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(AI 3+) centers of Pt/AI203 and Pt-Sn/AI203 catalysts, ... and in the isomerization rate of heptane, respectively. ... various catalysts against its formation. Coke is ...
React. Kinet. Catal. Lett., Vol. 41, No. 2, 277-282 (1990)

DEACTIVATION

OF R E F O R M I N G METALLIC

N.M.

Ostrovskii,

E.M.

Department

COKE F O R M A T I O N

AND A C I D I C

CENTERS

Chalganov,

Yu.K.

Kolomytsev Omsk

CATALYSTS.

and O.B.

of I n s t i t u t e

Demanov,

ON

Yu.N.

Bogomolova of Catalysis,

Omsk,

USSR Received July 28, 1989 Accepted October 12, 1989

To c h e c k (AI 3+)

coke

formation

centers

of Pt/AI203

the a p p l i c a t i o n detecting bonds

Pt~

(2070 cm -I)

of active

Pt ~ and A 1 3 +

that

in the d e h y d r o g e n a t i o n

and

in the

~ns

KOHTpOnS

AI203

UeHTpOB

HcHonbaOBaHHe

(2070

CM -I) H A I 3 + - C O qHc~a

SKTHBHbIX

CKOpOCTH

H3OMepHBa~HH

The m a i n is coke

of coke

support

(2190

to c o r r e l a t e

of c y c l o h e x a n e respectively.

(Pt ~

Pt/AI203

H KHCH Pt-Sn/

N~-cneKTpOCKOnHH CBSae~

CM-I).

~eHTpOB

~eFH~pHpOBaHH~

reason

catalysts

(2190 cm -I)

a~cop-

Pt~

HOKaSaHO,

qTO CHH-

Pt ~ K o p p e ~ H p y e T

C yMeHb-

I~HK~OFeKCaHa , a A13+

FeHTaHa.

formation.

the nature various

rate

MeTannHqecKHX

CO c ~ e T e K T H p O B a H H e M

~eHHe

is shown

KaTanMsaTOpOB

CO for

in the number

rate of heptane,

3aKOKCOBaHHS

O6OCHOBSHO

6HpOBaHHOFO

meHHeM

centers

catalysts,

of a d s o r b e d

Decrease

with

(AI 3+)

and acidic

and A I 3 + - C O

substantiated.

isomerization

(Pt ~

and P t - S n / A I 2 0 3

of IR s p e c t r o s c o p y

has been

nOTHbIX

both

on m e t a l l i c

for the d e a c t i v a t i o n The a v a i l a b l e formed,

against

(AI203)

its its

of r e f o r m i n g

literature

localization formation.

and m e t a l s

has m a n y and

Coke

(Pt, Pt-Re,

catalysts data about

stability

is d e p o s i t e d

Pt-Sn).

of on

Nevertheless,

Akad~miai Kiad6, Budapest

OSTROVSKII e t a ] .

: REFORMING CATALYSTS

the l i t e r a t u r e direct

blocking

acidic

(AI 3+)

contains

almost

no q u a n t i t a t i v e

of m a i n

active

sites

and s p e c i f i c

to Pt 2+ and w h i c h Besides,

exist

the m a i n

those

involved

in reforming)

In the p r e s e n t using

state

(Pt~ is close

s y s t e m [i]. solved,

namely

of w h a t r e a c t i o n

and to w h a t e x t e n t

investigated

of a d s o r b e d

dehydrogenation

whose

the

so

(among

is d e a c t i v a t e d

center?

study we have

IR s p e c t r o s c o p y

hexane

has not been

to the q u e s t i o n

of a p a r t i c u l a r

about

that are m e t a l l i c

centers,

in the P t ( C I ) / A I 2 0 3

problem

far we have no a n s w e r

by b l o c k i n g

(P~)

data

this p r o b l e m

CO and also k i n e t i c s

and h e p t a n e

of cyclo

reforming.

EXPERIMENTAL TO r e c o r d

IR spectra,

dried

samples

in v a c u u m

directly

vessel

were

drogen

at 773 K for 1 h and then a g a i n

773 K for 1 h. S p e c t r a were recorded

in the r e a c t i o n

at 393 K for 1 h, r e d u c e d

of CO a d s o r b e d

on a S p e c o r d - 7 5

treated

by hy-

in v a c u u m

at

on Pt ~ and A 1 3 + c e n t e r s -I cm and T=293 K

IR at 1 8 0 0 - 2 3 0 0

and 77 K, r e s p e c t i v e l y . The a c t i v i t y hexane

of f r e s h l y

hydrogenation

prepared

was d e t e r m i n e d

at 0.i M P a and 553-613

K with

and c o k e d

samples

in a g r a d i e n t l e s s

simultaneous

studies

in cyclo reactor

of k i n e t i c s

like in Ref.[2]. Heptane reactor

dehydrocyclization

same c o n d i t i o n s Catalyst 0.36%

7-A1203

surface

with

were

were:

