Ag-Decorated TiO₂ in a fluidized bed photoreactor: A high-efficiency system for the direct photocatalytic epoxidation of propylene to propylene oxide

The selective photocatalytic epoxidation of propylene represents a sustainable alternative to traditional industrial processes, offering milder operating conditions and reduced environmental impact. In this study, TiO2-based photocatalysts decorated with noble metals (Pt, Pd, Au, and Ag) were synthesised via photodeposition and evaluated in a UV-A-irradiated fluidized bed photoreactor. Physicochemical characterisation confirmed the predominance of the anatase phase, successful noble metal incorporation, and enhanced optical properties. Among the tested materials, Ag/TiO2 demonstrated the best performance, achieving the highest propylene conversion (43.5 %), the highest PO yield (20.5 %), and the lowest specific energy consumption (0.02 kWh molC3H6-1). Optimisation of operating conditions revealed a strong dependence of activity and selectivity on temperature, light intensity, and reactant concentration. Mechanistic analysis highlighted the role of Schottky barrier formation and reactive oxygen species generation in determining photocatalytic performance. Compared to previously studied systems Ag/TiO2 exhibited superior conversion and energy efficiency, confirming its potential for scalable, sustainable PO production. This work establishes a comprehensive framework for the development of efficient gas-phase photocatalytic processes aligned with green chemistry principles.