Characterization and Catalyst Development - American Chemical

Chapter 6

Preparation and Characterization of Magnesium Aluminate Spinel for SO Abatement in Fluid Catalytic Cracking Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 9, 2015 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0411.ch006

x

Alak A . Bhattacharyya, Gerald M. Woltermann, and William E . Cormier Katalistiks International, 4810 Seton Drive, Baltimore, M D 21215

Recent s t u d i e s have demonstrated t h a t cerium c o n t a i n i n g magnesium aluminate s p i n e l s such as MgAl O and Mg Al O a r e very e f f e c t i v e SOx r e d u c t i o n c a t a l y s t s f o r FCC u n i t s . These magnesium aluminate s p i n e l s can be prepared by t h r e e d i f f e r e n t techniques: ( i ) thermal co-condensation ( i i ) c o - p r e c i p i t a t i o n and (iii) Co-gel formation. Some o f the important p h y s i c a l and chemical p r o p e r t i e s o f a s p i n e l depends on t h e p r e p a r a t i v e route used. T h i s paper will d i s c u s s the p r e p a r a t i o n methods and c h a r a c t e r i z a t i o n techniques utilized f o r these s p i n e l s and how the SOx abatement activity of these s p i n e l s a r e r e l a t e d t o the p r e p a r a t i v e route used. 2

4

2

2

5

Designing a c a t a l y s t f o r e f f e c t i v e removal o f SOx ( S 0 + S0 ) i n a f l u i d c a t a l y s t c r a c k i n g u n i t regenerator i s a c h a l l e n g i n g problem. One must come up with a p a r t i c l e having p h y s i c a l p r o p e r t i e s s i m i l a r t o FCC c a t a l y s t s which w i l l : 1) o x i d i z e S 0 t o S 0 , 2) chemisorb t h e S 0 , and 3) be able t o r e l e a s e i t as H S as i t enters t h e r e a c t o r s i d e o f the u n i t . A cerium c o n t a i n i n g magnesium aluminate s p i n e l was found t o be very e f f e c t i v e f o r t h i s purpose (1). The p r e p a r a t i o n methods and c h a r a c t e r i z a t i o n techniques u t i l i z e d f o r t h i s s p i n e l c a t a l y s t and how the SOx abatement a c t i v i t y of t h i s c a t a l y s t i s r e l a t e d t o the p r e p a r a t i v e route used are d i s c u s s e d i n t h i s paper.

2

3

2

3

3

2

EXPERIMENTAL Psuedoboehmite alumina (Condea Chemie), h i g h s u r f a c e area magnesium oxide (Basic Chemicals), magnesium 0097-6156/89/0411-0046$06.00/0 c 1989 American Chemical Society

In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

6. B H A T T A C H A R Y Y A E T A L .

Magnesium Aluminate Spinel for SO Abatement x

n i t r a t e hexahydrate ( M a l l i n c k r o d t ) , sodium aluminate (Nalco), and cerium n i t r a t e hexahydrate (Molycorp) were used as r e c e i v e d . P r e p a r a t i o n o f M a A l n Q by Co-condensation Method. A psuedoboehmite alumina (95.55g, 75% A 1 0 ) was thoroughly mixed with high s u r f a c e area magnesium oxide (30.45g, 93% MgO). T h i s m a t e r i a l was c a l c i n e d a t 1400°C f o r 5 h. The m a t e r i a l was cooled, thoroughly p u l v e r i z e d , and c a l c i n e d again a t 1400°C f o r 2 h. T h i s process was repeated f o r two more times. The s u r f a c e area o f the m a t e r i a l was measured t o be 2 m /g. Anal. Calcd f o r M g A l 0 : MgO, 28.33%. Found: MgO, 26.4%. 4

