473021 Manganese As a Redox Reactant for Sustainable Thermochemical Ammonia Synthesis
A chemical loop is experimentally demonstrated here using manganese as a cycled redox reactant for ammonia production from nitrogen, water, and methane at atmospheric pressure. Manganese is used to reduce the nitrogen which is then reacted with steam to form ammonia in the presence of a sodium promotor. The corresponding manganese oxide is reduced by a dilute methane stream also producing syngas. The role of sodium hydroxide in the promotion of ammonia liberation is investigated. The thermodynamic predictions of the system are discussed, and the reaction kinetics are evaluated.
The thermochemical cycle appears a promising method to sustainably produce ammonia at near-ambient pressures. Separating the ammonia synthesis into nitrogen reduction and subsequent protonation steps introduces an additional degree of freedom for optimizing the redox reactant and process conditions. Reduced carbon dioxide emissions, and valuable syngas coproduct are advantageous for this novel approach going forward.