Alkaline-mediated mesoporous mordenite zeolites for acid-catalyzed conversions☆

Groen, Johan C.; Sano, Tsuneji; Moulijn, Jacob A.; Pérez‐Ramírez, Javier

doi:10.1016/j.jcat.2007.07.020

Cited by 222 publications

(110 citation statements)

References 29 publications

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“…In the case of the mesoporous crystals, during the desilication treatment not only silicon is removed from the framework but also, to a lesser extent, aluminum, as reflected by the Si/Al ratio of the filtrate, which was determined to be 1000. [22] In addition, a higher degree of silicon extraction and accompanying mesoporosity formation is expected to occur at the crystal boundaries, that is, the intergrowth regions, leading to an inhomogeneous Si/Al ratio over the long axis of the crystals (Figure 1 c). The reported Si/Al ratios are in good agreement with earlier values determined by inductively coupled plasma atomicemission spectrometry (30 and 24 for microporous and mesoporous crystals, respectively).…”

Section: Resultsmentioning

confidence: 99%

“…This approach has been successfully applied to both ZSM-5 [21] and mordenite crystals. [22] Transient uptake measurements of neopentane over large crystals demonstrated a two orders of magnitude higher rate of diffusion for the combined micro-and mesoporous zeolite as compared to the purely microporous parent sample. Apart from this key result, little is known about the role of the mesopores during catalytic reactions, that is, whether their surface participates in the catalytic reaction or merely provides highways to the Brønsted acid sites confined in the micropores; also, the exact location in the crystal is not precisely known.…”

Section: Introductionmentioning

confidence: 96%

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Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

Kox

Stavitski

Groen

et al. 2008

Chemistry A European J

116

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A combination of optical and fluorescence microscopy was used to study the morphology of micro‐ and mesoporous H‐ZSM‐5 zeolite crystals (17×4×4 μm) and to evaluate, in a spatially resolved manner, the effect of mesoporosity, introduced via desilication, on catalytic performance. For this purpose, the oligomerization of various styrene molecules was used as a model reaction, in which the carbocation intermediates formed in the zeolite pores act as reporter molecules. In situ confocal fluorescence measurements after the template removal process showed that the crystals generally consist of three different subunits that have pyramidal boundaries with each other. Examination of these crystals during styrene oligomerization revealed differences in the catalytic activity between the purely microporous and the combined micro‐ and mesoporous crystals. The introduction of intracrystalline mesoporosity limits the formation to dimeric carbocation intermediates and facilitates the transport of styrene molecules inside the zeolite volume. This leads to a more uniform coloration and fluorescence pattern of the crystals. Moreover, the oligomerization of various styrene compounds, which differ in their reactivity, provides a good way of estimating the Brønsted acid strength in a spatially resolved manner, showing a nonhomogeneously distributed Brønsted acidity over the volume of the crystals. More detailed information on the structure of the ZSM‐5 crystals was revealed for mesoporous crystals during the oligomerization of 4‐methoxystyrene. This reaction induced an “explosion” of the crystal leading to the formation of a complex system with at least eight different subunits. Finally, polarized‐light microscopy was used to unravel the pore geometry in these individual building blocks. The observed differences in catalytic behavior between micro‐ and mesoporous ZSM‐5 crystals are strengthened by the microspectroscopic techniques employed, which show that upon desilication the crystal morphology is affected, the product distribution is changed towards less conjugated carbocation intermediates, and that a gradient in Brønsted acid strength appears to be present.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

Kox

Stavitski

Groen

et al. 2008

Chemistry A European J

116

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“…Nevertheless, most of these extracted Al species are able to realuminate on the mesopore surface, resulting in the lowering the Si/Al ratio of the hierarchical [9,10]. Zeolite desilication has been successfully applied to produce a large number of hierarchically structured zeolites MFI [11,12]MTW [13], MOR [14,15], FER [16,17], FAU [18], and Beta [19,20]. Nevertheless, the benefits of desilicated zeolite Beta for catalytic cracking reaction have not been shown in previous studies.…”

Section: Introductionmentioning

confidence: 99%

Catalytic cracking performance of alkaline-treated zeolite Beta in the terms of acid sites properties and their accessibility