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2

3

2

2

4

P r e p a r a t i o n o f MaAl2p4 by C o - P r e c i p i t a t i o n Method(5-7). A s o l u t i o n c o n t a i n i n g Mg(N0 ) .6H 0 (128.22g, 100%) and H 0 (225 mL) was added t o a 2 L beaker c o n t a i n i n g 600 mL o f H 0. A s o l u t i o n c o n t a i n i n g NaA10 (112.87g, 45.14% A 1 0 ) and H 0 (400 mL) was then added dropwise v i a a separatory funnel t o the beaker. The pH was adjusted with e i t h e r NaOH o r HN0 t o keep i t w i t h i n the 8.5 - 9.0 range. The p r e c i p i t a t e was f i l t e r e d and washed with 3000 mL o f d e i o n i z e d H 0. T h i s m a t e r i a l was d r i e d a t 135°C f o r 8 h and c a l c i n e d a t 700°C f o r 2 h. The s u r f a c e area o f t h i s m a t e r i a l was 180 m /g. Anal. Calcd f o r M g A l 0 : Mgo, 28.33%. Found: MgO, 26.1%. The high magnesium s p i n e l , M g A l 0 , can be s y n t h e s i z e d f o l l o w i n g the same procedure and u s i n g the r e q u i r e d amounts o f Mg(N0 ).6H 0 and NaA10 . Anal. Calcd f o r M g A l 0 : MgO, 44.15%. Found MgO, 45.9%. 3

2

2

2

2

2

2

3

2

3

2

2

2

4

2

3

2

2

2

2

5

2

5

P r e p a r a t i o n o f MaA1^0 bv Co-ael Formation Method (8). A g e l having a pH o f 9 was prepared u s i n g aqueous s l u r r i e s o f psuedoboehmite alumina (71.7 g A l p 0 ) , MgO (28.3 g ) , and an a c i d . The m a t e r i a l was d r i e d a t 110°C f o r 8 h and c a l c i n e d a t 700°C f o r 2 h. The s u r f a c e area o f t h i s m a t e r i a l was 169m2/g. Anal. Calcd f o r M g A l 0 : MgO, 28.33%. Found: MgO, 26.3%. The high magnesium s p i n e l can be prepared u s i n g the same procedure and u s i n g the r e q u i r e d amounts o f psuedoboehmite alumina and MgO. Anal. C a l c d f o r M g A l 0 . MgO, 44.15%. Found: 44.1%. 4

3

2

2

4

2

5

Cerium Impregnation. A l l o f the above s p i n e l s were impregnated(1) by cerium n i t r a t e hexahydrate. A p o r t i o n (87.7 g) o f the s p i n e l prepared by any o f t h e above methods was impregnated with a s o l u t i o n c o n t a i n i n g 42.9 g o f 70% Ce(N0 ) .6H9O (Ce0 content 28.7%) and 40 g water. T h i s m a t e r i a l was d r i e d a t 120°C f o r 3 h and c a l c i n e d a t 700°C f o r 1 h. 3

3

2

Thermal S t u d i e s . Thermogravimetric s t u d i e s were performed f o r the t e s t i n g o f these m a t e r i a l s . T h i s was

American Chemical Society Library 15th St., N.W. Bradley, S., et al.; In Characterization1155 and Catalyst Development; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. Washington, D.C. 20036

47

48

CHARACTERIZATION AND CATALYST DEVELOPMENT

accomplished by p l a c i n g a small amount (5 t o 25 mg) of v i r g i n sample on a quartz pan and p a s s i n g a d e s i r e d gas. T h i s experiment was d i v i d e d i n t o f o u r zones: Zone A: Zone B:

Under N , the sample was heated t o 700°C. N i t r o g e n was r e p l a c e d by a gas c o n t a i n i n g 0.32% S 0 , 2.0% O^, and balance N^. The flow r a t e was 200 mL/mm. The temperature was kept constant a t 700°C. T h i s c o n d i t i o n was maintained f o r 15 min. Passage o f S 0 c o n t a i n i n g gas was ceased and r e p l a c e d by . Temperature was reduced t o 650°C. T h i s i s a 10 min. time zone. N i t r o g e n was replaced by pure H . This c o n d i t i o n was maintained f o r 10 minutes. 2

2


Zone C:

2

Zone D:

