Modifications of H-ZSM-5 Catalysts by NaOH Treatment

Lietz, G.; Schnabel, K.‐H.; Peuker, Ch.; Groß, Th.; Storek, W.; Völter, J.

doi:10.1006/jcat.1994.1242

Cited by 65 publications

(46 citation statements)

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“…Over the Pt/MgAl 2 O 4 (curve a), two reduction peaks appear, one near 230°C and another around 470°C. Two types of Pt oxides are considered in literatures [29][30][31]. The former is reduced at low temperatures due to weak interaction with the support, the latter requires higher temperatures on account of strong interaction.…”

Section: Catalytic Propertiessupporting

confidence: 41%

Propane Dehydrogenation Over PtSn Catalysts Supported on ZnO-Modified MgAl2O4

Wang

et al. 2009

Catal Lett

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Platinum and tin supported on ZnO-modified MgAl 2 O 4 constitutes a new and efficient catalyst for the dehydrogenation of propane. The structure of the catalyst has been studied by XRD, TEM, BET, TG, H 2 -TPR and H 2 chemisorption and catalytic properties for propane dehydrogenation have been tested on a microreactor. It has been shown that the catalyst is superior to conventional aluminasupported PtSn systems and PtSn/MgAl 2 O 4 in terms of lifetime stability, activity and propene selectivity. The characterization results of catalysts revealed that ZnOmodified catalysts can increase the Pt dispersion and enhance the interaction between metal and support, resulting in the increase of catalytic activity for propane dehydrogenation.

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Section: Catalytic Propertiessupporting

confidence: 41%

Propane Dehydrogenation Over PtSn Catalysts Supported on ZnO-Modified MgAl2O4

Wang

et al. 2009

Catal Lett

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“…The apparent affinity of the Al(OH) 4 À complex to the zeolite surface is in line with previous work that evidenced surface enrichment of Al on ZSM-5 upon alkaline treatment. [37] The increased yield (7 %) greatly exceeds the increase in mass due to the deposition of aluminum (hydr)oxides (< 1 %), which suggests, in agreement with other work, [27] that the external aluminum addition protects the zeolite from dissolution. Remarkably, the shape of the isotherm, the degree of mesoporosity, the obtained mesopore size distribution, and the protection from dissolution are in good agreement to the results obtained by conventional desilication of MFI zeolites within the optimal framework Si/Al range.…”

Section: Samplementioning

confidence: 42%

“…This agrees well with other works in which similar coordination of Al was obtained by means of post-synthesis modifications of zeolites. [37,[41][42][43] We put forward that during alkaline treatment Al(OH) 4 À is partially integrated into the zeolite framework, giving rise to both Brønsted and Lewis acid sites. Depending on the application, these sites could either have a beneficial or detrimental influence on catalyzed reactions.…”

mentioning

confidence: 44%

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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“…The Brønsted acidity seems to be preserved (FTIR and NH 3 -TPD), [17,18] and even increases due to the lower Si/Al ratio of the resulting alkaline-treated sample; this suggests that most of the Al atoms in the alkaline-treated sample are in framework positions and indicates that part of the Al extracted during the alkaline treatment has been re-inserted in the zeolite framework (re-alumination), as has already been noticed on the basis of FTIR [42,43] and 27 Al MAS-NMR measurements. [43,44] The re-aluminated Al species should preferably be located close to the mesopores since this is where most of the vacancies are created during the desilication process.…”

mentioning

confidence: 44%

“…Re-alumination of Al EF species upon alkaline treatment has been reported previously by Lietz et al, [42] who investigated the modification of the catalytic properties, for conversion of propane and methanol, of calcined and steamed ZSM-5 zeolite upon treatment in NaOH solution. Disappearance of the IR absorption band at 3660 cm…”

mentioning

confidence: 45%

Mechanism of Hierarchical Porosity Development in MFI Zeolites by Desilication: The Role of Aluminium as a Pore‐Directing Agent

Groen

Peffer

Moulijn

et al. 2005

Chemistry A European J

495

453

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The role of the concentration and the nature of aluminium in the creation of hierarchical porosity in both commercial and synthesized MFI zeolites have been investigated through controlled mesoporosity development by desilication in alkaline medium. Framework aluminium controls the process of framework silicon extraction and makes desilication selective towards intracrystalline mesopore formation. An optimal molar Si/Al ratio in the range 25-50 has been identified; this leads to an optimal mesoporosity centred around 10 nm and mesopore surface areas of up to 235 m(2) g(-1) while preserving the intrinsic crystalline and acidic properties. At lower framework Si/Al ratios the relatively high Al content inhibits Si extraction and hardly any mesopores are created, while in highly siliceous ZSM-5 unselective extraction of framework Si induces formation of large pores. The existence of framework Al sites in different T positions that are more or less susceptible to the alkaline treatment, and the occurrence of re-alumination, are tentative explanations for the remarkable behaviour of Al in the desilication process. The presence of substantial extra framework Al, obtained by steam treatment, inhibits Si extraction and related mesopore formation; this is attributed to re-alumination of the extraframework Al species during the alkaline treatment. Removal of extraframework Al species by mild oxalic acid treatment restores susceptibility to desilication, which is accompanied by formation of larger mesopores due to the enhanced Si/Al ratio in the acid-treated zeolite.

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Modifications of H-ZSM-5 Catalysts by NaOH Treatment

Cited by 65 publications

References 0 publications

Propane Dehydrogenation Over PtSn Catalysts Supported on ZnO-Modified MgAl2O4

Propane Dehydrogenation Over PtSn Catalysts Supported on ZnO-Modified MgAl2O4

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

Mechanism of Hierarchical Porosity Development in MFI Zeolites by Desilication: The Role of Aluminium as a Pore‐Directing Agent

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