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Adsorptive Properties of Aluminumphosphate Molecular Sieves
M. Che and G.C. B o n d (Editors), Adsorption and Catalysis o n Oxide Surfaces 0 1985 Elsevier Science Publishers B.V., Amsterdam - P r i n t e d in The Netherlands
163
ADSORPTIVE PROPERTIES O F ALUMINUMPHOSPHATE MOLECULAR S I E V E S
1
Genadi j D w o r e r k o v , Gerd Rumplmayr’, H e l m u t Mayer’
and Johannes A.
Lercher
1
i:(
I n s t i t u t f u r P h y s i k a l i s c h e Chemie, T e c h n i s c h e U n i v e r s i t a t Wien, G e t r e i d e m a r k t 9, A-1060 ‘Institut
V I E N N A , AUSTRIA
f u r M i n e r a l o g i e , K r i s t a l l o g r a p h i e und S t r u k t u r c h e m i e
G e t r e i d e m a r k t 9, A-1060
VIENNA, AUSTRIA
ABSTRACT M i c r o p o r o u s a l u m i n o p h o s p h a t e s h a v e been s y n t h e s i z e d and c h a r a c t e r i z e d b y i n t e r c a t i o n w i t h bases. M o d e r a t l y s t r o n g L e w i s a c i d s i t e s and v e r y weak base s i t e s were found. The Br’dnsted a c i d s i t e s p r e s e n t c o u l d o n l y p r o t o n i z e ammon i a , b u t n o t p y r i d i n e . The a c i d - b a s e p r o p e r t i e s o f t h e a l u m i n o p h o s p h a t e s r e s e m b l e d t h o s e o f s i l i c a and amorphous a l u m i n o p h o s p h a t e s , s u g g e s t i n g t h a t t h e c h a n n e l s t r u c t u r e ( 0 . 6 nm d i a m e t e r ) d i d n o t i n d u c e new a c i d b a s e p r o p e r t i e s .
INTRODUCTION Using
Sanderson’s
concept o f e l e c t r o n e g a t i v i t y ( r e f . 1 )
t h a t t h e e l e c t r o n p a i r a c c e p t o r (EPA, be
it
t h e h i g h e r ( a n d t h e c o r r e s p o n d i n g e l e c t r o n p a i r d o n o r (EPD.
strength
t h e lower),
t o Sanderson i s intermediate fully
.
was
predicted
L e w i s a c i d ) s t r e n g t h o f an o x i d e w o u l d Lewis
t h e higher t h e intermediate e l e c t r o n e g a t i v t y according
I n general t h i s implies a higher a c i d strength f o r
electronegativity
by M o r t i e r ( r e f . 2 )
as b y L e r c h e r e t a l .
.
(ref.4)
higher
R e c e n t l y t h i s c o n c e p t was a p p l i e d s u c c e s s -
and H o c e v a r and D r z a j ( r e f . 3 ) f o r mixed oxides.
f o r z e o l i t e s as
well
I n an e a r l i e r p a p e r , however,
we h a v e p o i n t e d o u t t h a t an u p p e r l i m i t o f EPA s t r e n g t h o f o x i d e s may because
base)
exist,
o f l i m i t e d a c c e s s t o t h e EPA s i t e s w i t h e v e r i n c r e a s i n g i n t e r m e d i a t e
electronegativity (ref.5). Aluminophosphates
s h o u l d be good o b j e c t s t o s t u d y t h e s e
cause o f t h e i r r a t h e r h i g h i n t e r m e d i a t e e l e c t r o n e g a t i v i t y . dies (ref.6) sites. of
be-
c l a s s i f i e d t h e m as s t r o n g l y a c i d i c c a t a l y s t w i t h v e r y weak b a s i c
However,
t h e r e s u l t s o f c h a r a c t e r i z a t i o n o f Wendt e t a l . ( r e f . 7 - 9 )
m e c h a n i s t i c i n v e s t i g a t i o n s of Thomke ( r e f . 1 0 )
would
constraints
P e r i l s e a r l y stu-
suggest r a t h e r a moderate a c i d s t r e n g t h .
summarizes t h e s e c h a r a c t e r i z a t i o n s .
*To whom c o r r e s p o n d e n c e s h o u l d be a d d r e s s e d .
and B a u e r e t
al.
A review by Moffat
and
(ref.11) (ref.12)
164 Recently
the synthesis o f
t u r e was r e p o r t e d ( r e f . 1 3 . 1 4 ) . with
new a l u m i n o p h o s p h a t e s w i t h m i c r o p o r o u s Gne A1PG4 ( t y p e 5 ) h a d a s t r u c t u r e
t h e o r e t i c a l f r a m e w o r k o f t y p e 81,
the
as p r o p o s e d b y S m i t h
T h i s p h o s p h a t e has 1 2 - r i n g c h a n n e l s w i t h 6 - r i n g c o n n e c t i o n s . claimed
to
cracking and
possess a c i d s i t e s s u f f i c i e n t l y a c t i v e t o
and o t h e r a c i d c a t a l y z e d r e a c t i o n s .
characterization
(ref.15).
The m a t e r i a l was
catalyze
hydrocarbon preparation
We r e p o r t h e r e o n
o f t h i s p h o s p h a t e and some
struc-
identical
derivatives
from
it.
EXPERIMENTAL Catalysts The
porous aluminophosphates were prepared a c c o r d i n g t o
chiometric
amounts
o f aluminiummonohydroxide ( P u r a l
distilled
water.
tripropylamine
ref.13.
CONOEA,
Stoi75.1
w%
85 w% H PO ) were m i x e d 3 4 The s u s p e n s i o n was s t i r r e d u n t i l homogeneous. Then
A1203) and o r t h o p h o s p h o r i c a c i d ( M e r c k , p . a . with
SB,
quality,
was added and t h e r e s u l t i n g m i x t u r e h a d t h e f o r m u l a
1.0 ( C H ) N : A1203 : P205 : 40 H20. 3 7 3 I t was s e a l e d i n an PTFE l i n e d a u t o c l a v e and k e p t a t 423K f o r 1 0
composi-
tion:
hours.
The
r e s u l t i n g p r o d u c t was f i l t e r e d and washed w i t h d i s t i l l e d w a t e r u n t i l n e u t r a l . X-ray type
diffraction 5
measurements showed t h a t t h e m a t e r i a l was p u r e
structure (ref.13).
83m2. g-’
f o r A1 P04-5,
The BET s u r f a c e a r e a s w e r e
NaOH/A1P04-5,
280,
58,
A1P04
of
210
and
( NH4)2HP04/A1 PO4-5 and S i 0 2 / A 1 PO4-5 r e -
spectively. To
modify
t h e s u r f a c e p r o p e r t i e s t h e a l u m i n o p h o s p h a t e was
0.02 m o l a r NaOH and (NH4)2HP04
s o l u t i o n s f o r 4 h o u r s , f i l t e r e d , washed,
a t 373K a n d c a l c i n e d a t 873K f o r t w o h o u r s . A n o t h e r p h o s p h a t e using in
The
0.01Si02:40H20. 72
r e a c t i o n m i x t u r e had a c o m p o s i t i o n o f This
dried by
dissolved
1.0TPAOH:A1203:P205:
m i x t u r e was h e a t e d i n an PTFE l i n e d a u t o c l a v e a t
h o u r s and t r e a t e d s u b s e q u e n t l y l i k e A1P04-5.
in
W ~ S prepared
tetrapropylammoniumhydroxide (TPAOH) and a d d i n g some s i l i c a
TPAOH.
for
suspended
The
only
423K
crystalline
p r o d u c t was A1P04-5 a l t h o u g h some amorphous m a t e r i a l may be p r e s e n t . R e a c t a n t s and a d s o r b e n t s Pyridine
and
acetone
w e r e o b t a i n e d f r o m M e r c k (p.a.
quality)
and
not
f u r t h e r p u r i f i e d . A l l g a s e s u s e d h a d a t l e a s t 99.999 v o l % p u r i t y . I n f r a r e d measurements The p h o s p h a t e s h a v e been i n v e s t i g a t e d b y means o f t h e t r a n s m i s s i o n - a b s o r p t i o n technique.
in
situ.
The
The
c e l l u s e d p e r m i t t e d a l l s a m p l e h a n d l i n g s t o b e done 8 -2 p h o s p h a t e w a f e r ( c o m p a c t i n g p r e s s u r e = lo8 - 3.10 Nm ) was
heated o u t s i d e t h e ture
from
1.r.
1.r.
beam.
