Fluorine-mediated acidity of alumina-pillared fluorohectorite

Journal Article · Sun Jan 31 23:00:00 EST 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1058· OSTI ID:6236329

Butruille, J R; Pinnavaia, T J ^[1]; Michot, L J; Barres, O ^[2]

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1. Michigan State Univ., East Lansing (United States)
2. URA 235 du CNRS, Vandoeuvre (France)

Structural fluorine atoms in the 2:1 layered silicate framework of fluorohectorite have a profound effect on the acidity of alumina-pillared derivatives prepared by intercalation of Al[sub 13] polycations and subsequent calcination at elevated temperatures. The alumina-pillared clay formed by calcination at 350[degrees]C exhibits greatly enhanced catalytic activity for propylene alkylation of biphenyl, relative to nonfluorinated smectite hosts. However, calcination of the Al[sub 13] intercalate at 500[degrees]C results in a relatively inactive clay with greatly diminished NH[sub 3] and pyridine chemisorption properties. The effect of the calcination process on the clay layer structure was carefully studied by [sup 27]Al, [sup 29]Si, and [sup 19]F MAS-NMR and FTIR spectroscopic methods and by mass spectrometric analysis of volatile by-products. It was shown that between 30 and 500[degrees]C, specific lattice fluorine atoms adjacent to charged sites in the octahedral sheet of the layers are replaced by hydroxyl groups. At calcination temperatures below 350[degrees]C the Broensted acidity of protonated hydroxyl groups in the layers is enhanced by the electron-withdrawing effect of near-neighbor fluorine atoms at neutral sites in the octahedral sheet. A mechanism for fluorine hydrolysis is proposed in which gallery water molecules, formed by the dehydroxylation of the alumina pillars, migrate to hexagonal oxygen cavities above the reactive fluorine positions. Between 350 and 500[degrees]C, a second process occurs that causes dehydroxylation of the layers, and this results in a sharp decrease in the acidity and catalytic activity of the pillared clay. The relationships between structure and reactivity suggest that the acid-catalytic activity of an alumina-pillared clay can be mediated by controlling the relative amounts of hydroxyl groups at charged octahedral sites and fluorine atoms at neutral octahedral sites in the host clay. 22 refs., 13 figs., 3 tabs.

• OSTI ID: 6236329
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 139:2; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKENES
ALKYLATION
ALUMINIUM 27
ALUMINIUM COMPOUNDS
ALUMINIUM ISOTOPES
AMMONIA
AROMATICS
AZINES
BIPHENYL
BROENSTED ACIDS
CALCINATION
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
CHEMISORPTION
CLAYS
DECOMPOSITION
ELEMENTS
EVEN-ODD NUCLEI
FLUORINE 19
FLUORINE COMPOUNDS
FLUORINE ISOTOPES
HALOGEN COMPOUNDS
HETEROCYCLIC COMPOUNDS
HETEROGENEOUS CATALYSIS
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROLYSIS
HYDROXYL RADICALS
INORGANIC ACIDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOTOPES
LAYERS
LIGHT NUCLEI
LYSIS
MAGNETIC RESONANCE
MASS SPECTROSCOPY
MATERIALS
MINERALS
MONTMORILLONITE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN
OXYGEN COMPOUNDS
PROPYLENE
PYRIDINE
PYRIDINES
PYROLYSIS
RADICALS
REACTIVITY
RESONANCE
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON 29
SILICON COMPOUNDS
SILICON ISOTOPES
SMECTITE
SOLVOLYSIS
SORPTION
SORPTIVE PROPERTIES
SPECTROSCOPY
STABLE ISOTOPES
SURFACE PROPERTIES
THERMOCHEMICAL PROCESSES
WATER