The role of lanthanum hydride species in La2O3 supported Ru cluster catalyst for ammonia synthesis

To exploit the ammonia as a carrier for sustainable energy, development of efficient catalysts is highly desired. Oxide supported Ru catalysts have been widely studied in ammonia synthesis for their superior catalytic performances under mild conditions. Here, sub-nanometer Ru clusters on La2O3 (Ru clusters/La2O3) catalyst has been synthesized and exhibits superior catalytic performance in ammonia synthesis under mild conditions. Multiple characterizations results reveal that surface La-H species, in situ generated on the surface of catalyst, can significantly boost the activity of Ru clusters/La2O3 catalyst in ammonia synthesis. Detailed mechanistic studies demonstrate that the active La-H species on the La2O3 can not only promote activation and dissociation of nitrogen molecules but also directly involve in ammonia synthesis reaction process via a La-H species-mediated reaction pathway. This work promotes molecular level understanding the active sites and reaction mechanism under real reaction conditions, and will also offer opportunity for guiding the design of efficient Ru-based catalysts for ammonia synthesis.