Isomerization of n-butane over zeolites depending on catalyst structure

223

Applied Catalysis, 25 (1986) 223-230 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

ISOMERIZATION OF n-BUTANE

MICHAEL

ST6CKERa'*,

JOSTEIN

K. GREPSTADc

OVER ZEOLITES

PETER HEMMERSBACHa,

DEPENDING

ON CATALYST

STRUCTURE

JOHAN HENRIK RIEDERb'** AND

aDepartment of Petrochemistry, Center for Industrial P.O.Box 350 Blindern, N-0314 Oslo 3 (Norway),

Research,

bDepartment of Chemistry, University of Oslo, P.O.Box 1033 Blindern, N-0315 Oslo 3 (Norway) and 'National Laboratory for Surface Technology, N-7034 Trondheim-NTH

Studies (NALOS), Norwegian (Norway)

Institute

of

ABSTRACT The isomerization of n-butane in the gasphasg , catalyzed by H-Y zeolite, RE-Y zeolite, H- and Na-offretite, was studied at 200 C and atmospheric pressure. The rate of isobutane formation was found to be higher for the Y zeolites (H- and cation-Y) than for the corresponding offretites (H- and cation-offretite), indicating some sterical restrictions of the offretites due to their smaller pore sizes and possible stacking faults. The protonated zeolites showed higher rates of isobutane formation than the corresponding cation exchanged catalysts. The selectivities of the zeolites during the first 20 h of the reaction were found to exceed 75%, whereas the maximum yield of isobutane for the active catalysts was in the range of 33-43%. Several physical and spectroscopical characterization methods were applied. The appropriate crystal structures of the offretite samples were verified by X-ray diffraction measurements. Furth ore te ahedrally coordinated Si- and Al-sites were identified by solid-state sgi_ ind $5 Al-MAS NMR spectroscopy, in both the offretites and the Y zeolites. Scanning electron microscopy (SEM) and chemical analysis disclosed the formation of coke during isomerization. Finally, XPS-measurements indicate the coexistence of exchangeable and non-exchangeable Na-ions in Na-offretite, the latter being located in a more electron-rich environment in the zeolite lattice.

INTRODUCTION Several

attempts

have been made to study the isomerization

cially with regard to arrive at a compromise since this parameter years,

of different

in n-butane zeolites *Author **Present

of research

catalysts,

isomerization

as catalysts

0166-9834/86/$03.60

and, consequently,

for this type of reaction.

In recent

on the acid of super-acids

report the use of

Their discussion

is mainly

should be addressed.

Det norske Veritas,

0

the application

very few authors

P.O.Box

300, N-1322 Hijvik (Norway).

1986 Elsevier Science Publishers B.V.

espe-

temperature,

control.

in this field has been focused

[l-lo]. Furthermore,

to whom correspondence address:

the reaction

plays a vital role in product distribution

the main interest

strength

concerning

of n-butane,

based

224

. I

on kinetic arguments Little

effort

isomerization this paper,

[ll-141. has been devoted

and the application we report

H- and Na-offretite, work

structure

to the study of sterical

of shape-selective

data on the catalytic with emphasis

aspects

zeolites

behaviour

of n-butane

in this reaction.

of H-Y zeolite,

on the influence.of

acidic

In

RE-Y zeolite,

sites and the frame-

of the zeolite.

EXPERIMENTAL The synthesis ported

of the catalysts

previously

(Philips

structure

NMR spectroscopy,

The scanning

of Namur,

have been re-

was verified

the Na-offretite

by X-ray

dif-

was checked

shift of the tetrahedrally

by

coordinated

operating

at

Belgium).

micrographs

were recorded

eV) and Mg KCZ (1253.6

were obtained

on a Vacuum

on a JEOL JSM-50A

Generators

ESCALAB

instrument,

Mk II,

using AL

eV) X-rays.

AND DIiCUSSION

Isomerization

tests

The isomerization

TABLE

and the chemical

electron

and the XPS-spectra

spheric

samples

Furthermore,

to 53.9 ppm (Bruker CXP 200 NMR spectrometer,

52.1 MHz, University

RESULTS

of the offretite

PW 1710 instrument).

Al was determined

Ku (1486.6

procedure

[151.

The appropriate fraction 27 Al-MAS

and the isomerization

pressure.

of n-butane

The results

in thegasphase

was studied

of the test runs are shown

at 200 'C and atmo-

in Table

1.

1

Isomerization

of n-butane

over zeolites

at 200 'C

Reaction

Catalyst

ratesa

(lo-6 mol g-' h-l)

15.7

H-V zeolite

2.8

RE-Y zeolite H-offretite

5.3

"‘('

0.1

Na-offretite

aDetermined at 15% conversion, Na-offretite.

