The initial rate of carbon formation during cyclopentane reaction has been studied on different Pt/AI203 catalysts of varying metal dispersity. It has been shown ...
React. Kinet. Catal. Lett., Vol. 28, No. 2, 245-250 (1985)
STRUCTURE
SENSITIVITY
AND COKE FORMATION
ON P t / A I 2 0 3
CATALYSTS J. B a r b i e r ,
G. Corro,
P. M a r e c o t ,
J.P.
Bournonville
and J.P.
Franck ~ Facult~
des
40, A v e n u e ~Institut 92506
Sciences, du R e c t e u r
Francais
initial
reaction varying
has
been
metal
preferably
I-4 A v e n u e
350
France
Bois Pr~au,
France
of c a r b o n
studied
on the w h o l e
formation
and
the i n i t i a l
is p r o p o r t i o n a l
Hccne~oBaHa DeaK~HH
HO~ ~ z c n e p c z e ~
MeTa~na.
Tanne
peaKaHe~,
SBnSeTCS
Ka~e~
Hpe~HOqTHTe~bHO
~pyFo~
CTOpOHM)
HaFapa
catalysts
of
that coke d e p o s i reaction which
particles.
catalyst
is
On the o t h e r
is r e l e v a n t
to
insensitive
re-
on the w h o l e
to the m e t a l l i c
surface
area.
o6pa3OBaHHH
yFn~
CKOpOCTB
Ha K a T a n H a a T o p a x qTO
Pt/AI203
BbIca~eHHe
qyBCTBHTe~bHO~
Ha 6 0 ~ b m H X
C pasnHq-
KoKca
K CTpyKType
MeTannHqeCKHX
B
Ha Me-
H HpOTe-
qaCTHHaX.
C
yFnepo~a
Ha B C e M K a T a n H s a T o p e
BAH-
HHKnoneHTa~HeHa
H T e M CaMb[M S B n S e T C S
pe-
HeqyBCTBHTe~BHOH
OTnO~eHHS
shown
is a s t r u c t u r e
HoKaaaHO,
OTAOKeHHe
SeT Ha o 6 p a s o B a H H e
Pt/AI203
cyclopentane
r a t e of coke d e p o s i t i o n
HaqanbHa~
KHKnOHeHTaHa
during
sensitive
on large m e t a l l i c
coke d e p o s i t i o n
catalyst
It has b e e n
is a s t r u c t u r e
produced
since
formation
on d i f f e r e n t
dispersity.
cyclopentadiene
aKuHe~)
au C N R S
86022 P o i t i e r s ,
du P ~ t r o l e ,
rate
t i o n on the m e t a l
action
Associ~
Received October 31, 1984 Accepted November 29, 1984
The
xo~e
Pineau,
Rueil Malmaison,
ABSTRACT
hand,
Laboratoire
K cTpyKType)
Ha B C e M K a T a n H s a T o p e
T.K.
HaqahbHas
HpOHOpHHOHanbHa
cKOpOCTb noBepx-
HOCTH M e T a ~ a . INTRODUCTION During coke
reactions
is d e p o s i t e d
altering proved
its s e l e c t i v i t y
[I] d u r i n g
platinum
of h y d r o c a r b o n s
o n the c a t a l y s t
catalysts
[I-3].
a comparative partially
on h e t e r o g e n e o u s
decreasing
In this m a n n e r study
covered
catalysts,
its a c t i v i t y
and
it has b e e n
of s e v e r a l
reactions
with preadsorbed
on
carbon-
Akad~miai Kiadd, Budapest
BARBIER et al. : STRUCTURE SENSITIVITY
aceous
species
toxicity
that coke
of coke
(defined
sites d e a c t i v a t e d pentane
for e x c h a n g e
sites
for
reaction, that
no further
steady
state
surface
hydrogenation
and ~ 0
These
were
results
ex-
sensi-
o n the active
of m e t a l
reactions
with
deposited
dispersity
was
studied
It has
of the coking
by an amount
of coke
the time of reaction. per p l a t i n u m
decreases
surface
while
on
on a
accessibility.
15 m i n u t e s
is c o v e r e d
of coverage,
The site,
platinum
at
dis-
increases.
In this paper effect
the
: 2.5 for cyclo-
is a "structure
of v a r y i n g
change
atoms
So,
of c y c l o p e n t a n e .
from the first
surface
were
preferentially
[4] the e f f e c t
catalysts
out that
of c a r b o n
persity
place
from c y c l o p e n t a n e
the m e t a l
shows
this
work
of Pt/AI203
been p o i n t e d
number
formation
the h y d r o g e n o l y s i s
formation
series
w i t h deuterium.
takes
poison.
of p l a t i n u m
for b e n z e n e
that coke
which
In a p r e v i o u s coke
as the number
0.6
of b e n z e n e
by a s s u m i n g
tive r e a c t i o n "
as a s e l e c t i v e
by one a t o m of carbon)
hydrogenolysis,
plained
acts
of p l a t i n u m
position
we r e p o r t dispersity
on the m e t a l l i c
of d i f f e r e n t i a l
on the r e s u l t s
metal
on the
phase
of a study of the
initial
of a series
rate
of coke de-
of Pt/Al203
catalysts
loadings.
