Catalytic Activation of Carbon Monoxide - American Chemical Society

6 The Water Gas Shift Reaction as Catalyzed by Ruthenium Carbonyl in Acidic Solutions P E T E R C . F O R D , P A U L Y A R R O W , and HAIM C O H E N

Downloaded by TUFTS UNIV on October 3, 2016 | http://pubs.acs.org Publication Date: May 5, 1981 | doi: 10.1021/bk-1981-0152.ch006

Department of Chemistry, University of California, Santa Barbara, C A 93106

The p a s t s e v e r a l y e a r s have s e e n renewed i n t e r e s t i n t h e c a t a l y s t c h e m i s t r y o f t h e w a t e r g a s s h i f t r e a c t i o n (WGSR, E q . 1 ) . CO + H 0 5 = i 2

CO + H

(1)

2

T h i s h a s been l a r g e l y s t i m u l a t e d b y t h e r e c o g n i t i o n t h a t t h e s h i f t r e a c t i o n i s a key step i n t h e p r o d u c t i o n o f t h e copious hydrogen a n d / o r s y n t h e s i s g a s (H2/CO) r e q u i r e d f o r t h e g a s i f i c a t i o n o r liquifaction of coal. I n 1977, we r e p o r t e d t h a t r u t h e n i u m c a r b o n y l i n a l k a l i n e aqueous e t h o x y e t h a n o l s o l u t i o n formed a homogeneous WGSR c a t a l y s t 01,2,) . S u b s e q u e n t l y , a number o f o t h e r r e p o r t s o f homogeneous s h i f t r e a c t i o n c a t a l y s t s have a p p e a r e d (3-12). Our r a t i o n a l e f o r c h o o s i n g a n a l k a l i n e s o l u t i o n r e a c t i o n medium f o r o u r i n i t i a l s t u d i e s d e r i v e d f r o m t h e h i s t o r i c a l p r e c e d e n t by H e i b e r (14) t h a t m e t a l c a r b o n y l s u n d e r g o r e a c t i o n s w i t h aqueous b a s e s t o g i v e m e t a l c a r b o n y l h y d r i d e a n i o n s ( e . g . , Eq. 2 ) . A c i d i f i c a t i o n o f t h e s e s o l u t i o n s r e l e a s e d b o t h Fe(C0)

5

+ 30H~
σ* t r a n s i t i o n o f t h e c l u s t e r m e t a l - m e t a l bond f r a m e w o r k (20) a n d t h a t o t h e r r u t h e n i u m c l u s t e r s show s i m i l a r n e a r UV o r v i s i b l e a b s o r p t i o n b a n d s , i t seems l i k e l y that the ruthenium c a r b o n y l s p e c i e s i n the a c i d i c diglyme c a t a l y s t a r e mononuclear o r d i n u c l e a r . The k i n e t i c s r e s u l t s o f t h e b a t c h r e a c t o r r u n s l e a d t o t h e f o l l o w i n g q u a l i t a t i v e o b s e r v a t i o n s : A t l o w CO p r e s s u r e s ( l e s s t h a n a b o u t 1 atm) t h e c a t a l y s i s a p p e a r s t o be f i r s t o r d e r i n r u t h e n i u m o v e r t h e r a n g e 0.018 M t o 0.072 M and a l s o i n P a s i l l u s t r a t e d by the l o g P v s t i m e p l o t s o f F i g . 2 and a l s o shown by t h e method o f i n i t i a l r a t e s . Changes i n t h e s u l f u r i c a c i d and w a t e r c o n c e n t r a t i o n s o v e r t h e r e s p e c t i v e r a n g e s 0.25 M t o 2.0 M and 4 M t o 12 M have r e l a t i v e l y s m a l l e f f e c t s o n t h e c a t a l y s i s r a t e s , a l t h o u g h t h e f u n c t i o n a l i t i e s a r e c o m p l i c a t e d and show c o n c a v e r a t e v s c o n c e n t r a t i o n c u r v e s w i t h maximum r a t e s c o

