High Activity of Nickel-Promoted Mn4n in Chemical Looping Ammonia Synthesis

Abstract

Chemical looping ammonia synthesis (CLAS) stands out as a promising sustainable method for producing ammonia, enabling reactions to occur under ambient pressure through chemical looping. This approach reduces carbon emissions and enhances energy utilization efficiency. In our study, we introduce a new strategy to address the challenge of the limited ability of Mn4N to extract lattice nitrogen. We propose the nickel-facilitated Mn4N-mediated CLAS. H2 has considerable mobility on nickel and can react directly with lattice nitrogen on the Mn4N surface to form ammonia. Under reduction conditions at 600 ℃, 16 wt% Ni/Mn4N achieves an impressive ammonia yield of up to 826 μmol g-1 h-1, marking a 72.3 % increase compared to Mn4N. The introduction of nickel into Mn4N enabled the production of ammonia at a lower temperature of 350 °C, compared to limited ability of Mn4N to generate only a small amount of ammonia at 500 °C. This breakthrough represents a major advancement, as the synthesis of ammonia from manganese nitride at such temperatures has never been documented before. The ammonia conversion and generation selectivity were as high as 51.46 % and 91.21 %, and such conversion and selectivity were also the highest among the transition metal-mediated CLAS that have been reported. These findings underscore the significant potential of our proposed nickel-facilitated Mn4N-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.

Keywords: Chemical looping, Ammonia Synthesis, Nickel-loaded, Manganese nitride, Lattice nitrogen