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

The development of efficient catalysts for hydrogen generation via ammonia decomposition is crucial for the use of ammonia as an energy carrier. Here, we report the effect of pore confinement of NaNH₂ and KNH₂ on ammonia decomposition catalysis. For the first time, Ni- or Ru-doped NaNH₂ and KNH₂ were confined in carbon nanopores using a combination method of solution impregnation and melt infiltration. Structure characterization indicates the nanoscale intimacy between transition metals and alkali metal amides inside the pores of the carbon support. As a result, 8 wt % Ni-doped NaNH₂ and KNH₂ nanocomposites give NH₃ conversions of 79 and 60%, respectively at 425 °C, close to the performance of a 5 wt % Ru/C reference catalyst. 0.8 wt % Ru-doped nanocomposites exhibit even better catalytic performance, with about 95% NH₃ conversion at a moderate temperature of 375 °C. The hydrogen production rates of these Ni- and Ru-doped nanocomposites in a pure NH₃ flow are about 3-4 times higher than for the recently reported novel catalysts such as Ni-Li₂NH and Ru-Li₂NH/MgO. Interestingly, the apparent activation energies of the Ru- or Ni-based catalysts decrease 20-30 kJ mol^-1 by co-confinement with alkali metal amides. The strategy of nanoconfinement of alkali metal amides in porous hosts may open a new avenue for effectively generating H₂ from NH₃ at low temperatures.