Defect-engineered Ru–Co/TiO2−x catalysts for highly efficient plasma-catalytic ammonia synthesis under 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 plasma-generated 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/TiO_2−x-500 exhibited an optimal anatase–rutile heterojunction with abundant oxygen vacancies, delivering a high NH₃ synthesis rate of 15 000 μmol g_cat⁻¹ h⁻¹ and an energy efficiency of 6.38 g-NH₃ kWh⁻¹, outperforming most reported plasma catalysts. Comprehensive characterization revealed that moderate hydrogen reduction induced electron-rich Ru sites, balanced Co oxidation states, and stabilized surface hydroxyl groups, while avoiding excessive structural ordering. The OES and in-situ DRIFTS showed that the defect-rich TiO_2−x support enhanced plasma-induced N₂ excitation and stabilized key *NH_x 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 the plasma-catalyst synergy and provided guidance for the rational design of energy-efficient plasma-catalytic NH₃ synthesis catalysts.