Two‐Step Chemical Looping Cycle for Renewable NH₃ Production Based on Non‐Catalytic Co₃Mo₃N/Co₆Mo₆N Reactions

Abstract

A two‐step solar thermochemical looping cycle based on Co3Mo3N/Co6Mo6N reduction/nitridation reactions offers a pathway for green NH3 production that utilizes concentrated solar irradiation, H2O, and air as feedstocks. The NH3 production cycle steps both derive process heat from concentrated solar irradiation and encompass 1) the reduction of Co3Mo3N in H2 to Co6Mo6N and NH3; and 2) nitridation of Co6Mo6N to Co3Mo3N with N2. Co3Mo3N reduction/nitridation reactions are examined at different H2 and/or N2 partial pressures and temperatures. NH3 production is quantified in situ using liquid conductivity measurements coupled with mass spectrometry (MS). Solid‐state characterization is performed to identify a surface oxygen layer that necessitates the addition of H2 during cycling to prevent surface oxidation by trace amounts of O2. H2 concentrations of > 5% H2/Ar and temperatures >500 °C are required to reduce Co3Mo3N to Co6Mo6N and form NH3 at 1 bar. Complete regeneration of Co3Mo3N from Co6Mo6N is achieved at conditions of 700 °C under 25–75% H2/N2. H2 pressure‐swings are observed to increase NH3 production during Co3Mo3N reduction. The results represent the first comprehensive characterization of and definitive non‐catalytic production of NH3 via chemical looping with metal nitrides and provide insights for technology development.

Design Principle of Molybdenum-Based Metal Nitrides for Lattice Nitrogen-Mediated Ammonia Production

“…Therefore, the conventional ammonia process struggles to align with the imperatives of sustainable development. The chemical looping process emerges as a promising technology for atmospheric pressure ammonia synthesis as it enables the ammonia synthesis to be divided into several independent steps, which leads to the breaking of thermodynamic limits and individual process intensification for each process. − It is reported that the chemical looping ammonia synthesis (CLAS) process can achieve ammonia production through the interconversions between redox pairs of the nitrogen carriers . Typically, metal nitrides are classical nitrogen carrier materials for both CLAS processes ,− and conventional ammonia synthesis processes via the lattice nitrogen-involved MvK mechanism. − In addition, metal nitrides also have great potential in the field of electrochemical N 2 to ammonia due to their unique structures. − Unfortunately, the introduction of N induces significant changes in the electronic properties and geometric features of nitrides compared to pure metals, and the complexity of chemical composition might have an immeasurable impact on the reaction performance. − These characteristics lead to the development of novel nitrogen carriers remaining in the inefficient trial-and-error approach.…”