A review on catalytic pyrolysis for high-quality bio-oil production from biomass

Biomass is a renewable source and potentially sustainable fossil fuel replacement due to its availability, lower processing cost, high conversion, and lower life cycle carbon emissions. Pyrolysis can be used to convert biomass into bio-oil, but the quality of bio-oil is usually poor exhibiting high viscosity, thermal instability, and corrosiveness. This review article is focused on the application of catalytic pyrolysis towards obtaining high-quality bio-oil and advanced techniques for bio-oil characterisation. Structural arrangement (i.e., mesoporous, microporous), number of acid sites (Lewis and Bronsted acid sites), and amount of metal loading play a key role on deoxygenation reactions and selective production of aromatic hydrocarbons. Hierarchical zeolites doped with noble metals favour hydrogenation of C-O or C=O and reduce coke deposition in the production of polycyclic aromatics. Overall reaction mechanisms, aromatic yield and selectivity, the effect of Si/Al ratio, and process challenges of metal loaded zeolites are summarized. The advantages and disadvantages of different types of advanced analytical techniques for bio-oil characterisation are also discussed. The results showed that two-dimensional gas chromatography (2D GC) technique can identify 70% of chromatograph from bio-oil analysis. However, there is need to combine analytical techniques to accurately quantify bio-oil components.