Hydrous Sodium Titanate Ion-Exchange Materials for Use as Catalyst

Chapter 8

Hydrous Sodium Titanate Ion-Exchange Materials for Use as Catalyst Supports Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 26, 2017 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0411.ch008

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B. C . Bunker , C . H . F . Peden , S. L . Martinez , E . J. Braunschweig , and A. K . Datye 2

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Sandia National Laboratories, Albuquerque, N M 87185 University of New Mexico, Albuquerque, N M 87131 2

Understanding how the activity of a catalyst is related to the concentration and dispersion of active metals on the catalyst support is c r i t i c a l to designing materials having the optimum catalytic properties. We have developed synthetic techniques for controlling both the concentration and dispersion of nickel on hydrous sodium titanate catalyst supports. The techniques require an understanding of the solution chemistry of both the support material and dissolved metal species (hydrolysis products). In this paper, we present the results of a study of three nickel-loaded samples of hydrous sodium titanate in which the scale of the nickel dispersion ranges from the atomic level to the scale of large (50 nm) clusters. The catalysts are characterized by transmission electron microscopy (TEM), hydrogen chemisorption, and BET surface area measurements. In a d d i t i o n , the a c t i v i t y and selectivity of the Ni catalysts for the n-butane hydrogenolysis reaction is used to monitor the surface structures of Ni in the catalysts.

A group o f hydrous o x i d e i o n exchangers o f T i , Z r , Nb, and Ta, p r e p a r e d v i a h y d r o l y s i s o f r e s p e c t i v e m e t a l a l k o x i d e s , have shown g r e a t promise f o r use as c a t a l y s t s u b s t r a t e s ( 1 ) . F o r example, c o a l l i q u i f a c t i o n c a t a l y s t s p r e p a r e d on hydrous sodium t i t a n a t e s are up t o two o r d e r s o f magnitude more 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 o f m o d e l s o l v e n t s s u c h a s p y r e n e t h a n a r e c a t a l y s t s p r e p a r e d on t r a d i t i o n a l a l u m i n a s u p p o r t s on a p e r gram o f m e t a l b a s i s ( 2 ) . One r e a s o n f o r improved c a t a l y t i c a c t i v i t y may be t h a t a c t i v e m e t a l s such as n i c k e l c a n be a t o m i c a l l y d i s p e r s e d a t h i g h (> 5%) m e t a l l o a d i n g s on sodium t i t a n a t e v i a i o n exchange i n aqueous s o l u t i o n s .

0097-6156/89/0411-0065$06.00/0 © 1989 American Chemical Society

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

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 26, 2017 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0411.ch008