4000-1000 cm-l
The s p e c t r a w e r e r e c o r d e d a t a m b i e n t t e m p e r a -
u s i n g a P e r k i n Elmer
infrared
spectrophotometer
165 ( t y p e 325) w i t h 3 cm-’
r e s o l u t i o n a t 3600 cm-’.
T e m p e r a t u r e programmed d e s o r p t i o n ( t . p . d . ) T.p.d.
was c a r r i e d o u t i n v a c u o ( c a . f r o m 300K t o 1000K.
o f 10K.min-’
measurements 10-lPa) u s i n g a temperature increment
The r e a c t o r was a q u a r t z g l a s s t u b e connec-
ted
w i t h a vacuum pump and a B a l z e r s 311 mass s p e c t r o m e t e r f o r d e t e c t i o n
the
species
phosphate
The mass s p e c t r o m e t e r and t h e
by a D i g i t a l M I N C computer.
controlled ambient
desorbed.
were
calcined
temperature
t.p.d.
furnace
F o r e a c h measurement 100 mg
i n t h e r e a c t o r a t 873K f o r
one
and c o n t a c t e d w i t h t h e a d s o r b e n t .
e v a c u a t e d a t a m b i e n t t e m p e r a t u r e and t . p . d .
hour,
of were
of
the
cooled
Then t h e s a m p l e
to was
was s t a r t e d .
T h e r m o g r a v i m e t r i c measurements Quantitative
a n a l y s i s o f t h e w e i g h t changes d u r i n g a c t i v a t i o n and
t.p.d.
measurements was p e r f o r m e d b y an M e t t l e r t h e r m o a n a l y z e r TRl, w h i c h D e r m i t t e d simultaneous
r e c o r d i n g o f t h e r m o g r a v i m e t r i c and d i f f e r e n t i a l
t r i c d a t a . The i n s t r u m e n t was p u r g e d w i t h N2 ( 5 l . m i n
1 0 Fig.1.
-1
thermogravime-
).
3500 3000 2500
1800 1600 WAVENUMBERS [cm-’I
1400
A c t i v a t i o n o f A1P04-5 i n vacuum.
( 1 ) l h . 298K;
( 2 ) l h , 373K; ( 3 ) l h , 473K; ( 4 ) l h , 673K
RESULTS I n f r a r e d s p e c t r o s c o p i c measurements Activation washed
a f t e r synthesis.
A f t e r evacuation a t ambient temperature t h e
and d r i e d ( 3 7 3 1 0 A1P04 e x h i b i t e d bands a t
2880,
2805,
after
evacuation
1463,
1388 and 1337 cm-’. at
3100,
2970,
These b a n d s d e c r e a s e d i n
1) b u t d i d n o t
2940.
intensity
change
their
They w e r e n o t o b s e r v e d a f t e r e v a c u a t i o n a t
573K.
373K and 473K ( s e e F i g .
wavenumbers s i g n i f i c a n t l y .
3380,
166 A f t e r i n i t i a l t r e a t m e n t a t 573K, A1P04 showed OH s t r e t c h i n g bands a t 3678 and The NaOH and t h e ( N H ) HP04 t r e a t e d a l u m i n o p h o s p h a t e s had o n l y a 4 2 w h i l e t h e p h o s p h a t e s y t h e s i z e d w i t h Si02 d i d n o t show a
3652
cm-l.
band
a t 3680 cm-’,
h y d r o x y l s t r e t c h i n g band.
W i t h a l l phosphates,
bands o f l a t t i c e
vibrations
c o u l d b e o b s e r v e d a t 1655 and 1450 cm-l. Adsorption A1P04-5,
o f ammonia.
NaOH/A1PO4-5
The s p e c t r a o f NH
and (NH4)2HP04/klP04-5
3 ( 1 3 kPa p a r t i a l p r e s s u r e ) on c a n be seen i n f i g u r e 2. A l l
p h o s p h a t e s had bands a t 1613 and 1450 cm-l.
three
t h e l a t t e r was l o w w i t h NaOH/A1P04. bands
The r e l a t i v e i n t e n s i t y o f
A f t e r e v a c u a t i o n a t room t e m p e r a t u r e , t h e
disappeared almost completely i n d i c a t i n g low thermal s t a b i l i t y o f
the
a d s o r b a t e complex. Adsorption 19a,b
o f pyridine.
The wavenumbers o f t h e c h a r a c t e r i s t i c 8 a - b
v i b r a t i o n s o f p y r i d i n e adsorbed on aluminophosphates a r e
compiled
and in
t a b l e 1. The a d s o r b a t e s p e c t r a w i t h p u r e A1P04 c a n be seen i n f i g u r e 3. Pyridine
formed
temppratures 1450-1447 cm-l.
of
s t a b l e a d s o r b a t e s w i t h a l l p h o s p h a t e s up
873K.
The wavenumber o f one 19b band was f o u n d
evacuation always
at
The NaOH t r e a t e d sample had an a d d i t i o n a l band a t 1442 cm-l.
However, a band a t 1540 cm-l the
to
catalysts investigated.
was n o t o b s e r v e d w i t h s i g n i f i c a n t i n t e n s i t i e s o n T h i s s u g g e s t s t h a t o n l y a v e r y s m a l l amount
of
p y r i d i n e a d s o r b e d may b e r e t a i n e d as p y r i d i n i u m i o n s . TABLE 1 Wavenumbers o f 8 a , b and 19a,b bands o f p y r i d i n e a d s o r b e d on a l u m i n o p h o s p h a t e s
A1 PO4-5
NaoH/A1 p04-5
298K. 1.3kPa
298K, ev.
473K,ev.
673K. ev.
1609,1577 1492.1480 1447.1438
1610,1577 1491 1448
1620 1490 1449
1620 1490 1449
1595 1490 1448, 442
1595 1490 1448,1442
1609,1590,1577 161 0,1595,1577 1492.1480 1495.1490 1447; 1440.1438 1447; 1442
(NH4)2HP04/ A1 PO4-5
1610.1575 1490,1480 1448.1438
1611,1578 1490 1448
1612 1491 1450
1612 1491 1450
”02/A1 p04-5
161 0,1580 1492,1480 1447,1438
1610 1490 1447
1612 1490 1447
1615 1490 1448
A d s o r p t i o n o f CO A f t e r a d m i s s i o n o f l 3 k P a CO i n t o t h e i . r . c e l l o n l y 22 1 t w o bands o f C02 c o u l d b e o b s e r v e d a t 2340 and 2356 cmThey c o r r e s p o n d t o
.
linearly
adsorbed
C02 ( r e f . 1 6 ) and d i s a p p e a r e d a f t e r e v a c u a t i o n a t
ambient
167 t e m p e r a t u r e . No t r a c e s o f bands o f c a r b o n a t e s c o u l d be d e t e c t e d .
I T-
I
I
I
7
I
I
/
1800
1600
I i I u 1600 1400
,L
1800
1400
WAVENUMBERS [ern-']
WAVENUMBERS [crn-’]
F i g . 2. A d s o r p t i o n o f ammonia
F i g . 3. A d s o r p t i o n o f p y r i d i n e on AlPO
( 1 3 kPa, 298K).
( 1 ) 1.3 kPa p y r i d i n e , 298K;(2)
( 1 ) A1P04-5
( 2 ) NaOH/A1P04-5
298K, l h ; ( 3 )
( 3 ) ( NH4)2HP04/A1 P04-5
(4)10-2
Adsorption o f acetone. can b e seen i n f i g u r e 4. ved a t 1710, room
4 Pa,
lo-’
Pa, 373K, l h ;
Pa, 523K, l h
A t y p i c a l s p e c t r u m o f a c e t o n e a d s o r b e d o n A1P04-5 A f t e r a d m i s s i o n o f 650 Pa a c e t o n e bands were o b s e r -
1660, 1630. 1600, 1445, 1425. 1375 and 1362 cm-l.
Evacuation a t
t e m p e r a t u r e l e d t o t h e d i s a p p e a r a n c e o f t h e 1710 and 1425
cm-l
bands,
while
t h e bands a t 1380 and 1365 cm-l were s t r o n g l y d i m i n i s h e d i n i n t e n s i t y .
After
outgassing
CH
appeared. adsorbate acetone
a t 373K bands a t 1630.
1470,
1400,
s t r e t c h i n g bands were f o u n d a t 2960,
1370 and
2905 and 2870
bands c o u l d b e d e t e c t e d a f t e r e v a c u a t i o n a t
573K.
