Homogeneous Catalysis of the Water Gas Shift Reaction - American

9 Homogeneous Catalysis of the Water Gas Shift Reaction: Pentacarbonyliron and the Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 20, 2016 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch009

Metal Hexacarbonyls as Active Catalyst Precursors

1

C. C. FRAZIER, R. M. HANES, A. D. KING, JR., and R. B. KING Department of Chemistry, University of Georgia, Athens, GA 30602 Methanol or 1-butanol solutions of the mononuclear metal carbonyls M(CO) (M = Cr, Mo, and W) and Fe(CO) in the presence of aqueous sodium or potassium hydroxide are active homogeneous catalysts for the water gas shift reaction (CO + H O--C O + H ). The effects of temperature, pressure, and base concentration on the rate of hydrogen production from C O and H O in the presence of Fe(CO) and NaOH have been investigated. The observation by IR spectroscopy that HFe(CO) - reacts with C O under pressure in 1-butanol or T H F to give Fe(CO) suggests the following catalytic cycle for the water gas shift reaction catalyzed by basic solutions of Fe(CO) : (1) HFe(CO) - + C O -> Fe(CO) + H ; (2) H + H O -> OH + H2; (3) Fe(CO) + OH -> Fe(CO) C(O)OH ; (4) Fe(CO) C(O)OH -> HFe(CO) - + CO . 6

5

2

2

2

2

5

4

5

5

-

4

-

5

-

2

-

5

-

-

4

4

4

2

T n c r e a s e d recent interest i n t h e h o m o g e n e o u s catalysis of t h e w a t e r gas shift r e a c t i o n ( R e a c t i o n 1) b y r u t h e n i u m ( I ) a n d r h o d i u m (2) c a r b o n y l d e r i v a t i v e s has p r o m p t e d us to r e e x a m i n e R e p p e ' s o b s e r v a t i o n d u r i n g W o r l d W a r I I ( 3 ) that F e ( C O )

i n t h e presence of a base c a n

5

c a t a l y z e this r e a c t i o n . T h e aqueous s o d i u m h y d r o x i d e u s e d as a base b y CO +

1

MN.

H 0 *± H + C0 2

2

2

(1)

Current address: Department of Chemistry, University of Minnesota, Deluth, 0-8412-0429-2/79/33-173-094$05.00/0 © 1979 American Chemical Society

King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.

9.

FRAZIER E TA L .

Petitacarbonyliron

95

and Metal Hexacarbonyls

R e p p e l e d to systems that w e r e c a t a l y t i c i n m e t a l b u t n o t i n base f o r t h e w a t e r gas shift r e a c t i o n . W e h a v e f o u n d r e c e n t l y that b y u s i n g aqueous 1 - b u t a n o l rather t h a n p u r e w a t e r as t h e s o l v e n t i n t h e N a O H / F e ( C O )

5

system, a catalyst c a n b e g e n e r a t e d f o r t h e w a t e r gas shift r e a c t i o n w h i c h is n o t o n l y c a t a l y t i c i n i r o n b u t also i n base a b o v e 1 2 0 ° C .

T o facilitate

m e c h a n i s t i c s t u d y of the N a O H / F e ( C O ) - c a t a l y z e d w a t e r gas shift reac5

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t i o n , t h e rate of h y d r o g e n e v o l u t i o n n o w has b e e n

d e t e r m i n e d as a

f u n c t i o n of i n i t i a l C O pressure, r e a c t i o n t e m p e r a t u r e , a n d base c o n c e n tration.

