Effects of A-site composition of perovskite (Sr 1- x Ba x ZrO 3 ) 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- x Ba x ZrO 3 ; 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 Ba 2+ substitution for Sr 2+ sites provoked local distortion at the Sr 1- x Ba x ZrO 3 oxide surface, which led to a decrement in the H atom adsorption energy. Furthermore, the effect of Sr 2+ /Ba 2+ 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 Sr 2+ sites with a small amount of Ba 2+ ( x = 0.125) contributed to enhancement of ammonia synthesis rate in an electric field, which showed good agreement with predictions made using DFT calculations.