1350
ern-'.
cm-l No
Adsorption
of
a t 373K r e s u l t e d i n s i m i l a r C=O s t r e t c h i n g and CH d e f o r m a t i o n bands,
b u t t h e bands a t 1630, 1470 1380 and 1370 cm-l t y a f t e r s u b s e q u e n t e v a c u a t i o n a t 373 K.
had a l a r g e r r e l a t i v e i n t e n s i -
Again.
n o a d s o r b a t e bands c o u l d be
d e t e c t e d a f t e r e v a c u a t i o n a t 573K. T e m p e r a t u r e programmed d e s o r p t i o n measurements A c t i v a t i o n a f t e r synthesis.
With t h e p h o s p h a t e i m m e d i a t e l y a f t e r s y n t h e -
s i s t h r e e d e s o r p t i o n maxima had been o b s e r v e d . f i r s t peak (367K).The
Only water desorbed w i t h
s u b s t a n c e s d e s o r b i n g i n t h e o t h e r t w o maxima were
the mix-
t u r e s o f t r i p r o p y l - and d i p r o p y l a m i n e as w e l l a s some propene. The maximum a t 599K i s caused m a i n l y b y d i p r o p y l a m i n e , (see Fig.5). ved
t h e maximlm a t 658K b y t r i p r o p y l a m i n e
A t o t a l w e i g h t l o s s o f 0.17g p e r gram o f c a t a l y s t was o b s e r -
by thermogravimetry.
T h i s c o r r e s p o n d s t o an amount o f 0.06 g o f
amines
168 r e t a i n e d on t h e p h o s p h a t e a f t e r p r e p a r a t i o n . A f t e r f i r s t a c t i v a t i o n t h e t o t a l u p t a k e c a p a c i t y f o r w a t e r was 0.17 g p e r grani c a t a l y s t .
4000
3500
3000 2500
F i g . 4. A d s o r p t i o n o f a c e t o n e o n A l P O -5.
(2)
lo-'
Pa, 298K, l h ;
( 3 ) lo-'
D e s o r p t i o n o f bases. While
1800
1600
W A V E N U M B E R S [crn-l]
4
Pa, 373K,
1400
( 1 ) 650 Pa a c e t o n e , 298K, l h ; lh;
( 4 ) lo-'
Pa, 523K.
F i g u r e 6 shows d e s o r p t i o n c u r v e s f o r v a r i o u s b a s e s .
ammonia ana p y r i d i n e showed o n l y one d e s o r p t i o n r a t e
thylamine
and
t r i e t h y l a m i n e had a second maximum i n d i c a t i n g
desorption states. However,
since
lh
maximum. at
trime-
least
two
F o r ammonia and p y r i d i n e t h e s e d e s o r p t i o n s t a t e s c o i n c i d e .
formation
o f p r o p e n e has been o b s e r v e d n e a r 673K w i t h
e t h y l a m i n e f u r t h e r s t r o n g a c i d s i t e s may be p r e s e n t .
tri-
Nevertheless desorption
was c o m p l e t e a t a b o u t 700K f o r a l l bases. D e s o r p t i o n o f acetone.
Acetone desorbed i n t h r e e s t e p s from t h e s u r f a c e
f o r m i n g m e s i t y l o x i d e and a m i x t u r e o f h i g h e r h y d r o c a r b o n s . A r o u n d 363K m a i n l y acetone
desorbed,
followed by mesityloxide.
maximum
a t 423K - 453K.
w h i c h showed a d e s o r p t i o n r a t e
A t 350K a m i x t u r e o f h i g h e r h y d r o c a r b o n s
w h i c h c o u l d n o t be i d e n t i f i e d .
desorbed,
The r e l a t i v e amount o f t h i s l a t t e r d e s o r p t i o n
r a t e c o u l d b e enhanced d r a s t i c a l l y i f a c e t o n e was a d s o r b e d a t 373K.
DISCUSSION Activation The thesis
i n f r a r e d and t . p . d .
s p e c t r a o f t h e phophate immediately
after
show t h a t amines a r e r e t a i n e d i n t h e c h a n n e l s t r u c t u r e a f t e r
syn-
washing
and d r y i n g . A l l i n f r a r e d bands a r e c o m p a t i b l e w i t h t r i p r o p y l a m i n e a d s o r b e d o n acidic
sites.
T h e r m o g r a v i m e t r i c d a t a s u g g e s t t h a t t h e c h a n n e l s o f t h e phos-
p h a t e a r e c o m p l e t e l y f i l l e d w i t h w a t e r and amines.
373K.
A f t e r release o f water a t
a r o u n d 523K f i r s t d i p r o p y l a m i n e ( w e a k e r b a s e ) and t h e n
d e s o r b p a r a l l e l t o t h e r e l e a s e o f some propene.
tripropylamine
The d e s o r p t i o n i s a l s o m a n i -
169 f e s t e d b y a s h a r p i n c r e a s e o f BET s u r f a c e a r e a s t u r e was i n c r e a s e d f r o m 473K t o 573K. between
when t h e a c t i v a t i o n t e m p e r a -
Because no d i f f e r e n c e
in
spectra
1.r.
samples c a i c i n e d i n a i r and s a m p l e s c a l c i n e d i n v a c u o was
observed,
we c o n c l u d e t h a t n o c a r b o n a c e o u s r e s i d u e s w e r e f o r m e d d u r i n g d e c o m p o s i t i o n o r d e s o r p t i o n o f t h e amines.
0~
=. .... ~ . ~
_
273
,'
I
~
.
.
-
?
L73
Fig.
_
A M I N E S >.I(. - - ........... ~...
673
5. T.p.d.
1073
073
PROPEYE
K
spectrum o f a c t i v a -
t i o n o f A1P04-5.
F i g . 6. T.p.d.
spectra o f various
b a s e s f r o m A1P04-5.
The l a t t e r o b s e r v a t i o n c o r r e s p o n d s w e l l w i t h t h e w e l l known c o k e i n g r e s i s tance
o f s i l i c a l i t e s o r ZSM5 z e o l i t e s ( r e f .
structure
.
12),
which have
similar
pore
I t seems f e a s i b l e t h a t t h e n a r r o w 12-member r i n g c h a n n e l w i t h no
channel i n t e r s e c t i o n s ( r e f .
15) imposes s t e r i c
c o n s t r a i n t s upon c o k e f o r m a -
tion. A f t e r t h i s i n i t i a l d e c o m p o s i t i o n o f t h e amines. t h e p h o s p h a t e s show one OH band n e a r 3680 crnWendt
e t al.
1
.
Such a wavenumber h a s been r e p o r t e d b y P e r 1 ( r e f . 6 )
7-9)
(ref.
f o r OH g r o u p s a t t a c h e d t o t h e p h o s p h o r o u s atom.
band f o r OH g r o u p s a t t a c h e d t o aluminum, i n t h e present study.
as r e p o r t e d ( r e f .
6).
and
A
was n o t f o u n d
U n f o r t u n a t e l y t h e l o w i n t e n s i t y and t h e h i g h l e v e l
of
d i d n o t p e r m i t us t o e s t i m a t e a c i d s t r e n g t h b y d e t e r m i n i n g t h e OH
scattering
band s h i f t a f t e r a d s o r p t i o n o f a d o n o r m o l e c u l e . A c i d base D r o D e r t i e s I n an e a r l i e r p a p e r we h a v e d e m o n s t r a t e d t h a t t h e o v e r a l l a c i d s t r e n g t h o f an o x i d e , oxide, son
and p h o s p h a t e s may b e t r e a t e d as m i x e d o x i d e s o f P205 and a
metal
i n c r e a s e s w i t h t h e i n t e r m e d i a t e e l e c t r o n e g a t i v i t y a c c o r d i n g t o Sander-
(ref.1).
Thus
aluminurnphosphate.
one
would expect t o f i n d r a t h e r s t r o n g
Nevertheless
acid
sites
a d s o r p t i o n ( a n d d e s o r p t i o n ) o f ammonia
p y r i d i n e i n d i c a t e L e w i s a c i d s i t e s o f m o d e r a t e s t r e n g t h and,
on and
n o t unequivocal-
170 ly,
some
B r z n s t e d a c i d s i t e s ( o n l y NH3 was p r o t o n i r e d
weak
in
detectable
amounts).
If
one
estimate
u s e s t h e wavenumber o f t h e 19b v i b r a t i o n o f a d s o r b e d p y r i d i n e t h e s t r e n g t h o f i n t e r a c t i o n w i t h t h e Lewis a c i d s i t e ,
i n t e r a c t i o n s i m i l a r t o t h a t o f Si02 ( r e f . It
is
s i g n i f i c a n t l y weaker t h a n t h a t w i t h p u r e
sphates.
strength
of
18) o r s i l i c a - a l u m l n a i s i n d i c a t e d .
c o n c l u s i o n was a l s o drawn b y Wendt e t a l . ( r e f .
alumina
7-9)
(ref.18).
