48, No. I, 315-323 (1992). RKCL2087. HIGHLY DISPERSED PLATINUM HONEYCOMB REFORMING CATALYSTS: SINTERING BEHAVIOR AND ACTIVITY a.
React. Kinet. Catal. Lett., Vol. 48, No. I, 315-323 (1992)
RKCL2087 HIGHLY
DISPERSED
PLATINUM
SINTERING F. F r u s t e r i
a,
HONEYCOMB
BEHAVIOR
A. P a r m a l i a n a b ,
CNR-TAE,
bDipartimento Messina C.P.
Salita
CATALYSTS:
AND ACTIVITY
A. M e z z a p l c a
P. T s i a k a r a s a * a n d aIstituto Italy
REFORMING
a
, A.L.
Chuvilin c,
N. Giordano a
S. Lucia
S. Lucia,
Messina,
di Chimica Industriale, U n i v e r s i t ~ degli 29, 98166 S. Agata, Messina, Italy
Studi di
CInstitute of Catalysis, Prospekt 630090 N o v o s i b i r s k 90, Russia
39,
98126
Akademika
Lavrentieva
5,
Received May 12, 1992 Accepted June 19, 1992
The influence
of chlorine
ment and of operation
conditions
tion of m e t h y l c y c l o h e x a n e chlorided
Pt/y-Al203
vestigated
by means
copy
(TEM).
The
the sintering
while
the reaction
honeycomb
by steam treat-
in the dehydrogenaon the dispersity
catalysts
of transmission
chlorine
testing
for the d e h y d r o g e n a t i o n
An original sensitive
of MCH on highly
in-
micros-
greatly
does not affect
structure
of
has been
electron
of small Pt crystallites
of the catalysts.
of the antipathetic Pt catalyst
(MCH)
loss of surface
motes
dispersities
regulation
pro-
( 0.85)
Pt/y-Al203 catalysts
e i t h e r in o x i d i z i n g or r e f o r m i n g conditions. N e i t h e r has the r e a c t i v i t y of small m e t a l p a r t i c l e s been a d e q u a t e l y addressed. s e n s i t i v e character, tion
Indeed,
in r e f o r m i n g c a t a l y s i s the c o n c e p t of s t r u c t u r e in-
g e n e r a l l y c l a i m e d for t y p i c a l d e h y d r o g e n a -
reactions, m e r i t s to be r e v i s e d for the c a t a l y t i c
with a metal dispersity Therefore,
systems
(D) h i g h e r than 0.5 [7].
this w o r k is aimed
(i) to i n v e s t i g a t e the sin-
tering of h i g h l y d i s p e r s e d Pt r e f o r m i n g c a t a l y s t s d u r i n g both the c h l o r i n e r e g u l a t i o n t r e a t m e n t and the o p e r a t i n g conditions, and
(ii) to g i v e
p r e l i m i n a r y insights into the i n f l u e n c e of
Pt p a r t i c l e size on the specific a c t i v i t y of r e f o r m i n g cata-
316
FRUSTERI et al. : HONEYCOMB CATALYSTS
lysts
in the d e h y d r o g e n a t i o n
of MCH.
EXPERIMENTAL A 0.26% Pt/AI203 wet i m p r e g n a t i o n
solution a c c o r d i n g Catalysts
honeycomb
catalyst
of a w a s h - c o a t e d
to the p r o c e d u r e
For comparison,
(cat Z-l) was used.
catalyst
Z-I was
Z-2).
further
ticle
size was d e t e r m i n e d
ultrasonically
dispersed
ited on a thin carbon
flowing h y d r o g e n ticle
size
5 ~),
film s u p p o r t e d
at 400
~
and p r o c e d u r e differential frequency
Further
details
have been d e s c r i b e d
s -1)
in
the m e a n par-
formulae were used by sample.
were carried out at 400 operating
concerning
elsewhere
calculations,
depos-
copper grid.
for each c a t a l y s t
conversion measurements,
(TOF,
samples,
for 2 h. To estimate
flow f i x e d - b e d m i c r o r e a c t o r
pressure.
