Ni-Mn-N derived composite nitrogen carriers for enhanced chemical looping ammonia production

Abstract

Chemical looping ammonia production (CLAP) technology provides additional freedom for the optimization of operating conditions via the strategy of stepwise reactions, which is promising to achieve green ammonia synthesis under mild conditions. Mn-based nitrogen carriers are ideal redox materials by virtue of their moderate thermodynamic properties and abundant crystalline phases, but their performance of hydrogenation in CLAP is still limited by the low reactivity. Herein, a series of Ni-Mn-N composite nitrogen carriers with different Ni/Mn ratios were prepared, and the effect of Ni doping on the performance of NH3 production was investigated at atmospheric pressure. The nitrogen carriers modified with low level of Ni (<20 wt%) showed high activity and selectivity of hydrogenation, and the effective conversion of lattice nitrogen in 80Mn20Ni-N reached 36.1% at 750 °C, which was 15.7% higher than the undoped 100Mn-N. The introduction of low level of Ni can simultaneously enhance the bulk migration and interfacial reaction of lattice nitrogen and achieve the optimal kinetic matching between the both processes, thus promoting the activity and selectivity of lattice nitrogen converted to NH3. This study presents new insights into the design of composite nitrogen carriers to enhance ammonia production in CLAP.