Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 3. Impact of Superficial WOz and VxOy/WOz Groups on the Heats of Adsorption of Adsorbed NH3 Species

Giraud, François; Geantet, Christophe; Guilhaume, N.; Loridant, S.; Gros, Sébastien; Porcheron, Lynda; Kanniche, Mohamed; Bianchi, Daniel

doi:10.1021/acs.jpcc.5b04143

Cited by 25 publications

(80 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Each catalyst had a predominant peak at 450-465 • C with a shoulder at 280-350 • C and a broad peak at temperatures >600 • C, depending on the sample, as seen in profiles S1-S4. As for NO and N 2 O in Figure 6a,b, all those N 2 peaks would be associated with ammonium ions and NH x on Bronsted and Lewis acid centers [43][44][45]. The NH x species are oxidized to N 2 via NO-assistant route, as discussed [11,39,48].…”

Section: Role Of Fe 2 O 3 Species For the Suppression Of N 2 O Formationmentioning

confidence: 85%

The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts

Kim

Yang

2018

Catalysts

View full text Add to dashboard Cite

Promotion of 2.73% Fe 2 O 3 in an in-house-made V 2 O 5 -WO 3 /TiO 2 (VWT) and a commercial V 2 O 5 -WO 3 /TiO 2 (c-VWT) has been investigated as a cost effective approach to the suppression of N 2 O formation in the selective catalytic reduction of NO by NH 3 (NH 3 -SCR). The promoted VWT and c-VWT catalysts all gave a significantly decreased N 2 O production at temperatures >400 • C compared to the unpromoted samples. However, such a promotion led to the loss in high temperature NO conversion, mainly due to the oxidation of NH 3 to N-containing gases, particularly NO. Characterization of the unpromoted and promoted catalysts using X-ray diffraction (XRD), NH 3 adsorption-desorption, and Raman spectroscopy techniques could explain the reason why the promotion showed much lower N 2 O formation levels at high temperatures. The addition of Fe 2 O 3 to c-VWT resulted in redispersion of the V 2 O 5 species, although this was not visible for 2.73% Fe 2 O 3 /VWT. The iron oxides exist as a highly-dispersed noncrystalline α-Fe 2 O 3 in the promoted catalysts. These Raman spectra had a new Raman signal that could be tentatively assigned to Fe 2 O 3 -induced tetrahedrally coordinated polymeric vanadates and/or surface V-O-Fe species with significant electronic interactions between the both metal oxides. Calculations of the monolayer coverage of each metal oxide and the surface total coverage are reasonably consistent with Raman measurements. The proposed vanadia-based surface polymeric entities may play a key role for the substantial reduction of N 2 O formed at high temperatures by NH 3 species adsorbed strongly on the promoted catalysts. This reaction is a main pathway to greatly suppress the extent of N 2 O formation in NH 3 -SCR reaction over the promoted catalysts.

show abstract

Section: Role Of Fe 2 O 3 Species For the Suppression Of N 2 O Formationmentioning

confidence: 85%

The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts

Kim

Yang

2018

Catalysts

View full text Add to dashboard Cite

show abstract

“…[6] By comparison, L NH 3 is more resistant to desorption at agiven temperature [7] and demonstrates higher heat of adsorption than B NH 3 . [8] Although the two reaction pathways probably do not exclude each other, it is essential to understand whether either or both species are relevant.Spectroscopy contributed considerably to the formulation of the proposed reaction mechanisms. [2b-d, 9] However,wenote that this precious mechanistic information was derived under steady-state conditions,thus under less suitable experimental conditions and inappropriate time scales to observe active and intermediate species and to describe the working catalyst.…”

mentioning

confidence: 99%

The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium‐Based Catalysts

et al. 2016

View full text Add to dashboard Cite

show abstract

“…Themechanistic aspects of SCR using vanadium were summarized by Busca et al [4] Ther eaction proceeds according to the stoichiometry of Reaction (1) and the two nitrogen atoms of the N 2 product originate,o ne each, from NO and NH 3 .I ti sg enerally accepted that the mechanism comprises an acid site where NH 3 is activated and ar edox site that requires oxygen to be regenerated. [8] Although the two reaction pathways probably do not exclude each other, it is essential to understand whether either or both species are relevant. While Brønsted acid sites bind NH 3 to form NH 4 + (B NH 3 ), Lewis acid sites coordinate NH 3 directly with ametal atom (L NH 3 ).…”

