Catalyst-free valorization of biomass resources to value-added products

The development of a sustainable and green system to utilize biomass resources will be an exemplification move in delivering the global goal of a sustainable economy and environment. Herein, for the first time, we review the research on the catalyst-free valorization of abundant and renewable biomass to high-value bio-based chemicals and fuel. The catalyst-free strategy is proving to be superior to catalyst-assisted methods, especially in simple, low-infectant, low-cost methods, which is very attractive for potential industrial applications. Various biomass conversion routes based on catalyst-free systems and their corresponding reaction mechanisms, including valorization of lignin and cellulose to useful monomers and polymeric products, production of biodiesel via transesterification, and conversion of platform molecules to value-added compounds, are discussed. Moreover, the opportunities and challenges in the development of catalyst-free biomass conversion are proposed preliminarily. This review on the catalyst-free valorization of biomass resources is intended to spark the interest of the sustainable chemical community. An overview on the catalyst-free conversion of biomass resources into value-added products is provided. Significantly, the opportunities and challenges in the development of catalyst-free biomass conversion are proposed preliminarily.