Aqueous ammonia abatement on Pt- and Ru-modified TiO2 : selectivity effects of the metal nanoparticles deposition method

A series of TiO2 – based photocatalysts obtained by deposition of Pt nanoparticles (NPs) has been tested in the photocatalytic decomposition of aqueous ammonia under UVA irradiation. Two main deposition routes were employed, i.e. (i) the deposition of surfactant-stabilized preformed metal NPs and (ii) a modified version of the well-known deposition-precipitation technique, employing urea as precipitating agent. The effects that the deposition route and the amount of deposited metal have on both ammonia conversion (XNH3) and selectivity (SY) towards the different N-containing products (Y = N2, NO2–, NO3–) have been investigated systematically, in relation to the morphological distribution of NPs on TiO2, as evidenced by HR-TEM analysis. The combination of Pt (0.8 wt.%) with a relatively low amount of Ru NPs (0.1 wt.%) as co-catalysts, both deposited on TiO2 under optimized conditions, results in an exceptional stabilization of nitrite ions (SNO2– ~ 70%), from which N2, the most desired ammonia oxidation product, might subsequently be obtained catalytically.