2

X-Ray powder d i f f r a c t i o n p a t t e r n s o f these m a t e r i a l s were obtained on a P h i l i p s APD 3720 Automated Powder XRay d i f f r a c t o m e t e r u s i n g CuK alpha r a d i a t i o n . Surface areas were measured with a M i c r o m e r i t i c s Flowsorb I I Model 2300 A n a l y z e r with P/Po = 0.3 u t i l i z i n g the BET isotherm. RESULTS AND DISCUSSION S e v e r a l redox oxides such as P t 0 , V ^ , F e 0 , and CeO^ can be used f o r the o x i d a t i o n o f S 0 t o S 0 . Cerium d i o x i d e i s p r e f e r r e d over other oxides because platinum i s expensive and vanadium and i r o n oxides are poisons f o r FCC c a t a l y s t s . U s u a l l y an aqueous s o l u t i o n of a cerium s a l t i s used t o impregnate a s p i n e l base which i s then c a l c i n e d t o o b t a i n t h e Ce0 a c t i v e form. We have found t h a t a 10 t o 12% Ce0 i s s u f f i c i e n t f o r effective S0 oxidation(1). The magnesium aluminate s p i n e l s t h a t we have t e s t e d a r e M g A l 0 and M g A l 0 . The l a t t e r i s a s o l i d s o l u t i o n (2,3) o f pure s p i n e l (MgAl 0 ) and MgO. The s p i n e l s t r u c t u r e (4) i s based on a c u b i c c l o s e packed array o f oxide i o n s . T y p i c a l l y , t h e c r y s t a l l o g r a p h i c u n i t c e l l c o n t a i n s 32 oxygen atoms; one e i g h t h of the t e t r a h e d r a l h o l e s are occupied by t h e d i v a l e n t metal ions ( M g ) , and one h a l f o f the o c t a h e d r a l h o l e s are occupied by t h e t r i v a l e n t metal ions ( A l ) . Magnesium aluminate s p i n e l s can be prepared(5-8) by v a r i o u s methods such as i ) thermal co-condensation of oxides, i i ) c o - p r e c i p i t a t i o n o f hydroxides, and i i i ) co-gel formation. The r e s u l t s obtained from each of these procedures are b r i e f l y d i s c u s s e d below. 2

2

2

3

3

2

2

2

2

4

2

2

5

2

4

2+

3 +

Co-condensation o f oxides. The s t o i c h i o m e t r i c s p i n e l MgA1^0 can be prepared (4) by r e a c t i n g boehmite type r e a c t i v e alumina with high s u r f a c e area MgO a t a temperature h i g h e r than 1200°C (equation 1 ) . 4


6. BHATTACHARYYA ET AL.

MgO + A 1 0 2


>

3

MgAl 0 2

1)

4

T h i s procedure i s very u s e f u l when p r e p a r i n g ceramic spinel. The MgO can be replaced with MgC0 i f d e s i r e d which e v e n t u a l l y a t 1200°C y i e l d s MgO. R e p e t i t i v e p u l v e r i z a t i o n and c a l c i n a t i o n steps are r e q u i r e d t o q u a n t i t a t i v e l y generate high q u a l i t y s p i n e l , M g A l 0 . X-ray d i f f r a c t i o n o f t h i s m a t e r i a l i s shown i n Figure 1. A t a temperature below 1200°C, the s p i n e l formation i s very poor (Figure 1). High temperature c a l c i n a t i o n which i s e s s e n t i a l f o r the formation o f good q u a l i t y s p i n e l causes s i n t e r i n g . Because o f s i n t e r i n g the s p i n e l m a t e r i a l becomes denser (sharper X-Ray peaks) and l o s e s s u r f a c e area and pore volume (Table I ) . When impregnated with C e ( N 0 ) s o l u t i o n and c a l c i n e d t h i s s p i n e l produces a m a t e r i a l t h a t has a very poor SOx removal a c t i v i t y (Table I, F i g u r e 2) because o f a l a c k o f s u r f a c e area and low pore volume. The amount o f S 0 picked up by t h i s c a t a l y s t i s 3% o f i t s i n i t i a l weight. T h i s , we b e l i e v e , i s because o f a l a c k o f s u r f a c e area and low pore volume. In Zone D when the s u l f a t e d c a t a l y s t i s r e a c t e d with H t h e r e d u c t i o n i s very u n s a t i s f a c t o r y . The r a t e o f r e d u c t i o n i s slow and the m a t e r i a l does not r e l e a s e a l l the absorbed s u l f u r even a f t e r 10 minutes o f H reduction. The s o l i d s o l u t i o n s p i n e l , M g A l 0 , cannot be prepared by t h i s method because such a h i g h e r temperature (>1200°C) causes the MgO t o d i s s o c i a t e out of the s p i n e l framework (equation 2) 3


2

3

4

3

3

2

2

2

Mg Al 0 2

2

>

5

2

MgO + M g A l 0 2

5

2)

