Uncovering the nature of electron-enriched state of Ru accelerating ammonia synthesis

Ammonia is a carbon-free fuel and hydrogen carrier. Ru promoted by Cs, Ba, or La can catalyze NH3 synthesis at relatively mild conditions at 10 bar at 300 oC. It was recently observed that Ru and BaO supported on conductive carbon can separately store e− and H+, like a chemical capacitor. When the work function of carbon decreases, Ru should gradually become enriched with e−, facilitating N2 activation via π-backdonation and alleviating H2 poisoning evidenced by accelerated NH3 synthesis. Ru 3d5/2 XPS binding energy measured in vacuum demonstrates a correlation with the NH3 synthesis catalytic rate, confirming the electron enrichment of 2 nm Ru nanoparticles enhanced by BaO on low work function carbon support. However, in situ Ru K-edge XAS appeared to be not very sensitive to charged state of Ru, probably due to large life time broadening. Here, we propose to measure in situ Ru L3-edge HERFD XAS in tender X-ray range under more relevant catalytic conditions not yet possible with XPS.