In addition products

to the isomerization

(propane,

isopentane

fines was not detected. isomerization

of n-butane,

and n-pentane)

As an example,

of n-butane

is shown

except

for the

disproportionation

were observed.

the time dependence

and cracking

The formation of composition

in Fig. 1 for H-Y zeolite.

of olein the

225 The rate of isobutane cation-Y) eating

some sterical

and possible higher lysts

formation

proved

than for the corresponding restrictions

stacking

faults.

rates of isobutane

to be higher

offretites

in the offretites

The protonated

formation

for the Y zeolites

(H- and cation-offretite), due to their

zeolites

(stronger

than the corresponding

smaller

(H- and indi-

pore sizes

acid sites)

cation

exchanged

showed cata-

(RE-Y and Na-offretite).

n-Butan o lsobutane l

0 Pentanes

FIGURE

Time dependence

1

of composition

in the reaction

of n-butane

at 200 'C over

H-Y zeol ite.

of the catalyzed

The mechanism

[13,16].

ly described

as the (intramolecular)

other

is described

carbenium

proceeds

ring mechanism

would

form a primary

carbenium

counts

For strongly

The product

rization cular

require

acidic

the opening

on zeolites

process

carbenium

is probably

ions as more

The

formation

In both reaction

as compared studies

because

three-membered

this energy

it involves and these

argument

ac-

n-alkanes

that n-butane

process

isome-

1131. The bimole-

the fOrWtiOn species

ring to

and hence

to that of other

indicate

by an intramolecular

intermediates,

cyclopropane

very unfavourable,

like super acids,

and kinetic

preferred

stable

dimer

to the intramolecular

of the protonated

of butane

does not occur

one normal-

ring mechanism.

promotes

ring system).

is energetically

systems,

distribution

cyclopropane which

has been extensively

can be indicated,

intermediates.

according

ion. ThSs

for the slow isomerization

11,21.

mechanism,

via a cyclopropane

of n-butane

of n-butane

patterns

protonated

ions are.thq,crucial

The isomerization

unlikely.

two reaction

as the bimolecular

(also this mechanism schemes

Typically,

isomerization

investigated

of octYT

can rearrange

easily.

226 The dimers ments,

are cracked

with a high selectivity

but the additional

Ii-offretite, however, channel

there

intersections.

than in H-Y zeolite formation cerning

makes

formation

As a consequence,

the discrete

channel

the loss of acidic be related

sites.

systems

To a minor

to the smaller

ions, Our findings ports

the reaction caused

cannot

rate is lower

extent,

The dimer

sensitive

are, of course,

this lowering

caused

of a transition-state

in H-offretite

acidities).

much more

In

state at the

con-

state.

and Na-offretite

pore sizes,

of C4-frag-

be prevented.

transition

by different

in zeolites

of the transition

The lower rates for RE-Y zeolite

may

the formation

is less space for a bimolecular

(beside differences

shape selectivity

towards

of C3- and C5-fragments

of the reaction

by the ion exchange

selectivity

mainly

due to

rates

to larger

are in line with

recent

cat-

re-

[17]. The selectivity

Y zeolites

to isobutane

(see Fig. 2) has been found

than for the offretites,

indicating

a higher

to be higher

shape

selectivity

for the in Y

zeolites. The n-butane highest

activity

butane

disproportionation (H-Y zeolite).

over H-Y zeolite

equimolar pected

ratios

of propane

probably

Characterization Several

previously

and pentanes

mechanism.

atoms,

[15,18,191.

retite

electron

other

energy. energy

microscopy

belonging

Si-sites,

25%, as exformation

is

of the C3-fragment.

to the Y-group

surrounded

showed

of the framework

After

obtained [20-221.

chemical

shifts

of n-butane

formed

XPS-measurements

energies

(SEM) and chemical

for the deactivated

to 0.5% for H-Y zeolite

zeolites

through

of zeolites

of offretite

the conversion

were observed

Finally,

binding

stability

with

methods have been applied for the char29 Si-MAS NMR studies have been published

coordinated

pattern

(see Fig. 4), which

energies

Solid-state

The framework

the signal

tion of coke during

compared

propane

the of n-

contains

by up to four Al-

two different

tetrahedrally

Si-sites.

Scanning

particles

reaction

of about

conversions,

thermodynamic

and spectroscopical

of the zeolites.

whereas

with

of the catalysts

only one type of tetrahedrally

coordinated

simple

up to conversions

At higher

due to the higher

physical

acterization

for the catalyst

in Fig. 3, the disproportionation

took place as a stoichiometrically

from the suggested

preferred,

has been studied

As shown

amount

the forma-

to a different

in particular

zeolites,

the highest

were performed

elements

of coke

extent.

Coke

for the H-off-

(about 2% carbon,

to determine

cations

Si2p and 01s correspond two types

in the Nals binding to H-offretite, kinetic

in order

and the zeolite

For Na-offretite,

ion exchange

, although

unveiled

as

and 0.2% for RE-Y zeolite).

for A12p,

and the higher Auger

analysis

energy

energy

the binding

(see Table

of Na-sites

with

were disclosed

and the NaKLL Auger

only the lower photoelectron sites-remained

2). The

to those observed

occupied,

kinetic binding

in reduced

221

10

FIGURE

2

Selectivity

200 'C over different

FIGURE lite.

