Advanced biomass pyrolysis: Bio-oil upgrading and nanostructured carbon materials – A bibliometric and critical review

Pyrolysis is one of the most effective thermochemical routes for converting renewable biomass into high-value products, including bio-oil, syngas and biochar. This review synthesizes recent advances in pyrolysis mechanisms, with specific focus on how operating conditions (temperature, heating rate, residence time, catalysts and feedstock properties) govern the yield and quality of products. Bio-oil remains the most versatile output, yet its high oxygen content (45–50 wt%), instability and low energy density require upgrading. A bibliometric analysis reveals a strong and continuous increase in scientific output related to bio-oil upgrading, reflecting growing industrial interest. State-of-the-art strategies are critically discussed, including hydrodeoxygenation (HDO), catalytic cracking, and solvent fractionation. The hydrodeoxygenation process achieves oxygen removal efficiencies up to 90–93%, reducing oxygen content from 44 wt% to below 20 wt% and increasing higher heating values to 41–44 MJ kg −1 . The emerging use of bio-oil as a precursor for advanced carbon nanostructures is also highlighted. Bio-oil derived porous carbons exhibit specific surface areas exceeding 2500 m 2 g −1 and carbon yields up to 45%, demonstrating strong potential for energy storage and catalytic applications. Porous carbons, carbon nanotubes, and graphene-like materials are now obtained via pyrolytic carbonization, hydrothermal treatment or chemical activation, showing promising performance in energy storage, catalysis and environmental remediation. Overall, this review positions pyrolysis as a dual platform: enabling bio-oil upgrading for energy applications and generating high-value carbon materials, in line with circular bioeconomy concepts.