Subnanometer-sized CuO_x Clusters on TiO₂ as Active Photocatalysts for Ammonia Production from Photocatalytic Nitration Reduction Reaction

The Haber-Bosch process is commonly used to produce ammonia while consuming energy and yielding huge emissions of carbon dioxide. Finding an alternative way to produce ammonia sustainably is a promising research direction with less CO2 emission. Photochemical nitrate reduction reaction (NtRR) to ammonia (NH3) could solve the nitrate pollutant problem in water and approach to produce ammonia with a more environmentally friendly process and lower energy consumption. In this work, the subnanometer-sized copper oxide clusters decorated on titanium oxide nanoparticles (CuOx-TiO2) were synthesized through the hydrothermal method and calcination treatment. CuOx-TiO2 demonstrated impressively conversion rate of NO3− to NH3 with a yield of 153.09 μg-gcat−1-h−1 in KNO3 solution. The characteristic structure analysis revealed CuOx clusters with ~less than 1 nm decorated on TiO2 nanoparticles. From in-situ X-ray absorption fine structure (XAFS) spectroscopic technique, the transformation of the oxidation state of Cu clusters and the changes of local structure in the CuOx-TiO2 were observed. The photocatalytic reaction mechanism of nitrate reduction on the CuOx-TiO2 was successfully revealed. These discoveries have broad implications for the functional advancement of catalysts based on subnanometer-sized clusters. Our findings may pave the way for exploring advanced ammonia synthesis routes with reduced energy consumption and carbon emissions. © 2024 Wiley-VCH GmbH.