I n a d d i t i o n , a s i m i l a r i n v e s t i g a t i o n of t h e g r o u p V I m e t a l car-

bonyls M ( C O )

(M =

6

C r , M o , a n d W ) has i d e n t i f i e d these c o m p l e x e s

as v e r y active w a t e r gas shift catalysts i n t h e presence o f a l c o h o l i c s o d i u m or p o t a s s i u m h y d r o x i d e . T h i s c h a p t e r discusses t h e k i n e t i c results a n d the information obtained b y a n I R spectroscopic catalytic Fe(CO)

solutions 5

obtained

and M ( C O )

6

from

e x a m i n a t i o n of t h e

the mononuclear

metal

carbonyls

( M = C r , M o , and W ) and hydroxide ion using

a s p e c i a l l y d e s i g n e d h i g h pressure I R c e l l ( 4 ) . Experimental

Procedures

A l l reactions w e r e c a r r i e d o u t i n 7 0 0 - m L stainless steel, h i g h pressure r e a c t i o n vessels. T h e r e a c t i o n s o l u t i o n w a s a d d e d , a l o n g w i t h a T e f l o n c o a t e d s t i r r i n g b a r , to a vessel that w a s f l u s h e d a n d l o a d e d w i t h C O to t h e d e s i r e d pressure. T h e vessel w a s h e a t e d i n a n i n s u l a t e d o v e n , w h i c h rests o n a m a g n e t i c s t i r r i n g m o t o r . T e m p e r a t u r e c o n t r o l ( ± 1 ° C after the desired reaction temperature was reached) was maintained using a proportional temperature controller w i t h a thermocouple inserted i n a t h e r m o w e l l , . w h i c h e x t e n d e d b e l o w t h e s o l u t i o n l e v e l of t h e r e a c t i o n vessel as a sensor. H e a t i n g t h e r e a c t i o n vessel f r o m r o o m t e m p e r a t u r e to 1 6 0 ° C t y p i c a l l y r e q u i r e d f r o m 40 to 45 m i n u t e s . G a s samples w e r e p e r i o d i c a l l y r e m o v e d t h r o u g h a v a l v e - c o n t r o l l e d p o r t at the t o p of the r e a c t i o n vessel. A p o r t i o n of e a c h s a m p l e w a s i n j e c t e d i n t o a V a r i a n A e r o g r a p h M o d e l 920 gas c h r o m a t o g r a p h w i t h either a 5 A m o l e c u l a r sieve c o l u m n f o r m e a s u r i n g H a n d C O o r a s i l i c a c o l u m n for measuring C 0 a n d C O . K n o w n H / C O mixtures were used f o r c a l i b r a t i o n of t h e m o l e c u l a r sieve c o l u m n . T h e F e ( C O ) solutions u s e d i n these experiments w e r e p r e p a r e d b y d i s s o l v i n g N a O H i n 30 m L (1.67 m o l ) of d i s t i l l e d w a t e r a n d c o m b i n i n g this base s o l u t i o n w i t h 170 m L of 1 - b u t a n o l p r e v i o u s l y a d d e d t o t h e r e a c t i o n vessel. T h i s s o l u t i o n w a s b u b b l e d w i t h N f o r 2 0 - 3 0 m i n b e f o r e a d d i t i o n of 0.3 m L (0.00223 m o l ) of F e ( C O ) . T h e r e a c t i o n vessel w a s c l o s e d u n d e r N a n d c o n n e c t e d to a h i g h pressure m a n i f o l d f o r flushing and loading with C O . T h e M ( C O ) solutions ( M = C r , M o , a n d W ) w e r e p r e p a r e d b y d i s s o l v i n g a w e i g h e d s a m p l e of t h e m e t a l h e x a c a r b o n y l i n 100 m L of solvent ( u s u a l l y m e t h a n o l ) a n d a d d i n g the a p p r o p r i a t e a m o u n t of base as 1 0 M aqueous K O H . A f t e r c o m p l e t i o n of a n e x p e r i m e n t a l r u n , t h e aqueous l a y e r w a s s e p a r a t e d f r o m b u t a n o l , e v a p o r a t e d , a n d a p o r t i o n of the d r i e d r e s i d u e i n c o r p o r a t e d i n t o a K B r p e l l e t f o r e x a m i n a t i o n b y I R 2