2

=

m a

3

5

3

1 2

c

c

o

Ford; Catalytic Activation of Carbon Monoxide ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

o

CATALYTIC ACTIVATION OF CARBON MONOXIDE


98

Figure 1. UV-visible spectrum (0ΛΟcm cell) of a catalyst solution prepared from Ru (CO) (3 X 10 Μ), H SO (0.5M), H 0 (8.0M) under a CO atmos phere (Pco = 1 atm) in diglyme at 100°C. The upper curve represents the spectrum 5 min after the solution was prepared at this temperature, the lower curve is the spectrum after 6 h. 3

3

12

2

h

2

500

300

[Ru3(C0)12] 1

.006 M

II

.012 M

III

.024 M

0.5

0

III

II l 10

0

20 Time (hours)

Figure 2. First-order rate plots for the consumption of CO in a 100-mL batch reactor (catalyst solution is 5 mL of aqueous diglyme with 8.5M H O 1.0M H SO, Τ = 100°C and ? o (initial) = 0.9 atm). Slopes of the three linear plots are 2 X 10' , 4.4 χ 10 , and 9.3 X 10~ h' for the respective Ru (CO) initial concentra tions of (I) 0.006U, (II) 0.012M, and (III) 0.024U. 2

C

2

2

2

1

3

I2


t

2

lf

6.

FORD ET AL.

99

Ru-Catalyzed Water Gas Shift

f o u n d a t ~4 M H 2 O and a t -0.5 M H S0i, w i t h P o « However, u s i n g H3POU, CH3CO2H o r C F C 0 H i n s t e a d a s t h e added a c i d decreased the a c t i v i t y markedly. The s y s t e m i s t e m p e r a t u r e s e n s i t i v e w i t h a n a c t i v a t i o n e n e r g y o f a b o u t 14 k c a l / m o l e d e r i v e d from a l i n e a r A r r h e n i u s p l o t f o r t h e c a t a l y s i s r a t e s over t h e t e m p e r a t u r e r a n g e 90-140°C i n t h e l o w P region. A dramatic t u r n a r o u n d i n a c t i v i t y o c c u r s a t CO p r e s s u r e s much l a r g e r t h a n 1 atm w i t h t h e p r o d u c t i o n o f H and C 0 b e i n g i n h i b i t e d b y increasing P under t h e c o n d i t i o n s . Notably, a batch reactor r u n i n i t i a t e d a t l o w p r e s s u r e s and d e m o n s t r a t e d t o be a c t i v e d i s p l a y s a much l o w e r r a t e when t h e b u l b i s c h a r g e d w i t h a h i g h P . The i n i t i a l c a t a l y t i c a c t i v i t y i s r e g e n e r a t e d when t h e system i s r e c h a r g e d a t t h e l o w e r P , t h u s showing t h e i n h i b i t i o n at higher P t o be r e v e r s i b l e . Another c h a r a c t e r i s t i c o f the batch r e a c t o r runs i s that a f t e r a number o f f l u s h i n g / r e c h a r g i n g c y c l e s ( s e e E x p e r i m e n t a l ) o v e r a p e r i o d o f d a y s t h e r e i s a marked d e g r a d a t i o n o f t h e system's c a t a l y t i c a c t i v i t y . Whether t h i s i s t h e r e s u l t o f i r r e v e r s i b l e transformations o f the catalyst to inactive species ( f o r example i n t r o d u c t i o n o f a i r t o a h o t c a t a l y s t s o l u t i o n causes i r r e v e r s i b l e d e s t r u c t i o n o f the a c t i v i t y ) o r o f the l o s s of v o l a t i l e ruthenium s p e c i e s d u r i n g the freeze/thaw, degassing/ recharging cycles i s not clear. The l a t t e r i s c e r t a i n l y a m a j o r c o n t r i b u t o r t o the slow d e g r a d a t i o n o f the a c t i v i t y i n the f l o w r e a c t o r runs where, d e s p i t e t h e presence o f a condensor designed t o r e t u r n s o l v e n t and c a t a l y s t t o t h e r e a c t i o n v e s s e l , v o l a t i l e r u t h e n i u m c a r b o n y l s p e c i e s a r e t r a p p e d downstream f r o m t h e reactor (see below). I f a fresh, active catalyst i n acidic d i g l y m e i s c o o l e d t o room t e m p e r a t u r e a f t e r o p e r a t i n g u n d e r a l o w P , t h e s o l u t i o n i s l i g h t y e l l o w and u n d e r g o e s a s l o w t r a n s f o r m a t i o n t o g i v e Ru3(CO)i which p r e c i p i t a t e s from s o l u t i o n Over a p e r i o d o f s e v e r a l d a y s . A s much a s 95% o f t h e o r i g i n a l R u 3 ( C 0 ) i c a n be r e c o v e r e d u n d e r t h e s e c o n d i t i o n s . I n contrast a s o l u t i o n o p e r a t i n g under a h i g h e r P (2.7 atm) p r e c i p i t a t e s R u 3 ( C 0 ) i q u i c k l y upon c o o l i n g i n d i c a t i n g t h a t t h e p r i n c i p a l ruthenium s p e c i e s p r e s e n t under such c o n d i t i o n s i s R u ( C O ) o r one e a s i l y c o n v e r t e d t o t h i s c l u s t e r . = 1