4

C o - p r e c i p i t a t i o n o f Hydroxides. Some o f the important f a c t o r s f a v o r i n g s o l i d s t a t e r e a c t i o n s are h i g h surface area and homogeneous mixing o f s t a r t i n g m a t e r i a l s . A l l these c o n d i t i o n s would be met i f the hydroxides o f aluminum and magnesium could be c o - p r e c i p i t a t e d i n the appropriate p r o p o r t i o n s t o produce s p i n e l s . Various workers (5-7) have used t h i s c o - p r e c i p i t a t i o n technique to prepare s p i n e l s M g A l 0 and M g A l 0 u s i n g water s o l u b l e s a l t s o f aluminum and magnesium. 2

Mg(N0 ) 3

2

+ NaA10 x

3

2

2

5

> [MgAl(OH) _ ](N0 )

2

[MgAl(0H) _ ](N0 ) 5

4

5

7 x

0

0 C

Mg Al 0 2

2

5

x

+ N0

3

x

3)

2

T h i s method, u n l i k e the co-condensation method, does not r e q u i r e a very high temperature c a l c i n a t to produce s p i n e l s t r u c t u r e from c o - p r e c i p i t a t e d double hydroxides. U s u a l l y a temperature o f 700 t o 800°C and 2 t o 3 hours o f c a l c i n a t i o n i s s u f f i c i e n t t o convert the c o - p r e c i p i t a t e d double hydroxide t o s p i n e l . The c h a r a c t e r i s t i c X-Ray d i f f r a c t i o n p a t t e r n s o f M g A l 0 and M g A l 0 are presented i n Figure 3. I t may be 2

2

2

5


4

49

50

CHARACTERIZATION AND CATALYST D E V E L O P M E N T

42.9° MgO (200)

44.8° MgAI 0 (400)

62.3° MgO (220)

2

65.25° MgAI 0 (440)

4

2

59.5° MgAI 0 (511)


2

A

I

I

B

I I I I I I I I I I I I II

42

50

58

I

l

42

66

4

4

I I I I I I I I I I

I

50

58

66

F i g u r e 1. X-Ray D i f f r a c t i o n P a t t e r n s o f MgAÔ^ P r e p a r e d b y Thermal Co-Condensation Method. A=Incomplete (1000°C, 7 h ) ; B=Complete.

Table I .

P h y s i c a l and Chemical P r o p e r t i e s o f S p i n e l s Prepared by D i f f e r e n t Methods

Preparative Route

Spinel Type

Surface Area (in /g)

Pore Volume (cc/g)

2 180 150 169 165

0.15 0.40 0.41 0.32 0.36

2

Co-condensation Co-precipitation

MgAl 0 MgAl 0 Mg Al 0 MgAl 0 Mg Al 0 2

4

?

4

2

Co-gellation

2

2

2

5

4

2

5

Zone 8

%so

3

Absorbed

3.0 10.9 13.6 8.8 11.4

Zone 0

Zone C

I00%: at 0-0 Min S 0 2 1 0 3 % ! 1 5 . 0 Min S 0 2 ;. Wi#,ftfter 10 Min H2 = 101, :

i 13.2

17.6

22

26.4

Time (Min)

i

i 30.8

i

i 35.2

i

\ r 39.6

48.4

F i g u r e 2. TGA T e s t o f a Ce02/MgAl 04 C a t a l y s t P r e p a r e d b y Co-Condensation Method. 2


6.

Magnesium Aluminate Spinel for S0 Abatement

BHATTACHARYYA ET AL.

