Synergistic Photothermal Acceleration of Ammonia Synthesis Using Defective TiO2 Supported Ru Catalysts

The industrial production of ammonia predominantly relies on the well-established Haber-Bosch process, which operates under harsh conditions (350–500 °C and 15–35 MPa). This process consumes nearly 2% of the world’s energy production and is associated with significant carbon emissions. Consequently, there is an urgent need to develop efficient catalytic processes for ammonia synthesis that can operate at milder temperatures and pressures. In this work, we introduce a synergistic photothermal ammonia synthesis process using ruthenium (Ru) catalysts supported on defective titania (TiO2-x). A solid-state mechanical reduction method was employed to create oxygen vacancies in TiO2, resulting in the formation of TiO2-x. The Ru nanoparticles on TiO2-x with moderate oxygen vacancies exhibited high dispersion, with an average particle size of 2–3 nm. Owing to the plasmonic hybridization effect between TiO2-x and Ru nanoparticles, the Ru/TiO2–x system demonstrated full-spectrum solar-light absorption and enabled photothermal ammonia synthesis at low temperature (250 °C). This system achieved nearly a 300% enhancement in activity compared to that of traditional thermal catalytic processes. Kinetic studies revealed a decrease in apparent activation energy and reaction orders of N2 and NH3 upon solar illumination of Ru/TiO2–x, indicating its remarkable photothermal promotion of nitrogen activation and ammonia desorption. Our findings underscore the significance of the photothermal effect in activating inert nitrogen molecules and achieving ammonia synthesis under mild conditions, providing valuable insights into the design of future catalysts.