Review on Ru-Based and Ni-Based Catalysts for Ammonia Decomposition: Research Status, Reaction Mechanism, and Perspectives

Hydrogen (H-2) is a zero-carbon and high-energy-densityfuel promising to replace fossil fuels for power generation and cleanenergy. However, hydrogen still faces enormous challenges in termsof production, transportation, and storage. Ammonia (NH3) is a promising H-2 (17.7 wt %) carrier that easily overcomesthe difficulties associated with H-2 storage and transport.However, for the NH3 decomposition hydrogen productionreaction, the biggest challenge at present is to achieve completeconversion of ammonia under a relatively high space velocity (about30,000 mL center dot g(cat) (-1)center dot h(-1)) at low-temperature conditions (about 350 degrees C) with reasonableprice catalysts. At present, the most efficient ammonia decompositioncatalyst is a Ru-based catalyst doped with K, Ba, and Cs and supportedon various carbon supports and metal oxides. Otherwise, the catalyststhat exhibited the most outstanding activity among non-noble metalcatalysts are nickel-based, and because of their low cost, nickelis regarded as a reasonable alternative candidate material for NH3 decomposition. Advances in the study of reaction kineticsof ammonia decomposition reactions and whether the rate-determiningstep of the ammonia decomposition reaction is the cleavage of thefirst N-H bond or the desorption of nitrogen gas are also discussed.This review provides a comprehensive consideration of the recent developmentof Ru-based and Ni-based catalysts and proposed mechanisms of ammoniadecomposition on them are examined. The effects of preparation methods,support, and promoters on catalyst activity were studied and theoreticalbases for the design of future catalysts are presented. At last, abrief introduction to catalytic membrane reactor technology in recentyears is given. This review can serve as a comprehensive work fordesigning novel catalysts.