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SiO2 Catalysts
Guczi, L. ef al. (Editors), New Fronriers in Catalysis Proceedings of the 10th International Congress on Catalysis, 19-24 July, 1992,Budapest, Hungary @ 1993 Elsevier Science Publishers B.V. All rights reserved
PARTIAL HYDROGENATION OF ALKYNES AND DIENES ON HIGHLY SELECTIVE Fe-Cu/SiOz CATALYSTS
Y. Nitta, Y. Hiramatsy Y. Okamoto and T. Imanaka Department of Chemical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan
Abstract A Fe-Cu/SiO, c a t a l y s t , p r e p a r e d by c o p r e c i p i t a t i o n of i r o n and c o p p e r s u l f a t e s o v e r u l t r a f i n e s i l i c a g e l w i t h a n e x c e s s amount o f sodium o r potassium c a r b o n a t e a t a low t e m p e r a t u r e , was found t o b e h i g h l y s e l e c t i v e i n t h e p a r t i a l h y d r o g e n a t i o n of v a r i o u s a l k y n e s and c o n j u g a t e d d i e n e s . The u s e o f p o t a s s i u m c a r b o n a t e a s t h e p r e c i p i t a n t r e s u l t e d i n a catalyst w i t h an improved s e l e c t i v i t y i n a t a i l - e n d h y d r o g e n a t i o n of p h e n y l a c e t y l e n e , p r o b a b l y because of a n e l e c t r o n i c e f f e c t of t h e K i o n s r e m a i n i n g on t h e catalyst surface. INTRODUCTION I r o n c a t a l y s t s a r e known t o have h i g h s e l e c t i v i t y , b u t e x t r e m e l y low a c t i v i t y , f o r p a r t i a l h y d r o g e n a t i o n of a l k y n e s t o a l k e n e s . Development of i r o n c a t a l y s t s w i t h h i g h a c t i v i t y f o r a l k y n e h y d r o g e n a t i o n is r e q u i r e d f o r industrial applications. R e c e n t l y w e have r e p o r t e d t h a t , i n t h e p a r t i a l h y d r o g e n a t i o n of p h e n y l a c e t y l e n e (PA) t o s t y r e n e (ST), t h e a c t i v i t y and s e l e c t i v i t y o f F e / S i O z c a t a l y s t a r e e x t r a o r d i n a r i l y i m p r o v e d by s i m u l t a n e o u s a d d i t i o n o f c o p p e r and s u l f a t e i o n s [ l ] . The e f f e c t s o f t h e p r e p a r a t i o n v a r i a b l e s , e s p e c i a l l y t h e p r e c i p i t a t i o n t e m p e r a t u r e , and t h e doping of c o p p e r and s u l f a t e i o n s h a v e been s t u d i e d by u s i n g XPS, TPR, XRD, a n d TGA [ 2 ] . I t was f o u n d t h a t t h e h i g h a c t i v i t y a n d s e l e c t i v i t y a r e a t t r i b u t a b l e t o t h e i n c r e a s e d d i s p e r s i o n o f F e metal, I n dehydrogenation of e t h y l b e n z e n e t o s t y r e n e , p o t a s s i u m d o p i n g o f i r o n c a t a l y s t s are known t o i n c r e a s e a c t i v i t y and s e l e c t i v i t y [ 3 , 4 1 . It i s i n t e r e s t i n g t o know i f t h e potassium-promoted i r o n c a t a l y s t s are a l s o e f f e c t i v e i n t h e p a r t i a l h y d r o g e n a t i o n o f a l k y n e s and o t h e r r e l a t e d r e a c t i o n s . I n t h i s work, we r e p o r t t h a t t h e u s e of p o t a s s i u m c a r b o n a t e i n s t e a d o f sodium c a r b o n a t e as t h e p r e c i p i t a n t much improves t h e s e l e c t i v i t y of t h e r e s u l t i n g c a t a l y s t i n a tail-end h y d r o g e n a t i o n of p h e n y l a c e t y l e n e . P a r t i a l h y d r o g e n a t i o n s of d i f f e r e n t a l k y n e s and d i e n e s were a l s o examined on these c a t a l y s t s . EXPERIMENTAL
