One-step synthesis, characterization and catalytic performance of hierarchical Zn-ZSM-11 via facile ZnO routes

Abstract

Hierarchical Zn-ZSM-11 zeolite with an olive-shaped intergrowth morphology was synthesized via a novel and facile one-step hydrothermal method by using tetrabutylammonium bromide (TBABr) and zinc oxide (ZnO) as a difunctional template and zinc source, respectively. Structural characterizations (XRD, IR, TG-DTA, SEM, and N₂ adsorption–desorption) were conducted to analyze the textural properties of Zn-ZSM-11 samples. Compared with the Zn containing ZSM-11 samples prepared by other methods (ZnSO₄ method, ZnO-impregnated-seed method and impregnation method), the Zn-ZSM-11 prepared by ZnO method exhibited enriched mesopores as well as good catalytic activity in methanol conversion. TEM images showed that Zn species were well incorporated into the zeolite framework, while the different morphology of Zn-ZSM-11 from ZSM-11 further verified that the Zn species had been involved in the formation of the ZSM-11 framework. ²⁷Al and ²⁹Si MAS NMR spectra revealed that Zn species in the zeolite framework significantly impacted the coordination of Si. The XRD pattern variation of the ZnO containing gel was also tracked to illustrate the crystallization process. It was found that the ZnO would be gradually dissolved under the severely alkaline environment and subsequently incorporated into the ZSM-11 framework in the crystallization process. This facile new synthesis strategy can also be extended to prepare other Zn containing zeolites and is potentially important for practical utilization.