EXPERIMENTAL The c a t a l y s t s (Degussa
Oxide
C,
were
propriate
amount
different
Pt loadings.
stant
system.
~ room
then
surface
outgassed
titration
were measured
zero p r e s s u r e and
246
for
under
60 Torr.
pump
samples
at r o o m
of the a d s o r p t i o n
to g i v e
in order
of the ap-
catalysts
to o b t a i n
of
a con-
in all the catalysts.
created were
2 h at this vacuum.
of y-Al203
solutions
acid,
area was m e a s u r e d
The r e d u c e d
temperature
aqueous
HCI was added
of c h l o r i n e
A turbo m o l e c u l a r
the system.
by i m p r e g n a t i o n
with
of c h l o r o p l a t i n i c
concentration Metallic
prepared
1OO m2/g)
with
a gas-volumetric -6 a v a c u u m of 10 Torr in
pretreated
temperature
Hydrogen
for 2 h at 500 and c o o l e d
chemisorption
temperature isotherms
to
and o x y g e n
by e x t r a p o l a t i o n
determined
between
to 5
BARBIER et al. : STRUCTURE SENSITIVITY
Coking
reaction
I g of the r e d u c e d duced ~
catalyst
for
purum)
was p e r f o r m e d
catalyst
was r e d u c e d
again u n d e r for
flowing
to 400
was
by a s a t u r a t o r - c o n d e n s e r
introduced
~
the time of r e a c t i o n
so a l l o w e d
us to c a l c u l a t e
The r e a c t i o n
of a c y c l o p e n t a n e / n i t r o g e n The q u a n t i f i c a t i o n perature
programmed
at a rate
phase was
atmospheric
PC5HIo/PH2
carbon
deposited
dizable
at higher
the c a r b o n
(below
temperature
on the a l u m i n a
leads
270 ~
surface
could
[I,
to
of the gas
by c h r o m a t o g r a p h y .
obtained
into the m e t a l l i c
by tem-
increased
to the volume
( V c o ) from w h i c h the m a s s of carbon 2 It has been p r o v e d in p r e v i o u s works that the a m o u n t at low t e m p e r a t u r e
pressure
was m a d e
was
of CO 2 p r o d u c e d
oxidizable
and
= 0.14/0.86.
m n -I , and the analysis
of the r e s u l t s
let
rate of coking.
Temperature
out every m i n u t e
Integration
at 500 (Fluka
line w h i c h
of the coke d e p o s i t
13 ~
hydrogen
one and ten m i n u t e s
out under
oxidation.
of
carried
between
mixture
The prere-
1 h. C y c l o p e n t a n e
the initial
was c a r r i e d
flow reactor.
for each run.
1 h and c o o l e d
us c h a n g e
500 ~
in a c l a s s i c a l
was u s e d
is obtained. of coke
lets out the when
the coke oxi-
be in r e l a t i o n s h i p
with
4].
RESULTS The c a t a l y s t s times v a r y i n g ditions less
from
the amount
than 0.1%.
coke d e p o s i t e d very
were
coked
of coke d e p o s i t e d
In this
case
on the m e t a l
for d i f f e r e n t
In these is very
low,
the d i s c r i m i n a t i o n (% C M)
reaction
experimental being
between
and on the w h o l e
con-
always the
catalyst
is
easy.
Initial
rate
Figure per
described
I to 10 minutes.
of coking I shows
accessible
metal
the time of coking. determined
from
on the m e t a l
that
the number
atom The
(CM/Macc)
initial
rate
of c a r b o n varies
atoms
deposited
proportionally
of coking
to
on the m e t a l
was
the slope of each curve.
247
BARBIER et al. : STRUCTURE SENSITIVITY
OM
PT~-~ 2
1
5 Time (rain)
Fig.
I.
Variation
of
sited
platinum
of
per
the
time
catalysts
Figure
tance
o = 3.6
x = 4.7
;
m = 6.59
;
9 = 8.7
2 gives
the e v o l u t i o n
rate
of c o k i n g .