2

3

a t m

C

2

c

o

2

2

c o

c o

c o


c

o

c o

2

2

c

o

2

3

1 2

In S i t u Spectroscopic Studies: B e s i d e s t h e e l e c t r o n i c s p e c t r a l s t u d i e s n o t e d a b o v e , we h a v e also c a r r i e d out i n s i t u studies o f the a c i d i c ruthenium c a t a l y s t u s i n g nmr and i n f r a r e d s p e c t r a l t e c h n i q u e s . A k e y s e t o f o b s e r v a t i o n s d e r i v e f r o m t h e *H and C nmr s p e c t r a o f a n o p e r a t i n g c a t a l y s t a t 90° and P 1 atm w h i c h i n d i c a t e t h e p r e s e n c e o f o n l y one m a j o r r u t h e n i u m s p e c i e s . The p r o t o n s p e c t r u m shows a s h a r p s i n g l e t a t 24.0 τ w h i c h r e m a i n s s u c h when t h e s o l u t i o n i s c o o l e d t o room t e m p e r a t u r e , a l t h o u g h t h e s l o w f o r m a t i o n o f o t h e r s p e c i e s was o b s e r v e d o v e r a p e r i o d o f h o u r s at the l a t t e r conditions. The ^ - d e c o u p l e d C spectrum o f the 1 3

