characterization of clay based k catalysts

7/23/2019 Characterization of Clay Based K Catalysts

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LS VT R

Applied Catalysis A: General 132

(

1995) 141-155

Characterization of clay-based K catalysts and their

application in Friedel-Crafts alkylation of arom atics

Tivadar Cseri a,b, Sfmdor B6kAssy a, Fraqois Figueras b,*,

Eleonbra Cseke , Louis-Charles de Menorval

,

Roger Dutartre

echnical U niversi& of Budapest, Department ojOrganic Chem ica/ Technology, 1521 Budapest, Hungu)

Institut de Recherche s SW la Catalyze du CNR S, 2 Avenue Albert Eimtein 69626, Villeurhanne Cedeu. France

L&oratoire de Matdriaux Catalytiques et Catalyse erl C/like Organique, URA 4/K du CNR S, ENSC M, 8 rue

de 1 Ecole Norm als, 340.53 Montpellier Cedex, France

Received 20 April 1995: revised 27

June

1995; accepted 27

July

1995

Abstract

Toluene was alkylated with benzyl chloride and benzyl alcohol using a series of clays KSF, KSF/

0, KO, KPI 0, KlO, KS from Siid Chemie) obtained by treating a bavarian bentonite by different acids

and a Hungarian bentonite Mid) as catalysts in a batch reactor. The catalysts w ere characterized by

chemical analysis, thermal analysis, nitrogen adsorption, solid state nuclear magnetic resonance, X-

ray diffraction. The acidity of these solids was determined by infrared spectroscopy using pyridine as

molecular probe. The structure. specific surface area, and distribution of Lewis/Br@nsted acidity of

these clays can be changed to a great extent by acidic or thermal treatment. The rate of alkylation is

related to BrGnsted acidity when the substrate is benzyl alcohol. When benzyl chloride is used as

alkylating agent, the Fe+ content of the clay controls the activity, and iron containing clays show

high activities in spite of their low Lewis acidities.

Keywords: Aromatics; Alkylation: K catalysts; Acidic clays; Brensted acidity; Fe

1 Introduction

Solid acids offer many advantages by their nature, over soluble counterparts such

as aluminium chloride and hydrogen fluoride. The substitution of liquid acids by

solids as catalysts for organic synthesis offers a potential for superior effectiveness

and environmental integrity. However the origin of their activity is generally poorly

understood. Although they differ in structure from liquid acids, solid acid catalysts

* Corresponding author. Tel. ( + 33) 72445300, fax. ( + 33) 72445300.

0926-860X/95/ 09.50 0 1995 Elsevier

Science

B.V. All rights reserved

SSDIO926-860X 95)00158-1


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42 T. Cseri et al. /Applied Cutnl~sis A: Gmeral 132 1995) 141-155

work by the same principle. Clays have been proposed as suitable c atalysts for this

purpose [ l-31. Friedel-Crafts alkylation is one of the most important reactions in

synthetic and industrial organic chem istry, thus an interesting model. The alkylation

of toluene by benzyl chloride or benzyl alcohol is interesting for the preparation of

substitutes of polychlorobenzenes used as dielectrics. These reactions are usually

catalysed by Lewis acids in liquid phase [ 41 in homogeneous phase and an indus-

trial process is based on FeCl,

[ 51.

In heterogeneous catalysis, zeolites [6]

,

sulfated zirconia [7] and clays

exchanged by metallic cations [8-l 1 ] have been described. Particulary good results

have been obtained using as catalyst a zinc chloride impregnated on KlO mont-

morillonite, called clayzic [ 12-161. Clark et al. [ 171 recently reviewed the work

published on clays impregnated by zinc chloride, and activated at low temperature

T KSF > KPlO > KS > KlO > KO > Bavarian bentonite,

Hungarian bentonite.

Indeed it is doubful that this scale of acidity in water is valid in organic solvents

due to a different solvation of the acid sites. The adsorption of pyridine in the gas

phase, followed by infrared spectrometry is probably more representative in that

case. It also permits to establish the nature of the acid sites. The relative intensities

of the bands of pyridine adsorbed on Bronsted and Lewis sites are reported in


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148

T. Cseri et al. /Applied

Catdyh

A: Grnerul 132 199.5) 141-155

I

,

ollm

150

I

100

I

54

I

I

0

I

-50

1

-100

I

-150

1

-200

-250 -300

Fig.

3. Al MA 9 NMR

spectrum of KPlO

Table 6, assum ing that the vibrations at 1448-14 55 cm-

are associated to pyridine

coordinated to Lewis sites, and the vibration at 1545 cm- to pyridinium ions.

Small shifts are observed in the bands of pyridine adsorbed on Lewis sites, but the

magn itude of these shifts is not large enough to establish clear changes of the acid

strength between the different solids.

The intensities are normalized to the vibrations of the lattice in the spectral range

1920 cm- and 1800 cm- . The patterns of acidity obtained by this method are:

KS < KlO < KPlO < KSF < KSF/O, for Bronsted acidity and KPlO < KSF

< K SF/O < KS < KIO for Lewis acidity. C ompared to the pattern obtained in

Table 3

Chemical shifts (ppm) of the different Si species observed on the K clays

Catalyst

Hungarian bentonite

- 90.6

Bavarian bentonite

-90.9

K10

-90.7

- 101.3

- 110.5

KO

- 90.5

- 101.1

- 109.3

KPIO

-91.5

- 102.0

- 109.8

KS

- 90.6

- 99.9

- 109.8

KSF

-90.2

KSFIO

-91.0

- 103.3

- 108.6


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T. Cseri et al. Appl ied Catal ysis A: General 132 1995) 141-155

149

Table 4

Chemical shifts (ppm) of the different Al species observed on the K clays

Catalyst a, tetrahedral

a, tetrahedral

i17 etrahedral

?I, octahedral

Hungarian bentonite 61.3

61.2 53.0

2.5

Bavarian bentonite 70.0

55.5

2.9

KlO

70.7

3.6

KO 72.7

4.1

KPlO 73.8

3.9

KS 71.7

3.8

KSF

71.8

56.8 3.7

KSF/O 75.0

Table 5

pH of the suspension of the K catalysts (10% in

w ater)

Catalyst pH of 10% suspension

Hungarian bentonite

7

Bavarian bentonite

7

K 10

4.5

KO

5.5

KPlO

1.8

KS

3

KSF

1.5

KSF/O

1.3

Table 6

Relative intensities of the infrared bands of adsorbed pyridine on the clays dried at 393 K

Catalyst Lewis acidity

Br nsted acidity

KlO

1.91

2.23

KPlO

0.42

2.32

KS

1.02

1.76

KSF

0.59

2.35

KSF/O

0.61

3.09

water Bavarian bentonite, H ungarian bentonite < KO < KlO < KS < KPlO

characterization of clay based k catalysts

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