2

2

5

2

5

2

6


96

INORGANIC

COMPOUNDS WITH UNUSUAL PROPERTIES

II

spectroscopy. I n some experiments s o l i d m a t e r i a l p r e c i p i t a t e d o n c o o l i n g the r e a c t i o n vessel to r o o m t e m p e r a t u r e . T h e s e solids w e r e also a n a l y z e d b y I R spectroscopy. F o r m a t e (1600 a n d 1360 c m " ) , c a r b o n a t e (1440 c m " ) , a n d b i c a r b o n a t e (1650, 1605, a n d 1310 c m " ) w e r e i d e n t i f i e d b y their characteristic I R frequencies. T o e x c l u d e the p o s s i b i l i t y of heterogeneous r a t h e r t h a n h o m o g e n e o u s catalysis, p r e c i p i t a t e d solids w e r e filtered f r o m the s u p e r n a t a n t l i q u i d a n d a d d e d to a f r e s h s o l u t i o n of solvent a n d base f o r f u r t h e r r e a c t i o n . T h e observed catalytic activity was insignificant. T h e supernatant l i q u i d , i n contrast, d e m o n s t r a t e d a c t i v i t y s i m i l a r to that m e a s u r e d i n the initial run. T h e stainless steel h i g h pressure I R c e l l w i t h I r t r a n - 1 w i n d o w s a n d associated h i g h pressure e q u i p m e n t a n d spectrometer has b e e n d e s c r i b e d elsewhere ( 4 ) . A i r - s e n s i t i v e i r o n c a r b o n y l solutions, w h i c h w e r e to b e e x a m i n e d b y I R spectroscopy, w e r e l o a d e d i n t o the h i g h pressure c e l l u n d e r N a n d w e r e t h e n q u i c k l y p l a c e d u n d e r a n a t m o s p h e r e of C O to insure their stability. 1


1

1

2

The

Catalytic Hydrogen

System Derived

from

Fe(CO)

5

production turnover numbers have been

measured

t e m p e r a t u r e , pressure, a n d base c o n c e n t r a t i o n w e r e v a r i e d (see

as

Tables

I a n d I I ) i n a n effort to d e t e r m i n e the m e c h a n i s m of t h e c a t a l y t i c system d e r i v e d f r o m 1 - b u t a n o l solutions of F e ( C O )

5

a n d base. T u r n o v e r n u m -

bers are g i v e n as moles of h y d r o g e n p e r m o l e of m e t a l p e r six h o u r s to a l l o w a l l of the experiments to b e c o m p a r e d o n a m e a n i n g f u l basis. U n d e r c e r t a i n c o n d i t i o n s , some e x p e r i m e n t a l r u n s use a l l of the a d d e d C O i n less t h a n one

day.

To

i n s u r e that

the t u r n o v e r n u m b e r s

represent

k i n e t i c a l l y u s e f u l i n f o r m a t i o n , the t u r n o v e r o b t a i n e d at a n e a r l y stage i n t h e r e a c t i o n are p r e s e n t e d . I n t e r p r e t a t i o n of the results of these experiments has u n f o r t u n a t e l y b e e n h a m p e r e d b y c o m p e t i n g side reactions of b o t h C O a n d C 0

2

with

Table I. Effect of Base Concentration on the Reactivity of the F e ( C O ) - C a t a l y z e d Water Gas Shift Reaction 0

5

Run Number 1 2 3 4 5 6 7

CO

Initial Pressure (atm) 23.1 28.2 28.2 28.2 28.2 14.6 14.6

Mol H per Mol Metal per 6 Hr 2

Base: Mol

Temperature (°C)

Metal Ratio

150 160 163 160 160 161 160

0 14 28 224 448 7.5 28

~ 0.002 78 54 24 3 109 83

° A l l runs used 170 m L of 1-butanol, 30 m L H 0 , and 0.30 m L of F e ( C O ) . 2


5

9.

FRAZIER E T AL.

