CO-Tolerant Ru-Oxide Catalysts for NEC Hydrogenation under Unpurified Hydrogen: Role of Metal–Support Interactions and Effective Oxygen Vacancies

Developing CO-tolerant hydrogenation catalysts is critical for realizing one-step hydrogen purification and storage via liquid organic hydrogen carriers (LOHCs) using crude hydrogen. Herein, a series of Ru-based catalysts supported on oxides with varying reducibility (TiO2, Al2O3, ZrO2, and CeO2) were systematically investigated for N-ethylcarbazole (NEC) hydrogenation under CO/H2 mixed gas atmospheres. The results demonstrate that NEC hydrogenation can proceed in CO/H2 mixed gas primarily because CO is continuously consumed via methanation, which effectively mitigates its inhibitory effect on the hydrogenation reaction. A complex interplay of competition and synergy between CO conversion and NEC hydrogenation is further revealed. Mechanistic analysis reveals that metal–support interactions and the concentration of effective oxygen vacancies, which are surface-accessible and dynamically regenerable sites that can continuously participate in the reaction, are key descriptors governing the CO-tolerant NEC hydrogenation performance. Among them, 2Ru–TiO2 exhibited the best CO-tolerant NEC hydrogenation performance, primarily attributed to the moderate metal–support interaction and the highest concentration of effective oxygen vacancies, achieving over 90% degree of hydrogenation (DOH) within 4 h in the presence of 2% CO. This work establishes a structure–function framework for designing CO-tolerant catalysts for direct hydrogen storage from unpurified hydrogen, with broad implications for LOHC and other CO-sensitive catalytic systems.