Catalytic role of biochar surface groups in phenol formation from lignin pyrolysis: Experimental and DFT insights

Biomass fast pyrolysis offers a promising route to biofuels and chemicals, yet its byproduct, biochar, remains an underutilized catalyst. Using vanillyl alcohol as a lignin model, we tailored biochar surfaces via KOH, CO₂, and HNO₃ activation. Characterization by XRD, XPS, FTIR, Raman, and EPR unveiled synergy between carbon-centered radicals and hydroxyl groups driving catalysis. Catalytic pyrolysis boosted monophenol selectivity to 35.4 % through defect-mediated radical stabilization. In situ SVUV-PIMS identified 4-methyl-2-hydroxyphenoxyl as a key intermediate, while non-catalytic pyrolysis favored methoxy derivatives (68.2 %), with catalytic reactions yielding methyl-phenols. DFT calculations revealed cooperative catalysis on zigzag edges: carbon radicals stabilize intermediates (−29.8 kcal/mol adsorption energy), and hydroxyls enable hydrogen transfer (ΔG‡ = 41.1 kcal/mol). This synergy informs a sustainable biochar catalyst design, harnessing zigzag edge activity for efficient phenolic production in biorefining.