Design and synthesis of core shells HZSM-5@MCM-41 with variable acidity and mesoporosity for lignin-catalyzed fast pyrolysis to prepare aromatics

Abstract

Zeolites are a class of catalysts with specific pore structures as well as different pore sizes, which are now widely used in various shape-selective catalytic reactions. In this paper, a uniform micro/mesoporous core–shell composite HZSM-@MCM-41 comprising zeolite was successfully prepared by coating mesoporous MCM-41 shells on nanosized ZSM-5 cores using a two-step hydrothermal method. Nanoscale ZSM-5 cores with different acidity were successfully prepared by changing the Si/Al of the initial solution of pristine ZSM-5, and three different thicknesses of MCM-41 shell layers were easily encapsulated on the surface of ZSM-5 with different acidity by varying the amount of silicon source added in the secondary hydrothermal crystallization process. The synthesized series of micro-mesoporous core–shell catalysts were also applied to the catalytic fast pyrolysis in lignin. In the catalytic fast pyrolysis of lignin, the mesoporous structure promoted the transition of biomass pyrolysis intermediate to liquid products, and the acidity of the HZSM-5 core facilitated their catalytic transformation to aromatic hydrocarbons. Among all the tested catalysts, the HZ@M-80-ll catalyst with an internal Si/Al = 80 and MCM-41 shell thickness of ∼25 nm exhibited the highest production of light aromatics and phenols.