3

20

90 30 40 CONVERSION(*/. 1

to isobutane

vs. conversion

90

70

in the reaction

of n-butane

at

zeolites.

Yield vs. conversion

in the reaction

of n-butane

at 200 'C over H-Y zeo-

b

FIGURE

4

Scanning

electron

microqraphs

of (a) H-offretite

and

(b) deactivated

H-offretite.

H-offretite

FIGURE spectra

5

NaKL2,3L2,3

electron

for H- and Na-offretite

(AlKa-X-rays).

996.6 966.6 976.6 Auger kinetic energy (eVJ

Auger

229

amounts,

though

exchangeable a more

TABLE

(cf. Fig. 5). This observation

and exchangeable

electron-rich

Na-ions

environment

indicates

the existence

of both non-

in Na-offretite, the former being locatedin

in the zeolite

framework.

2

Binding

energies

and Auger

Catalyst

kinetic

Binding

energies

A12p

SiZp

H-Y zeolite

74.3

102.3

532.2

H-offretite

74.5

102.7

532.1

Na-offretite

74.2

102.6

531.8

Binding

energy

aReference:

energies

01s

of zeolitesa

(eV)

Nals(1)

Auger

Nals(I1)

kinetic

NaKLi,3L2,3(I)

energies

NaKL2,3L2,3(II)

1071.3 1072.5

(eV)

990.2

1071.3

987.9

of Cls = 284.6 eV, experimental

990.3

error * 0.2 eV.

CONCLUSION The isomerization fluence

of acidic

relationships tained.

results

between

the isomerization

From the examination

of reactor catalytic

testing

progress,

of zeolites.

structure

especially

Further

some useful

structure

it is concluded

methods

measurements

lattice

description

concerning

on the catalytic

(IR-

about

the in-

Further,

some

were ob-

that the combined

give a detailed

investigations

of offretite/erionite

acidity

information

of the zeolites.

test runs and the zeolite

of our results

and characterization

behaviour

of framework

have provided

sites and the framework

use

of the

the influence

activity

are under

and TPD-studies).

ACKNOWLEDGEMENTS We are indebted

to the Royal

Research

for financial

carrying

out the NMR-measurement.

support

Norwegian

Council

and to Dr. J.B.

Nagy

for Scientific (University

and

Industrial

of Namur)

for

REFERENCES : : ; 7 8 9 iy

12

M. SWcker, J. Mol. Catal., 29 (1985) 371. M. Stb'cker and B.P. Nilsen, Acta Chem. Stand. B39 (1985) 153. K. Tanabe and h. Hattori, Chem. Lett., (1976) 625. H. Hattori, 0. Takahashi, M. Takagi and K. Tanabe, J. Catal., 68 (1981) 132. M. Hino and K. Arata, Chem. Commun., (1979) 1148 and (1980) 851. M. Hino, S. Kobayashi and K. Arata, J. Am. Chem. Sot., 101 (1979) 6439. K. Arata and M. Hino, React. Kinet. Catal. Lett., 25 (1984) 143. V.L. Magnotta and B.C. Gates, J. Catal., 46 (1977) 266. G.A. Fuentes, J.V. Boegel and B.C. Gates, J. Catal., 78 (1982) 436. E.A. Crathorne, I.V. Howell and R.C. Pitkethly, U.S. Pat. 3 975 299 (1976): N.N. Kruplna, A.Z. Dorogochinskii, N.F. Meged and V.I. Shmailova, React. Klnet. Catal. Lett., 23 (1983) 273. T.M. Tri, J. Massardier, P. Gallezot and B. Imelik, J. Catal., 85 (1984) 244.

230 13 14

1: 1: 19 20 21 22

C. Bearez, F. Chevalier and M. Guisnet, React. Kinet. Catal. Lett., 22 (1983) 405. P. Hilaireau, C. Bearez, F. Chevalier, G. Perot and M. Guisnet, Zeolites, 2 (1982) 69. M. Stb'cker and J.H. &der, Finn. Chem. Lett., (1984) 159. W.C. van Zijll Langhout, Proc. 9th World Petrol. Congr., 5 (1975) 197. S.M. Csicsery, Zeolites, 4 (1984) 202. J.H. -T&der; Zeolites, 4 (1984) 311. C.A. Fyfe, G.C. Gobbi, G-J. Kennedy, J.D. ,Graham, R.S. Ozubko, W.J. Murphy, A. Bothner-By, J. Dadok and A.S. Chesnick, Zeolites, 5 (1985) 179. P. Lorenz, J. Finster, G. Wendt, J.V. Salyn, E.K. Zumadilov and V.I. Nefedov, J. Electron Spectrosc. Relat. Phenom., 16 (1979) 267. 5. Narayanan, Zeolites, 4 (1984) 231. B.A. Sexton, T.D. Smith and J.V. Sanders, J. Electron. Spectrosc. Relat. Phenom., 35 (1985) 27.