The preparation of WO sub 3 /TiO sub 2 and WO sub 3 /Al sub 2 O sub 3 and characterization by temperature-programmed reduction

Journal Article · Sat Apr 01 00:00:00 EST 1989 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(89)90098-5· OSTI ID:6331135

Vermaire, D C; van Berge, P C ^[1]

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1. Rand Afrikaans Univ., Johannesburg (South Africa)

An equilibrium adsorption technique was used to prepare WO{sub 3}/TiO{sub 2} and WO{sub 3}/Al{sub 2}O{sub 3} samples. The tungsten loading could be controlled by varying the pH and concentration of the aqueous solutions. For both supports there was a definite maximum to the amount of tungsten that adsorbed spontaneously, viz. 988 {+-} 21 and 669 {+-} 19 {mu}mol per 100 m{sup 2} for alumina and titania, respectively. The hydroxyl group to tungsten ratio was 2:1 on alumina for a fully hydroxylated surface. On titania the ratio was 1:1, based on the reacting hydroxyl group density. These stoichiometries point to a very specific interaction between the tungstate ions and the hydroxyl groups on the support surface during adsorption. Unlike on alumina, the reduction of tungsten oxide on titania (anatase) takes place in two well-separated steps viz., W{sup 6+} {yields} W{sup 4+} {yields} W{sup 0}. During reduction the titania is transformed from anatase to rutile which has the same crystal structure and metal to oxygen bond length as WO{sub 2} and can thus facilitate and stabilize the W{sup 4+} ions. A stepwise reduction of tungsten oxide was not observed on alumina, probably due to the inability of alumina to stabilize the intermediate oxidation states of tungsten.

• OSTI ID: 6331135
• Journal Information: Journal of Catalysis; (USA), Vol. 116:2; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CATALYSTS
CHEMICAL PREPARATION
TUNGSTEN OXIDES
REDUCTION
ADSORPTION
ALUMINIUM OXIDES
CATALYST SUPPORTS
CRYSTAL STRUCTURE
HYDROXYL RADICALS
PH VALUE
QUANTITY RATIO
STABILITY
SURFACE PROPERTIES
TEMPERATURE CONTROL
TITANIUM OXIDES
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
CONTROL
OXIDES
OXYGEN COMPOUNDS
RADICALS
REFRACTORY METAL COMPOUNDS
SORPTION
SYNTHESIS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS
400201* - Chemical & Physicochemical Properties