Highly Efficient Ru-VO/TiO₂ Catalysts for Hydrodeoxygenation of Amides to Amines: The Promotion Effect of Monolayer...

The hydrodeoxygenation of amide to amine is one of the most important amine synthetic approaches in chemical engineering. However, low amide reactivity and poor amine selectivity remain big challenges for catalytic hydrodeoxygenation of amides. Here, Ru-VO/TiO₂ catalysts with different V/Ru atomic ratios were prepared with the sequential impregnation method. The physicochemical properties of catalysts were characterized by using XRD, Raman, TEM, CO chemisorption, NH₃-TPD, H₂-TPR, XPS, and Formamide-DRIFTS. The hydrogenation of butyramide as a model reaction was used to evaluate the catalytic performance. The butyramide conversion and butylamine selectivity varied with V/Ru atomic ratio in a volcano-type relationship, and the 2V-4Ru/TiO₂ catalyst (V/Ru atomic ratio = 1) presented the best catalytic performance (96% conversion and 82% butylamine selectivity) at 423 K with 5 MPa H₂. The catalyst was also reused five successive times without an obvious decline in either activity or selectivity, showing excellent stability. Based on characterization and evaluation results, the interaction between Ru nanoparticles (∼2 nm) and VO species promoter generated abundant Ru-VO boundary with V⁴⁺ species adjacent to oxygen vacancies (Ru-Vo-V⁴⁺). As the V/Ru atomic ratio was 1, the 2V-4Ru/TiO₂ catalyst, with monolayer dispersed VO species, presented the maximum Ru-VO boundary and showed the best catalytic activity and selectivity to amine. The monolayer dispersed VO species also minimized the catalyst surface acidity and suppressed the secondary side reaction. Moreover, the hydrodeoxygenation reaction evaluations of various amides including aliphatic primary amides and cyclic amides showed 90-99% conversion and 78-99% selectivity to corresponding amines, suggesting wide applicability of 2V-4Ru/TiO₂ catalyst. The study provides a highly efficient strategy to improve amine selectivity in the hydrodeoxygenation of amides by optimizing the interaction between metal and metal oxide promoters.