A MÖSSBAUER STUDY OF THE IRON-CHROMIUM TYPE CATALYST FOR CO CONVERSION UNDER THE REACTION CONDITIONS

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A MÖSSBAUER STUDY OF THE IRON-CHROMIUM TYPE CATALYST FOR CO CONVERSION UNDER

THE REACTION CONDITIONS

Ding Ying-Ru, Yen Qi-Jie, Hsia Yuan-Fu, Yeh Shun-Hao, Chen Yi, Jin Yong-Shu, Qiu Jin-Heng

To cite this version:

Ding Ying-Ru, Yen Qi-Jie, Hsia Yuan-Fu, Yeh Shun-Hao, Chen Yi, et al.. A MÖSSBAUER STUDY OF THE IRON-CHROMIUM TYPE CATALYST FOR CO CONVERSION UNDER THE REACTION CONDITIONS. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-341-C1-342.

�10.1051/jphyscol:19801127�. �jpa-00219610�

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JOURNAL DE PHYSIQUE Colloque Cl

,

supplkment au no 1, Tome 41, janvier 1980, page C1-341

A I@SSBAUER ^STUDYOF THE IRON-CHROMIUM TYPE CATALYST FOR CO CONVERSION UNDER THE REACTION CONDITIONS

Ding Ying-Ru, Yen Qi-Jie, Hsia Yuan-&, Yeh Shun-Hao, Chen Yi, Jin Yong-Shu and Qiu Jin-Heng Nanking University, flanking, China.

1. Introduction.

-

I n c a r r y i n g act t h e water-ga_s s h i f t r e a c t i o n a t about 350°C.

iron-chromium c a t a l y s t s a r e o s t e n used.

Although a g r e a t amount of research work has been done in t h i s f i e l d , n o t much examination of t h e s t r u c t u r e of t h e cata- l y s t s a t t h e r e a c t i o n temperatures and i n t h e r e a c t i o n gases has been made, However, we have made some comparison between t h e s t r u c t u r e s of some iron-chromium c a t a l y s t s before and a f t e r r e a c t i o n s .

2. &xperimental,- The c a t a l y s t used w a s an i r o n oxide

-

chromium oxide c a t a l y s t containing ~ r O ~ / I ? e ~ 0 ~ = 1 7 . 7 w t % , K O H / F ~ ~ O ~ = 0.6 w t $ and g r a p h i t e 1.5 w

₁ .

^MBssbauer^-

absorption s p e c t r a of t h e Fe 14.4KeV gamma-radiation have been q a s u r e d by keeping t h e source (15 m C i Co d i f f u s e d i n a palladium matrix) at room temperature and t h e absorber a t temperature ranging from room temperature t o 5500C. A constant a c c e l e r a t i o n Mdssbauer spectrometer [2 3 has been used. A 25pm thick high p u r i t y metalic i r o n f o i l and a high p u r i t y 86% iron-57 en- riched d- Fe20j sample was used as a c a l i b r a t i o n standard. The absorber w a s put i n t o a q u a r t z r e a c t i o n c e l l . The d a t a out- put of t h e Ndssbauer spectrometer had t o be handled by l e a s t - square f i t t i n g using d i g i t a l computer TQ-16.

3. Results.

-

^Fig. ¹i s shown MBssbauer s p e c t r a f o r water-gas s h i f t r e a c t i o n cata- l y s t S in a i r at room temperature, t h e msgnetfc hyperfine component of t h e p a t t e r n

is contributed by d-Fe203 and Y-Fe 0 2 3' while t h e c e n t r a l component of t h e p a t t e r n i s contributed by some superparamagnetic c r y s t a l l i t e and Fe203

-

Cr20g s o l i d solu-

bl

. . .

^- , ..

veloc#tt

(qg)

. . . . . --

Fig.1 MBssbauer spectrum f o r water-gas s h i f t r e a c t i o n c a t a l y s t S8 i n a i r at room temperature

After reducing t h e sample at 3 5 0 ' ~ under t h e stream of water-gas f o r 20 hours, we g e t t h e MBssbauer spectrum (Fig. 2a) a t

t h i s temperature. T h i s spectrum was com- pared with t h e spectrum which w a s obtained a t t h e same temperature but a f t e r being t r e a t e d a t 5500C f o r 5 hours (Fig. 2c). The M6ssbauer parameters of t h e s e p a t t e r n s a r e shown i n Table 1. The a r e a r a t i o ^S is

defined as t h e a r e a of t h e c e n t r a l compQ-:

nent divided by t h e h.f. magnetic s p l i t t i n g component. For t h e sample t r e a t e d before 5500C. s = 28.8%. while f o r %he sample t r e a t e d a f t e r 550°C. S = 49.7%. The spectrum of t h e sample a t 5500C under t h e stream of water-gas i s shown i n Fig. 2b It is i n a g r e e ~ e n t with t h e r e f e r e n c e

[3J:

. . . . . . ,. ?! . &.:.- ! ... *..#<.+,:-

. . . --

. .

