Vanadia supported on TiO sub 2 -SiO sub 2 mixed oxide gels: Structure of the dispersed phase and activity for the selective catalytic reduction of NO with NH sub 3

Journal Article · Wed Jan 01 04:00:00 EST 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90182-H· OSTI ID:7253016

Handy, B E; Baiker, A ^[1]; Schraml-Marth, M; Wokaun, A ^[2]

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1. Swiss Federal Inst. of Tech., Zurich (Switzerland)
2. Univ. of Bayreuth (Germany)

Supported vanadia catalysts were prepared by reacting vanadyl triisopropoxide with titania-silica mixed oxide supports of fixed Ti:Si mol ratio (1:4 and 1:1), but of varying pore structure, surface area, and crystallinity. The latter properties were controlled by varying the sol-gel preparation parameters. Although the selectivity pattern for the selective catalytic reduction (SCR) remained essentially the same over all catalysts, the specific activity, defined on a per V{sup 5+} basis, varied with the support. The vanadia content in all catalysts corresponded to less than one monolayer (defined as 0.10 wt% V{sub 2}O{sub 5}m{sup 2} or 11 {mu}mol V{sup 5+}/m{sup 2}), and structural data indicate that the vanadia is will dispersed. Raman spectroscopy was used to differentiate between vanadia species immobilized on TiO{sub 2} and SiO{sub 2} domains, respectively. These results revealed that the mixed oxide gels can be categorized into two main types exhibiting titania- or silica-like behavior. A weak interaction that results from a two-stage hydrolysis procedure of the alkoxide precursors of the constituents is characteristic for silica-like supports. This contrasts with the titania-like behavior observed for TiO{sub 2}-SiO{sub 2} mixed oxides prepared by single-stage hydrolysis, where the vanadia-support interaction is strong. No crystalline V{sub 2}O{sub 5} phases were detected. TPR profiles show that the reducibility of vanadia, as evidenced by shifts in the temperature of maximum hydrogen consumption, is dependent upon the composition and preparation method of the mixed gel supports. An increase in the value of T{sub max} can be correlated with a decrease in the turnover frequency (NO converted per V{sup 5+} site) of the SCR reaction.

• OSTI ID: 7253016
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 133:1; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
AMMONIA
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
COLLOIDS
CONTROL
CRYSTAL STRUCTURE
DENITRIFICATION
DISPERSIONS
FLUE GAS
GASEOUS WASTES
GELS
HYDRIDES
HYDROGEN COMPOUNDS
LASER SPECTROSCOPY
MICROSTRUCTURE
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
POROSITY
QUANTITY RATIO
RAMAN SPECTROSCOPY
REDUCTION
SELECTIVE CATALYTIC REDUCTION
SILICON COMPOUNDS
SILICON OXIDES
SOLS
SPECTROSCOPY
SURFACE AREA
SURFACE PROPERTIES
SYNTHESIS
TEMPERATURE CONTROL
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS
VANADIUM OXIDES
WASTES