High activity of nickel-promoted Mn4N in chemical looping ammonia synthesis

• At 350 °C, NH 3 yield of Ni/Mn 4 N is 204 μmol g −1 h −1 . • At 350 °C, NH 3 yield of Ni/Mn 4 N remained stable over 11 cycles. • At 600 °C, NH 3 yield of Ni/Mn 4 N is 826 μmol g −1 h −1 . • NH 3 conversion and selectivity of Ni/Mn 4 N are 51.46 % and 91.21 %. • Ni increases N vacancies to promote lattice N migration. Chemical looping ammonia synthesis (CLAS) stands out as a promising method for the highly selective synthesis of ammonia, which allows reactions to be carried out under ambient pressure and can reduce carbon emissions. Herein a nickel-facilitated Mn 4 N-mediated strategy was introduced to enhance the extraction of lattice nitrogen in the CLAS process. H 2 is highly mobile on nickel and reacts with lattice nitrogen on the Mn 4 N surface to form ammonia. Ni increases nitrogen vacancies in Mn 4 N, enhancing nitrogen activation. At 600 ℃, 16 wt% Ni/Mn 4 N achieves an ammonia yield of 826 μmol g −1 h −1 , which is about four times higher than that of Mn 4 N. Moreover, with 16 wt% Mn 4 N, ammonia production starts at 350 °C with a rate of 204 μmol g −1 h −1 , whereas with Mn 4 N ammonia production starts at 550 °C with an ammonia yield of 194 μmol g −1 h −1 , and the minimum temperature of ammonia production is reduced by 200 °C with Ni loading. Furthermore, 16 wt% Mn 4 N had excellent ammonia conversion rate and selectivity of 51.46 % and 91.21 %, respectively. The nitrogen carrier maintained a stable ammonia yield at a reduction temperature of 350 ℃ over 11 cycles. These findings underscore the significant potential of our proposed Ni-facilitated Mn 4 N-mediated CLAS, offering prospects for synthesizing ammonia at lower temperatures and enhancing ammonia synthesis efficiency. This approach holds promise for advancing towards a more environmentally friendly and efficient technology for ammonia synthesis.