Strong Interaction of Ruthenium Species with Graphite Structure for the Self-Dispersion of Ru under Solvent-Free Conditions

Carbon materials-supported Ru catalysts are some of the most efficient catalysts for ammonia synthesis. Usually they are prepared by impregnation for the dispersion of the Ru metal. In the present study, we report that a strong interaction of ruthenium species (with triruthenium dodecacarbonyl as the precursor) with a graphite structure enables the self-dispersion of Ru under solvent-free conditions. Via simple mixing and heat treatment, sub-nano Ru particles over high surface area graphite (HSAG) are obtained with uniform distribution. The ammonia yields or ammonia synthesis rate is almost 50% higher than the catalysts prepared via impregnation whether the support is activated carbon or HSAG. During catalyst preparation, Ru 3 (CO) 12 is adsorbed on the surface of HSAG via CO groups in Ru 3 (CO) 12 and surface oxygen groups on HSAG. Subsequently, Ru 3 (CO) 12 undergoes decarbonylation reaction at very low temperatures. Then, CO has a dismutation reaction over the Ru surface leading to the formation of RuO 2 at temperatures between 180 and 190 °C. During heat treatment, RuO 2 was partially reduced by carbon at elevated temperatures, and the resulting Ru has strong interaction with HSAG, which further leads to the dispersion and stabilization of Ru nanoparticles.