Density functional theory study on direct catalytic decomposition of ammonia on Pd (1 1 1) surface

The adsorption and step dehydrogenation mechanism of NH ₃ on Pd (1 1 1) have been studied using density functional theory (DFT) together with periodic slab models. According to the optimized structural and energetic properties, it was found that NH ₃ and N ₂ prefer to adsorb on the top site, whereas NH, N, H prefer to adsorb on the fcc site and NH ₂ prefers on the bri site. In addition, this work identified the optimum configurations for the stable co-adsorption configurations of NH _x + H, and N + N. Finally, three transition states were found for analyzing the mechanism of dehydrogenation of NH ₃ , and the N recombination reaction was also considered. The results show that NH is the most abundant intermediate on Pd (1 1 1) surface and the dehydrogenation of NH ₃ is the rate-determining step in the overall reaction. The distinct differences over Pd (1 1 1) and Pd (1 0 0) surface imply that ammonia decomposition over Pd-based catalyst is a structure-sensitive reaction.