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The Preparation of Moo3-CoO-Al2O3 Catalyst and its Characteristics
Preparation of Catalysts, edited by B. Delmon, P.A. Jacobs and G . Poncelet o 1976, Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands TIIE PR1~PARATIO.UOF
M O O S -C0O-Al2O3
CATALYST AND ITS
CIIARACTERI STICS Y . KOTEIIA, K . OGAWA, )I.
OBA, K.
SIII>lOblURA, M.
YONEPKJRA,
A , U E N O and N . TODO
N a t i o n a l Chemical L a b o r a t o r y f o r I n d u s t r y , Gth D i v i s i o n , 2 - 1 9 - 1 9 , Flita, 'leguro-ku,
Tokyo, JAPAN 15.3.
When t h e m i x t u r c o f t h e o x i d e of c o h a l t o r molybdenum and a l u m i n a was c a l c i n e d a t 5 0 0 - 9 0 0
O C ,
the oxidation or
r c d u c t i o n hetween COO and C O ~ O I , , o r t h e p a r t i a l r e d u c t i o n o f H003 t o ? l 0 0 ~ s- p~e c i e s o c c u r r e d i n t h e r e s p e c t i v e c a s e . The m i x t u r c o f t h e o x i d e s of c o b a l t and molybdenum and a l u m i n a formed t h c h i g h - t e m p e r a t u r e m o d i f i c a t i o n o f CoPloOb above 5 0 0 O C i n t h c d i f f e r e n t d e g r e e d e p e n d e n t upon t h e t e m p e r a t u r e and t h e h i n d of a l u m i n a .
From t h e d e s u l f u r i z a t i o n a c t i v i t y € o r t h c c a t a l y s t s p r e p a r c d e i t h e r by i m p r c g n a t i o n o r k n e a d i n g , i t was found t h a t t h e f o r m e r method i s more f a v o r a b l e and t h a t t h e d i f f e r e n t optimum Co/!40 r a t i o f o r b o t h methods c x i s t s . The m e c h a n i c a l s t r e n g t h measured f o r t h e Coo-and/or No03-supportcd c a t a l y s t s s u g g e s t s t h a t t h e dominating f a c t o r s t o a f f e c t t h e s t r e n g t h r ~ o u l d he t h e p a r t i c l e s i z e , t h e s u r f a c e a r e a , t h e adsorbed water c o n t e n t , t h e d i s p e r s e d s t a t e of t h e i n g r e d i e n t s and s o o n . INTRODUCTION E x t e n s i v c works [ l - 5 1 on t h c a c t i v i t y o f MoOp-CoO-Al203 flowever, o n l y
d c s i i 1f u r i za t on c a t a l y s t h a v e been d e v e l o p e d .
a fcw p a p e r s t r i e d t o c l a r i f y t h c r e l a t i o n s h i p b e t w e e n t h e s t r u c t u r e o r s u r f a c e p r o p e r t i e s and t h e p r e p a r a t i o n c o n d i t i o n s , nd t h i s h a s n o t y e t heen f u l l y u n d e r s t o o d . I n t h e p r e s e n t p a p e r i t was shown t h a t t h e s o l i d - s t a t e r e a c t i o n o c c u r s between c o h a l t o x i d e and molybdenum o x i d e t o form c o h a l t molybtlate and t h e e x c e s s o x i d e s which e x i s t s a b o v e t h e s t o i c h i o m e t r i c r a t i o o f 1 : 1 i s i n t h e same s t a t e a s was c a l c i n e d w i t h a l u m i n a [ 6 , 7 ] , w h i l e t h e u n r e a c t e d o x i d e
372
changes to Co30b or MOO^-^. From the measurements of the catalytic activity for hydrodesulfurization, it was elucidated that the activity of the catalysts prepared by the method similar to the practical procedure depends considerably upon the preparation methods and upon the amount of cobalt and molybdenum supported on alumina [S]. The mechanical strength varied with the supported amount of cobalt and molybdenum and with the calcination temperature. EXPERIMENTAL Starting materials were cobalt salt, molybdenum salt, =-alumina and y-alumina, the last one being prepared in our laboratory [9] or obtained commercially, The solid-state reaction was followed by the high-temperature X-ray diffraction apparatus. The catalysts used for measurement of the catalytic activity were prepared both by impregnation and kneading methods, the latter being common to the sample for measurement of the mechanical strength. Impregnation was carried out as follows; aqueous solutions of ammonium paramolybdate and cobalt nitrate were mixed, while pelletized alumina was added to this solution and dried. The disoarsed state of the individual component, cobalt and molybdenum, was investigated by means of an electron mjcroprobe X-ray analyser. The initial catalytic activity for hydrodesulfurization of atmospheric distilled khafji residue was determined by a semi-batch reactor system under the standard conditions, temperature of 4 O O 0 C , hydrogen pressure of 100 kg/cm2and hydrogen flcw rate of 3@n/hr for 9 0 min. The mechanical strength of extruded pellets prepared by kneading method was calculated from the value obtained by compression in the direction of radial axis. EXPERIMENTAL RESULTS AND DISCUSSION When the mixture of alumina and cobalt salt was calcined in the temperature range between 500 and 9 0 0 O C , the
373
formation o f cobalt aluminate begins at temperature higher than 8 5 0 O C , while at lower temperature the oxidation or reduction of cobalt oxide occurs, as in the case of cobalt oxide without alumina [ 6 ] . The X-ray pattern of the calcined products is shown in Fig 1 (a).