Initial
rate
of c o k i n g 3 points
catalyst
the
on
out
of a c c e s s i b l e
the
catalysts
initial
the w h o l e
catalzs_~t
the
initial
platinum
rate
of
coking
It is n o t e w o r t h y
present
particles
in a l i n e a r
Pt/AI203
% Pt
large
that
varies
as a f u n c t i o n
of Pt d i s p e r s i t y .
platinum
deposition,
of
depo-
loadings
;
as a f u n c t i o n
atoms
for d i f f e r e n t metal
1.91
initial
amount
of c o k i n g
of v a r i o u s
atom
9 =
dispersed
Figure
surface
;
to c o k e
the w h o l e
of c a r b o n
[] = O.1
on the m e t a l that well
the n u m b e r
10
rate
a strong showing
resis-
a higher
of c o k i n g
relationship
with
on the
atom.
DISCUSSION The catalysts This
248
initial
rate
depends
result
can
of c o k i n g
linearly
by c y c l o p e n t a n e
on the n u m b e r
be e x p l a i n e d
by a s s u m i n g ,
of P t / A I 2 0 3
of m e t a l as has
surface been
atoms.
shown
in
BARBIER et al. : STRUCTURE SENSITIVITY
-E E
0.5
:>
I
I
50
100
D%
Fig.
2.
Initial
rate of coke deposition
Vm as a function
on the metal
of the dispersity
of Pt
c.) u 2 1
9 F
i
200
400
I
600
800
D . a t . Pt a c c . %
Fig.
3.
Initial
rate of deposition
as a function platinum a previous
work,
of the number
deposition
is proportional
pentadiene
in the gas phase
structure
insensitive
is proportional 2
catalyst
of accessible
atoms.
that during
Dehydrogenation
on the whole
coking by cyclopentane,
to the partial
of cyclo-
[5].
of cyclopentane reaction
to the metal
pressure
carbon
to cyclopentadiene
for which
the catalyst
is a
activity
surface. 249
BARBIER et al. : STRUCTURE SENSITIVITY
On the other face
atom
sity.
Thus
surface higher This
hand,
the
for the c o k i n g the
initial
of a c a t a l y s t
rate with
shows
that
is a s t r u c t u r e
sensitive with
agreement
proved
that
resistant
atoms
to coke
electron ticles
an a d s o r b e d ion.
from m e t a l
than on small
case of coking
This
species
other
non-desorbable
ones
cyclopentadiene
carbonaceous
placed
on large
This
electon
could
induce
the v e r y
could
and
is in
are
less
on the edges
be e x p l a i n e d
to dienes
approaching
adsorption
catalysts
crystallites.
could
[7,8].
by c y c l o p e n t a n e ,
strong
zation w i t h
sensitivity
100%.
[3], w h o has
of c r y s t a l l i t e s
the atoms
of the p l a t i n u m
structure transfer
[6] on p l a t i n u m
on the faces
of
of m e t a l l i c
of S o m o r j a i
than
is 20 times
dispersion
reactiQn
sur-
disper-
on the m e t a l
dispersity
a metal
reaction
formation
and on the c o r n e r s This
with
the f i n d i n g s
placed
of one m e t a l
on p l a t i n u m
of coke d e p o s i t i o n
the coking
good
activity
depends
3% m e t a l
than for a c a t a l y s t
result
initial
reaction
deposits
parin the
the f o r m a t i o n
stable
on the
platinum
transfer,
then enhance, molecules,
by easier
of
cyclopentadienyl by p o l y m e r i -
the f o r m a t i o n largest
of
platinum
particles. REFERENCES I.
2.
3. 4. 5. 6. 7. 8.
250
J. Barbier, P. M a r e c o t , N. Martin, L. Elassal, R. Maurel: Studies in S u r f a c e S c i e n c e and C a t a l y s i s , C a t a l y s t Deactivation, E l s e v i e r , 6, 53 (1982) P.P. L a n k h o r s t , H.C. De Jongste, V. Ponec: Studies in Surface S c i e n c e and Catalysis, C a t a l y s t D e a c t i v a t i o n , E l s e v i e r 6, (1982) S.M. Davis, F. Zaera, G.A. Somorjai: J . C a t a l . , 77, 439 (1982) ; G.A. Somorjai, D.W. Blakely: Nature, 25~, 580 (1975) J. Barbier, G. Corro, Y. Zhang, J.P. B o u r n o n v i l l e , J.P. Franck: Appl. Catal., (in press) J. Barbier, L. Elassal: B u l l . S o c . C h i m . F r a n c e (in press) M. Boudart, A.W. Aldag, L.D. Ptak, J.E. Benson: J . C a t a l . , 11, 35 (1968) G.C. Bond, P.A. Sermon: Gold. Bull., 6, 102 (1973) R.A. B a l l a b e t t a , M. Boudart: Proc. 5th Int.Congr. on Catal., 1329 (1972)
