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. US005336656AUnited States Patent [ 1 9 1 [ 1 1 ] P a t e n t N u m b e r : 5 , 3 3 6 , 6 5 6C a m p b e l l [ 4 5 ] D a t e o f P a t e n t : A u g . 9 , 1 9 9 4[ 5 4 ] CATALYST FOR PRODUCTION OFNITRIC 4 , 0 8 8 , 6 0 7 8 / 1 9 7 8 Weidenbach e t a 1 . . . . . . . . . . . . . . . 5 0 2 / 3 2 9

ACID BY OXIDATION OFAMMONIA 4 , 2 3 3 , 1 8 5 1 1 / 1 9 8 0 Knapton e t a 1 . . . . . . . . . . . . . . . . . 502/339 X_ 4, 2 5 1 , 2 3 9 2 / 1 9 8 1 Clyde et a l _ . . . . . . . . . . . . . . . . . . 5 5 / 1 3 2

[ 7 5 ] I n v e n t o r : L a r r y R a m p b e l l , K n 0 x v 1 l 1 e , T e n n - 4 , 2 5 3 , 3 0 2 3 / 1 9 8 1 A s a n o e t a 1 . 6 0 / 2 7 6. . . . 4,308,233 12/1981 N ' 422/502[73] Asslgnem sflentl?c Desg CmPany, Inc" 4,465,458 8/1984 . . . . . . . . . . . . 431/208Llt?e erry,N-J'- 4,568,595 2/1986 Morris . . . . . . . . . . .. 428/116

_ N: 306 4,792,435 1 2 / 1 9 8 8 Nakayama . . . . . . 4 2 2 / 1 1 0[ 2 1 ] Appl 1 2 0 4 , 8 1 0 , 6 8 5 3 / 1 9 8 9 T w i f f e t a 1 . 5 0 2 / 6 0[22] Filed: Sep. 10, 1993 4,863,712 9/1989 Twiff t a 1 . . . . . . . . . . . . . . 423/651

4,863,823 5 / 9 8 9 Farrento e t a l . . . . . . . . 5 0 2 / 3 2 57 R U. 1 i - 5,217,939 6/1993 Campbell . . . . . . .. 502/325e l a t e d S App mm a ta 5 , 2 4 2 , 8 8 2 9 / 1 9 9 3 Campbell . . . . . . 5 0 2 / 4 3 9

[ 6 0 ] C o n t i n u a t i o n o f S e r . No- 3 9 , 7 3 3 , Mar- 3 0 , 1 9 9 3 , a b a n - 5 , 2 5 6 , 3 8 7 1 0 / 1 9 9 3 Campbell . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 3 / 3 9 2c l o n e d , which s a d i v i s i o n o f S e r . N o . 9 8 3 , 0 4 2 , Nov. 0 ,1 9 9 2 , P a t . N o . 5 , 2 4 2 , 8 8 2 , which s a d i v i s i o n o f S e r . N o . OTHER PUBLICATIONS8 8 1 , 0 7 3 , M ay 1 , 1 9 9 2 , P a t . N o . 5 , 2 1 7 , 9 3 9 . C o l l e g e D i c t i o n a r y , R e v . e d . ( 1 9 8 2 ) , Random H o u s e ,

[ 5 1 ] I n t . C l . 5 . . . . . . . . . . . . . . . . . . . . . . . . B 0 1 J 2 3 / 0 6 ; B01J 2 3 / 7 4 ; I n c . , p . 8 5 1 .B01J 23/80 F a r r a n t i e t a 1 , Ammonia O x i d a t i o n C a t a l y s t with En~[ 5 2 ] US . C l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 0 2 / 3 2 9 ; 5 0 2 / 3 3 2 ; hanged A c t i v i t y , I n d , E n g , Chem, R e v , , v 0 1 . 2 9 , N0. 7 ,

5 0 2 / 3 4 2 ; 5 0 2 / 3 4 3 ; 5 0 2 / 4 3 9 1 9 9 0 , p p - 1 1 2 5 - 1 1 2 9F ' 1 f S h . . . . . . . . . . . . . . 5 0 2 329, 3 3 2 , 3 4 2 , 343, ,[ 5 8 ] 1 e d o e a r c / 5 o 2 / 4 3 9 Pnmary Examiner-Anthony McFarlane

A t t o r n e y , A g e n t , o r Firm-Kenneth H . Johnson[ 5 6 ] R e f e r e n c e s C i t e d [ 5 7 ] ABSTRACTU.S.PATENTDOCUMENTS , _ _R e t l c u l a t e d cerarmc or m e t a l s u b s t r a t e coated wlthg g g g i z 5 2 ; ; c o b a l t c o m p o u n d s , n o b l e m e t a l s o r m i x t u r e s t h e r e o f , a r e3 9 o 4 5 5 3 9 / 1 9 7 5 " " 2 5 2 / 4 6 5 s u p e r i o r c a t a l y s t s f o r t h e o x i d a t i o n o f ammonia t o p r o

3,957,685 5 / 1 976 . . . . . . . 5 0 2 / 1 0 duce mmcIde3 , 9 7 2 , 8 3 4 8 / 1 9 7 6 5 0 2 / 2 0 03 , 9 9 8 , 7 5 8 1 2 / 1 9 7 6 C l y d e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 0 2 / 3 0 7 10 C l a i m s , N0 rawings

7/28/2019 catalyst for nitric acid production

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5 , 3 3 6 , 6 5 61CATALYSTFOR PRODUCTION OF ITRIC ACIDBY OXIDATIONOF lVIMONIA

T h i s a p p l i c a t i o n i s a c o n t i n u a t i o n o f a p p l i c a t i o n S e r .N o . 0 8 / 0 3 9 , 7 3 3 , ? l e d M a r . 3 0 , 1 9 9 3 , now a b a n d o n e d ,which s a d i v i s i o n o f a p p l i c a t i o n S e r . No. 0 7 / 9 8 3 , 0 4 2 ,? l e d Nov. 3 0 , 1 9 9 2 , now U . S . P a t . No. 5 , 2 4 2 , 8 8 2 , whichi s a d i v i s i o n o f a p p l i c a t i o n S e r . No. 0 7 / 8 8 1 , 0 7 3 , ? l e dM a y 1 1 , 1 9 9 2 , now U . S . P a t . N o . 5 , 2 1 7 , 9 3 9 .

BACKGROUNDOFTHEINVENTION1 . F i e l d o f Th e I n v e n t i o nTh e p r e s e n t i n v e n t i o n r e l a t e s t o a n o v e l c a t a l y s t

s t r u c t u r e and t h e p r o c e s s f o r t h e p r e p a r a t i o n o f n i t r i ca c i d e m p l o y i n g t h e s t r u c t u r e .

