Dynamic CuII/CuI speciation in Cu-CHA catalysts by in situ Diffuse Reflectance UV–vis-NIR spectroscopy

Negri, Chiara; Signorile, Matteo; Porcaro, Natale G.; Borfecchia, Elisa; Berlier, Gloria; Janssens, Ton V. W.; Bordiga, Silvia

doi:10.1016/j.apcata.2019.03.018

Cited by 68 publications

(92 citation statements)

References 65 publications

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“…% due to an increase in the population of Cu absorption sites [17]. This observation agrees with Negri et al and Ipek et al [17,18] and it is linked to a homogeneous distribution of -OH coordinated to Cu ions in their hydrated state. The first absorption band appears at 230 nm in the 2.1/SSZ-13 catalyst and shifts after reaction towards 250 nm (Cu 2+ species).…”

Section: Ultraviolet-visible Diffuse Reflectance Spectroscopysupporting

confidence: 89%

“…Both bands increased in intensity as the Cu loading increased from 1.2 to 2.1 wt. % due to an increase in the population of Cu absorption sites [17]. This observation agrees with Negri et al and Ipek et al [17,18] and it is linked to a homogeneous distribution of -OH coordinated to Cu ions in their hydrated state.…”

Section: Ultraviolet-visible Diffuse Reflectance Spectroscopysupporting

confidence: 89%

“…When the loading of Cu increased to 2.8 wt. % all bands increased in intensity also suggesting a change in the distribution of Cu species [17,18]. It corresponds to a homogeneous distribution of -OH coordinated to Cu ions in their hydrated state.…”

Section: Ultraviolet-visible Diffuse Reflectance Spectroscopymentioning

confidence: 83%

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On the Structure-Activity Relationship for NO-SCR with NH3 Catalyzed by Cu-exchanged Natural Chabazite and SSZ-13

López-Curiel¹,

Hernández-Salgado²,

Hernández-Terán³

et al. 2021

J. Mex. Chem. Soc.

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Abstract. In spite of their similar structures, the catalytic properties of natural and synthetic (SSZ-13) Chabazite during the selective reduction of NO with NH3 have a different dependence on the Cu exchange level when tested under conditions equivalent to those found in Diesel vehicles. At low (1-2 wt.%) and high copper loadings (6-14 wt.%), their activities differ, because there are variations in the different species of Cu (Cu+, Cu2+, Cu-O-Cu) detected by UV-Vis. At intermediate Cu loadings (2-3 wt.%) they have similar high activities, reaching 100 % conversion. High deNOx activity per Cu site appears to correlate with the predominance of charge compensation Cu2+ species over CuOx moieties. There are changes in the distribution of Cu moieties during operation of both catalysts, evidenced by DR-UV-Vis. Resumen. A pesar de sus estructuras similares, las propiedades catalíticas de Chabazita natural y sintética (SSZ-13) durante la reducción selectiva de NO con NH3 dependen de manera diferente frente al nivel de intercambio con Cu cuando se prueban bajo condiciones equivalentes a las de vehículos Diesel. A bajos (1-2 % p/p) y altos contenidos de Cu (6-14 % p/p) la reducción de NO es diferente debido a variaciones en las distintas especies de Cu (Cu+, Cu2+, Cu-O-Cu) observadas por UV-Vis. Por su parte, los catalizadores intercambiados con 2-3 % p/p de Cu tuvieron alta actividad por sitio de Cu, alcanzando 100 % de conversión de NO, lo que parece deberse a la predominancia de especies de Cu2+ sobre especies CuOx de acuerdo con el análisis por DR-UV-Vis, el que también muestra la existencia de variaciones en la distribución de especies de Cu debido a la reacción.

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Section: Ultraviolet-visible Diffuse Reflectance Spectroscopysupporting

confidence: 89%

Section: Ultraviolet-visible Diffuse Reflectance Spectroscopysupporting

confidence: 89%

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On the Structure-Activity Relationship for NO-SCR with NH3 Catalyzed by Cu-exchanged Natural Chabazite and SSZ-13

López-Curiel¹,

Hernández-Salgado²,

Hernández-Terán³

et al. 2021

J. Mex. Chem. Soc.

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“…The data shown in the left‐hand panel of Figure (reported for comparison) are obtained exposing the fresh O 2 ‐activated catalyst (grey curve) to NH 3 (light blue curve). The starting point is the typical spectrum of O 2 ‐activated Cu−CHA and can be explained with the presence a variety of Cu‐oxo/hydroxo monomeric and dimeric cores . The spectrum obtained after NH 3 exposure is characterized by a broad

d - d

transition centered at 14100 cm −1 and by a CT transition at 31500 cm −1 (measured at half height).…”