>
1
I
4 3
4 1
4
f 1 1
a
8 1
4
2
1 I
diffraction pattern of the mixture of oxides at a MoO,/a-A120~ ratio of 2/1 after heated at 650OC for 2 hr. l-MoO,, 2-M04011, 3-M0s0zaS4-
In the case of the mixture of alumina and molybdenum oxide, the reduction of molybdenum trioxide occurs in the temperature range of 600 6 0 0 and 700'C to form M ooOOl ~, n, as ,a , M002,76 MOO^,,^ and MOO^.^^, as shown in Fig l(b) [7]. When the mixture of alumina and molybdenum and cobalt 500 and 8 O O 0 C , salts was calcined in the temperature ranged 500 the formation of cobalt molybdate begins at temperature
374
higher than 500°C. Cobalt molybdate has 3 polymorphic modifications, that is, the solvated cobalt molybdate by coprecipitation, the low-temperature and the high-temperature modifications as described in detail ( 3 , 10, 111. When the mixtures of cobalt oxide,molybdenum trioxide and a - or y alumina with a molar ratio of 1:l:l were calcined the hightemperature X-ray diffraction patterns, shown in Fig. 2(a) and (b), were obtained.
(a1 (b1 Fig. 2.X-ray diffraction patterns of the mixture of oxides at a MoO~/CoO/a-A120~(a) or y-AlzO, (b) ratio of l/l/l, 20 min. after indicated temperatures were reached. 1 - COO, 2 - CO,O*, 3 - MOO,, 4 - COh1004, 5 - “ - A 1 ~ 0 3 ,6 MosO11,7
-
N0170s7.
It was observed that a low-temperature modification of cobalt molybdate appeared on cooling to room temperature independent of the sort of alumina used. When the composition deviated from the stoichiometric ratio or the reaction did not proceed completely, the oxide of ingredient, cobalt o r molybdenum, was shown t o undergo the changes as described
375
above and c o b a l t a l u m i n a t e could n o t be formed t i l l 8 5 O o C i n t h e presence of e x c e s s c o b a l t o x i d e .
2
L
6
8 1 0 1 2 M O 011w t %I
tL
1
F i g . 3. R e l a t i o n between d e s u l f u r i z a t i o n a c t i v i t y and MOOS c o n c e n t r a t i o n a t v a r i o u s c o n c e n t r a t i o n s of COO. 1 - COO 3.7-3.9 w t % impregnated w i t h homemade Y - A l z O , . 2 - COO 4.0-4.3 wtib kneaded w i t h homemade y - A l i O 3 . 3 - COO 2.6-3.3 w t % impregnated w i t h commercial Y - A l z O 3 , 4 - COO 3.0-3.1 w t S kneaded w i t h commercial y-AlzOa 6): A f t e r t r e a t e d w i t h ammoniacal s o l u t i o n .
In Fig. 3, t h e d e s u l f u r i z a t i o n a c t i v i t y f o r t h e c a t a l y s t s prepared by impregnation and kneading methods, s u p p o r t i n g v a r i o u s c o n c e n t r a t i o n s o f c o b a l t o x i d e , were p l o t t e d a g a i n s t molybdenum t r i o x i d e c o n c e n t r a t i o n s . The r e s u l t s c l e a r l y i n d i c a t e t h a t t h e impregnated c a t a l y s t s e x h i b i t e d h i g h e r c a t a l y t i c a c t i v i t i e s t h a n t h e kneaded ones and t h a t t h e d i f f e r e n t optimum Co/Mo r a t i o e x i s t s f o r b o t h p r e p a r a t i o n methods. The p l o t s f o r t h e c a t a l y s t s from which f r e e molybdenum t r i o x i d e was e x t r a c t e d w i t h aqueous ammonia i n d i c a t e t h a t n e c e s s a r y amount of c o b a l t oxide/molybdenum t r i o x i d e i s found f o r b o t h methods r e g a r d l e s s of t h e combined s t a t e of molybdenum t r i o x i d e . I t was found by an e l e c t r o n microprobe X-ray a n a l y s i s t h a t t h e d i s p e r s i o n of c o b a l t tended t o be more inhomogeneous t h a n t h a t of molybdenum when t h e c a t a l y s t s were p r e p a r e d by impregnation method, a s shown i n F i g . 4 .