mentioning

confidence: 99%

“…Va rious experimental and theoretical studies have tackled the crucial issue of the involvement of either B NH 3 or L NH 3 sites in the standard SCR reaction without reaching unequivocal conclusions.R amis et al [2b] reported am echanism based on L NH 3 active species that encompasses the formation of aN H 2 NO reaction intermediate.B NH 3 was later proposed by Topsøe [2c] as the active center. [8] Although the two reaction pathways probably do not exclude each other, it is essential to understand whether either or both species are relevant. [5] However,t wo considerations seem to complicate the Brønsted acid mechanism.…”

mentioning

confidence: 99%

The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium‐Based Catalysts

et al. 2016

View full text Add to dashboard Cite

The long debated reaction mechanisms of the selective catalytic reduction (SCR) of nitric oxide with ammonia (NH 3 )o nv anadium-based catalysts rely on the involvement of Brønsted or Lewis acid sites.T his issue has been clearly elucidated using ac ombination of transient perturbations of the catalyst environment with operando time-resolved spectroscopyt oobtain unique molecular level insights.N itric oxide reacts predominantly with NH 3 coordinated to Lewis sites on vanadia on tungsta-titania (V 2 O 5 -WO 3 -TiO 2 ), while Brønsted sites are not involved in the catalytic cycle.The Lewis site is amono-oxovanadyl group that reduces only in the presence of both nitric oxide and NH 3 .Wewere also able to verify the formation of the nitrosamide (NH 2 NO) intermediate,which forms in tandem with vanadium reduction, and thus the entire mechanism of SCR. Our experimental approach,d emonstrated in the specific case of SCR, promises to progress the understanding of chemical reactions of technological relevance.Abatement of harmful NO x is amajor objective of environmental and health protection policies as ar esult of the increasing emissions from power plants and vehicles in rapidly developing countries.E fficient NO x removal from exhaust gases of stationary sources is achieved by reacting NH 3 on as olid catalyst, typically consisting of dispersed vanadia on tungsta-titania (V 2 O 5 -WO 3 -TiO 2 ), according to the standard selective catalytic reduction (SCR) process. [1] 4NOþThei ncreasingly stringent emission regulations in the transport sector also make this technology attractive for controlling the exhaust of mobile sources;e specially diesel trucks,r ailroad diesel engines,a nd more recently,s hip engines.Despite the widespread use of SCR, some molecular aspects of the reaction mechanism remain controversial. [2] Thea dvent of powerful computational resources,t he search for catalyst formulations counteracting the implicit drawbacks of vanadium-based catalysts, [3] and the development of low-temperature SCR catalysts for automotive applications, have rejuvenated the debate on the nature of the active center. Themechanistic aspects of SCR using vanadium were summarized by Busca et al. [4] Ther eaction proceeds according to the stoichiometry of Reaction (1) and the two nitrogen atoms of the N 2 product originate,o ne each, from NO and NH 3 .I ti sg enerally accepted that the mechanism comprises an acid site where NH 3 is activated and ar edox site that requires oxygen to be regenerated. TheB rønsted and Lewis acid sites are responsible for the adsorption of NH 3 and have thus been anticipated to be essential for the reaction mechanism. While Brønsted acid sites bind NH 3 to form NH 4 + (B NH 3 ), Lewis acid sites coordinate NH 3 directly with ametal atom (L NH 3 ). NO reacts on the acid sites according to an Eley-Rideal mechanism, accompanied by the reduction of V 5+ to V 4+ .I ti sa lso recognized that the role of oxygen is to restore the V 5+ O x active center. Va rious experimental and theoretical studies hav...

show abstract

Experimental Microkinetic Approach of De-NO_x by NH₃ on V₂O₅/WO₃/TiO₂ Catalysts. 3. Impact of Superficial WO_z and V_xO_y/WO_z Groups on the Heats of Adsorption of Adsorbed NH₃ Species

Cited by 25 publications

References 27 publications

The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts

The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts

The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium‐Based Catalysts

The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium‐Based Catalysts

Contact Info

Product

Resources

About