Tailoring Pt valence states in TiO2 thin-film photocatalysts for efficient and durable ammonia-to-N2 conversion

Abstract

A platinum-loaded TiO2 thin-film photocatalyst was synthesized via the sol-gel method and applied for the selective catalytic oxidation (photo-SCO) of ammonia to nitrogen under UV irradiation. The catalytic performance was strongly influenced by both the Ti content in the sol and the Pt incorporation method. Increasing Ti loading enhanced the formation of the anatase phase, which promoted higher photocatalytic activity. Two Pt deposition methods were evaluated: UV-assisted photodeposition (M1) and direct addition into the TiO2 sol (M2). Among these, the M2 method enabled precise control of Pt loading, simplified the preparation process, and significantly reduced the amount of Pt required while maintaining excellent N2 selectivity. The catalytic activity and durability were further optimized through thermal treatment in various atmospheres. A 50 vol% O2 atmosphere promoted the formation of higher-valent Pt species, which were positively correlated with NH3 removal efficiency, N2 yield, and long-term stability. The Pt-Ti catalyst prepared via the M2 route and calcined in 50 vol% O2 exhibited over 95 % N2 yield for 100 h, despite using approximately 1/50 the Pt content compared to M1. Mechanistically, Lewis acid sites on the catalyst surface were identified as the active centers for ammonia activation and selective oxidation to nitrogen. In contrast, the generation of Br & Oslash;nsted acid sites during prolonged operation led to catalyst deactivation. These findings demonstrate a rational design strategy for highly efficient and durable photo-SCO catalysts using minimal noble metal content.