Influence of downsizing of zeolite crystals on the orthorhombic ↔ monoclinic phase transition in pure silica MFI-type

Kabalan, Ihab; Michelin, Laure; Rigolet, Séverinne; Marichal, Claire; Daou, T. Jean; Lebeau, Bénédicte; Paillaud, Jean‐Louis

doi:10.1016/j.solidstatesciences.2016.06.009

Cited by 6 publications

(4 citation statements)

References 26 publications

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“…In addition, the resulting 3D pore network contains larger spherical voids at the channel intersections of ∼10 Å in diameter. The MFI topology is influenced by temperature, Si/Al ratio, and the type of guest molecules and can exist in a monoclinic ( P 2 1 / n symmetry) and an orthorhombic structure ( Pnma symmetry) with 24 and 12 crystallographically distinct tetrahedral sites (T sites), respectively. − …”

Section: Introductionmentioning

confidence: 99%

Distribution of Aluminum over the Tetrahedral Sites in ZSM-5 Zeolites and Their Evolution after Steam Treatment

et al. 2018

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Zeolite ZSM-5 is one of the most widely used zeolites, in particular in heterogeneous catalysis. This work investigates the incorporation of Al in the silica framework of monoclinic ZSM-5 and the Al speciation during steam treatment for four ZSM-5 samples with different Si/Al ratios, using ultrahigh field 27 Al NMR (22.3 T), 29 Si NMR, X-ray diffraction, and IR spectroscopy. 27 Al MQMAS NMR at 22.3 T allows identification and quantification of 10 distinct tetrahedral framework resonances which are assigned to the crystallographic sites by their average T−O−T angles, determined from powder XRD patterns for the same samples. A clear Al site preference is observed and found to be dependent on the Si/Al ratio of the parent zeolite. The framework sites facing the intersections in ZSM-5 are found to be most prone to dealumination, whereas Al in the straight and sinusoidal-shaped channels are more stable toward steam treatment at high temperatures. Extra-framework Al species with 5-and 6-fold coordination and two distorted tetrahedral AlO 4 sites have also been identified. The spectroscopic data are supported by catalytic activities from α-test cracking experiments which are in accordance with a reinsertion of Al in the framework at mild steaming and the onset of dealumination at higher temperatures.

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Section: Introductionmentioning

confidence: 99%

Distribution of Aluminum over the Tetrahedral Sites in ZSM-5 Zeolites and Their Evolution after Steam Treatment

et al. 2018

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“…42 The observed satellite resonances can be attributed to the 12 crystallographically distinct tetrahedral sites originating from the orthorhombic crystal lattice of ZSM-5. 43,44 On the other hand, the 27 Al NMR spectra (Fig. 7B) of both zeolites have shown a single peak around '56 ppm' indicating tetrahedral aluminium coordination in the framework structure (Al T ).…”

Section: Computational Detailsmentioning

confidence: 96%

Nanostructured zeolite with brain-coral morphology and tailored acidity: a self-organized hierarchical porous material with MFI topology

et al. 2020

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“…The ZSM-5 (Si/Al = 36) zeolite was synthesized following the procedure described in the literature [52] . A detailed synthesis description is provided in the Supplementary Material.…”

Section: Zsm-5 Zeolite Preparation and Steam Treatmentmentioning

confidence: 99%

Dynamic evolution of HZSM-5 zeolite framework under steam treatment

He,

Li,

Han

et al. 2023

Chem Synth

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Understanding the dynamic evolution of zeolite framework structures and the interactions between various hydroxyl groups or aluminum species under different steam conditions at the atomic scale is extremely crucial. Herein, using a series of characterization methods, the framework structures of HZSM-5 zeolites (Si/Al = 36) following exposure to steam in the temperature range of 100 to 500 °C are investigated. Under mild steam conditions (T ≤ 200 °C), dealumination is nearly absent, and the silanol nests directly condense to create new framework Si-O-Si bonds. Conversely, under severe steam conditions (T ≥ 300 °C), the framework tetrahedral aluminum atoms Al(IV)-1 can be sequentially converted to partially coordinated framework aluminum Al(IV)-2 and extra-framework aluminum (EFAL) through partial and complete hydrolysis, which cause an increase in the framework Si/Al ratio and a decrease in crystallinity. Al(IV)-2 is recognized as a significant intermediate species for framework complete dealumination. The Brønsted acid sites on Al(IV)-2 can be perturbed by the framework Al-OH groups due to hydrogen bonding interactions, leading to a shift in 1H chemical shifts to lower fields, appearing at 6.0-9.0 ppm and 12.0-15.0 ppm. The newly generated EFAL and silanol nests further evolve through condensation as well. Meanwhile, during dealumination, the spatial correlations (or interactions) of various hydroxyl groups on structurally distinct aluminum species [Al(IV)-1, Al(IV)-2, and EFAL] and aluminum species become extremely intricate. Based on these findings, the dynamic evolution path of HZSM-5 zeolite framework structures under mild and severe steam conditions is proposed.

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Influence of downsizing of zeolite crystals on the orthorhombic ↔ monoclinic phase transition in pure silica MFI-type

Cited by 6 publications

References 26 publications

Distribution of Aluminum over the Tetrahedral Sites in ZSM-5 Zeolites and Their Evolution after Steam Treatment

Distribution of Aluminum over the Tetrahedral Sites in ZSM-5 Zeolites and Their Evolution after Steam Treatment

Nanostructured zeolite with brain-coral morphology and tailored acidity: a self-organized hierarchical porous material with MFI topology

Dynamic evolution of HZSM-5 zeolite framework under steam treatment

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