X

noted here t h a t t h e d i f f r a c t i o n p a t t e r n o f M g A l 0 i s very s i m i l a r t o M g A l 0 and does not e x h i b i t a MgO peak. In a same plane (hkl) t h e r e f l e c t i o n occurs a t a s l i g h t l y lower angle (20) i n M g A l 0 compared t o M g A l 0 (Figure 3 ) . The p h y s i c a l p r o p e r t i e s o f t h e s p i n e l s prepared by t h i s method (Table I) are very d i f f e r e n t from those prepared by t h e co-condensation method. The s p i n e l s prepared by t h i s method have a v e r y h i g h surface area (-150 m /g). When impregnated with C e ( N 0 ) s o l u t i o n and c a l c i n e d t h e r e s u l t i n g c a t a l y s t s a r e extremely a c t i v e towards SOx abatement (Table I , F i g u r e 4). The s o l i d s o l u t i o n s p i n e l c a t a l y s t i s n e a r l y 25% more a c t i v e than the s t o i c h i o m e t r i c s p i n e l c a t a l y s t . T h i s can be e x p l a i n e d by assuming t h a t -MgO- s t r u c t u r a l fragments of t h e s p i n e l a r e the chemisorption a c t i v e s i t e s (1). There a r e more a c t i v e s i t e s i n M g A l 0 c than i n MgA1^0 . We a l s o see t h a t t h e c a t a l y s t prepared by cop r e c i p i t a t i o n method i s 4 times more a c t i v e than the c a t a l y s t prepared by the thermal co-condensation method. In Zone D we see t h a t t h e s u l f a t e d c a t a l y s t i s very e f f e c t i v e l y reduced by . Nearly 70% o f the absorbed s p e c i e s i s reduced w i t h i n 2 min. o f r e d u c t i o n . The Ce0 e x i s t s i n the c a t a l y s t as a w e l l d i s p e r s e d but X-Ray i d e n t i f i a b l e m i c r o c r y s t a l l i n e solid. The X-Ray d i f f r a c t i o n peaks a t 20 = 47.9° (220) and 56.7° (311) (Figures 3 and 5) a r e c h a r a c t e r i s t i c o f Ce0 c r y s t a l l i t e s . 2

2

2

2

2

5

4

2

5

4

2


3

3

2

2

4

2

2

Co-gel formation. In a d d i t i o n t o t h e c o - p r e c i p i t a t i o n of t h e two hydroxides we have found t h a t a very homogeneous mixture o f M g and A l s p e c i e s can be obtained by co-gel formation (8). T h i s c o - g e l , u s u a l l y prepared by combining aqueous s l u r r i e s o f psuedoboehmite alumina, high s u r f a c e area MgO, and an a c i d , i s d r i e d and c a l c i n e d a t 700 t o 800°C t o produce both s t o i c h i o m e t r i c and high magnesium s p i n e l s (reaction 4). 2+

Mg

2 +

3 +

+ A c i d i c AIO(OH) MgAl(0H)

7 5

0

0

M g

> MgAl(0H) 2

A l

2

0

5

4)

5

The c h a r a c t e r i s t i c X-Ray d i f f r a c t i o n p a t t e r n s of these s p i n e l s , which are very s i m i l a r t o the one prepared by t h e c o - p r e c i p i t a t i o n method, a r e presented i n F i g u r e 5. The d i f f r a c t i o n p a t t e r n o f MgÂÔg i s very s i m i l a r t o M g A l 0 and does not e x h i b i t a MgO peak. Again, i n a same plane (hkl) t h e r e f l e c t i o n occurs a t a s l i g h t l y lower angle (20) i n M g A l 0 compared t o M g A l 0 (Figure 5 ) . The p h y s i c a l p r o p e r t i e s such as surface area and pore volume o f these s p i n e l s a r e very s i m i l a r t o the ones prepared by c o - p r e c i p i t a t i o n method (Table I ) . 2

4

2

2

2

5

4


51

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CHARACTERIZATION AND CATALYST DEVELOPMENT


37.0

44.8

47.9

56.7

65.2°

i

1

1

1

r

34

42

50

58

66

F i g u r e 3. X-Ray D i f f r a c t i o n P a t t e r n s o f M g A l 0 4 (A) and M g A l 0 5 (B) P r e p a r e d by C o - P r e c i p i t a t i o n Method. 2

2

2

(166) 105.00

(16.3) -

103.00 (16.0) 101.00 (15.6) 99.00 (153) 97.00 (15.0) 95.00 (14.7) 93.00 (14.4) 91.00

Zone A

ZoneB

\

Zone C

/

Zone D

A — \ \

/

, / 91.8%.at; 0.0 Min S 0 2 104.3% at 15.0 Min S 0 2

/ - M i l l

V

W l % After 10 Mm H2 = 92.1 I • I I

I 13.2

\

17.6

f 22

\

I

26.4

I I I

I I ! 30.8

35.2

M

39.6

t 48.4

Time (Min)

F i g u r e 4. TGA T e s t o f C e 0 / M g A l 0 5 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 Method. 2