2 . Relevant ArtN i t r i c a c i d i s m ade by x i d i z i n g ammonia v e r a w i r em e s h g a u z e c a t a l y s t p r o d u c e d b y w e a v i n g w i r e s o fp r e c i o u s m e t a l s ( e . g . p l a t i n u m , O s t w a l d p r o c e s s ) a n d

t h e i r a l l o y s . Th e p r o c e s s o p e r a t e s a t t e m p e r a t u r e s from8 0 0 t o 1 1 0 0 C . Th e h o t n i t r i c o x i d e f o r m e d i squenched and i r i s added s o t h e n i t r i c o x i d e o x i d i z e s t oN 0 2 n i t r o g e n ( I V ) o x i d e s ) which r e a c t s w i t h w a t e r t oform n i t r i c a c i d . Th e w i r e mesh g a u z e i s a l l o y e d t oi n c r e a s e h i g h t e m p e r a t u r e s t r e n g t h a n d t o r e d u c e c o s t s .T y p i c a l l y , p l a t i n u m i s u s e d a s t h e p r i m a r y c a t a l y s t a n di s a l l o y e d w i t h r u t h e n i u m t o i m p r o v e h i g h t e m p e r a t u r es t r e n g t h and p a l l a d i u m t o r e d u c e c o s t s . Th e r i o r a r t i nt h e n i t r i c a c i d p r o c e s s , determined t h a t a m ass of a t al y t i c m a t e r i a l , e . g . , p l a t i n u m was n e c e s s a r y b e c a u s e o ft h e c o n t i n u a l e r o s i o n o f t h e p l a t i n u m by v o l a t i l i z a t i o n .Ammonia o x i d a t i o n c a t a l y s t s f o r n i t r i c a c i d p r o d u ct i o n a r e based on p r e c i o u s m e t a l ?ne w i r e s w o v e n t og e t h e r on a loom i n t o t h e form o f a g a u z e . Th e t y p i c a lg a u z e c o n t a i n s 1 . 7 8 t r o y o u n c e s o f p l a t i n u m o r p r e c i o u sm e t a l a l l o y p e r s q u a r e f o o t . Fo r s o m e p l a n t s a s m a n y a s2 7 - 3 0 o f t h e s e g a u z e s e a c h 6 0 t o 1 2 0 i n c h e s i n d i a m e t e rm a y be s t a c k e d . These g a u z e s w i l l l a s t f o r s i x weeks t oa y e a r depending on t h e s e v e r i t y o f u s e ( h i g h p r e s s u r ev e r s u s lo w p r e s s u r e ) a nd can f a i l f o r a s v a r i e t y of r e as o n s i n c l u d i n g b u r n t h r o u g h ( c a u s e d by c h a n n e l i n g o rd i f ? c u l t s t a r t u p ) a n d l o s s o f p l a t i n u m m e t a l c l u e t ov o l a t i l i z a t i o n .Th e c o n v e n t i o n a l c a t a l y s t s a r e f r a g i l e a n d l o s e p l a t inu m t h i g h t e m p e r a t u r e v i a Pt02 o l a t i l i z a t i o n . Otherg a u z e s ( g e t t e r g a u z e s ) a r e u s e d downstream t o c a p t u r et h e v o l a t i l e p l a t i n u m s p e c i e s t h r o u g h a c o l l e c t i o n a n dr e d u c t i o n p r o c e s s .Th e gauze c a t a l y s t s a r e composed o f s c r e e n s with 3t o 3 0 s t a c k e d s c r e e n s u s e d . A i g h p r e s s u r e o x i d a t i o np r o c e s s r e q u i r e s more s c r e e n s and r e s u l t s i n h i g h e rl o s s e s o f p l a t i n u m m e t a l . T h i s s t a c k e d s c r e e n con?gurat i o n i s d i m e n s i o n a l l y u n s t a b l e i n t h a t t e x p a n d s a n d s a g sa n d a l l o w s n o n - u n i f o r m ?o w and t e m p e r a t u r e d i s t r i b ut i o n a n d p o o r m i x i n g .

F i n e w i r e s a r e d e s i r e d f o r improved c a t a l y s t p e r f o rmance b u t r e s u l t i n poor p h y s i c a l i n t e g r i t y and r e d u c e dl i f e . Th e p r o b l e m s w i t h t h e p l a t i n u m m e t a l a l l o y g a u z e sb e g i n a t s t a r t - u p . I t h a s b e e n c o n c l u d e d t h a t t h i s r e a ct i o n c a r r i e d ou t over p r e c i o u s m e t a l m e s h s mass t r a n sf e r l i m i t e d . M o s t gauze r e a c t o r s a r e over d e s i g n e d i nt e r m s of t h e number of g a u z e s . Th e over d e s i g n i s r eq u i r e d t o c o m p e n s a t e f o r p o o r u t i l i z a t i o n o f c a t a l y s t du et o poor ?ow i s t r i b u t i o n . Poor ?ow i s t r i b u t i o n du e t ono n u n i f o r m i t y and lo w p r e s s u r e drop c a u s e s ? i c k e ri n g a c o n d i t i o n i n which i n c r e a s e d ?ow h r o u g h agauze e c t i o n can e l e a s e more e a t . These i g h temper

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2a t u r e h o t s p o t s can l o s e p l a t i n u m a s t h e o x i d e a t t h eh i g h e r t e m p e r a t u r e . Th e non u n i f o r m i t y a n d low p r e ss u r e d r o p o f g a u z e s g i v e s r i s e t o a d d i t i o n a l l o s s o f e f f ic i e n c y i f t h e g a s e s a r e n o t t h o r o u g h l y m i x e d , a s l i t t l ea d d i t i o n a l m i x i n g i s a c h i e v e d b y t h e g a u z e c a t a l y s ts t r u c t u r e .One a t t e m p t t o s o l v e t h e p l a t i n u m l o s s i s shown i nU . S . P a t N o . 4 , 8 6 3 , 8 9 3 . A n o t h e r a p p r o a c h i s d e s c r i b e dby R o b e r t J . F a r t a u t o a n d Hg o C . Lee i n AmmoniaO x i d a t i o n C a t a l y s t w i t h E n h a n c e d A c t i v i t y , I n d . E n g .Chem. R e s . V o l . 2 9 , N o . 7 , 1 9 9 0 , p a g e s 1 1 2 5 - 1 1 2 9w h e r e h i g h s u r f a c e a r e a i s o b t a i n e d b y d e p o s i t i n g p l a t inu m from s o l u t i o n on t h e p l a t i n u m a l l o y g a u z e .

Ceramics and m a n y m e t a l s a r e s t r o n g , r e s i s t a n t t oc o r r o s i o n , r e s i s t a n t t o r e l a t i v e l y h i g h t e m p e r a t u r e s a n dwould g e n e r a l l y be d e s i r a b l e a s s t r u c t u r a l m a t e r i a l s i nt h e n i t r i c a c i d p r o c e s s and m a y be u s e d i n v a r i o u s c o mp o n e n t s . C o n v e n t i o n a l c e r a m i c s were n o t s u i t a b l e b ec a u s e o f i n s u f ? c i e n t p o r o s i t y and an i n s u f ? c i e n t quant i t y o f p l a t i n u m t o a l l o w f o r v o l a t i l i z a t i o n l o s s .