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The method o f p r e p a r i n g t h e t i t a n a t e s u p p o r t powder o f f e r s t h e p o s s i b i l i t y o f c o n t r o l l i n g t h e ion-exchange p r o p e r t i e s ( c a p a c i t y , pH dependence, e t c . ) o f t h e m a t e r i a l d u r i n g t h e s y n t h e s i s . In a d d i t i o n , o t h e r i m p o r t a n t m a t e r i a l p r o p e r t i e s such as t h e s u r f a c e area are, i n p r i n c i p l e , c o n t r o l l a b l e by the s o l u t i o n chemical t e c h n i q u e s u s e d t o p r e p a r e the powders. To o p t i m i z e t h e use o f t h e amorphous sodium t i t a n a t e powders as c a t a l y s t substrates, i t i s important t o f u l l y c h a r a c t e r i z e the ionexchange p r o p e r t i e s o f t h e m a t e r i a l . Further, the solution p r o p e r t i e s o f t h e a c t i v e m e t a l t o be l o a d e d onto t h e s u p p o r t w i l l be an i m p o r t a n t parameter i n t h e c o n t r o l o f t h e a d s o r p t i o n process. For example, exposure o f sodium t i t a n a t e t o a n i c k e l s a l t s o l u t i o n does n o t g u a r a n t e e t h a t n i c k e l w i l l be l o a d e d o n t o t h e sodium t i t a n a t e , o r t h a t t h e n i c k e l , i f l o a d e d , w i l l be d i s p e r s e d on an atomic l e v e l . Sodium t i t a n a t e o n l y behaves as a c a t i o n exchange m a t e r i a l u n d e r c e r t a i n pH c o n d i t i o n s . The s o l u t i o n pH a l s o i n f l u e n c e s t h e h y d r o l y s i s and s p e c i a t i o n o f d i s s o l v e d n i c k e l i o n s (3.) , w h i c h c a n form l a r g e p o l y m e r i c c l u s t e r s o r c o l l o i d a l p a r t i c l e s w h i c h a r e n o t adsorbed b y t h e sodium t i t a n a t e v i a a s i m p l e i o n exchange p r o c e s s . T h i s paper d e s c r i b e s some o f o u r i n i t i a l s t u d i e s o f t h e s o l u t i o n p r o p e r t i e s o f sodium t i t a n a t e powders i n o r d e r t o u n d e r s t a n d and control the metal-loading process i n the preparation of a heterogeneous c a t a l y s t from t h e m a t e r i a l s . The purposes o f t h i s study are: 1) t o d e f i n e t h e pH and c o n c e n t r a t i o n regimes i n w h i c h n i c k e l i s l o a d e d onto sodium t i t a n a t e as monomeric i o n s v i a i o n e x c h a n g e , as p o l y m e r i c c l u s t e r s v i a h y d r o l y s i s , o r as d i s c r e t e p a r t i c l e s o f c o l l o i d a l n i c k e l h y d r o x i d e , and 2) t o c h a r a c t e r i z e t h e c a t a l y s t s w i t h r e s p e c t t o t h e d i s p e r s i o n o f t h e a c t i v e m e t a l under r e a c t i o n c o n d i t i o n s by m e a s u r i n g 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 t h e c a t a l y s t s f o r a known " s t r u c t u r e - s e n s i t i v e " r e a c t i o n , t h e h y d r o g e n o l y s i s o f n-butane. Experimental Hydrous sodium t i t a n a t e was p r e p a r e d by t h e method o f Dosch and Stephens (1) . T i t a n i u m i s o p r o p o x i d e was s l o w l y added t o a 15 wt% s o l u t i o n o f sodium h y d r o x i d e i n methanol. The r e s u l t i n g s o l u t i o n was h y d r o l y z e d b y a d d i t i o n t o 10 v o l % w a t e r i n a c e t o n e . The h y d r o l y s i s p r o d u c t i s an amorphous hydrous o x i d e w i t h a Na:Ti r a t i o o f 0.5 w h i c h c o n t a i n s , a f t e r vacuum d r y i n g a t room t e m p e r a t u r e , a p p r o x i m a t e l y 13.5 wt% w a t e r and 2.5 wt% r e s i d u a l a l c o h o l . The i o n exchange c h a r a c t e r i s t i c s o f t h e sodium t i t a n a t e and t h e h y d r o l y s i s b e h a v i o r o f t h e n i c k e l n i t r a t e s o l u t i o n s were c h a r a c t e r i z e d u s i n g a c o m b i n a t i o n o f p o t e n t i o m e t r i c t i t r a t i o n s , i n d u c t i v e l y c o u p l e d plasma atomic emission (ICP) a n a l y s i s o f f i l t r a t e s , and s u r f a c e charge measurements o b t a i n e d u s i n g a Matec e l e c t r o s o n i c a m p l i t u d e d e v i c e . Three d i f f e r e n t n i c k e l - l o a d e d sodium t i t a n a t e s were p r e p a r e d by e x p o s i n g 5 gm o f t h e sodium t i t a n a t e powder t o aqueous s o l u t i o n s o f n i c k e l n i t r a t e c o n t a i n i n g s u f f i c i e n t n i c k e l t o i n c o r p o r a t e one mole o f n i c k e l f o r e v e r y two moles o f sodium on t h e s u p p o r t (corresponding t o t h e s t o i c h i o m e t r y a s s o c i a t e d w i t h complete i o n exchange). Each sample was p r e p a r e d u s i n g d i f f e r e n t pH c o n d i t i o n s (and t h u s , d i f f e r e n t N i ( I I ) c o n c e n t r a t i o n s ) t o v a r y the mechanism o f



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Hydrous Sodium Titanate Ion-Exchange Materials

