Defect-engineered Ru-Co/TiO2-x catalysts for highly efficient plasma-catalytic ammonia synthesis at ambient conditions

Abstract

Plasma-catalytic ammonia synthesis offers a promising route toward decentralized and sustainable NH3 production under mild conditions. However, its efficiency remains limited by insufficient nitrogen activation and poor utilization of plasmagenerated species. Herein, we reported a systematic support-engineering strategy to regulate the electronic structure and interfacial properties of Ru-Co catalysts via hydrogen pre-reduction of TiO2 at different temperatures. Among the investigated catalysts, Ru-Co/TiO2-x-500 exhibited an optimal anatase-rutile heterojunction with abundant oxygen vacancies, delivering a high NH3 synthesis rate of 15,000 μmol•gcat -1 •h -1 and an energy efficiency of 6.38 g•kWh -1 , outperforming most reported plasma catalysts. Comprehensive characterization revealed that moderate hydrogen reduction induced electronrich Ru sites, balanced Co oxidation states, and stabilized surface hydroxyl groups, while avoiding excessive structural ordering. The OES and in-situ DRIFTS demonstrated that the defect-rich TiO2-x support enhanced plasma-induced N2 excitation and stabilized key * NHx intermediates, thereby promoting stepwise hydrogenation toward NH3. These results established a clear structure-activity relationship in which oxygen vacancies, heterojunction-induced charge separation, and Ru-Co interfacial synergy collectively governed nitrogen activation and hydrogen transfer under plasma conditions. This work highlighted defect-engineered oxide supports as an effective platform for maximizing plasma-catalyst synergy and provided guidance for the rational design of energy-efficient plasma-catalytic NH3 synthesis catalysts.