Pentdcarhonyliron

and

Metal

97

Hexacarbonyls

Table II. Effect of Pressure and Temperature on the Reactivity the F e ( C O ) - C a t a l y z e d Water Gas Shift Reaction" 5


Run Number

CO

1 2 3 4 5 6 7 8 9

Initial Pressure ( atm)

Mol H per Mol Metal per 6 Hr 2

Base: Mol

28.2 28.2 28.2 28.2 28.2 7.8 14.6 21.4 28.2

Metal Ratio

Temperature (°C)

21 23 54 57 60 19 83 70 54

137 145 164 181 183 162 160 160 163

28 28 28 28 28 28 28 28 28

° A l l runs used 170 m L of 1-butanol, 30 m L of H 0 , and 0.30 m L of F e ( C 0 ) . 2

5

base to p r o d u c e f o r m a t e a n d b i c a r b o n a t e , r e s p e c t i v e l y . W i t h i n the C O pressure r a n g e that has b e e n u s e d to date, the rate of f o r m a t e p r o d u c t i o n at 1 6 0 ° C i n the absence of F e ( C O )

5

a c c o r d i n g to R e a c t i o n 2 has b e e n

d e t e r m i n e d to b e significant at the base concentrations m o s t i n these studies.

CO + hydroformylation Fe(CO)

5

(5).

(0.31M)

used

F o r m a t e p r o d u c t i o n also has b e e n o b s e r v e d i n

reactions

of

OH'

HC0 "

olefins

i n basic

(2)

2

aqueous

solutions

of

H o w e v e r , b y o b s e r v i n g the t o t a l system pressure as w e l l

as h y d r o g e n p r o d u c t i o n d u r i n g c a t a l y t i c runs at 7.8 a n d 28.2 a t m C O at 160 ° C , w e h a v e d e t e r m i n e d that w h i l e there is a n i n i t i a l r a p i d rate of f o r m a t e p r o d u c t i o n , the rate of f o r m a t e p r o d u c t i o n d i m i n i s h e s a p p r e c i a b l y as the c a t a l y t i c p r o d u c t i o n of h y d r o g e n p r o c e e d s .

Hydrogen production

m e a s u r e d at l o w pressures of C 0

2

2

w i t h excess H 0 f o l l o w s

k i n e t i c s as s h o w n i n F i g u r e s 1 a n d 2.

graphs is a n artifact r e s u l t i n g f r o m the loss of C O c a u s e d b y production. C0

2

first-order

T h e n o n z e r o i n t e r c e p t of these formate

W h i l e these observations c o u l d i n d i c a t e that t h e H

p r o d u c t s result f r o m c a t a l y z e d f o r m a t e d e c o m p o s i t i o n , the

2

and more

l i k e l y i n t e r p r e t a t i o n is that b o t h the r a t e of f o r m a t e f o r m a t i o n a n d of h y d r o g e n p r o d u c t i o n are r a p i d i n the presence of a n i n i t i a l l y h i g h c o n c e n t r a t i o n of base a n d f a l l off as O H ' c o n c e n t r a t i o n d r o p s as the i o n c o m b i n e s w i t h C O to p r o d u c e f o r m a t e . W h e n f o r m a t e i o n is a d d e d to the b o m b a l o n g w i t h the b a s i c b u t a n o l / H 0 2

s o l u t i o n of F e ( C O ) , h y d r o g e n p r o d u c t i o n u n d e r the u s u a l t e m 5

p e r a t u r e a n d pressure r e a c t i o n c o n d i t i o n s is essentially i n d i s t i n g u i s h a b l e f r o m t h e o b s e r v e d rate of runs w i t h o u t a d d e d f o r m a t e .

C o n t r o l experi-

ments w i t h f o r m a t e i o n a d d e d to the charge a n d u n d e r N

2

pressure, not


98

INORGANIC COMPOUNDS W I T H UNUSUAL PROPERTIES

II

C O , p r o d u c e n e g l i g i b l e q u a n t i t i e s of h y d r o g e n . T h e s e results c o n f i r m t h e s u p p o s i t i o n that f o r m a t e i o n does n o t h a v e a d i r e c t r o l e i n a c c o u n t i n g f o r t h e w a t e r gas s h i f t p r o d u c t s . T h e d a t a i n T a b l e I s h o w that as t h e c o n c e n t r a t i o n of base is i n c r e a s e d i n the r e a c t i o n m i x t u r e h y d r o g e n p r o d u c t i o n accelerates, levels off, a n d then- decreases w h e n l a r g e q u a n t i t i e s of base are a d d e d . A t the Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 20, 2016 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch009

h i g h e s t b a s e : m e t a l ratios g i v e n , c o p i o u s a m o u n t s of f o r m a t e are p r o d u c e d , severely d e p l e t i n g the C O reservoir, w h i c h m a y i n p a r t e x p l a i n the o b s e r v e d decrease

i n the rate of h y d r o g e n p r o d u c t i o n at the

b a s e : m e t a l ratios.

