Research on Ammonia Synthesis by Alkali Metal Compounds

Abstract

For ammonia synthesis, the dissociation of nitrogen molecules with stable triple bond is an important issue. Since alkali metals such as Li and Na possess high nitrogen dissociation properties, their compounds are useful for ammonia synthesis. In this work, synthesis techniques by using alkali metal compounds were proposed and investigated. The chemical looping process of lithium hydride is composed of two step reactions, and ammonia is synthesized under 0.1 MPa below 400 °C. The nitrogen dissociation properties of Li compounds were correlated with the chemical state of Li. The more metallic Li can dissociate nitrogen at lower temperatures. Considering the nitrogen dissociation properties, the chemical looping process by alloys composed of Li and group 14 elements was proposed. The chemical looping of Li alloys consists of three step reactions and can generate ammonia under 0.1 MPa as well. For alloys composed of Na and group 14 elements, catalytic ammonia synthesis properties were investigated since Na does not form stable nitrides and amides like Li. All the Na alloys showed catalytic activity for ammonia synthesis, and then the ammonia generation temperature and ammonia formation rate depended on thermal stability and chemical state of the alloys, respectively.