I n s e v e r a l f u l l s i z e i n d u s t r i a l r e a c t o r s r e t i c u l a t e d c er a m i c foam s t r u c t u r e s have e e n s u c c e s s f u l l y t e s t e d a s a?o w d i s t r i b u t o r , t h e r m a l r a d i a t i o n g u a r d a n d p h y s i c a ls u p p o r t . T h e s e g u a r d b e d s h a v e b e e n shown t o i m p r o v et h e l i f e o f t h e g a u z e a n d p e r f o r m a n c e a n d t o w i t h s t a n dt h e h a r s h c h e m i c a l e n v i r o n m e n t and h i g h r e a c t i o n temp e r a t u r e . Th e foams c a n b e produced n a v a r i e t y o f e l ld e n s i t i e s w i t h t h e most c o m m o n e i n g i n t h e r a n g e o f 1 0t o 7 0 p o r e s p e r l i n e a r i n c h .

R e t i c u l a t e d c e r a m i c s a n d m e t a l s h a v e b e e n e m p l o y e da s ? l t e r s , s c r u b b e r s , p a c k i n g s u p p o r t s a n d more e c e n t l yi n a u t o m o b i l e c a t a l y t i c e x h a u s t c o n v e r t e r s . Th e r e t i c ul a t e d c e r a m i c s were n i t i a l l y d e v e l o p e d f o r ? l t r a ti o n o fm o l t e n m e t a l s .

V a r i o u s r e t i c u l a t e d c e r a m i c s t r u c t u r e s a r e d e s c r i b e di n t h e a r t : U . S . P a t . No. 4 , 2 5 1 , 2 3 9 d i s c l o s e s ? u t t e d f i l t e ro f p o r o u s c e r a m i c h a v i n g i n c r e a s e d s u r f a c e a r e a ; U . S .P a t . N o . 4 , 5 6 8 , 5 9 5 d i s c l o s e s r e t i c u l a t e d c e r a m i c f o a m sw i t h a s u r f a c e h a v i n g a c e r a m i c s i n t e r e d c o a t i n g c l o s i n go f f t h e c e l l s ; U . S . P a t . N o . 3 , 9 0 0 , 6 4 6 d i s c l o s e s c e r a m i cf o a m w i t h a n i c k e l c o a t i n g f o l l o w e d b y p l a t i n u m d e p o si t e d i n a vapor r o c e s s ; U . S . P a t . No. 3 , 9 5 7 , 6 8 5 d i s c l o s e sn i c k e l o r p a l l a d i u m c o a t e d on a n e g a t i v e image c e r a m i cm e t a l / c e r a m i c o r m e t a l f o a m ; U . S . P a t . No. 3 , 9 9 8 , 7 5 8d i s c l o s e s c e r a m i c foam w i t h n i c k e l , c o b a l t o r copperd e p o s i t e d i n tw o a y e r s w i t h t h e s e c o n d l a y e r r e i n f o r c e dw i t h a l u m i n u m , magnesium o r z i n c ; U . S . P a t . N o .4 , 8 6 3 , 7 1 2 d i s c l o s e s a n e g a t i v e i m a g e r e t i c u l a t e d foamc o a t e d w i t h c o b a l t , n i c k e l o r molybdenum o a t i n g ; U . S .P a t . No. 4 , 3 0 8 , 2 3 3 d i s c l o s e s a r e t i c u l a t e d c e r a m i c foamh a v i n g a n a c t i v a t e d a l u m i n a c o a t i n g and a n o b l e m e t a lc o a t i n g u s e f u l a s an e x h a u s t g a s c a t a l y s t ; U . S . P a t . No.4 , 2 5 3 , 3 0 2 d i s c l o s e s a f o a m e d c e r a m i c c o n t a i n i n g p l a t inum/ h o d i u m c a t a l y s t f o r e x h a u s t g a s c a t a l y s t ; a n d U . S .P a t . No. 4 , 0 8 8 , 6 0 7 d i s c l o s e s a c e r a m i c foam h a v i n g a na c t i v e aluminum o x i d e l a y e r c o a t e d by a n o b l e m e t a lc o n t a i n i n g c o m p o s i t i o n s u c h a s z i n c o x i d e , p l a t i n u ma n d p a l l a d i u m .

C a t a l y s t s i t e s f o r p r e c i o u s m e t a l s a r e m a x i m i z e d b yd e p o s i t i o n o f s m a l l c r y s t a l l i t e s , u s u a l l y f r o m s o l u t i o n .Th e u s e o f c h l o r i n a t i o n t o produce p r e c i o u s m e t a l s o l ut i o n s i s u n i v e r s a l . M a n y c a t a l y s t s a r e p r o d u c e d f r o mt h e s e c h l o r i d e s o l u t i o n s v i a h y d r o l y s is o r p r e c i p i t a t i o nand i n some c a s e s by d r y i n g and t h e r m a l r e d u c t i o n . I na l l t h e s e c a s e s t h e r e a r e r e s i d u a l h a l i d e s .

C e r t a i n g a s e o u s s p e c i e s can adsorb s o s t r o n g l y t h a tt h e y t i e up t h e s i t e s p r e v e n t i n g c a t a l y s i s o r i n some a s e st h e a d s o r b e d s p e c i e s r e a c t w i t h t h e s u r f a c e s i t e s t o form

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5 , 3 3 6 , 6 5 63new c h e m i c a l compounds which m a y undergo s t r u ct u r a l ( c h e m i c a l a n d p h y s i c a l ) c h a n g e . E x a m p l e s o f h e s et y p e o f p o i s o n s a r e S 0 2 , C 1 2 , H 2 5 , 1 2 , F 2 , e t c .I m p r o v e d c a t a l y s t s h a v e p r e v i o u s l y b e e n f o u n dwhich a r e p r e p a r e d from c h l o r i d e f r e e s o l u t i o n s . E x a mp l e s a r e n i t r a t e s o f p a l l a d i u m and rhodium a n d t h e h e x ah y d r o x y p l a t i n a t e s a n d p l a t i n u m s u l ? t o c o m p l e x e s .

I t i s an advantage of h e p r e s e n t i n v e n t i o n t o p r o v i d ea n i m p r o v e d c a t a l y s t f o r ammonia o x i d a t i o n w i t h i nc r e a s e d p e r f o r m a n c e ( y i e l d a n d s e l e c t i v i t y ) , l o n g e r l i f ea n d w i t h g r e a t l y r e d u c e d c o s t s b y d e p o s i t i n g m e t a l l i cc a t a l y s t s on ceramic or m e t a l l i c s t r u c t u r e s , which a r eb e t t e r a b l e t o w i t h s t a n d u p s e t s and n o t r e s u l t i n burnt h r o u g h .

