Studies on the Dual-Templating Function of TBA for the Formation of ZSM-11 Intergrowth Morphology

Abstract

Hierarchically structured ZSM-11 microspheres with an intergrowth morphology have been hydrothermally synthesized using only one organic templating molecule (TBABr). An investigation of the effects of the structure-directing agent on the zeolite particle morphology and textural properties was performed. It was found that the template tetraalkylammonium ions TBA + (or TPA + ) not only were located in the channel intersections of ZSM-11 (or ZSM-5), but were also attached to the external surface of the precursors, which prevented these precursors from further condensation. Finally, a morphology of numerous nanocrystals inserting into each other was formed, and the voids among these intergrowth crystals endowed these materials with mesoporosity.

A Remarkable Catalytic Activity of Hierarchical Zeolite (ZH‐5) for Tertiary Butylation of Phenol with Enhanced 2,4‐Di‐t‐Butylphenol Selectivity

“…Such results can be attributed to the stable interactions of organosilanes with the growing zeolitic phase not only through the Si−C bond but also with the quaternary ammonium head group (R 4 N + ) (Figure ). Such co‐templating action of organosilanes alongside the TPA + templates can result in periodic MFI/MEL intergrowths and hence the serrated outgrowths on the crystals, which is in accordance with the literature ,,. Furthermore, we have observed such type of morphologies only at lower temperatures which clearly reveal that the micellar aggregates of organosilanes are stable only under such conditions and hence can interact strongly with the inorganic zeolite phase.…”

“…Therefore, at such conditions, the organosilane interacts strongly with the zeolite not only through the silyl group but also with the quaternary ammonium cation resulting in stable hierarchical assembly, which is in accordance with literature . Although co‐templating action is commonly seen in zeolites prepared by using multiple templates, the dual‐templating nature of organosilanes as supramolecular templates to direct the mesostructure and molecular templates to encourage zeolitization has not been reported so far ,,,…”

“…Among the various strategies, desilication, nanocasting, dry‐gel conversion, recrystallization, etc., are most commonly used to synthesize hierarchical ZSM‐5 . In addition, the mesoporosity was also induced by the repetitive branching of MFI/MEL intergrowths caused by the co‐templating action of auxiliary templates ,. Although supramolecular templating has been one of the best methods to prepare mesoporous solids, the conventional surfactants have failed to construct such structures of zeolites owing to the phase segregation ,.…”

Hydrocarbon-Rich Bio-Oil Production from Catalytic Pyrolysis of Biomass over the Undervalued ZSM-11 Zeolites

“…That is, while ZSM-11 with lower Si/Al ratios (SAR = 30, 40, and 50) features loose-stacking nanorods with a size of ∼40 nm, those with higher Si/Al ratios (SAR = 100, 200, and ∞) are separate rugbylike crystals (∼100 nm). Such a morphological variation was attributed to the multiple functions of TBA + cations . First, the positive TBA + balanced the negative framework charges caused by Al 3+ substitution for Si 4+ .…”

“…Such a morphological variation was attributed to the multiple functions of TBA + cations. 21 First, the positive TBA + balanced the negative framework charges caused by Al 3+ substitution for Si 4+ . However, TBA + played a dual-template role by occupying the intersections of 10-MR channels, as well as adsorbing on the external surface of precursors to prevent their growth and facilitate the formation of loose-stacking nanorods as in ZSM-11 (SAR = 30, 40, and 50).…”