^* ^.-.T-S---

^-

..I.> ^-

vrloc;t8 ("'%I

Fig. 2 Iv~dssbauer s p e c t r a f o r water-gas s h i f t r e a c t i o n c a t a l y s t S8 a t low space v e l o c i t y and a t various stages:

( a ) exposed t o a CC+CC2+H2C mixture a t 35O0C

( b ) a f t e r (a), a t 5 5 0 ' ~ ( c ) a f t e r ^(bj,a t 3 5 0 ~ ~

When t h e v e l o c i t y of stream i n c r e a s e s , t h e reduction is imcomplete

.

^The ^formation

of y'-Fe203 can be seen from t h e spectrum (Fig, 3 ) .

he

r e s u l t of X-rziy mecsurement a l s o proves t h i s . I n F i g . 3b, i t may be seen t h a t t h e h.f. s p l i t spectrun almost vanishes.

Fig. 3 Mdssbauer s p e c t r a f o r water-gas s h i f t r e a c t i o n s c a t a l y s t S a t high space v e l o c i t y and a t v a r i o u s s t k e s :

( a ) expgsed t o a CO+C02+H2Q mixt6re a t 350 C

,(b) a f t e r ( a ) , a t 5 5 0 ~ ~ ( c ) a f t e r ( b ) , a t 350°C

The s p e c i f i c s u r f a c e d a t a and a c t i v i t y

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801127

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JOURNAL DE PHYSIQUE

Table 1. l-l6ssbai:.er p a r m e t e r s of h . f . magnetic s p l i t t i n g component o f S c a t a l y s t sample s p e c t r a under 350°C r e a c t i o n a t & s p h e r e

---

^-.---

--

I n t e r n a l Isomer a a a r u p o l e FwHd i i a t i o c f m ~ g n e t i c s h i f t * s p l i t t i n g f o r 1st a r e a f o r

f i e l d peak 1st peak

(kOe ) ( m m / s

1

( m n l / s )

-- ---

^{I m/s}

- ---

HA Hg ISA ISB $SA 3"

-

_"3

_--- r l ~ ^{f - 1 ~}

d L J L - - - " - - ^A ^/A

Before b e i n g

hented at 5500C 395.5 346.4 0.048 0.046 0.020 C.024 0.412 1.046 4.19

---

A

--- - ---

--.---

.After b e i n g 412.6 359.0 0.076 0.444 0.020 C.041 0.567 0.505 1.94 h e a t e d at-% - - - , - - - e - - - - . - - - . - - - _ - . - - - . - - -

--- ---

( * ) w i t h r e s p e c t t o m e t a l l i c i r o n a t roon t e m p e r a t u r e .

Table 2. d p e c i f i c s ~ r f a c e are; and z c t . i v i t y of t h e sample b e f o r e and a f t e r r e a c t i o n

,---

--- - -

"peciI"ic s u r f a c e c r e a

---

s c t i v i t y

C a t d y s t ('350°C, s p a c e v e l o c i t y

measured % d e c r e a s e

.---

-

^.--- ^.---

----

^1000/hr)

B e f c r e r e a c t i o n .

-

Trea.ted f o r 1 0 h r s under 350°'

,

^89.28^{46 -44} _46.0

^----

_81.0 ^.^-^-^y^e^-

r e a c t i o n a t n o s ~ & z % - - - . - - - - . - . - - - . - - - ~ - - -

--- A f t e r b e i c g h e a t e d f o r 5 h r s e t 24.11

2 0 0 C and ~ c t i v i t y measurements 73.0 86.9

-

---.--.- -.-.---.-.-

measurement d a t a is shown i n t h e Table 2.

4. uiscussiori. ,- I t c m be s e e n t h a t a t t h e lower v e l o c i t y o f s t r e o n c a t a l y s t J8 i s s u f f i c i e n t l y r e d c c e and belongs t o

Fe7-xCrx04 s y s tem.

-

^{-. -.}^, 1'1 'A' s i t e ( t e t r a h e d r a l s i t e o f s p i n e l ) h a s a s e t of narrow spectrum l i n e s , whereas t h e l i n e s o f 'B' s i t e ( o c t a - h e d r a l s i t e o f s p i n e l ) a r e much b r o a d e r . I t i n d i c s t e s t h a t t h e s u r r o u n d i n g s o f ' A ' s i t e have some s l i g h t changes w i t h t h e c r 3 + i o n doped i n ' 5 ' s i t e , and t h e hopping r a t e between ~ e and ~ "Fe3+ i n ' 5 ' s i t e h a s an obvious change, which b r i n g about t h e

broadening of 'B' s p e c t r a . I n t h e s e s p e c t r a , t h e sample system i s d i s t o r t e d from t h e in- v e r s i o n o b v i o u s l y changes. A f t e r t h e t r e a t - c e n t , t h e l o c a l magnetic f i e l d i n c r e a e s , t h e i.somer s h i f t a l s o i n c r e a s e s a l i t t l e , and t h e r a t i o o f a r e a o f 'B' s i t e t o ' A ' s i t e approaches 2 . These chaEges i n d i c a t e d t h e t the sarcple S," changes back toward F S ~ O ~ . [ ~ ]

.

