STRUCTURE AND CATALYTICAL INVESTIGATION OF Fe-Mo AND Fe-Ni CATALYSTS FOR AMMONIS SYNTHESIS

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STRUCTURE AND CATALYTICAL

INVESTIGATION OF Fe-Mo AND Fe-Ni CATALYSTS FOR AMMONIS SYNTHESIS

Yu. Maksimov, R. Arents, I. Suzdalev, V. Yatsimirski

To cite this version:

Yu. Maksimov, R. Arents, I. Suzdalev, V. Yatsimirski. STRUCTURE AND CATALYTICAL INVES- TIGATION OF Fe-Mo AND Fe-Ni CATALYSTS FOR AMMONIS SYNTHESIS. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-337-C1-337. �10.1051/jphyscol:19801125�. �jpa-00219608�

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JOURNAL DE PHYSIQUE Colloque C1, supplkment au n ^O1 , Tome 41, janvier 1980, page (3-337

SIRUCTURE AND CATALYTICAL INVESTIGATION OF Fe-Mo AND Fe-Ni CATALYSTS FOR M N I S SYNTHESIS

Yu.V. Maksimov, R. A r e n k s , I.P. Suzdalev and V.K, Yatsimirski Institute of ChemicaZ Physics, Moscow, USSR.

The s t r u c t u r e of Fe-Blo and Be-I:i metal c a t a l y s t s w a s s t u d i e d by means of Mossbauer spectroscopg, X-ray d i f f r a c t i o n

and ESCA spectroscopy and compared w i t h t h e a c t i v i t y i n the s y n t h e s i s of nTI13.

Mossbauer s p e c t r a of t h e Fe-Xo sgs- tem c o n s i s t of HE'S f o r cC -Fe and a s i n g l e asymmetric l i n e i n t h e c e n t r e of t h e s p e c t r a w i t h isomer s h i f t r e l a t i v e t o

d. -Fe of - 0 , I nm!sec. T-his l i n e c o r r e s - ponds t o a n o n o r d e r i q s o l i d s o l u t i o n of

n i t r o g e n atoms i n

d

^{- ~ e (}d - ~ e l ~ a u s t e - n i t e )

/I/ .

X-ray d a t a show t h e presence of -Fe and MoN n i t r i d e without t h e Lines of -FeN. These d a t a a r e s a t i s- f y i n g t h e p r e p o s i t i o n , t h a t t h e f ormetion

of a c a t a l y s t w i t h 8-FeN and n o n s t o i c h i - m e t r i c Ho-I? t a k e s p l a c e d u r i n g t h e syn-

t h e s i s of VH3. Ordinary,

X-F~N

^system

decomposes i n t o t e t r a g o n a l m a r t e n s i t e

and & -Fe a t a temperature 1ov:er than

9 1 0 ~ ~ /2/. The s t a b i l i z a t i o n of

8-

FeE phase a t 2 0 ' ~ i s supported i n our c a s e

by t h e presence of e x c e s s of n i t r o g e n atoms i n t h e nonordered r e g i o n a t t h e i n t e r f a c e of d -Pe and MonT n i t r i d e . It was observed t h a t both t h e c a t a l y t i c ac- t i v i t y and t h e -PeN c o n t e n t depending on Mo c o n c e t r a t i o n had a maximum vihen r a t i o of Mo/Fe w a s about 0.55. This cor- r e l a t i o n s u p p o r t s t h e c o n c l u s i o n on t h e p a r t i c i p a t i o n of a p olimorphous t r a n s i - t i o n i n t h e a c t i v a t i o n of molecules du- ring t h e c a t a l y s i s .

I n t h e c a s e of t h e low c o n c e n t r a t i - ons of N i ( 4 10%) f o r FeNi systems t h e Mossbauer and X-ray d a t a agree: a homo- genious s01id s o l u t i o n of &-FeEi i s p r e - s e n t . I n t h e c a s e of a h i g h e r concentra- t i o n of N i a simulteneous f o r n a t i o n of

d -FeITi and 8-FeN3. t a k e s p l a c e . It i s

i n t e r e s t i n g t o note t h a t f o r semples m i t h h i g h e r Bi c o n c e n t r a t i o n t h e c o m ~ o s i - t i o n of t h e 8-phase &oes n o t degend on t h e c o n c e n t r a t i o n 5 f iTi. Uossbauer r;pect- r a shov~ t h a t t h e magnetic f i e l d value a t i r o n n u c l e i i s 29,550.5 T which c o r r e s - ponds t o a c o n c e n t r a t i o n of about 50~1; lfi

i n BeNi /3,4/. T h i n r e s u l t demonstrates t h a t t h e c a t a l y t i c r e a c t i o n i t s e l f c r e - a t e s heterogeneous compositions w i t h an optimum c o n c e n t r a t i o n of components. Under t h e s e circumstances i n v a r a l l o y s 135th lower magnetic moment ^an&magnetic f i e l d v a l u e s on ~ e ~ ~ n u c l e l /4/ a r e n o t formed.

The c a t a l y t i c a c t i v i t y of PeNi systems depends on t h e c o n c e n t r a t i o n af Xi. I n i - t i a l l y t h e a c t i v i t y of this system dro2s w i t h i n c r e a s i n g X i c o n t e n t , but then it reaches a maximum. This m a x i m u c o r r e s - ponds t o a c o n c e n t r a t i r ~ n of 50.5 T i i i n

8-

2eXi and t o t h e presence of 50-60% of

$- FeWi phase.

On the b a s i s of the ESCA d a t a t h e decreasing a c t i v i t y i n t h e homogeni oun r e g i o n i s connected w i t h a decrease of t h e number of a c t i v e C7-centers of Pe atoms i n t h e s u r f a c e r e g i o n ivhen t h e f r a c t i o n of N i increased/5/.

References. I. Maksimov Yu.V., Suzdalev

LP.

Arents B.A. ,Xakarov E.F., Kushnerev hl.Ya, Kuznetaov L.D.9 DAN 222 (1975) 392.

2.Grigorovitch V.K., E l e c t r o n i c s t r u c t u r e and thermodynamics of i r o n a l l o y s , I 9 7 0 , hl.Nauka. 3. Sy dorova S.K., Doro shenko A .V.

,

B b m y a (1965) 786. 4.Dash I.G.,DunlapE?.C., Harward D.G.Phys. Rev.

,u

(1966)376, 5. Dowden, D.A. ,Proc

.

5-th Intern.Congr, C a t a l . ,Miami Beach F l o r i d a , I 9 7 2 , p .621.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801125