Modulating the acidity and accessibility of HZSM-5@Al-KIT-6 catalysts for the tandem catalytic upgrading of lignin pyrolysis vapors

In this paper, a surface encapsulation method has been developed to synthesize the HZSM-5 @Al-KIT-6 hierarchical zeolites, due to the poor mono-aromatic hydrocarbons (MAHs) selectivity and rapid coke deactivation during the catalytic upgrading lignin pyrolysis vapors. Results showed that the acidity and accessibility of HZSM-5 @Al-KIT-6 hierarchical zeolite can be modulated by changing the TEOS/HZSM-5 mass ratio during catalyst synthesis. The three-dimensional (3-D) cubic mesoporous shell can capture the bulky phenolic oligomers and pre-crack for further reforming. The highest MAH content (44.03%) and lower polycyclic aromatic hydrocarbons (PAHs) (23.79%) were produced when the TEOS/HZSM-5 mass ratio was 1.0. The hierarchical zeolites improved the yield of xylenes due to the enhanced alkylation reaction. In addition, the micro-mesoporous highway reduced the formation of coke deposition. The catalytic mechanism of hierarchical zeolites was then proposed based on the obtained results. This study provides a reference for pilot-scale experiments for the catalytic upgrading lignin pyrolysis vapors.