Effects of SiO2 modification on the hydrothermal stability of the V2O5/WO3–TiO2 NH3-SCR catalyst: TiO2 structure and vanadia species

Liu, Xuesong; Chen, Hongfeng; Wu, Xiaodong; Cao, Li; Jiang, Peng; Yu, Qifan; Ma, Yue

doi:10.1039/c9cy00385a

Cited by 19 publications

(19 citation statements)

References 50 publications

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“…However, the apex of the reduction peak in OP (468°C) was slightly lower than that in IW (474°C). According to previous reports (Bond et al, 1986;Liu et al, 2016;Chen et al, 2018;Gan, et al, 2018), this broad reduction peak can be attributed to the co-reduction of dispersed V 5+ (and V 4+ ) to V 3+ and disperse W 6+ to W 4+ . e reduction temperature of monomeric surface V species was lower than that of polymeric V species.…”

Section: Analysis Of Surface-active Speciessupporting

confidence: 68%

“…Hence, monomeric and polymeric V on the surface of TiO 2 tend to migrate to form crystalline V 2 O 5 or V x Ti 1-x O 2 solid solutions at high temperatures, resulting in a decrease in the VWT catalytic activity. In addition, the crystallization of tungsten oxides decreases catalyst acidity (Went et al, 1992;Liu et al, 2016). (2) Loss of the surface area of TiO 2 .…”

Section: Introductionmentioning

confidence: 99%

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Enhanced Durability of Monolithic V2O5–WO3/TiO2 Catalysts Prepared by a Novel One-Pot Method for the Selective Catalytic Reduction of NOx with NH3

Feng¹,

Wei²,

Zhang³

et al. 2021

J. Chem. Eng. Japan / JCEJ

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In the present work, V 2 O 5 -WO 3 /TiO 2 (VWT) catalysts were loaded onto a cordierite monolith through a novel one-pot method (OP) and a traditional incipient wetness impregnation method (IW). The catalysts were characterized and evaluated for NH 3 -SCR before and after hydrothermal aging at 600°C for 36 h. An analysis of catalyst activity showed that the hydrothermal stability of OP was much higher than that of IW. N 2 -sorption and X-ray di raction (XRD) results suggested that there were no signi cant di erences in the textural and structural properties of the two catalysts before and after aging, except for the formation of a small amount of WO 3 crystallites on the surface of aged OP. Separate NH 3 -oxidation tests revealed that the NO selectivity of aged OP was signi cantly lower than that of aged IW, which resulted in a much higher NO x conversion at high temperatures during NH 3 -SCR. X-ray photoelectron spectroscopy (XPS), H 2 -temperature programmed reduction (H 2 -TPR), and Raman spectroscopy indicated that V and W species were more stable on the surface of OP during aging rather than IW, thus inhibiting the aggregation of surface-active species and leading to a better hydrothermal stability. Furthermore, OP exhibited better adhesion of the washcoat when compared to IW and this VWT catalyst exhibited a good tolerance for SO 2 .

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Section: Analysis Of Surface-active Speciessupporting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Enhanced Durability of Monolithic V2O5–WO3/TiO2 Catalysts Prepared by a Novel One-Pot Method for the Selective Catalytic Reduction of NOx with NH3

Feng¹,

Wei²,

Zhang³

et al. 2021

J. Chem. Eng. Japan / JCEJ

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“…The amount of NH3 produced in each peak should be related to the amounts of the different acid sites. However an accurate quantification is rarely allowed because the TPD peaks generally overlap as for the NH3-TPD on V2O5-WO3-TiO2 catalysts [20][21][22][23][24][25][26][27][28]. This is due to (a) the presence of NH3ads-L and NH4 + species having activation energies of desorption depending on the coverages : Ed() and (b) the contribution of NH3 readsorption during the TPD which is rarely prevented on conventional catalysts as shown by Demmin and Gorte [29].…”

Section: Introductionmentioning

confidence: 99%

“…Then this provides the adsorption coefficient i for each IR bands and finally the amount of adsorbed NH3 and NH4 + species. However, one disadvantage of TPD procedures, considering the measurement of the amounts of LAS and BAS, is the isothermal desorption performed before the increase in T often at Td= 373 K [16,20,[25][26][27][28] and for 1 h. The purpose of this procedure is the removal of NH3 physisorbed like species. However, calculations show that this leads to the desorption of a significant fraction of NH3 species formed on strong acid sites.…”

Section: Introductionmentioning

confidence: 99%

Individual amounts of Lewis and Brønsted acid sites on metal oxides from NH3 adsorption equilibrium: Case of TiO2 based solids

