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.　©　2021　Science　Press