I t i s a f u r t h e r advantage t h a t t h e r e t i c u l a t e d s t r u c t u r ep r o v i d e s h i g h s u r f a c e a r e a and u n i f o r m and o n t r o l l a b l ep o r o s i t y . T h e s e p r o p e r t i e s g i v e e x c e l l e n t g a s c o n t a c t i n gand u n i f o r m p r e s s u r e drop which c a n be c r i t i c a l f o rg o o d c a t a l y s t p e r f o r m a n c e f o r a m m o n i a o x i d a t i o n . F u rt h e r m o r e , t h e r e t i c u l a t e d s t r u c t u r e p r o v i d e s a s t r u c t u r ewhich p r e s e n t s a s u r f a c e o f c a t a l y t i c m a t e r i a l b u t u n l i k et h e w i r e gauze c a t a l y s t t h e i n n e r c o r e i s i n e r t m a t e r i a la n d n o t c o s t l y a n d i n a c c e s s i b l e p r e c i o u s m e t a l .

I t i s a f e a t u r e o f t h e p r e s e n t i n v e n t i o n t h a t c a t a l y s t s i nwhich t h e p r e c i o u s m e t a l s a r e p r o d u c e d from m e t a l l oo r g a n i c c o m p o u n d s d i s s o l v e d i n o r g a n i c s o l v e n t s w h i c hh a v e s u p e r i o r c a t a l y t i c a c t i v i t y ( c o n v e r s i o n a t l o w e rt e m p e r a t u r e ) a n d s t a b i l i t y . T h e s e c a t a l y s t s h a v e s u p er i o r p r o p e r t i e s t o t h o s e p r o d u c e d by known a n d p r a ct i c e d t e c h n o l o g y b a s e d on i n o r g a n i c c h l o r i d e o r c h l or i d e f r e e a q u e o u s c o m p o u n d s .

SUMMARY OFTHEINVENTIONB r i e ? y t h e p r e s e n t i n v e n t i o n r e l a t e s t o a n o v e l ammo

n i a o x i d a t i o n c a t a l y s t s t r u c t u r e c o m p r i s i n g a r e t i c u l a t e dceramic o r m e t a l s u b s t r a t e c o a t e d with from 1 t o 70w e i g h t p e r c e n t b a s e d on t h e t o t a l c a t a l y s t s t r u c t u r ec o b a l t compounds r a n o b l e m e t a l , t h e method o f m a ki n g t h e c a t a l y s t a n d t h e p r o c e s s o f o x i d i z i n g ammoniaby c o n t a c t i n g ammonia a n d a f r e e o x y g e n c o n t a i n i n gg a s i n vapor p h a s e a t t e m p e r a t u r e s i n t h e r a n g e o f 7 0 0 t o 1 2 0 0 C . ( e x i t t e m p e r a t u r e ) , i n a ?xed bed o f t h ec a t a l y s t . Th e n o b l e m e t a l p r e f e r a b l y c o m p r i s e s 2 t o 5 0w t .% b a s e d on t h e t o t a l c a t a l y s t s t r u c t u r e . A o b a l tc o a t i n g p r e f e r a b l y r e q u i r e s more o f t h e a c t i v e m e t a lc o m p o n e n t , i . e . a b o u t 1 0 t o 7 0 w e i g h t p e r c e n t , morep r e f e r a b l y 1 5 t o 5 0 w e i g h t p e r c e n t b a s e d on t h e t o t a lc a t a l y s t s t r u c t u r e .

Th e o v e l c a t a l y s t s t r u c t u r e s o f t h e p r e s e n t i n v e n t i o nm a y e p r e p a r e d by i m m e r s i n g a foamed c e r a m i c s t r u ct u r e o r foamed metal s t r u c t u r e i n a s o l u t i o n comprisingan o r g a n i c s o l v e n t and from about 1 t o 30 w t . % o f ac a r b o x y l a t e s a l t o f c o b a l t , n o b l e m e t a l o r m i x t u r et h e r e o f . Th e d e s i r e d amount o f m e t a l s a l t i s p r e f e r a b l yd e p o s i t e d b y s e q u e n t i a l i m m e r s i o n o f t h e f o a m e d s t r u ct u r e f o l l o w e d by ? r i n g a t 2 6 0 t o 8 0 0 C . , f o r a s u f ? c i e n tt i m e t o r e d u c e t h e s a l t , e . . 3 0 t o 9 0 m i n u t e s and r e p e a ti n g t h e s e s t e p s a s r e q u i r e d .Th e a c t i v e p r e c i o u s m e t a l c o a t i n g o f t h e f r e s h l y p r ep a r e d c a t a l y s t s t r u c t u r e i s s u b s t a n t i a l l y c o n t i n u o u s a n de x h i b i t s e l e c t r i c a l c o n d u c t i v i t y . Th e manner o f a p p l i c at i o n from an o r g a n i c m e t a l s o l u t i o n p r o v i d e s an evend i s t r i b u t i o n t h r o u g h o u t t h e r e t i c u l a t e d s u b s t r a t e s t r u ct u r e . P r e f e r a b l y t h e n o b l e m e t a l c o m p r i s e s p l a t i n u m ,p a l l a d i u m , r h o d i u m , r u t h e n i u m , osmium a n d m i x t u r e st h e r e o f . Th e f r e s h l y p r e p a r e d c a t a l y s t m a y b e c h a r a ct e r i z e d a s c o n t i n u o u s and e l e c t r i c a l l y c o n d u c t i v e , b u t

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4a f t e r u s e t h e c o a t i n g i s c h a r a c t e r i z e d a s c r y s t a l l i z e d andn o n c o n d u c t i v e .

A n o t h e r f e a t u r e o f c e r a m i c foam b a s e d c a t a l y s t s , i st h a t t h e y h a v e s u b s t a n t i a l l y h i g h e r t h e r m a l m a s s ( h e a tc a p a c i t y p e r u n i t o f s u r f a c e a r e a ) t h a n p l a t i n u m g au z e so f e q u a l s u r f a c e a r e a . The h i g h e r t h e r m a l mass o f c eramic foam a l l o w s i t t o a t t e n u a t e l o c a l d i s t u r b a n c e swhich can l e a d t o ? i c k e r i n g . T h e r e f o r e , r e d u c i n g h o ts p o t s a n d t h e l o s s o f p l a t i n u m t o o x i d a t i o n a t h i g h e rt e m p e r a t u r e s .DETAILEDDESCRIPTIONOF PREFERRED

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duction does not need t o be d e s c r i b e d h e r e . Fo r examp l e r e t i c u l a t e d c e r a m i c foams a r e a v a i l a b l e from S e l e eC o r p o r a t i o n o f H e n d e r s o n v i l l e , NC, i - T e c h C e r a m i co f A l f r e d , New ork a n d F o e s c o , I n c .