Giraud

Geantet²,

Guilhaume³

et al. 2021

Catalysis Today

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The present study is dedicated to the development of an original method f or the measurement of the individual amounts QASi of the acid sites ASi (acidity of Le wis and Brønsted) present on three TiO2 based solids of increasing composition compl exity: TiO2-P25, 6% WO3/TiO2-P25 and a sulfated 0.7% V2O5/9% WO3/TiO2 NH3-SCR catalyst. The method is based on quantitative characterizations of the NH3 adsor ption equilibrium (adsorption temperature Ta and pressure Pa) by the association of (a) the AEIR method providing the individual coverage qASi(Ta, Pa) of the adsorbed NH3 species on the ASi sites and (b) the total amount (in µmol/g) of the adsorbed NH3 spec ies: QTNH3(Ta, Pa) by using a mass spectrometer. For a solid having n types of ASi si tes, the QASi values are obtained from the numerical solution of linear equation system s (with at least n equation) obtained considering that QTNH3(Ta, Pa) is equal to the su m of the contribution of each adsorbed NH3 species: QASi qASi(Ta, Pa).This imposes the measurement of at least n QTNH3(Ta, Pa) in a Ta range preventing the contributio n of parallel surface processes (i.e NH3 oxidation). On TiO2-P25, n= 3 (two Lewis and one weak Brønsted acid sites) and the QASi amounts are ob tained from three QTNH3(Ta, Pa) values. The others solids having two Lewis (L1 and L 2) and two Brønsted (B1 and B2) acid sites impose a series of m measurements of QT NH3(Ta, Pa) with m>> n: the QASi are obtained by optimization between theoretical an d experimental QTNH3(Ta, Pa) curves such as 109, 202, 70 and 130 µmol/g for QL2, QL1, QB2 and QB1 respectively of 0.7% V2O5/9% WO3/TiO2. It is shown that these fo ur amounts of sites permit to conclude that the L2 Lewis acid site is the one forming the pivotal NH3ads-L2 species of the reaction by using nitrogen mass balances between the amounts of a dsorbed NH3 species and the N2 production in the presence of NO.

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“…The research effort is directed to the development of catalysts with high SCR efficiency, broad operation temperature window, superb durability, hydrothermal stability, and high resistance against SO 2 /alkali/heavy metals [21,22]. To achieve these goals as well as fully elucidate the SCR mechanism, the scientific community strives for structure-reactivity relationships by focusing on the study of the structural properties of the active sites [25][26][27][28][29], tries to find the optimum surface density of vanadium [30], synthesizes binary systems concerning either the active phase (VO x ) or the support (TiO 2 ) [18,[31][32][33][34], dopes the support [35], synthesizes metal vanadates [36], and tries to find the optimum thermal treatment of the catalysts [37] etc. It is generally agreed that a very crucial factor in the SCR process (as well as in the other above-mentioned catalytic processes) is the identification of the vanadia active site, which, despite the extensive research, is still under debate.…”

Section: Introductionmentioning

confidence: 99%

Advanced Synthesis and Characterization of Vanadia/Titania Catalysts through a Molecular Approach

et al. 2021

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Vanadia/titania catalysts were synthesized by the equilibrium deposition filtration (EDF) method, which is a synthesis route that follows a molecular-level approach. The type of interfacial deposition as well as the interfacial speciation of the deposited oxo-V(V) species were determined by means of a model that takes into account experimental “proton-ion” curves and “adsorption edges”. It is shown that at pH ≥ 9.5, the deposition proceeds exclusively through the formation of mono-substituted inner sphere monomeric species in an “umbrella”-like Ti–OV(OH)2O configuration, whilst with lowering of the pH, a second species, namely the disubstituted inner sphere quadrameric species in a (Ti-O)2V4O10 configuration possessing two mono-oxo V=O and two di-oxo V(=O)2 terminations gradually prevails, which is in co-existence with the monomeric species. Raman spectroscopy is used for verifying the solution speciation, which is different compared to the interfacial speciation of the deposited oxo-V(V) species. Furthermore, in situ Raman spectroscopy was used to verify the model-predicted interfacial speciation of the deposited oxo-V(V) species and to monitor the temperature-dependent evolution up to 430 °C. Hence, a controlled formation of a specific vanadia species on a titania surface is enabled, which, depending on the synthesis conditions, can result in specific catalyst characteristics and thus possibly different catalytic behavior for a specific reaction.

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Effects of SiO₂ modification on the hydrothermal stability of the V₂O₅/WO₃–TiO₂ NH₃-SCR catalyst: TiO₂ structure and vanadia species

Abstract: The addition of silica could produce the SixTi1−xO2 solid solutions at the interface in the doped catalyst, which inhibit the direct contact among anatase crystals and improve the stable textural property of V2O5/WO3–TiO2 catalyst.

Cited by 19 publications

References 50 publications

Enhanced Durability of Monolithic V<sub>2</sub>O<sub>5</sub>–WO<sub>3</sub>/TiO<sub>2</sub> Catalysts Prepared by a Novel One-Pot Method for the Selective Catalytic Reduction of NO<sub>x</sub> with NH<sub>3</sub>

Enhanced Durability of Monolithic V<sub>2</sub>O<sub>5</sub>–WO<sub>3</sub>/TiO<sub>2</sub> Catalysts Prepared by a Novel One-Pot Method for the Selective Catalytic Reduction of NO<sub>x</sub> with NH<sub>3</sub>

Individual amounts of Lewis and Brønsted acid sites on metal oxides from NH3 adsorption equilibrium: Case of TiO2 based solids

Advanced Synthesis and Characterization of Vanadia/Titania Catalysts through a Molecular Approach

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