Toward rational design of narrowly-distributed mesopore on ZSM-22 zeolite for enhanced Pt dispersion and n-alkane isomerization performance

Abstract

In present work, the narrowly-distributed intracrystalline mesopore was rationally designed and developed on ZSM-22 zeolites via a controllable desilication route. The intracrystalline mesoporosity with a diameter distribution in the range of 2.9, 4.3 and 9.3 nm were precisely exposed on ZSM-22 zeolite due to the stability effect of surfactant on the NaOH-leached structure. Importantly, the controllable desilication not only exposed Brønsted acid sites and preserved the original framework but also enhanced the dispersion and aggregation resistance of Pt particles in bifunctional catalysts through providing confined mesopore space and defect sites for the anchoring of Pt sites. All desilicated catalysts exhibited higher isomerization yield in n -dodecane isomerization in comparison to the purely microporous Pt/ZSM-22 catalyst. Moreover, compared to the conventionally desilicated catalyst with broadly distributed mesopore, well-balanced bifunctional behavior and much higher selectivity of multi-branched isomers were achieved on the controllably-desilicated catalyst with optimally narrow mesopore. Evidently, the highly dispersed and aggregation resistant Pt particles in the narrowly-distributed mesopores satisfied the high C Pt /C H+ ratios and high degree of intimacy between the hydrogenation and acid functions. Therefore, this work provided a detailed guidance for the rational design and fabrication of efficient catalysts for n -alkane isomerization.