.24 .22 .20 .18 .16 .14 .12 .10 .08 .06 .04 .02

200

400

600

t

800

1000 1200 1400

1600

(minutes)

Figure 1. Plot of -log ( l - f ]+*[C0]) ' for the reaction of CO at 7.8 atm and 162°C with a solution of Fe(CO) in aqueous butanol containing 0.31UNaOH H

VS

U

m

6

5


highest


9.

FRAZIER E T AL.

Pentacarbonyliron

and

200

t Figure 2.

Plot of -log

99

Metal Hexacarbonyls

300

(minutes) (l -

/+'/

c o

j)

w

-

*

i m

*

/or rTie reaction of CO at 28.2 atm and 163°C with a solution of Fe(CO) in aqueous butanol containing 0.31MNaOH 5

A s C O pressure is i n c r e a s e d f r o m 7.8 to 28.2 a t m the rate of h y d r o g e n p r o d u c t i o n rises a n d t h e n falls, as c a n b e seen f r o m t h e d a t a i n T a b l e I I . S i n c e a m i x t u r e of s o l i d s o d i u m b i c a r b o n a t e is o b s e r v e d i n the

bomb

u p o n c o o l i n g at t h e c o n c l u s i o n of a r u n w i t h 7.8 a t m of i n i t i a l C O pressure, i t c a n b e i n f e r r e d that R e a c t i o n 3 also p l a y s a p a r t i n c o n t r o l l i n g t h e p H of the r e a c t i o n m i x t u r e . W h e n experiments u s i n g 14.6 a n d 28.2 a t m of C O are t e r m i n a t e d , f o r m a t e is the p r e d o m i n a n t i n o r g a n i c a n i o n f o u n d . T h u s t h e c o m p o s i t i o n of i n o r g a n i c solids, carbonate,

bicarbonate,

and

f o r m a t e w h i c h c a n b e f o u n d i n the b o m b is d e t e r m i n e d b y t h e i n i t i a l c o n c e n t r a t i o n of base, i n i t i a l C O pressure, a n d the a m o u n t of C 0 C0

2

+ 20H" -» C 0

3

2

" +

H 0 2


2

that (3)

100

INORGANIC

COMPOUNDS W I T H UNUSUAL PROPERTIES

II

has a c c u m u l a t e d at the e n d of a r u n . B e c a u s e of the c o m p l e x i n t e r a c t i o n b e t w e e n these v a r i a b l e s , w e are c u r r e n t l y q u a n t i t a t i v e l y m e a s u r i n g C O , H , and C 0 2

2

vs. t i m e u n d e r a v a r i e t y of e x p e r i m e n t a l c o n d i t i o n s i n o r d e r

to define the c o m p l i c a t i n g side reactions of C O a n d C 0

2

a n d to establish

the true r e l a t i o n of base a n d of C O pressure to the k e y m e c h a n i s t i c steps of the m e t a l c a r b o n y l - c a t a l y z e d w a t e r gas shift r e a c t i o n . Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 20, 2016 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch009

T h e d a t a i n T a b l e I I also demonstrate

that the rate of h y d r o g e n

p r o d u c t i o n increases as the r e a c t i o n t e m p e r a t u r e is r a i s e d . T h e rate c o n stants g o v e r n i n g the a p p a r e n t comparable

reactions

first-order

performed

at

u p t a k e of C O f o r a series of

v a r i o u s temperatures

are

p l o t t e d l o g a r i t h m i c a l l y as a f u n c t i o n of r e c i p r o c a l t e m p e r a t u r e

shown (K)

in

F i g u r e 3. A n a c t i v a t i o n e n e r g y of 20 k c a l / m o l is d e r i v e d f r o m the slope of this p l o t . T h i s v a l u e is s u r p r i s i n g l y close to the a c t i v a t i o n energy of the i r o n o x i d e heterogeneous w a t e r gas shift r e a c t i o n

0.00210

0.00220

0.00230

0.00240

(6).

