NH3 OXIDATION OVER UV-IRRADIATED TIO2 AT ROOM-TEMPERATURE

NH3 oxidation into N2 and N2O by O2 in the 30-250-torr pressure range has been carried out over UV-irradiated TiO2 (anatase) at room temperature. It has been checked that photons of energy greater than the band gap of TiO2 are needed and that the formation rates, rN2 and rN2O, in N2 and N2O are both proportional to UV light intensity. The electrical photoconductivity of TiO2 is not affected by NH3, N2 and N2O, i.e., these compounds do not compete with O2 for surface free electrons. A kinetic study showed that rN2 and rN2O both depend on O2 pressure, whereas NH3 pressure influences only rN2. The selectivity is not affected by PO2, the ratio rN2/rN2O being ∼4 for 100-torr NH3 pressure. The formal kinetics corresponds to a Langmuir-Hinshelwood model with reaction between O2 and NH3 adsorbed on different types of sites for N2 formation, and with reaction between O2 and a nitrogen-containing intermediate for N2O formation. A step mechanism taking into account the activation of the catalyst by photons is tentatively proposed. © 1979 American Chemical Society.