Studies of the hydrogen held by solids X. Fluorided aluminas as acid catalysts

Gerberich, H. R.; Lutinski, Frank E.; Hall, W. Keith

doi:10.1016/0021-9517(66)90051-0

Cited by 31 publications

(1 citation statement)

References 7 publications

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“…The changes caused by fluorination are also accompanied by an increase in surface area and porosity, mainly in the meso-and rnacropore range. Treatment of sepiolite with F could likewise result in changes in the texture and the number and strength of the surface acidic sites after substitution, through anionic exchange, of surface -OH groups by the more electro-negative anion F- (Gerberich et al 1966;O'Reily 1966;Matulewicz et al 1980;Barthomeuf 1985) and subsequent protonization of vicinal OH s. Ammonium fluoride has also been used to introduce additional acidity to various samples (Matulewicz et al 1980, Urabe et al 1988) by anionic and/or cationic interchange with surface -OH or with the exchangeable cations in the sample, giving rise after thermal treatment to protonic acidity by NH 3 evolution. For this reason, 2 N NH4F and different concentrations of HF were used in this work as activating agents for sepiolite and their effects on the structure, surface area and pore distribution of the treated material were studied.…”

Section: Introductionmentioning

confidence: 99%

Modification of Sepiolite by Treatment with Fluorides: Structural and Textural Changes

Belzunce

Mendioroz

Haber

1998

Clays and clay miner.

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Abstract--In the search for new applications of natural silicates, various F-treatments have been applied to sepiolite to increase its acidic properties and for use as a catalyst in reactions occurring via carbonium ions. Two types of treatments including hydrofluoric acid (HF) at different concentrations and 2 N NH4F have been utilized and the physicochemical characteristics of the resulting materials studied using standard techniques. The X-ray diffractogram (XRD) patterns indicate a decrease in crystallinity of the original material as well as the appearance of amorphous silica. SEM micrographs showed a shortening and aggregation of the sepiolitic fibers. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), thermogravimetric analysis/differential thermal analysis (TGA/DTA), N2 adsorption-desorption isotherms aild Hg intrusion were used to study the changes occurring in the structure, surface area and pore distribotion of samples and acidity was evaluated by IR and thermoprogrammed desorption (TPD) of adsorbed ammonia and pyridine. It was found that acidity increased in most of the samples after anionic and cationic interchange between the activating agents and the surface sites, or extralattice cations. Additionally, structural changes induced by treatments modified the BrOnsted and Lewis acidity. Mild treatments with ammonium fluoride are more effective than HF treatments in acidity generation.

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Section: Introductionmentioning

confidence: 99%

Modification of Sepiolite by Treatment with Fluorides: Structural and Textural Changes

Belzunce

Mendioroz

Haber

1998

Clays and clay miner.

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Microcatalytic reactors: Kinetics and mechanisms with isotopic tracers

Galeski

Hightower

1970

Can J Chem Eng

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Pulsed microcatalytic reactors have found extensive application in the petroleum and chemical industries where rapid catalyst screening and evaluation are demanded. Automated, continuous‐operation test units allow the accumulation of considerable amounts of data in a minimum of time. The technique is also useful in research where the small pulse size enables one to study “initial” interactions between surface and reactants. In this way, information about many kinetic parameters, such as intrinsic reaction rates, orders, poisoning effects, and catalyst deactivation, can be obtained. Both stable and radioactive isotopic tracers may be used economically in microcatalytic reactors to provide significant mechanistic information which cannot be obtained conveniently by other methods. For example, one can explore the chemical nature and number of active sites, as well as the fate of individual atoms and molecules as they interact with the catalyst. Although the technique may be applied to both “simple” and complex catalytic reaction systems, the discussion will be limited to a review of data obtained from (1) “unimolecular” reactions such as cyclopropane and butene isomerization and cumene dealkylation over the mixed oxides silica‐alumina, silica‐magnesia, and zeolites and (2) “bimolecular” reactions such as ethylene hydrogenation over alumina. Some of the limitations of microcatalytic reactors will also be given.

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