Ammonia decomposition is an important technology for extracting hydrogen from ammonia toward the realization of a hydrogen economy. Herein, it is reported that large oblate hemispheroidal Ru particles on Ca(NH ) function as efficient catalysts for ammonia decomposition. The turnover frequency of Ru/Ca(NH ) increased by two orders of magnitude when the Ru particle size was increased from 1.5 to 8.4 nm. More than 90 % ammonia decomposition was achieved over Ru/Ca(NH ) with large oblate hemispheroidal Ru particles at 360 °C, which is comparable to that of alkali-promoted Ru catalysts with small Ru particle sizes. XAFS analyses revealed that Ru particles are immobilized on Ca(NH ) by Ru-N bonds formed at the metal/support interface, which lead to oblate hemispheroidal Ru particles. Such a strong metal-support interaction in Ru/Ca(NH ) is also substantiated by DFT calculations. The high activity of Ru/Ca(NH ) with large Ru particles primarily originates from the shape and appropriate size of the Ru particles with a high density of active sites rather than the electron-donating ability of Ca(NH ) .
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