STRUCTURAL STUDIES BY EXAFS/XANES SPECTROSCOPIES OF THE ACTIVE SPECIES CATALYSING THE OXYCHLORATION OF ETHYLENE

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STRUCTURAL STUDIES BY EXAFS/XANES SPECTROSCOPIES OF THE ACTIVE SPECIES

CATALYSING THE OXYCHLORATION OF ETHYLENE

M. Loos, J. Goulon, M. Bertucci, R. Bachelard

To cite this version:

M. Loos, J. Goulon, M. Bertucci, R. Bachelard. STRUCTURAL STUDIES BY EX- AFS/XANES SPECTROSCOPIES OF THE ACTIVE SPECIES CATALYSING THE OXYCHLO- RATION OF ETHYLENE. Journal de Physique Colloques, 1986, 47 (C8), pp.C8-285-C8-288.

�10.1051/jphyscol:1986854�. �jpa-00226176�

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STRUCTURAL STUDIES BY EXAFS/XANES SPECTROSCOPIES OF THE ACTIVE SPECIES CATALYSING T H E OXYCHLORATION OF ETHYLENE

M. LOOS'. J. GOULON*.", M. BERTUCCI"" and R. BACHELARD*"' ' ~ a b o r a t o i r e d e Chimie Theorique, Universite d e Nancy-I, U.A. 510 CNRS, BP 239, F-54506 Vandoeuvre-les-Nancy Cedex, France

" " L U R E , L.P. CNRS, M E N , CEA, universite de paris-Sud, Bstiment 2090, F-91405 Orsay Cedex, France

"'"centre d e Recherche RhSne-Alpes, ATOCHEM, BP 2, F-69310 Pierre-Benite, France

RBsumB

.

Dans le but de preciser la nature de la sphere de coordination du cuivre dans les catalyseurs utilis6s pour la reaction industrielle d'oxychloration de l'ethyldne, nous avons enregistre les spectres EXAFS au,,seuil K du cuivre de catalyseurs neufs de diverses provenances et d'6chantillons test" pr6levbs dans des reacteurs industriels. Les T.F. des spectres de catalyseurs neufs presentent d'evidentes similitudes avec la T.F. du spectre de l'atacamite alors que des modifications sensibles liees B la coordination d'atomes de chlore se manifestent dans les T.F. des spectres de catalyseurs usag6s. Des spectres M S enregistres au seuil K du chlore avec un nouveau detecteur de fluorescence sont aussi pr6sentes.

Abstract.

In order to characterize the structure of the active copper centers involved in the catalytic oxychloration of ethylene, we have recorded the copper K-edge spectra of several yet unused catalysts and of "test" samples taken out from industrial reactors. Whereas the FT spectra of unused catalysts exhibit marked similarities with the spectrum of atacamite, notable changes associated with the coordination of chlorine atoms are observed in the FT spectra of used catalysts. Rreliminary results regarding the measurements of chlorine K-edge X f F E S spectra recorded with a novel fluorescence detector are presented.

I INTRODUCTION.

llynil chloride monomer is produced in industrial processes by catalytic oxychloration of ethylene. The purpose of this study is to characterize the Cu(I)/CulIIl species involved in the catalytic cycle:

1/2

oe

Pyrolyse

C1, + CeH4C1,

-

^HC1

⁺

^CH2=CHC1

+

I

1 _CuC1, ₂_HC1_-₄

I

_HC1

We have recorded at L.U.R.E., on the EXAFS-I1 station the copper K-edge EWlFS spectra of several fresh catalysts and of a series of "test" samples taken out from industrial reactors. XflWS spectra were also recorded at the chlorine K-edge with a novel fluorescence detector.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986854

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C8-286 JOURNAL DE _PHYSIQUE

I 1 ANALYSES OF THE Cu K-EDGE SPECTRA.

The FT spectra Im[Cj(R1] shown below were all corrected for the phase shifts and amplitude functions of a standard Cu*

. . .

0 pair j according to [I]:

where w(k) is a KAISER-BESSEL window function, Ul, (k) and F,lkl being tabulated phase shifts and backscattering amplitude functions. A (k) refers also to standard corrections for inelastic processes and multielectron relaxation effects [ I 1.

Fitting procedures were used only for refining some quantitative analyses. As industrial catalysts often are polluted by trace amounts of,zinc (=" 300 ppml, the absor tion spectra had to be truncated beyond k,,,= 12.75 A-

.

This limitation has een more or less overcome by recording the most recent spectra in the fluorescence

&

mode

and by filtering the Zn-Ka emission.

I a ~ m r n - m m ,

-

^1A

- ^uwu^1'⁵¹

-, 0.5 -

E

Cux KK-mer sPrciaA 0s l l E S W C A T A L Y S I S OF O I F P L R E X T OIIGINI.

