Anionic Defects Enhanced Ammonia Synthesis Over Ru Catalyst Supported on Barium Niobate Reduced with CaH 2

Anionic defects of H − ( H ∙ O ) and oxygen vacancies with trapped electrons ( V ∙ O ) have been built in the lattice of a hydrothermally derived perovskite (Ba 5 Nb 4 O 15, BNO) by CaH 2 reduction in Ar flow at 600 °C for 12 h. The formed anionic defects in the CaH 2 -reduced BNO (CaBNO) have been found to improve drastically the ammonia synthesis activity of Ru/CaBNO by donating electrons from both H ∙ O and/or V ∙ O to Ru atoms. The stoichiometry of H ∙ O and V ∙ O has been determined by TPR and TPO method, respectively. The H ∙ O defects have been proved to react with N 2 under ammonia synthesis conditions via TPD, XPS measurements and isotope (D 2 ) reaction, which provides secondary pathways for ammonia synthesis. Kinetic studies revealed that oxygen vacancies accept spilledover H atoms from Ru particles to alleviate the H 2 poisoning effect. Cs-promoter has been demonstrated to accelerate the formation of anionic defects in CaBNO under ammonia synthesis reactions. Graphical Abstract Anionic defects ( V ∙ O and H ∙ O ) formed in the lattice of Ba 5 Nb 4 O 15 perovskite via CaH 2 -reduction drastically promote the ammonia synthesis activity of Cs-Ru/CaBNO catalyst