Thermal stability of hydroxy groups in dealuminated mordenites

Fejes, P.; Hannus, I.; Kiricsi, Imre; Pfeifer, H.; Freude, D.; Oehme, Wolfgang

doi:10.1016/0144-2449(85)90011-9

Cited by 31 publications

(10 citation statements)

References 16 publications

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“…In the beginning of the dealumination, up to four SiOH defects per However, the decrease of this number to lower values as dealumination proceeds can be the result of a partial healing of the structure defects. Similar conclusions have been arrived at by Beyer et al12 and Fejes et al 18 Figure 8 presents the HRMAS 29Si NMR spectra with and without enhancement due to CP for samples dealuminated by acid leaching and consecutive steaming (S-M-6) and by ammonium exchange and subsequent SiCl4 treatment (SiCl4-Z). The spectrum of the highly dealuminated sample (S-M-6) shows three lines corresponding to Si(OAl) configurations.…”

Section: Resultssupporting

confidence: 84%

Aluminum siting in mordenite and dealumination mechanism

Bodart¹,

Nagy²,

Debras³

et al. 1986

J. Phys. Chem.

133

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Section: Resultssupporting

confidence: 84%

Aluminum siting in mordenite and dealumination mechanism

Bodart¹,

Nagy²,

Debras³

et al. 1986

J. Phys. Chem.

133

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“…samples, the presence of non-zeolitic phases can be appreciated for the raw material, especially the ~10 wt.% content of metallic elements that are distinct from Si and Al. These results indicate that the structure of mordenite loses aluminum atoms, leaving vacant sites (structure defects) that probably become stabilized by the formation of hydroxyl nests [31]. As seen in Figure 5, ZL and ZAM samples show similar Si/Al values, which means that the ZAM structure was not affected by the cation exchange process with NH4Cl(aq).…”

Section: Resultsmentioning

confidence: 79%

“…These results indicate that the structure of mordenite loses aluminum atoms, leaving vacant sites (structure defects) that probably become stabilized by the formation of hydroxyl nests [31]. As seen in Figure 5, ZL and ZAM samples show similar Si/Al values, which means that the ZAM structure was not affected by the cation exchange process with NH 4 Cl (aq) .…”

Section: Resultsmentioning

confidence: 80%

Dealumination and Characterization of Natural Mordenite-Rich Tuffs

et al. 2022

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The present study evaluates the feasibility of partially dealuminated natural mordenite as a catalyst support by studying improvement in its textural properties. This is the first study that reports the dealumination of natural zeolite-based tuffs from Ecuador. For this purpose, mordenite-rich tuffs were obtained from deposits close to Guayaquil, Ecuador. The raw material was micronized in order to increase its surface, and treated with NH4Cl. NH4+ cation-exchanged samples were finally reacted with HCl(aq) to complete the dealumination process. The partially dealuminated samples were characterized using techniques such as XRD, FT-IR, SEM-EDS, and identification of their textural properties. Dealumination with HCl(aq) increased the Si/Al ratio up to 9 and kept the crystallographic structure of natural mordenite, as XRD results showed that the structure of mordenite was not altered after the dealumination process. On the other hand, textural properties such as surface area and microporosity were improved as compared to natural mordenite. In view of these results, the feasibility of using natural mordenite as a catalyst support is discussed in this study.

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“…We thus assume that the water normally liberated during deep-bed oxidative calcination procedures is the main cause of the formation of aluminum species active in the MPV reaction. Liberation of water by the annealing of silanol nests may also contribute (26). In a deep bed, the water formed will spend more time in the zeolite sample than in a shallow bed and consequently has an increased chance to get involved in hydrolysis (autosteaming).…”

Section: Activation Of the Nh 4 Beta Samplesmentioning

confidence: 99%

Zeolite Beta: The Relationship between Calcination Procedure, Aluminum Configuration, and Lewis Acidity

Kunkeler

Zuurdeeg

Waal

et al. 1998

Journal of Catalysis

223

145

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Zeolite Beta was calcined under a variety of carefully controlled conditions to study the influence of (hydro)thermal treatments on the catalytic activity of zeolite Beta in the Lewis acid-catalyzed Meerwein-Ponndorf-Verley reduction of ketones. The activity of (H)Beta can be increased by several orders of magnitude by mild steaming. The catalytic activity of the materials following reactivation can be diminished again by adsorption of ammonia followed by an induction period. For these changes, an explanation is offered in terms of Lewis acidic framework aluminum atoms which undergo a change of configuration depending on the ligands present, rather than becoming extraframework aluminum. FTIR, 29 Si, and 27 Al MAS NMR spectroscopy were applied to investigate the changes induced by the (hydro)thermal procedures.

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Thermal stability of hydroxy groups in dealuminated mordenites

Cited by 31 publications

References 16 publications

Aluminum siting in mordenite and dealumination mechanism

Aluminum siting in mordenite and dealumination mechanism

Dealumination and Characterization of Natural Mordenite-Rich Tuffs

Zeolite Beta: The Relationship between Calcination Procedure, Aluminum Configuration, and Lewis Acidity

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