Medium‐Pore (Ten‐Ring) Zeolites

Kärger, Jörg; Ruthven, Douglas M.; Theodorou, Doros N.

doi:10.1002/9783527651276.ch18

Cited by 2 publications

(1 citation statement)

References 164 publications

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“…Using the results from sorption and desorption isotherms, heats of adsorption, 29 Si NMR, N 2 physisorption, and X-ray diffraction, we hypothesize that the increase in water uptake for the larger crystals is caused primarily by capillary condensation occurring in the “microfissures” between dislocated unit cells (type B defects). Due to the growth mechanism that has been reported for this type of zeolite, it is postulated that these dislocations occur along intracrystalline barriers that result from the faceted-terrace growth mechanism, twinned substructures, and “fused” platelets. , Our results indicate that the microfissure/dislocation defects must be present in higher concentrations in the larger crystals (most likely due to increased framework strain in the aforementioned regions). Additional studies would be necessary to further define the structure and cause of these microfissures, but our current results reveal the importance of crystal size for dilute biofuel recovery from aqueous streams.…”

Section: Resultsmentioning

confidence: 50%

Effect of Crystal Size on Framework Defects and Water Uptake in Fluoride Mediated Silicalite-1

Dose¹,

Zhang

Thompson

et al. 2014

Chem. Mater.

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The relationship between framework defects and crystal size in fluoride mediated silicalite-1 was investigated through nitrogen physisorption, X-ray diffraction, and vapor adsorption of ethanol and water on samples with crystal sizes ranging from 0.4 to 30 μm in the b direction of the silicalite-1 crystals. X-ray diffraction reveals a shift in the lattice system from a predominantly monoclinic phase in smaller crystals to an orthorhombic phase in the larger crystals. 29 Si MAS studies reveal minimal differences in framework silanol defect concentration. An H-4 type hysteresis in 77 K N 2 adsorption isotherm and BdB-FHH pore size analysis reveal the presence of slit-like pores and a larger average pore size as well as a larger volume fraction of "microfissures" in the larger crystals. Pure vapor adsorption measurements show more than a 2-fold increase in water uptake from 0.21 mmol/g to 0.51 mmol/g from the smallest to largest samples at 308 K near unit activity, while ethanol uptake remains on the order of 2.4 mmol/g for all samples. An increase in desorption hysteresis with crystal size and negligible differences in isosteric heats of adsorption of water lend support to the presence of microfissure defects in the larger samples. IAST predications for binary adsorption of ethanol and water in the silicalite-1 samples reveal a 2-fold ethanol/water selectivity enhancement for dilute (<5 wt % EtOH) solutions when crystal size is reduced. This systematic study of N 2 physisorption, framework composition, and ethanol/water adsorption highlights the critical role that crystal size plays in the adsorption process, which can have significant implications for biofuel processes that produce dilute aqueous ethanol as a raw product.

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Section: Resultsmentioning

confidence: 50%

Effect of Crystal Size on Framework Defects and Water Uptake in Fluoride Mediated Silicalite-1

Dose¹,

Zhang

Thompson

et al. 2014

Chem. Mater.

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Influence of Nanoscale Intimacy and Zeolite Micropore Size on the Performance of Bifunctional Catalysts forn-Heptane Hydroisomerization

et al. 2020

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In this study, Pt nanoparticles on zeolite/γ-Al 2 O 3 composites (50/50 wt) were located either in the zeolite or on the γ-Al 2 O 3 binder, hereby varying the average distance (intimacy) between zeolite acid sites and metal sites from “closest” to “nanoscale”. The catalytic performance of these catalysts was compared to physical mixtures of zeolite and Pt/γ-Al 2 O 3 powders, which provide a “microscale” distance between sites. Several beneficial effects on catalytic activity and selectivity for n -heptane hydroisomerization were observed when Pt nanoparticles are located on the γ-Al 2 O 3 binder in nanoscale proximity with zeolite acid sites, as opposed to Pt nanoparticles located inside zeolite crystals. On ZSM-5-based catalysts, mostly monobranched isomers were produced, and the isomer selectivity of these catalysts was almost unaffected with an intimacy ranging from closest to microscale, which can be attributed to the high diffusional barriers of branched isomers within ZSM-5 micropores. For composite catalysts based on large-pore zeolites (zeolite Beta and zeolite Y), the activity and selectivity benefitted from the nanoscale intimacy with Pt, compared to both the closest and microscale intimacies. Intracrystalline gradients of heptenes as reaction intermediates are likely contributors to differences in activity and selectivity. This paper aims to provide insights into the influence of the metal–acid intimacy in bifunctional catalysts based on zeolites with different framework topologies.

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Medium‐Pore (Ten‐Ring) Zeolites

Cited by 2 publications

References 164 publications

Effect of Crystal Size on Framework Defects and Water Uptake in Fluoride Mediated Silicalite-1

Effect of Crystal Size on Framework Defects and Water Uptake in Fluoride Mediated Silicalite-1

Influence of Nanoscale Intimacy and Zeolite Micropore Size on the Performance of Bifunctional Catalysts forn-Heptane Hydroisomerization

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