Catalytic role of assembled Ce Lewis acid sites over ceria for electrocatalytic conversion of dinitrogen to ammonia

Abstract

CeO2-based catalysts are emerging as novel candidates for catalyzing nitrogen reduction reaction (NRR). However, despite the increasing amount of experimental and theoretical research, the design of more efficient ceria catalysts for NRR remains a challenge due to the poor knowledge of the catalytic mechanism, particularly the nature of the active sites and how they catalyze NRR. Here, using first-principle calculations, we investigated the NRR catalysis process involving adjacent Ce Lewis acid clusters formed on (111), (110), and (100) facets of CeO2 as active sites. Our results revealed that the assembled structures of the Ce Lewis acid as active centers after the oxygen vacancies (Ovs) were opened. The exposed Ce sites on CeO2(111), CeO2(110), and CeO2(100) can cause N2 to be adsorbed in a “lying-down” manner, which facilitates the N2 activation and thus leads to much higher NRR activity. Furthermore, from the perspective of electronic structure, we establish two useful descriptors for assessing the NRR activity on ceria with Ovs: The N–N bond strength of the adsorbed N2 and the adsorption energy of the *N2H intermediate. This work thus provides direct guidance for the design of more-effective oxide catalysts without the use of scarce metals.