Surface and catalytic properties of Vanadia-Titania and Tungsta-Titania systems in the Selective Catalytic Reduction of nitrogen oxides

Lietti, Luca; Švachula, J.; Forzatti, Pio; Busca, Guido; Ramis, Gianguido; Bregani, P.

doi:10.1016/0920-5861(93)80016-t

Cited by 100 publications

(70 citation statements)

References 11 publications

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“…Went et al characterized the surface vanadia species with in situ Raman spectroscopy as well as temperature-programmed reduction/temperature-programmed oxidation and concluded that both monomeric vanadyl and polymeric vanadate surface species were present on the titania support (3); corresponding SCR studies suggested that the polymeric species were about 10 times more active than the monomeric species, but the polymeric species were less selective toward N 2 formation (4). The increase in the SCR specific activity with surface vanadia coverage on titania has also been reported by other investigators (5,6). Lietti et al proposed that the redox properties of the catalyst are a major factor governing activity and that the reaction involved primarily a coordinated ammonia species on Lewis acid sites (6,7).…”

Section: Introductionmentioning

confidence: 51%

“…The increase in the SCR specific activity with surface vanadia coverage on titania has also been reported by other investigators (5,6). Lietti et al proposed that the redox properties of the catalyst are a major factor governing activity and that the reaction involved primarily a coordinated ammonia species on Lewis acid sites (6,7). The potential participation of a protonated ammonium on a surface Brønsted acid site was also proposed because of the possible interconversion of these species (6,7).…”

Section: Introductionmentioning

confidence: 66%

“…The mechanism of the selective catalytic reduction of NO with ammonia over vanadia-titania catalysts has been proposed to occur both by an Eley-Rideal mechanism (1,2,6,7,12,15) and by a Langmuir-Hinshelwood mechanism (4,16,17). However, significant amounts of adsorbed NO are not found on the vanadia-titania catalyst surface under reaction conditions (15).…”

Section: Introductionmentioning

confidence: 99%

“…Lietti et al proposed that the redox properties of the catalyst are a major factor governing activity and that the reaction involved primarily a coordinated ammonia species on Lewis acid sites (6,7). The potential participation of a protonated ammonium on a surface Brønsted acid site was also proposed because of the possible interconversion of these species (6,7). Ramis et al also proposed that promoters affect the Lewis acidity of V= =O bonds which affects the adsorption of ammonia, the first step in the SCR reaction (8).…”

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

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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Section: Introductionmentioning

confidence: 51%

Section: Introductionmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Selective Catalytic Reduction of NO with NH3over Supported Vanadia Catalysts

Wachs

Deo²,

Weckhuysen³

et al. 1996

Journal of Catalysis

244

111

View full text Add to dashboard Cite

show abstract

“…Moreover, the shape of the ammonia desorption peak for the WO 3 /TiO 2 -based catalysts was shifted towards higher temperatures, thus indicating that the associated acid sites are of higher strength. Other researchers [Lietti et al, 1993] also found that the acid sites of WO 3 /TiO 2 are stronger than those of V 2 O 5 -TiO 2 . It was also concluded that the ternary oxides (W, V, Ti) are more active than any combination of the binary ones due to strong electrostatic interactions involving these three oxides [Alemani et al, 1995].…”

Section: Hours At 450 O C the Aged Vanadium Oxalate Solution Was Usementioning

confidence: 96%

DEVELOPMENT OF MULTI-TASK CATALYSTS FOR REMOVAL OF NOx AND TOXIC ORGANIC COMPOUNDS DURING COAL COMBUSTION

Smirniotis¹,

Jenkins²

2002

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Nitrogen Oxides Removal – Industrial

Forzatti¹,

Lietti²,

Tronconi³

2002

Encyclopedia of Catalysis

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The heterogeneous selective catalytic reduction (SCR) of NO x by NH 3 from stationary sources is addressed in this review. The typical commercial De‐NO x SCR catalysts are presented, along with their performances in both the NO x reduction and the SO 2 oxidation reactions. Mechanistic and kinetic aspects of the reactions involved in the SCR process, the reactor and process configurations, and the design and modeling of the SCR systems are also illustrated.

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Surface and catalytic properties of Vanadia-Titania and Tungsta-Titania systems in the Selective Catalytic Reduction of nitrogen oxides

Cited by 100 publications

References 11 publications

Selective Catalytic Reduction of NO with NH3over Supported Vanadia Catalysts

Selective Catalytic Reduction of NO with NH3over Supported Vanadia Catalysts

DEVELOPMENT OF MULTI-TASK CATALYSTS FOR REMOVAL OF NOx AND TOXIC ORGANIC COMPOUNDS DURING COAL COMBUSTION

Nitrogen Oxides Removal – Industrial

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