(JEOL I00 CX
on a standard
statistical
Pt par-
finely ground and
the samples were r e d u c e d
at least 500 p a r t i c l e s
in a c o n t i n u o u s
atmospheric
1 are listed
contents.
catalyst
Tests on the MCH d e h y d r o g e n a t i o n ~
the HCI ac-
In Table
using
(in ethanol)
(dn) , the normal
considering
method.
for 40 h
by d i s s o l u t i o n
by e l e c t r o n m i c r o s c o p y
Prior to the TEM m e a s u r e m e n t s
honeycomb
"as received"
acid and t i t r a t i n g
used w i t h their Pt and chlorine
TEM, point to point r e s o l u t i o n
[8].
a C-I
to d e c h l o r i n a t i o n
c o n t e n t was d e t e r m i n e d
sulfuric
to the V o l h a r d - C h a r p e n t e r
the c a t a l y s t s
0.24% Pt/AI203
An aliquot of the
subjected
The chlorine
of the c a t a l y s t w i t h cording
elsehwere
for 15 and 40 h, r e s p e c -
a commercial
catalyst
(cat.
described
~
by
with a H2PtCI 6
C-2 and C-3 were o b t a i n e d by treating
sample in a wetted N~ flow at 500 tively.
(C-l) was p r e p a r e d
honeycomb
[83.
suitable
at
the apparatus In addition,
for turnover
have been performed.
RESULTS AND D I S C U S S I O N Sintering (PSD's)
of the
behavior. "fresh"
shown in Fig. I. despite
being
reduction
The p a r t i c l e
C-l,
It is w o r t h n o t i n g
subjected
at 400 ~
size d i s t r i b u t i o n s
C-2 and C-3 c a t a l y s t
that the c a t a l y s t
to c a l c i n a t i o n
presents
samples
at 500 ~
an a p p r e c i a b l e
are
C-l,
and s u b s e q u e n t
retention
of 317
FRUSTERI et al.: HONEYCOMB CATALYSTS
Table Chlorine
regulation
Catalyst
i
of P t / y - A I 2 0 3
Pt content
C1 content
(wt. %)
(wt. %)
C-I
0
0.24
1.75
C-2
15
0.24
0.95
C-3
40
0.24
0.53
Z-I
0
0.26
1.00
Z-2
40
0.26
0.50
(see Table
by a q u a s i - u n i m o d a l lower than
PSD c o m p r i s i n g
to the chlorine
sintering
a wide b r o a d e n i n g fact,
i) and a high Pt d i s p e r s i t y
at 400 ~
(see Table
with d
of this
i), causes
of the small Pt c r y s t a l l i t e s
n sample,
a sig-
w h i c h allows
in the PSD's of the C-2 and C-3 samples.
such s a m p l e s d i s p l a y
w i t h particle
loss
characterized
Pt c r y s t a l l i t e s
i0 ~. The steam t r e a t m e n t
in addition nificant
time
catalysts
(h)
chlorine
Treatment
honeycomb
a non-homogeneous
sizes in the range of 4-30 ~
In
Pt d i s t r i b u t i o n (cat. C-2)
and 8-40
(cat. C-3). Moreover, values,
the mean particle
summarized
in Table
2, evidence
Z-i c a t a l y s t does not undergo chlorination is similar
treatment,
a relationship
stability,
for the c o m m e r c i a l
In order to r a t i o n a l i z e
500 ~
chlorine
C-l,
unaffected
content
loss we
and Pt
C-2 and C-3 c a t a l y s t s by the chlorine
such findings,
chlorine
of our c a t a l y s t s
are very
[5]. Then, 318
between
(Table i). Therefore,
the de-
loss,
Z-I catalyst.
count that the Pt(IV) on the surface
effect during
though the extent of its chlorine
for the highly d i s p e r s e d
and a r e m a r k a b l e
that the c o m m e r c i a l
any sintering
to that of the s~mple C-I
have o b s e r v e d mobility
sizes and m e t a l d i s p e r s i t y
stable
containing during
in the p r e s e n c e
we take into ac-
complexes
[5], formed
the air c a l c i n a t i o n
at
of steam up to 600 ~
we argue that the d e c h l o r i n a t i o n
of our r e f o r m i n g
FRUSTERI et al.: HONEYCOMB CATALYSTS
100 0
~
8O
50
o"
4O
2o
H
L.
