Microwave-induced biomass pyrolysis coupled with hydrothermal char composites catalysis to selectively prepare phenols-rich liquid products

[Display omitted] •Biomass-derived hydrothermal char coated with metal nanoparticles were synthesized.•The composites exhibit both high microwave heating behavior and catalytic activity.•The catalysts achieved a rapid heating rate of 5.49 °C/s by microwave heating.•HCM-Co achieved a high liquid yield of 38.4 % at 500 °C.•The phenolic compounds reached a high relative content of 54.9%. In this study, three types of hydrothermal char-supported metal nanoparticle composites (HCM-Fe, HCM-Co, and HCM-Ni) were prepared using pinewood as the raw material via an ion hydrothermal pretreatment followed by microwave heating method, which were then served as both catalysts and microwave absorbers to enhance the rapid pyrolysis of pine wood particles for the selective preparation of phenols-rich bio-oil. The combined effects of hydrothermal carbonization and microwave heating enriched the pore structure of the composite surface, yielding ordered carbon structures such as carbon microspheres, carbon nanotubes, and graphite layers. Also, metal nanoparticles were generated and uniformly anchored on the hydrothermal char matrix by the graphite layers. The three types of hydrothermal carbon-based catalysts exhibit excellent microwave absorption performance, facilitating rapid heating of pine particles at a rate as fast as 5.49 °C/s. Among these catalysts, HCM-Co demonstrates the best catalytic performance, efficiently promoting the cleavage of the β-O-4 bond in lignin and achieving a liquid product yield of 38.4 % at 500 °C. The resulting bio-oil is characterized by its richness in phenolic compounds, accounting for 54.9 % of its composition, and partial mitigation of acidity.