Tungsten-oxo-species deposited on alumina. II. Characterization and catalytic activity of unpromoted W{sup (vi)}/{gamma}-Al{sub 2}O{sub 3} catalysts prepared by equilibrium deposition filtration (EDF) at various pH`s and non-dry impregnation (NDI)
- Univ. of Patras-Institute of Chemical Engineering and High Temperature Chemical Processes (Greece)
A series of W{sup (vi)}/{gamma}-Al{sub 2}O{sub 3} catalysts of varying W{sup (vi)} content in the range 3.3-21.2% WO{sub 3} was prepared at various pH`s using equilibrium deposition filtration (EDF). These catalysts were then characterized using various physicochemical techniques (BET, XPS, XRD, DRS, NO chemisorption, TPD of NH{sub 3}, microelectrophoresis, and DTGA) and the surface characteristics achieved were related with the nature of the W{sup (vi)} species and the structure and dispersity of the W{sup (vi)}-supported phase: Deposition through adsorption or reaction of the monomeric WO{sub 4}{sup 2-} species in the pH range 7.4-4.9 resulted in a well-dispersed, presumably monolayered, W{sup (vi)} phase relatively rich in tetrahedral W{sup (vi)}. In contrast, deposition through adsorption of the polymeric HW{sub 6}O{sub 20}(OH){sub 2}{sup 5-} species at pH`s 4.0 and 3.5 resulted in a supported phase with relatively low dispersity and a relatively small amount of tetrahedral W{sup (vi)}. Supported WO{sub 3} crystallites with size greater than 40 nm are formed in this case. Moreover, it was inferred that the mode of deposition of the monomeric WO{sub 4}{sup 2-} species is reflected in the properties of the supported W{sup (vi)} phase of the calcined samples. Catalytic tests, using the hydrodesulfurization of thiophene and the hydrogenation of cyclohexene as probe reactions, showed that EDF provides more active catalysts than non-dry impregnation (NDI) and this is another example showing that EDF with controlled regulation of the impregnation parameters is a promising methodology for preparing supported catalysts even with relatively low loadings. Finally, it was found that EDF provides more acidic samples than NDI. 47 refs., 19 figs., 1 tab.
- OSTI ID:
- 494282
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 162; ISSN JCTLA5; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
Similar Records
Codeposition of Mo{sup (VI)} species and Ni{sup 2+} ions on the {gamma}-alumina surface: Mechanistic model
Advances in the mechanism of deposition of MoO{sub 4}{sup 2{minus}} and Mo{sub 7}O{sub 24}{sup 6{minus}} species on the surface of titania consisted of anatase and rutile
Related Subjects
02 PETROLEUM
36 MATERIALS SCIENCE
40 CHEMISTRY
ALUMINIUM OXIDES
AMMONIA
CATALYST SUPPORTS
CATALYTIC EFFECTS
CHEMICAL PREPARATION
CHEMISORPTION
CYCLOALKENES
DEPOSITION
DESORPTION
DESULFURIZATION
DIFFERENTIAL THERMAL ANALYSIS
ELECTROPHORESIS
HETEROGENEOUS CATALYSIS
HYDROGENATION
NITRIC OXIDE
PH VALUE
PHOTOELECTRON SPECTROSCOPY
SURFACE AREA
THIOPHENE
TUNGSTEN OXIDES
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY