cumene dehydrogenation processes. Moreover, the catalytic activity results can be well interpreted through differ- ences in the number and strength of acid sites, ...
React.
Kinet.
Catal.
Lett., Vol.
53, No.
i, 55-63
(1994)
RKCL2434 CHROMIUM-ALUMINIUM
ORTHOPHOSPHATES,
AND CATALYTIC PERFORMANCE
III. ACIDITY
IN CYCLOHEXENE AND CUMENE
CONVERSIONS ON CrPO4-AIPO 4 (20-50 wt.% AIPO 4) CATALYSTS OBTAINED IN AQUEOUS AMMONIA F.M. Bautista,
J.M. Campelo*,
J.M. Marinas,
A. Garcia,
D. Luna,
A.A. Romero and M.R. Urbano
Organic Chemistry Department, S. Alberto Magno,
Cordoba University,
Avda.
s/n ~ , E-14004 Cordoba, EspaSa
Received November 15, 1993 Accepted January 4, 1994
The modification
of CrPO4-A catalyst with AIPO 4 leads to
CrPO4-AIPO 4 (CrAIP-A)
catalysts
exhibiting not only an in-
creased total acidity but also an increased
number
of
strongest Lewis acid sites as compared to CrPO 4 and AIPO 4 catalysts. Besides,
surface acidity is slightly influ-
enced by AIPO 4 loading
(5-50 wt.%).
face Lewis acidity is responsible lytic activity in cyclohexene cumene dehydrogenation
This increased sur-
for the improved cata-
skeletal isomerization
processes.
Moreover,
activity results can be well interpreted
and
the catalytic
through differ-
ences in the number and strength of acid sites, measured gas-chromatographically, dimethylpyridine (573-673 K).
in terms of pyridine and 2,6-
chemisorbed at different temperatures
w
To whom correspondence
should be addressed
Akad4miai Kiad6, Budapest
BAUTISTA
et al.: CrPO4-AIPO 4 C A T A L Y S T
INTRODUCTION In a previous
paper
[i] we have
tion of AIPO 4 into CrPO 4 afforded better
textural
properties
shown that the incorpora-
CrPO4-AIPO 4 catalysts
and higher
surface
acidities
pure CrPO 4 [2, 3]. Moreover,
in order
promotion
by the incorporation
of CrPO 4 catalysts
the preceding pore volume
increase,
at any calcination
CrPO 4 to crystalline In the present both surface (CrAIP-A, tion
from 20 wt.%.
up the t r a n s f o r m a t i o n
below At the
of amorphous
B-CrPO 4.
work we study the effect of AIPO 4 amount of
acidity
and catalytic
and cumene
with those
AIPO 4 catalysts
in
area and
temperature
performance
20-50 wt.% AIPO 4) for cyclohexene
(CSI)
compared
in AIPO 4 content
AIPO 4 speeds
than
about the
of AIPO4,
paper [4] we showed that the surface
1273 K, with the rise same time,
to learn more
with
conversion
of CrPO4-AIPO 4
skeletal
(CC). The results
found previously
isomeriza-
obtained
are
for pure CrPO 4 [ 3 ] and
[5].
EXPERIMENTAL Catalysts Three
CrPO4-AIPO 4 catalysts
were used.
Their
were:
CrPO4:AIPO4,
80:20
(CrAIP-A-20);
50:50
(CrAIP-A-50)
wt.%.
All they were calcined
923 and 1073 K to obtain position.
The calcination
designation previously
directly. reported
three
thermal products
temperature
Details
70:30
compositions
(CrAIP-A-30)
and
for 3 h at 773, Eor every com-
(in K) follows
of their preparation
the sample
have been
[i, 4].
Methods The surface measured
acidity
in a dynamic
(sum of Br6nsted
mode by means
(573 and 673 K) of pyridine (DMPY) pulse
in the range
so as to approach
56
conditions
sites)
of the gas-phase
was
adsorption
(PY) and 2,6-dimethylpyridine
using a p u l s e - c h r o m a t o g r a p h i c size was
and Lewis
technique
corresponding
[6, 7].
The
to 0.1-0.5 monolayers
of g a s - c h r o m a t o g r a p h i c
linearity.
BAUTISTA
The catalytic CC
(craking.
were
CK,
studied
between
properties
and dehydrogenation,
the sample
ditions:
(a) CSI,
to a method
catalysts
DH)
previously
pulse,
carrier
with FID and two columns
gas,
(1/8"/,
series
packed with,
rings)
and 5% squalane,
323 K.
(b) CC, hydrocarbon
(at 50 K intervals);
(1/8",
(6-rings)
column
of a
described
HP-
[6, 7].
steel,
i~i;
stainless
2 m each)
G AW-DMCS
in (6-
80/100 573-773
(20 mL min-l).
steel)
on Chromosorb
GC
ether)
temperature,
nitrogen
con-
523-623K
(40 mL min-l).
5% poly(phenyl
gas,
inserted
temperature,
both on Chromosorb
carrier
with FID and 2 m column
i~i;
stainless
pulse,
processes
reactor
under the following
nitrogen
respectively,
in CSI and
reaction
pulse
were performed
hydrocarbon
(at 50 K intervals);
ether)
CrPO4-AIPO 4 CATALYST
inlet and the analytical
measurements
poly(phenyl
of CrAIP-A
by u s i n g a m i c r o c a t a l y t i c
589000 G C , according Catalytic
et al.:
GC
packed with
G AW-DMCS
at K
80/100
5% at
373 K. The reaction detector;
products,
60 m SPB-I
methylcyclopentenes
characterized
capillary
column
(i- and 3-MCPE)
by GC-MS
(HP-5970 MSD-
at 308 K), were
I- and 3-
for CSI and e-methylstyrene
for CC. Cyclohexene lation
and cumene
and purification
calcined
with a column
were used after
of alumina
distil-
previously
at 573 for 3 h.
