Excellent catalytic performance over hierarchical ZSM-48 zeolite: Cooperative effects of enhanced mesoporosity and highly-accessible acidity

Abstract

Hydroisomerization has been considered as an effective and efficient route for production of transportation fuels and lubricants with superior cold-flow properties. In current work, n-hexadecane (n-C16) hydroisomerization was investigated over Pt catalysts supported on hierarchical ZSM-48, which was post-treated by multi-step procedures including alkaline-acid, acid-alkaline-acid, steaming-alkaline-acid, and fluorination-alkaline-acid leaching. This work was purposed to construct the secondary mesoporous network, enhance the accessible acid sites in hierarchical ZSM-48 zeolite, and investigate their cooperative effects on hydroisomerization performance. The results demonstrated that the microporosity and the crystallinity were preserved after the controllable leaching, coupled with more exposed accessible acidity and enhanced mesoporosity. High dispersion of Pt particles and quantitative metal-acid balance were unable to be the threats for the sequential acid-catalyzed reaction. The cooperative effects of enhanced mesoporosity and highly-accessible acidity accelerated the diffusion and promoted the proximity of metal sites and acid sites, thereby persuading the treated ZSM-48 samples to exhibit excellent activity and iso-selectivity. The i-C16 yield over Pt/ZSM-48(H) catalyst could reach around 86 wt% at conversion rates of 90 wt% with iso-selectivity of 96 wt%. However, the excessively accessible acid sites in Pt/ZSM-48(F) could induce further skeletal transformation and deteriorate the iso-selectivity, although the mesoporous structure was as well established.