Low-Temperature Photo-Thermal Synthesis of Ammonia over K-Promoted Ru/CeO2 Catalyst

Haber-Bosch process has enabled large-scale ammonia (NH3) production for over a century. Yet, its high energy demand and carbon footprint reinforces the need to develop new approaches for sustainable NH3 synthesis. In this study, a K-promoted Ru/CeO2 catalyst is investigated for photo-thermal NH3 synthesis under continuous flow conditions, leveraging light and heat to enhance catalytic efficiency. The optimized Ru(3)/CeO2 catalyst achieved an NH3 production rate of 20 mmol g⁻1 h⁻1 at 350 °C and 20 bar, representing the highest reported performance for a photo-thermal system. Mechanistic studies revealed that light-driven charge transfer processes accelerate NH3 formation via an associative pathway, as confirmed by in-situ DRIFTS analysis. Notably, the system remained stable for over 50 h without deactivation. Beyond NH3 synthesis, the catalyst also demonstrated high efficiency for photo-thermal NH3 decomposition, achieving 656 mmol H2 g⁻1 h⁻1 at a temperature as low as 215 °C, a significant improvement over conventional thermocatalytic methods. These findings highlight the potential of Ru/CeO2-based catalysts for integrated photo-thermal NH3 synthesis and decomposition, offering a promising route for sustainable NH3-based energy storage and utilization.