Determination of the oxidation and coordination state of copper on different Cu-based catalysts by XANES spectroscopy in situ or in operando conditions

Lamberti, Carlo; Bordiga, Silvia; Bonino, Francesca; Prestipino, Carmelo; Berlier, Gloria; Capello, L.; d’Acapito, Francesco; Xamena, Françesc X. Llabrés i; Zecchina, Adriano

doi:10.1039/b305810g

Cited by 178 publications

(212 citation statements)

References 74 publications

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“…To quantify such interactions at the molecular level requires a detailed understanding of the nature of the active sites, and it is necessary to employ a range of physico-chemical, operando and spectroscopic characterisation techniques, that are best complemented when integrated with atomic level modelling studies. [9][10][11][12][13][14][15] In our recent work 16 we extended the family of transition-metal doped aluminophosphate (AlPO) frameworks, 10,17,18 to obtain isomorphous incorporation of bimetallic active centres, that display superior catalytic activity in oxidation reactions ( Figure S1 and Table S1). 16 Through a rational selection of appropriate metal combinations and synthetic strategy, it is possible to engineer and exploit synergic interactions between individual metal sites, deliberately placed within sufficiently close proximity such that their local geometry and electronic structure is modified to facilitate catalytic improvements.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

et al. 2015

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A combined electronic structure computational and X-ray absorption spectroscopy study was used to investigate the nature of the active sites responsible for catalytic synergy in Co-Ti bimetallic nanoporous frameworks. Probing the nature of the molecular species at the atomic level has led to the identification of a unique Co-O-Ti bond, which serves as the loci for the superior performance of the bimetallic catalyst, when compared with its analogous monometallic counterpart. The structural and spectroscopic features associated with this active site have been characterized and contrasted, with a view to affording structureproperty relationships, in the wider context of designing sustainable catalytic oxidations with porous solids.

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Section: Introductionmentioning

confidence: 99%

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

et al. 2015

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“…The beam transmitted through the sample passed further through a second ionization chamber, a Cr foil, and a third ionization chamber to ensure the correct energy calibration for any acquisition. 34 To avoid contamination of the samples, the Cp 2 Cr/ toluene reference and the Cp 2 Cr/NaY system (in the presence or absence of CO) have been measured inside sealed capillaries (1.5 mm in diameter), following the well-established procedure adopted for X-ray powder diffraction (XRPD) experiments. 35 For this reason, the beam was vertically focused in order to reach a dimension on the sample of 0.3 mm.…”

Section: Methodsmentioning

confidence: 99%

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

et al. 2009

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Chromocene (Cp 2 Cr) hosted inside the supercage cavities of a NaY zeolite undergoes a structural distortion induced by the strong local electric fields generated by charge-balancing counterions. This effect, clearly observed by an in situ Cr K-edge extended X-ray absorption fine structure (EXAFS) study, is the key factor in enhancing the reactivity of Cp 2 Cr toward CO. The Cp 2 Cr(CO) adducts initially formed are not as stable as when hosted in nonpolar environments such as toluene solution or polystyrene. The presence of strong anionic/ cationic pairs (Y -/Na + ) favors, in a CO atmosphere, the loss of a Cp ring driven by an electron transfer mechanism (accompanied by ligand rearrangement) that results in the formation of the charged [CpCr(CO) 3 ] - and [Cp 2 Cr(CO)]+ carbonyl species that are stabilized by Na + and Y -pairs. Shape selectivity of the supercage cavity of the Y zeolite is necessary for this reaction, as it can host the two Cp 2 Cr molecules needed for disproportionation. Fast Fourier transform infrared (FTIR) spectroscopy, working in operando conditions, allows us to follow the time evolution of the IR stretching modes peculiar of reactants and products and thus to infer a reaction mechanism. The combination of quantum mechanical calculation with an in situ EXAFS study supports the hypothesis made on the basis of IR results. The work is further demonstration that zeolitic voids act as "nanoscale reaction chambers", where the reactivity of guest organometallic complexes can provide molecular insights into the elementary steps of heterogeneous catalysis. In this context, the investigation of metallocene reactivity inside a polar matrix can be extremely useful to understanding their properties in polymerization conditions, where they are usually found as part of an ion pair, together with the anionic form of the activator (e.g., MAO).

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“…[1][2][3][4][5] Since each species has a specific spectroscopic fingerprint, it has been shown that such reaction mechanisms can only be built up by making use of multiple characterization techniques. Because of the need for a multitechnique approach, it is not surprising that scientists in recent years have tried to combine two characterization techniques in one reaction setup.…”

Section: Introductionmentioning

confidence: 99%

Synchrotron Radiation Effects on Catalytic Systems As Probed with a Combined In-Situ UV−Vis/XAFS Spectroscopic Setup

et al. 2005

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UV-vis spectroscopy was used in a combined in-situ UV-vis/XAFS spectroscopic setup to study the synchrotron radiation effect on aqueous homogeneous copper solutions. Two different systems were studied. In the first study, the focus was on a copper bipyridine-catalyzed oxidation of benzyl alcohol to benzaldehyde with 2,2,6,6-tetramethylpiperidinyl-1-oxy and base as cocatalysts. It was found that when the reaction mixture is exposed to the X-ray beam, the features present in the in-situ UV-vis spectrum develop differently compared to the situation when the reaction mixture is not exposed to the X-ray beam. Besides a temperature effect of the X-ray beam, both the UV-vis analysis and the XAFS analysis showed a reducing influence of the X-ray beam on the sample. To investigate this in more detail, we studied a series of dilute aqueous copper solutions from different precursor salts, viz., Cu(NO 3 ) 2 ‚3H 2 O, CuSO 4 ‚5H 2 O, CuCl 2 , and CuBr 2 . It was found that the different aqueous copper solutions have different stabilities under the influence of the X-ray beam. Especially the solution from the CuCl 2 precursor salt was found to be unstable and to be subjected to reduction. These examples illustrate the need for a second technique, such as in-situ UV-vis spectroscopy, to evaluate the effect of synchrotron radiation used to measure in-situ XAFS on catalytic systems.

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Determination of the oxidation and coordination state of copper on different Cu-based catalysts by XANES spectroscopy in situ or in operando conditions

Cited by 178 publications

References 74 publications

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

Synchrotron Radiation Effects on Catalytic Systems As Probed with a Combined In-Situ UV−Vis/XAFS Spectroscopic Setup

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