Acid Zeolites: An Attempt to Develop Unifying Concepts (P. H. Emmett Award Address, 1981)

Jacobs, Peter A.; Leuven, KU

doi:10.1080/03602458208079659

Cited by 220 publications

(49 citation statements)

References 33 publications

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“…Figure 6 shows the overall dehydration activity and the yields to ethylene (Yo) and ethylether (YE) vs. time on stream. As expected (Jacobs, 1982) from the acidity values in Table 1, catalyst S-1 is the more active and the less stable.…”

Section: Catalytic Activitysupporting

confidence: 49%

“…The catalytic behaviour of the prepared samples was evaluated in the o-xylene isomerization and ethanol dehydration. These reactions take place on acid sites (Ward & Hansford, 1969;Jacobs, 1982) but they are also sensitive to the texture and structure of the catalyst (Jacobs & Martens, 1986). On the other hand, as sepiolite is an effective catalyst for dehydration of ethanol (Dandy & Nadiye-Tarbiruka, 1982), comparative experiments were performed with samples of the material modified treatment.…”

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confidence: 99%

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Physicochemical and Catalytic Properties of a Modified Natural Clinoptilolite

et al. 1994

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Samples of natural clinoptilolite modified by treatment with NH4C1 or HCI solutions, followed by thermal treatments, have been characterized, and their catalytic activity evaluated, in o-xylene isomerization and ethanol dehydration reactions. The substitution of the compensating cations by NH4 ~ does not produce structural changes in the original material, but it opens the channels and increases its acidity and thermal stability. The treatment with HCI increases both the acidity and the effective diameter of the channels and pores but it produces an important loss of zeolite phase. Calcination of the acidic forms above 973 K leads to the breakdown of the zeolite structure. Catalytic activity of the samples is related to the surface acidity. For the original and NH4Cl-treated samples, however, the conversion of o-xylene is limited by the access of the reactant inside the channels of the zeolite. A comparative study with modified sepiolite in dehydration of ethanol has also been performed.

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Section: Catalytic Activitysupporting

confidence: 49%

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confidence: 99%

Physicochemical and Catalytic Properties of a Modified Natural Clinoptilolite

et al. 1994

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“…9 is shown these DRIFT spectra, in the range between: 3,200-3,800 cm -1 . Between, the bands present in the recorded DRIFTS spectra, the most important are the OH stretching vibrations related to the hydroxyl functionalities, specifically: silanol groups: Si-OH that is, terminal hydroxyl groups showing low acidity bridged hydroxyl groups: Si-OH-Al in which the proton shows Brönsted acid character and non-acidic extra-framework hydroxyl groups [50]. In the specific case of the DRIFTS spectrum corresponding to the ZSM-5, reported in related to extra-framework, Al-OH, that is: positively charged extra-framework aluminum, and a peak located at 3,740 cm -1 related to terminal silanol groups [26].…”

Section: Resultsmentioning

confidence: 99%

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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“…Binary and multicomponent oxides typically contain surface hydroxyl groups (11) and zeolites may contain protons as charge-compensating ions [ 79,80). The O-H stretching frequency of unperturbed hydroxyl groups depends on the electronegativity of the coordination center of the group, the number of cationic coordination centers it is bonded to, the oxygen coordination number of these centers and the overall bond character of the particular material.…”

Section: Characterization Of Protonic Sitesmentioning

confidence: 99%

“…Si(OH)Al [79,80]. H-bonding occurs when co is adsorbed at 77 K and leads to AVOH shifts of 250 to 340 cm-I , depending on the type of zeolite and its composition.…”

Section: Hydrogen-bondingmentioning

confidence: 99%

Infrared Spectroscopy as a Probe of Surface Acidity

Knözinger

1993

Elementary Reaction Steps in Heterogeneous Catalysis

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ABSTRACT. The application of infrared spectroscopy for the study of surface acidity requires suitable probe molecules. A classification of such probe molecules is given and their suitablility for discrimination between protonic (Bronsted) and non-protonic (Lewis) acidity, and for the determination of surface acidity in terms of acid strength and site density is discussed. Selected examples are described with special emphasis being payed to acidic properties of simple binary oxides, supported oxides and zeolites.

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Acid Zeolites: An Attempt to Develop Unifying Concepts (P. H. Emmett Award Address, 1981)

Cited by 220 publications

References 33 publications

Physicochemical and Catalytic Properties of a Modified Natural Clinoptilolite

Physicochemical and Catalytic Properties of a Modified Natural Clinoptilolite

Study of the Adsorption Space of Modified Clinoptilolites

Infrared Spectroscopy as a Probe of Surface Acidity

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