxy groups. CH 3 O(a) on TiO 2 is photooxidized to H 2 O(a) and HCOO(a) in the presence of O 2 . On the other hand, C 2 H 5 O(a) is photooxidized to H 2 O(a), HCOO(a), and CH 3 COO(a). A Russell-like mechanism is invoked to explain the formation of the reaction products. Possible reaction steps that control the photoreactivity of the monodentate and bidentate adsorption forms are discussed in terms of this mechanism.

The photochemistry of CH3OH(a) and CH3O(a) adsorbed on TiO2 and the effect of O2 have been studied by infrared spectroscopy and mass spectrometry. In the absence of O2, CH3OH(a) desorbs molecularly, while CH3O(a) decomposes to form CH2O(g) under UV irradiation. The rate of CH3O(a) decomposition reaches maximum in the initial stage of UV irradiation and then decreases significantly. On the other hand, for the reaction in O2, the behavior of CH3O(a) depletion upon UV irradiation is very different, giving rise to adsorbed HCOO(a) and H2O(a). A radical mechanism is proposed to explain the variation of CH3O(a) depletion upon UV irradiation, the role of O2, and the formation of the reaction products.

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