Photocatalytic Co-Reduction of N₂ and CO₂ with CeO₂ Catalyst for Urea Synthesis

The effective conversion of carbon dioxide (CO₂ ) and nitrogen (N₂ ) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO_2-x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H₂ (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N₂ and CO₂ by introducing oxygen vacancies. Particularly, CeO₂ -500 (CeO₂ nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C-N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC-TEM) and Fourier transform infrared (FT-IR) spectroscopy were used to research the atomic surface structure of CeO₂ -500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C-N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.