Material Engineering of Cu⁰/Cu⁺ Sites and Oxygen Vacancies for Efficient In Situ Hydrodeoxygenation of Lignin-Based...

The synthesis of value-added chemicals from lignin has gained much attention in recent years. However, despite the extensive use of noble metal-based catalysts and high-pressure hydrogen, the hydrodeoxygenation (HDO) of lignin derivatives is still challenging. In this work, non-noble metal-based heterogeneous catalysts derived from layered double hydroxide have been explored for HDO reaction without molecular hydrogen. A series of CuMgAl (CMA) catalysts has been studied, wherein CMA1.5 catalyst shows a high catalytic activity for HDO of vanillin with 100% conversion and 87% yield of 4-methyl-2-methoxyphenol (MMP) within 30 min at 180°C in isopropyl alcohol. The detailed investigations show that superior catalytic activity is attributable to synergistic role of Cu⁰/Cu⁺ ratio, acidic-basic sites, and oxygen vacancies (O_v). Furthermore, density functional theory studies and various control reactions confirm the reaction mechanism, role of O_v, acidic and basic sites for HDO of vanillin. In addition, catalyst shows excellent activity for various other lignin derivatives, demonstrating its broad substrate scope. The catalyst also exhibits excellent productivity (49.71 mmol_MMP g_cat ^-1 h^-1), superior to earlier reports. Hence, this work can pave the way toward a green and sustainable catalytic transfer HDO of lignin derivatives to value-added chemicals within short reaction times.