Unraveling the role of CaO and MgO as supports in the vanadium-based nitrogen carrier for chemical looping ammonia production

The limited reactivity of single transition metal nitrogen carrier (NC) is a significant factor contributing to the suboptimal performance of chemical looping ammonia production (CLAP). This research proposes a strategy of loading alkaline earth metal oxides to construct a vanadium-based NC loading CaO (VN/CaO composite NC) with enhanced reactivity. The results demonstrate that the incorporation of CaO increases the lattice nitrogen conversion rate of VN from 4 % to 21 % and reduces the ammonia production temperature. The ammonia production rate of VN/CaO composite NC reaches 481.25 μmol·g −1 ·h −1 at 800 °C. In contrast, the electron-donating ability of MgO is weaker than that of CaO, and the ammonia production rate of the VN/MgO is 350 μmol·g −1 ·h −1 . Theoretical calculations and experimental characterizations reveal that CaO maintains the surface basicity of the NC, creating an electron-rich surface that weakens the V N bond strength, promotes H 2 adsorption and dissociation, and enhances the reactivity of vanadium-based NC. The reaction mechanism of VN/CaO composite NC follows the Mars-van Krevelen mechanism, with the hydrogenation of NH 3 intermediates identified as the rate-determining step. This study provides theoretical support for the development of multi-component composite NC.