Alloyed Ni-Fe nanoparticles as catalysts for NH₃ decomposition

A rational design approach was used to develop an alloyed Ni-Fe/Al₂O₃ catalyst for decomposition of ammonia. The dependence of the catalytic activity is tested as a function of the Ni-to-Fe ratio, the type of Ni-Fe alloy phase, the metal loading and the type of oxide support. In the tests with high temperatures and a low NH₃-to-H₂ ratio, the catalytic activity of the best Ni-Fe/Al₂O₃ catalyst was found to be comparable or even better to that of a more expensive Ru-based catalyst. Small Ni-Fe nanoparticle sizes are crucial for an optimal overall NH3 conversion because of a structural effect favoring the smallest particles in terms of catalytic activity per active site. Compared with SiO₂, ZrO₂ and TiO₂, the support materials Al₂O₃ or Mg-Al-spinel give the highest performance in the high temperature range.