0.00250

VT(°K) Figure 3. Plot of log k vs. 1/T (K) leading to an activation energy of 20 kcal/mol for the reaction of CO at 28.2 atm with a solution of Fe(CO) in aqueous butanol containing 0.31M NaOH 5



M o (CO)

M o (CO)

M o (CO) Mo(CO) W(C0)

6

6

W(CO)

3

4

5 6 7

8

6

6

6

6

6

4

KOH

MeOH

MeOH MeOH MeOH

none KBH KOH

7.7

4.3 4.3 7.7

11

MeOH

KOH

MeOH

4.3

MeOH MeOH

KOH KOH

KOH

7.8 4.3

Solvent

Base

0.00105

0.0D255 0.0036 0.00132

0.00208

0.0022

0.00182 0.00207

Metal Cone. (M)

(M =

1600

0 3 1265

800

760

1100 87

140 120 140 115 135 160 120 130 145 160 140 95 110 130 170

T

280 5 24 9 10 40 0 3 130 0 30 0 13 140 ~ 900

2

H :M Per Day (Mol)

C r , M o , W ) as Catalysts

Base: Metal (Mol)

G

° A l l runs used 100 m L of M e O H . When K O H is indicated, this was added as a 10M aqueous solution.

Cr(CO) M o (CO)

1 2

6

Carbonyl

Initial COP (atm)

Systems Derived from the G r o u p V I Metal Carbonyls M ( C O ) for the Water Gas Shift Reaction"

Run No.

Table III.


102

INORGANIC COMPOUNDS W I T H UNUSUAL

The Catalytic Systems Derived from (M = Cr, M o , and W)

PROPERTIES

II

M(CO)

6

T a b l e I I I presents t u r n o v e r n u m b e r s f o r t h e p r o d u c t i o n of h y d r o g e n b y t h e w a t e r gas shift r e a c t i o n ( R e a c t i o n 1) u s i n g catalysts d e r i v e d f r o m the m e t a l h e x a c a r b o n y l s

M(CO)

6

( M =

C r , M o , a n d W ) . Runs 2


t h r o u g h 4 c l e a r l y s h o w that as t h e r e a c t i o n t e m p e r a t u r e increases i n t h e experiments w i t h M o ( C O ) , t h e rate of h y d r o g e n p r o d u c t i o n accelerates. 6

R u n 7 indicates that t h e same effect occurs f o r runs u s i n g W ( C O ) the catalyst p r e c u r s o r .

R u n 5 demonstrates

6

as

that a base is r e q u i r e d f o r

catalysis.

R u n 6 illustrates that bases other t h a n h y d r o x i d e c a n a c t as

catalysts.

Since K B H

4

is k n o w n to react w i t h M ( C O )

a n d W ) i n d o n o r solvents

at e l e v a t e d

( M == C r , M o ,

6

temperatures

to p r o d u c e t h e

c o r r e s p o n d i n g H M ( C O ) i ' anions ( 7 ) , t h e results of r u n 6 suggest that 2

0

these anions m a y b e i n v o l v e d i n the c a t a l y t i c c y c l e .

High

Pressure Spectroscopic Studies T h e I R spectra of 1 - b u t a n o l solutions of F e ( C O )

(M =

5

and M ( C O )

6

M o a n d W ) c o n t a i n i n g aqueous N a O H o r K O H w e r e e x a m i n e d

u n d e r pressure u s i n g a stainless steel h i g h pressure I R c e l l w i t h I r t r a n 1 w i n d o w s (4)

i n attempts t o i d e n t i f y t h e v a r i o u s m e t a l c a r b o n y l species

present i n t h e r e a c t i o n solutions u n d e r c a t a l y t i c c o n d i t i o n s . I n t h e cases of M ( C O )

( M =

6

M o a n d W ) , the only metal carbonyl v ( C O )

fre-

q u e n c i e s o b s e r v e d at temperatures a n d pressures c o m p a r a b l e w i t h those u s e d f o r catalysis w e r e those that c o r r e s p o n d t o t h e respective hexacarbonyl.