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n i c k e l l o a d i n g ( s e e R e s u l t s and D i s c u s s i o n ) . To o b t a i n atomic d i s p e r s i o n s o f N i ( I I ) v i a i o n exchange, t h e t i t a n a t e powder was added t o pH 5-6 s o l u t i o n s o f aqueous Ni(N03)2T h i s p r o c e d u r e was p e r f o r m e d t h r e e times w i t h i n t e r m e d i a t e f i l t r a t i o n s . To f a v o r t h e formation of small, hydrolyzed c l u s t e r s , a stoichiometric n i c k e l s o l u t i o n was added dropwise t o a s l u r r y o f t h e t i t a n a t e powder i n d e i o n i z e d w a t e r a t a pH o f 11. C o n c u r r e n t w i t h t h e N i a d d i t i o n , NaOH was added t o m a i n t a i n t h e pH a t o r n e a r 11. To f a v o r t h e f o r m a t i o n and a d s o r p t i o n o f c o l l o i d a l n i c k e l h y d r o x i d e , sodium h y d r o x i d e was u s e d t o a d j u s t t h e pH o f t h e n i c k e l n i t r a t e s o l u t i o n t o pH 12.7 p r i o r t o t h e a d d i t i o n o f t h e sodium t i t a n a t e . The pH adjustment caused the d i s s o l v e d n i c k e l to form a c o l l o i d a l s u s p e n s i o n o f n i c k e l h y d r o x i d e w h i c h was t h e n a d s o r b e d on t h e sodium t i t a n a t e support. A l l t h r e e samples were a n a l y z e d f o r Na, N i , and T i b y r e d i s s o l v i n g t h e t i t a n a t e powders i n s t r o n g a c i d and a n a l y z i n g the s o l u t i o n s u s i n g atomic a d s o r p t i o n and ICP s p e c t r o s c o p i e s . T r a n s m i s s i o n e l e c t r o n m i c r o g r a p h s were o b t a i n e d from e i t h e r a JEM 200CX i n s t r u m e n t o r a JEOL 2000FX TEM/STEM u s i n g l o w beam i n t e n s i t y t o a v o i d beam a l t e r a t i o n o f t h e samples. The powders were s u p p o r t e d on h o l e y c a r b o n f i l m s mounted on copper g r i d s . Powder s u r f a c e a r e a s were measured u s i n g N2 a d s o r p t i o n i n a M i c r o m e r i t i c s D i g i s o r b 2600 a n a l y z e r . The samples were o u t g a s s e d a t 150 °C f o r 4 h o u r s i n f l o w i n g He b e f o r e t a k i n g t h e measurements. Metal surface a r e a was d e t e r m i n e d b y s t a t i c v o l u m e t r i c c h e m i s o r p t i o n using r e s e a r c h p u r i t y gases o b t a i n e d from Matheson. The c h e m i s o r p t i o n was p e r f o r m e d a t room temperature and t o t a l uptake o f H2 was used as a measure o f t h e s u r f a c e c o n c e n t r a t i o n o f N i . A l l c a t a l y s t s h a d a n o m i n a l l o a d i n g o f 10-11% N i . The c a t a l y t i c a c t i v i t y f o r n-butane h y d r o g e n o l y s i s was measured i n , a q u a r t z U-tube r e a c t o r u s i n g a f e e d s t r e a m c o n t a i n i n g H2 and n - C ^ ^ o i n t h e r a t i o 20:1 a t a t o t a l p r e s s u r e o f 101.4 kPa. UHP (99.999%) H2 was o b t a i n e d from B i g Three I n d u s t r i e s and r e s e a r c h p u r i t y (99.99%) n - C ^ ^ o from Matheson. Both gases were u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n . The r e a c t i o n p r o c e e d e d w i t h l i t t l e o r no d e a c t i v a t i o n o v e r s e v e r a l (10-15) h o u r s . R a t e s a r e r e p o r t e d as a t u r n o v e r f r e q u e n c y (TOF) , o r t h e number o f n-butane m o l e c u l e s r e a c t e d p e r second p e r s u r f a c e N i atom, w i t h t h e l a t t e r q u a n t i t y b e i n g d e t e r m i n e d by H2 c h e m i s o r p t i o n . Chemisorption measurements were p e r f o r m e d a f t e r r e d u c t i o n a t 673 K f o l l o w e d by c o o l i n g t o room temperature i n vacuum. R e s u l t s and D i s c u s s i o n I n o r d e r t o c o n t r o l t h e mechanism by w h i c h n i c k e l i s l o a d e d onto sodium t i t a n a t e and t o c o n t r o l t h e degree o f n i c k e l d i s p e r s i o n , we n e e d t o u n d e r s t a n d t h e i o n - e x c h a n g e p r o p e r t i e s o f t h e sodium t i t a n a t e support, the h y d r o l y s i s chemistry o f the d i s s o l v e d n i c k e l , and how t h e d i f f e r e n t n i c k e l s p e c i e s a r e e x p e c t e d t o i n t e r a c t w i t h the t i t a n a t e s u p p o r t . Ion-Exchange Behavior o f Sodium T i t a n a t e . The i o n - e x c h a n g e c h a r a c t e r i s t i c s o f sodium t i t a n a t e s u p p o r t s a r e summarized i n F i g . 1 ( 2 ) . I n t h e f i g u r e , p r o t o n consumption i s p l o t t e d by t h e s o l i d l i n e as t h e N a o . s T i i s t i t r a t e d from a b a s i c pH (=-12) w i t h HC1. Na+ (+) l o s s from and C I " (-) a d s o r p t i o n onto t h e s u p p o r t a r e f o l l o w e d by