Catalyst p r e c u r s o r s were p r e p a r e d by a p r e c i p i t a t i o n method as f o l l o w s : a s o l u t i o n of a n e x c e s s amount of sodium or p o t a s s i u m c a r b o n a t e (1.5-1.7 m o l a r e q u i v a l e n t ) i n 25 m l o f d i s t i l l e d water was a d d e d a t 2 O o C t o a n a q u e o u s s u s p e n s i o n (150 ml) c o n t a i n i n g 2 g o f non-porous u l t r a f i n e s i l i c a
2334 g e l (Nippon A e r o s i l , A-300, 320 m'g-' ), i r o n ( I I 1 ) s u l f a t e , and c o p p e r ( I 1 ) s u l f a t e ( t o t a l amount o f metal = 36 m m o l , Fe:Cu = 7 : 3 i n atomic r a t i o ) i n 1-2 min under v i g o r o u s s t i r r i n g . The p r e c i p i t a t e was a g e d f o r 15 min a t 75-80°C and f i l t e r e d , f o l l o w e d by w a s h i n g t h r e e times w i t h h o t water and d r y i n g a t 110 " C f o r 20 h. One gram o f a d r i e d p r e c u r s o r was r e d u c e d by h e a t i n g i n a stream o f hydrogen t o 500 " C and h o l d i n g a t t h i s t e m p e r a t u r e f o r 1 h. The h y d r o g e n a t i o n o f a l k y n e s o r d i e n e s (0.6 m l ) w a s c a r r i e d o u t u s u a l l y i n e t h a n o l ( 2 7 m l ) a t 60 " C u n d e r 1.0 MPa o f hydrogen by u s i n g a g l a s s a u t o c l a v e e q u i p o e d w i t h a m a g n e t i c s t i r r i n g system. RESULTS AND DISCUSSION A s shown i n T a b l e 1, t h e u s e o f p o t a s s i u m c a r b o n a t e i n s t e a d of sodium c a r b o n a t e as t h e p r e c i p i t a n t r e s u l t e d i n a c a t a l y s t w i t h h i g h e r s e l e c t i v i t y t o ST i n t h e h y d r o g e n a t i o n of PA b u t l o w e r a c t i v i t y f o r b o t h PA and ST h y d r o g e n a t i o n s . The s e l e c t i v i t y was improved e s p e c i a l l y a t t h e end o f t h e Therefore, a tail-end hydrogenation r e a c t i o n : 99.6% a t 99.9% c o n v e r s i o n . w i t h a m i x t u r e of PA and ST (5:95) i n n-propanol was examined on t h e s e two c a t a l y s t s a t 60 "C under a n a t m o s p h e r i c p r e s s u r e o f h y d r o g e n . A s shown i n F i g u r e 1, catalyst-B e x h i b i t e d h i g h e r s e l e c t i v i t y (99.6%) t h a n catalyst-A (98.7%) a t 100%c o n v e r s i o n o f PA a l t h o u g h t h e a c t i v i t y o f catalyst-B was a l i t t l e lower t h a n t h a t of c a t a l y s t - A . TGA and XRD measurements showed t h a t b o t h c a t a l y s t s are similar t o e a c h o t h e r i n t h e r e d u c t i o n b e h a v i o u r o f t h e p r e c u r s o r s and i n t h e d i s p e r s i o n o f Fe metal i n t h e r e d u c e d c a t a l y s t s . T h e r e f o r e , t h e h i g h e r s e l e c t i v i t y o f c a t a l y s t - B may b e a t t r i b u t e d t o t h e e l e c t r o n i c e f f e c t o f p o t a s s i u m i o n s r e m a i n i n g on t h e c a t a l y s t s u r f a c e (ca. 0.2% of F e ) r a t h e r t h a n t h e d i f f e r e n c e i n c a t a l y s t morphology. T h e r e l a t i v e a d s o r p t i o n s t r e n g t h o f a l k y n e a n d a l k e n e o n t h e s e two c a t a l y s t s a r e a s s e s s e d f r o m i n d i v i d u a l a n d c o m p e t i t i v e r e a c t i o n r a t e s o f PA and ST. Assuming t h a t t h e h y d r o g e n a t i o n r a t e of r e a c t a n t PA ( o r ST) is p r o p o r t i o n a l t o t h e amount o f a d s o r b e d PA ( o r ST) and t h a t t h e a d s o r p t i o n of PA (or ST) f o l l o w s t h e Langmuir i s o t h e r m , t h e f o l l o w i n g e q u a t i o n i s o b t a i n e d when t h e r e a c t i o n r a t e i s i n d e p e n d e n t of t h e c o n c e n t r a t i o n o f PA ( o r ST) [ 5 , 61 as was c o n f i r m e d i n s e p a r a t e e x p e r i m e n t s .
