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Bio-oil as a carbon source can be used to prepare hybrid metal@carbon material while the polymerization of which generally prevents metals from exposure. In this study, melamine was used as a structural regulating agent for preparing Co/N/C catalyst via heating the mixture of cobalt nitrate, melamine and bio-oil for hydrogenation of o-chloronitrobenzene (o-CNB). The results showed that the Co species was encapsulated in the carbon structure from cross-polymerization of melamine and bio-oil at 600 °C. The further heating to 900 °C led to decomposition of melamine-derived substance, and meanwhile cobalt oxide was reduced and confined in the resulting carbon structure. The formed metallic Co catalyzed the growth of long carbon nanotube with cobalt on the tip, forming the Co/N/C catalyst of higher specific surface area (128.2 m2/g) and metallic Co dispersion (3.7%), rendering the superior activity for hydrogenation of o-CNB with the yield of o-chloroaniline up to 90.2%. The encapsulation or exposure of Co species was closely related to relative ratio of bio-oil and melamine in the catalyst precursors. Additionally, leaching of cobalt, due to dechlorination of o-CNB, was found to be an issue of Co/N/C catalyst but not for that of Ni/N/C catalyst. [Display omitted] • Heating mixture of CoNO 3 , bio-oil and melamine produces pin-like Co/N/C catalyst. • Bio-oil acts as a source of carbon skeleton to confine Co from aggregation. • Complexation with Co is essential for dispersion of Co in Co/N/C. • Balance of bio-oil and melamine determines exposure and access of metallic Co. • Catalyst obtained at 900 °C minimizes Co encapsulation, rendering superior activity. [ABSTRACT FROM AUTHOR]