Such
a
f o r amorphous a l u m i n o p h o -
T r e a t m e n t w i t h NaOH c a u s e d a new band a t 1442 cm-'
a t t r i b u t e d t o p y r i d i n e a d s o r b e d on Na'
was
to
cations.
t o appear, which
The o t h e r m o d i f i c a t i o n s
d i d n o t change t h e a p p a r e n t L e w i s a c i d s t r e n g t h . The q u e s t i o n m u s t b e r a i s e d
as t o why p u r e a l u m i n a e x h i b i t s t h e s t r o n g e r
EPA s i t e s . T h i s may be a c c o m p l i s h e d b y s e p a r a t i n g EPA s t r e n g t h i n t o "maximum" and " a p p a r e n t a c c e p t o r s t r e n g t h " .
As p o i n t e d o u t p r e v i o u s l y ,
i n general t h e
oxide (phosphate) w i t h t h e higher intermediate e l e c t r o n e g a t i v i t y according t o Sanderson
I f t h e strength o f these
w i l l have t h e s t r o n g e r L e w i s a c i d s i t e s .
s i t e s i n c r e a s e s , however, t h e c a t i o n s a r e b e t t e r c o v e r e d b y oxygen. "maximum a c c e p t o r s t r e n g t h " may b e h i g h e r i n A1P04 t h a n i n A1 0 overcompensated phosphate.
by
Thus
Hence t h e
but t h i s i s
s i g n i f i c a n t lower a c c e s s i b i l t y o f t h e A15+3'ion
the
in
d i s t a n c e between t h e L e w i s a c i d s i t e and t h e
the
electron
p a i r d o n o r ( E P D ) m o l e c u l e w i l l be l a r g e r , d e c r e a s i n g t h e s t r e n g t h o f i n t e r a c i n d i c a t i n g a weaker L e w i s a c i d s i t e .
t i o n and hence,
N e v e r t h e l e s s i t may a l s o be p o s s i b l e t h a t a t l e a s t a p a r t o f t h e 1 4 4 8 cm-l i s c a u s e d b y p y r i d i n e a d s o r b e d on P-OH g r o u p s ( 3 6 8 0 cm-').
band
and A l P O on
4
h a v e s i m i l a r i n t e r m e d i a t e e l e c t r o n e g a t i v i t i e s and p y r i d i n e a d s o r b e d
Si-OH
groups
feasible. which
Si02
Since
c a u s e s a band a t 1447 cm-l
(ref.
18) t h e
proposal
(NH4)2HP04
It i s supported by t h e o b s e r v a t i o n t h a t t r e a t m e n t w i t h
should
increased
lead
t o a d e c r e a s e i n t h e number o f
t h e r e l a t i v e i n t e n s i t y o f t h e 1447 cm-l
accessible
band,
seems
A13+
and NaOH
ions,
treatment
decreased it. The be
must
f r a c t i o n o f BrEnsted a c i d s i t e s capable o f p r o t o n i z i n g p y r i d i n e
very
small.
Lack o f s u c h B r h s t e d a c i d i c
OH
g r o u p s m u s t be e x p e c t e d
o n l y b r i d g e d hydroxyl groups can donate p r o t o n s t o p y r i d i n e ( r e f .
19).
if
Cer-
c a n r e a d i l y be p r o t o n a t e d b y w e a k e r a c i d i c OH g r o u p s . F o r A1P04, 3 l i k e f o r Si02. i t i s n o t necessary t o balance a n e g a t i v e charge w i t h a p r o t o n
t a i n l y NH or
a cation.
present should
T h e r e f o r e t h e s e s u b s t a n c e s w i l l l a c k b r i d g e d h y d r o x y l s a s e.g.
in t y p e Y z e o l i t e s ( r e f . not
change t h e s i t u a t i o n .
s t r o n g Brldnsted a c i d i t y . coordination
20).
The a d d i t i o n o f
Indeed,
(NH4)2HP04
such t r e a t m e n t s d i d
Si02
or not
induce
Only i n c o r p o r a t i o n o f excess alumina i n t e t r a t h e d r a l
m i g h t n e c e s s i t a t e c h a r g e b a l a n c e b y p r o t o n s and c r e a t e B r ' l n s t e d
a c i d s i t e s s i m i l a r t o those o f zeolites. T.p.d.
spectra
o f t r i m e t h y l - and t r i e t h y l a m i n e s u g g e s t a t l e a s t t w o
de-
171 sorption states. Because
T h e i r n a t u r e c o u l d n o t be r e v e a l e d u n e q u i v o c a l l y u n t i l now.
o n l y one d e s o r p t l o n s t a t e was f o u n d w i t h p y r i d i n e
and
ammonia,
we
s t r e n g t h o f b a s i c s i t e s m u s t be e s t i m a t e d t o be v e r y l o w ( s i m i l a r
to
c o n c l u d e d t h a t t h e t w o s t a t e s m u s t c o i n c i d e f o r t h e l a t t e r bases. The silica
and s i l i c a - a l u m i n a )
s i n c e CO
2
d i d n o t f o r m any s t a b l e s u r f a c e
carbo-
nates. While hexane
c a t a l y t i c a l l y i n a c t i v e f o r t h e methanol t o g a s o l i n e r e a c t i o n o r cracking
mesityloxide deposits The
to
t h e c a t a l y s t forms condensates from acetone a m i x t u r e o f higher hydrocarbons).
Again
o r c a r b o x y l a t e s t r u c t u r e s c o u l d be detected by
(ranging no
1.r.
nfrom
carbonaceous spectroscopy.
h i g h e r r e a c t i v i t y o f t h e NaOH t r e a t e d p h o s p h a t e s u g g e s t s t h e
importance
o f t h e b a s i c s i t e s , w h i c h w e r e enhanced b y NaOH t r e a t m e n t . CONCLUSION vicroporous AlPO
The
4 aluminophosphates.
phous
e x h i b i t s s i m i l a r a c i d base p r o p e r t i e s as t h e This
shows t h a t n o new a c i d - b a s e p r o p e r t i e s
been i n d u c e d b y t h e c h a n n e l s t r u c t u r e . protonire
pyridine)
evaluation
were found.
b y a d s o r p t i o n o f C02.
have
Lewis a c i d s i t e s o f moderate s t r e n g t h
t h a n t h o s e o f a l u m i n a ) and weak G r E n s t e d a c i d s i t e s ( n o t c a p a b l e
(weaker
Si02
amor-
The b a s e s t r e n g t h was b e l o w t h e Having i d e n t i c a l c r y s t a l
limit
to of
structures
with
t h e aluminophosphates appear t o have s i m i l a r a c i d base p r o p e r t i e s
too.
Thus i n c o r p o r a t i o n o f t e t r a h e d r a l l y c o o r d i n a t e d e x c e s s a l u m i n a m i g h t c r e a t e a surface
chemistry
similar t o that o f the zeolites,
w h i l e excess
phosphate
w i l l n o t enhance t h e a c i d s t r e n g t h s o r change t h e t y p e o f a c i d s i t e s .
AC K id 0 W L E DG ENE N l S We
t h a n k t h e "Fonds z u r Forderune, d e r w i s s e n s c h a f t l i c h e n
providing the
i.r.
Forschung"
for
spectrometer.
REFERENCES
1 2 3 4 5
6
7
8
9 10 11 12 13
R.T.
Sanderson, " C h e m i c a l Bond and Bond E n e r g y " , Academic P r e s s , New York, London, 2nd ed., 1976. W. J. M o r t i e r . J. C a t a l . , 55 ( 1 9 7 8 ) 138. S. H o c e v a r and B. D r z a j . J. C a t a l . , 73 ( 1 9 8 2 ) 205. J.A. L e r c h e r and H. N o l l e r , J. C a t a l . , 77 ( 1 9 8 2 ) 152. J.A. L e r c h e r , H. V i n e k and H. N o l l e r , J.Chem.Soc., F a r a d a v T r a n s . I 80 ( 1 9 8 4 ) 1239. J.B. P e r i , D i s c . F a r a d a y SOC., 52 ( 1 9 7 1 ) 55. G. Wendt, Z. Chem., 1 7 ( 1 9 7 7 ) 118. G. Wendt and C.F. L i n s t r o m , Z. Chem.. 17 ( 1 9 7 7 ) 37. G. Wendt and C.F. L i n s t r o m , Z. Chem.. 16 ( 1 9 7 6 ) 500. K. Thomke, J. C a t a l . , 44 ( 1 9 7 6 ) 339. R. Bauer, K. Thomke and H. N o l l e r , P r o c . 8 t h I n t . Congr. C a t a l . , B e r in, V e r l a g Chemie, Weinheim. 1984, 101.3, 439. J.B. M o f f a t , C a t a l . Rev. S c i . Eng., 1 8 ( 1 9 7 8 ) 199. S.T. W i l s o n , B.M. Lok and E.M. F l a n i g e n , U.S. P a t e n t 4,385,994 ( 1 9 8 3
172 and U. S.
