Facile formation of barium titanium oxyhydride on a titanium hydride surface as an ammonia synthesis catalyst

Abstract

Oxyhydrides are promising compounds as supports for ammonia synthesis catalysts because they suppress hydrogen poisoning on the catalyst surface and enhance the ammonia synthesis activity. Herein, we developed a facile method for preparing BaTiO_2.5H_0.5, a perovskite oxyhydride, on a TiH₂ surface via the conventional wet impregnation method using TiH₂ and Ba hydroxide. Scanning electron microscopy and high-angle annular dark-field scanning transmission electron microscopy observations revealed that BaTiO_2.5H_0.5 crystallized as nanoparticles of ca. 100–200 nm on the TiH₂ surface. The Ru-loaded catalyst Ru/BaTiO_2.5H_0.5-TiH₂ exhibited 2.46 times higher ammonia synthesis activity (3.05 mmol-NH₃ g⁻¹ h⁻¹ at 400 °C) than the benchmark Ru catalyst Ru–Cs/MgO (1.24 mmol-NH₃ g⁻¹ h⁻¹ at 400 °C) because of the suppression of hydrogen poisoning. The analysis of reaction orders showed that the effect of suppressing hydrogen poisoning on Ru/BaTiO_2.5H_0.5-TiH₂ was equivalent to that of the reported Ru/BaTiO_2.5H_0.5 catalyst, thus supporting the formation of BaTiO_2.5H_0.5 perovskite oxyhydride. This study demonstrated that the selection of appropriate raw materials facilitates the formation of BaTiO_2.5H_0.5 oxyhydride nanoparticles on the TiH₂ surface using the conventional synthesis method.