G e n e r a l l y , t h e GHSV i l l b e b e t w e e n a b o u t 1 0 0 , 0 0 0a n d 5 , 0 0 0 , 0 0 0 . C o n t a c t t i m e s a r e e x t r e m e l y b r i e f froma b o u t 0 . 0 0 2 s e c o n d . The c o n t a c t t i m e i s t h e c a l c u l a t e dd w e l l t i m e o f t h e r e a c t i o n m i x t u r e i n t h e r e a c t i o n z o n e ,a s s u m i n g t h e m o l e s o f f e e d m i x t u r e . For t h e p u r p o s e o fc a l c u l a t i n g r e s i d e n c e t i m e s , t h e r e a c t i o n z o n e i s t h ep o r t i o n o f t h e r e a c t o r c o n t a i n i n g c a t a l y s t . I n c a l c u l a t i n gs p a c e v e l o c i t i e s , t h e volume of a ?xed bed zone o n t a i ni n g c a t a l y s t s t h a t o r i g i n a l v o i d volume f r e a c t o r s p a c ec o n t a i n i n g c a t a l y s t . The g a s e o u s h o u r l y s p a c e v e l o c i t y(GHSV) s t h e volume f t h e ammonia o b e o x i d i z e d , i nt h e form o f v a p o r c a l c u l a t e d u n d e r s t a n d a r d c o n d i t i o n sof 2 5 C . and 760 mm. f mercury, per volume of e a ct o r s p a c e c o n t a i n i n g c a t a l y s t p e r h o u r .Th e foam s t r u c t u r e i s c h a r a c t e r i z e d by t h e number fp o r e s p e r l i n e a r i n c h a n d t y p i c a l f o a m s a r e producedw i t h 1 0 t o 1 0 0 p o r e s p e r l i n e a r i n c h . T a b l e 1 belowshows t h e c o m p a r i s o n s o f g e o m e t r i c a l s u r f a c e a r e a o rg l o b a l s u r f a c e a r e a f o r t y p i c a l w i r e g a u z e s a n d t h e foams t r u c t u r e s o f t h i s i n v e n t i o n . S p e c i ? c a l l y T a b l e 1 showst h e s u r f a c e a r e a of t h e g a u z e s p e r u n i t a r e a and t h et h i c k n e s s o f foam s t r u c t u r e which would b e r e q u i r e d t ob e e q u a l t o t h i s s u r f a c e a r e a . A o m p a r i s o n o f o t h e rp r o p e r t i e s o f t h e foams and g a u z e s a r e s h o wn i n T a b l e s2 and 3 .

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1The t h i c k n e s s o f foam e q u i r e d t o g i v e t h e sam e l o b a l a r e a o f on e g a u z e e i t h e r 4 0or 80 mesh.

To p r o d u c e t h e c a t a l y s t s s t r u c t u r e s o f t h i s i n v e n t i o nt h e abov e mentioned s t r u c t u r e s a r e coated with m e t a l l oo r g a n i c compounds o f c e r t a i n p r e c i o u s m e t a l s a n d b a s em e t a l s t o p r o d u c e c a t a l y s t s which have t h e s t r u c t u r e o ft h e foam and smooth and s u b s t a n t i a l l y c o n t i n u o u s c a t al y t i c s u r f a c e s .

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5 , 3 3 6 , 6 5 6Th e t h i c k n e s s o f foam r e q u i r e d t o g i v e t h e same g l o b a l a r e a o f oneg a u ze e i t h e r 40 or 8 0 mesh.

P r e f e r a b l e m e t a l compounds f o r d e p o s i t i o n on t o t h efoamed s t r u c t u r e a r e t h e c a r b o x y l a t e s , p r e f e r a b l y c o r r es p o n d i n g t o l o n g c h a i n a c i d b e i n g 4 t o 2 0 c a r b o n a t o m s ,s u c h a s p l a t i n u m n e o d e c a n o a t e , p l a t i n u m 2 e t h y l h e xa n o a t e , p a l l a d i u m n e o d e c a n o a t e a n d p a l l a d i u m 2 - e t h y lh e x a n o a t e . The same s a l t s o f rhodium and s i l v e r havea l s o shown x c e l l e n t r e s u l t s o f u n i f o r m , d i s t r i b u t i o n a n dh i g h m e t a l d i s p e r s i o n . W h i l e t h e c h e m i s t r y o f m e t a lc a r b o x y l a t e s h a v e b e e n known f o r some t i m e t h e p r ec i o u s m e t a l compounds have n o t b e e n a v a i l a b l e i n s u f f ic i e n t p u r i t y o r q u a n t i t y u n t i l r e c e n t l y . I t wa s n o t o b v io u s t h a t t h e s e m a t e r i a l s c o u l d b e decomposed t o formgood c a t a l y t i c p r e c u r s o r s o r t h a t t h e s e p r e c u r s o r swould h a v e e n h a n c e d d i s p e r s i o n i n t h e a b s e n c e o f h a l og e n o r h y d r o x i d e s p e c i e s .

G e n e r a l l y a n y o r g a n i c l i q u i d i n w h i c h t h e m e t a l s a l ti s s o l u b l e m a y b e u s e d . S u i t a b l e s o l v e n t s f o r t h e m e t a ls a l t component o f t h e d e p o s i t i n g s o l u t i o n i n c l u d e a r om a t i c s h a v i n g 6 t o 1 2 c a r b o n a t o m s , l o w e r a l c o h o l sh a v i n g 1 t o 8 c a r b o n a t o m s , s y m m e t r i c a l a n d unsymm e t r i c a l k e t c h e s and e t h e r s h a v i n g 3 t o 9 c a r b o n atomsand l i n e a r e s t e r s having 3 t o 7 carbon a t o m s . P r e f e r r e ds o l v e n t s f o r t h e c o b a l t and n o b l e m e t a l c a r b o x y l a t e si n c l u d e a r o m a t i c s s u c h a s t o l u e n e and x y l e n e , a l c o h o l ss u c h a s e t h a n o l , i s o p r o p a n o l a n d b u t a n o l , k e t o n e s l i k em e t h y l e t h y l k e t o n e , a c e t o n e , e t h e r s s u c h a s m e t h y lt e r t i a r y b u t y l e t h e r t e r t i a r y a m y l m e t h y l e t h e r a n d e st e r s l i k e p r o p y l a c e t a t e , and e t h y l a c e t a t e .W h e n p l a t i n u m i s d e p o s i t e d on c e r a m i c foam fromt h e e t h y l h e x a n o a t e s a l t d i s s o l v e d i n t o l u e n e a m e t a l l i c?lm s f o r m e d . A f t e r h e a t i n g t o 5 0 0 F . t h e c o n d u c t i v i tycan be measured with an ohm e t e r . Fo r e x a m p l e ,w hen a one i n c h t h i c k 3 0 c e l l p e r l i n e a r i n c h a l u m i n ac e r a m i c f o a m s c o a t e d w i t h a p p r o x i m a t e l y p l a t i n u m b yweight t h e r e s i s t a n c e w a s measured a t an average of . 4ohm s c r o s s t h e t h i c k n e s s . The e r a m i c p i e c e w a s a b o u t1 2 i n c h e s on t h e d i a g o n a l d i s t a n c e . The r e s i s t a n c ea c r o s s t h i s d i a g o n a l w a s measured a t an average 6 ohms.

