Valorization of lignin to phenols over highly dispersed NiRu/Al2O3 without extra H2: Effect of reaction conditions and insight into the resulting phenols distributions

Valorization of lignin to value-added chemicals is attractive and exploiting highly active catalyst is vital. In our recent work, a highly dispersed and active NiRu/Al2O3 catalyst was prepared based on layered double hydroxide. Herein, the effect of reaction conditions on NiRu/Al2O3 catalytic hydrogenolysis of enzymatic hydrolysis lignin (EHL) with isopropanol and the composition of the resulting soluble portion (SP) were well examined. The results show that high dispersion and strong interaction between Ni and Ru benefit hydrogenolysis of EHL for producing phenols. The maximum SP yield was obtained at 220 degrees C for 4 h. Meanwhile, SP acquired at the optimum con-ditions exhibits the lowest molecular masses and highest monomers/dimers content. Comparing with SPnon, the yield of monomeric phenols in SPcat increased to double (38.1 %). The phenols in SPs were further analyzed with a Fourier transform ion cyclotron resonance mass spectrometer. More lowly condensed phenols with less oxygen atoms were detected in SPcat than in SPnon. The results suggest that hydrogenolysis and deoxygenation were significantly promoted with NiRu/Al2O3, which was also verified by 2D HSQC NMR analysis.

Automated summary

In this study, a highly dispersed and active NiRu/Al2O3 catalyst was prepared using layered double hydroxide for the hydrogenolysis of enzymatic hydrolysis lignin (EHL). The results showed that the strong interaction between Ni and Ru promoted the hydrogenolysis of lignin, leading to the production of more monomeric phenols. The soluble portion obtained under the optimal conditions had lower molecular masses and higher content of monomers/dimers.