I n a d d i t i o n , a b a n d at 2300 c m

- 1

metal

gradually appeared i n

the I R spectra of s u c h m e t a l h e x a c a r b o n y l solutions a b o v e 1 1 0 ° C u n d e r C O pressure.

T h i s b a n d c a n b e assigned to t h e C 0

2

produced i n the

w a t e r gas shift r e a c t i o n ( R e a c t i o n 1) p r o c e e d i n g u n d e r these c o n d i t i o n s . S i m i l a r I R s p e c t r o s c o p i c studies of b a s i c solutions of F e ( C O ) C O pressures l e d t o s o m e w h a t m o r e c o m p l e x results. temperature

of F e ( C O )

under

5

A d d i t i o n at r o o m

(0.10 m L , 0.76 m m o l ) to 49.4 m L of a N -

5

2

saturated s o l u t i o n of 1:20 w a t e r - b u t a n o l c o n t a i n i n g 0.12 g ( 3 m m o l ) of NaOH

resulted

i n the r a p i d formation

of H F e ( C O ) " . 4

N o further

changes w e r e o b s e r v e d i n t h e I R s p e c t r u m o f s u c h a n H F e ( C O ) " s o l u 4

t i o n w h e n i t w a s k e p t at 2 5 ° C f o r 4 h r u n d e r 330 a t m C O . H o w e v e r , u p o n g r a d u a l h e a t i n g u n d e r C O pressure, t h e characteristic strong 1885 cm"

1

b a n d of H F e ( C O ) " g r a d u a l l y d i s a p p e a r e d w i t h t h e c o n c u r r e n t 4

a p p e a r a n c e of a 1995 c m " b a n d i n d i c a t i v e of t h e presence o f r e g e n e r a t e d 1

Fe(CO) . 5

T h e s e s p e c t r a l changes are d e p i c t e d i n F i g u r e 4. T h e f o r m a -

t i o n of F e ( C O ) 93°-98°C.

5

f r o m H F e ( C O ) " a n d 330 a t m C O w a s c o m p l e t e at 4

C o o l i n g the solution to r o o m temperature

w h i l e still under



9.

FRAZIER E T AL.

25UD

Pentacarbonyliron

2doo

iebo bvr 25 oD

1

103


2ctao

1

isbo b M"

(C)

Figure 4. IR spectra of a solution of 0.10 mL of Fe(CO) , 0.12 g of NaOH, 1.4 mL of H 0, and 48 mL of 1-butanol under 330 atm CO. (A) At 28°C; (B) after heating to 82°-91°C; (C) after heating to 93°-98°C; (D) after cooling the heated solution back to 38°C. Weak bands from the 1-butanol solvent are observable at 2015 cm' in Figure I A and at 1906,1851, and 1775 cm' in Figure 1C. As CO dissolves in the solvent a broad band at 2130 cm' progressively intensifies. 5

2

1

1

1

330 a t m C O i n t h e h i g h pressure c e l l r e s u l t e d i n p a r t i a l r e g e n e r a t i o n of H F e ( C O ) " f r o m r e a c t i o n of F e ( C O ) 4

5

w i t h r e s i d u a l base.

T h e a b o v e observations suggest that a c o m p l e t e c y c l e f o r t h e w a t e r gas s h i f t r e a c t i o n c a n b e d e s c r i b e d b y t h e f o l l o w i n g r e a c t i o n s :


104

INORGANIC COMPOUNDS W I T H UNUSUAL PROPERTIES

H F e ( C 0 ) " + C O*± F e ( C O ) 4

IT + H 0

OH"+ H

2


OH" + Fe(CO)

5

-»

(4a)

+ H "

5

(4b)

2

(4c)

Fe(C0) C(0)0H" 4

Fe(CO) C(0)OH--> HFe(CO) " + C 0 4

II

4

(4d)

2

T h e changes o b s e r v e d i n t h e I R s p e c t r u m i n t h e v ( C O ) r e g i o n o f a n a n h y d r o u s T H F s o l u t i o n of [ ( C H ) P ] N H F e ( C O ) - u p o n h e a t i n g t h e 6

