X-Ray Photoelectron and X-Ray Excited Auger Electron Spectroscopic Analysis of Surface Modifications of Chromia during Heterogeneous Catalyzed Chlorine/Fluorine Exchange

Kemnitz, Erhard; Kohne, A.; Grohmann, I.; Lippitz, Andreas; Unger, Wolfgang

doi:10.1006/jcat.1996.0088

Cited by 58 publications

(45 citation statements)

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“…It is proposed that residual H 2 O is trapped within the channels, that it is lost slowly and that this process leads to some hydration and hydroxylation of the surface (II in Scheme 1). Although surface hydrolysis can occur during prolonged exposure to moist air, for example, previous XPS work 24 indicates that the surface atom ratio O 2Ϫ : Al 3ϩ in β-AlF 3 can be as high as 0.25, in view of the handling procedures used here, extensive hydrolysis of the surface was unlikely.…”

Section: The Behaviour Of H 18 F or H 36 CL Towards -Alf 3 And Fluorimentioning

confidence: 91%

Reactivity of fluorinated γ-alumina and β-aluminium(iii) fluoride surfaces towards hydrogen halides and tert-butyl chloride

Barclay

Bozorgzadeh

Kemnitz

et al. 2001

J. Chem. Soc., Dalton Trans.

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The Lewis acids β-aluminium() fluoride and γ-alumina, fluorinated at room temperature with sulfur tetrafluoride, both interact with hydrogen fluoride and chloride, as demonstrated by radiotracer measurements using [ 18 F] and [ 36 Cl]. The different behaviour of HCl towards the two surfaces is rationalised by considering plausible surface sites and, in the case of β-AlF 3 , the role of residual water. Both materials promote dehydrochlorination of tert-butyl chloride. β-Aluminium() fluoride also has some catalytic activity in Friedel-Crafts alkylation whereas oligomerisation of Bu t Cl dominates on fluorinated γ-alumina. The different behaviour appears to be due to the presence of both Lewis and Brønsted surface acidity on γ-alumina that has been fluorinated under static conditions. A description for this surface is proposed.

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Section: The Behaviour Of H 18 F or H 36 CL Towards -Alf 3 And Fluorimentioning

confidence: 91%

Reactivity of fluorinated γ-alumina and β-aluminium(iii) fluoride surfaces towards hydrogen halides and tert-butyl chloride

Barclay

Bozorgzadeh

Kemnitz

et al. 2001

J. Chem. Soc., Dalton Trans.

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“…Three species corresponding to 2p 3/2 binding energies of 581.0 ± 0.2, 577.5 ± 0.3 and 576.6 ± 0.2 eV are present. The binding energy at 581 eV could be attributed to a ''Cr-F'' bond in a structure which is difficult to determine but which does not correspond to CrF 3 [21]. According to the literature [22], the 576.6 eV binding energy corresponds to ''Cr-O'' bond in Cr 2 O 3 -like species.…”

Section: Characterization Of the Catalysts By Xpsmentioning

confidence: 99%

Catalytic Fluorination of Various Chlorinated Hydrocarbons by HF and a Chromium Based Catalyst: Effect of the Presence of Zinc

et al. 2010

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International audienceThe Cl/F exchange of chlorinated hydrocarbons with HF was carried out in the gas phase (P = 1 atm. and T = 380 A degrees C) on chromium catalysts doped with zinc. A promoting effect of zinc has been found for various chlorinated hydrocarbons. This positive effect was more significant for CF(3)CH(2)Cl than for CF(3)CHCl(2) or CH(2)Cl(2). CF(3)CH(2)Cl was less reactive than the two other reactants. The promoting effect observed for an atomic ratio Zn/(Zn + Cr) = 0.15 was higher with a low (Zn + Cr) content, which corresponds to a better dispersion of the different elements on the surface. The presence of zinc is supposed to promote the dispersion of chromium and to favour its fluorination to form the centers which are active in Cl/F exchange and were characterized in XPS by energies corresponding to the presence of "CrOF" and "Cr-F" species

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“…Models of the β-AlF 3 surface have been suggested based on its chemical activity and the assumption that the (100) plane provides the dominant surface 11 . Consequently, we have previously used density functional theory (DFT) calculations to investigate the phase stability of β-AlF 3 (100) in contact with gaseous F 2 , as a function of the partial pressure and temperature of the gas 12,13 .…”

Section: Introductionmentioning

confidence: 99%

Characterization of Lewis acid sites on the (100) surface of β-AlF3: Ab initio calculations of NH3 adsorption

Bailey

Wander

Mukhopadhyay

et al. 2008

The Journal of Chemical Physics

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The current study employs hybrid-exchange density functional theory to show that the Lewis base, NH 3 , binds to the β-AlF 3 (100) surface with a binding energy of up to -1.96 eV per molecule. This is characteristic of a strong Lewis acid. The binding of NH 3 to the surface is predominately due to electrostatic interactions. There is only a small charge transfer from the NH 3 molecule to the surface. The binding energy as a function of coverage is computed and used to develop a lattice Monte Carlo model which is used to predict the temperature programmed desorption (TPD) spectrum. Comparison with experimental TPD studies of NH 3 from β-AlF 3 strongly suggests that these structural models and binding mechanisms are good approximations to those that occur on real AlF 3 surfaces.

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X-Ray Photoelectron and X-Ray Excited Auger Electron Spectroscopic Analysis of Surface Modifications of Chromia during Heterogeneous Catalyzed Chlorine/Fluorine Exchange

Cited by 58 publications

References 0 publications

Reactivity of fluorinated γ-alumina and β-aluminium(iii) fluoride surfaces towards hydrogen halides and tert-butyl chloride

Reactivity of fluorinated γ-alumina and β-aluminium(iii) fluoride surfaces towards hydrogen halides and tert-butyl chloride

Catalytic Fluorination of Various Chlorinated Hydrocarbons by HF and a Chromium Based Catalyst: Effect of the Presence of Zinc

Characterization of Lewis acid sites on the (100) surface of β-AlF3: Ab initio calculations of NH3 adsorption

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