Dissociative and Associative Concerted Mechanism for Ammonia Synthesis over Co-Based Catalyst

摘要

The current catalytic reaction mechanism for ammonia synthesis relies on either dissociative or associative routes, in which adsorbed N_2 dissociates directly or is hydrogenated step-by-step until it is broken upon the release of NH_3 through associative adsorption. Here, we propose a concerted mechanism of associative and dissociative routes for ammonia synthesis over a cobalt-loaded nitride catalyst. Isotope exchange experiments reveal that the adsorbed N_2 can be activated on both Co metal and the nitride support, which leads to superior low-temperature catalytic performance. The cooperation of the surface low work function (2.6 eV) feature and the formation of surface nitrogen vacancies on the CeN support gives rise to a dual pathway for N_2 activation with much reduced activation energy (45 kj·mol~(-1)) over that of Co-based catalysts reported so far, which results in efficient ammonia synthesis under mild conditions.