Supported on Activated Carbon - American Chemical Society

19 Evidence of a Metal-Surface Phase Oxide Interaction for Re on WOx Supported on Activated Carbon Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 31, 2018 | https://pubs.acs.org Publication Date: February 10, 1986 | doi: 10.1021/bk-1986-0298.ch019

L. L. Murrell, N. C. Dispenziere, Jr., R. T. K. Baker, and J. J. Chludzinski Corporate Research Science Laboratories, Exxon Research and Engineering Company, Annandale, NJ 08801 Hydrogen and CO chemisorption of Re, W, and Re-W on a carbon black support reduced in H2 confirm metallic phases are present in a l l three systems. The tempera tures at which reduction occurs, as well as an appar ent strong metal support interaction between Re and supported WOx, was followed by chemisorption. In addition, the catalytic gasification of the carbon black by the very active Re component in H2 was sig nificantly retarded for the Re-W system. Controlled atmosphere electron microscopy examination of the Re-W system confirmed the marked decrease in the catalyzed gasification of graphite in H2 compared to the very active Re component. In the gasification of graphite in O2, however, the Re-W bicomponent alloy system was significantly more active than either tungsten or rhenium. It was concluded that at high temperatures in O2, Re covers the Re-W alloy particles, and at high temperatures in H2, W covers the Re-W alloy parti cles. At low temperatures highly-dispersed Re parti cles interact with aWOxsurface phase complex either on the carbon surface or on the Re particle surface to retard both H2 and CO chemisorption. There i s c o n s i d e r a b l e c u r r e n t i n t e r e s t i n t h e s t r o n g i n t e r a c t i o n between c e r t a i n o x i d e s u p p o r t s and a metal phase (SMSI) ( 1 , 2 ) , In a d d i t i o n , t h e i n t e r a c t i o n between o x i d e s u p p o r t s and h i g h l y d i s persed o x i d e phases i s r e c e i v i n g i n c r e a s i n g a t t e n t i o n ( 3 - 6 ) , This paper p r e s e n t s e v i d e n c e t h a t a r e l a t i v e l y i n e r t a c t i v a t e d carbon b l a c k s u p p o r t , ( C a r b o l a c , c o n t a i n i n g 20 wt% oxygen, Cabot C o r p o r a t i o n ) , when used as a support f o r a t r a n s i t i o n metal o x i d e (TMO) a l t e r s t h e p r o p e r t i e s o f t h e supported TMO i n s i g n i f i c a n t ways. Bulk t u n g s t e n o x i d e does not behave as an SMSI support whereas t u n g sten o x i d e when supported on a c t i v a t e d carbon i s an SMSI s u p p o r t . The e x t e n t o f r e d u c t i o n o f T i 0 has been i m p l i c a t e d i n t h e SMSI phenomenon ( 7 , 8 ) , In t h i s paper we present c l e a r evidence t h a t t h e number o f systems which can g i v e r i s e t o t h e SMSI phenomenon i s not l i m i t e d t o p r i m a r y o x i d e s such as TiOo, Nbo0 , or b i n a r y o x i d e s such as B a T i 0 o r Z r T i 0 . 2

5

3

4

0097-6156/86/0298-0195S06.00/0 © 1986 American Chemical Society

Baker et al.; Strong Metal-Support Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