Patent
14 S.T. W l l s o n , B.M.
4,310,440 (1 982). Lok, C.A.
M e s s i n a , T.R.
J. Am. Chern. S O C . , 104 (1982) 1146.
15 J.V. S m i t h , Am. M i n e r a l . 63 (1978) 960.
Cannan and E.M.
Flan-igen,
1 6 S. J. Gregg and J.D. Ramsay, J. Chem. SOC. A (1970) 2784. 17 S. Yurchak, S.E. V o l t z and J . P. Warner, I n d . Eng. Chem. P r o c e s s Des. Dev.. 15 (1979) 527. 18 E.P. P a r r y , J. C a t a l . , 2 (1963) 371. 19 W. J. M o r t i e r , J. Sauer, J.A. L e r c h e r and H. N o l l e r , J . Phys. Chem. 88
(1984) 905. 20 3. W . Ward, 3. C a t a ? . , 1 1 (1968) 251
163
ADSORPTIVE PROPERTIES O F ALUMINUMPHOSPHATE MOLECULAR S I E V E S
1
Genadi j D w o r e r k o v , Gerd Rumplmayr’, H e l m u t Mayer’
and Johannes A.
Lercher
1
i:(
I n s t i t u t f u r P h y s i k a l i s c h e Chemie, T e c h n i s c h e U n i v e r s i t a t Wien, G e t r e i d e m a r k t 9, A-1060 ‘Institut
V I E N N A , AUSTRIA
f u r M i n e r a l o g i e , K r i s t a l l o g r a p h i e und S t r u k t u r c h e m i e
G e t r e i d e m a r k t 9, A-1060
VIENNA, AUSTRIA
ABSTRACT M i c r o p o r o u s a l u m i n o p h o s p h a t e s h a v e been s y n t h e s i z e d and c h a r a c t e r i z e d b y i n t e r c a t i o n w i t h bases. M o d e r a t l y s t r o n g L e w i s a c i d s i t e s and v e r y weak base s i t e s were found. The Br’dnsted a c i d s i t e s p r e s e n t c o u l d o n l y p r o t o n i z e ammon i a , b u t n o t p y r i d i n e . The a c i d - b a s e p r o p e r t i e s o f t h e a l u m i n o p h o s p h a t e s r e s e m b l e d t h o s e o f s i l i c a and amorphous a l u m i n o p h o s p h a t e s , s u g g e s t i n g t h a t t h e c h a n n e l s t r u c t u r e ( 0 . 6 nm d i a m e t e r ) d i d n o t i n d u c e new a c i d b a s e p r o p e r t i e s .
INTRODUCTION Using
Sanderson’s
concept o f e l e c t r o n e g a t i v i t y ( r e f . 1 )
t h a t t h e e l e c t r o n p a i r a c c e p t o r (EPA, be
it
t h e h i g h e r ( a n d t h e c o r r e s p o n d i n g e l e c t r o n p a i r d o n o r (EPD.
strength
t h e lower),
t o Sanderson i s intermediate fully
.
was
predicted
L e w i s a c i d ) s t r e n g t h o f an o x i d e w o u l d Lewis
t h e higher t h e intermediate e l e c t r o n e g a t i v t y according
I n general t h i s implies a higher a c i d strength f o r
electronegativity
by M o r t i e r ( r e f . 2 )
as b y L e r c h e r e t a l .
.
(ref.4)
higher
R e c e n t l y t h i s c o n c e p t was a p p l i e d s u c c e s s -
and H o c e v a r and D r z a j ( r e f . 3 ) f o r mixed oxides.
f o r z e o l i t e s as
well
I n an e a r l i e r p a p e r , however,
we h a v e p o i n t e d o u t t h a t an u p p e r l i m i t o f EPA s t r e n g t h o f o x i d e s may because
base)
exist,
o f l i m i t e d a c c e s s t o t h e EPA s i t e s w i t h e v e r i n c r e a s i n g i n t e r m e d i a t e
electronegativity (ref.5). Aluminophosphates
s h o u l d be good o b j e c t s t o s t u d y t h e s e
cause o f t h e i r r a t h e r h i g h i n t e r m e d i a t e e l e c t r o n e g a t i v i t y . dies (ref.6) sites. of
be-
c l a s s i f i e d t h e m as s t r o n g l y a c i d i c c a t a l y s t w i t h v e r y weak b a s i c
However,
t h e r e s u l t s o f c h a r a c t e r i z a t i o n o f Wendt e t a l . ( r e f . 7 - 9 )
m e c h a n i s t i c i n v e s t i g a t i o n s of Thomke ( r e f . 1 0 )
would
constraints
P e r i l s e a r l y stu-
suggest r a t h e r a moderate a c i d s t r e n g t h .
summarizes t h e s e c h a r a c t e r i z a t i o n s .
*To whom c o r r e s p o n d e n c e s h o u l d be a d d r e s s e d .
and B a u e r e t
al.
A review by Moffat
and
(ref.11) (ref.12)
164 Recently
the synthesis o f
t u r e was r e p o r t e d ( r e f . 1 3 . 1 4 ) . with
new a l u m i n o p h o s p h a t e s w i t h m i c r o p o r o u s Gne A1PG4 ( t y p e 5 ) h a d a s t r u c t u r e
t h e o r e t i c a l f r a m e w o r k o f t y p e 81,
the
as p r o p o s e d b y S m i t h
T h i s p h o s p h a t e has 1 2 - r i n g c h a n n e l s w i t h 6 - r i n g c o n n e c t i o n s . claimed
to
cracking and
possess a c i d s i t e s s u f f i c i e n t l y a c t i v e t o
and o t h e r a c i d c a t a l y z e d r e a c t i o n s .
characterization
(ref.15).
The m a t e r i a l was
catalyze
hydrocarbon preparation
We r e p o r t h e r e o n
o f t h i s p h o s p h a t e and some
struc-
identical
derivatives
from
it.
EXPERIMENTAL Catalysts The
porous aluminophosphates were prepared a c c o r d i n g t o
chiometric
amounts
o f aluminiummonohydroxide ( P u r a l
distilled
water.
tripropylamine
ref.13.
CONOEA,
Stoi75.1
w%
85 w% H PO ) were m i x e d 3 4 The s u s p e n s i o n was s t i r r e d u n t i l homogeneous. Then
A1203) and o r t h o p h o s p h o r i c a c i d ( M e r c k , p . a . with
SB,
quality,
was added and t h e r e s u l t i n g m i x t u r e h a d t h e f o r m u l a
1.0 ( C H ) N : A1203 : P205 : 40 H20. 3 7 3 I t was s e a l e d i n an PTFE l i n e d a u t o c l a v e and k e p t a t 423K f o r 1 0
composi-
tion:
hours.
The
r e s u l t i n g p r o d u c t was f i l t e r e d and washed w i t h d i s t i l l e d w a t e r u n t i l n e u t r a l . X-ray type
diffraction 5
measurements showed t h a t t h e m a t e r i a l was p u r e
structure (ref.13).
83m2. g-’
f o r A1 P04-5,
The BET s u r f a c e a r e a s w e r e
NaOH/A1P04-5,
280,
58,
A1P04
of
210
and
( NH4)2HP04/A1 PO4-5 and S i 0 2 / A 1 PO4-5 r e -
spectively. To
modify
t h e s u r f a c e p r o p e r t i e s t h e a l u m i n o p h o s p h a t e was
0.02 m o l a r NaOH and (NH4)2HP04
s o l u t i o n s f o r 4 h o u r s , f i l t e r e d , washed,
a t 373K a n d c a l c i n e d a t 873K f o r t w o h o u r s . A n o t h e r p h o s p h a t e using in
The
0.01Si02:40H20. 72
r e a c t i o n m i x t u r e had a c o m p o s i t i o n o f This
dried by
dissolved
1.0TPAOH:A1203:P205:
m i x t u r e was h e a t e d i n an PTFE l i n e d a u t o c l a v e a t
h o u r s and t r e a t e d s u b s e q u e n t l y l i k e A1P04-5.
in
W ~ S prepared
tetrapropylammoniumhydroxide (TPAOH) and a d d i n g some s i l i c a
TPAOH.
for
suspended
The
only
423K
crystalline
p r o d u c t was A1P04-5 a l t h o u g h some amorphous m a t e r i a l may be p r e s e n t . R e a c t a n t s and a d s o r b e n t s Pyridine
and
acetone
w e r e o b t a i n e d f r o m M e r c k (p.a.
quality)
and
not
f u r t h e r p u r i f i e d . A l l g a s e s u s e d h a d a t l e a s t 99.999 v o l % p u r i t y . I n f r a r e d measurements The p h o s p h a t e s h a v e been i n v e s t i g a t e d b y means o f t h e t r a n s m i s s i o n - a b s o r p t i o n technique.
in
situ.