Note t h a t a f t e r e x p o s u r e t o t e m p e r a t u r e s i n e x c e s s o f8 0 0 C . t h e f i l m s a r e o p t i c a l l y c o n t i n u o u s b u t have noe l e c t r i c a l c o n t i n u i t y .Th e f o l l o w i n g e x a m p l e s a r e i n t e n d e d t o d e m o n s t r a t e

t h e i n v e n t i o n .EXAMPLE

A oam s t r u c t u r e 8 i n c h e s i n d i a m e t e r and 0 . 8 i n c h e st h i c k and o n t a i n i n g 3 0 p o r e s p e r i n c h was p r o d u c e d byimmersing a p o l y u r e t h a n e expanded foam i n t o a c er a m i c s l u r r y o f a l p h a a l u m i n a p o w d e r . A f t e r ? r i n g t ot e m p e r a t u r e s i n e x c e s s of 1 4 0 0 C . t h e foam w a s d i p p e di n t o a s o l u t i o n o f 1 1 % p l a t i n u m a s p l a t i n u m e t h y l h e xa n o a t e i n t o l u e n e . A f t e r t h r e e c l i p s w i t h i n t e r m i t t e n td r y i n g a n d ? r i n g s t h e f o a m c o n t a i n e d 1 0 . 5 wt.% p l a t inum r 1 . 3 8 troy ounces. This foam w a s placed i n t o as m a l l ammonia o x i d a t i o n r e a c t o r and 6 . 7 volume %ammonia i n a i r wa s p a s s e d over t h e p l a t i n u m c o a t e df o a m . Th e m i x t u r e w as i g n i t e d w i t h a s p a r k i g n i t o r .A f t e r a s h o r t t i m e , t h e e n t i r e s t r u c t u r e glowed r e d d i s ho r a n g e . The c o n c e n t r a t i o n of t h e i n p u t ammonia w ascon?rmed a t 6 . 7 volume % y d r a w i n g a g a s s a m p l eand a n a l y z i n g by wet c h e m i c a l m e t h o d s . S e v e r a l samp l e s were t a k e n o f t h e g a s e s a f t e r t h e foam o x i d a t i o nc a t a l y s t a n d t h e y i e l d ( s e l e c t i v i t y x c o n v e r s i o n ) wasf o u n d t o b e 9 6 mole % n t h e form o f i t r i c o x i d e ( N O ) .T h i s c a t a l y s t w as l e f t i n p l a c e and w as o p e r a t e d i n t e rm i t t e n t l y f o r o v e r 9 0 d a y s . Th e c a t a l y s t was removed

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6f o r c h a r a c t e r i z at i o n . There w a s no m e t a l l o s t and t h ea s s a y of t h e P t w a s t i l l 1 0 . 5 % .

EXAMPLETh e r e a c t o r o f e x a m p l e 1 w as ? t t e d w i t h 1 5 l a y e r s o f

Pt/Rh gauz e weighing a t o t a l o f 9 . 9 4 t r o y o u n c e s . Ammonia i n a i r w a s p a s s e d over t h e gauze and t h e a n a l y s i sshowed 9 5 mole % o n v e r s i o n o f t h e ammonia t o n i t r i co x i d e .

EXAMPLES e v e r a l c e r a m i c foams c a t a l y s t s u p p o r t s were madeb y d i p p i n g 2 0 a n d 3 0 p p i ( p o r e s p e r i n c h ) p o l y u r e t h a n efoam 1 i n c h t h i c k and 8 i n c h e s i n d i a m e t e r i n t o a s l u r r y

o f m u l l i t e ( a l u m i n a s i l i c a t e ) p o w d e r . A f t e r ? r i n g t ot e m p e r a t u r e s i n e x c e s s o f 1 2 0 0 C . , s t r o n g c e r a m i c foams t r u c t u r e s r e s u l t e d . These s t r u c t u r e s were d i p p e d i na c c o r d a n c e w i t h t h e p r o c e d u r e i n e x a m p l e 1 , i n t o a 8%P t a s p l a t i n u m e t h y l h e x a n o a t e d i s s o l v e d i n t o l u e n e . On ef o a m , 3 0 p p i , w a s d i p p e d once and w a s found t o havep i c k e d u p a p p r o x i m a t e l y 3% r 0 . 3 7 t r o y o u n c e s o f P t .A e c o n d f o a m , 2 0 p p i , w as c o a t e d w i t h f o u r d i p s andw a s found t o h a v e picked u p 1 . 5 4 t r o y ounces or abou t12% b y w e i g h t .

Th e 3 w t . % P t on m u l l i t e foam w a s t e s t e d i n t h eam m onia o x i d a t i o n r e a c t o r with 1 0 volume % ammon i a . The c o n v e r s i o n t o NO a s found t o be 9395 mole% s d e t e r m i n e d by c h e m i l u m e n e s c e n t a n a l y s i s .Th e 1 2 w t .% P t on 20 p p i foam w a s t e s t e d i n t h eammonia o x i d a t i o n r e a c t o r and t h e ammonia i n and t h eNO ut were measured by a chemiluminescence. Th ec o n v e r s i o n w a s found t o be between 9 7 and 10 0%.

EXAMPLEA oa m s t r u c t u r e 8 i n c h e s i n d i a m e t e r a n d 0 . 8 i n c h e s