STRONG METAL-SUPPORT INTERACTIONS

196

In a r e l a t e d study of Rh on T i 0 - d o p e d SiO? (9) i t was shown t h a t a h i g h l y - d i s p e r s e d s u r f a c e phase complex o f TTD on an i n e r t S i O 2 s u p p o r t i n t r o d u c e d c o o r d i n a t i v e l y u n s a t u r a t e d s i t e s (CUS) (1012) of T i which were " t i t r a t e d " by the reduced metal clusters. Tiïis R h - T i 0 2 "i° CO 2 * Pt s u p p r e s s i o n when reduced i n H at 500°C. S i m i l a r s t u d i e s o f FeO on Ti0 and I r - F e on T i 0 (13) show i n t e r a c t i o n of the CUS s i t e s of T i 0 w i t h both F e c e n t e r s and an I r - F e b i m e t a l l i c c l u s t e r . Acti vated carbon i n the present study and g r a p h i t e model systems have been employed as s u p p o r t s f o r WO3, ReoOy and W 0 - R e 0 y . The p r o p e r t i e s of t h e s e t h r e e systems i n r e d u c i n g and o x i d i z i n g environments have been s t u d i e d by H and CO c h e m i s o r p t i o n , x - r a y d i f f r a c t i o n ( 1 4 ) , and C o n t r o l l e d Atmosphere E l e c t r o n M i c r o s c o p y ( 1 5 ) . Rhenium, W, and Re-W are i n t e r e s t i n g systems t o i n v e s t i g a t e as f a r as t h e g r a p h i t e g a s i f i c a t i o n i n o x i d i z i n g and r e d u c i n g c o n d i t i o n s i s c o n cerned ( 1 6 , 1 7 ) . This i s due t o the f a c t t h a t t h e s i n g l e component systems Re and W, i n both o x i d i z i n g and r e d u c i n g environments show such extremes i n c a t a l y t i c a c t i v i t y . Tungsten i s c o m p l e t e l y i n e r t toward g r a p h i t e g a s i f i c a t i o n i n H whereas rhenium i s one o f t h e most a c t i v e c a t a l y s t s ( 1 5 ) . Tungsten i s a l s o o n l y m a r g i n a l l y more a c t i v e than t h e u n c a t a l y z e d g r a p h i t e g a s i f i c a t i o n i n 0 whereas rhenium i s an a c t i v e c a t a l y s t . S t u d i e s o f t h e mixed component s y s t e m , Re-W, are t h e r e f o r e of c o n s i d e r a b l e i n t e r e s t ( 1 6 , 1 7 ) s i n c e t h e s i n g l e component systems have such d i f f e r e n t c a t a l y t i c activity toward g r a p h i t e g a s i f i c a t i o n . The Re-W system shows complete r e v e r s a l i n g a s i f i c a t i o n a c t i v i t y f o r o x i d i z i n g and r e d u c i n g c o n d i t i o n s . The Re-W system f o r g r a p h i t e g a s i f i c a t i o n i n oxygen i s more a c t i v e than rhenium i t s e l f . This i s c o n s i s t e n t w i t h a model wherein a p a r t i c l e o f W i s s u r r o u n d ed by an o u t e r Re metal phase. T h i s " c h e r r y m o d e l " of the Re-W system e x p l a i n s enhanced a c t i v i t y f o r g r a p h i t e o x i d a t i o n e i t h e r v i a t h e t h i n " o u t e r s k i n " of Re a l l o w i n g f a s t e r carbon d i f f u s i o n and/or v i a the Re phase b e i n g a l t e r e d e l e c t r o n i c a l l y by the i n n e r W c o r e . In any case the Re-W g a s i f i c a t i o n i n oxygen i s c l e a r l y more c h a r a c t e r i s t i c o f Re t h a n W, which i s n e a r l y i n e r t . The Re-W system f o r g r a p h i t e g a s i f i c a t i o n i n hydrogen i s j u s t the o p p o s i t e t o g a s i f i c a t i o n i n o x y g e n . Rhenium-tungsten i s com p l e t e l y i n e r t f o r g r a p h i t e g a s i f i c a t i o n i n hydrogen! This r e s u l t argues t h a t under r e d u c i n g c o n d i t i o n s t h e o u t e r s u r f a c e of t h e Re-W metal p a r t i c l e s are covered by an " o u t e r s k i n " o f W. The W s u r f a c e s e g r e g a t i o n c o m p l e t e l y r e t a r d s t h e a c t i v i t y of one o f the most a c t i v e g r a p h i t e h y d r o - g a s i f i c a t i o n c a t a l y s t s known. The CAEM s t u d i e s o f Re, W and Re-W on g r a p h i t e are o n l y one a s p e c t o f t h e i r i n t e r e s t ing c h e m i s t r y . C h e m i s o r p t i o n and x - r a y d i f f r a c t i o n s t u d i e s o f the Re, W and Re-W systems shows t h a t W0 on a c t i v a t e d carbon t o be SMSI support ( 1 , 2 ) . The H and CO c h e m i s o r p t i o n uptake f o r W on a c t i vated samples reduced at 500°C i n f l o w i n g Ho was v e r y low d e s p i t e W metal p a r t i c l e s b e i n g d e t e c t e d by x - r a y d i f f r a c t i o n , see Tables 1 and 2. Since bulk WO3 does not reduce u n t i l 550°C we s u s p e c t e d oxygen c o n t a m i n a t i o n of the W metal p a r t i c l e s u r f a c e . Reduction of both a 10 and a 25% W on a c t i v a t e d carbon sample at 700°C i n c r e a s e d both the H and CO c h e m i s o r p t i o n t o t h a t expected o f a d i s p e r s e d metal p a r t i c l e o f ca 10 nm d i a m e t e r , see Tables 1 and 2 . 2

2

+ 4

2

o

n

S

l

0

i

n

t

e

r

a

c

t

n

l

e

a

d

t

0

a

n

d

H

c h e m l

s o r

2

2

2

+ Z

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 31, 2018 | https://pubs.acs.org Publication Date: February 10, 1986 | doi: 10.1021/bk-1986-0298.ch019

2

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2

2

2

2

X

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l o n

MURRELL ET AL.

