The increasing demand for renewable chemicals and fuels requires the exploitation of alternative feedstock to replace petroleum-derived chemicals and fuels. Lignocellulosic biomass has been considered as the most promising feedstock for the production of sustainable biofuels. Catalytic fast pyrolysis (CFP) is more amenable to directly converting biomass into high quality biofuel. However, even in the presence of a highly efficient catalyst, the CFP of biomass can solely manufacture a low yield of aromatic hydrocarbon but a high formation of coke. The addition of a hydrogen-rich co-reactant (e.g. waste plastics) in CFP can significantly improve the yield of aromatics and lower the coke formation. Catalytic co-pyrolysis can also reduce the disposal of waste polymers (plastics and waste tires) in landfills, solve some environmental issues, and further increase energy security. In this regard, this article reviews the catalytic co-pyrolysis process from several points of view, starting from feedstock characteristics and availability, current understanding of the chemistry in non-catalytic co-pyrolysis, and focusing on the chemistry in the catalytic co-pyrolysis of biomass with various categories of polymers. Recent progress in the experimental studies on both the non-catalytic pyrolysis and catalytic co-pyrolysis of biomass with polymers is also summarized with the emphasis on the liquid yield and quality. In addition, reaction kinetics and several outlooks in the light of current studies are also presented in the review. Consequently, this review demonstrates both highlights of the remarkable achievement of catalytic co-pyrolysis and the milestones that are necessary to be garnered in the future.

The focus of this study is to investigate the influences of biochar as a catalyst in biomass pyrolysis and bio-oil upgrading. The biochar catalyst enhanced the syngas and improved the bio-oil quality in biomass pyrolysis. The high concentrations of phenols (46 area%) and hydrocarbons (16 area%) were obtained from torrefied biomass catalytic pyrolysis over biochar catalysts. High-quality syngas enriched in H₂, CO, and CH₄ was observed. The amounts of H₂ and CO in syngas were up to 20.43 vol% and 43.03 vol% in raw biomass catalytic pyrolysis, and 27.02 vol% and 38.34 vol% in torrefied biomass catalytic pyrolysis. Thermal gravimetric (TG) analysis showed that the raw and recycled biochar catalysts had good thermal stability. Upgraded bio-oil was dominated by phenols (37.23 area%) and hydrocarbons (42.56 area%) at high biochar catalyst loadings. The biochar catalyst might be used as a cost-competitive catalyst in biomass conversion and bio-oil upgrading.