Tarach

Góra‐Marek

Tekla

et al. 2014

Journal of Catalysis

162

111

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The zeolite Beta is considered as a promising additive for FCC catalyst in diesel oil production. In this article, it is shown that hierarchical zeolite Beta obtained by an optimized desilication procedure increases Diesel and propylene yields during gas-oil cracking reaction.The alkaline treatment of zeolite Beta (Si/Al = 22) by desilication with NaOH and NaOH&TBAOH was investigated. The catalytic performance improvement of desilicated zeolite Beta has been rationalized by deep characterization of the samples including X-ray diffraction, low temperature adsorption of nitrogen, solid-state 29 Si MAS NMR and IR studies of acidity. Finally, the catalytic performance of the zeolites Beta was evaluated in the cracking of n-decane, 1,3,5-tri-iso-propylbenzene and vacuum gas oil. It was found that desilication with NaOH&TBAOH ensures the more uniform intracrystalline mesoporosity with the formation of narrower mesopores, while preserving full crystallinity resulting in catalysts with the most appropriated acidity and then, with better catalytic performance.

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“…[6][7][8][9][10][11][12] Nowadays, an impressive variety of approaches forms a nanoscale toolbox that can be used to design high-performance zeolite catalysts by optimizing porosity, as well as other key parameters as, for example, acidity and composition. [12][13][14][15][16][17] The selective extraction of silicon from the zeolite framework in alkaline medium (typically NaOH) has proven to be an effective, versatile, and simple post-synthesis treatment to introduce mesoporosity in a broad variety of zeolite structures such as MFI, [18] MTW, [19] MOR, [20] BEA, [21] AST, [22] FER, [23] MWW, [24] IFR, [25] and STF. [26] Nevertheless, a major drawback of desilication remained that its applicability is limited by the silicon/aluminum ratio in the framework.…”

Section: Introductionmentioning

confidence: 99%

Desilication Mechanism Revisited: Highly Mesoporous All‐Silica Zeolites Enabled Through Pore‐Directing Agents

Verboekend

Pérez‐Ramírez

2011

Chemistry A European J

247

246

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The role of pore-directing agents (PDAs) in the introduction of hierarchical porosity in silicalite-1 in alkaline medium was investigated. By incorporation of various PDAs in aqueous NaOH, homogenously distributed mesopores were introduced in 2.5 μm silicalite-1 crystals. It was proven for the first time that framework aluminum is not a prerequisite for the introduction of intracrystalline mesoporosity by desilication. The pore-directing role is not directly exerted by framework trivalent cations metals, but by species on the external surface of the zeolite. The inclusion of metal complexes (Al(OH)(4)(-), Ga(OH)(4)(-)) and tetraalkyl ammonium cations (tetramethyl ammonium (TMA(+)), tetrapropyl ammonium (TPA(+))) in the alkaline solution led to distinct mesopore surface areas (up to 286 m(2) g(-1)) and pore sizes centered in the range of 5-20 nm. In the case alkaline treatment was performed in the presence of Al(OH)(4)(-), all aluminum partially integrated in the zeolite giving rise to both Lewis and Brønsted acidity. Apart from the concentration and location, the affinity of the PDA to the zeolite surface plays a crucial role in the pore formation process. If the PDA is attracted too strongly (e.g., TMA(+)), the dissolution is reduced dramatically. When the pore-directing agent is not attracted to the zeolite's external surface, excessive dissolution occurs (standard alkaline treatment). TPA(+) proved to be the most effective PDA as its presence led to high mesopore surface areas (>200 m(2) g(-1)) over a broad range of PDA concentrations (0.003-0.1 M). Importantly, our results enable to extend the suitability of desilication for controlled mesopore formation to all-silica zeolites.

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Alkaline-mediated mesoporous mordenite zeolites for acid-catalyzed conversions☆

Cited by 222 publications

References 29 publications

Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

Catalytic cracking performance of alkaline-treated zeolite Beta in the terms of acid sites properties and their accessibility

Desilication Mechanism Revisited: Highly Mesoporous All‐Silica Zeolites Enabled Through Pore‐Directing Agents

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