Mechanistic aspects of the isomerization reactions of 1,1,2,2-tetrafluoroethane on a cfc-conditioned chromia catalyst

Kemnitz, Erhard; Niedersen, K.-U.

doi:10.1016/s0022-1139(96)03419-7

Cited by 13 publications

(9 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Using deuterium-labeled HCFC-124, they showed that olefins were not formed as intermediates on the surface of the catalyst. Reactions by Kemnitz et al, however, did support the formation of these olefinic intermediates in similar reactions . HFC-134 (CF 2 HCF 2 H) over a chlorine-conditioned catalyst reacts to form CHClCCl 2 and HCFC-133 (CF 3 CH 2 Cl) as the initial major products.…”

Section: Discussionmentioning

confidence: 95%

Structural Characterization and Hydrochlorofluorocarbon Reactivity on Zinc-Exchanged NaX

et al. 1998

View full text Add to dashboard Cite

Solid-state MAS NMR and synchrotron X-ray powder diffraction have been used to study the reactivity and structure of Zn2+-exchanged NaX. Dehydrated ZnX with a Zn:Na ratio of 3.6:1 was refined in the space group Fd3m. The zinc cations were located in four distinct positions all along the [111] direction. Residual sodium cations were found in the supercage at the site II position. A tetrahedral extraframework aluminum species, AlO4 5-, was refined in the center of the sodalite cage; this anion was also observed by 27Al MAS NMR. The reactions of hydrochlorofluorocarbon (HCFC)-124a (CF2HCF2Cl) over NaX, and two Zn2+-exchanged NaX samples, were studied with NMR and a mass spectrometry (MS)-equipped catalysis unit. The products of both the dehydrofluorination and dehydrochlorination reactions are observed over all zeolites: the unsaturated products (CF2CF2 and CF2CFCl) desorb from the zeolites and are detected by MS. In contrast, saturated products are primarily observed when the reaction is followed with 19F NMR in sealed ampules. Both CF2CF2 and HFC-125 (CF3CF2H) are observed for reactions over NaX, while on Zn2+ exchange, CF2CF2 is no longer observed. Instead, a resonance is observed at −123 ppm, which is tentatively assigned to (CF2) n groups. No evidence is seen by 27Al and 19F NMR for attack of the zeolite framework when the reactions are performed at low temperatures. An in situ X-ray diffraction study of HCFC-124a loaded ZnX shows significant structural changes at the same temperature as the onset of HCFC reactivity.

show abstract

Section: Discussionmentioning

confidence: 95%

Structural Characterization and Hydrochlorofluorocarbon Reactivity on Zinc-Exchanged NaX

et al. 1998

View full text Add to dashboard Cite

show abstract

“…176 HFCs themselves can be isomerized over chromia, which has been preconditioned with a CFC additive, as was developed and mechanistically probed by Kemnitz and Niedersen. 600 VF3 can also react with surface HCl to form 133 which can undergo the same isomerization to 133a via HCFO-1122. If chlorine-free conditioning agents are used, the formation of chlorofluoroethylenes is avoided and the dominant pathway of 134 → VF3 → 134a is maintained.…”

Section: Kellner Et Al (Du Pontmentioning

confidence: 99%

“…HFCs themselves can be isomerized over chromia, which has been preconditioned with a CFC additive, as was developed and mechanistically probed by Kemnitz and Niedersen …”

Section: Hydrofluorocarbons (Hfcs3rd Generation)mentioning

confidence: 99%

Fluorocarbon Refrigerants and their Syntheses: Past to Present

2020

View full text Add to dashboard Cite

This Review chronicles the progress made in the field of small fluorocarbon synthesis since their invention in the early 1930s by Thomas Midgley, Jr., and his coworkers, with special focus on their application as refrigerants, foam expansion agents, aerosol propellants, and precision solvents. Divided into four generations of C1–C4 halocarbons from CFCs through HCFCs, HFCs, and HFOs, the merits and challenges of each will be discussed in the context of market demands, as well as the evolution of industrial manufacturing methods. Vital transformations, such as exchange (Swarts) fluorination, hydrodehalogenation, dehydrohalogenation, and additions (Kharasch or Prins) will feature prominently and will be discussed in detail, as well as catalysts therefor. Of the myriad of fluorocarbons described herein, the models which have reached particular commercial significance (such as chlorodifluoromethane and 1,1,1,2-tetrafluoroethane) are given special consideration as flag-bearers for the generation to which they belong. Regulatory constraints to which this industry is bound will be outlined in brief, as well as an introduction to safety designations and nomenclature put forth by the American Society for Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). This Review includes predominantly works which can only be found in the patent literature, but should be of equal interest to both academic and industrial practitioners of the art as it centers on fundamentals of organofluorine chemistry, which could equally be applied to the synthesis of larger molecules and building blocks for other applications.

show abstract

“…The alternative pathway of dehydrochlorination or dehydrofluorination followed by hydrofluorination of the olefin formed can be promoted by using a chromia prefluorinated by an HFC. The isomerisation of CHF 2 CHF 2 to CH 2 FCF 3 occurs via this route [28,29].…”

Section: Fluorinated Chromiamentioning

confidence: 99%

Investigating acidity of metal fluoride surfaces by spectroscopic and chemical methods

Winfield

2009

Journal of Fluorine Chemistry

View full text Add to dashboard Cite

Mechanistic aspects of the isomerization reactions of 1,1,2,2-tetrafluoroethane on a cfc-conditioned chromia catalyst

Cited by 13 publications

References 13 publications

Structural Characterization and Hydrochlorofluorocarbon Reactivity on Zinc-Exchanged NaX

Structural Characterization and Hydrochlorofluorocarbon Reactivity on Zinc-Exchanged NaX

Fluorocarbon Refrigerants and their Syntheses: Past to Present

Investigating acidity of metal fluoride surfaces by spectroscopic and chemical methods

Contact Info

Product

Resources

About