K(r) = K(PA)/K(ST) = [A(PA)/A(ST)]/[r(PA)/r(ST)] Table 1 H y d r o g e n a t i o n o f p h e n y l a c e t y l e n e and s t y r e n e on Fe-Cu/SiOn p r e p a r e d w i t h Na,C03 (A) a n d K,CO, (B)
Catalyst
Precipitant
A
Na,C03
B
K2CO3
a b c d
r o a / m o l . rnin-lg-' r(PA)
r(ST)
0.36
1.o 0.82
0.23
S,,,/Zb
99.4 99.8
r(PA)
catalysts
r(ST)
A(PA)' A(ST)
K(r)d
0.36 0.28
2 . 7 ~ 1 0 ' ~7.6~1023 5.0~10 1.8~10
I n i t i a l h y d r o g e n a t i o n rates of p h e n y l a c e t y l e n e (PA) and s t y r e n e (ST). S t y r e n e s e l e c t i v i t y a t 50% c o n v e r s i o n o f p h e n y l a c e t y l e n e . C o n v e r s i o n r a t i o of PA t o ST i n c o m p e t i t i v e h y d r o g e n a t i o n . Relative adsorption c o e f f i c i e n t of phenylacetylene t o styrene.
2335 5
a)
3 2 1-
- 100
-+%
\
A
u
.rl
>
98.7%
.d
c,
u
aJ rl
b)
4
L
i
r
LA
L
1
3 -
F i g u r e 1. T a i l - e n d - h y d r o g e n a t i o n of p h e n y l a c e t y l e n e o n Fe-Cu/SiOn c a t a l y s t s p r e p a r e d by u s i n g a ) NazC03 a n d b ) K2C03 a s t h e p r e c i p i t a n t . O : P h e n y l a c e t y l e n e , A:S t y r e n e , 0: Ethylbenzene, .:Selectivity to styrene. w h e r e K(r) is t h e a d s o r p t i o n c o e f f i c i e n t o f PA r e l a t i v e t o t h a t o f ST, r(PA)/r(ST) t h e r a t i o o f t h e i n d i v i d u a l r e a c t i o n r a t e s , a n d A(PA)/A(ST) t h e r a t i o o f t h e c o n v e r s i o n o f PA t o t h a t of ST i n a n i n i t i a l s t a g e of t h e c o m p e t i t i v e r e a c t i o n . T h e v a l u e o f K(r) i s u s e d a s a m e a s u r e o f t h e r e l a t i v e a d s o r p t i o n s t r e n g t h of PA t o ST. A s l i s t e d i n T a b l e 1, t h e K(r) v a l u e s f o r b o t h c a t a l y s t s a r e much l a r g e r t h a n u n i t y , m e a n i n g t h a t t h e a d s o r p t i o n o f PA is much s t r o n g e r t h a n t h a t of ST. M o r e o v e r , K(r) f o r c a t a l y s t - B is l a r g e r t h a n t h a t f o r catalyst-A. This indicates that the r e l a t i v e a d s o r p t i o n s t r e n g t h of PA t o ST is l a r g e r o n c a t a l y s t - B t h a n on catalyst-A. I n o t h e r w o r d s , t h e i n t e r m e d i a t e p r o d u c t ST on c a t a l y s t - B is more e a s i l y r e p l a c e d by t h e r e a c t a n t m o l e c u l e PA b e f o r e b e i n g h y d r o g e n a t e d t o e t h y l b e n z e n e , which w i l l l e a d t o t h e i m p r o v e d s e l e c t i v i t y of c a t a l y s t - B .
