Biochar: From by-products of agro-industrial lignocellulosic waste to tailored carbon-based catalysts for biomass thermochemical conversions

• This review is structured around the theme of biochar catalysts/catalyst supports. • Synthesis of application-oriented catalysts for biorefinery reactions is discussed. • Agro-industrial lignocellulosic waste is feedstock. • Thermochemical methods are the main synthesis methods. • Pore size/surface area/mineral content are main factors affect catalytic ability. Producing chemicals and energy from renewable biomass is critical in tackling the energy crisis. As a by-product of biomass conversion, biochar with its low price, extensive sources, has attracted much attention in fields such as environment, agriculture, materials, energy, and so on. However, many studies of biochar have been focused on its application in the environmental remediation field, little attention has been put on biochar as catalyst or catalyst support. Nevertheless, biochar has a promising application as a carbon-based catalyst and catalyst support due to its huge specific surface area (SSA), rich functional groups, and complex network structure. Besides, the introduction of biochar as catalysts favorably increases the economic benefits of biomass conversion processes. This review focuses on the biochar synthesis from agricultural and forestry waste as carbon-based catalysts and catalyst support, and their applications, especially in biorefinery. By reviewing the formation mechanism, catalytic mechanism, synthesis conditions, modification of biochar catalyst or catalyst support, and its applications, we aim to offer instructions for producing application-oriented biochar catalysts and catalyst supports for thermochemical reactions in biorefinery.