Photoinduced Decomposition of Formaldehyde on Rutile TiO2(100)-(1x1)

We have investigated the photoinduced decomposition of formaldehyde (CH2O) on a rutile TiO2(100)-(1x1) surface at 355 nm using temperature-programmed desorption. Products, formate (HCOO-), methyl radical (CH3 center dot), ethylene (C2H4), and methanol (CH3OH) have been detected. The initial step in the decomposition of CH2O on the rutile TiO2(100)-(1x1) surface is the formation of a dioxymethylene intermediate in which the carbonyl O atom of CH 2 O is bound to a Ti atom at the five-fold-coordinated Ti4+ (Ti-5c) site and its carbonyl C atom bound to a nearby bridge-bonded oxygen (O-b) atom, respectively. During 355 nm irradiation, the dioxymethylene intermediate can transfer an H atom to the O-b atom, thus forming HCOO directly, which is considered as the main reaction channel. In addition, the dioxymethylene intermediate can also transfer methylene to the O-b row and break the C-O bond, thus leaving the original carbonyl O atom at the Ti-5c site. After the transfer of methylene, several pathways to products are available. Thus, we have found that O-b atoms are intimately involved in the photoinduced decomposition of CH2O on the rutile TiO2(100)-(1x1) surface.