Photoinduced decomposition of formaldehyde on rutile TiO2(100)-(1×1)

We have investigated the photoinduced decomposition of formaldehyde (CH2O) on a rutile TiO2(100)-(1×1) surface at 355 nm using temperature-programmed desorption. Products, formate (HCOO−), methyl radical (CH3·), ethylene (C2H4), and methanol (CH3OH) have been detected. The initial step in the decomposition of CH2O on the rutile TiO2(100)-(1×1) surface is the formation of a dioxymethylene intermediate in which the carbonyl O atom of CH2O is bound to a Ti atom at the five-fold-coordinated Ti4+ (Ti5c) site and its carbonyl C atom bound to a nearby bridge-bonded oxygen (Ob) atom, respectively. During 355 nm irradiation, the dioxymethylene intermediate can transfer an H atom to the Ob atom, thus forming HCOO− directly, which is considered as the main reaction channel. In addition, the dioxymethylene intermediate can also transfer methylene to the Ob row and break the C−O bond, thus leaving the original carbonyl O atom at the Ti5c site. After the transfer of methylene, several pathways to products are available. Thus, we have found that Ob atoms are intimately involved in the photoinduced decomposition of CH2O on the rutile TiO2(100)-(1×1) surface.