Ammonia Decomposition over Water-Durable Hexagonal BaTiO_3-xN_y-Supported Ni Catalysts

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 & DEG;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 (NH3)-N-15 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.