^. and t h e

cr3+

which v e n t i n t o t h e i n v e r s e - s p i n e l s t r u c t u r e ncw r e s o l v e s o u t p a r t l y and forms f i n e - p a r t i c l e s o l i d s o l u - t i o n w i t h i r o n - o x i d e , t h u s i n c r e a s i n g t h e a r e a of t h e c e n t r a l component.

$hen t h e v e l o c i t y of s t r e a m i n c r e a s e , under t h i s r e d u c t i o n c o n d i t i o n ,

I -

Fe203 is t h e i n t e r m e d i a t e phase o f d-Fe203 r e d u c i n g t o Fe 0 3 4' C 6 9 7 9 8 3 A f t e r corn- p a r i n g F i g . 1 w i t h Fig. 3a i n o u r work, i t cen be s e e n c l e a r l y t h ~ t j--Peg03 i s formed f i r s t l y u n d e r o u r r e a c t i n c o n d i t i o n acd then Fe 0 is produced. This h a s been a l s o proved3b$ L-rsy d e t e r m i n a t i o n . ige c o n s i d e r t h a t t h e more t h e #-phase e x i s t s i n t h e sample, t h e c a s i e r t h e d-phase w i l l be c o n v e r t e d and reduced. E91 Hence, under p r o p e r r e d u c i n g c o n d i t i o n s , whan

a-;hme c o n v e r t s i n t o Fe30q, i t i s

; ? o s s i S l e t h a t t h e -phase w ~ l l p r e s e n t

i t s e l f as .s m e t m t z b l e s t a t e d x r i n g t h e p r o c e s s .

Pig. 7 shows t h a t a s t h e sample i s t r a a t a d und?r h i g h s p r c e v e l o c i t y f o r s e v e r a l c',ecades of h o u r s , t h e r e d u c t i o n p r o c e s s i s s t i l l n o t sompleted, s o ooviouslj/ t h e d i f f u s i o n f a c t o r co!itrals t h s p r o c e s s . !;'e a l s o deterinined t h e

-.

,,,,%r,itude o s u r f z c e e r e a of p a r t i c l e s and t h a s i z e o f p n r t i c l e s o f t h e s a n 2 l e . I t i s found t h a t the s u r f a c e a r e a s o f t h e j , z r t i c l c s c c n t r ~ c t s3ron;l:q a f t e r h e a t t r e z k b e n t . llc';i;aLly, a f t e r t h e c c . t a l y s t i s reciucod w a d e r 350°C f o r 1 0 h o u r s , t h e s ~ r f a c e a r e a has ~ 0 n t r : i c t e d by 48$, i t i s about 2/3 of t h e t o t a l c o n t r a c t i n g amount of s u r f a c e a r e a . The change o f s i z e of p a r t i c l e s a s i t was determined by X-ray d i f f r a c t i o n i s a s o confirmed t o t h i s . According t o t h e r e s u l t o f 1~~8ssba1.1er spec- t r a , we c o n s i d e r t h a t as l o n g as t h e p r e s - e n c e of C r 3 + , t h e s i n t e r i n g o f t h e c a t a - . l y s t i s i n h i b i t e d , t h e h e a t t r e a t m e n t en- hances t h e r e d u c t i o n and d i s p e r s i o n o f t h e sample t o produce more a c t i v e f i n e s o l i d s o l u t i o n partic:es.Thus may b e a r e a s o n o f t h e i n c r e a s e of t h e c a t a l y t i c a c t i v i t y .

We would l i k e t o e x p r e s s o u r t h a n k s t o 1Irs Chen Yi-mei and Yao Chong-gao who h e l 2 e d u s i n o u r computation.

1 The Research Grou of W6ssbau.er Spec- t r s c o

,

e t a l , l & k l n g U n l v . J o u r . 1 719783 54.

2 i b i d ; 1. (1978) 48.

Acta Biochimica e t B i o p h y s i c a S i n i c a (Chinese) 9 (1977) 305.

van d e r Woude,~.

,

e t a1 ,Phys

.

^Rev.167

{$@$&$@%

^al

^,

J.Phys .Chern.Solids 32 Boekma,C. , e t al,J.Phys. ( ~ ) 9 ( 1 9 7 6 ) 2 4 3 9

fj&.i~~i.Xep.Bitu,Tohuko U n n . ( A )

.

, e t a1,Proc .Roy.Soc. (A)239

@ ~ g ~ ~ i ~ $ ~ , e t al,J.Phys.Chem.Solids 2 3 Colomb,U. , e t a l , l \ ~ a t e r . ~ c i . Eng.2(1967)125