Mechanistic aspects of ammonia synthesis on Ta3N5 surfaces in the presence of intrinsic nitrogen vacancies

A possible dinitrogen activation and the ammonia synthesis mechanism were studied on the (100), (010) and (001) surfaces of Ta3N5 that contain intrinsic nitrogen vacancies. The study suggests that intrinsic nitrogen vacancies can become catalytic centers for the ammonia synthesis reaction on Ta3N5via a Langmuir-Hinshelwood mechanism, which may explain the moderate production of ammonia at high temperatures. In the proposed mechanism, dinitrogen is activated in a peculiar side on a sandwich-like configuration between two surface Ta atoms. Calculation of reaction activation barriers suggests that the mechanism proceeds via moderate barriers but some elementary reaction steps involve the strong adsorption of ammonia which appears to poison the surface catalytic sites on Ta3N5.