Catalytic depolymerization of lignin by metal and metal oxide: a review

Lignin, with its rich reserves of phenolic compounds, holds great promise as a candidate for renewable energy and valuable chemical production. However, the complex molecular structure and low reactivity of lignin have impeded progress in this research direction. Consequently, the depolymerization of lignin into high-value small-molecule chemicals has become a new area of focus. Metal and metal oxides have emerged as a promising catalyst to overcome this obstacle due to their high selectivity in depolymerizing lignin and the mild reaction conditions required. This paper reviews the properties, and products of various metal and metal oxides used for lignin depolymerization under microwave, pyrolysis, hydrogenolysis, and oxidation conditions. The research prospects and challenges of metal oxide degradation of lignin are summarized to pave the way for future applications and development of lignin depolymerization.