The
The
c e l l u s e d p e r m i t t e d a l l s a m p l e h a n d l i n g s t o b e done 8 -2 p h o s p h a t e w a f e r ( c o m p a c t i n g p r e s s u r e = lo8 - 3.10 Nm ) was
heated o u t s i d e t h e ture
from
1.r.
1.r.
beam.
4000-1000 cm-l
The s p e c t r a w e r e r e c o r d e d a t a m b i e n t t e m p e r a -
u s i n g a P e r k i n Elmer
infrared
spectrophotometer
165 ( t y p e 325) w i t h 3 cm-’
r e s o l u t i o n a t 3600 cm-’.
T e m p e r a t u r e programmed d e s o r p t i o n ( t . p . d . ) T.p.d.
was c a r r i e d o u t i n v a c u o ( c a . f r o m 300K t o 1000K.
o f 10K.min-’
measurements 10-lPa) u s i n g a temperature increment
The r e a c t o r was a q u a r t z g l a s s t u b e connec-
ted
w i t h a vacuum pump and a B a l z e r s 311 mass s p e c t r o m e t e r f o r d e t e c t i o n
the
species
phosphate
The mass s p e c t r o m e t e r and t h e
by a D i g i t a l M I N C computer.
controlled ambient
desorbed.
were
calcined
temperature
t.p.d.
furnace
F o r e a c h measurement 100 mg
i n t h e r e a c t o r a t 873K f o r
one
and c o n t a c t e d w i t h t h e a d s o r b e n t .
e v a c u a t e d a t a m b i e n t t e m p e r a t u r e and t . p . d .
hour,
of were
of
the
cooled
Then t h e s a m p l e
to was
was s t a r t e d .
T h e r m o g r a v i m e t r i c measurements Quantitative
a n a l y s i s o f t h e w e i g h t changes d u r i n g a c t i v a t i o n and
t.p.d.
measurements was p e r f o r m e d b y an M e t t l e r t h e r m o a n a l y z e r TRl, w h i c h D e r m i t t e d simultaneous
r e c o r d i n g o f t h e r m o g r a v i m e t r i c and d i f f e r e n t i a l
t r i c d a t a . The i n s t r u m e n t was p u r g e d w i t h N2 ( 5 l . m i n
1 0 Fig.1.
-1
thermogravime-
).
3500 3000 2500
1800 1600 WAVENUMBERS [cm-’I
1400
A c t i v a t i o n o f A1P04-5 i n vacuum.
( 1 ) l h . 298K;
( 2 ) l h , 373K; ( 3 ) l h , 473K; ( 4 ) l h , 673K
RESULTS I n f r a r e d s p e c t r o s c o p i c measurements Activation washed
a f t e r synthesis.
A f t e r evacuation a t ambient temperature t h e
and d r i e d ( 3 7 3 1 0 A1P04 e x h i b i t e d bands a t
2880,
2805,
after
evacuation
1463,
1388 and 1337 cm-’. at
3100,
2970,
These b a n d s d e c r e a s e d i n
1) b u t d i d n o t
2940.
intensity
change
their
They w e r e n o t o b s e r v e d a f t e r e v a c u a t i o n a t
573K.
373K and 473K ( s e e F i g .
wavenumbers s i g n i f i c a n t l y .
3380,
166 A f t e r i n i t i a l t r e a t m e n t a t 573K, A1P04 showed OH s t r e t c h i n g bands a t 3678 and The NaOH and t h e ( N H ) HP04 t r e a t e d a l u m i n o p h o s p h a t e s had o n l y a 4 2 w h i l e t h e p h o s p h a t e s y t h e s i z e d w i t h Si02 d i d n o t show a
3652
cm-l.
band
a t 3680 cm-’,
h y d r o x y l s t r e t c h i n g band.
W i t h a l l phosphates,
bands o f l a t t i c e
vibrations
c o u l d b e o b s e r v e d a t 1655 and 1450 cm-l. Adsorption A1P04-5,
o f ammonia.
NaOH/A1PO4-5
The s p e c t r a o f NH
and (NH4)2HP04/klP04-5
3 ( 1 3 kPa p a r t i a l p r e s s u r e ) on c a n be seen i n f i g u r e 2. A l l
p h o s p h a t e s had bands a t 1613 and 1450 cm-l.
three
t h e l a t t e r was l o w w i t h NaOH/A1P04. bands
The r e l a t i v e i n t e n s i t y o f
A f t e r e v a c u a t i o n a t room t e m p e r a t u r e , t h e
disappeared almost completely i n d i c a t i n g low thermal s t a b i l i t y o f
the
a d s o r b a t e complex. Adsorption 19a,b
o f pyridine.
The wavenumbers o f t h e c h a r a c t e r i s t i c 8 a - b
v i b r a t i o n s o f p y r i d i n e adsorbed on aluminophosphates a r e
compiled
and in
t a b l e 1. The a d s o r b a t e s p e c t r a w i t h p u r e A1P04 c a n be seen i n f i g u r e 3. Pyridine
formed
temppratures 1450-1447 cm-l.
of
s t a b l e a d s o r b a t e s w i t h a l l p h o s p h a t e s up
873K.
The wavenumber o f one 19b band was f o u n d
evacuation always
at
The NaOH t r e a t e d sample had an a d d i t i o n a l band a t 1442 cm-l.
However, a band a t 1540 cm-l the
to
catalysts investigated.
was n o t o b s e r v e d w i t h s i g n i f i c a n t i n t e n s i t i e s o n T h i s s u g g e s t s t h a t o n l y a v e r y s m a l l amount
of
p y r i d i n e a d s o r b e d may b e r e t a i n e d as p y r i d i n i u m i o n s . TABLE 1 Wavenumbers o f 8 a , b and 19a,b bands o f p y r i d i n e a d s o r b e d on a l u m i n o p h o s p h a t e s
A1 PO4-5
NaoH/A1 p04-5
298K. 1.3kPa
298K, ev.
473K,ev.
673K. ev.
1609,1577 1492.1480 1447.1438
1610,1577 1491 1448
1620 1490 1449
1620 1490 1449
1595 1490 1448, 442
1595 1490 1448,1442
1609,1590,1577 161 0,1595,1577 1492.1480 1495.1490 1447; 1440.1438 1447; 1442
(NH4)2HP04/ A1 PO4-5
1610.1575 1490,1480 1448.1438
1611,1578 1490 1448
1612 1491 1450
1612 1491 1450
”02/A1 p04-5
161 0,1580 1492,1480 1447,1438
1610 1490 1447
1612 1490 1447
1615 1490 1448
A d s o r p t i o n o f CO A f t e r a d m i s s i o n o f l 3 k P a CO i n t o t h e i . r . c e l l o n l y 22 1 t w o bands o f C02 c o u l d b e o b s e r v e d a t 2340 and 2356 cmThey c o r r e s p o n d t o
.
linearly
adsorbed
C02 ( r e f . 1 6 ) and d i s a p p e a r e d a f t e r e v a c u a t i o n a t
ambient
167 t e m p e r a t u r e . No t r a c e s o f bands o f c a r b o n a t e s c o u l d be d e t e c t e d .
I T-
I
I
I
7
I
I
/
1800
1600
I i I u 1600 1400
,L
1800
1400
WAVENUMBERS [ern-']
WAVENUMBERS [crn-’]
F i g . 2. A d s o r p t i o n o f ammonia
F i g . 3. A d s o r p t i o n o f p y r i d i n e on AlPO
( 1 3 kPa, 298K).