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

a n a l y s i s o f t h e s o l u t i o n s by ICP. A t pH v a l u e s above t h e i s o e l e c t r i c p o i n t ( i e p ) o f sodium t i t a n a t e (pH 5 ) , the s u r f a c e s o f the sodium t i t a n a t e p a r t i c l e s are c o v e r e d w i t h a n i o n i c s u r f a c e s i t e s t h a t a r e charge compensated by c a t i o n s such as sodium. Above pH 5, t h e t i t a n a t e s u p p o r t can f u n c t i o n as a c a t i o n e x c h a n g e r . For example i f C a ( I I ) i o n s a r e added t o a sodium t i t a n a t e s l u r r y , s o l u t i o n a n a l y s e s i n d i c a t e t h a t one c a l c i u m i o n i s adsorbed by the s u p p o r t f o r e v e r y two sodium i o n s r e l e a s e d i n t o s o l u t i o n . Below pH 5, s u r f a c e s i t e s on the t i t a n a t e s u p p o r t a r e p r i m a r i l y c a t i o n i c , and the s u p p o r t behaves as an a n i o n r a t h e r t h a n a c a t i o n exchanger. In the above example, n e i t h e r C a ( I I ) o r N a ( I ) i o n s a r e adsorbed by the t i t a n a t e powder when the s o l u t i o n pH i s h i g h l y a c i d i c (below pH 4 ) . T h e r e f o r e , the s o l u t i o n c h e m i s t r y o f sodium t i t a n a t e s u g g e s t s t h a t i f the powder i s exposed t o N i ( I I ) , and i f the N i ( I I ) i s t o be l o a d e d v i a an ion-exchange p r o c e s s , l i t t l e or no N i ( I I ) a d s o r p t i o n i s t o be e x p e c t e d below pH 5. A l s o a p p a r e n t i n F i g . 1 (note the two regimes o f H consumption a t n e a r l y c o n s t a n t pH o f about 8 and 12) and i n s u r f a c e charge measurements as a f u n c t i o n o f pH (not shown, see Ref. 4) , i s the p r e s e n c e o f a t l e a s t two a n i o n i c s u r f a c e s i t e s above pH 5. The d i s t r i b u t i o n o f these two s i t e s i s c o n t r o l l a b l e d u r i n g the s y n t h e s i s o f the sodium t i t a n a t e powder. U s i n g Raman and s o l i d s t a t e 1^0 NMR s p e c t r o s c o p i e s (5) we are a t t e m p t i n g t o i d e n t i f y s p e c i f i c a d s o r p t i o n s i t e s r e s p o n s i b l e f o r t h e d i f f e r i n g s o l u t i o n b e h a v i o r , and t o c h a r a c t e r i z e changes i n the d i s t r i b u t i o n o f such s i t e s . In this way, the t a i l o r i n g o f the s u p p o r t ' s ion-exchange p r o p e r t i e s can be r e a l i z e d . We have a l s o found (4.5) t h a t i r r e v e r s i b l e changes i n the t i t a n a t e s u p p o r t s t r u c t u r e , and i n the type and number o f i o n exchange s i t e s can o c c u r d u r i n g i o n exchange i n a c i d i c s o l u t i o n s . T h i s r e s u l t demonstrates t h a t the c h e m i c a l s t a b i l i t y o f the s u p p o r t d u r i n g m e t a l l o a d i n g needs t o be c o n s i d e r e d . +

