Selective Cleavage of Ester Linkages in Lignin Catalyzed by La-Doped Ni/MgO

Novel strategies for converting renewable lignin to bulk petrochemicals are highly desirable for achieving sustainable practices in the age of environmental awareness. Herein, we propose an efficient approach for the selective hydrogenolysis of lignin promoted by a cost-effective La3+-doped Ni/MgO catalyst. The results reveal that 84.44% lignin is converted at 270 °C for 4 h, yielding 16.50% volatile products. Importantly, approximately 43.45% of these volatile products are identified as 4-ethyl phenol (7.17% yield), an important intermediate in the fine chemical industry. Intensive analysis of the lignin before and after the reaction confirms that efficient cleavage of the ester linkages is achieved, which correlates directly with the high selectivity of 4-ethyl phenol after a readily decarboxylation reaction. Furthermore, the catalyst characterization demonstrates that La3+ suppresses the formation of a NiMgOx solid solution. Consequently, a greater degree of Ni2+ becomes reducible and the catalyst basicity becomes stronger, both of which are essential for the efficient lignin depolymerization and char reduction. As a result, a significant increase of the yield of volatile products is shown along with a substantial inhibition of biochar formation over the La-doped Ni/MgO catalyst in comparison with that without La doping. Therefore, the present work provides a new insight on producing fine chemicals via a sustainable route.