A NGR STUDY OF IRON CATALYSTS IN CO HYDROCONDENSATION REACTIONS

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A NGR STUDY OF IRON CATALYSTS IN CO HYDROCONDENSATION REACTIONS

N. Nahon, V. Perrichon, P. Turlier, P. Bussière

To cite this version:

N. Nahon, V. Perrichon, P. Turlier, P. Bussière. A NGR STUDY OF IRON CATALYSTS IN CO

HYDROCONDENSATION REACTIONS. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-339-

C1-340. �10.1051/jphyscol:19801126�. �jpa-00219609�

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JOURNAL DE PHYSIQUE Colloque C1, suppl6ment au n O 1, Tome 41, janvier 1980, page C1-339

A NGR STUDY OF IRON CATALYSTS IN CO HM)ROCONDENSATION REACTIONS

N. Nahon, V. Perrichon, P. Turlier and P. Bussiere

Institut de Recherches SUP Za CataZyse

-

CNRS, 2 Avenue Einstein, 69626 ViZZeurbanne Cgdex, France.

Several iron 10 % by weight containing sup- ported on alumina c a t a l y s t s were studied using transmission Hitssbauer Spectroscopy i n s i t u , i n addition t o magnetic measurements, X Rays d i f f r a c - tion, thermodesorption and measurements of cataly- t i c a c t i v i t y and s e l e c t i v i t y . The aim of t h i s work was 'to study ( I ) the evolution of the c a t a l y s t during the f i r s t steps of the CO hydrocondensation reaction up t o the stationnary conditions, (11) the differences during the same treatment betwen cata- l y s t s modified by an additive : molybdenum which improves the l i g h t hydrocarbons formation, manga- nese and potassi um which increase t h e olefi n content.

The c a t a l y s t precursor was prepared by a modi- f i c a t i o n of P i c h l e r ' s method ( I ) , wherein a hot sus- penstion of y-A1203 in aqueous FeC12/FeC13 was treated with Na2C03. The resulting mixture was b r i e f l y boiled and the p r e c i p i t a t e washed with boi- l i n g water prior to being dried 20 hours a t 378 K.

This precursor was modified by impregnation with solutions of K2C03, (NH4)6H07024. 4 H20, o r MnC12.

4 H20. The f i n a l atomic percentages of K, No, Mn w i t h respect t o Fe a r e respectively 50, 6 and 6.

Magnetic and radiocrystallographic measurements and NGR spectra taken a t 293, 77 and 4 K des-

c r i be t h e precursor a s a mixture of f i n e l y dispersed y-Fe203 and a-FeOOH.

The reduction i s performed i n a stream of hydrogen during 18 hours a t 873 K and followed by NGR.

The final composition of t h e s o l i d s (Table 1) has been obtained from spectra recorded a t 523 K.

Table 1

-

Reduced c a t a l y s t s

Catalyst Fe/A1203

-

Reduction (magnetism) : 77 %

(

Catalyst Fe/Al 203

+

K

-

Reduction (magnetism):82%

I

1

_(SNP) _{(mm s-1)}^rexp ^QS _(kOe)^H

I

Catalyst Fe/Al 203

+

Mo

-

Reduction (magneti sm) :7W Attribution (% i n spectra)

I t r e s u l t s ' t h a t additives influence the f i n a l

0.18 0.32 0 313

0.99 0.58 1.55 0 1.22 0.34 1.08 0

reduction percentage and the phase composition.

tloreover no Fe a l l o y formation i s detected.

A desorption a t 873 K of hydrogen from the Fe (71.0)

~ e ' + (17 .O)

~ e ' + (13.0)

Fe/A1203 c a t a l y s t r e s u l t s in oxidation of surface iron atoms ( 2 ) . I t i s a reversible process, which

Catalyst Fe/A1 203 + Fln

-

Reduction (magneti sm) :84%

can be described a s a whole by the equilibrium : Fe

+

2 H+ ^f~ e " + HZ where a1 umi na plays a role, a s previously reported i n the case of Fe/MgO cata- l y s t s (3). A similar bqhaviour i s evidenced by magnetic measurements on the modified c a t a l y s t s .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801126

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JOURNAL DE PHYSIQUE

The e v o l u t i o n of the Fe/A1203 s o l i d during CO hydrocondensation i s represented by the s e t o f spectra i n f i g u r e 1, recorded a t 523 K i n the mixture lCO/lH2. M e t a l l i c i r o n i s no longer detec- t e d a f t e r 3 hours. I t i s replaced by E-Fe2C (4,5,6) and a species the isomeric s h i f t o f which could be t h a t o f a ~ e ~ + . This i s confirmed by the spectrum taken a t 4 K, where i t appears as a sextet w i t h a maximum e f f e c t i v e f i e l d about 500 kOe. The carbide and the f e r r i c phase could a r i s e from the dissocia- t i v e adsorption o f CO on i r o n .

The study o f Fe/A1203

+

K s o l i d i n the same conditions shows a s i m i l a r behaviour. I n the case o f Fe/A1203

+

Mn the main feature o f the e v o l u t i o n

i s the formation o f cementite Fe3C i n a d d i t i o n t o .c-Fe2C. As t o Fe/A1 203

+

Mo, no carbide appears during the f i r s t hours. Since the formation o f

hydrocarbons i s evidenced as soon as the r e a c t i o n i s started, i t i s t o be thought t h a t bulk carbide i s n o t an intennediate i n the r e a c t i o n mechanism.

Figure 1 and Table 2.-Evolution o f Fe/A1203 cata- References

l y s t during CO hydrocondensation reaction. (1) H.H. STORCH, N. COLUMBIC, and R.B. ANDERSON, t : r e a c t i o n time ; T : temperature o f the sample. "The F i scher-Tropsch and r e l a t e d synthesis",

kfiley, New-York 1951, p. 251.

(2) N. NAHON, V. PERRICHDN, P. TURLIER, and P. BUSSIERE, React. Kin. Catal. Lett., t o be pub1 i shed.

(3) R. DUTARTRE, P. BUSSIERE, J.A. DALMON, and G.A. MARTIN, J. Catal

. ,

t o be published.

(4) Yu. V. MAKSIMOV, I.P. SUZDALEV, R.A. ARENTS, arid S.H. LOKTEV, Kinet. Catal

. , 15

(1974), 1293.

(5) J.A. AMELSE, J.B. BUTT, and L.H. SCHWARTZ, J. Phys. Chem.,

82

(1978), 558.

A t t r i b u t i o n (% i n spectra) I t

(h)

(6) G. LECAER, J.H. DUBOIS, and J.P. SENATEUR, J. S o l i d State Chem.,.g (1976), 19.

0 2.5

19

T

'

(K)

I S lexp QS H

(SNP) (m 5'') (kOe)

0.41

1:; ;

¹³¹ E-Fe2C (52.011

sL

0.24 184 E-Fe2C

0.6 500 ~ e ~ +

%

523 523

523

f i r s t s e t o f data i n Table 1

0.17 0.30 0 313

0.61 0.50 0 0

0.90 0.62 1.57 0 0.39 0.54 0

.

^13'

0.40 0.24 0 196

0.35 0.46 0.53 0 1.15 1.22 1.34 0

Fe (12.0)

~ e (12.0) ~ +

~ e (18.5) ~ +

}r-Fe2C(67.5)

~ e (18.0) ~ +

~e'+ (30.0)