N i C I I ) H y d r o l y s i s Chemistry. A l t h o u g h N i ( I I ) e x i s t s i n s o l u t i o n as a s i m p l e a q u a t e d c a t i o n i n a c i d i c s o l u t i o n s , i n c r e a s e s i n the s o l u t i o n pH can l e a d t o the d e p r o t o n a t i o n o f bound w a t e r m o l e c u l e s , l e a d i n g t o h y d r o l y s i s and c o n d e n s a t i o n o f N i ( I I ) t o form i n s o l u b l e polymeric c l u s t e r s . The c a l c u l a t e d h y d r o l y s i s d i a g r a m (3) f o r N i ( I I ) ( F i g . 2 ) , shows t h a t f o r a 3 x 1 0 " M nickel nitrate s o l u t i o n , h y d r o l y s i s and c o n d e n s a t i o n commence a t a pH o f 6.5. This is evidenced by the c o i n c i d e n c e of the c a l c u l a t e d N i ( I I ) c o n c e n t r a t i o n and the t o t a l N i c a l c u l a t e d t o be s o l u b l e ( F i g . 2) above pH 6.5. F u r t h e r i n c r e a s e s i n pH l e a d t o the f o r m a t i o n o f l a r g e r i n s o l u b l e p o l y m e r i c s p e c i e s w i t h n i c k e l becoming l e s s and l e s s s o l u b l e as the pH i s r a i s e d t o pH 10. A l t h o u g h the s o l u b i l i t y i n c r e a s e s w i t h pH above pH 10, the c a l c u l a t e d s o l u b i l i t y i s s t i l l below 1 0 M even a t pH 14. The h y d r o l y s i s diagram s u g g e s t s t h a t N i ( I I ) can o n l y be l o a d e d by a s i m p l e ion-exchange p r o c e s s a t pH v a l u e s below 6.5 where h y d r o l y s i s i s n e g l i g i b l e . Above pH 6.5, p o l y m e r i c n i c k e l c l u s t e r s w i l l be p r e s e n t w h i c h can e i t h e r condense w i t h s u r f a c e s i t e s on the t i t a n a t e s u p p o r t v i a r e a c t i o n s such as: 2

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50

550 K ) , methane i s t h e predominant p r o d u c t . I n the case o f t h e c a t a l y s t p r e p a r e d by p r e - h y d r o l y s i s (Sample #3), methane i s t h e p r i m a r y p r o d u c t f o r a l l temperatures s t u d i e d . These r e s u l t s confirm our e a r l i e r conclusions concerning the d i s p e r s i o n o f n i c k e l i n t h e two c a t a l y s t s b a s e d on t h e TEM and c h e m i s o r p t i o n d a t a . That i s , r e a c t i v i t y o n Sample #3 i s c h a r a c t e r i s t i c o f l a r g e m e t a l p a r t i c l e s w h i l e t h e s e l e c t i v i t y o b s e r v e d on Sample #1 c l e a r l y i n d i c a t e s t h a t a t most v e r y s m a l l , h i g h l y d i s p e r s e d N i p a r t i c l e s a r e formed even a t these h i g h m e t a l l o a d i n g s (10 % ) . +