P o t a s s i u m i o n s r e m a i n i n g on t h e s u r f a c e of c a t a l y s t - B seem t o i n c r e a s e e l e c t r o n i c a l l y t h e a d s o r p t i o n s t r e n g t h o f a l k y n e s rathe'r t h a n a l k e n e s . The s e l e c t i v i t i e s i n p a r t i a l h y d r o g e n a t i o n o f d i f f e r e n t a l k y n e s and d i e n e s were examined on t h e s e two c a t a l y s t s and found t o b e e x t r e m e l y h i g h f o r b o t h c a t a l y s t s , a l t h o u g h t h e a c t i v i t i e s o f c a t a l y s t - B were a l i t t l e l o w e r t h a n those o f catalyst-A. T a b l e 2 lists t h e a c t i v i t i e s and s e l e c t i v i t i e s a t v a r i o u s c o n v e r s i o n s on catalyst-A. I t is n o t e w o r t h y t h a t 1 , 3 - c y c l o o c t a d i e n e i s e a s i l y h y d r o g e n a t e d t o c y c l o o c t e n e w i t h 100% s e l e c t i v i t y , w h e r e a s t h e catalyst is almost i n a c t i v e f o r t h e h y d r o g e n a t i o n of 1 , 5 - c y c l o o c t a d i e n e . I n t h i s case, c y c l o o c t e n e i s p r o b a b l y h y d r o g e n a t e d from 1 , 3 - c y c l o o c t a d i e n e a f t e r t h e i s o m e r i z a t i o n r e a c t i o n of 1,5cyclooctadiene. T h u s , t h e Fe-Cu/SiOz c a t a l y s t i s h i g h l y u s e f u l n o t o n l y f o r p a r t i a l hydrogenation of alkynes i n t h e presence of a l k e n e s b u t a l s o f o r s e l e c t i v e h y d r o g e n a t i o n of c o n j u g a t e d d i e n e s t o m o n o e n e s i n t h e presence of nonconjugated d i e n e s . Table 2 P a r t i a l h y d r o g e n a t i o n o f v a r i o u s a l k y n e s and d i e n e s on Fe-Cu/SiOzcatalyst-A Reactant
S e l e c t i v i t y b /mol%
roa/mmol- min-lg-' s2 0
s50
99.4
99.4 99.7 100 100 100
SlOO
~
Phenylacetylene 1-Phenyl-1-propyne 1-Heptyne 2-Butyne-1,4-diol 1,3-Cyclooctadiene 1,5-Cyclooctadiene
-~
a b c
3 . 6 x lo-' 2.9 x lo-' 1.8 x lo-'
4.8
2.2 x 7.4
lo-"
99.2 100 100 100 2 100( 3)'
-
9 9 . 4 ( 90)' 99.7(92) 2100 (100) 1100 (100) 2100 (100)
-
~~
~
I n i t i a l hydrogenation rate. S e l e c t i v i t i e s o f monoene a t c o n v e r s i o n s o f 2 0 % ( S 2 0 ) , 50%(Sso ) , a n d a r o u n d ) lOO%(S Numbers i n p a r e n t h e s e s a r e e x a c t c o n v e r s i o n s of t h e r e a c t a n t .
.
