Ruthenium Nanocatalysts for Ammonia Synthesis: A Review

Despite technological developments within the past century, ammonia synthesis from nitrogen and hydrogen is still highly energy intensive due to high-pressure operation. Even with recently introduced Ru-based catalysts with superior performance over conventional iron-based catalysts, there is still room for improvements to approach the theoretical minimum energy consumption. A novel approach is to use nanostructured components in catalyst formulation. Reducing Ru crystallite size to nanometers could greatly increase catalytic activity by increasing surface area as well as by the structure sensitivity of ammonia synthesis over Ru-based catalysts due to the increase of the density of highly active B5 sites. The control of Ru particle size and shape in the nanometer range and stabilization of the particles by appropriate innovative preparation techniques are key factors for development of commercial Ru nanocatalysts. Theoretical and experimental studies on actives sites and metal-promoter and metal-support interactions by advanced computational and characterization methods are also essential.