Large Oblate Hemispheroidal Ruthenium Particles Supported on Calcium Amide as Efficient Catalysts for Ammonia Decomposition

Abstract

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 ) .

Enhanced Catalysis of Pt 3 Clusters Supported on Graphene for N–H Bond Dissociation

“…[1][2][3] Among the available catalysts for ammonia decomposition under mild conditions, Pt has been identified as one of the most promising candidates. 4,5 The polycrystalline surfaces of Pt, including (100), (111), and (533), have been employed as active substrates for ammonia decomposition to produce N 2 and H 2 . [6][7][8][9][10] However, the Pt catalysts for ammonia decomposition, including the use of doped Pt, 11 are to the best of our knowledge still not sufficiently effective at low temperatures (e.g., <350°C) and thus are not economically viable for large-scale applications.…”

Effect of Pore Confinement of NaNH2 and KNH2 on Hydrogen Generation from Ammonia

“…Such an increase in oxidation state has been reported for other TM-amide-based catalysts, and was attributed to charge transfer between Ru and KNH 2 to form Ru–N bonds (or ternary nitride species) and thereby catalyzing the decomposition of NH 3 . 38 For example, it has been reported that NH 3 decomposition over Li 2 NH doped with 3d transition metals (nitrides) such as Fe, Co, and MnN involve two steps: 28 (1) the reaction of Li 2 NH and transition metal (nitride) to form ternary nitride and H 2 ; (2) the ammoniation of the ternary nitride to Li 2 NH, transition metal (nitride), and N 2 . Ternary nitride is not expected to be formed in systems such as Ru–Li 2 NH, MnN–NaNH 2 , and MnN–KNH 2 .…”

Recent progress towards mild-condition ammonia synthesis

“…Recently, we developed a composite catalyst system of Li 2 NH-3 d transition metal or transition metal nitride (TM(N)), in which Li 2 NH synergized with 3 d TM(N) (from Ti to Cu) leading to universal high catalytic activities towards NH 3 decomposition [54,55] . In addition to 3 d metals, Ru was also found to synergize with amides and imides of alkali and alkaline earth metals, such as LiNH 2 /Li 2 NH, Ca(NH 2 ) 2 and Ba(NH 2 ) 2 , and these composites exhibited remarkably high activities towards ammonia decomposition [56][57][58] . An efficient ammonia decomposition catalyst may catalyze the reverse reaction, i.e., ammonia synthesis, as well.…”