c

o

1 3


CATALYTIC

100

ACTIVATION

OF

CARBON

MONOXIDE

o p e r a t i n g c a t a l y s t a l s o shows a s i n g l e t a t 198.2 ppm d o w n f i e l d f r o m TMS) w h i c h becomes a d o u b l e t (Jc-H=10 Hz) when p r o t o n coupled. The same s p e c t r u m i s s e e n when t h e s o l u t i o n i s c o o l e d t o room t e m p e r a t u r e . N o t a b l y t h e s e nmr s p e c t r a a r e i n c o n s i s t e n t w i t h t h o s e o f H 2 R u ( C 0 ) u o r HRu(C0)"£ ( T a b l e I ) w h i c h s h o u l d be k e y s p e c i e s i n a c a t a l y s i s c y c l e b a s e d s o l e l y on m o n o n u c l e a r c o m p l e x e s . For e x a m p l e , t h e p r o t o n r e s o n a n c e a t 24.0 τ i s c o n s i d e r a b l y h i g h e r f i e l d than those seen f o r the mononuclear s p e c i e s w i t h t e r m i n a l h y d r i d e s (17.6 and 17.2 τ, r e s p e c t i v e l y ) and f a l l s i n t h e r e g i o n where b r i d g i n g h y d r i d e s a r e n o r m a l l y s e e n . Further c o m p a r i s o n o f t h e s p e c t r a i n T a b l e I shows t h a t t h e c a t a l y s t s o l u t i o n C resonance occurs at a p o s i t i o n d o w n f i e l d from those f o u n d f o r c a t i o n i c r u t h e n i u m c a r b o n y l h y d r i d e s s u c h a s HRu(C0)+ and HRu3(C0)"i2 i i n a r e g i o n more c o n s i s t e n t w i t h a n e u t r a l o r a n i o n i c c o m p l e x . Thus we c o n c l u d e t h a t t h e p r i n c i p a l s p e c i e s p r e s e n t i n t h e a c i d i c c a t a l y s t s o l u t i o n has a s i n g l e h y d r i d e , i s n e u t r a l o r a n i o n i c and i s f l u x i o n a l a t room t e m p e r a t u r e and a b o v e . Given the c o n c l u s i o n from the U V - v i s i b l e s p e c t r a t h a t the n u c l e a r i t y o f t h e c o m p l e x i s l e s s t h a n t h r e e ( s e e a b o v e ) and t h e c o n c l u s i o n f r o m t h e nmr d a t a t h a t t h e h y d r i d e i s b r i d g i n g , t h e c i r c u m s t a n t i a l evidence i s that the p r i n c i p a l ruthenium species under the c a t a l y s i s c o n d i t i o n s i s a d i n u c l e a r complex. A l o g i c a l p r o p o s i t i o n i s t h a t t h i s i s t h e d i n u c l e a r a n i o n HRu (C0)e w h i c h i s unknown f o r r u t h e n i u m , a l t h o u g h t h e i r o n a n a l o g i s known and has been shown t o be f l u x i o n a l e v e n t o l o w t e m p e r a t u r e s ( 2 1 ) . Attempts to o b t a i n i n s i t u i n f r a r e d s p e c t r a of t h i s c a t a l y s t system u t i l i z i n g a h i g h temperature i n f r a r e d c e l l s i m i l a r to t h a t d e s c r i b e d by K i n g (25) h a v e met w i t h m i x e d s u c c e s s o w i n g t o t h e s t r o n g a b s o r p t i o n o f t h e s o l v e n t medium i n t h e c a r b o n y l region. B r o a d p e a k s a t 2084, 2040, 2013 and 1 9 6 0 ( b r ) cm" a l l o f medium t o s t r o n g i n t e n s i t y w e r e o b s e r v e d f o r t h e r e a c t i o n s o l u t i o n a t 100°C u n d e r an a t m o s p h e r e o f CO. A survey of r u t h e n i u m c a r b o n y l i n f r a r e d s p e c t r a i n d i c a t e t h a t t h e s e bands a r e not c o n s i s t e n t w i t h those expected f o r Ru(C0)s, R u ( C O ) i 2 , H2Ru(C0)i* o r R u ( C O ) among t h e s i m p l e r known s p e c i e s o f t h i s type. Lowering the temperature of the r e a c t i o n s o l u t i o n to 25°C does n o t l e a d t o m a j o r d i f f e r e n c e s i n t h e s p e c t r u m a l t h o u g h t h e r e a r e some c h a n g e s i n t h e r e l a t i v e peak h e i g h t s . Whether t h i s i s the r e s u l t of s h i f t s i n the c o n c e n t r a t i o n s of s e v e r a l s p e c i e s p r e s e n t i n s o l u t i o n o r o f medium e f f e c t s on t h e band s h a p e s i s n o t c l e a r ; h o w e v e r , t h e f o r m e r i s an u n l i k e l y p r o s p e c t g i v e n t h e nmr r e s u l t s n o t e d above t h a t t h e p r o t o n and c a r b o n - 1 3 s p e c t r a do n o t u n d e r g o i m m e d i a t e c h a n g e s upon l o w e r i n g t h e c a t a l y s t s o l u t i o n t e m p e r a t u r e f r o m 90° t o 25°.


13

a

n

(

2

1

3

2

9

A Proposed Mechanism f o r C a t a l y s i s : The i n f o r m a t i o n c u r r e n t l y a v a i l a b l e f o r t h e a c i d i c r u t h e n i u m c a t a l y s t s y s t e m , i s c o n s i s t e n t w i t h a c y c l i c mechanism s u c h as


6.

FORD

X

T a b l e I : H and

13


Complex

Ru^CO)^

1 3

C N.M.R. D a t a f o r R u t h e n i u m C a r b o n y l Complexes.