Summary and C o n c l u s i o n s We have p r e p a r e d and s t u d i e d t h e p r o p e r t i e s o f a sodium hydrous t i t a n i u m ion-exchange m a t e r i a l w h i c h shows g r e a t promise f o r u s e as a heterogeneous c a t a l y s t support. I n t h e s e s t u d i e s we h a v e i d e n t i f i e d t h e s o l u t i o n c o n d i t i o n s ( e . g . . pH) i n w h i c h t h e sodium t i t a n a t e s c o n t a i n s i t e s f o r the a d s o r p t i o n o f e i t h e r metal c a t i o n s or anions. F o r t h e exchange o f Na f o r N i ( I I ) c a t i o n s , s o l u t i o n s w i t h a pH o f 5 o r more a r e r e q u i r e d . However, N i ( I I ) undergoes e x t e n s i v e h y d r o l y s i s and c o n d e n s a t i o n r e a c t i o n s above a pH o f about 7-8 w h i c h competes w i t h ion-exchange onto t h e s u p p o r t when b o t h a r e present i n s o l u t i o n . We have p r e p a r e d t h r e e N i - l o a d e d hydrous t i t a n a t e s u n d e r d i f f e r e n t s o l u t i o n c o n d i t i o n s t o compare t h e i r m a t e r i a l and c a t a l y t i c p r o p e r t i e s . The c a t a l y s t s were c h a r a c t e r i z e d by s o l u t i o n a n a l y s e s , TEM, hydrogen c h e m i s o r p t i o n , BET s u r f a c e a r e a measurements, and 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 t h e n-butane hydrogenolysis reaction. The c a t a l y s t p r e p a r e d v i a i o n exchange d i s p l a y e d a h i g h degree o f s e l e c t i v i t y f o r ethane from s c i s s i o n o f t h e c e n t r a l C-C bond i n n-butane i n d i c a t i v e o f h i g h l y d i s p e r s e d



8.

BUNKER ET AL.

F i g u r e 5:


D a r k - f i e l d TEM m i c r o g r a p h o f Sample #3 as p r e p a r e d .

F i g u r e 6: A r r h e n i u s p l o t o f t h e r a t e o f n-butane h y d r o g e n o l y s i s o v e r S a m p l e #1 ( i o n - e x c h a n g e d N i c a t a l y s t ) and Sample #3 (precipitated Ni catalyst).


76

CHARACTERIZATION AND CATALYST DEVELOPMENT

100 T


£

Ion-Exchanged Ni Catalyst

80

REACTION TEMPERATURE

Precipitated Ni Catalyst 100T

£

60

C ,

523K

m

573K

598K

c

. r

623K

LEGEND

REACTION TEMPERATURE F i g u r e 7: S e l e c t i v i t y f o r C i (CH4) , C2 (C2H6) , and C3 (C3H8) h y d r o c a r b o n f o r m a t i o n from t h e h y d r o g e n o l y s i s o f n-butane o v e r Sample #1 and Sample #3.



