A comparative study on the structural and catalytic properties of zeolites type ZSM-5, mordenite, Beta and MCM-41

Dimitrova, R.; Gündüz, Gönül; Spassova, M.

doi:10.1016/j.molcata.2005.08.015

Cited by 28 publications

(20 citation statements)

References 15 publications

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“…In these studies, some products with a retention time higher than terpinolene in gas chromatography, which is likely to contain dimers, were found as byproducts. [5,15,16] According to the literature, the ordered mesoporous acidic materials with large pore size and high surface area were the most suitable for the heterogeneously catalyzed dimerization of pinene.…”

Section: Introductionmentioning

confidence: 99%

Isomerization and Dimerization of Pinene using Al‐Incorporated MCM‐41 Mesoporous Materials

et al. 2012

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A series of Al‐incorporated mobile crystalline materials (Al‐MCM‐41) were prepared by hydrothermal synthesis and characterized by XRD, N2 adsorption (isotherms), inductively coupled plasma (ICP) analysis, 27Al magic angle spinning (MAS) NMR spectroscopy, and in situ pyridine adsorption (IR analysis). All samples exhibit an ordered structure with the majority of Al species in framework positions, except those with an SiO2/Al2O3 ratio ≤10. The concentration of acid sites is closely related to the Al content in the unit cell. In the presence of Al‐MCM‐41, both α‐ and β‐pinenes are quickly transformed into isomerized products, which then couple to form homo‐ and heterodimers. Lewis acid sites are active in triggering both the isomerization and dimerization reactions, but weak Brønsted acid sites seem inactive for the dimerization. Al‐MCM‐41 has a greater activity than many other microporous and layered materials, and can be easily regenerated. The activity correlates well with the concentration of acid sites, and the sample with an SiO2/Al2O3 ratio of 20 shows the highest activity.

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Section: Introductionmentioning

confidence: 99%

Isomerization and Dimerization of Pinene using Al‐Incorporated MCM‐41 Mesoporous Materials

et al. 2012

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“…Various acidic catalysts, such as oxides [2,3], oxides treated with acids [4], zeolites [5][6][7][8][9][10][11][12], mesoporous materials [12][13][14], activated clays [15][16][17][18][19], resins [20,21] and heteropolyacids [22], have been explored in isomerization of a-pinene. Currently, the acid-impregnated TiO 2 is used as an industrial catalyst for this purpose, but due to the low rate of the reaction, there is still a great interest in developing novel, viable contacts for the process.…”

Section: Introductionmentioning

confidence: 99%

Properties of Desilicated ZSM-5, ZSM-12, MCM-22 and ZSM-12/MCM-41 Derivatives in Isomerization of α-Pinene

2008

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Limited information is available on the isomerization of a-pinene proceeding on zeolites and related desilicated materials. We wish therefore to report on the title reaction proceeding over ZSM-5, ZSM-12 and MCM-22 type zeolites, parent and modified by the sodium hydroxide treatment. The NaOH solutions of various concentrations (0.05-1 M) were used as a desilicating agent. Such treatments with basic solutions were applied: (i) under atmospheric pressure, and (ii) under hydrothermal conditions. It was shown that ZSM-12 was more resistant towards the basic solutions treatment, and its structure was retained over a whole range of NaOH concentrations studied. Nitrogen sorption revealed strong influence of the desilication process on the pore structure of modified materials-the mesopores system was formed in the zeolite crystals. Finally, catalytic studies were carried out using ZSM-5, ZSM-12, MCM-22, their desilicated derivatives and a ZSM-12/MCM-41 composite material. Catalytic properties of the samples studied were affected to a large extent by the NaOH treatment.

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“…In that context, several studies were carried out using alkaline treatments to obtain more efficient materials by taking advantage of the combined effects of high acidity and high selectivity by optimizing the relative contributions of the mesoporosity and microporosity in the materials. [49][50][51] In the case of H-FER, analogous low ionization is observed for p-PTZ and e-PTZ, much too large to be able to diffuse in the micropore volume. This feature most likely results not only from adsorption on the external surface of molecules plugging into the pore entry, but also from adsorption sites in the mesopore volume, which represents 40 % of the total pore volume.…”

Section: Discussionmentioning

confidence: 68%

Spontaneous Ionization of N‐Alkylphenothiazine Molecules Adsorbed in Channel‐Type Zeolites: Effects of Alkyl Chain Length and Confinement on Electron Transfer

Carré¹,

Luchez²,

Moissette³

et al. 2011

ChemPhysChem

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The mere mixing of N-alkylphenothiazines with three channel-type acid zeolites with various structures (ferrierite, H-MFI, and mordenite) induces the spontaneous ionization of the heterocyclic molecule in high yield upon adsorption. The diffuse reflectance UV-visible absorption and Raman scattering spectra show that the accessibility of the highly polarizing acid sites is not indispensable to induce the spontaneous ionization process. Due to their particularly low ionization potential values (6.7 eV), the adsorption of the molecules on the external surface or in the inner volume is the key parameter to generate the radical cation. However, the ionization yield and charge stabilization are intimately correlated to the possibility of the zeolites accommodating molecules inside their channels. Moreover, the higher electrostatic field gradient induced by high confinement is required to favor the second ionization and dication formation. The alkyl chain length plays a decisive role by either slowing down the diffusion process or blocking the molecule at the pore entry. Therefore, the efficiency of the ionization process that depends on the number of adsorbed molecules decreases significantly from phenothiazine to the N-alkylphenothiazines. The spectral data demonstrate that deformation of the alkyl group is necessary to allow the diffusion of the molecules into the channels.

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A comparative study on the structural and catalytic properties of zeolites type ZSM-5, mordenite, Beta and MCM-41

Cited by 28 publications

References 15 publications

Isomerization and Dimerization of Pinene using Al‐Incorporated MCM‐41 Mesoporous Materials

Isomerization and Dimerization of Pinene using Al‐Incorporated MCM‐41 Mesoporous Materials

Properties of Desilicated ZSM-5, ZSM-12, MCM-22 and ZSM-12/MCM-41 Derivatives in Isomerization of α-Pinene

Spontaneous Ionization of N‐Alkylphenothiazine Molecules Adsorbed in Channel‐Type Zeolites: Effects of Alkyl Chain Length and Confinement on Electron Transfer

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