Products distribution during the gas phase photocatalytic oxidation of ammonia over the various titania based photocatalysts

Abstract

The adsorption and photooxidation of gaseous ammonia have been investigated by the FTIR spectroscopy method in a static reactor using TiO2 and modified TiO2 as photocatalysts. Two types of modified TiO2 were tested: TiO2 impregnated with transition metal oxides (NiO, V2O5, MoO3, and Fe2O3) and TiO2 doped with noble metals like Ag, Au, Pt, Pd by the chemical and photochemical deposition methods. Molecular nitrogen, NO3−, N2O and water were found as the major final products of ammonia photocatalytic oxidation (PCO). One of the purposes of the current study was to minimize the N2O formation during PCO. The pure unmodified TiO2 (anatase, SBET∼350m2/g) turned out to be the best photocatalyst for this purpose giving only 7% of initial NH3 quantity converted into N2O. Long-term experiments were carried out to determine the photocatalysts stability in PCO of NH3. All the catalysts exhibited stable performance; the rate of deactivation was low due to the transformation of NH3 nitrogen mainly into N2. Only ≈30% of initial NH3 quantity was oxidized into HNO3 which was adsorbed on the catalysts surface in all cases.