Modification of Zeolites

Kühl, Günter H.

doi:10.1007/978-3-662-03764-5_3

Cited by 42 publications

(10 citation statements)

References 649 publications

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“…For instance, the K 1.00 β sample was obtained by conducting at 80 o C the ion-exchanging reaction of Naβ in an aqueous solution of 0.5 M KBr for four times, while the Rb 1.00 β and Cs 1.00 β samples could not be obtained simply by repeating four times the ion-exchange reaction in 0.5 M RbNO 3 or 0.5 M CsNO 3 solution unless an interim high-temperature (500 o C) calcination step was added. This is because that some Na + ions in the parent Naβ are located inside the cages with small openings and are not accessible to the larger Rb + (1.48 Å) and Cs + (1.69 Å) ions but smaller K + ions (1.33 Å) [31], and the calcination of the partially exchanged samples can cause redistribution by thermal migration of the alkali ions within the zeolite, making those Na + accessible to and replaced by the coexisting Rb + or Cs + ions [32,33]. The displaced Na + ions then became exchanged with the Rb + or Cs + ions during the later ion-exchange steps.…”

Section: Composition and Physicochemical Propertiesmentioning

confidence: 99%

Sustainable production of acrylic acid: Rb+- and Cs+-exchanged Beta zeolite catalysts for catalytic gas-phase dehydration of lactic acid

Yan

Mahmood

et al. 2016

Catalysis Today

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Rb + -and Cs + -exchanged Beta zeolites (Rb x Na 1-x β and Cs x Na 1-x β) of varying exchange degrees (x = 0~1.00) were employed to catalyze the gas-phase dehydration of lactic acid (LA) for sustainable production of acrylic acid (AA) in a flow fixed-bed reactor at 360 o C, using an aqueous solution of LA (10 mol% or 35.7%) as the reaction feed at a weight hourly space velocity by LA of 2.1 h -1 . An appropriate window of the ion exchange degrees for highly selective AA production (≥ 60 mol%) was determined for either series of the samples, i.e., x = 0.85~0.98 for the Rb x Na 1-x β and x = 0.71~0.90 for the Cs x Na 1-x β samples. The best performing catalysts Rb 0.95 Na 0.05 β, and Cs 0.81-0.90 Na 0.19-0.10 β offered the highest AA selectivity (ca. 70 mol%) and yield (ca. 60~65 mol%) for reaction periods of longer than 10 h. Measurements of the surface acidity and basicity of the catalyst samples bytemperature-programmed desorption of NH 3 and CO 2 showed that the highly selective catalysts in such widows should have both weakly acidic and weakly basic surface sites with suitably balanced acidity and basicity. The acid-catalyzed decarbonylation/decarboxylation and base-catalyzed condensation of LA, which lead respectively to formation of acetaldehyde and 2,3-pentanedione, always occurred as the competing reactions over the investigated catalysts. Observations on the catalyst selectivity changes for these competing reactions clearly demonstrate that the suitably balanced acidity and basicity at the catalyst surface is the key to the high selectivity for the desired dehydration reaction.

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Section: Composition and Physicochemical Propertiesmentioning

confidence: 99%

Sustainable production of acrylic acid: Rb+- and Cs+-exchanged Beta zeolite catalysts for catalytic gas-phase dehydration of lactic acid

Yan

Mahmood

et al. 2016

Catalysis Today

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“…This zeolite was thereafter filtered, washed exhaustively with bi-distilled water and dried in an oven at 70 °C. Further, the ammonium clinoptilolite was dealuminated with a 0.1 M solution of ammonium hexafluorosilicate (HFSi), explicitly: (NH 4 ) 6 SiF 6 [24]. This solution was prepared with 0.05 g of (NH 4 ) 6 SiF 6 in 500 mL of DDW.…”

Section: Materials and Modification Proceduresmentioning

confidence: 99%

“…The hydroxyl bridged groups have been widely studied by, IR spectrometry [24], microcalorimetry [25], nuclear magnetic resonance [26], and other methods [27,28]. Between other conclusions, it was proposed that the acidity of these sites is related with the ease of the proton to be released, i.e., if the interaction between the proton and the oxygen is weaker the Brönsted site should be more acid and the zeolite more active as an acid catalyst [24][25][26][27][28][29]. This inference, however, is not totally exact, since other effects, influences the properties of these acid sites [28].…”

Section: Introductionmentioning

confidence: 99%

“…This process can be done for example: by hydrothermal treatments (steaming), acid leaching, or with treatments in flowing silicon tetrachloride (SiCl 4 ) or hexafluorsilicates ((NH 4 ) 6 SiF 6 ) [24]. These dealumination methods could increase the amount of zeolite in the sample, eliminate charge compensating cations to open the zeolite channels, create mesopores and increase the adsorption field.…”

Section: Introductionmentioning

confidence: 99%

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Study of the Adsorption Space of Modified Clinoptilolites

