Catalytic applications of biochar from organic waste and woody biomass in pyrolysis product upgrading: A comprehensive review

Biochar, a carbonaceous residue with diverse applications as a solid fuel, soil enhancer, activated carbon, and adsorbent, has recently gained prominence for its catalytic potential in various chemical transformations. Its intrinsic porosity and high mineral content make it an attractive candidate for the catalytic upgrading of biomass pyrolysis products. This review critically evaluates the properties of biochar relevant to catalysis and the strategies for tailoring these characteristics through feedstock selection, pre-treatment, activation, and modifications in pyrolysis conditions, including temperature, sweeping gas, and reactor configuration. Advances in employing biochar as a standalone catalyst and as a support for active phases, including metal oxides, are systematically assessed. Agricultural residues and animal manures emerge as the most suitable feedstocks for catalytic applications due to the high ash and mineral content of their resulting biochars. These feedstocks also exhibit abundant oxygenated functional groups, favorable for bio-oil cracking. In contrast, woody biomass yields low-ash, carbon-rich biochar with higher heating values, making it more suitable for energy applications. Sewage sludge also produces mineral-rich biochar with promising catalytic activity, though its limited availability is a constraint. This review provides practical guidelines for optimizing biochar yield and functionality, offering a roadmap for designing next-generation biochar-based catalysts. • Biochar's catalytic role in biomass pyrolysis upgrading is critically reviewed. • Feedstock choice strongly affects biochar's catalytic activity and composition. • Strategies to tailor biochar properties via pyrolysis and activation are discussed. • Biochar is evaluated as both a catalyst and support for active catalytic phases. • Practical guidelines are provided for designing biochar-based catalytic systems.