Synthesis of new catalysts and catalyst supports by secondary (IV) isomorphic substitutions in phyllosilicates: Vermiculites and sepiolites

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7283801

d'Espinose de la Caillerie, J.B.

Secondary modifications of the (Si/Al)[sup IV] ratio of two clay minerals, vermiculite and sepiolite, were achieved. In vermiculite, a high-charge phyllosilicate, (Al)[sup IV] by (Si)[sup IV] substitutions were performed using (NH[sub 4])[sub 2]SiF[sub 6]. [sup 29]Si MAS-NMR revealed that the lowering of the charge was also due to (Mg[sup 2+])[sup VI] by (Al[sup 3+]) exchange. The tetrahedral charge remained high, circa 0.16 per basal oxygen, even as the CEC decreased from 220 to 90 meq/100 g. Dealuminated vermiculite did not intercalate Al[sub 13] but other Al oligomers. Intercalation products showed a high surface area (230 m[sup 2]/g) but a small inter-layer spacing of 5 [angstrom]. Sepiolite was aluminated in a basic medium using NaAlO[sub 2]. The CEC increased to 45 meq/100 g. [sup 27]Al MAS-NMR and chemical analysis revealed that alumination occurred in tetrahedral as well as in octahedral positions in the structure. Alumination was accompanied by an increase in the sodium context of the sample and an improvement of the thermal stability. Both framework and non-framework aluminum participated in the Lewis acidity of aluminated sepiolite, responsible for a three-fold increase in activity for ethanol dehydration at 400[degrees]C to 85%, while the selectivity for ethylene increased from 25% in the natural sepiolite to 50%. The cation exchange capacity of aluminated sepiolite allowed for the dispersion of vanadyl cations without loss of crystallinity. Under flow reactions at 280[degrees]C, V-exchanged aluminated sepiolite was more selective toward dehydration products of ethanol, diethylether (69%) and ethylene (25%), than toward dehydrogenation products, acetaldehyde (9%) and butadiene (2%). Upon dispersion of vanadyl cations, butadiene was formed via a Prins reaction on acid sites between a dehydration product (ethylene) and a dehydrogenation product (acetaldehyde).

• Research Organization: Wisconsin Univ., Milwaukee, WI (United States)
• OSTI ID: 7283801
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALUMINIUM
CHEMICAL REACTIONS
CATALYST SUPPORTS
CHEMICAL PREPARATION
STRUCTURAL CHEMICAL ANALYSIS
SEPIOLITE
VERMICULITE
ALKALINE EARTH METAL COMPOUNDS
CLAYS
ELEMENTS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MATERIALS
METALS
MICA
MINERALS
OXYGEN COMPOUNDS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SYNTHESIS
400201* - Chemical & Physicochemical Properties