C0(ppm)

^(τ)

J^C-^HiHz)

22 29.3

HRujCO)^"

203.7

25.8

HRu (CO)

202.2

22.6

6

198.2

27.0

7.3

1 ] L

"

H Ru (CO) ~ l t

1 2

HRu (CO) NO 3

Ru (C0) 3

1 0

3

2

2,22 23 T h i s work

17.6

180.4 178.4

HRu(CO)*

2

(average)

202.9,195.5 21.9 194.5,185.8

192.5 190.1

HRu (CO)|

22

198.0

1 2

22

10.3 ( t r a n s ) 5.9 ( c i s )

220.0

2

3

References

223.7

2

H^u^CCO)^ ""

3

101

Ru-Catalyzed Water Gas Shift

ET AL.

191.0,188.0 184.5,178.9

17.2

9

Q

β

24

7 (cis) (trans) 4 (cis) 24 ( t r a n s )

T h i s work

T h i s work


CATALYTIC

102

ACTIVATION

OF

CARBON

MONOXIDE

i l l u s t r a t e d by Scheme I I . The k e y f e a t u r e s o f t h i s scheme a r e t h a t a t low P t h e r u t h e n i u m i s p r e s e n t l a r g e l y a s t h e HRu (CO)7 c o

2

CO HRu (C0) 2

C0

2

+

r

Ru(C0)

5

HRuCCO)^

8

If

H

HRu (C0) (C0 H) 2

8

-H

H Ru(C0)

2

2


H2O-

? Ru (C0)9

Ru(CO)

2

4

CO Ru(CO)1 -CO

Ru(CO). Scheme I I

a n i o n and t h e r a t e l i m i t i n g s t e p i s t h e r e a c t i o n o f t h i s i o n w i t h CO t o c l e a v e t h e m e t a l - m e t a l l i n k a g e g i v i n g R u ( C 0 ) s p l u s HRu(CO)^. Under s u c h c o n d i t i o n s t h e r a t e s h o u l d be f i r s t o r d e r i n b o t h [Ru] and P s i n c e t h e c o n c e n t r a t i o n o f H R u ( C 0 ) e w o u l d be p r o p o r t i o n a l to the t o t a l c o n c e n t r a t i o n of r u t h e n i u m p r e s e n t . The n e x t s t e p w o u l d be p r o t o n a t i o n o f H R u ( C 0 K t o g i v e t h e d i h y d r i d e w h i c h u n d e r goes r e d u c t i v e e l i m i n a t i o n o f d i h y d r o g e n . Although the f i r s t pK of H Ru(C0) i s as y e t unknown, v a l u e s f o r t h e i r o n and osmium a n a l o g s (26) c l e a r l y i n d i c a t e t h a t HRu(CO)^ s h o u l d be s u f f i c i e n t l y s t r o n g a b a s e t o be f u l l y p r o t o n a t e d u n d e r t h e s o l u t i o n c o n d i t i o n s . The d i h y d r i d e i s r e p o r t e d t o be u n s t a b l e i n t o l u e n e s o l u t i o n above -20°C; however i n t h a t c a s e e x c e s s CO was n o t p r e s e n t and t h e p r o d u c t s p r e s u m a b l y w e r e r u t h e n i u m c l u s t e r s (24) ( s e e b e l o w ) . I n h i b i t i o n of c a t a l y s i s at high P may be e x p l a i n e d as r e f l e c t i n g c o n d i t i o n s where t h e e q u i l i b r i u m c o

a

2

2

l t

c o

CO + R u ( C 0 ) 2

9

ς=±

2 Ru(C0)

5

(3)

becomes a d o m i n a n t f a c t o r i n t h e c a t a l y s i s . Support f o r t h i s p r o p o s i t i o n comes f r o m t h e f l o w r e a c t o r k i n e t i c s c u r r e n t l y i n progress. At v e r y low ruthenium c o n c e n t r a t i o n s , f i r s t o r d e r b e h a v i o r i n [Ru] a p p a r e n t l y no l o n g e r h o l d s and t h e r e a c t i o n k i n e t i c s i n d i c a t e o r d e r s c l o s e r t o two t h a n one, t h u s s u p p o r t i n g t h e p o s s i b l e i m p o r t a n c e o f Eq. (3) t o t h e o v e r a l l c a t a l y s i s r a t e u n d e r t h e s e c o n d i t i o n s . F u r t h e r s u p p o r t i n g e v i d e n c e comes f r o m a c o m p l i c a t i o n i n the f l o w r e a c t o r k i n e t i c s . These s y s t e m s show


6.