19.

197

Interaction for Re on WO

x

Table I . Hydrogen C h e m i s o r p t i o n and X - r a y D i f f r a c t i o n S t u d i e s o f W, Re, and Re-W on C a r b o l a c

Reduction Temperature(°C)

Metal S u r f a c e A r e a by Ho Chemisorptionfnr/g)

Metal S u r f a c e Area Measured by X - r a y L i n e Broadening(mVg)

10% W/C

500

0.53

Very Broad L i n e

10% W/C

700

15.9

43

25% W/C

500

2.61

50

25% W/C

700

10.8

28

10% Re/C

300

91.5

NV

10% Re/C

500

37.9

23


Sample on Carbolac

1

2

10% Re-10% W/C

300

13.6

NV

10% Re-10% W/C

500

9.88

-60

2

The Ho c h e m i s o r p t i o n blank on C a r b o l a c was found t o be 0.056 c c / g reduced a t 300° o r 500°C and 0.067 cc/g reduced a t 700°C. This small gas uptake on t h e Carbolac support was s u b t r a c t e d from t h e v a l u e s f o r a l l t h e samples i n t h i s t a b l e . Not

visible.

In c o n t r a s t t o t h e s l u g g i s h r e d u c t i o n o f W on a c t i v a t e d carbon 10% Re on a c t i v a t e d carbon reduced r e a d i l y a t 300°C as c o n f i r m e d by H and CO c h e m i s o r p t i o n . T h i s f a c t w i l l become i m p o r t a n t when com p a r i s o n i s made t o Re-W on a c t i v a t e d c a r b o n . Reduction o f Re on a c t i v a t e d carbon i n f l o w i n g H a t 500°C f o r 1 h r . r e s u l t e d i n about 50% g a s i f i c a t i o n o f t h e a c t i v a t e d c a r b o n . Considerable s i n t e r i n g of t h e 500°C reduced sample occured compared t o t h e 300°C reduced sam p l e as c o n f i r m e d both by x - r a y d i f f r a c t i o n and by H and CO c h e m i sorption. R e d u c t i o n o f a sample o f 10% Re on a c t i v a t e d carbon a t 700°C i n f l o w i n g H? r e s u l t e d i n n e a r l y complete carbon g a s i f i c a t i o n i n 5 m i n . The high carbon g a s i f i c a t i o n a c t i v i t y o f Re on g r a p h i t e i s c o n s i s t e n t w i t h t h e observed g a s i f i c a t i o n o f a c t i v a t e d c a r b o n . A 10 w t . % Re-10 w t . % W on a c t i v a t e d carbon sample was next i n v e s t i g a t e d by H and CO c h e m i s o r p t i o n . The sample was prepared by f i r s t i n t r o d u c i n g t h e W component f o l l o w e d by i n t r o d u c t i o n o f t h e Re component. The Ho and CO c h e m i s o r p t i o n o f t h e Re-W on a c t i v a t e d carbon reduced a t 300°C was reduced by a f a c t o r o f 10 compared t o Re on a c t i v a t e d c a r b o n . T r i v i a l s i n t e r i n g o f Re t o g i v e l a r g e p a r t i c l e s was d i s c o u n t e d as x - r a y d i f f r a c t i o n showed t h a t no Re p a r t i c l e c o u l d be d e t e c t e d . I n c r e a s i n g t h e r e d u c t i o n temperature t o 500°C f o r Re-W on carbon f a i l e d t o i n c r e a s e t h e H and CO c h e m i s o r p t i o n uptake. A l s o , t h e carbon g a s i f i c a t i o n observed f o r t h e 10% Re on 2

2

2

2

2


198

STRONG METAL-SUPPORT INTERACTIONS

a c t i v a t e d carbon sample was c o m p l e t e l y suppressed i n t h e case o f ReW on a c t i v a t e d c a r b o n . These o b s e r v a t i o n argues t h a t Re i n t e r a c t s w i t h t h e h i g h l y d i s p e r s e d W0 phase on a c t i v a t e d carbon a t both 300 and 500°C i n H ^ . This i n t e r a c t i o n a l t e r s both c h e m i s o r p t i o n and carbon g a s i f i c a t i o n c h a r a c t e r i s t i c o f t h e Re component. The model X


Table I I . Carbon Monoxide C h e m i s o r p t i o n and X - r a y D i f f r a c t i o n S t u d i e s o f W, Re, and Re-W on C a r b o l a c

Reduction Temperature(°C)

Metal Surface A r e a by Ho « Chemisorptionfm /g)

