Synthesis and performance of pillared HZSM-5 nanosheet zeolites for n-decane catalytic cracking to produce light olefins

Abstract

Owing to the hierarchical porosity and proper acid site, nanosheet ZSM-5 zeolite (ZN-2) has been reported good performance for catalytic cracking of hydrocarbons, but faces mesopores sacrifice by interlayer condensation after calcination during preparation. In this work, two pillared nanosheet HZSM-5 zeolites were successfully synthesized to stabilize the hierarchical structure between nanosheet layers, by dual-template ([C22H45N(CH3)2C6H12N(CH3)2C6H13]Br2 and tetrapropylammonium hydroxide) method and Si-precursor (tetraethylorthosilicate) intercalation. Dual-template strategy (DZN-2) was demonstrated preserving more mesopores between individual nanosheet with better channel connections than Si-intercalation method (PZN-2). Effects of pillared structure on catalytic activity, light olefins selectivity as well as catalytic stability for n-decane catalytic cracking were systematically investigated. The uniquely pillar-designed structure facilitated diffusion of product and restricted the secondary reaction such as hydride transfer or aromatization which consumed light olefins (including ethylene, propylene and butene). DZN-2 catalyst gave the highest light olefins selectivity up to 37.8% at 500 °C compared with PZN-2 and the parent ZN-2, with n-decane conversion of ca.92%. PZN-2 prepared by Si intercalation also exhibited a higher light olefin selectivity of 28.2% than ZN-2 (21.2%), whereas a lower conversion ascribing to the decreased Brønsted acidity with the introduction of Si-pillars. Moreover, DZN-2 displayed an outstanding anti-coking stability with deactivation rate (rd) of only 0.88 during 16 h test at 500 °C, ascribing to the facilitated diffusion of coke precursors.