Reactivity of USY extraframework alumina in alkaline medium

Calsavara, Valmir; Sousa-Aguiar, Eduardo Falabella; Machado, Nádia Regina Camargo Fernandes

doi:10.1016/0144-2449(96)00071-1

Cited by 24 publications

(13 citation statements)

References 14 publications

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“…Spectra were recorded in He at 473 K. Table 3). droxyl nests, as was previously observed when zeolite beta was treated with Al isopropoxide [35] or Na aluminate, [36] and de-aluminated ultra-stable Y-sieve (USY) zeolite in alkaline medium, [37,38] and results in a further decrease in the corresponding absorption band at 3590 cm À1 . The possibility of re-alumination is further discussed below.…”

Section: Resultsmentioning

confidence: 60%

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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Section: Resultsmentioning

confidence: 60%

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 latter relates to the realumination of the surface. [31,49] Upon subsequent acid wash (DA4-AT1-AW1-H), the intensity and definition of all bands increased strongly again, attending to the removal of Alrich debris, confirming the strong suppressive effect on the bands in the OH stretching region. Using NH 3 -TPD a more conclusive idea of the bulk acidity was provided (Supporting Information, Figure SI5).…”

Section: Acidity Adsorption and Catalytic Evaluation Of Y Zeolitesmentioning

confidence: 71%

Hierarchical Y and USY Zeolites Designed by Post‐Synthetic Strategies

Verboekend

Vilé

Pérez‐Ramírez

2011

Adv Funct Materials

302

218

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Strategic combinations of affordable and scalable post‐synthetic modifications enabled to design a broad family of hierarchical Y and USY zeolites (FAU topology) independent on the Si/Al ratio. Pristine (Y, Si/Al = 2.4), steamed (USY, Si/Al = 2.6), and steamed and dealuminated (USY, Si/Al = 15 and 30) zeolites were exposed to a variety of acid (H4EDTA and Na2H2EDTA) and base (NaOH) treatments, which led to the introduction of mesopore surfaces up to 500 m2 g−1, while preserving the intrinsic zeolite properties. Pristine Y and USY zeolites (Si/Al ∼ 2.5) required mild dealumination (to Si/Al > 4 in the case of Y) to facilitate subsequent efficient desilication. Alkaline treatment of Y and USY zeolites with low Si/Al ratios (∼4–6) led to an abundance of Al‐rich debris, which could be removed by a subsequent mild acid wash. On the other hand, severely steamed and dealuminated, hence Si‐rich, USY zeolites (Si/Al = 15 and 30) proved extremely sensitive to the alkaline solution, displaying facile dissolution and substantial amorphization. For the latter group of ultra‐stable Y zeolites, the presence of TPA+ in the alkaline solution enables to protect the zeolite structures upon the introduction of mesoporosity by desilication, preserving crystallinity and micropore volume. The sorption and catalytic properties of the hierarchical Y and USY zeolites were superior compared to the conventional counterparts.

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“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 19 resonance at 0 ppm, (less than 5%), related to some extra-framework aluminum atoms (EFAL) respectively. 33, [43][44][45] With prolonged NH 4 OH treatment the spectra evolution reveals a correlated decrease of the 63 ppm resonance to the growth of a resonance at 57…”

Section: Resultsmentioning

confidence: 99%

Hierarchization of USY Zeolite by NH₄OH. A Postsynthetic Process Investigated by NMR and XRD

et al. 2014

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Ammonia treatment of USY zeolite has led to a new hierarchical material. The local and global structural changes during the transformation have been monitored by XRD and by 1 H, 29 Si, and 27 Al solid-state NMR. A wealth of 1D and 2D NMR protocols were applied, including 1 H DQ-SQ, 27 Al MQMAS, 29 Si MAS and CPMAS as well as 1 H-29 Si HETCOR. The effects of aqueous ammonia treatment, different thermal post-treatments and rehydration were studied. An increasing loss of crystallinity was observed upon increasing duration of ammonia treatment. Under the experimental conditions a few percent of silica was lost into solution and no loss of aluminum was observed. But, increasing numbers of silanol groups were detected. The progressive transformation induces formation of mesopores, reduction of the fraction of the sample exhibiting Bragg crystallinity and apparition of a dense, amorphous aluminosilicate phase. The latter contains ammonium ions and strongly bound water which both are resistant to thermal decomposition up to 350 °C. After about 24 hours of treatment the zeolite fraction has been completely transformed into the amorphous phase. At intermediate stages a complexhierarchical material is obtained with mesopores and zeolitic micropores next to a dense amorphous aluminosilicate, containing ammonium ions, highly structured water and silanols nests.

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Reactivity of USY extraframework alumina in alkaline medium

Cited by 24 publications

References 14 publications

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

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

Hierarchical Y and USY Zeolites Designed by Post‐Synthetic Strategies

Hierarchization of USY Zeolite by NH₄OH. A Postsynthetic Process Investigated by NMR and XRD

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Reactivity of USY extraframework alumina in alkaline medium

Cited by 24 publications

References 14 publications

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

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

Hierarchical Y and USY Zeolites Designed by Post‐Synthetic Strategies

Hierarchization of USY Zeolite by NH4OH. A Postsynthetic Process Investigated by NMR and XRD

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Hierarchization of USY Zeolite by NH₄OH. A Postsynthetic Process Investigated by NMR and XRD