Synthesis of Mordenite Aggregates of Nanometer-Sized Crystallites

Nosheen, Shaneela; Galasso, Francis S.; Suib, Steven L.

doi:10.1166/sam.2009.1005

Cited by 5 publications

(18 citation statements)

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Section: ■ Results and Discussionmentioning

confidence: 99%

“…The site-specific interactions of different framework 27 Al species with OSDA molecules are established by solid-state two-dimensional (2D) heteronuclear correlation (HETCOR) NMR spectra of HOU-4 (Figure 5). The 2D NMR correlation spectra exploit internuclear dipole−dipole (through-space) or J (through-covalent-bond) couplings and are plotted as 2D contour plots, where correlated signal intensities manifest the mutual proximities or covalent connectivities of the corre- sponding 1 H, 13 C, 27 Al, or 29 Si species. 39,40 For example, covalent 27 Al−O− 29 Si bonds within the HOU-4 frameworks are unambiguously established by the 2D 27 Al{ 29 Si} J-mediated NMR correlation spectrum (Figure 5A), which shows a distribution of correlated signal intensity at 54 ppm in the 27 Al dimension and −109 to −99 ppm in the 29 Si dimension arising from framework aluminum atoms bonded to fully or partially cross-linked 29 Si atoms.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The 2D NMR correlation spectra exploit internuclear dipole−dipole (through-space) or J (through-covalent-bond) couplings and are plotted as 2D contour plots, where correlated signal intensities manifest the mutual proximities or covalent connectivities of the corre- sponding 1 H, 13 C, 27 Al, or 29 Si species. 39,40 For example, covalent 27 Al−O− 29 Si bonds within the HOU-4 frameworks are unambiguously established by the 2D 27 Al{ 29 Si} J-mediated NMR correlation spectrum (Figure 5A), which shows a distribution of correlated signal intensity at 54 ppm in the 27 Al dimension and −109 to −99 ppm in the 29 Si dimension arising from framework aluminum atoms bonded to fully or partially cross-linked 29 Si atoms. Previously, such 2D 27 Al{ 29 Si} through-bond-mediated correlation spectra of aluminosilicate zeolites have been limited due in part to the low natural isotopic abundance of 29 Si (4.7%) and weak 27 Al−O− 29 Si J couplings (<20 Hz) but are enabled here by the improved sensitivity of low-temperature measurement conditions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Alternatively, the synthesis of crystallites with submicrometer dimensions of the [001] facet can extend the catalyst lifetime. Suib and co-workers have reported sizes as small as 40–60 nm using complicated synthesis protocols that include the use of crystalline seeds, alcohol additives, and/or microwave heating . Mordenite nanorods (ca.…”

Section: Introductionmentioning

confidence: 99%

“…Suib and co-workers have reported sizes as small as 40−60 nm using complicated synthesis protocols that include the use of crystalline seeds, 26 alcohol additives, and/or microwave heating. 27 Mordenite nanorods (ca. 10 × 100 nm) have been synthesized using seeds or cationic gemini surfactants by Xiao 28 and Ryoo 29 and their co-workers, respectively.…”

Section: ■ Introductionmentioning

confidence: 99%

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Crystallization of Mordenite Platelets using Cooperative Organic Structure-Directing Agents

et al. 2019

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Organic structure-directing agents (OSDAs) are exploited in the crystallization of microporous materials to tailor the physicochemical properties of the resulting zeolite for applications ranging from separations to catalysis. The rational design of these OSDAs often entails the identification of molecules with a geometry that is commensurate with the channels and cages of the target zeolite structure. Syntheses tend to employ only a single OSDA, but there are a few examples where two or more organics operate synergistically to yield a desired product. Using a combination of state-of-the-art characterization techniques and molecular modeling, we show that the coupling of N,N,N-trimethyl-1,1adamantammonium and 1,2-hexanediol, each yielding distinct zeolites when used alone, results in the cooperative direction of a third structure, HOU-4, with the mordenite framework type (MOR). Rietveld refinement using synchrotron X-ray diffraction data reveals the spatial arrangement of the organics in the HOU-4 crystals, with amines located in the large channels and alcohols oriented in the side pockets lining the one-dimensional pores. These results are in excellent agreement with molecular dynamics calculations, which predict similar spatial distributions of organics with an energetically favorable packing density that agrees with experimental measurements of OSDA loading, as well as with solid-state two-dimensional 27 Al{ 29 Si}, 27 Al{ 1 H}, and 13 C{ 1 H} NMR correlation spectra, which establish the proximities and interactions of occluded OSDAs. A combination of high-resolution transmission electron microscopy and atomic force microscopy is used to quantify the size of the HOU-4 crystals, which exhibit a platelike morphology, and to index the crystal facets. Our findings reveal that the combined OSDAs work in tandem to produce ultrathin, nonfaulted HOU-4 crystals that exhibit improved catalytic activity for cumene cracking in comparison to mordenite crystals prepared via conventional syntheses. This novel demonstration of cooperativity highlights the potential possibilities for expanding the use of dual structure-directing agents in zeolite synthesis.

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