Structural Determination of Copper Species on the Alumina-Supported Copper Chloride Catalyst:  A Detailed EXAFS Study

Prestipino, Carmelo; Bordiga, Silvia; Lamberti, Carlo; Vidotto, Sandro; Garilli, M.; Cremaschi, B.; Marsella, A.; Leofanti, G.; Fisicaro, P.; Spoto, Giuseppe; Zecchina, Adriano

doi:10.1021/jp027507b

Cited by 55 publications

(53 citation statements)

References 56 publications

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“…On the basis of previous results 22- 26 it is known that only two copper phases are present at the surface of undoped CuCl 2 /Al 2 O 3 catalysts activated in vacuo (or in inert gas) up to the minimum oxychlorination temperature (500 K): (i) a surface Cu-aluminate, where Cu 2+ cations occupies the cationic octahedral vacancies of the g-Al 2 O 3 surface and (ii) an amorphous, highly dispersed, CuCl 2 anhydrous phase. In fact other phases such as hydrated amorphous CuCl 2 and crystalline paratacamite (Cu 2 (OH) 3 Cl) are transformed into anhydrous CuCl 2 during the thermal treatment by release of H 2 O and HCl this last adsorbed on alumina surface during paratacamite formation.…”

Section: Activated Catalystsmentioning

confidence: 78%

Quantification of copper phases, their reducibility and dispersion in doped-CuCl2/Al2O3 catalysts for ethylene oxychlorination

Muddada

Olsbye

Leofanti³

et al. 2010

Dalton Trans.

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The comprehensive understanding of the composition, behaviour and reactivity of a catalyst used inside industrial plants is an extremely hard task that is rarely achieved. It requires the use of different spectroscopic techniques, applied under in situ or in operando conditions, and combined with the investigation of the catalyst activity. Often the operating experimental conditions are different from technique to technique and the different results must be compared with care. In the present contribution, we combined in situ XANES/EXAFS, IR spectroscopy of adsorbed CO, CO chemisorption and catalytic tests performed using a pulse reactor in depletive mode. This multitechnical approach resulted in the understanding of the role that dopants (LiCl, KCl, CsCl, MgCl(2) LaCl(3)) have in the nature, relative fraction, reducibility and dispersion of Cu-phases on CuCl(2)/gamma-Al(2)O(3) catalysts for oxychlorination reaction, a key step of the PVC chemistry. In the undoped catalyst two Cu phases coexist: Cu-aluminate and supported CuCl(2), being the latter the only active one [J. Catal., 2000, 189, 91]. EXAFS and XANES highlighted that all dopants contribute more or less efficiently in increasing the fraction of the active copper species, that reaches a value of almost 100% in the case of MgCl(2) or LaCl(3). EXAFS directly, and IR indirectly, proved that the addition of KCl or CsCl (and less efficiently of LiCl) results in the formation of mixed CuK(x)Cl(2+x) or CuCs(x)Cl(2+x) phases, so altering the chemical nature of the active phase. XANES spectroscopy indicates that addition of MgCl(2) or LaCl(3) does not affect the reducibility by ethylene (under static conditions) of the active CuCl(2) phase and that the reducibilility of the new copper-dopant mixed chloride are in the order CuCl(2)> CuLi(x)Cl(2+x) > CuK(x)Cl(2+x) > CuCs(x)Cl(2+x). However, when reduction is done inside a pulse reactor, a more informative picture comes out. The last technique is able to differentiate all samples, and their ability to be reduced by ethylene resulted in the order: La- > Mg- > Li-doped > undoped > K- > Cs-doped catalyst. To understand this apparent discrepancy the dispersion of the active phase, measured by CO chemisorption, was needed: it has been found that addition of LiCl increases enormously the dispersion of the active phase, LaCl(3) significantly and MgCl(2) barely, while addition of both KCl and CsCl results in a decrease of the surface area of the active phase. The mechanism of the enhancing effect of La and Mg on catalytic activity is still not clear, but it could be associated to the modification that they induce to the support surface: the Cu is so highly dispersed that almost all is in direct contact with support surface. It is finally worth noticing that the previous EXAFS and XANES study allowed us to refer the chemisorption data to the active phase only, while the IR study allowed us to fix the Cu(+)/CO surface stoichiometry. Summarizing the use of a multidisciplinary approach has been the conditio sine qua non (mandator...

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Section: Activated Catalystsmentioning

confidence: 78%

Quantification of copper phases, their reducibility and dispersion in doped-CuCl2/Al2O3 catalysts for ethylene oxychlorination

Muddada

Olsbye

Leofanti³

et al. 2010

Dalton Trans.