Rolando¹,

Roque-Malherbe²,

Alba³

et al. 2013

JMSE-B

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Carbon dioxide (CO 2 ) adsorption is an important adsorbent characterization method and a significant industrial process. In separation and recovery technology, the adsorption of the CO 2 is important to reduce the concentration of this gas considered as one of the greenhouse gases. Natural zeolites, particularly clinoptilolite, are widely applied as adsorbents. In this regard, in the present research, the structure, composition and morphology of modified with hexafluorosilicate (HFSi) and orthophosphoric acid (H 3 PO 4 ) clinoptilolites were investigated by characterizations and measurements made with, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDAX) and gravimetric adsorption. Additionally, the surface Chemistry of the modified clinoptilolites was analyzed by applying diffuse reflectance fourier transform infrared spectrometry (DRIFTS). Further, the interaction of CO 2 within the adsorption space of these modified clinoptilolites and a synthetic ZSM-5 zeolite was studied with the help of adsorption measurements. After all, an appropriate theoretical methodology for the analysis of the XRD and adsorption data was applied. The calculated cell parameters of the tested are similar to those reported for a typical clinoptilolite of: a = 17.662 Ǻ, b = 17.911 Ǻ, c = 7.407 Ǻ and β = 116.40 The resolution of the TGA derivative profiles indicated the presence of two steps for water release, one of them represents the loss of majority of the water present in the micropores. This was evidenced as a broad peak centered at about 50 0 C for the CSW-HFSi-0.1, but at 100 °C for the samples CSW-HFSi-0.4. The SEM micrographs corresponding to the modified clinoptilolites, was evidenced that the CSW zeolite shows secondary particles exhibiting diameters from 3 to 40 μm, formed by primary clinoptilolite crystallites showing a crystallite size, Φ = 40 nm. The EDAX elemental analysis it can be demonstrated that the exchange process replaced about 85% of the charge compensating ions. The DRIFT spectra of the modified clinoptilolites, specifically, CSW-HFSi-0.1, show a narrow band at about: 3,740 cm -l corresponding to terminal silanol groups (Si-OH) and a band 3,600-3,650 cm -1 resulting from extra-framework Al-OH. With the precision of the measured micropore volumes related to the excellent fitting of the adsorption data by the D-R isotherm equation, it can be affirm that carbon adsorption took only place in the micropore region. The isosteric heat of adsorption calculated for the modified clinoptilolites was greater than those values reported of ZSM-5 zeolite, particle packing silica, dealuminated Y zeolite (DAY) Cd, Zn and Ni-nitroprussides and Cu-nitroprusside and a Ni-MOF. With the obtained result it can be concluded that the modified clinoptilolites with HFSi showed a quality as adsorbent comparable to commercial synthetic zeolites.

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“…Silicate structure of zeolite is degenerated by acid treatment. The increase of Si/Al ratio in this way is called dealumination process (Kuhl, 1999). The advantages of dealumination are removal of cations in zeolites, increase in heat-sensitivity, extension of pore size and increase in adsorbent feature of zeolite (Gottardi, 1986).…”

Section: Introductionmentioning

confidence: 99%

Effect of activated clinoptilolite in aflatoxin B1 contaminated laying hen diets on aflatoxin B1 residues and quality of eggs

Demir

Eseceli

Özcan

2017

Zb Mat srp prir nauk

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This study was carried out to determine the effect of a high level of aflatoxin B1 in laying hen diets, supplemented with deactivated and activated clinoptilolite, on inner and outer quality and aflatoxin B1 residues in eggs. Two experimental groups were formed and fed high aflatoxin B1 diets (965 ppb) containing deactivated and activated (450 °C for 60 minutes) clinoptilolite (2% of diet) for 49 days. In the experiment, a total of 960 55-week-old Lohmann LSL (white) laying hens were used. Each group had 8 replicates and 480 hens. Egg weight, inner and outer egg quality parameters and egg aflatoxin B1 levels were determined in a total of 90 eggs collected on the 15 th , 30 th and 49 th days of the experiment. Diets containing deactivated or activated clinoptilolite decreased aflatoxin B1 production in laying hen diets after incubation period of 15 days. Activation of clinoptilolite by heat treatment significantly reduced aflatoxin B1 level in eggs (p<0.05). In addition, the use of clinoptilolite as an antifungal agent in the presence of high aflatoxin B1level in layer hen diets significantly increased the weight of eggs and significantly reduced the ratio of brokencracked and dirty eggs (p<0.05). Chicken blood albumin, creatinine and calcium levels were higher in hens fed diet containing activated clinoptilolite (p<0.05). However, triglyceride and VLDL levels decreased significantly in the blood of these animals (p <0.05). In conclusion, the supplementation of hen diets containing high aflatoxin B1 with activated clinoptilolite improves production performance, egg quality and decreases aflatoxin B1 residue in the egg.

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Modification of Zeolites

Cited by 42 publications

References 649 publications

Sustainable production of acrylic acid: Rb+- and Cs+-exchanged Beta zeolite catalysts for catalytic gas-phase dehydration of lactic acid

Sustainable production of acrylic acid: Rb+- and Cs+-exchanged Beta zeolite catalysts for catalytic gas-phase dehydration of lactic acid

Study of the Adsorption Space of Modified Clinoptilolites

Effect of activated clinoptilolite in aflatoxin B1 contaminated laying hen diets on aflatoxin B1 residues and quality of eggs

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