REFERENCES
1 Y . N i t t a , S. M a t s u g i a n d T. Imanaka, Catal. L e t t . , 5 (1990) 6 7 . 2 Y . N i t t a , Y. H i r a m a t s u , Y. Okamoto a n d T. Imanaka, S t u d . S u r f . S c i . C a t a l . , 63 ( 1 9 9 1 ) 103. 3 W. D. Mross, Catal. Rev.-Sci. Eng., 2 5 ( 1 9 8 3 ) 591. 4 T. H i r a n o , Appl. Catal., 26 ( 1 9 8 6 ) 65 and 81. 5 T. C h i h a r a and K . T a n a k a , Chem. L e t t . , (1977) 843. 6 M. K a j i t a n i , N . S u z u k i , T. Abe, Y. Kaneko, K. Kasuya, K. T a k a h a s h i and A. S u g i m o r i , B u l l . Chem. SOC. J p n . , 5 2 ( 1 9 7 9 ) 2343.
PARTIAL HYDROGENATION OF ALKYNES AND DIENES ON HIGHLY SELECTIVE Fe-Cu/SiOz CATALYSTS
Y. Nitta, Y. Hiramatsy Y. Okamoto and T. Imanaka Department of Chemical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan
Abstract A Fe-Cu/SiO, c a t a l y s t , p r e p a r e d by c o p r e c i p i t a t i o n of i r o n and c o p p e r s u l f a t e s o v e r u l t r a f i n e s i l i c a g e l w i t h a n e x c e s s amount o f sodium o r potassium c a r b o n a t e a t a low t e m p e r a t u r e , was found t o b e h i g h l y s e l e c t i v e i n t h e p a r t i a l h y d r o g e n a t i o n of v a r i o u s a l k y n e s and c o n j u g a t e d d i e n e s . The u s e o f p o t a s s i u m c a r b o n a t e a s t h e p r e c i p i t a n t r e s u l t e d i n a catalyst w i t h an improved s e l e c t i v i t y i n a t a i l - e n d h y d r o g e n a t i o n of p h e n y l a c e t y l e n e , p r o b a b l y because of a n e l e c t r o n i c e f f e c t of t h e K i o n s r e m a i n i n g on t h e catalyst surface. INTRODUCTION I r o n c a t a l y s t s a r e known t o have h i g h s e l e c t i v i t y , b u t e x t r e m e l y low a c t i v i t y , f o r p a r t i a l h y d r o g e n a t i o n of a l k y n e s t o a l k e n e s . Development of i r o n c a t a l y s t s w i t h h i g h a c t i v i t y f o r a l k y n e h y d r o g e n a t i o n is r e q u i r e d f o r industrial applications. R e c e n t l y w e have r e p o r t e d t h a t , i n t h e p a r t i a l h y d r o g e n a t i o n of p h e n y l a c e t y l e n e (PA) t o s t y r e n e (ST), t h e a c t i v i t y and s e l e c t i v i t y o f F e / S i O z c a t a l y s t a r e e x t r a o r d i n a r i l y i m p r o v e d by s i m u l t a n e o u s a d d i t i o n o f c o p p e r and s u l f a t e i o n s [ l ] . The e f f e c t s o f t h e p r e p a r a t i o n v a r i a b l e s , e s p e c i a l l y t h e p r e c i p i t a t i o n t e m p e r a t u r e , and t h e doping of c o p p e r and s u l f a t e i o n s h a v e been s t u d i e d by u s i n g XPS, TPR, XRD, a n d TGA [ 2 ] . I t was f o u n d t h a t t h e h i g h a c t i v i t y a n d s e l e c t i v i t y a r e a t t r i b u t a b l e t o t h e i n c r e a s e d d i s p e r s i o n o f F e metal, I n dehydrogenation of e t h y l b e n z e n e t o s t y r e n e , p o t a s s i u m d o p i n g o f i r o n c a t a l y s t s are known t o i n c r e a s e a c t i v i t y and s e l e c t i v i t y [ 3 , 4 1 . It i s i n t e r e s t i n g t o know i f t h e potassium-promoted i r o n c a t a l y s t s are a l s o e f f e c t i v e i n t h e p a r t i a l h y d r o g e n a t i o n o f a l k y n e s and o t h e r r e l a t e d r e a c t i o n s . I n t h i s work, we r e p o r t t h a t t h e u s e of p o t a s s i u m c a r b o n a t e i n s t e a d o f sodium c a r b o n a t e as t h e p r e c i p i t a n t much improves t h e s e l e c t i v i t y of t h e r e s u l t i n g c a t a l y s t i n a tail-end h y d r o g e n a t i o n of p h e n y l a c e t y l e n e . P a r t i a l h y d r o g e n a t i o n s of d i f f e r e n t a l k y n e s and d i e n e s were a l s o examined on these c a t a l y s t s . EXPERIMENTAL