FORD

ET AL.

103

Ru-Caialyzed Water Gas Shift

slow decreases i n a c t i v i t y over a p e r i o d o f time owing t o the l o s s of r u t h e n i u m f r o m t h e s o l u t i o n , a p r o b l e m e s p e c i a l l y a p p a r e n t a t h i g h P . E x a m i n a t i o n o f a low t e m p e r a t u r e t r a p downstream from t h e c a t a l y s i s v e s s e l showed t h e p r e s e n c e o f a c l e a r s o l u t i o n , m o s t l y aqueous d i g l y m e , w h i c h when warmed t o room t e m p e r a t u r e t u r n e d y e l l o w and s l o w l y p r e c i p i t a t e d R u ( C 0 ) i 2 . Thus t h e g a s s t r e a m o f t h e f l o w s y s t e m s e r v e d t o sweep a v o l a t i l e r u t h e n i u m s p e c i e s out o f the r e a c t i o n s o l u t i o n , p r o b a b l y R u ( C 0 ) but p o s s i b l y l ^ R u C C O ) ^ . T h e r e i s a n o t h e r p o t e n t i a l s o u r c e o f t h e CO i n h i b i t i o n i n Scheme I I . S t u d i e s i n p r o g r e s s i n t h i s l a b o r a t o r y (27) have shown t h a t t h e i n i t i a l s t e p i n t h e d e c o m p o s i t i o n and c l u s t e r i f i c a t i o n o f H2Ru(G0)i» i n s o l u t i o n i s n o t H e l i m i n a t i o n b u t i s CO dissociation. Thus i t i s p o s s i b l e t h a t t h e e l i m i n a t i o n o f H from H R u ( C 0 ) t i r e q u i r e s p r i o r CO d i s s o c i a t i o n v i a a mechanism s i m i l a r to t h a t proposed f o r H e l i m i n a t i o n from H 0 s ( C 0 ) (28) a n d t h u s w o u l d be i n h i b i t e d a t t h e h i g h e r P . T h i s q u e s t i o n i s c u r r e n t l y being i n v e s t i g a t e d . c o

