The Porosity, Acidity, and Reactivity of Dealuminated Zeolite ZSM‐5 at the Single Particle Level: The Influence of the Zeolite Architecture

Abstract

A combination of atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), focused-ion-beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron-based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM-5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol-to-olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM-5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM-5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 5-50 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Brønsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity.

Styrene oligomerization as a molecular probe reaction for Brønsted acidity at the nanoscale

“…[13][14][15][16] Among the latter approaches, dealumination by steaming has become a cheap and efficient way to simultaneously modify the topological and acidic properties of zeolites. 17,18 To optimize the variation of zeolite characteristics, an in-depth understanding of the physicochemical processes that determine the catalytic properties of zeolite materials is needed. Such information can be obtained in some cases by performing a suitable probe reaction in combination with appropriate spectroscopic methods, such as UV-Vis and (confocal) fluorescence micro-spectroscopy.…”

Hydroisomerization of n-hexadecane: remarkable selectivity of mesoporous silica post-synthetically modified with aluminum

“…37,38 However, it is noteworthy to mention that in zeolite catalysis systematic characterization of the change in number and strength of acidic sites has been extremely difficult because of concomitant structural changes occurring within the zeolite. 39,40 Nevertheless, post-synthetic aluminum doping method used in this work enables more controlled design of aluminosilicate catalysts to explore the world of acid catalysis.…”

Recent Trends in Operando and In Situ Characterization: Techniques for Rational Design of Catalysts

“…One possible measure against excessive coking is to apply a dealumination process to the H-ZSM-5 crystals via postsynthesis steaming [125,126]. Dealumination leads to the formation of mesopores in the microporous zeolites and reduced Brønsted acidity [127]. The nature of the mesoporous network depends on the steaming treatment conditions.…”