Ammonia Synthesis over Ruthenium Supported on Metastable Perovskite Oxyhydrides BaREO₂H (RE = Y, Sc) Prepared by Mechanochemical Method

Abstract

Oxyhydrides have attracted attention as materials with various unique properties derived from lattice hydride ions (H⁻). However, their instability makes synthesis by conventional thermal synthesis methods difficult, so an appropriate synthesis strategy is required. Here, the mechanochemical synthesis of perovskite oxyhydrides BaREO₂H (RE = Y, Sc) for catalyst applications is reported. The formation of BaYO₂H is known to be thermodynamically unstable; however, a mechanochemical process that inevitably proceeds under non‐equilibrium conditions enables the synthesis of such a metastable oxyhydride material without any heat treatment. Furthermore, BaScO₂H, which is typically obtained at very high temperatures (1000 °C) and pressure (>4 GPa), is successfully synthesized at room temperature by the mechanochemical method. The ammonia synthesis reaction over these oxyhydrides supporting Ru is significantly enhanced at low temperatures, and the ammonia synthesis rates are significantly higher than conventional oxide‐supported Ru catalysts. The mechanochemically synthesized BaREO₂H has many anionic electrons with low work function at the site of H⁻ vacancies, which enables strong electron donation to Ru and the storage of excess hydrogen adatoms from the Ru surface that results in high catalytic performance.