Xiangyou Kong,Jinyang Zhao,Kai Huo,Ling Shi,Zhenhua Yao,Jianan Yang,Maocong Hu,Xia Li,Xuguang Liu
Alkali metal cations showed significant effects on the zeolite synthesis process as well as its structure while the mechanism is still under debate. In this work, ZSM-11 zeolites were synthesized with the addition of four alkali metal cations (Li + , Na + , K + , Cs + ). Except for different morphology and pore structure observed in the four samples, ZSM-11 synthesized with the presence of Li + demonstrated low synthesis efficiency and weak acidic properties compared to those with the addition of Na + , K + , and Cs + ions. Both DFT calculations and MD simulations were further performed to investigate the precursor reactions between silicates and aluminates as well as the polycondensation of two silicon-aluminum tetrahedral structural units. Except for the widely used factors including polarizable ability parameter ( g i ) and structural parameter ( 0 W ), two new parameters, i.e., polarizability ( α 0 ) and first hyperpolarizability ( β 0 ), were first employed as the descriptor to unravel the effects of alkali metal ion on ZSM-11 zeolite synthesis and properties. Obtained ZSM-11 samples exhibited the distinct catalytic performance for benzene alkylation with ethanol, which was attributed to the different structure and acidity properties. This work provides new insights into the deep understanding of the effects of alkali metal cations on zeolite synthesis in a closely mechanistic view.
Meng Li,En-Hui Yuan,Weijiong Dai,Yan Wang,Anning Zhou,Zhong-Wen Liu
Rapid and precise crystallization of zeolites with targeted topologies remains a significant challenge. Herein, we report a facile strategy for synthesizing ZSM-11 within 12 h by introducing cationic poly(dimethyl diallyl ammonium chloride) (PDDA) into the precursor gels. This approach achieves an 80-fold acceleration versus conventional methods while yielding nanosized crystals with hierarchical pore architectures. We demonstrate that unique confined nano-interfaces/nano-microenvironment formed via electrostatic assembly of cationic PDDA and negatively charged silica precursors facilitate enrichment of crystallization nutrients, e.g. tetrabutylammonium hydroxide, water, and silica/alumina species. This unique confined nano-interfaces/nano-microenvironment promotes in-situ depolymerization-condensation reactions of the silica/aluminum species and shortens nutrient transport pathways, collectively accelerating nucleation and crystallization. The mechanism is further supported by the comparative experiments via changing synthesis parameters including PDDA(C 8 H 16 NCl)/SiO 2 ratio, polymerization degree of PDDA, and addition of silicalite-2 seeds. The rapidly synthesized ZSM-11 exhibits superior methanol-to-olefins (MTO) performance, demonstrating tremendously extended catalyst lifetime and high coke resistance relative to conventionally prepared counterparts. This work advances a generalizable route to efficient synthesis of zeolite catalysts.
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