Photocatalytic Selective Oxidation of Ammonia in a Semi-Batch Reactor: Unravelling the Effect of Reaction Conditions and Metal Co-Catalysts

Photocatalysis has been used for the oxidation of ammonia/ammonium in water. A semibatch photoreactor was developed this purpose, and nanostructured TiO2-based materials, either commercial P25 or prepared by flame spray pyrolysis (FSP), were as catalysts. In present work, we investigated effect (i) metal co-catalysts, (ii) pH, (iii) ammonia concentration on efficiency selectivity to undesired overoxidation byproduct, i.e., nitrites nitrates. Several metals added both titania samples, physicochemical properties every sample studied XRD, BET, UV-Vis spectroscopy. The which range 2.5–11.5, most important parameter. optimum pH values, resulted 11.5 4.8 FSP respectively, matching best compromise between an acceptable conversion a limited toward nitrite nitrate formation. For samples (P25 FSP), vs. formation highly dependent pH. At ? 9, initial rate photooxidation high, with selective overoxidized byproducts, whereas, at more acidic lower, but nitrogen higher. noble co-catalysts (0.1 mol% Ag, Au, Pd, Pt) = remarkably increased nitrate, while, case (pH 4.8), N2 respect unpromoted catalyst also Au Pt. Reactivity discussed, leading proposing mechanism that correlates activity surface adsorption (depending charge pH) homogeneous reactivity oxidizing species.