A THEORETICAL-ANALYSIS OF NH3 ADSORPTION ON TIO2

From periodic Hartree-Fock calculations NH3 chemisorption is shown to occur on TiO2 without dissociation. It is bound as a base on the vacan t titanium sites from the surface. The coadsorption with water (dissoc iated on the titanium oxide) is favorable since it allows the formatio n of hydrogen bonds. On the hydrated surface, when all the Ti(IV) site s are hydroxylated, NH3 binds to the proton of one hydroxyl group. Thi s leads to a weaker adsorption mode. The formation of ammonium ions is very endothermic unless they are bonded by three hydrogen bonds to O( -II) sites from the surface or oxygen atoms From the adsorbed hydroxyl groups.