376
F i g . 4 . L i n e p r o b e s o f Co, Mo and A 1 of an i m p r e g n a t e d c a t a l y s t of 9 . 6 M O O S - 3.18 COO - y-AlrO3 ( W t t ) .
100
100 0 100 Oirtancr from c m t r r rlfl
200
T h i s r e s u l t s u g g e s t s t h a t t h e u n i f o r m i t y of i m p r e g n a t e d components s h o u l d b e a s s u r e d when t h e c a t a l y t i c a c t i v i t y i s e s t i m a t e d i n terms of t h e Co/Mo c o m p o s i t i o n . F i g . 5 . R e l a t i o n between c o m p r e s s i v e s t r e n g t h and M O O 3 concentration a t various calcination temperatures. 0 : 50, 0 : 1 2 0 , 0 : 3 0 0 , A: 450, 0 : 650, x : 900(°C)
The r e l a t i o n s b e t w e e n t h e m e c h a n i c a l s t r e n g t h and t h e c o n t e n t o f molybdenum t r i o x i d e o r c o b a l t o x i d e a t v a r i o u s c a l c i n a t i o n temperatures,respectively,were o b t a i n e d , a s e x e m p l i f i e d i n F i g . 5 and F i g . 6 . The c o n t e n t o f molybdenum t r i o x i d e showed l i t t l e i n f l u e n c e o n t h e m e c h a n i c a l s t r e n g t h w h i l e t h e c o b l a t o x i d e c o n t e n t up t o 2 % i n c r e a s e d t h e s t r e n g t h , t h i s b e i n g a l m o s t c o n s t a n t i n f u r t h e r a d d i t i o n . The a d s o r b e d water reduced t h e compressive s t r e n g t h a s p r e s e n t e d i n Table 1. The s t r e n g t h o f t h i s c a t a l y s t a f t e r u s e i n t h e d e s u l f u r i z a t i o n r e a c t i o n f o r 400 h o u r s remained o n l y 12-13%
377
Fig. 6. Relation between compressive strength and COO concentration at various calcination temperatures. The same temperatures indicated as in Fig. 5 .
0
1
1
5
10
coo ‘I.
I 15
less independent of the composition. The behaviour o f the strength of the cobalt oxide-and/or molybdenum trioxidesupported catalysts might be affected with the particle size, the surface area, the adsorbed water content, the dispersed Table 1 Effects of
H20
adsorbed on compressive strength.
(wt % 1
coo
MOO 5 (wt 9 0 )
3
0
3
12
adsorbe (m mol/g)
1120
5
20.5
Compress ive strength (kg/cm2) 16
12
5
9
9
7 4
22
state of ingredients and so on. The dominating parameters, however, in this respect would require further investigations. REFERENCES 1. 2.
J. 11. Ashley and P. C. €1. Mitchel, J . Chem. S O C . Ser. A, (1958) 2 8 2 1 ; ibid., (1969) 2 7 3 0 . 0 . V. Krylov and L . Ya. Margolis, Kinet. katal., 11 (1970)
432.
378
J. M. J. G. Lipsch and G. C. A. Schuit, J. Catal., 1 5 (1969) 163, 174, 179. P. Ratnasamy, R. P. Mehrotra and A . V. Ramaswamy, ibid., 4. 26 (1972) 352; ibid., 32 (1974) 63. P. Ratnasamy, L. Rodrique and A . J. Leonard, J. Phys. 5. Chem., 77 (1973) 2242. T. Nishina, M. Yonemura and Y . Kotera, J. Inorg. Nucl. 6. Chem., 34 (1972) 3279. Y . Kotera and A . Ueno, Bull. Chem. SOC. Japan, 46 7. (1973) 3431. Y . Kotera, N. Todo, K. Muramatsu, K. Ogawa, M. Kurita, 8. T. Sato, M. Ogawa and T. Kabe, Kogyo Kagaku Zasshi, 74 (1971) 330. S. Yamadaya, K. Shimomura, T. Kinoshita and H. Uchida, 9. Kogyo Kagaku Zasshi, 73 (1970) 847. 10, J. Chojnacki and R. Kozlowski, J. Solid State Chem., 11 (1974) 106. 11. P. Courtine, P. P. Cord, C. Pannetier, J. C. Daumas and P. Montarnall, Bull. SOC. Chin. France, 12 (1968) 4816.
