Effect of crystal morphology in selective catalytic reduction of nitric oxide over V2O5 catalysts

Ozkan, Umit S.; Cai, Yeping; Kumthekar, M. W.

doi:10.1016/0926-860x(90)80023-8

Cited by 36 publications

(13 citation statements)

References 25 publications

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“…The influence of the oxide support on the surface vanadia redox properties and the SCR TOF suggests that the bridging V-Osupport bond may contribute to the rate determining step of the DeNOx reaction. This conclusion is consistent with model SCR studies with unsupported V 2 O 5 crystals that reported that the crystallographic planes possessing V-O-V or V-OH bonds rather than V= =O bonds were the selective sites for the SCR reaction (12,13). The in situ Raman experiments during the SCR reaction further support the above conclusion since V= = 18 O was formed to be relatively stable during the SCR reaction (t ex /t rx ∼ 10).…”

Section: Discussionsupporting

confidence: 79%

“…The role of Brønsted acidity in the SCR reaction over supported vanadia catalysts was also suggested by other research groups (10,11). Model SCR studies with unsupported V 2 O 5 crystals concluded that the crystallographic planes possessing V-O-V or V-OH bonds rather than V= =O bonds were the selective sites for the SCR reaction (12,13). In a recent series of detailed studies over vanadia-titania catalysts, Topsoe et al combined in situ FT-IR and on-line mass spectrometry studies, transient as well as steady state, to provide convincing evidence that both surface Brønsted acid sites and surface V= =O sites are involved in the SCR catalytic cycle (14,15).…”

Section: Introductionmentioning

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

243

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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Section: Discussionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Selective Catalytic Reduction of NO with NH3over Supported Vanadia Catalysts

Wachs

Deo²,

Weckhuysen³

et al. 1996

Journal of Catalysis

243

111

View full text Add to dashboard Cite

show abstract

“…Furthermore, the decrease in BET surface area of this sample suggests that some vanadium can be buried in the micropores. The dramatic decrease of selectivity in this sample agrees with the results of Ozkan et al [37]. These authors studied the SCR reaction with vanadia crystals having a preferential exposure of different crystal planes.…”

Section: Discussionsupporting

confidence: 89%

Structure of vanadium oxide supported on mesoporous carbon-coated monoliths and relationship with its catalytic performance in the SCR of NO at low temperatures

García‐Bordejé

2004

Journal of Catalysis

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“…Ozkan et al [47] studied the morphological aspects of unsupported vanadia catalysts. Two types of vanadia were prepared.…”

Section: A Supported Vanadia Catalystsmentioning

confidence: 99%

“…In lieu of co-feeding oxygen as described previously, air can be used in a separate step to reactivate used catalyst [45]. Many metals in combination with Cr are also effective such as Al, Co, Mn, Mg [47], Zn [48], as well as others. Many of the catalysts capable of fluorinating HCFC-133a are chromium based, such as the Cr2O3 examples described above.…”

Section: Introductionmentioning

confidence: 99%