( 1 ) 1.3 kPa p y r i d i n e , 298K;(2)
( 1 ) A1P04-5
( 2 ) NaOH/A1P04-5
298K, l h ; ( 3 )
( 3 ) ( NH4)2HP04/A1 P04-5
(4)10-2
Adsorption o f acetone. can b e seen i n f i g u r e 4. ved a t 1710, room
4 Pa,
lo-’
Pa, 373K, l h ;
Pa, 523K, l h
A t y p i c a l s p e c t r u m o f a c e t o n e a d s o r b e d o n A1P04-5 A f t e r a d m i s s i o n o f 650 Pa a c e t o n e bands were o b s e r -
1660, 1630. 1600, 1445, 1425. 1375 and 1362 cm-l.
Evacuation a t
t e m p e r a t u r e l e d t o t h e d i s a p p e a r a n c e o f t h e 1710 and 1425
cm-l
bands,
while
t h e bands a t 1380 and 1365 cm-l were s t r o n g l y d i m i n i s h e d i n i n t e n s i t y .
After
outgassing
CH
appeared. adsorbate acetone
a t 373K bands a t 1630.
1470,
1400,
s t r e t c h i n g bands were f o u n d a t 2960,
1370 and
2905 and 2870
bands c o u l d b e d e t e c t e d a f t e r e v a c u a t i o n a t
573K.
1350
ern-'.
cm-l No
Adsorption
of
a t 373K r e s u l t e d i n s i m i l a r C=O s t r e t c h i n g and CH d e f o r m a t i o n bands,
b u t t h e bands a t 1630, 1470 1380 and 1370 cm-l t y a f t e r s u b s e q u e n t e v a c u a t i o n a t 373 K.
had a l a r g e r r e l a t i v e i n t e n s i -
Again.
n o a d s o r b a t e bands c o u l d be
d e t e c t e d a f t e r e v a c u a t i o n a t 573K. T e m p e r a t u r e programmed d e s o r p t i o n measurements A c t i v a t i o n a f t e r synthesis.
With t h e p h o s p h a t e i m m e d i a t e l y a f t e r s y n t h e -
s i s t h r e e d e s o r p t i o n maxima had been o b s e r v e d . f i r s t peak (367K).The
Only water desorbed w i t h
s u b s t a n c e s d e s o r b i n g i n t h e o t h e r t w o maxima were
the mix-
t u r e s o f t r i p r o p y l - and d i p r o p y l a m i n e as w e l l a s some propene. The maximum a t 599K i s caused m a i n l y b y d i p r o p y l a m i n e , (see Fig.5). ved
t h e maximlm a t 658K b y t r i p r o p y l a m i n e
A t o t a l w e i g h t l o s s o f 0.17g p e r gram o f c a t a l y s t was o b s e r -
by thermogravimetry.
T h i s c o r r e s p o n d s t o an amount o f 0.06 g o f
amines
168 r e t a i n e d on t h e p h o s p h a t e a f t e r p r e p a r a t i o n . A f t e r f i r s t a c t i v a t i o n t h e t o t a l u p t a k e c a p a c i t y f o r w a t e r was 0.17 g p e r grani c a t a l y s t .
4000
3500
3000 2500
F i g . 4. A d s o r p t i o n o f a c e t o n e o n A l P O -5.
(2)
lo-'
Pa, 298K, l h ;
( 3 ) lo-'
D e s o r p t i o n o f bases. While
1800
1600
W A V E N U M B E R S [crn-l]
4
Pa, 373K,
1400
( 1 ) 650 Pa a c e t o n e , 298K, l h ; lh;
( 4 ) lo-'
Pa, 523K.
F i g u r e 6 shows d e s o r p t i o n c u r v e s f o r v a r i o u s b a s e s .
ammonia ana p y r i d i n e showed o n l y one d e s o r p t i o n r a t e
thylamine
and
t r i e t h y l a m i n e had a second maximum i n d i c a t i n g
desorption states. However,
since
lh
maximum. at
trime-
least
two
F o r ammonia and p y r i d i n e t h e s e d e s o r p t i o n s t a t e s c o i n c i d e .
formation
o f p r o p e n e has been o b s e r v e d n e a r 673K w i t h
e t h y l a m i n e f u r t h e r s t r o n g a c i d s i t e s may be p r e s e n t .
tri-
Nevertheless desorption
was c o m p l e t e a t a b o u t 700K f o r a l l bases. D e s o r p t i o n o f acetone.
Acetone desorbed i n t h r e e s t e p s from t h e s u r f a c e
f o r m i n g m e s i t y l o x i d e and a m i x t u r e o f h i g h e r h y d r o c a r b o n s . A r o u n d 363K m a i n l y acetone
desorbed,
followed by mesityloxide.
maximum
a t 423K - 453K.
w h i c h showed a d e s o r p t i o n r a t e
A t 350K a m i x t u r e o f h i g h e r h y d r o c a r b o n s
w h i c h c o u l d n o t be i d e n t i f i e d .
desorbed,
The r e l a t i v e amount o f t h i s l a t t e r d e s o r p t i o n
r a t e c o u l d b e enhanced d r a s t i c a l l y i f a c e t o n e was a d s o r b e d a t 373K.
DISCUSSION Activation The thesis
i n f r a r e d and t . p . d .
s p e c t r a o f t h e phophate immediately
after
show t h a t amines a r e r e t a i n e d i n t h e c h a n n e l s t r u c t u r e a f t e r
syn-
washing
and d r y i n g . A l l i n f r a r e d bands a r e c o m p a t i b l e w i t h t r i p r o p y l a m i n e a d s o r b e d o n acidic
sites.
T h e r m o g r a v i m e t r i c d a t a s u g g e s t t h a t t h e c h a n n e l s o f t h e phos-
p h a t e a r e c o m p l e t e l y f i l l e d w i t h w a t e r and amines.
373K.
A f t e r release o f water a t
a r o u n d 523K f i r s t d i p r o p y l a m i n e ( w e a k e r b a s e ) and t h e n
d e s o r b p a r a l l e l t o t h e r e l e a s e o f some propene.
tripropylamine
The d e s o r p t i o n i s a l s o m a n i -
169 f e s t e d b y a s h a r p i n c r e a s e o f BET s u r f a c e a r e a s t u r e was i n c r e a s e d f r o m 473K t o 573K. between
when t h e a c t i v a t i o n t e m p e r a -
Because no d i f f e r e n c e
in
spectra
1.r.
samples c a i c i n e d i n a i r and s a m p l e s c a l c i n e d i n v a c u o was
observed,
we c o n c l u d e t h a t n o c a r b o n a c e o u s r e s i d u e s w e r e f o r m e d d u r i n g d e c o m p o s i t i o n o r d e s o r p t i o n o f t h e amines.
0~
=. .... ~ . ~
_
273
,'
I
~
.
.
-
?
L73
Fig.
_
A M I N E S >.I(. - - ........... ~...
673
5. T.p.d.
1073
073
PROPEYE
K
spectrum o f a c t i v a -
t i o n o f A1P04-5.
F i g . 6. T.p.d.
spectra o f various
b a s e s f r o m A1P04-5.
The l a t t e r o b s e r v a t i o n c o r r e s p o n d s w e l l w i t h t h e w e l l known c o k e i n g r e s i s tance
o f s i l i c a l i t e s o r ZSM5 z e o l i t e s ( r e f .
structure
.
12),
which have
similar
pore
I t seems f e a s i b l e t h a t t h e n a r r o w 12-member r i n g c h a n n e l w i t h no
channel i n t e r s e c t i o n s ( r e f .
15) imposes s t e r i c
c o n s t r a i n t s upon c o k e f o r m a -
tion. A f t e r t h i s i n i t i a l d e c o m p o s i t i o n o f t h e amines. t h e p h o s p h a t e s show one OH band n e a r 3680 crnWendt
e t al.
1
.
Such a wavenumber h a s been r e p o r t e d b y P e r 1 ( r e f . 6 )
7-9)
(ref.
f o r OH g r o u p s a t t a c h e d t o t h e p h o s p h o r o u s atom.
band f o r OH g r o u p s a t t a c h e d t o aluminum, i n t h e present study.
as r e p o r t e d ( r e f .
6).
and
A
was n o t f o u n d
U n f o r t u n a t e l y t h e l o w i n t e n s i t y and t h e h i g h l e v e l
of
d i d n o t p e r m i t us t o e s t i m a t e a c i d s t r e n g t h b y d e t e r m i n i n g t h e OH
scattering
band s h i f t a f t e r a d s o r p t i o n o f a d o n o r m o l e c u l e . A c i d base D r o D e r t i e s I n an e a r l i e r p a p e r we h a v e d e m o n s t r a t e d t h a t t h e o v e r a l l a c i d s t r e n g t h o f an o x i d e , oxide, son
and p h o s p h a t e s may b e t r e a t e d as m i x e d o x i d e s o f P205 and a
metal
i n c r e a s e s w i t h t h e i n t e r m e d i a t e e l e c t r o n e g a t i v i t y a c c o r d i n g t o Sander-
(ref.1).
