First-Principles Study on the Mechanism of Photoselective Catalytic Reduction of NO by NH₃ on Anatase TiO₂(101) Surface

A promising method for NO abatement is photoselective reduction with a proper semiconductor, such as TiO 2 . Here we report a systematic theoretical study on NO abatement through an adsorbed NH 3 molecule on the anatase TiO 2 (101) surface. The reaction mechanism proposed by experiments has been verified. The key process, namely, the oxidation of the adsorbed NH 3 molecule by photogenerated hole, has been investigated by two different methods: one is to use the triplet state to mimic the real excited state and the other is to inject a hole to the slab by the adsorption of ·OH radical. Both methods give almost the same result, and the oxidation of the NH 3 molecule is found to be a concerted proton coupled charge transfer process. The ·NH 2 radical, resulting from the oxidation of NH 3, can be attacked by a NO molecule from the gas phase to form a NH 2 NO complex spontaneously. The decomposition of this complex to N 2 and H 2 O is the rate limiting step of the overall reaction. This multistep decomposition process consists of the following sequences: the H atom transfers to the O atom in the molecule first to form HNNOH that further decomposes to N 2 and OH groups, and the latter group recombines to produce the H 2 O molecule.