RESULTS
AND DISCUSSION
Surface
acid properties
The acidity
of each CrAIP-A
mined by m e a s u r i n g on the surface
method
conditions
close
to distinguish probes
the amount
sample
permitted
surface
were used.
and Lewis Thus,
was deter-
(at saturation)
(573 and 673 K). The gaseous acidity measurements
to those of catalytic
BrSnsted
investigated
of base retained
at two temperatures
adsorption
basic
(from Merck)
reactions
but is unable
acid sites unless
two basic
probes
under
specific
were used:
57
B A U T I S T A et al.: C r P O 4 - A I P O 4 C A T A L Y S T
pyridine sites
(PY), that is a d s o r b e d on both B r ~ n s t e d
[8], and 2 , 6 - d i m e t h y l p i r i d i n e
according
to their pK a values)
selectively
adsorbed
Lewis ones because
and,
on B r ~ n s t e d
(DMPY)
and Lewis
acid
(more basic than PY
in principle,
acid sites
of the steric h i n d r a n c e
able to be
[9, 10] but not on of two methyl
groups.
The amount of base r e t a i n e d at 573 K is assumed to be a measure of the total number of acid sites while 673 K is a measure
of only stronger
The d i s t r i b u t i o n catalysts ously
for C r P O 4 - A
the surface
was d e t e r m i n e d
it is evident
from Table
h i b i t e d not only an i n c r e a s e d number of strongest
independently
the amount of adsorbed in c a l c i n a t i o n
disappeared
crystallization
should indicate Br6nsted
58
of Table
to
1 also indicate
i n f l u e n c e d by AIPO 4 temperature.
still r e m a i n e d
Moreover,
at 1073 K
the acidity
fact is due to CrPO 4 and AIPO 4 to pure C r P O 4 - A catalysts [ 3],
increased
acidity,
estimations
for C r A I P - A catalysts
the amounts
especially
at
However,
[ii] indicate
summarized
calcined
in
at 773-1073 K,
there was no s i g n i f i c a n t
of DMPY at 573 and 673 K. This
that these catalysts
acid sites.
DMPY a d s o r p t i o n
This
of AIPO 4 loading,
between
ex-
temperatures.
1 showed that
difference
Adsorption
the q u a n t i t a t i v e
and i n d e p e n d e n t l y
catalysts
(results not shown here),
displayed
calcination
Furthermore,
in all
temperature.
and the number of strong acid
are slightly
[4]. As c o m p a r e d
C r A I P - A catalysts
Table
[i]
PY and DMPY d e c r e a s e d with the increase
at 1273
completely.
interaction
1 that C r A I P - A
of the c a l c i n a t i o n
temperature.
on t r e a t m e n t
chemical
by the a d s o r p t i o n
The results
sites on the C r A I P - A catalyst
higher
and C r A I P - A - 1 0
(titrated at 673 K) c o m p a r e d
that the site e n e r g y d i s t r i b u t i o n
but,
found previ-
total acidity but also an increased
acid sites
CrPO 4 and AIPO 4 catalysts.
loading,
the results
[3], A I P O 4 [5], C r A I P - A - 5
catalysts
Besides,
i, where
CrAIP-A
are also collected.
As was expected, CrAIP-A
at
acid sites.
of acid sites on the d i f f e r e n t
is given in Table
catalysts
the base retained
had d o m i n a n t l y
preliminary
IR results
strong of PY and
the absence of B r ~ n s t e d acidity
BAUTISTA et al.: CrPO4-AIPO 4 CATALYST Table 1 Surface acidity
(~mol g-l)
for cyclohexene
and apparent
skeletal
and cumene dehydrogenation
Py"
rate constants
isomerization
(kKcDHI
(kKsKI)
on CrPO4-AIPO 4 catalysts
DMPYb
kKsra
573 K 673 K
(mol/atm g s)
o~
kKcoa
CATALYSTS 573 K
673 K
(mol/atm g s)
CrA1P-A-5-773
40
35
21
21
77.5
3.2
2.4
CrA1P-A-5-923
25
14
13
13
86.3
3.1
2.9
CrA1P-A-5-1073
10
4
3
2
48.6
2.6
2.2
CrAIP-A-10-773
37
27
20
20
106.3
3.4
3.4
CrAIP-A-10-923
26
26
8
8
126.6
3.1
2.3
CrAIP-A-10-1073
17
13
7
7
46.9
3.3
1.3
CrA1P-A-20-773
42
43
14
14
84.6
3.0
2.4
CrAIP-A-20-923
27
22
6
6
90.3
3.1
1.7
CrAIP-A-20-1073
23
12
5
5
43.6
2.9
1.9
CrA1P-A-30-773
41
38
34
29
103.3
3.0
3.2
CrA1P-A-30-923
38
37
17
10
93.2
3.2
2.6
CrA1P-A-3.0-1073
22
23
11
10
60.2
2.8
1.7
CrAIP-A-50-773
75
59
25
25
129.7
3.2
4.3
CrA1P-A-50-923
76
26
15
15
76.3
3.0
4.1
CrA1P-A-50-1073
48
22
11
11
60.6
2.9
1.5
AP-A-923
15
_d
4
-a
3.2
1.3
0.2
CrP-A-773
36
24
9
-~
68.2
3.0
3.3
CrP-A-923
18
17
8
_d
70.3
3.0
1.1
CrP-A-1073
17
12