8. BUNKER ETAL.


11

m e t a l even a t the l o a d i n g o f 10% used i n t h i s s t u d y . The absence o f m e t a l l i c N i i n TEM images o f t h i s c a t a l y s t i s f u r t h e r s u p p o r t f o r such a morphology. T h i s i s good e v i d e n c e t h a t a t o m i c l e v e l d i s p e r s i o n s o f N i a r e p r e s e n t i n the as p r e p a r e d c a t a l y s t and t h a t h i g h m e t a l d i s p e r s i o n s a r e m a i n t a i n e d upon hydrogen r e d u c t i o n a t 400 °C. However, H2 c h e m i s o r p t i o n i n d i c a t e s t h a t o n l y a s m a l l p o r t i o n o f the N i i s a c c e s s i b l e on the s u r f a c e o f the c a t a l y s t . We b e l i e v e t h a t the c r y s t a l l i z a t i o n o f the t i t a n a t e s u p p o r t t h a t accompanies the r e d u c t i o n o f N i a t 400 °C i n H2, e n c a p s u l a t e s most o f the m e t a l w i t h i n the d e n s i f i e d t i t a n a t e p a r t i c l e s making i t i n a c c e s s i b l e t o gas-phase s p e c i e s . The h i g h d i s p e r s i o n o f the m e t a l i n c a t a l y s t s p r e p a r e d b y i o n exchange onto the hydrous t i t a n a t e s u p p o r t s may w e l l e x p l a i n the h i g h a c t i v i t y (on a p e r gram o f m e t a l b a s i s ) o f t h e s e c a t a l y s t s r e l a t i v e t o c a t a l y s t s p r e p a r e d b y more c o n v e n t i o n a l methods ( 1 , 2 ) . I n these l a t t e r s t u d i e s , the metal i s reduced i n - s i t u during r e a c t i o n a t much lower temperatures t h a n used h e r e t o reduce N i . Thus, the a c c e s s i b i l i t y o f the m e t a l may n o t be compromised b y the r e s t r u c t u r i n g o f the c a t a l y s t s u p p o r t m a t e r i a l . I n the f u t u r e , we w i l l i n v e s t i g a t e more moderate m e t a l r e d u c t i o n methods, more e a s i l y r e d u c i b l e m e t a l s , and m o d i f i c a t i o n s o f the s y n t h e s i s o f the sodium t i t a n a t e powders. I n t h i s w a y , we h o p e t o m a i n t a i n t h e a c c e s s i b i l i t y o f the m e t a l w h i l e s t i l l a c h i e v i n g the good d i s p e r s i o n a t h i g h m e t a l l o a d i n g s a f f o r d e d b y t h e u s e o f i o n exchange t o p r e p a r e a c a t a l y s t on the hydrous t i t a n a t e s . Acknowledgments The a u t h o r s would l i k e t o thank K. M. K i m b a l l f o r p r e p a r i n g the t h r e e N i - l o a d e d c a t a l y s t s , T. J . Headley f o r a p o r t i o n o f the TEM work, a n d D. H. Doughty f o r c a r r y i n g out the n i c k e l s o l u b i l i t y computations. T h i s work was s u p p o r t e d b y the Advanced R e s e a r c h and Technology Development Program, O f f i c e o f F o s s i l Energy o f the U. S. Department o f Energy. A p o r t i o n o f the e l e c t r o n m i c r o s c o p y was p e r f o r m e d a t the E l e c t r o n Microbeam A n a l y s i s F a c i l i t y s u p p o r t e d b y the Department o f Geology a t the U n i v e r s i t y o f New Mexico. Sandia N a t i o n a l L a b o r a t o r y i s s u p p o r t e d by U.S. Dept. of Energy c o n t r a c t No. DE-AC04-76DP00789. Literature Cited 1. a) Stephens, H. P.; Dosch, R. G.; Stohl, F. V. I&EC Prod. Res. Dev. 1985, 24, 15. b) Dosch, R. G.; Stephens, H. P. U.S. Patent 4 511 455, 1985. 2. Stephens, H. P.; Dosch, R. G. In Preparation of Catalysts IV; Delmon, B.; Grange, P.; Jacobs, P. A . ; Poncelet, G . , Eds.; Studies in Surface Science and Catalysis Series; Elsevier: Amsterdam, 1987; Vol. 31, p. 271. 3. Baes, C. F . , J r . ; Mesmer, R. E. The Hydrolysis of Cations; John Wiley & Sons: New York, 1976; pp. 241-247. 4. Braunschweig, E. J.; Datye, A. K.; Peden, C. H. F . ; Bunker, B. C.; Martinez, S. L. In preparation. 5. Bunker, B. C.; Peden, C. H. F . ; Martinez, S. L . ; Tallant, D. R.; Turner, G. L. In Better Ceramics Through Chemistry III; Brinker, C. J.; Clark, D. E . ; Ulrich, D. R., Eds.; Materials Research Society: New York, 1988; p. 105.


78 6. 7. 8. 9.

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

Boudart, M. Adv. Catal. 1969, 20, 153. Carter, J . T.; Cusumano, J . Α.; Sinfelt, J . H. J . Phys. Chem. 1966, 70, 2257. Foger, K.; Anderson, J . R. J . Catal. 1979, 59, 325. Engstrom, J . R.; Goodman, D. W.; Weinberg, W. H. J . Am. Chem. Soc. 1986, 108, 4653; and references therein. 1989


R E C E I V E D January 10,


Hydrous Sodium Titanate Ion-Exchange Materials for Use as Catalyst

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