Effect of NaOH post-treatment on the catalytic performance of hierarchical Hβ zeolites in the pyrolysis of lignin

A series of hierarchical Hβ zeolites were prepared by using NaOH post-treatment methods, viz., desilication under alkaline conditions; the effect of NaOH concentration on the catalytic performance of hierarchical Hβ zeolites in the pyrolysis of lignin was investigated. The results illustrated that with the increase of NaOH concentration up to 0.2 mol/L, the amount of mesopores in the hierarchical Hβ zeolites is increased, accompanying with a significant increase in the yield of liquid products for the lignin pyrolysis over Hβ zeolites. By the alkaline treatment with a NaOH concentration lower than 0.5 mol/L, the microporous structure of hierarchical Hβ zeolites remains basically intact and over them a good deoxidation effect is observed for the lignin pyrolysis; the product is mainly composed of aromatic hydrocarbons and the yield of oxygenates is always less than 3%. However, if the NaOH concentration for post-treatment is further increased to 1 mol/L, the microporous structure of Hβ zeolites is substantially destroyed, leading to a decrease in the yield of liquid products for lignin pyrolysis as well as a poor deoxidization effect.