278

in a flow isothermal

covered

Centers.

in coked,

m2/g

w i t h the coke

in 02 a d s o r p t i o n

and V ~ = 0 . 6

Measurements

supported

present

Under

certain

catalysts

[5]. Only CO c h e m i s o r p t i o n

C3-

Sn s u p p o r t e d

on

cm3/g.

of the a c c e s s i b l e by t r a d i t i o n a l

difficulties.

and H 2 t r a n s f e r

the

formed.

C1 - 0.5% Pt, C2 - 0.4% Pt,

02 and H 2 and the H 2 - O 2 t i t r a t i o n results

studied

K like in Ref.[3].

Sn and C4 - 0.3% Pt + 0.22%

SBET=I80-230

Active

tion m e t h o d s tion

catalysts

samples

Pt + 0.27%

Metallic

was

at 1.0 MPa and 808-823

metal

chemisorp-

Due to coke p a r t i c i p

[4], the a d s o r p t i o n

do not p r o v i d e

of

reliable

[5] can be c o n s i d e r e d

as

OSTROVSKI et al,: REFORMN I GCATALYSTS reliable m e t h o d

to measure

Dehydrogenation

coke-free

of naphthene

on metal centers of catalysts formation

platinum.

is known to take place only

for reforming.

Hence d u r i n g o c o k e

a c o r r e l a t i o n m u s t be o b s e r v e d between

of the intensity

the decrease

(measured at the band maximum)

in the IR

spectra of CO adsorbed on Pt ~ (2070 cm -I [6])

and the catalyst

activity

is c o n f i r m e d

in c y c l o h e x a n e

both q u a l i t a t i v e l y

dehydrogenation.

and q u a n t i t a t i v e l y

sults given in Fig.

This

by the e x p e r i m e n t a i

ci

3.0

b)

o~

e - C = 0.85%

Q)

1.0

re-

la.

o

Jo

~-C = 0.13%

o

2.0 C~

0.6 0

'- tO

0.2 0

I

i

0 C

Fig.

r

0

T

i

8

2.0

1.0

(wt.~

I. D e a c t i v a t i o n

I

t

of Pt ~ centers.

a) Decrease of free Pt ~ (~) and of relative constant

for c y c l o h e x a n e

dehydrogenation

growing coke c o n c e n t r a t i o n b) Reaction kinetics r - reaction

I

I

12 16 PEH (kPa)

rate,

rate

(aD) with

(C).

on coked catalysts

at 553 K.

PCH - partial pressure

of

cyclohexane

This permits centers

to suggest that coke only blocks

and does not change

experiments

them qualitatively.

active

Special

on coked Pt, Pt-Re and Pt-Sn catalysts

kinetic

confirm

279

OSTROVSKIi et a l . : REFORMING CATALYSTS

this suggestion. equation

A type of the kinetic

curve

(Fig.

ib),

its

[2]

r=k PCH #/ (l+b PB ) z

y=l - PBzP~2/KpPCH ,

and also values

of the activation

energy

heat of benzene

Q are independent

of the coke concentration,

which evidences

qualitative

freshly prepared values were: AI203

identity

kJ/mol

increase

the nonuniformity

centers

For Pt/AI203

and Q=147•

does its deactivation

thus indicating

of active

and coked catalysts.

E=80•

E and chemisorption

kJ/mol.

on

the measured

Only on Pt-Sn/

E from 109•

to 134•

of their active

centers

kJ/no] for

dehydrogenation. Aprotic

Acidic

also measured

Centers

bond

coked catalysts

causes

intensity

proportional centration

is possible

reactions

kinetic

on AAC.

AAC,

to

of the

(y), which

is

on the coke con-

catalytic

properties

since none of them takes

participation

of the supported

of

place

metal [9].

step of some of these

In accordance

with Refs.

are likely to be isomerization

cyclohexane

dehydrogenation,

period of catalyst Hence

coke

operation (Co

(Fig.

they,

[i0-i13,

and dehydrocyc-

data should be carried

however,

in the flowing

2a))

out only

of spectral

need a

raw materi-

partly blocks

in this case a comparison

ing y and rate constants

280

of this method

2a.

is to determine

only when the limiting

al. The accumulated and AAC.

CO [8] with monitor-

of paraffins.