Catalyst p r e c u r s o r s were p r e p a r e d by a p r e c i p i t a t i o n method as f o l l o w s : a s o l u t i o n of a n e x c e s s amount of sodium or p o t a s s i u m c a r b o n a t e (1.5-1.7 m o l a r e q u i v a l e n t ) i n 25 m l o f d i s t i l l e d water was a d d e d a t 2 O o C t o a n a q u e o u s s u s p e n s i o n (150 ml) c o n t a i n i n g 2 g o f non-porous u l t r a f i n e s i l i c a
2334 g e l (Nippon A e r o s i l , A-300, 320 m'g-' ), i r o n ( I I 1 ) s u l f a t e , and c o p p e r ( I 1 ) s u l f a t e ( t o t a l amount o f metal = 36 m m o l , Fe:Cu = 7 : 3 i n atomic r a t i o ) i n 1-2 min under v i g o r o u s s t i r r i n g . The p r e c i p i t a t e was a g e d f o r 15 min a t 75-80°C and f i l t e r e d , f o l l o w e d by w a s h i n g t h r e e times w i t h h o t water and d r y i n g a t 110 " C f o r 20 h. One gram o f a d r i e d p r e c u r s o r was r e d u c e d by h e a t i n g i n a stream o f hydrogen t o 500 " C and h o l d i n g a t t h i s t e m p e r a t u r e f o r 1 h. The h y d r o g e n a t i o n o f a l k y n e s o r d i e n e s (0.6 m l ) w a s c a r r i e d o u t u s u a l l y i n e t h a n o l ( 2 7 m l ) a t 60 " C u n d e r 1.0 MPa o f hydrogen by u s i n g a g l a s s a u t o c l a v e e q u i p o e d w i t h a m a g n e t i c s t i r r i n g system. RESULTS AND DISCUSSION A s shown i n T a b l e 1, t h e u s e o f p o t a s s i u m c a r b o n a t e i n s t e a d of sodium c a r b o n a t e as t h e p r e c i p i t a n t r e s u l t e d i n a c a t a l y s t w i t h h i g h e r s e l e c t i v i t y t o ST i n t h e h y d r o g e n a t i o n of PA b u t l o w e r a c t i v i t y f o r b o t h PA and ST h y d r o g e n a t i o n s . The s e l e c t i v i t y was improved e s p e c i a l l y a t t h e end o f t h e Therefore, a tail-end hydrogenation r e a c t i o n : 99.6% a t 99.9% c o n v e r s i o n . w i t h a m i x t u r e of PA and ST (5:95) i n n-propanol was examined on t h e s e two c a t a l y s t s a t 60 "C under a n a t m o s p h e r i c p r e s s u r e o f h y d r o g e n . A s shown i n F i g u r e 1, catalyst-B e x h i b i t e d h i g h e r s e l e c t i v i t y (99.6%) t h a n catalyst-A (98.7%) a t 100%c o n v e r s i o n o f PA a l t h o u g h t h e a c t i v i t y o f catalyst-B was a l i t t l e lower t h a n t h a t of c a t a l y s t - A . TGA and XRD measurements showed t h a t b o t h c a t a l y s t s are similar t o e a c h o t h e r i n t h e r e d u c t i o n b e h a v i o u r o f t h e p r e c u r s o r s and i n t h e d i s p e r s i o n o f Fe metal i n t h e r e d u c e d c a t a l y s t s . T h e r e f o r e , t h e h i g h e r s e l e c t i v i t y o f c a t a l y s t - B may b e a t t r i b u t e d t o t h e e l e c t r o n i c e f f e c t o f p o t a s s i u m i o n s r e m a i n i n g on t h e c a t a l y s t s u r f a c e (ca. 0.2% of F e ) r