10% W/C

500

2.86

Sample on Carbolac

1

z

Metal S u r f a c e Area Measured by X - r a y L i n e Broadening(nr/g)

Very Broad

10% W/C

700

13.1

43

25% W/C

500

6.29

50

25% W/C

700

17.4

28

10% Re/C

300

123

NV

10% Re/C

500

19.0

23

10% Re-10% W/C

300

21.2

NV

10% Re-10% W/C

500

12.7

60

2

2

The CO c h e m i s o r p t i o n blank on Carbolac was found t o be 0.09 cc/g when reduced a t 500°C and zero when reduced a t 700°C. The uptake on t h e C a r b o l a c support was s u b t r a c t e d from t h e v a l u e s f o r a l l t h e samples d e s c r i b e d i n t h i s t a b l e employing t h e double i s o t h e r m technique. t h a t p a r t i a l r e d u c t i o n of t r a n s i t i o n metal o x i d e phases leads t o t h e SMSI phenomenon must be expanded t o a d i s p e r s e d t r a n s i t i o n metal o x i d e phase on a carbon s u p p o r t . CAEM s t u d i e s s u p p o r t t h e view t h a t W0 on carbon i s a h i g h l y d i s p e r s e d and s t r o n g l y i n t e r a c t i n g phase w i t h the carbon s u b s t r a t e . A recent paper (18) d e s c r i b i n g Pt-Mo b i m e t a l l i c c a t a l y s t s supported on X - z e o l i t e s r e p o r t s a s i g n i f i c a n t d e c r e a s e i n H and CO c h e m i s o r p t i o n as Mo i n t e r a c t s w i t h t h e s u r f a c e of t h e 1.0 nm Pt p a r t i c l e s i n t h e z e o l i t e c a g e s . The p a r a l l e l s among t h e r e s u l t s f o r Pt-Mo on X - z e o l i t e , t h e r e s u l t s f o r Re-W on a c t i v a t e d carbon i n t h i s p a p e r , and t h e r e s u l t s f o r SMSI systems on T i 0 (1,2,7,8,13) are s t r i k i n g . X

2

2


19.

M U R R E L L E T AL.

Interaction for Re on WO

x

199

References 1. 2. 3.


4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Tauster, S. J., Fung, S. C. and Garten, R. L . ; J . Am. Chem. Soc. 1978, 100, 170. Tauster, S. J. and Fung, S. C.; J . Catal. 1978, 54, 29. Lund, C. R. F. and Dumesic, J . A . ; J . Phys. Chem. 1981, 85, 3175. Yermakov, Yu. I . , Kuznetsov, Β. N. and Zakharov, V. Α., "Ca talysis by Supported Complexes"; Elsevier, 1981. Yuen, S., Chen, Υ., Kubsh, J. E. and Dumesic, J . Α.; J. Phys. Chem. 1982, 86, 3022. Soled, S., Murrell, L . , Wachs, I. and McVicker, G.; Am. Chem. Soc. Div. Pet. Chem. Prepr. 1983, 28, 1310. Baker, R. T. K., Prestridge, Ε. B. and Garten, R. L.; J. Catal. 1979, 59, 293. Baker, R. Τ. Κ., Prestridge, Ε. B. and Murrell, L. L.; J . Catal. 1983, 79, 348. Murrell, L. L. and Yates, D. J. C . ; Stud. Surf. Sci. Catal. 1981, 7, 1470. Basset, J . M. and Ugo, R., In R. Ugo (Ed.); "Aspects of Homo geneous Catalysis", Reidel: Dordecht, 1976; Vol. I I I , p. 170. Anderson, J. R., Elmes, D. S., Howe, R. F. and Mainwaring, D. E.; J . Catal. 1977, 50, 508. Peri, J. B.; J. Phys. Chem. 1982, 86, 1615. Murrell, L. L. and Garten, R. L.; Applications of Surface Sci ence, (in press). Murrell, L. L. and Dispenziere, N. C. Jr., (submitted to J. Applied Catalysis). Baker, R. Τ. Κ., Chludzinski, J . J. Jr., Dispenziere, N. C. J r . and Murrell, L. L . ; Carbon, 1983, 21, 579. Baker, R. Τ. Κ., Sherwood, R. D. and Dumesic, J. Α.; J. Catal. 1980, 62, 221. Baker, R. Τ. Κ., Sherwood, R. D. and Dumesic, J . Α.; J. Catal. 1980, 66, 56. T r i , T. M., Cordy, J - P . , Gallezot, P . , Massandier J., Primet, M., Vedrine, J. C. and Imelik, B.; J . Catal. 1983, 79, 396.

RECEIVED September 17, 1985


Supported on Activated Carbon - American Chemical Society

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