ESR Study of Cu Centers Supported on Al-,Ti-,and Zr-Pillared Montmorillonite Clays

Abstract

Cu-doped Al-, Ti-, and Zr-pillared montmorillonites obtained by various procedures have been investigated with the aid of electron spin resonance (ESR). The major species present in pillared montmorillonites exchanged with copper at low pH are physisorbed square planar tetraaquo-complexes [Cu(H₂O)₄]²⁺. Only at the surface of uncalcined Al pillars does a chemisorption of copper ions occur, giving an inner-sphere square planar complex [Cu(AlO)_n (H₂O)_4-n]^x. Calcination of the samples at 673 K brings about a significant change of the Cu²⁺ ion environment reflected in the change of ESR parameters. The most characteristic feature is the increased covalency of the Cu–O in-plane σ bonding due to the attachment of copper to lattice oxygens. The spectra show that cupric ions form links with the pillars rather than with the silicate sheet. In the case of Al- and Ti-pillared samples, copper species of different degrees of σ in-plane covalency are obtained depending on the preparative procedure. Catalytic tests with hydroxylation of phenol demonstrate that copper centers of higher covalency show superior catalytic performance. This effect is interpreted in terms of the higher in-plane σ covalency facilitating electron transfer between the donor and the acceptor sites at the catalyst surface. The ESR spectra of almost all copper-exchanged samples show, besides the isolated Cu²⁺ ions, a component due to the exchange-coupled clustered cupric ions.

Keywords

ESR Montmorillonite Pillared clays Copper catalysts

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References

Brindley

G. W.

and Sempels

R. E

, Clay Miner. 12, 229 (1977).

Lahav

Shani

and Shabtai

, Clays Clay Miner. 26, 107 (1978).

Yamanaka

and Brindley

G. W

, Clays Clay Miner. 27, 119 (1979).

Vaughan

D. E. W.

and Lussier

R. J

, “Preparation of Molecular Sieves Based on Pillared Interlayered Clays”, in Proceedings of the 5th International Conference on Zeolites, Rees

L. V. C.

, Ed. (Heyden, London, 1980), p. 94.

Pinnavaia

T. J.

Tzou

Landau

S. D.

and Raythatha

, J. Mol. Catal. 27, 195 (1984).

Tennakoon

D. T. B.

Jones

and Thomas

J. M

, J. Chem. Soc., Faraday Trans. 1 82, 3081 (1986).

Sterte

, Clays Clay Miner. 34, 658 (1986).

Yamanaka

Nikishira

and Hattori

, Mater. Chem. Phys. 17, 87 (1987).

Jones

S. L.

, Catal. Today 2, 209 (1988).

10.

Bartley

G. J. J.

, Catal. Today 2, 233 (1988).

11.

Tzou

M. S.

and Pinnavaia

T. J

, Catal. Today 2, 261 (1988).

12.

Vaughan

D. E. W.

, Catal. Today 2, 187 (1988).

13.

Bahranowski

and Serwicka

E. M

, Colloids Surf. 72, 153 (1993).

14.

Bahranowski

Dula

Komorek

Romotowski

and Serwicka

E. M

, Stud. Surf. Sci. Catal. 91, 747 (1995).

15.

Bahranowski

Dula

Grabowski

Grzybowska-Świerkosz

Serwicka

E. M.

and Wcisło

, “Vanadium-Containing Pillared Montmorillonites as Catalysts for the Oxidative Dehydrogenation of Propane”, in Proceedings of the Europacat-II Conference, Maastricht, (1995), p. 210.

16.

Bahranowski

Janas

Machej

Serwicka

E. M.

and Vartikian

L. A

, Clay Miner., paper submitted for publication.

17.

Yang

R. T.

and Li

, J. Catal. 155, 414 (1995).

18.

Srasra

N. Frini

Ayadi

Messad

Crespin

van Damme

and Bergaya

, “Cu Clays and Pillared Clays by Mixed Al-Cu Solutions: Preparation and Physicochemical Properties”, in Proceedings of the Euroclay '95 Conference, Leuven (1995), p. 236a.

19.

Bahranowski

Gasior

Jagielska

Podobiński

Serwicka

E. M.

and Vartikian

L. A

, “Copper-Doped Alumina-Pillared Montmorillonites as Catalysts for Hydroxylation of Phenol by Hydrogen Peroxide”, in Proceedings of the Rosenquist Symposium, Oslo (1996), p. 7.

20.

Clementz

D. M.

Pinnavaia

T. J.

and Mortland

M. M

, J. Phys. Chem. 77, 196 (1973).

21.

McBride

Pinnavaia

T. J.

and Mortland

M. M

, J. Phys. Chem. 79, 2430 (1975).

22.

McBride

M. B.

, Clays Clay Miner. 30, 200 (1982).

23.

Harsh

J. B.

Doner

H. E.

and McBride

M. B

, Clays Clay Miner. 32, 407 (1984).

24.

Braddell

Barklie

R. C.

Doff

D. H.

Gangas

N. H. J.

and McKimm

, Zeit. f. Phys. Chem. 151, 157 (1987).

25.

Brown

D. R.

and Kevan

, J. Am. Chem. Soc. 110, 2743 (1988).

26.

Kukkadapu

and Kevan

, J. Phys. Chem. 92, 6073 (1988).

27.

Kukkadapu

and Kevan

, J. Phys. Chem. 93, 1654 (1989).

28.

Kukkadapu

and Kevan

, J. Chem. Soc. Faraday Trans. 86, 691 (1990).

29.

Comets

J.-M.

and Kevan

, J. Phys. Chem. 97, 120004 (1993).

30.

Yamada

Azuma

and Kevan

, J. Phys. Chem. 99, 2110 (1995).

31.

Bergaoui

Lambert

J.-F.

Duquet

and Che

, J. Phys. Chem. 99, 2155 (1995).

32.

Lozos

G. P.

Hoffman

B. M.

and Franz

C. G

, SIM 14 PROGRAM, QCPE No. 265.

33.

Hall

P. L.

, Clay Miner. 15, 321 (1980).

34.

Abragam

and Bleaney

, Electron Paramagnetic Resonance of Transition Metal Ions (Dover Publications, New York, 1986), p. 456.

35.

Kivelson

and Neiman

, J. Chem. Phys. 35, 149 (1961).

36.

Hathaway

B. J.

and Billing

D. E

, Coordin. Chem. Rev. 5, 143 (1970).

37.

Abragam

and Pryce

M. H. L

, Proc. Roy. Soc. (London) A205, 135 (1951).

38.

Abragam

and Pryce

M. H. L

, Proc. Roy. Soc. (London) A230, 206 (1951).

39.

Lewis

W. B.

Alei

and Morgan

L. O

, J. Chem. Phys. 44, 2409 (1966).

40.

Parfitt

G. D.

, Pure Appl. Chem. 48, 415 (1976).

41.

Bahranowski

and Serwicka

E. M

, Geologica Carpathica Clays 44, 17 (1993).

42.

Fujiwara

Katsumata

and Seki

, J. Phys. Chem. 71, 115 (1967).

43.

Hanuza

Je#żowska-Trzebiatowska

and Oganowski

, J. Mol. Catal. 29, 109 (1985).