7.5 2.5 3.5 4.5 R I J ) 5.5

Figure 1 : Comparison of the FT-spectra I~[~(R)] 2, of fresh catalysts from different sources :

A. ATOCHEM LAVERA 57 v , s . EUTECO CD-200 B. ATOCHEM VINYLFOS V.S. EUTECO CD-200

As illustrated by figure lA, fresh catalysts from different sources, but prepared in the same way, led to superposable F T - M S spectra. Differences in the preparation procedure can eventually be detected (figure 1Bl and be correlated with non equivalent catalytic activities. Nevertheless, the FT spectra of such yet unused catalysts were found to keep always marked similarities with the FT spectrum of a natural copper hydroxychloride Cu, (OH) ,121, i .e. the so-called "atacamite mineral from Chi le (figures 2A-2Bl. it is noteworthy that our E M S data do not agree perfectly with the rather old crystal structure of this mineral, especially for the average Cu*

...

⁰bond length which is found shorter by = 0.04, 6 (figures 3A-3Bl.

Figure 2 : Comparison of the FT spectra of fresh catalysts and atacamite A. EUTECO CD-200 V.S. atacamite

B. ATOCHEM VINYLFOS V.S. atacamite

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B. Comparison of real and simulated FT spectra.

The FT spectra of "used" catalysts are notably different-(figure 4): chlorine atoms get now shortly bound to,, copper at RICu

...

^{C 1 1} ⁼^2.3^{A ,} exactly as in CuCl,.W,O [figure 5 ) . An "extended difference FT analysis combining the spectra of used/unused catalysts made it possible to extract a nearly pure Cu

...

^C1

signature (figure 61.

Figure 4 : Comparison of the FT spectra Figure 5 : Comparison of the FT spectra of an "used"(EK-311B) and of an "unused" of the "used" catalyst EK-31 1B v.s.

(CD-200) catalyst. CuC12.2H20

.

Figure 6 : "Extended" difference FT analysis for (EK-311B)

* -

(CD-200) using the Cu...Cl phase shifts lbackscatter- ing amplitude correction in equation 0 )

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C8-288 JOURNAL DE PHYSIQUE

1 1 1 C H L O R I N E K-EBGE PlEASUREnENTS.

Soft X-ray measurements below 4 keV are difficult due to the strong absorbance of the samples and of the, windows which isolate the experiment from the storage ring. The presence of .arge amounts of harmonics in the output beam of the monochromator is another major source of troubles. The latter problem was solved by the adjunction of an efficient harmonic filter consisting of two parallel SiO, mirrors [ 2 Furthermore, with the recent development of a special solid-state detector [ d j we now can afford to record In the soft X-ray range fluorescence XANES/DVIFS Apectra, even for absorbing materials. Figure 7 reproduces for instance the Cl* K-edge XANES spectra of CuCl2.HZO and of an unused catalyst.

9 0 N P

T.

i

b 2 , 3 u d a l g

+ shake

Figure 7 : Chlorine K-edge spectra of Figure 8 : Pre-edgeledge structure CuC12.2H 0 and of a fresh catalyst assignment in CuC12.2H20.

(EUTECO $D-200) (single scan spectra, 2" per data point)

IS,

-

^Is2

Is, - Is,

table 1

Symmetry orbitalsfor CuC1, .H,O

As regards the Cl* K-edge XANES spectrum of CuC1,.H20, the observed preedge structures (figure 8 ) were tentatively assigned, uslng symmetry orbitals (table 11,to the following transitions:

a,. 1

-

^b ,,.(np.Cul b2,,,(Cls)

-

a i ~ f 4 s , ~ u l

b2,3, (Cl')

-

a,, (4s.C~) + shake down from the highest occupied ligand orbitals

It is also our interpretation that the electric dipole allowed direct transition:

b,,

,,

^fCla)- a, (3d,2 -,z,Cul cannot be observed because the overlap is about two orders of magnitude smaller than for 4s,, orbital.

References

[I] J.GOULON and C.QOaON-QINET

Pure and Appl

.

^Chem.^54,²³⁰⁷¹¹⁹⁸²⁾

[2] J.QOULON, R.CORTES, A.RETOURNARD, A.WORGES, J.P.BATTION1. R . F W and B.MOlWdFCK

"EXAFS and Near Edge Structure - 111" ed. by K.HODQSON, B.HEDWX-4 and J.E.PENNER-HAHN

Springer Proc. in Physics 2, ⁴⁴⁹⁽¹⁹⁸⁴⁾

131 A.RETOUWARD, M.LOOS, 1.ASCONE. J.aOULON, M.LEFiONNIER and R.GORl'ES [in the present proceedings)