Anionic Defects Enhanced Ammonia Synthesis Over Ru Catalyst Supported on Barium Niobate Reduced with CaH₂

Anionic defects of H- ((HO)-O-center dot) and oxygen vacancies with trapped electrons (V-O(center dot)) have been built in the lattice of a hydrothermally derived perovskite (Ba5Nb4O15, BNO) by CaH2 reduction in Ar flow at 600 degrees C for 12 h. The formed anionic defects in the CaH2- reduced BNO (CaBNO) have been found to improve drastically the ammonia synthesis activity of Ru/CaBNO by donating electrons from both H-O(center dot) and/or V-O(center dot) to Ru atoms. The stoichiometry of H-O(center dot) and V-O(center dot) has been determined by TPR and TPO method, respectively. The H-O(center dot) 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.