Self Cite

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“…In the 2000-2003 period, Leofanti et al achieved a significant improvement of the knowledge of the undoped CuCl 2 /Al 2 O 3 system [64][65][66][67][68]. In those studies several complementary techniques were adopted and, among them, EXAFS and XANES played a key role.…”

Section: Preliminary In Situ Xafs Experimentsmentioning

confidence: 99%

“…In those studies it has been proved that two different copper species are present on the activated catalyst (dried at 50 K in N 2 flux): a surface copper aluminate, where the copper ions are hosted in the octahedral vacancies of ı-Al 2 O 3 , and a highly dispersed copper chloride phase. The former phase is the only one present at low Cu loadings (up to 0.95 wt% Cu per 100 m 2 support); the latter precipitates directly from the solution once the adsorptive capacity of alumina is exhausted [66][67][68].…”

Section: Preliminary In Situ Xafs Experimentsmentioning

confidence: 99%

“…Successively it has been shown that the active phase in ethylene oxychlorination reaction (5.9) is the highly dispersed CuCl 2 [68], following the three-step redox mechanism reported below [64,65] This redox cycle has been determined by means of an in situ Cu K-edge XANES and EXAFS study, where the three reagents (C 2 H 4 , O 2 and HCl) have been separately dosed on the activated CuCl 2 /ı-Al 2 O 3 at 500 K in the given order ( Fig. 5.3).…”

Section: Catalyst Reactivity With the Separate Reactants: In Situ Xafmentioning

confidence: 99%

“…More recently Muddada et al [43,44,71,72] extended the works of Leofanti et al [64][65][66][67][68] from the bare to the LiCl-, KCl-, CsCl-, MgCl 2 -and LaCl 3 -doped CuCl 2 /Al 2 O 3 catalysts. Combining in situ XANES/EXAFS, IR spectroscopy of adsorbed CO, CO chemisorption and catalytic tests performed using a pulse reactor in depletive mode the authors succeeded in understanding the role of dopants (LiCl, KCl, CsCl, MgCl 2 LaCl 3 ) in determining the nature, relative fraction, reducibility and dispersion of Cuphases on CuCl 2 /ı-Al 2 O 3 catalysts for oxychlorination reaction (vide infra the main parts of Figure 5.5 for the reduction by ethylene at 500 K, Eq.…”

Section: Catalyst Reactivity With the Separate Reactants: In Situ Xafmentioning

confidence: 99%

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5. Structural and electronic characterization of nanosized inorganic materials by X-ray absorption spectroscopies

Borfecchia¹,

Agostini²,

Bordiga³

et al. 2013

Inorganic Micro- And Nanomaterials

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Starting from the late seventies, the progressively increased availability of synchrotron light sources has allowed the execution of experiments requiring a high X-ray flux in a continuous interval [1][2][3][4]. Among the various techniques developed, X-ray absorption spectroscopy (XAS, also known as X-ray absorption fine-structure, XAFS) [5][6][7][8][9][10][11][12][13] in both near (XANES) and post (EXAFS) edge regions, has become a powerful characterization technique widely employed in many research fields concerning inorganic chemistry, such as catalysis [13][14][15][16][17], organometallic and coordination complexes [18], metal nanoparticles [19, 20], electrochemical processes [21, 22], coordination polymers or metallorganic frameworks [23], bio-inorganic molecules including metalloproteins [24-27], chemistry of actinide elements [28], and solid state chemistry [12,[29][30][31].In this chapter, we will provide a brief introduction to the basic theory of XAS spectroscopy (Section 5.2), followed by selected examples having some didactic perspective (Sections 5.3-5.7). For the sake of brevity, only a fraction of the subjects mentioned above will be discussed; in particular, the chapter will deal with: the reactivity of the CuCl 2 /Al 2 O 3 -based catalysts for ethylene oxychlorination (Section 5.3); the structure, the electronic configuration and the reactivity of Cp 2 Cr molecules encapsulated in porous solids (Section 5.4); the structural characterization of metal complexes in solution (Section 5.5); the structural characterization of the UiO-66 and UiO-67 class of metallorganic frameworks (Section 5.6); and the determination of the local structure of an Alxw Gayw In 1−xw−yw As/Al xb Ga yb In 1−xb −yb As strained heterostructure grown on InP by metallorganic vapor phase epitaxy (Section 5.7) as an example of space-resolved EXAFS applied to a topic pertinent to solid state chemistry. XAS spectroscopy: Basic backgroundThe aim of this section is to provide the reader with a concise review of the basic physical principles on which the interpretation of EXAFS and XANES data is based. For a more detailed description of the theoretical background and the experimental aspects of XAS we refer to the extensive specialized literature (e.g., [5][6][7][8][9][10][11][12][13]).

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Structure and Redox Activity of Copper Sites Isolated in a Nanoporous P4VP Polymeric Matrix

et al. 2008

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Structural Determination of Copper Species on the Alumina-Supported Copper Chloride Catalyst: A Detailed EXAFS Study

Cited by 55 publications

References 56 publications

Quantification of copper phases, their reducibility and dispersion in doped-CuCl2/Al2O3 catalysts for ethylene oxychlorination

Quantification of copper phases, their reducibility and dispersion in doped-CuCl2/Al2O3 catalysts for ethylene oxychlorination

5. Structural and electronic characterization of nanosized inorganic materials by X-ray absorption spectroscopies

Structure and Redox Activity of Copper Sites Isolated in a Nanoporous P4VP Polymeric Matrix

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