0
"
4
4 8 12 16 20 24 28 32 35 40
8 12 16 20 2/, 28 32 36 40
dn(~)
100
80 60
,-
0
40 ',
20
4 8 1216202428323640 dn(~) Fig.
i.
Particle C-2
size d i s t r i b u t i o n
(b) and C-3
of "fresh"
(c) Pt/y-Al203
C-I
honeycomb
(a), cata-
lysts catalysts
involves
only the depletion
the AI203
surface.
Such a lower
ults
in a higher
mobility better
surface
chlorine
containing
Then,
Pt complexes,
to explain
to hypothesize
that it occurs
face m i g r a t i o n
of Pt particles.
content
Pt crystallites chlorine
content)
chlorine
Pt complexes
of catalyst (4 ~), while
C-I
content
nor their
the lower
to a
obvious
step by sur-
the higher
the m i g r a t i o n
surface
of the C-2 and C-3 samples
of
mobility
it seems
the reduction
impedes
res-
leading
surface
In particular,
to
favor the
the d e c o m p o s i t i o n
the Pt sintering, during
anchored
which would
if neither
can be invoked
chlorine
surface
availability
of the c h l o r i n e - c o n t a i n i n g
Pt distribution.
of chlorine
acidity
weakens
of small (lower
the in319
FRUSTERI et al. : HONEYCOMB CATALYSTS
Table Mean particles
2
size and Pt d i s p e r s i o n honeycomb
Catalyst
of P t / y - A l 2 0 3
catalysts
Mean p a r t i c l e size
Dpt
(~)
(~)
C-i
5
I00
C-2
13
82
C-3
21
60
C-I after testing
10
i00
C-2 after testing
14
80
C-3 after testing
18
63
Z-I
50
23
Z-2
53
22
teraction favoring
between
Pt crystallites. ples,
surface
the m o b i l i t y
The a n a l o g o u s
also c o n t r o l l e d according
w i t h the support
higher
than 500
samples
in Fig.
Pt/y-Al203
which
availability.
catalysts [9].
is
In fact,
for larger Pt
growth can occur at T
the PSD's of the C-l,
in MCH d e h y d r o g e n a t i o n
2. By c o m p a r i n g
only
Pt/Al203
signals
a larger number of i n t e r a c t i o n
i, it g e n e r a l l y preserve
contents,
[9], we think that
In addition,
conditions,
of the
of Z-I and Z-2 sam-
c r y s t a l l i t e size
and further
6 h testing
catalysts
cal r e f o r m i n g sintering,
~
after
are shown in Fig.
320
et al.
(>50 ~) there exists
points
reported
"initial"
support [2],
agglomeration
chlorine
on the c h l o r i d e d
by the
to S t r a g u z z i
particles
and AI203
dispersity
in spite of their d i f f e r e n t
that the Pt m o b i l i t y
C-3
Pt species
and the c o n s e q u e n t
these patterns emerges
C-2 and
at 400 ~
w i t h those
that our c h l o r i d e d
their high d i s p e r s i t i e s
in typi-
sample C-I e x p e r i e n c e s a s l i g h t
in any case does not affect
the Pt surface
FRUSTERI et al.: HONEYCOMB CATALYSTS
100
100 SO
80
,-
60
60
~
40
40
v
0
B
i,
200~ , 4 8 12 16 20 24 28 32 36 40
4 8 12 16 20 24 28 32 36 40 dn(.~)
100 80 0
'-
60
~s
4o
L,-
u_
20
4 8 12 IB Z0 24 2B 32 38 40
dn(~) Fig.
2.
