Cracking activity of some synthetic zeolites and the nature of the active sites

Hopkins, Philip D.

doi:10.1016/0021-9517(68)90116-4

Cited by 87 publications

(14 citation statements)

References 7 publications

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“…On comparing the exotherms of NH~Y and HY zeolites, it is observed that the exotherm associated with ammonia removal was absent for HY (around 500~ which was finally confirmed by microanalysis and gravimetric analysis. These observations agree with an earlier report [16]. Exothermic peaks (900-990 ~ and temperature of mullatization in the range 1030-1065 ~ are attributed to structural transformation, as confirmed by the X-ray analysis [17].…”

Section: Resultssupporting

confidence: 83%

Thermal behaviour of modified faujasites

Chandwadkar

Kulkarni

1980

Journal of Thermal Analysis

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A derivatograph was used to follow the modification of the skeleton structure and thermal stability of zeolites in sodium and ammonium forms. Analogous investigations were carried out by independent methods such as IR and X-ray. Comparison showed good agreement between the results. The controlled dealumination of the Y-type zeolite enhanced the thermal stability.Modified zeolites prepared by treatment with ethylene diamine tetraacetic acid (H4 EDTA) and subsequent activation profoundly alter their structures. Samples treated in this manner show differences in both catalytic activity and adsorptional properties, depending on the SiO~/A120 3 ratio. In particular, the crystallinity of the Y-type zeolite is maintained up to the elimination of roughly one-half of the aluminium [1 ], and then it begins to fall off while the catalytic activity incracking reactions rises [2]. The zeolite-based catalysts containing protons and polyvalent cations are more active [3] as compared to alkali metal zeolites.As regards the cation-deficient zeolites, the thermal behaviour of Y-type zeolites exchanged with ammonium ions has been reported [4,5] to some extent. The effects of the variation of the silica-alumina ratio and the bed geometry on the dehydroxylation and thermal stability of the products have been studied [4] and related [5] to the residual Na § ions in the Y-type zeolite. Kerr [4,6] proposed that ultrastabilization involved the removal of framework aluminum, which is held as AI(OH)~-, AI(OH) 2 § or A13 § ions. The present study was undertaken to obtain additional evidence on the thermal stability of dealuminated zeolites by thermal, X-ray and IR. ExperimentalBinder-free Y-type zeolites in the sodium (SK-40) and ammonium (SK-41) forms were obtained from Union Carbide (USA), dried at 120 ~ and kept for about a week over a saturated solution of ammonium chloride at room temperature. The chemical compositions of the dehydrated zeolites, determined by gravimetric analysis, were as follows:* NCL Communication No.

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Section: Resultssupporting

confidence: 83%

Thermal behaviour of modified faujasites

Chandwadkar

Kulkarni

1980

Journal of Thermal Analysis

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“…Compared with supercage and pocket, the zigzag and longer channel of sinusoidal pore is a more proper location for these kinds of reactions. Moreover, these two reactions can be effectively catalyzed by relatively weak acid sites [43,44], so the selectivities of toluene and paraffin (Table 3) on HM xy-DMQ are distinctively higher than those over HM and HM xy .…”

Section: Distribution Of Products In Different Pores Of Mcm-49mentioning

confidence: 99%

Catalytic role of different pore systems in MCM-49 zeolite for liquid alkylation of benzene with ethylene

Liu

Xie

Liu

et al. 2011

Journal of Catalysis

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“…We will briefly summarize the mechanistic characteristics of this type of reaction as catalyzed by crystalline aluminosilicates (56,59,60). The preponderance of evidence suggests a protoncatalyzed carbonium ion mechanism (12), although it appears likely that Lewis-type sites may indeed have a synergistic, amplifying effect (28). Thus, zeolite-catalyzed alkylations show ortho, para-substitution patterns, aromatic substrate selectivity preferences,, and promotion effects (33) that are analogous to those observed with similar reactants in the presence of HCIO4 , 98% H2 SO4 , HCI-AICI3 , HF, etc.…”

Section: Olefin-aromatic Interactions and Related Reactions Inmentioning

confidence: 84%

“…Such interactions are visualized in Figure 4, where benzene (28) and ethylbenzene (46) show heats of adsorption on HY-type zeolites ranging from 15 to 18 kcal/mole. In HY, hydroxyl groups may be specific adsorption sites for aromatics.…”

Section: Aromatic-zeolite Interactionsmentioning

confidence: 99%

Aromatic Reactions Over Molecular Sieve Catalysts: A Mechanistic Review

Venuto¹

1977

Catalysis in Organic Syntheses 1977

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Cracking activity of some synthetic zeolites and the nature of the active sites

Cited by 87 publications

References 7 publications

Thermal behaviour of modified faujasites

Thermal behaviour of modified faujasites

Catalytic role of different pore systems in MCM-49 zeolite for liquid alkylation of benzene with ethylene

Aromatic Reactions Over Molecular Sieve Catalysts: A Mechanistic Review

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