Ammonia Decomposition over Water-Durable Hexagonal BaTiO3−xNy-Supported Ni Catalysts
KiyaOgasawara,MasayoshiMiyazaki,KazukiMiyashita,HitoshiAbe,YasuhiroNiwa,MasatoSasase,MasaakiKitano,HideoHosono
Abstract
Nickel is a promising candidate as an alternative to ruthenium for an ammonia decomposition catalyst. However, the performance of Ni-based catalysts for ammonia decomposition is still not sufficient to achieve a good hydrogen production rate under low-temperature because the weak nitrogen affinity of Ni reduces the frequency of the ammonia decomposition reaction. Here, it is reported that Ni supported on barium titanium oxynitride (Ni/h-BaTiO3−xNy) with a hexagonal structure acts as a highly active and water-durable catalyst for ammonia decomposition. The operation temperature is reduced by over 140 °C when N3− ions are substituted onto the O2− sites of the BaTiO3 lattice, and the Ni/h-BaTiO3−xNy catalyst significantly outperforms conventional oxide-supported Ni catalysts for ammonia decomposition. Furthermore, the activity of Ni/h-BaTiO3−xNy remains unchanged after exposure to water. The 15NH3 decomposition reaction and Fourier transform-infrared spectroscopy (FT-IR) measurements reveal that lattice nitrogen vacancy sites on h-BaTiO3−xNy function as the active sites for ammonia decomposition. The ammonia decomposition activity of Ni/h-BaTiO3−xNy is also higher than that of the Ni/h-BaTiO3−xHy oxyhydride catalyst, making a contrast to the activity trend in ammonia synthesis.