Unlike certain

in Fig.

of AAC A13+ are

The dependence

of coke-free

reactions,

proceeds

these reactions lization

no difficulties.

is repesented

only on AAC without

Extension

for the band at 2190 cm -I

to the portion

AAC in reforming

of adsorbed

(2190 cm-l).

Much more difficult

This

Concentrations

using spectoscopy

ing the AI3+-CO

relative

(AAC).

both Pt ~ and

for C > Co, normaliz-

of isomerization

and aromatization

OSTROVSKII et al.: REFORMINGCATALYSTS 1.0 ~ a )

o -C2

1.0

9 -C3 9 - C4

0.8

A

C3

b)

0.8

,z. D

0.6

0.6

0./.

0.4

I I I I

0

Fig.

I

1

I

I

3 C(wt?/o) 2

4

5

0

[

2

I

f

5

3 C(wt,%)

2. AAC-AI 3+ deactivation. a) Dependence

of protion

concentration b) Variations

of relative

in Fig.

in heptane

(aA) on

at Co:

aA=kA/k ~

activities.

of these parameters 2b for catalyst

C3.

range for a I variations

well with a decrease isomerization

values

a i = K i / k ~,

Here a I and a A are relative

the confidence

rate constants

8 =u

(k I and k A) by the c o r r e s p o n d i n g

The dependence

(y) on coke

(a I) and aromatization

Pt-Sn/AI203.

6=WY O,

of free AAC

(C).

isomerization

are given

I

1

in the Portion

in its reforming

on coke concentration It is easily

seen that

correlates

sufficiently

of free AAC.

Thus heptane

can be treated

as a test reac-

tion for AAC deactivation. Dehydrocyclization

rate

than that of isomerization,

(aA) decreases although

than the rate of dehydrogenation, If one suggests

a bifunctional

[12],

taking

its steps

taking

mechanism

place on metal

1.5-2 times

faster

to a much lesser degree place only on Pt ~ of d e h y d r o c y c l i z a t i o n

and support

have compar-

281

OSTROVSKII et al .: REFORMING CATALYSTS

able rates. On the other hand, tivity of catalysts

as has been shown in Ref.

in heptane

aromatization

to the number of their Pt Y centers. suggested

compared to Pt ~ and a test reaction

adequate

In this case P ~

to possess higher stability

Pt Y centers can be heptane conclusions,

come d i f f i c u l t i e s

for the d e a c t i v a t i o n

it is n e c e s s a r y

in m e a s u r i n g

can be

against coke formation

aromatization.

tion steps of d e h y d r o c y c l i z a t i o n

[i], the ac-

is p r o p o r t i o n a l

of

To obtain more

to e s t a b l i s h what reac-

take place on P ~

and to over-

the number of Pt Y in coked cata-

lysts.

REFERENCES i. A.S. Be!yi, M.D. Smolikov, N.M. Ostrovskii, Yu.N. Kolomytsev, V.K. Duplyakin: React. Kinet. Catal. Lett., 3._7_7, 457 (1988). 2. N.M. Ostrovskii, L.A. Karpova, V.K. Duplyakin: Kinet. Katal., 15, 1117 (1984). 3. N.M. Ostrovskii, A.S. Belyi, Yu.N. Kolomytsev, V.K. Duplyakin: Khim. Tekhnol. Topliv, Masel, i_~0, 13 (1986). 4. S.M. Davis, F. Zaera, G.A. Somorjai: J. Catal., 7__7_7,439 (1982). 5. T.F. Garetto, C.R. Apesteguia: Appl. Catal., 20, 133 (1986) 6. M. Primet, J~ Basset, M. Mathieu, M. Prettre: J. Catal., 29, 213 (1973). 7. J.-P. Franck, G.P. Martino: in Chemical Industries, vol. 20, D e a c t i v a t i o n and P o i s o n i n g of Catalysts, N e w York 1985. 8. E.A. Paukshtis, P.I. Soltanov, E.N. Yurchenko, K. Jiratova: C o l l e c t i o n Czechosl. Chem. Commun., 4__7_7,2044 (1982). 9. A.J. Silvestri, P.A. Naro, R.L. Smith: J. Catal., 14, 386 (1969). 10. W.L. Callender, S.G. Brandenberger, W.K. Meerbott: Proc. 5th Intern. Congr. Catal., Amsterdam, 1973, vol. 2, p. 1265. Ii. E.G, Christoffel, Z. Pa~l: J. Catal., 7_33, 30 (1982). 12. G.A. Mills, H. Heinemann, T.H. Milliken, A.G. Oblad: Ind. Eng. Chem., 45, 134 (1953).

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