Section: Resultsmentioning

confidence: 99%

Evidence of Mixed‐Ligand Complexes in Cu−CHA by Reaction of Cu Nitrates with NO/NH₃ at Low Temperature

et al. 2019

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The reactivity with a NO/NH3 mixture of Cu‐nitrate complexes formed on the surface of a Cu−CHA catalyst active in the Selective Catalytic Reduction of NOx with NH3 (NH3−SCR) was followed at 50 °C by in situ spectroscopic techniques. The catalyst (Si/Al=15; Cu/Al=0.5) was first exposed to NO/O2 (mimicking the SCR oxidative half‐cycle), mainly resulting in the formation of chelating bidentate framework‐interacting CuII‐nitrates. These intermediates were gradually detached from the framework in the presence of NO/NH3 (or NH3 alone), forming mixed‐ligand mobile [CuII(NH3)3(NO3)]+ complexes, with infrared bands at 1624 (δNH3), 1430 and 1325 cm−1 (monodentate nitrate νNO2asym and νNO2sym, respectively). X‐ray absorption and Diffuse Reflectance UV‐Vis spectroscopies showed that during this transformation the CuII/CuI reduction, observed under similar conditions at 200 °C, hardly occurred. DFT calculations confirmed the stability of nitrate ligands in the monodentate conformation in [CuII(NH3)3(NO3)]+ complexes when solvated by ammonia. The resulting structure was successfully used to fit the corresponding experimental EXAFS spectra. The gradual change of ligands in the CuII coordination sphere was confirmed by the blue shifts of both d-d and Ligand to Metal Charge Transfer bands in Diffuse Reflectance UV‐Vis spectra, with formation of features (27500, 32000 and 38000 cm−1) ascribable to the mixed‐ligand configuration.

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“…Indeed, all the hybrid-material spectra showed signals in this region that were a mixture of the vibrational modes of SiO 2 (Si-OH overtone υ 0-2 OH , υ + δ H2O /υ + δ OH combination modes of physisorbed water and of Si-OH groups) and those of CD (υ 0-2 OH , υ + δ H2O , υ 0-2 CH , υ OH + υ CO ). On the other hand, the UV-Vis region of Si-NH-CD-Cu clearly showed the typical fingerprint of hexacoordinated Cu(II) ions, with a CT component at 260 nm and an intense and broad d-d band at 700 nm [64]. These results were in agreement with the structures proposed in [65], which involved hexacoordinated Cu(II) ions in the cavity and at the rim of the CD cavity, coordinated by H 2 O molecules, OH/O − CD groups, and/or extra ligands.…”

Section: Resultsmentioning

confidence: 99%

Sonochemically-Promoted Preparation of Silica-Anchored Cyclodextrin Derivatives for Efficient Copper Catalysis

et al. 2019

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Silica-supported metallic species have emerged as valuable green-chemistry catalysts because their high efficiency enables a wide range of applications, even at industrial scales. As a consequence, the preparation of these systems needs to be finely controlled in order to achieve the desired activity. The present work presents a detailed investigation of an ultrasound-promoted synthetic protocol for the grafting of β-cyclodextrin (β-CD) onto silica. Truly, ultrasound irradiation has emerged as a fast technique for promoting efficient derivatization of a silica surface with organic moieties at low temperature. Three different β-CD silica-grafted derivatives have been obtained, and the ability of β-CD to direct and bind Cu when CD is bonded to silica has been studied. A detailed characterization has been performed using TGA, phenolphthalein titration, FT-IR, diffuse reflectance (DR), DR UV-Vis, as well as the inductively-coupled plasma (ICP) of the β-CD silica-grafted systems and the relative Cu-supported catalysts. Spectroscopic characterization monitored the different steps of the reaction, highlighting qualitative differences in the properties of amino-derivatized precursors and final products. In order to ensure that the Cu-β-CD silica catalyst is efficient and robust, its applicability in Cu(II)-catalyzed alkyne azide reactions in the absence of a reducing agent has been explored. The presence of β-CD and an amino spacer has been shown to be crucial for the reactivity of Cu(II), when supported.

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Dynamic CuII/CuI speciation in Cu-CHA catalysts by in situ Diffuse Reflectance UV–vis-NIR spectroscopy

Cited by 68 publications

References 65 publications

On the Structure-Activity Relationship for NO-SCR with NH3 Catalyzed by Cu-exchanged Natural Chabazite and SSZ-13

On the Structure-Activity Relationship for NO-SCR with NH3 Catalyzed by Cu-exchanged Natural Chabazite and SSZ-13

Evidence of Mixed‐Ligand Complexes in Cu−CHA by Reaction of Cu Nitrates with NO/NH₃ at Low Temperature

Sonochemically-Promoted Preparation of Silica-Anchored Cyclodextrin Derivatives for Efficient Copper Catalysis

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Dynamic CuII/CuI speciation in Cu-CHA catalysts by in situ Diffuse Reflectance UV–vis-NIR spectroscopy

Cited by 68 publications

References 65 publications

On the Structure-Activity Relationship for NO-SCR with NH3 Catalyzed by Cu-exchanged Natural Chabazite and SSZ-13

On the Structure-Activity Relationship for NO-SCR with NH3 Catalyzed by Cu-exchanged Natural Chabazite and SSZ-13

Evidence of Mixed‐Ligand Complexes in Cu−CHA by Reaction of Cu Nitrates with NO/NH3 at Low Temperature

Sonochemically-Promoted Preparation of Silica-Anchored Cyclodextrin Derivatives for Efficient Copper Catalysis

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Evidence of Mixed‐Ligand Complexes in Cu−CHA by Reaction of Cu Nitrates with NO/NH₃ at Low Temperature