44.9° MgAI 0 2

42

2

2

65.2° MgAI 0

4

2

50

58

4

66

F i g u r e 5. X-Ray D i f f r a c t i o n P a t t e r n s o f M g A l 0 (B) P r e p a r e d by C o - G e l l a t i o n Method. 2

4

(A) and M g A l 0


2

2

5

6. BHATTACIIARYYA ET AL.


When these s p i n e l s are impregnated with C e ( N 0 ) and c a l c i n e d the r e s u l t i n g c a t a l y s t s a r e n e a r l y as a c t i v e as t h e c o - p r e c i p i t a t e d products (Table I, F i g u r e 5 ) . The amount o f S 0 absorbed i n Zone B by t h e h i g h magnesium s p i n e l c a t a l y s t i s 11.4% o f i t s i n i t i a l weight i n 15 min. which i s about f o u r times more than the c a t a l y s t prepared by co-condensation method (Figure 6). Once again the high magnesium s p i n e l i s about 25% more a c t i v e than the s t o i c h i o m e t r i c s p i n e l p o s s i b l y because o f higher a b s o r p t i o n a c t i v e s i t e d e n s i t y i n the former m a t e r i a l . In zone D the H r e d u c t i o n i s very effective. S i m i l a r t o t h e c a t a l y s t prepared by t h e c o p r e c i p i t a t i o n method t h i s m a t e r i a l r e l e a s e s 70% o f the absorbed s u l f u r w i t h i n 2 min. 3

3

3


2

Conclusion I t i s very apparent from t h i s work t h a t cop r e c i p i t a t i o n and c o - g e l formation methods f o r t h e p r e p a r a t i o n o f s p i n e l s p r o v i d e very a c t i v e c a t a l y s t s f o r FCC SOx r e d u c t i o n whereas the co-condensation method produces very dense ceramic type s p i n e l s with low a c t i v i t y . The high magnesium s p i n e l c a t a l y s t i s more a c t i v e than the s t o i c h i o m e t r i c s p i n e l c a t a l y s t . The c o - g e l formation method i s more convenient and a l s o p r o v i d e s a more a t t r i t i o n r e s i s t a n t product than t h e c o - p r e c i p i t a t i o n technique.

Zone C

Zone D

87.8% at 0,0 Min S 0 2 97,7% at 15.0 Min S 0 2 Wt% After 10 Min H2 - 87,4 I 1 1 I I I I V.

I I -1

7.6

22

26.4

Time (Min)

30.8

35.2 39.6

48.4

F i g u r e 6. TGA T e s t o f a C e 0 / M g A l 0 5 C a t a l y s t P r e p a r e d b y C o - G e l l a t i o n Method. 2

2

2

ACKNOWLEDGMENTS The authors wish t o thank John Karen, John Magee, Joseph Powell, and J i n Yoo f o r v a l u a b l e suggestions and Kathleen Kennedy f o r sample p r e p a r a t i o n s . LITERATURE CITED (1)

Bhattacharyya, A. A.; Woltermann, G. M.; Yoo, J .


53

54

(2) (3) (4)


(5) (6) (7) (8)

CHARACTERIZATION AND CATALYST DEVELOPMENT S.; Karen, J . A.; Cormier, W. E., Ind Eng. Chem. Res. 1988, 27, 1356. A l p e r , A.M.; McNally, R.N.; Ribbe, P.H.; Doman, R.C., J. Am. Ceram. Soc. 1962, 45, 263. Ramkin, G.A.; Merwin, H.W., J . Am. Chem. Soc. 1916, 38, 568. West, A.R., In S o l i d S t a t e Chemistry and I t s A p p l i c a t i o n s John Wiley and Sons, 1987, pp. 4-14. Mukherjee, S. G.; Samaddar, B. N. Trans. Indian Ceram. Soc. 1966, 25, 33 B r a t t o n , R. J. Amer. Ceram. Soc. Bull., 1969, 48, 759. Yoo, J. S.; Jaecker, J. A. U.S. Patent 4,469,589, Sept. 4, 1984 Bhattacharyya, A. A.; Cormier, W. E.; Woltermann, G. M. U.S. Patent No. 4,728,635, March 1, 1988

R E C E I V E D April 27, 1989


Characterization and Catalyst Development - American Chemical

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