Hydrocarbons are usually formed in very low yields during fast pyrolysis of bio­mass, but can be greatly increased by using proper cracking catalysts with deoxy­genation capability [16 ] . Zeolite catalysts (such as HZSM-5, HY, etc.) are very effective to convert the highly oxygenated crude bio-oils or pyrolysis vapors to hydrocarbons which are dominated by several light aromatic hydrocarbons (ben­zene, toluene, xylene, and naphthalene) [43, 67, 70, 95, 97] . For example, in the studies performed by Adjaye et al. [4, 5], catalytic cracking of the crude bio-oil by HZSM-5 catalysts obtained a organic liquid product with up to 90 wt% of aromatic hydrocarbons, and the aromatic hydrocarbons contained abundant toluene (31.8 wt%) and xylene (33.1 wt%).

Other catalysts were also investigated for the production of light aromatic hydro­carbons. For example, Wang et al. [94] reported that catalytic pyrolysis of biomass using CoMo-S/Al2O3 catalyst produced the four light aromatic hydrocarbons (ben­zene, toluene, xylene, and naphthalene) with the yield reaching 6.3 wt% at 590°C.