Jump to main content
Jump to site search


Deleterious effects of non-framework Al species on the catalytic performance of ZSM-5 crystals synthesized at low temperature

Author affiliations

Abstract

ZSM-5 is one of the most widely studied and commercially relevant zeolites. It is also one of the few zeolites that can be synthesized in an all-silica form (silicalite-1), and thus serves as a prototype for mechanistic studies of zeolite crystallization. The MFI framework of ZSM-5 is amenable to a broad range of synthesis conditions, which has led to numerous discoveries of materials with unique physicochemical properties. The exceptional performance of ZSM-5 among zeolite catalysts, coupled with its facile synthesis, has given rise to its widespread use in industrial applications. In this study we highlight the challenges associated with synthesizing ZSM-5 at low temperature (ca. 100 °C), which is often necessary to generate small crystals (<200 nm) with an appreciable quantity of acid sites (i.e. Si/Al < 25). We focus on the incorporation of non-framework Al, which includes extra-framework (octahedral) Al and penta-coordinated Al, as well as Al zoning – a common phenomenon where the density of Al sites within the framework is more prevalent at the outer rim and exterior surfaces of ZSM-5 crystals. We show that synthesis at low temperature, and most notably in growth mixtures containing high aluminum concentration, results in the incomplete incorporation of Al into the ZSM-5 framework that can be partially removed through post-synthesis mild acid treatment. We also show that higher synthesis temperature (170 °C) facilitates the incorporation of framework Al; however, in all cases the catalysts prepared in this study exhibit relatively low activity owing in part to the presence of Al defects. The library of ZSM-5 catalysts prepared herein are characterized using methanol to hydrocarbons as a benchmark reaction to assess the performance of various as-made and acid treated samples. Our findings suggest that ZSM-5 may be more difficult to synthesize than is commonly perceived, most notably when examining the various types of defects in crystalline products over a wide range of synthesis conditions.

Graphical abstract: Deleterious effects of non-framework Al species on the catalytic performance of ZSM-5 crystals synthesized at low temperature

Back to tab navigation

Supplementary files

Publication details

The article was received on 08 Jun 2019, accepted on 19 Jul 2019 and first published on 19 Jul 2019


Article type: Paper
DOI: 10.1039/C9RE00231F
React. Chem. Eng., 2019, Advance Article

  •   Request permissions

    Deleterious effects of non-framework Al species on the catalytic performance of ZSM-5 crystals synthesized at low temperature

    W. Qin, Y. Zhou and J. D. Rimer, React. Chem. Eng., 2019, Advance Article , DOI: 10.1039/C9RE00231F

Search articles by author

Spotlight

Advertisements