Ammonia Decomposition over Water‐Durable Hexagonal BaTiO_3−xN_y‐Supported Ni Catalysts

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‐BaTiO_3−xN_y) 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‐BaTiO_3−xN_y catalyst significantly outperforms conventional oxide‐supported Ni catalysts for ammonia decomposition. Furthermore, the activity of Ni/h‐BaTiO_3−xN_y 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‐BaTiO_3−xN_y function as the active sites for ammonia decomposition. The ammonia decomposition activity of Ni/h‐BaTiO_3−xN_y is also higher than that of the Ni/h‐BaTiO_3−xH_y oxyhydride catalyst, making a contrast to the activity trend in ammonia synthesis.