• A biomass waste and CO₂ to syngas conversion platform was constructed.
• Catalytic pyrolysis promoted conversion of Styrax japonicus to syngas under CO₂/N₂.
• CO₂ suppressed coke formation on Ni catalyst.
• Synergistic effects of Ni catalyst and CO₂ substantially improved syngas generation.

This work laid emphasis on catalytic pyrolysis of Styrax japonicus to construct a biomass-to-energy conversion platform. CO₂ was particularly chosen to enhance the catalytic pyrolysis of the biomass waste, in reference to N₂-purged pyrolysis. The specific roles of CO₂ on pyrolysis of S. japonicus in line with synergistic effect of Ni-based catalysts was investigated. It was shown that CO₂ played as an oxidant for CO formation via homogeneous gas phase reaction of CO₂ with volatile organic carbons (VOCs) liberated from the thermolysis of S. japonicus. Ni/SiO₂ catalyst expedited dehydrogenation (DH) of the VOCs, resulting in significant H₂ generation and alteration of aromaticity in VOCs. Each CO₂ and Ni catalyst independently enhanced CO and H₂ formation, respectively, and their synergistic effects were shown at ≥ 600 °C. Coke deposition on the Ni/SiO₂ catalyst was confirmed after catalytic pyrolysis, while the suppression of coke formation on the catalyst surface was achieved under the CO₂ environment.