t h i c k and o n t a i n i n g 3 0 p o r e s p e r i n c h w as p r o d u c e d byi m m e r s i n g a p o l y u r e t h a n e expanded foam i n t o a c er a m i c s l u r r y o f c o r d i e r i t e ( m a g n e s i a a l u m i n a s i l i c a t e )p o w d e r , A f t e r ? r i n g t o t e m p e r a t u r e s i n e x c e s s o f 1 3 0 0 C . t h e ceramic foam w a s dipped i n t o an aqueous c o l l o id a l d i s p e r s i o n o f a l u m i n a c o n t a i n i n g a b o u t 2 0 % b yw e i g h t o f A 1 2 0 3 . Th e s a m p l e w as d r i e d a n d c a l c i n e d t o5 0 0 C . f o r on e h o u r , Th e foam wa s found t o havep i c k e d u p 8 % b y w e i g h t a l u m i n a . Th e a l u m i n a c o a t e dfoam w a s dipped onto a o l u t i o n of 12% i n c a s z i n c neod e c a n o a t e i n t o l u e n e . Th e w e i g h t p i c k u p m e a s u r e da f t e r c a l c i n a t i o n t o 5 0 0 C . w a s 5% . T h i s z i n c o x i d e anda l u m i n a c o a t e d foam w a s t h e n dipped i n t o a 1 2 % c o b a l ta s c o b a l t ne o decanoate i n t o l u e n e a nd d r i e d and c a lc i n e d a t 5 0 0 C . The w e i g h t p i c k up w as 1 5 % a s c o b a l to x i d e . T h i s c a t a l y s t was p l a c e d i n t h e ammonia o x i d at i o n r e a c t o r a n d i g n i t e d w i t h t h e e l e c t r i c s p a r k i g n i t o r .Th e r e a c t o r w a s ru n f o r tw o weeks b e f o r e e v a l u a t i o n ,A n a l y s i s o f t h e ammonia i n p u t t o t h e r e a c t o r showed1 0 % ammonia i n a i r , The o u t p u t w a s measured a t b etween 9 . 1 and 9.4% N i v i n g a c o r r e c t e d c o n v e r s i o nof 9 2 t o 95%.P i l o t P l a n t T r i a l E x p e r i e n c e ( c o m p a r i s o n w i t h ' P tg a u z e )Th e r e a c t o r chamber o f t h e p i l o t u n i t u t i l i z e s l 6 , 8i n c h d i a m e t e r g a u z e s . The ?ow a t e i s 600 scfm whichg i v e s a l i n e a r v e l o c i t y o f 1 . 3 5 5 m e t e r s p e r second and a na p p r o x i m a t e p r e s s u r e d r o p o f 1 . 9 i n c h e s o f w a t e r . Th ef e e d i s a p p r o x i m a t e l y 6.7% ammonia n a i r . Th e e a c t o ro p e r a t e s a t 4 p s i g and a t m o s p h e r i c p r e s s u r e i s a b o u t 1 3p s i g .A l a t i n u m c a t a l y s t on foam wa s p r e p a r e d w i t h1 0 . 5 % P t on an 8 i n c h d i a m e t e r 0 . 8 0 i n c h e s t h i c k , 3 0

7/28/2019 catalyst for nitric acid production

5/5

5 , 3 3 6 , 6 5 67p o r e s p e r l i n e a r i n c h a l u m i n a f o a m . T h i s c a t a l y s t l o a di n g h a d a p l a t i n u m l o a d i n g o f 1 . 3 8 t r o y o u n c e s i n t h er e a c t o r . ( T h e m e t a l c o n t a i n e d i n t h e g a u z e s p a c k w as9 . 9 4 t r o y o u n c e s . ) At h i s m e t a l l o a d i n g t h e m e t a l l i z e dc e r a m i c c a t a l y s t i s e l e c t r i c a l l y c o n d u c t i v e w i t h a r e s i st a n c e o f a b o u t 0 . 4 ohm s p e r i n c h . T h i s m e t a l l i z e d foamw a s placed on a no n m e t a l l i z e d alumina support segment a nd mounted i n t h e r e a c t o r . Th e gauze r e a c t o rw a s o p e r a t e d a t 7 6 0 - 8 0 0 C .Th e p e r f o r m a n c e o f t h e c a t a l y s t was c h e c k e d byt a k i n g s a m p l e s o f t h e r e a c t e d g a s e s a n d t i t r a t i n g f o rn i t r i c a c i d a n d ammonia. Twelve s a m p l e s were t a k e nover a s i x hour r u n . Th e r e s u l t s s h owed t h a t t h e g a uzec o n v e r t e d 9 5 % o f t h e ammonia t o n i t r i c a c i d and f u rt h e r m o r e i n t h e a b s o r p t i o n s y s t e m u s e d a p p r o x i m a t e l y45-46% a c i d w a s p r o d u c e d . The m e t a l l i z e d foam conv e r t e d up t o 96% f t h e ammonia t o n i t r i c a c i d and f o ru n e x p l a i n e d r e a s o n s g a v e a s t r o n g e r a c i d s t r e n g t h o fa b o u t 50%. A f t e r t h e s e t e s t s were c o m p l e t e d o n l y t h ea c i d s t r e n g t h was u s e d t o m o n i t o r t h e p e r f o r m a n c e a n dn i t r i c a c i d w a s produced f o r an a d d i t i o n a l 6 0 d a y s . Att h e e n d o f t h e 6 0 d a y s , t h e c a t a l y s t was p e r f o r m i n ga c c e p t a b l y , w i t h no e v i d e n c e o f r e d u c e d a c t i v i t y a n dt h e run w a s stopped o n l y t o r e c o v e r t h e c a t a l y s t f o ra n a l y s i s . Assay showed t h a t t h e r e w as no m e t a l l o s s( a s s a y i n 1 0 . 5 0% a s s a y o u t 10.54%) and t h e r e w a s nol o s s o f p e r f o r m a n c e w a s d e t e c t e d .

TABLEC o m p a r i s o n s o f Foams t o Gauze T h i c k n e s s o f Foam

t o M atc h G auze( S u r f a c e Area o f 8 0 mesh g a u z e i s 1 . 5 3 S q u a r e m e t e r s o f w i r e p e r

square meter gauze)P r e s s u r e Drop t1 . 3 5 5 m / s e c , ( i nP o r e s P e r L i n e a r I n c h T h i c k n e ss o f Foam H20)

1 0 0 . 2 2 9 cm 0 . 7 22 0 0 . 1 1 4 cm 1 . 3 83 0 0 . 0 7 6 cm 1 . 9 05 0 0 . 0 4 6 cm 6 . 1 1

From a b o u t 1 2 t o 1 5 % P t by w e i g h t t h e m e t a l l i z e ds t r u c t u r e h a s a c o n t i n u o u s and e l e c t r i c a l l y c o n d u c t i v e? l m . Th e c e r a m i c s u r f a c e i s s u b s t a n t i a l l y c o a t e d .

T a b l e 3 below shows t h e p l a t i n u m r e d u c t i o n a c h i e va b l e b y u s i n g t h e c o a t e d f o r m . T h i s made p o s s i b l e b ec a u s e t h e ceramic makes up t h e c o r e and t h e p l a t i n u m i son t h e s u r f a c e where t i s e f f e c t i v e a s a c a t a l y s t .

