Fourier transform infrared study of the adsorption and coadsorption of nitric oxide, nitrogen dioxide and ammonia on TiO2 anatase

The adsorption and coadsorption of NO, NO2 and NH3 on TiO2 anatase has been studied by Fourier-transform infrared (FT-IR) spectroscopy. Upon NO adsorption, nitrosyl species adsorbed on two different Lewis sites are observed, together with N2O produced via the reduction of NO by Ti3+, and NO3- formed by oxidation of NO by Ti4+. Adsorption of NO2 produces several distinct adsorbed nitrate ions with different thermal stabilities. NH3 molecularly coordinated on two different Lewis sites is observed upon NH3 adsorption. Nitrosyls are not formed by contacting the NH3-covered surface of TiO2 with gaseous NO. Coadsorption of NH3 with NO and NO2 causes only a few perturbations, attributed to changes in the coordination of nitrates and of NH3 species. No evidence is found for the reaction of NOx with NH3 to 523 K, in line with the poor catalytic activity of TiO2 in the Selective Catalytic Reduction (SCR) of NOx by NH3.