Thus
aluminurnphosphate.
one
would expect t o f i n d r a t h e r s t r o n g
Nevertheless
acid
sites
a d s o r p t i o n ( a n d d e s o r p t i o n ) o f ammonia
p y r i d i n e i n d i c a t e L e w i s a c i d s i t e s o f m o d e r a t e s t r e n g t h and,
on and
n o t unequivocal-
170 ly,
some
B r z n s t e d a c i d s i t e s ( o n l y NH3 was p r o t o n i r e d
weak
in
detectable
amounts).
If
one
estimate
u s e s t h e wavenumber o f t h e 19b v i b r a t i o n o f a d s o r b e d p y r i d i n e t h e s t r e n g t h o f i n t e r a c t i o n w i t h t h e Lewis a c i d s i t e ,
i n t e r a c t i o n s i m i l a r t o t h a t o f Si02 ( r e f . It
is
s i g n i f i c a n t l y weaker t h a n t h a t w i t h p u r e
sphates.
strength
of
18) o r s i l i c a - a l u m l n a i s i n d i c a t e d .
c o n c l u s i o n was a l s o drawn b y Wendt e t a l . ( r e f .
alumina
7-9)
(ref.18).
Such
a
f o r amorphous a l u m i n o p h o -
T r e a t m e n t w i t h NaOH c a u s e d a new band a t 1442 cm-'
a t t r i b u t e d t o p y r i d i n e a d s o r b e d on Na'
was
to
cations.
t o appear, which
The o t h e r m o d i f i c a t i o n s
d i d n o t change t h e a p p a r e n t L e w i s a c i d s t r e n g t h . The q u e s t i o n m u s t b e r a i s e d
as t o why p u r e a l u m i n a e x h i b i t s t h e s t r o n g e r
EPA s i t e s . T h i s may be a c c o m p l i s h e d b y s e p a r a t i n g EPA s t r e n g t h i n t o "maximum" and " a p p a r e n t a c c e p t o r s t r e n g t h " .
As p o i n t e d o u t p r e v i o u s l y ,
i n general t h e
oxide (phosphate) w i t h t h e higher intermediate e l e c t r o n e g a t i v i t y according t o Sanderson
I f t h e strength o f these
w i l l have t h e s t r o n g e r L e w i s a c i d s i t e s .
s i t e s i n c r e a s e s , however, t h e c a t i o n s a r e b e t t e r c o v e r e d b y oxygen. "maximum a c c e p t o r s t r e n g t h " may b e h i g h e r i n A1P04 t h a n i n A1 0 overcompensated phosphate.
by
Thus
Hence t h e
but t h i s i s
s i g n i f i c a n t lower a c c e s s i b i l t y o f t h e A15+3'ion
the
in
d i s t a n c e between t h e L e w i s a c i d s i t e and t h e
the
electron
p a i r d o n o r ( E P D ) m o l e c u l e w i l l be l a r g e r , d e c r e a s i n g t h e s t r e n g t h o f i n t e r a c i n d i c a t i n g a weaker L e w i s a c i d s i t e .
t i o n and hence,
N e v e r t h e l e s s i t may a l s o be p o s s i b l e t h a t a t l e a s t a p a r t o f t h e 1 4 4 8 cm-l i s c a u s e d b y p y r i d i n e a d s o r b e d on P-OH g r o u p s ( 3 6 8 0 cm-').
band
and A l P O on
4
h a v e s i m i l a r i n t e r m e d i a t e e l e c t r o n e g a t i v i t i e s and p y r i d i n e a d s o r b e d
Si-OH
groups
feasible. which
Si02
Since
c a u s e s a band a t 1447 cm-l
(ref.
18) t h e
proposal
(NH4)2HP04
It i s supported by t h e o b s e r v a t i o n t h a t t r e a t m e n t w i t h
should
increased
lead
t o a d e c r e a s e i n t h e number o f
t h e r e l a t i v e i n t e n s i t y o f t h e 1447 cm-l
accessible
band,
seems
A13+
and NaOH
ions,
treatment
decreased it. The be
must
f r a c t i o n o f BrEnsted a c i d s i t e s capable o f p r o t o n i z i n g p y r i d i n e
very
small.
Lack o f s u c h B r h s t e d a c i d i c
OH
g r o u p s m u s t be e x p e c t e d
o n l y b r i d g e d hydroxyl groups can donate p r o t o n s t o p y r i d i n e ( r e f .
19).
if
Cer-
c a n r e a d i l y be p r o t o n a t e d b y w e a k e r a c i d i c OH g r o u p s . F o r A1P04, 3 l i k e f o r Si02. i t i s n o t necessary t o balance a n e g a t i v e charge w i t h a p r o t o n
t a i n l y NH or
a cation.
present should
T h e r e f o r e t h e s e s u b s t a n c e s w i l l l a c k b r i d g e d h y d r o x y l s a s e.g.
in t y p e Y z e o l i t e s ( r e f . not
change t h e s i t u a t i o n .
s t r o n g Brldnsted a c i d i t y . coordination
20).
The a d d i t i o n o f
Indeed,
(NH4)2HP04
such t r e a t m e n t s d i d
Si02
or not
induce
Only i n c o r p o r a t i o n o f excess alumina i n t e t r a t h e d r a l
m i g h t n e c e s s i t a t e c h a r g e b a l a n c e b y p r o t o n s and c r e a t e B r ' l n s t e d
a c i d s i t e s s i m i l a r t o those o f zeolites. T.p.d.
spectra
o f t r i m e t h y l - and t r i e t h y l a m i n e s u g g e s t a t l e a s t t w o
de-
171 sorption states. Because
T h e i r n a t u r e c o u l d n o t be r e v e a l e d u n e q u i v o c a l l y u n t i l now.
o n l y one d e s o r p t l o n s t a t e was f o u n d w i t h p y r i d i n e
and
ammonia,
we
s t r e n g t h o f b a s i c s i t e s m u s t be e s t i m a t e d t o be v e r y l o w ( s i m i l a r
to
c o n c l u d e d t h a t t h e t w o s t a t e s m u s t c o i n c i d e f o r t h e l a t t e r bases. The silica
and s i l i c a - a l u m i n a )
s i n c e CO
2
d i d n o t f o r m any s t a b l e s u r f a c e
carbo-
nates. While hexane
c a t a l y t i c a l l y i n a c t i v e f o r t h e methanol t o g a s o l i n e r e a c t i o n o r cracking
mesityloxide deposits The
to
t h e c a t a l y s t forms condensates from acetone a m i x t u r e o f higher hydrocarbons).
Again
o r c a r b o x y l a t e s t r u c t u r e s c o u l d be detected by
(ranging no
1.r.
nfrom
carbonaceous spectroscopy.
h i g h e r r e a c t i v i t y o f t h e NaOH t r e a t e d p h o s p h a t e s u g g e s t s t h e
importance
o f t h e b a s i c s i t e s , w h i c h w e r e enhanced b y NaOH t r e a t m e n t . CONCLUSION vicroporous AlPO
The
4 aluminophosphates.
phous
e x h i b i t s s i m i l a r a c i d base p r o p e r t i e s as t h e This
shows t h a t n o new a c i d - b a s e p r o p e r t i e s
been i n d u c e d b y t h e c h a n n e l s t r u c t u r e . protonire
pyridine)
evaluation
were found.
b y a d s o r p t i o n o f C02.
have
Lewis a c i d s i t e s o f moderate s t r e n g t h
t h a n t h o s e o f a l u m i n a ) and weak G r E n s t e d a c i d s i t e s ( n o t c a p a b l e
(weaker
Si02
amor-
The b a s e s t r e n g t h was b e l o w t h e Having i d e n t i c a l c r y s t a l
limit
to of
structures
with
t h e aluminophosphates appear t o have s i m i l a r a c i d base p r o p e r t i e s
too.
Thus i n c o r p o r a t i o n o f t e t r a h e d r a l l y c o o r d i n a t e d e x c e s s a l u m i n a m i g h t c r e a t e a surface
chemistry
similar t o that o f the zeolites,
w h i l e excess
phosphate
w i l l n o t enhance t h e a c i d s t r e n g t h s o r change t h e t y p e o f a c i d s i t e s .
AC K id 0 W L E DG ENE N l S We
t h a n k t h e "Fonds z u r Forderune, d e r w i s s e n s c h a f t l i c h e n
providing the
i.r.
Forschung"
for
spectrometer.
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1 2 3 4 5
6
7
8
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