Effects of A-site composition of perovskite (Sr_1−xBa_xZrO₃) oxides on H atom adsorption, migration, and reaction

Hydrogen (H) atomic migration over a metal oxide is an important surface process in various catalytic reactions. Control of the interaction between H atoms and the oxide surfaces is therefore important for better catalytic performance. For this investigation, we evaluated the adsorption energies of the H atoms over perovskite-type oxides (Sr_1−xBa_xZrO₃; 0.00 ≤x≤ 0.50) using DFT (Density Functional Theory) calculations, then clarified the effects of cation-substitution in the A-site of perovskite oxides on H atom adsorption, migration, and reaction. Results indicated local distortion at the oxide surface as a key factor governing H atom adsorption. Subtle Ba²⁺substitution for Sr²⁺sites provoked local distortion at the Sr_1−xBa_xZrO₃oxide surface, which led to a decrement in the H atom adsorption energy. Furthermore, the effect of Sr²⁺/Ba²⁺ratio on the H atoms' reactivities was examined experimentally using a catalytic reaction, which was promoted by activated surface H atoms. Results show that the surface H atoms activated by the substitution of Sr²⁺sites with a small amount of Ba²⁺(x= 0.125) contributed to enhancement of ammonia synthesis rate in an electric field, which showed good agreement with predictions made using DFT calculations.