Ethanolysis of enzymatic hydrolysis lignin with Ni catalysts on different supports: The roles of catalytic sites

Catalytic lignin solvolysis (CLS) holds promise for efficient lignin utilization, yielding small molecules with minimal or no char formation. However, the role of different active sites of catalyst in CLS are rarely discussed. Here, Ni catalysts on different supports, i.e., SiO₂, Al₂O₃, MgO, and ZrO₂, were prepared with the aim of manipulating the relative importance of metal and acid-base functionalities to investigate the role of different active sites in the enzymatic hydrolysis of lignin (EHL) ethanolysis. The main ether linkage, i.e., β-O-4, in EHL is cleaved without the participation of a catalyst. Metal sites suppress repolymerization through hydrogenating active intermediates, while acid and base sites facilitate the conversion of phenolic monomers into complex alkylated and etherified products and also promote repolymerization reactions. Among the catalysts, Ni/SiO₂ demonstrated the highest hydrogenation activity and yielded the most monomers (24.7 wt %) at 280 °C for 6 h under 2 MPa H₂ in ethanol. These findings shed light on the catalytic mechanisms in CLS, offering valuable insights for future catalyst design.