Particle and C-3
size d i s t r i b u t i o n (c) P t / y - A l 2 0 3
ter t e s t i n g
Catalytic
activity
of the c r y s t a l l i t e catalysts
honeycomb
(a), C-2
size on the
dehydrogenation. specific
studied
[7] c l a i m i n g
crystal
[i0]. No d a t a are a v a i l a b l e
its s t r u c t u r e
at 400
The
activity
dehydrogenation
sensitivity
af~
influence
of n o b l e m e t a l
has b e e n
on this
(b)
catalysts
in M C H d e h y d r o g e n a t i o n
in M C H
in c y c l o h e x a n e
of C-I
extensively
on a Pt s i n g l e
issue
for M C H de-
hydrogenation. In T a b l e genation
3 are
at 400
~
summarized on d i f f e r e n t
the TOF v a l u e s
for M C H d e h y d r o -
sized Pt/y-Al203
honeycomb
catalysts. For Pt m e a n p a r t i c l e TOF v a l u e
of ca.
sizes
5 s -I has b e e n
ranging between found,
while
5 and
on l a r g e r
21 ~ a Pt c r y s -
321
FRUSTERI et al. : HONEYCOMB CATALYSTS
Table TOF values
3
for MCH d e h y d r o g e n a t i o n honeycomb
Catalyst
at 400 ~
on P t ~ - A I 2 0 3
catalysts
Mean particle
size
TOF
(~) C-I
(s-1)
5
5.0
C-2
13
4.8
C-3
21
5.4
Z-I
50
13.0
Z-2
53
12.0
tallites
(50-53 ~)
findings
are d i a g n o s t i c
character
it equals
ca.
12-13 s -I. These p r e l i m i n a r y
of an a n i t p a t h e t i c
[7] of MCH d e h y d r o g e n a t i o n
structure
of highly d i s p e r s e d
forming catalysts.
Such an unusual c r y s t a l l i t e
could be e x p l a i n e d
by assuming
(D > 0.5) both the ensemble in d e t e r m i n i n g
re-
size dependence
that for high m e t a l d i s p e r s i o n s
and e l e c t r o n i c
the o b s e r v e d negative
size on the specific
sensitive
effects
influence
[7] concur
of particle
activity.
REFERENCES I. 2.
K. Foger, J.P.
H. Jaeger:
Bournonville,
G. Martino:
B. D e l m o n and G.F. Publ., 3.
J.P.
Amsterdam
M.J.
Krueger: 5.
J. Catal.,
322
III",
H. Lieske, 81,
p.
(1985).
159. Elsevier
G. Martino:
G. Poncelet, Publ.
B.V.,
Science
17
109,
407
P. Grange,
C.J.
P.A.
Jacobs
1983.
Carr,
M.H.
(1988).
H. Spindler,
(1983).
in "Prepara-
Amsterdam
Jr., D a v i d R. Monroe,
J. Catal.,
G. Lietz,
170
in "Catalyst D e a c t i v a t i o n "
(Eds)
J.P. Franck,
81. E l s e v i e r
D'Anielle,
96,
1980.
tion of C a t a l y s t s
4.
Froment
Bournonville,
(Eds), p.
J. Catal.,
W. Hanke,
J. Volter:
FRUSTERI et al. : HONEYCOMB CATALYSTS
6.
J. Barbier,
7.
M. Che,
D. Bahlou,
P. Marecot:
Catal.
Lett.,
8,
327
(1991). C.O.
H. Pines, Inc., 8.
A. Parmaliana,
i0.
G.I.
iii,
Straguzzi,
171
(1980).
R.K.
Herz,
J. Catal.,
Advances
P.B. Weisz,
San Diego
J. Catal., 9.
Bennett:
W.D. 67,
Eds),
in Catalysis
Vol.
(D.D. Eley,
36, p. 55. Academic
Press.
1989. F. Frusteri, 235 H.R.
Aduriz,
Gillespie, 371
A. Mezzapica,
N. Giordano:
(1988). C.E.
E.E.
Gigola:
Petersen,
J. Catal., G.A.
6_~6,
Somorjai:
(1981).
323
