From Lignocellulosic Residues to Reusable Biochar Catalysts: Stability, Regeneration, and Closed-Loop Biorefinery Integration

Residue-derived biochar catalysts can couple catalyst manufacture with biomass valorization, but renewable origin does not guarantee catalytic superiority, durability, or circularity. This critical review examines reusable biochar catalysts and catalyst supports from lignocellulosic residues across biodiesel synthesis, catalytic pyrolysis, tar reforming, hydrodeoxygenation, and platform-chemical production. It focuses on the limits of feedstock–process correlations, the distinction between biochar as catalyst and as support, the strength of active-site evidence, and the effects of deactivation, regeneration, shaping, and material loss. A 23-case quantitative benchmark shows that catalyst loading and repeated-use performance are reported more often than recovered dry mass, cycle-resolved elemental balances, or continuous validation. Closed-loop metrics are defined for catalyst yield, cumulative productivity, regeneration efficiency, elemental retention, water and chemical intensity, and carbon efficiency. The strongest case for residue-derived catalysts is therefore an integrated material loop with measured durability and resource balances, not feedstock origin or surface area alone.