Selective Conversion of Lignin Wastes into High-Value Aromatics: Catalyst Design and Process Sustainability Evaluation

Lignin, the most abundant natural source of aromatic scaffolds, is a main byproduct or waste of the pulping industry with an annual output of 50 million tons. In this work, an efficient reductive depolymerization approach is proposed for the selective conversion of lignin waste into guaiacols. We rationally design an efficient Ru-based catalyst by creating a chemically active surface of the nitrogen-doped carbon (NC) support via dispersing single Zn metal atoms on it and then supporting the Ru nanoparticles with enhanced electronic metal-support interactions (EMSIs). The as-synthesized Ru-Zn₁/NC catalyst is used to selectively convert the lignin into guaiacols, a type of high-value aromatics, achieving a total guaiacol yield of 25% (theoretical maximum value: 26.8%) and 96% selectivity to 4-propylguaiacols. Experiments and theoretical calculation results reveal that the electronic structure and coordination microenvironment of adjacent Ru nanoparticles could be regulated via electron transfer after Zn single-atom loading, forming greatly activated Ru sites with long-term stability. The sustainability evaluation confirms that this method offers lower costs and reduced carbon emissions compared to conventional methods, highlighting the sustainability of lignin upcycling using this method. This work helps to bridge the gap between single-site catalysis and the conversion of raw lignin wastes.