a t h e r t h a n t h e d i f f e r e n c e i n c a t a l y s t morphology. T h e r e l a t i v e a d s o r p t i o n s t r e n g t h o f a l k y n e a n d a l k e n e o n t h e s e two c a t a l y s t s a r e a s s e s s e d f r o m i n d i v i d u a l a n d c o m p e t i t i v e r e a c t i o n r a t e s o f PA and ST. Assuming t h a t t h e h y d r o g e n a t i o n r a t e of r e a c t a n t PA ( o r ST) is p r o p o r t i o n a l t o t h e amount o f a d s o r b e d PA ( o r ST) and t h a t t h e a d s o r p t i o n of PA (or ST) f o l l o w s t h e Langmuir i s o t h e r m , t h e f o l l o w i n g e q u a t i o n i s o b t a i n e d when t h e r e a c t i o n r a t e i s i n d e p e n d e n t of t h e c o n c e n t r a t i o n o f PA ( o r ST) [ 5 , 61 as was c o n f i r m e d i n s e p a r a t e e x p e r i m e n t s .
K(r) = K(PA)/K(ST) = [A(PA)/A(ST)]/[r(PA)/r(ST)] Table 1 H y d r o g e n a t i o n o f p h e n y l a c e t y l e n e and s t y r e n e on Fe-Cu/SiOn p r e p a r e d w i t h Na,C03 (A) a n d K,CO, (B)
Catalyst
Precipitant
A
Na,C03
B
K2CO3
a b c d
r o a / m o l . rnin-lg-' r(PA)
r(ST)
0.36
1.o 0.82
0.23
S,,,/Zb
99.4 99.8
r(PA)
catalysts
r(ST)
A(PA)' A(ST)
K(r)d
0.36 0.28
2 . 7 ~ 1 0 ' ~7.6~1023 5.0~10 1.8~10
I n i t i a l h y d r o g e n a t i o n rates of p h e n y l a c e t y l e n e (PA) and s t y r e n e (ST). S t y r e n e s e l e c t i v i t y a t 50% c o n v e r s i o n o f p h e n y l a c e t y l e n e . C o n v e r s i o n r a t i o of PA t o ST i n c o m p e t i t i v e h y d r o g e n a t i o n . Relative adsorption c o e f f i c i e n t of phenylacetylene t o styrene.
2335 5
a)
3 2 1-
- 100
-+%
\
A
u
.rl
>
98.7%
.d
c,
u
aJ rl
b)
4
L
i
r
LA
L
1
3 -
F i g u r e 1. T a i l - e n d - h y d r o g e n a t i o n of p h e n y l a c e t y l e n e o n Fe-Cu/SiOn c a t a l y s t s p r e p a r e d by u s i n g a ) NazC03 a n d b ) K2C03 a s t h e p r e c i p i t a n t . O : P h e n y l a c e t y l e n e , A:S t y r e n e , 0: Ethylbenzene, .:Selectivity to styrene. w h e r e K(r) is t h e a d s o r p t i o n c o e f f i c i e n t o f PA r e l a t i v e t o t h a t o f ST, r(PA)/r(ST) t h e r a t i o o f t h e i n d i v i d u a l r e a c t i o n r a t e s , a n d A(PA)/A(ST) t h e r a t i o o f t h e c o n v e r s i o n o f PA t o t h a t of ST i n a n i n i t i a l s t a g e of t h e c o m p e t i t i v e r e a c t i o n . T h e v a l u e o f K(r) i s u s e d a s a m e a s u r e o f t h e r e l a t i v e a d s o r p t i o n s t r e n g t h of PA t o ST. A s l i s t e d i n T a b l e 1, t h e K(r) v a l u e s f o r b o t h c a t a l y s t s a r e much l a r g e r t h a n u n i t y , m e a n i n g t h a t t h e a d s o r p t i o n o f PA is much s t r o n g e r t h a n t h a t of ST. M o r e o v e r , K(r) f o r c a t a l y s t - B is l a r g e r t h a n t h a t f o r catalyst-A. This indicates that the r e l a t i v e a d s o r p t i o n s t r e n g t h of PA t o ST is l a r g e r o n c a t a l y s t - B t h a n on catalyst-A. I n o t h e r w o r d s , t h e i n t e r m e d i a t e p r o d u c t ST on c a t a l y s t - B is more e a s i l y r e p l a c e d by t h e r e a c t a n t m o l e c u l e PA b e f o r e b e i n g h y d r o g e n a t e d t o e t h y l b e n z e n e , which w i l l l e a d t o t h e i m p r o v e d s e l e c t i v i t y of c a t a l y s t - B .
