On the nature and formation of the active sites in Re[sub 2]O[sub 7] metathesis catalysts supported on borated alumina
- Univ. of Amsterdam (Netherlands)
- Koninklijke/Shell Laboratorium, Amsterdam (Netherlands)
- Delft Univ. of Technology (Netherlands)
Re[sub 2]O[sub 7] catalysts on borated aluminas have been investigated with a view to correlating the structure of the active site and its activity in the metathesis of methyl oleate. Modification of alumina with boria results in much more active metathesis catalysts. Infrared spectroscopy was used for the characterization, pyridine adsorption measurements for determining the Lewis acid and Bronsted acid sites, and temperature-programmed IR measurements to follow the reactions occurring during calcination of the supports and catalysts. Boria binds to the surface via the alumina hydroxyls. Upon Re[sub 2]O[sub 7] loading of nonborated alumina, the ReO[sub 4] groups react first with Lewis acid sites, onto which they are strongly bonded. Above a Re[sub 2]O[sub 7] loading of 3 wt% surface hydroxyls are also substituted by Re[sub 2]O[sub 7] groups, resulting in an increase in catalytic activity. When the borated supports are loaded with Re[sub 2]O[sub 7], the ReO[sub 4] groups are also first bonded to the Lewis acid sites. During calcination these ReO[sub 4] groups substitute surface hydroxyls preferably on alumina hydroxyls. The substitution of the boron hydroxyls only takes place at a calcination time of at least 2 h at 823 K. At high borate loadings (>10 wt%) the reaction of ReO[sub 4] groups with boron hydroxyls competes with the condensation reaction of two neighbouring boron hydroxyls. Taking into account that a ReO[sub 4] group which has substituted in acidic OH group on the support is the precursor of an active site, the increase in activity of Re[sub 2]O[sub 7] catalysts by modification of the alumina support with boria can be ascribed to two effects, namely, the reduction of the bonding strength of Lewis acid sites with ReO[sub 4], making the ReO[sub 4]-OH substitution reaction possible during calcination even at low rhenium loadings, and the formation of acidic surface hydroxyls. 16 refs., 11 figs., 3 tabs.
- OSTI ID:
- 7046061
- Journal Information:
- Journal of Catalysis; (United States), Vol. 145:2; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
RHENIUM OXIDES
CATALYTIC EFFECTS
ABSORPTION SPECTROSCOPY
ALUMINIUM OXIDES
BORATES
CATALYST SUPPORTS
LEWIS ACIDS
ALUMINIUM COMPOUNDS
BORON COMPOUNDS
CHALCOGENIDES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
OXIDES
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
RHENIUM COMPOUNDS
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS
400201* - Chemical & Physicochemical Properties