Recent Advances in Heterogeneous Catalysis for Ammonia Synthesis

Even after a century, ammonia (NH3) synthesis from nitrogen and hydrogen through Haber-Bosch process is still energy intensive. Even with recently introduced second generation Ru based catalysts with superior performance over commercial Fe based catalysts, there is still place for upgrading with new approach using advanced materials in catalyst formulation. The alkali and alkaline metal promoted Ru supported carbon and metal oxide catalyst attracted attention at initial stage and extensively studied for NH(3)synthesis in the 20(th)century. Until recently, advanced materials such as electrides, hydrides, nitrides, oxides and oxy-hydrides-nitrides studied as support and active component of catalyst fascinated much attention, with milder reaction conditions for NH(3)synthesis. These materials with unique properties of reversible storage of electrons, hydrides, nitrides and oxygen vacancies enrich electron density on Ru catalyst and cleave N equivalent to N bond with very low activation energy (<60 kJ/mol). The mechanistic understanding of these materials leads to the fact that activation N equivalent to N bond is no more rate-determining step (RDS). Instead, formation of N-H bond is RDS, pushing towards an innovative research directions and scientific basis for development of new catalysts. Enormous maturation of experimental and theoretical methods with improved precession over worldwide research effort helped in gaining a fundamental understanding of these materials in NH(3)synthesis. The most of Ru supported on these advanced materials were better in performance compared to benchmark Cs-Ru/MgO and Ru/AC catalysts in NH(3)synthesis. Insights on these materials and their mechanism are covered in this review, which digs towards finding a realistic catalyst for NH(3)synthesis.