Synthesis and Structural Study of Substituted Ternary Nitrides for Ammonia Production

Over the past few decades, inorganic nitride materialshave grownin importance in part due to their potential as catalysts for thesynthesis of NH3, a key ingredient in fertilizer and precursorto industrial chemicals. Of particular interest are the ternary (ABN)or higher-order nitrides with high metal-to-nitrogen ratios that showpromise in enhancing NH3 synthesis reaction rates and yieldsvia heterogeneous catalysis or chemical looping. Although metal nitridesare predicted to be numerous, the stability of nitrogen triple bondsfound in N-2, especially in comparison to the metal-nitrogenbonds, has considerably hindered synthetic efforts to produce complexnitride compounds. In this study, we present an exhaustive down-selectionprocess to identify ternary nitrides for a promising chemical loopingNH(3) production mechanism. We also report on a facile andefficient two-step synthesis method that can produce well-characterized & eta;-carbide Co3Mo3N/Fe3Mo3N or filled & beta;-manganese Ni2Mo3N ternaries, as well as their associated quaternary, (Co,Fe)(3)Mo3N, (Fe,Ni)(2)Mo3N, and (Co,Ni)(2)Mo3N, solid solutions. To further explore the quaternaryspace, syntheses of (Co,Ni)(3)Mo3N (Ni & LE;10 mol %) and Co-3(Mo,W)(3)N (W & LE; 10 mol%) were also investigated. The structures of the nitrides were characterizedvia X-ray powder diffraction. The morphology and compositions werecharacterized with scanning electron microscopy. The multitude ofchemically unique, but structurally related, nitrides suggests thatproperties such as nitrogen activity may be tunable, making the materialsof great interest for NH3 synthesis schemes.