5

3

+

2

4

s o l u t i o n u n d e r 330 a t m C O i m p l y that R e a c t i o n 4 a c a n b e w r i t t e n as a n e q u i l i b r i u m w h e n a n h y d r o u s n o n h y d r o x y l i c solvents a r e u s e d so that t h e h y d r i d e i o n p r o d u c e d i n R e a c t i o n 4a c a n n o t b e p r o t o n a t e d to f o r m h y d r o g e n as i n R e a c t i o n 4 b . A f t e r c a r b o n y l a t i o n of [ ( C H ) P ] N H F e ( C O ) 6

to g i v e F e ( C O )

5

5

3

2

+

4

a n d p r e s u m a b l y [ ( C H ) P ] N H - is c o m p l e t e at 6 0 ° C 6

5

3

2

+

a n d 330 a t m C O , c o o l i n g t h e system w h i l e m a i n t a i n i n g t h e C O pressure leads to r e v e r s i o n of some of t h e F e ( C O )

5

to H F e ( C O ) ~ , p r e s u m a b l y 4

b y reaction w i t h the [ ( C H ) P ] 2 N H - . A d d i t i o n a l F e ( C O ) 6

5

3

+

reverts to

5

H F e ( C O ) " as t h e C O pressure is l o w e r e d i n stages. H o w e v e r , after t h e 4

C O pressure is b e l o w a p p r o x i m a t e l y 140 a t m , the c o n v e r s i o n of F e ( C O )

5

to H F e ( C O ) " b e c o m e s q u i t e r a p i d a n d is c o m p l e t e w i t h i n m i n u t e s . 4

Conclusions T h e studies o u t l i n e d i n this c h a p t e r suggest that a v a r i e t y of m e t a l c a r b o n y l s , i n c l u d i n g some of t h e simplest m o n o n u c l e a r m e t a l c a r b o n y l s , c a n generate active catalysts f o r t h e w a t e r gas shift r e a c t i o n

(Reaction

1) b y s i m p l e treatment w i t h h y d r o x i d e i o n . I n v e s t i g a t i o n of t h e m e c h a nisms of s u c h c a t a l y t i c reactions is c o m p l i c a t e d b y s i d e reactions o f t h e C O reactant a n d t h e C 0

2

p r o d u c t w i t h t h e strongly b a s i c system.

How-

ever, n o w that these side reactions, i n v o l v i n g p r o d u c t i o n of f o r m a t e a n d carbonate, that

a r e r e c o g n i z e d , i t s h o u l d b e p o s s i b l e to d e s i g n

experiments

p e r m i t i d e n t i f i c a t i o n o f t h e k e y steps i n these m e t a l

carbonyl-

c a t a l y z e d w a t e r gas shift reactions.

Acknowledgment W e are i n d e b t e d to t h e D i v i s i o n of B a s i c E n e r g y Sciences of t h e U . S . D e p a r t m e n t of E n e r g y f o r s u p p o r t of this w o r k u n d e r C o n t r a c t EY-76-S-09-0933.


9.

FRAZIER E T A L .

Pentacarbonyliron


105


Literature Cited 1. Laine, R. M., Rinker, R. G., Ford, P.C.,J.Am. Chem. Soc. (1977) 99, 252. 2. Cheng, C. H., Hendricksen, D. E., Eisenberg, R., J .Am .Chem. Soc. (1977) 99, 2791. 3. Reppe, W., Reindl, E., Liebigs Ann. (1953) 582, 116. 4. King, R. B., King, A. D., Jr., Iqbal, M. Z., Frazier, C.C.,J.Am. Chem Soc. (1978) 100, 1687. 5. Kang, H., Mauldin, C. H., Cole, T., Slegeir, W., Cann, K., Pettit, R.,J.Am. Chem. Soc. (1977) 99, 8323. 6. Laudien, K., Witzmann, W., Chem. Tech. (1967) 19(4), 232. 7. Hayter, R.G.,J.Am. Chem. Soc. (1966) 88, 4376. RECEIVED March 3, 1978.


Homogeneous Catalysis of the Water Gas Shift Reaction - American

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