The l-lysine-assisted synthesis of a nano-ZSM-5 zeolite as a catalyst for oleic acid pyrolysis to BTX

Abstract

A nano-ZSM-5 zeolite having a hierarchical pore structure was synthesized using L-lysine as a mesopore template and growth inhibitor. The effects of the L-lysine/Si and Si/Al molar ratios on the morphology and pore structure of the zeolite were studied. The products were characterized by scanning electron microscopy, transmission electron microscopy and N₂-Brunauer–Emmett–Teller surface area analysis. These assessments showed that the particle size of the ZSM-5 zeolite could be reduced to 60 nm with a surface area as high as 395 m² g⁻¹ and a high density of mesopores. These zeolites were applied to the catalytic pyrolysis of oleic acid in a fixed-bed reactor to generate benzene, toluene and xylenes (BTX). At a reaction temperature of 500 °C, the catalyst having L-lysine/Si and Si/Al ratios of 0.4 and 30, respectively, gave a BTX yield of 27.4 wt%. This yield decreased with increases in the Si/Al ratio whereas varying the L-lysine/Si ratio did not produce a specific trend. The spent catalyst was characterized by thermogravimetric analysis and exhibited superior anti-coking ability and longer catalytic lifetime compared with a standard ZSM-5 zeolite.