Photosynthesis of urea from N2 and CO2 using dual active site SiW6Mo6@MIL-101(Cr) at room temperature

Abstract

The one-step synthesis of urea at room temperature and pressure from N₂ and CO₂ has enormous economic and environmental benefits. In this study, a SiW₆Mo₆@MIL-101(Cr) photocatalyst was synthesized employing a dual active site regulation strategy, reaching 1148 μg h⁻¹ g_cat⁻¹ and 100% selectivity for urea under optimal experimental conditions. Both performance tests and DFT calculations unequivocally establish that SiW₆Mo₆@MIL-101(Cr) serves as a bifunctional photocatalyst, offering dual active sites for the proficient adsorption and activation of N₂ and CO₂. MIL-101(Cr) immobilizes SiW₆Mo₆, enhances dispersion and gas adsorption capacity, and supplies additional electrons through light absorption for reduction reactions. Importantly, the W site in SiW₆Mo₆ is assigned for the activation of nitrogen, whereas the Mo site is assigned for the activation of CO₂. The rate-limiting step of urea synthesis involves the interaction of *CO and *N₂, forming a tower-like intermediate *NCON*, where the dual active sites play a crucial role in reducing the reaction barrier.