Acidic properties of vanadium oxide on titania

Miyata, Hisashi; Fujii, Kazutoshi; Ono, Takehiko

doi:10.1039/f19888403121

Cited by 67 publications

(28 citation statements)

References 2 publications

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“…Such a feature is similar to that reported in the literature A c c e p t e d M a n u s c r i p t for V 5+ [34][35][36] and Ti 4+ [32]. The presence of Brønsted acid sites is of interest in the elucidation of the surface properties of the investigated catalysts, because, as reported in the literature devoted to paraffin dehydrogenation processes [29] these centres can promote the further transformation of initially produced olefins, in particular starting the processes leading to the deactivation of the catalysts by cocking.…”

Section: Page 10 Of 21supporting

confidence: 79%

CrO /SiO2 catalysts prepared by metal vapour synthesis: Physical–chemical characterisation and functional testing in oxidative dehydrogenation of propane

Botavina¹,

Evangelisti²,

Agafonov³

et al. 2011

Chemical Engineering Journal

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In the present work catalysts prepared by a new perspective method of metal vapour synthesis were studied in the reaction of propane oxidative dehydrogenation in the presence of CO 2 as a mild oxidant. This method let to obtain on the catalyst surface a high dispersed chromium species even at high chromium loadings. On the surface of the catalysts with the chromium loading up to 6.0 wt % only chromate species were found, the further increase of the chromium loading results in the appearance of the -Cr 2 O 3 . The catalyst with 6.0 wt % demonstrated also the highest catalytic activity with the yield in propene 69%.

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Section: Page 10 Of 21supporting

confidence: 79%

CrO /SiO2 catalysts prepared by metal vapour synthesis: Physical–chemical characterisation and functional testing in oxidative dehydrogenation of propane

Botavina¹,

Evangelisti²,

Agafonov³

et al. 2011

Chemical Engineering Journal

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“…The acidic properties of the surface vanadia species are slightly influenced by the oxide support since 1% V 2 O 5 on titania possesses a small amount of surface Brønsted acid sites and surface Brønsted acid sites are not present on the corresponding 1% V 2 O 5 on alumina and silica supports. However, comparable numbers of surface redox and Brønsted acid sites (per square meter) are present at monolayer coverages for alumina-and titania-supported vanadia catalysts (29,33) and the difference in TOF is still present. This suggests that the specific redox properties of the surface vanadia species are primarily responsible for the influence of the oxide support on the SCR TOF.…”

Section: Discussionmentioning

confidence: 99%

“…The titania support possesses only weak surface Lewis acid sites and no surface Brønsted acid sites as measured by pyridine adsorption (30). The number of surface Lewis acid sites slightly decreases and the number of surface Brønsted acid sites significantly increases as the surface vanadia loading is increased on the titania support (29).…”

Section: Surface Aciditymentioning

confidence: 99%

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Selective Catalytic Reduction of NO with NH3over Supported Vanadia Catalysts

Wachs

Deo²,

Weckhuysen³

et al. 1996

Journal of Catalysis

244

111

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The selective catalytic reduction (SCR) of NO with NH 3 was systematically investigated over a series of supported vanadia catalysts to obtain additional insight into this important industrial reaction. The influence of surface vanadia coverage, promoters (surface tungsten oxide, niobium oxide, and sulfate species), and the specific oxide support (TiO 2 , Al 2 O 3 , and SiO 2 ) was examined. The molecular structures of the surface metal oxide species were determined by in situ Raman spectroscopy, and the corresponding surface acidity properties were monitored with infrared spectroscopy employing pyridine adsorption. The redox properties of the surface metal oxide species were probed with the sensitive methanol oxidation reaction and temperature-programmed reduction. The SCR reactivity of the various catalysts was determined over a wide temperature range. The current findings suggest that a dual-site (a surface vanadia redox site and an adjacent nonreducible metal oxide site) mechanism is required for the efficient selective catalytic reduction of NO with NH 3 over supported vanadia catalysts. The SCR reaction is sensitive to the immediate environment of the surface vanadia species: overall surface coverage of the metal oxide overlayer (factor of 5 in turnover frequency), nature of adjacent surface metal oxide species (factor of 10 in turnover frequency) and oxide support ligands (factor of 3 in turnover frequency). The SCR reaction, however, does not appear to depend on the specific structure of the surface vanadia species. The SCR selectivity toward N 2 formation also varies with the immediate environment of the surface vanadia species. The selectivity depends on the specific oxide support (TiO 2 > Al 2 O 3 > SiO 2 ), temperature (decreases at higher temperature due to oxidation of NH 3 and NO to N 2 O), and surface concentration of redox sites (decreases with the concentration of pairs of redox sites). The SCR reaction is not related to the properties of the terminal V= =O bond since in situ Raman studies during SCR, employing V= = 18 O, demonstrate that this bond is relatively stable under reaction conditions (possessing a lifetime that is ∼10 times the characteristic reaction time). Thus, the bridging V-O-support bond appears to be involved in the rate-determining step.

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“…Surface acid-base properties are characterised via temperature-programmed desorption (TPD) of pyridine with mass spectrometric analysis of the products. This technique gives additional information as compared to the studies performed without gas-phase analysis [25][26][27][28]. The oxidation state and molecular structure of vanadia species are known to be influenced by the oxidative or reductive environment.…”

Section: Introductionmentioning

confidence: 99%

Implication of the acid–base properties of V/Ti-oxide catalyst in toluene partial oxidation

Kiwi‐Minsker

Bulushev

Rainone

et al. 2002

Journal of Molecular Catalysis A: Chemical

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The work presents the effect of K-doping on V/Ti-oxides taking into account: the surface acid-base properties and the structure of surface vanadia species in respect to the catalyst performance and deactivation. The structure of active surface species determines redox properties, which are related to the catalytic performance by the Mars-van Krevelen mechanism. The reducibility of surface vanadia is studied by temperature-programmed reduction (TPR) in H 2 . The molecular structure of surface vanadia is determined by FT-Raman spectroscopy in a controlled atmosphere. Surface acid-base properties are characterised via temperature-programmed desorption (TPD) of pyridine with mass spectrometric analysis of the products.Transient response techniques with continuous monitoring of the composition of gaseous phase are applied to follow the catalyst surface transformations. Evolution of benzaldehyde (BA) formed during interaction of toluene with the pre-oxidised catalyst (without gaseous oxygen) gives information about the nucleophilicity of surface oxygen. Addition of potassium to surface vanadia leads to an increased oxygen nucleophilicity, resulting in a higher selectivity towards BA formation.In general, increase in surface basicity decreases catalytic activity, but at the same time the catalyst deactivation due to coking is suppressed. This allows catalyst optimisation in view of a better control of the partial oxidation process.

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Acidic properties of vanadium oxide on titania

Cited by 67 publications

References 2 publications

CrO /SiO2 catalysts prepared by metal vapour synthesis: Physical–chemical characterisation and functional testing in oxidative dehydrogenation of propane

CrO /SiO2 catalysts prepared by metal vapour synthesis: Physical–chemical characterisation and functional testing in oxidative dehydrogenation of propane

Selective Catalytic Reduction of NO with NH3over Supported Vanadia Catalysts

Implication of the acid–base properties of V/Ti-oxide catalyst in toluene partial oxidation

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