3

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c o

Experimental

Procedures

I n f r a r e d s p e c t r a were r e c o r d e d o n a P e r k i n - E l m e r m o d e l 283 spectrophotometer. P r o t o n and c a r b o n - 1 3 n u c l e a r m a g n e t i c r e s o n a n c e s p e c t r a w e r e r e c o r d e d o n V a r i a n XL-100 and CFT-20 s p e c t r o m e t e r s , r e s p e c t i v e l y , o p e r a t i n g i n t h e p u l s e d mode. UV-visible s p e c t r a were r e c o r d e d o n a C a r y 118C r e c o r d i n g s p e c t r o m e t e r e q u i p ped w i t h a t h e r m o s t a t e d c e l l compartment. Gas s a m p l e a n a l y s e s were p e r f o r m e d o n a H e w l e t t - P a c k a r d 5830A p r o g r a m m a b l e g a s c h r o m a t o g r a p h , c a l i b r a t e d f o r t h e a p p r o p r i a t e s u b s t r a t e s . The c o l u m n s u s e d were C a r b o s i e v e Β (Mesh 80-100) c o l u m n s o b t a i n e d f r o m H e w l e t t P a c k a r d a n d t h e c a r r i e r gas u s e d was a L i n d e p r e p a r e d 8.5% H / 9 1 . 5 % He m i x t u r e . Gas s a m p l e s w e r e t a k e n w i t h A n a l y t i c a l P r e s s u r e Lok g a s s y r i n g e s o b t a i n e d f r o m P r e c i s i o n S a m p l i n g Corporation. C a l i b r a t i o n c u r v e s f o r the chromatographs and sampl i n g p r o c e d u r e s w e r e p r e p a r e d p e r i o d i c a l l y f o r CO, CH^, C 0 , a n d H f o r gas sample s i z e s r a n g i n g f r o m 0.05 t o 1.5 mL STP o f t h e g a s . These c a l i b r a t i o n c u r v e s were l i n e a r f o r CO, CH^, a n d C 0 b u t n o t f o r H . C a t a l y t i c a c t i v i t y a n d k i n e t i c s r u n s w e r e l a r g e l y done i n a l l - g l a s s b a t c h r e a c t o r s (100 mL) c o n s i s t i n g o f r o u n d b o t t o m f l a s k s w i t h s i d e a r m s t o p c o c k s d e s i g n e d f o r a t t a c h m e n t t o a vacuum l i n e and f o r p e r i o d i c gas p h a s e s a m p l i n g . Typically, theRu (C0) and s o l v e n t medium were added t o t h e r e a c t o r v e s s e l ( a t room t e m p e r a t u r e ) w h i c h was t h e n a t t a c h e d t o t h e vacuum l i n e , a n d t h e s o l u t i o n was d e g a s s e d by f reeze-pump-thaw c y c l e s t h e n c h a r g e d w i t h a CO/CH^ (94/6) gas m i x t u r e ( L i n d e ) a t t h e d e s i r e d p r e s s u r e . The r e a c t o r s were s u s p e n d e d i n t h e r m o s t a t e d o i l b a t h s a n d t h e s o l u t i o n s s t i r r e d m a g n e t i c a l l y . The s y s t e m s w e r e p e r i o d i c a l l y f l u s h e d a n d r e c h a r g e d w i t h t h e CO/CH^ m i x t u r e i n a manner s i m i l a r t o t h a t d e s c r i b e d a b o v e . Gas s a m p l e s were removed b y gas s y r i n g e a n d t h e c o m p o s i t i o n s were a n a l y z e d w i t h methane s e r v i n g a s a n i n t e r n a l c a l i b r a n t , thus a l l o w i n g f o r the c a l c u l a t i o n o f the a b s o l u t e 2

2

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CATALYTIC

104

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CARBON

MONOXIDE

q u a n t i t i e s o f H 2 and CO2 p r o d u c e d and CO consumed. These v a l u e s were c o r r e c t e d f o r t h e s m a l l b a c k g r o u n d s i g n a l s n o t e d when g a s s a m p l e s f r o m c o n t r o l r e a c t i o n s i n t h e a b s e n c e o f added c a t a l y s t were a n a l y z e d . Acknowledgements :


T h i s r e s e a r c h was s u p p o r t e d b y t h e D e p a r t m e n t o f E n e r g y , O f f i c e o f B a s i c Energy S c i e n c e s . I n i t i a l s t u d i e s on the a c i d i c ruthenium c a r b o n y l c a t a l y s t system were c a r r i e d out by Dr. C h a r l e s Ungermann i n t h i s g r o u p , P r o f e s s o r R . G . R i n k e r and h i s r e s e a r c h g r o u p o f t h e UCSB C h e m i c a l E n g i n e e r i n g D e p a r t m e n t c o n t r i b u t e d s i g n i f i c a n t l y t o t h e d i s c u s s i o n and i n t e r p r e t a t i o n o f t h e s e results.

Abstract: Solutions prepared from Ru (CO) in acidic aqueous diglyme solutions are shown to be catalysts for the water gas shift reaction under reasonably mild conditions (100°C, P =1 atm). This system shows an induction period of about six hours before constant activity is attained during which the Ru (CO) undergoes complete conversion to another ruthenium carbonyl complex. In situ nmr studies suggest this species to be the HRu (CO)-8 ion. Kinetic studies show complex rate profiles; however, a key observation is that the catalysis rate is first order in P at low pressures (P

Catalytic Activation of Carbon Monoxide - American Chemical Society

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