Temperature regulating the directional catalytic transfer hydrogenolysis of lignin over a in situ topologically prepared NiRu/Al2O3

Abstract

Exploiting highly active heterogeneous catalysts is vital for depolymerizing lignin. Herein, a NiRu/Al₂O₃-I_T catalyst via simple in situ topological transformation of layered double hydroxide was fabricated for catalytic transfer hydrogenolysis of enzymatic hydrolysis lignin (EHL). Model compounds containing aryl ether bonds and C–C linkages can be effectively cleaved and hydrogenated, respectively over the catalyst under mild conditions, indicating the high activity. Effect of reaction temperature on NiRu/Al₂O₃-I_T catalytic performance for EHL hydrogenolysis and the resulting soluble portion (SP) composition was comparatively explored. The results exhibit that strong interaction between Ni and Ru and high dispersion of NiRu/Al₂O₃-I_T are responsible for the efficient cleavage of ether bonds in EHL. The submaximum and maximum yields of SP with high monomers/dimers contents were acquired at 210 (SP₂₁₀) and 300 °C (SP₃₀₀), respectively. Monomeric phenols detected in SP₂₁₀ accounts for 69% of total organic compounds, while considerable hydrogenated compounds were identified in SP₃₀₀. In addition, more lowly condensed oxygenates with less oxygen atoms were analyzed in SP₃₀₀ with FTICRMS, indicating that hydrogenation and deoxygenation were significantly enhanced with NiRu/Al₂O₃-I_T at higher temperature, which was also proved by ultimate and 2D HSQC NMR analyses.