P o t a s s i u m i o n s r e m a i n i n g on t h e s u r f a c e of c a t a l y s t - B seem t o i n c r e a s e e l e c t r o n i c a l l y t h e a d s o r p t i o n s t r e n g t h o f a l k y n e s rathe'r t h a n a l k e n e s . The s e l e c t i v i t i e s i n p a r t i a l h y d r o g e n a t i o n o f d i f f e r e n t a l k y n e s and d i e n e s were examined on t h e s e two c a t a l y s t s and found t o b e e x t r e m e l y h i g h f o r b o t h c a t a l y s t s , a l t h o u g h t h e a c t i v i t i e s o f c a t a l y s t - B were a l i t t l e l o w e r t h a n those o f catalyst-A. T a b l e 2 lists t h e a c t i v i t i e s and s e l e c t i v i t i e s a t v a r i o u s c o n v e r s i o n s on catalyst-A. I t is n o t e w o r t h y t h a t 1 , 3 - c y c l o o c t a d i e n e i s e a s i l y h y d r o g e n a t e d t o c y c l o o c t e n e w i t h 100% s e l e c t i v i t y , w h e r e a s t h e catalyst is almost i n a c t i v e f o r t h e h y d r o g e n a t i o n of 1 , 5 - c y c l o o c t a d i e n e . I n t h i s case, c y c l o o c t e n e i s p r o b a b l y h y d r o g e n a t e d from 1 , 3 - c y c l o o c t a d i e n e a f t e r t h e i s o m e r i z a t i o n r e a c t i o n of 1,5cyclooctadiene. T h u s , t h e Fe-Cu/SiOz c a t a l y s t i s h i g h l y u s e f u l n o t o n l y f o r p a r t i a l hydrogenation of alkynes i n t h e presence of a l k e n e s b u t a l s o f o r s e l e c t i v e h y d r o g e n a t i o n of c o n j u g a t e d d i e n e s t o m o n o e n e s i n t h e presence of nonconjugated d i e n e s . Table 2 P a r t i a l h y d r o g e n a t i o n o f v a r i o u s a l k y n e s and d i e n e s on Fe-Cu/SiOzcatalyst-A Reactant
S e l e c t i v i t y b /mol%
roa/mmol- min-lg-' s2 0
s50
99.4
99.4 99.7 100 100 100
SlOO
~
Phenylacetylene 1-Phenyl-1-propyne 1-Heptyne 2-Butyne-1,4-diol 1,3-Cyclooctadiene 1,5-Cyclooctadiene
-~
a b c
3 . 6 x lo-' 2.9 x lo-' 1.8 x lo-'
4.8
2.2 x 7.4
lo-"
99.2 100 100 100 2 100( 3)'
-
9 9 . 4 ( 90)' 99.7(92) 2100 (100) 1100 (100) 2100 (100)
-
~~
~
I n i t i a l hydrogenation rate. S e l e c t i v i t i e s o f monoene a t c o n v e r s i o n s o f 2 0 % ( S 2 0 ) , 50%(Sso ) , a n d a r o u n d ) lOO%(S Numbers i n p a r e n t h e s e s a r e e x a c t c o n v e r s i o n s of t h e r e a c t a n t .
.
REFERENCES
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