Efficient Ammonia Synthesis over Phase-Separated Nickel-Based Intermetallic Catalysts
Tian‐Nan Ye, Yangfan Lu, Yasukazu Kobayashi, Jiang Li, Sang‐Won Park, Masato Sasase, Masaaki Kitano, Hideo Hosono
Abstract
Ammonia is one of the most important industrial intermediates due to the mass-demand for the production of various chemicals. Since the development of the Haber–Bosch process, most ammonia production has been conducted using Fe-, Co-, and Ru-based catalysts. Meanwhile, the low-cost and earth-abundant elements, such as Ni, typically show much inferior activity due to their weak nitrogen adsorption energy. Here, we show that LaNi5, a representative hydrogen-absorbing material, offers stable and high ammonia production through surface decomposition to a unique Ni–LaN core–shell structure. The reaction rate is as high as 4500 μmol·g–1·h–1, which is much higher than those of other reported Co and Ni intermetallic catalysts and comparable to those of reported Ru-based intermetallic catalysts. TEM observations demonstrated that the nanosized Ni–LaN core–shell structures were self-organized during ammonia synthesis and generated a Ni–LaN active nanostructure, accounting for the high and stable catalytic performance in ammonia synthesis. Since the Ni–LaN active structure allows for the transition metal–nitride composite to generate ammonia universally, these discoveries show that hydrogen-storage materials can be a promising playground for designing brand-new ammonia synthesis catalysts without including expensive rare metals.