TABLEC o m p a r i s o n s o f P t l o a d i n g s on Gauze a n d M e t a l l i z e d

Ceramic Foams( C o a t e d a t 1 2% b y w e i g h t )

( 8 0 mesh w i r e g a u z e h a s 1 . 7 8 t r o y ounce p e r s q u a r e f o o to f g a g z e )P o r e s p e r l i n e a r i n c h TO/Sq F t

1 0 0 . 1 1 4 520 0 . 0 5 7 23 0 0 . 0 3 8 25 0 0 . 0 2 2 9

I t i s e s t i m a t e d t h a t t h e c a t a l y s t s a n d p r o c e s s a c c o r di n g t o t h e p r e s e n t i n v e n t i o n , i f s u b s t i t u t e d f o r t h e conv e n t i o n a l p l a t i n u m gauze can reduce t h e m e t a l c o n t e n to f t h e c a t a l y s t c h a r g e o v e r 90%.The i n v e n t i o n c l a i m e d i s :1 . A a t a l y s t s t r u c t u r e f o r t h e o x i d a t i o n o f ammonia

t o p r o d u c e n i t r i c o x i d e c o n s i s t i n g e s s e n t i a l l y o f a s u bs t r a t e of r e t i c u l a t e d ceramic foam or r e t i c u l a t e d m e t a lf o a m h a v i n g c o a t e d s u b s t a n t i a l l y u n i f o r m l y t h e r e o v e r

1 5

20

2 5

3 0

3 5

5 0

5 5

6 0

6 5

8from 1 t o 7 0 w e i g h t % o b a l t compound and a minoramount o f a z i n c compound.

2 . Th e c a t a l y s t s t r u c t u r e a c c o r d i n g t o c l a i m 1wherein from 1 5 t o 5 0 weight % o b a l t i s c o a t e d on a i ds u b s t r a t e .

3 . Th e c a t a l y s t s t r u c t u r e a c c o r d i n g t o c l a i m 1wherein s a i d s u b s t r a t e h a s a s u b s t a n t i a l l y c o n t i n u o u sc o a t i n g .4 . The c a t a l y s t s t r u c t u r e a c c o r d i n g t o c l a i m 1w h e r e i n s a i d c o b a l t compound s c o b a l t o x i d e .

5 . The c a t a l y s t s t r u c t u r e a c c o r d i n g t o c l a i m 4w h e r e i n s a i d z i n c compound s z i n c o x i d e .

6 . The c a t a l y s t s t r u c t u r e a c c o r d i n g t o c l a i m 4w h e r e i n s a i d z i n c compound s p r e s e n t i n t h e amount o fa b o u t 5 %.

7 . Th e method o f p r e p a r i n g a c a t a l y s t s t r u c t u r e f o rt h e o x i d a ti o n o f ammonia t o produce n i t r i c o x i d e c o mp r i s i n g a s u b s t r a t e o f r e t i c u l a t e d c e r a m i c foam o r r e t i c ul a t e d m e t a l f o a m h a v i n g c o a t e d s u b s t a n t i a l l y u n i f o r m l yt h e r e o v e r f r o m 1 t o 7 0 w e i g h t % o b a l t c o m p r i s i n g :( a ) p r e p a r i n g a ? r s t s o l u t i o n c o m p r i s i n g a n o r g a n i c

s o l v e n t and a c a r b o x y l a t e s a l t o f z i n c ;( b ) i m m e r s i n g foamed c e r a m i c s t r u c t u r e o r foamedmetal s t r u c t u r e i n s a i d ? r s t s o l u t i o n t o cover s a i ds u b s t r a t e w i t h s a i d ? r s t s o l u t i o n ;( c ) p r e p a r i n g a s e c o n d s o l u t i o n c o m p r i s i n g a n o r g a n i cs o l v e n t and from a b o u t 1 t o 3 0 w t .% o f a c a r b o x y la t e s a l t o f c o b a l t ;

( d ) i m m e r s i n g s a i d foamed c e r a m i c s t r u c t u r e o rfoamed m e t a l s t r u c t u r e i n s a i d second s o l u t i o n t oc o v e r s a i d s u b s t r a t e w i t h s a i d s e c o n d s o l u t i o n ;( e ) r e m o v i n g s a i d s o l u t i o n c o v e r e d s u b s t r a t e f r o ms a i d s o l u t i o n ; a n d( f ) h e a t i n g a t 2 6 0 t o 8 0 0 C . f o r a s u f ? c i e n t t i m e t oo x i d i z e s a i d s a l t s t o produce a c o a t i n g o v e r t h es u b s t r a t e .

8 . The method a c c o r d i n g t o c l a i m 7 wherein s a i d ? r s ts o l u t i o n c o n t a i n s a b o u t 1 2 % o f s a i d z i n c s a l t .

9 . A a t a l y s t s t r u c t u r e f o r t h e o x i d a t i o n o f ammoniat o p r o d u c e n i t r i c o x i d e c o n s i s t i n g e s s e n t i a l l y o f a s u bs t r a t e o f r e t i c u l a t e d ceramic foam o r r e t i c u l a t e d m e t a lf o a m h a v i n g c o a t e d s u b s t a n t i a l l y u n i f o r m l y t h e r e o v e rf r o m 1 t o 7 0 w e i g h t % o b a l t compound a n d 5 w e i g h t% i n c c o m p o u n d .1 0 . A ethod o f p r e p a r i n g a c a t a l y s t s t r u c t u r e f o r t h eo x i d a t i o n o f ammonia t o p r o d u c e n i t r i c o x i d e c o m p r i si n g a s u b s t r a t e o f r e t i c u l a t e d ceramic foam o r r e t i c ul a t e d m e t a l f o a m h a v i n g c o a t e d s u b s t a n t i a l l y u n i f o r m l yt h e r e o v e r f r o m 1 t o 7 0 w e i g h t % o b a l t , c o m p r i s i n g :( a ) p r e p a r i n g a ? r s t s o l u t i o n c o m p r i s i n g a n o r g a n i c

s o l v e n t c o n t a i n i n g a b o u t 1 2 w e i g h t % f a c a r b o xy l a t e s a l t o f z i n c ;( b ) i m m e r s i n g foamed c e r a m i c s t r u c t u r e o r foamedm e t a l s t r u c t u r e i n s a i d ? r s t s o l u t i o n t o cover s a i ds u b s t r a t e w i t h s a i d ? r s t s o l u t i o n ;( 0 ) p r e p a r i n g a s e c o n d s o l u t i o n c o m p r i s i n g a n o r g a n i cs o l v e n t c o n t a i n i n g f r o m a b o u t 1 t o 3 0 w e i g h t % fa c a r b o x y l a t e s a l t o f c o b a l t ;( d ) i m m e r s i n g s a i d foamed c e r a m i c s t r u c t u r e o rfoamed m e t a l s t r u c t u r e i n s a i d second s o l u t i o n t oc o v e r s a i d s u b s t r a t e w i t h s a i d second s o l u t i o n ;( e ) r e m o v i n g s a i d s o l u t i o n c o v e r e d s u b s t r a t e f r o ms a i d s o l u t i o n ; a n d( i ) h e a t i n g a t 2 6 0 t o 8 0 0 C . f o r a s u f ? c i e n t t i m e t oo x i d i z e s a i d s a l t s t o produce a c o a t i n g over t h es u b s t r a t e .

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