Selective biomass photoreforming for valuable chemicals and fuels: A critical review

Abstract

Biomass photoreforming represents an attractive and promising approach to produce renewable and sustainable chemicals and fuels. A growing number of investigations aim to selectively attain valuable chemicals and high-quality fuels from the abundant biomass via UV/visible-light-driven photocatalysis. However, a cost-effective conversion process for biomass valorization to selective production of valuable chemicals and fuels is still difficult to achieve. This review mainly focuses on photocatalyst development and the effect of experimental conditions for selectivity enhancement of heterogeneous photocatalytic transformations. Photocatalyst development with high selectivity aims to avoid the formation of highly oxidative radicals such as •OH that are widely regarded as nonselective species. Electronic band structure and photochemical properties can be tailored to regulate the reaction pathway and selectively produce the desired chemicals via morphology modification, doping, co-catalyst metal loading, and the formation of special crystal facets and phase. The reaction conditions, such as solvent, pH, atmosphere, influence the interaction between photocatalyst and substrate, reaction kinetics, and the solubility of reactive species. The optimization of external factors can improve the reactivity and selectivity. In addition, the utilization of protection chemicals could effectively prevent the formation of destructive radical species and the mineralization of preferred products, thus enhancing the selectivity and productivity. This review provides insights into the photocatalytic upgrading of various biomass substrates to fine chemicals and fuels with an attempt to elucidate the mechanisms involved in the process of biomass photoconversion. Future perspectives and challenges for selective production of valuable chemicals and fuels from biomass photo-upgrading are discussed.