Subnanometer‐sized CuOx 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 CO 2 emission. Photochemical nitrate reduction reaction (NtRR) to ammonia (NH 3 ) 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 (CuO x ‐TiO 2 ) were synthesized through the hydrothermal method and calcination treatment. CuO x ‐TiO 2 demonstrated impressively conversion rate of NO 3 − to NH 3 with a yield of 153.09 μg‐g cat −1 ‐h −1 in KNO 3 solution. The characteristic structure analysis revealed CuO x clusters with ~less than 1 nm decorated on TiO 2 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 CuO x ‐TiO 2 were observed. The photocatalytic reaction mechanism of nitrate reduction on the CuO x ‐TiO 2 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.