Controlled Construction of Hierarchical ZSM-5 Zeolite with Highly Dispersed Surface-Metals for Catalytic Cracking of <i>n</i> -Pentane to Light Olefins

This study developed a hierarchical ZSM-5 zeolite supporting highly dispersed Pt–Zn bimetallic catalysts for cracking of naphtha to produce light olefins. Acid treatment was employed on presynthesized highly acidic hierarchical ZSM-5 zeolite (Si/Al = 20) to create surface defects. The residual structure-directing agents anchored metal precursors. After calcination and reduction, high dispersion of metal on the surface of the hierarchical ZSM-5 was achieved. In the cracking of n-pentane, the Pt–Zn alloy catalyzes the dehydrogenation of n-pentane to form pentene, which subsequently undergoes cracking at the Brønsted acid sites of the zeolite to produce ethylene and propylene. At 600 °C, the Pt–Zn/NC-Aci catalyst yields of ethylene and propylene of 31.5% and 40%, respectively. Furthermore, the dehydrogenation-cracking pathway effectively suppresses secondary aromatization and polymerization among olefin molecules. The synthesized catalyst exhibits a deactivation rate of only 8.1% after 16 h of reaction at 600 °C.