Accessibility and catalysis of acidic sites in hierarchical ZSM-5 prepared by silanization

Xue, Zhiwei; Zhang, Tuo; Ma, Jinghong; Miao, Hao; Fan, Wei; Zhang, Yanyu; Li, Ruifeng

doi:10.1016/j.micromeso.2011.10.026

Cited by 77 publications

(43 citation statements)

References 29 publications

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“…Molecular sieving can influence reactants and probe molecules. 90,91,97,[629][630][631][632][633][634]636,637,641,653 This section is divided into five subsections. This question is also valid for all sites, and not only for those that are catalytically active.…”

Section: Probe Molecules For Characterization Of Zeolite Basicitymentioning

confidence: 99%

Probing zeolites by vibrational spectroscopies

et al. 2015

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This review addresses the most relevant aspects of vibrational spectroscopies (IR, Raman and INS) applied to zeolites and zeotype materials. Surface Brønsted and Lewis acidity and surface basicity are treated in detail. The role of probe molecules and the relevance of tuning both the proton affinity and the steric hindrance of the probe to fully understand and map the complex site population present inside microporous materials are critically discussed. A detailed description of the methods needed to precisely determine the IR absorption coefficients is given, making IR a quantitative technique. The thermodynamic parameters of the adsorption process that can be extracted from a variable-temperature IR study are described. Finally, cutting-edge space- and time-resolved experiments are reviewed. All aspects are discussed by reporting relevant examples. When available, the theoretical literature related to the reviewed experimental results is reported to support the interpretation of the vibrational spectra on an atomic level.

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Section: Probe Molecules For Characterization Of Zeolite Basicitymentioning

confidence: 99%

Probing zeolites by vibrational spectroscopies

et al. 2015

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“…60 In more detail, the ACI was found to increase with increasing external surface area. In this regard, the percentage of Brønsted acid sites accessible to collidine is somewhat comparably dened as the ACI.…”

mentioning

confidence: 93%

“…However, the reduced Brønsted peak observed for all SARs studied suggests that collidine molecules can interact with Brønsted acid sites, which are possibly located at the pore mouth or at the external H-ZSM-5 crystal surface. 60 However, the Brønsted acid sites accessible to collidine are more likely to be located at the pore mouth than the external crystal surface.…”

mentioning

confidence: 99%

Effect of Al content on number and location of hydroxyl acid species in zeolites: a DRIFTS quantitative protocol without the need for molar extinction coefficients

Bräuer

Situmorang

et al. 2017

RSC Adv.

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In this work, we have systematically investigated the effect of the Al content on the number and location of bridging hydroxyls (Brønsted acid sites) and terminal hydroxyls (terminal silanol sites) in ZSM-5 zeolites with varying silica-alumina ratio (SAR ¼ SiO 2 /Al 2 O 3 ) using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) without molar extinction coefficients. Two base probe molecules with different kinetic diameters, pyridine (5.7Å) and collidine (7.4Å), were used. The total content of Brønsted acid sites is obtained by elemental analysis of the proton form and sodium exchanged form of ZSM-5. To quantify the number of internal and external Brønsted acid sites the change in area of the Brønsted acid site peak in the O-H stretching region is then used; thus, the need for molar extinction coefficients to quantify Brønsted acid sites is thereby eliminated. The results reported here show that for ZSM-5 the number of external Brønsted sites, in absolute terms, increases with increasing total Al content, as evidenced by collidine adsorption. The number of terminal silanol acid sites was found to be proportional to the external surface area probed by argon sorption experiments. In summary, this work shows that the use of DRIFTS in conjunction with elemental analysis is a valid alternative to qualitatively and quantitatively probe the number and location of hydroxyl acid sites without the use of molar extinction coefficients and gives a comprehensive picture of the effect of Al content on number and location of hydroxyl acid species in ZSM-5 zeolites with varying SAR. The work contributes to advancing the range of characterisation protocols for solid acid catalysts.

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“…Moreover, hierarchical ZSM-5 gave higher contents of alkyl aromatics and fewer contents of light alkenes and alkanes, suggesting that hierarchical ZSM-5 could effectively reduce the side reaction of methanol. Many literatures had investigated the parameters of conventional ZSM-5 and hierarchical ZSM-5 and compared their catalytic properties for the reactions such as the alkylation of benzene and the aromatization of methanol [17,18,23,[25][26][27]. Rownaghi et al [25] had observed that as compared to conventional ZSM-5, Nano-ZSM-5 catalyst gave the highest activity which could be attributed to the lower diffusion limitation and higher concentration of strong acid sites on the surface, while Meso-ZSM-5 gave higher yields of alkyl aromatics and paraffins and fewer light olefins due to the channel structure of mesoporos ZSM-5 crystals provided easier access to the active sites in micropores.…”

Section: Catalytic Alkylation Of Benzene With Methanol Over Conventiomentioning

confidence: 99%

Catalytic Activity of Pt Modified Hierarchical ZSM-5 Catalysts in Benzene Alkylation with Methanol

Zhang

Cen

et al. 2014

Catal Lett

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Hierarchical ZSM-5 zeolite showed an improved performance as compared to conventional ZSM-5 catalysts in the alkylation of benzene with methanol. However, ethylbenzene yet remains as a major problem. In this study, we modified hierarchical ZSM-5 with Pt to evaluate the alkylation of benzene with methanol in a fixed-bed continuous flow reactor. It was found that Pt modified hierarchical ZSM-5 could successfully combine the catalytic advantages of hierarchical ZSM-5 and the high suppression of Pt to ethylbenzene formation. Moreover, employing direct reduction could improve the utilization of Pt by avoiding Pt particles sintering.

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Accessibility and catalysis of acidic sites in hierarchical ZSM-5 prepared by silanization

Cited by 77 publications

References 29 publications

Probing zeolites by vibrational spectroscopies

Probing zeolites by vibrational spectroscopies

Effect of Al content on number and location of hydroxyl acid species in zeolites: a DRIFTS quantitative protocol without the need for molar extinction coefficients

Catalytic Activity of Pt Modified Hierarchical ZSM-5 Catalysts in Benzene Alkylation with Methanol

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