3.
319
DISCUSSION P. MARS : 1) What is the temperature of calcination of the catalysts dealt with in figure 3 ? 2 ) The heterogeneity of the catalyst with respect to the Mo and especially Co concentration (figure 4) suggests that in the outer layer of the catalyst particles, CoMo04 (Co/Mo : 1/1) is present. May this compound already have been formed in the solution ? 3 ) Was this heterogeneity also present after testing the catalytic activity ? Y. KOTERA : 1) The catalyst was calcined at 3 3 O o C for 30 min and at 55OoC for 2 hrs. 2 ) The solvated modification of cobalt molybdate which is usually prepared by coprecipitation would not be formed in the mixed solution of cobalt and molybdenum salts. The high temperature modification is formed during calcination at temperatures higher than 45OoC. We assume that cobalt compounds in the outer layer would be cobalt oxide, and the high temperature modification of cobalt molybdate since the catalyst was calcined at 5OO0C as cited above. 3 ) The same relative intensities of heterogeneously supported impregnants were found after the reaction, as well as more prominent line probes of S, Nil or V deposited during the reaction. (N. Todo et al., Bull.Japan Petroleum Inst., 14,89, 1972). E.J. NEWSON : My question concerns the nice maxima for curves 1 and 3 in Figure 3 . The optimum Co/Mo ratio for these curves is 0.5 for curve 1 and 0 . 3 for curve 3 . Does this mean that the optimum for HDS of Khafjii atmospheric residuum is different to 0.2 as is well known in the literature for distillate HDS ?
Y. KOTERA : We used the atmospheric Khafjii residue mixed with 6 % light oil and the result obtained is shown in Figure 3 . We do not have other experimental data, and we would not like to speculate on the difference of Co/Mo ratio when a different kind of oil to be desulfurized is used. (See reference in answer to question of P. Mars).
P. BERNUSSET : My question concerns table I of your communication. Are the results expressing the effects of adsorbed H20 on crushing strength specific for catalysts prepared by knea,ding and, if s o , do you think it would be possible that the same behaviour occurs with pure carrier ? Y. KOTERA : The results obtained are not exclusively specific for the kneaded series of catalysts. The effect of water content in the alumina powder on the pellet strength has been studied in detail to find the maximum strength at the water content of about lo%, that is, in the range of 5-7 mol/g. However, it seems rather difficult to discriminate the effect of water adsorbed from that of impregnants on the mechanical strength of pure carrier. (J. Yamahaya et al., J. Catal., 19, 264, 1970). P. GRANGE
:
Do you think that there is no sublimation of Mooj at
high temperature ? Y. KOTERA : Molybdenum trioxide sublimates above 8OO0C and the amount of sublimation is negligible in the temperature range lower than 7 0 0 ' C . (7).
M O O S -C0O-Al2O3
CATALYST AND ITS
CIIARACTERI STICS Y . KOTEIIA, K . OGAWA, )I.
OBA, K.
SIII>lOblURA, M.
YONEPKJRA,
A , U E N O and N . TODO
N a t i o n a l Chemical L a b o r a t o r y f o r I n d u s t r y , Gth D i v i s i o n , 2 - 1 9 - 1 9 , Flita, 'leguro-ku,
Tokyo, JAPAN 15.3.
When t h e m i x t u r c o f t h e o x i d e of c o h a l t o r molybdenum and a l u m i n a was c a l c i n e d a t 5 0 0 - 9 0 0
O C ,
the oxidation or
r c d u c t i o n hetween COO and C O ~ O I , , o r t h e p a r t i a l r e d u c t i o n o f H003 t o ? l 0 0 ~ s- p~e c i e s o c c u r r e d i n t h e r e s p e c t i v e c a s e . The m i x t u r c o f t h e o x i d e s of c o b a l t and molybdenum and a l u m i n a formed t h c h i g h - t e m p e r a t u r e m o d i f i c a t i o n o f CoPloOb above 5 0 0 O C i n t h c d i f f e r e n t d e g r e e d e p e n d e n t upon t h e t e m p e r a t u r e and t h e h i n d of a l u m i n a .
From t h e d e s u l f u r i z a t i o n a c t i v i t y € o r t h c c a t a l y s t s p r e p a r c d e i t h e r by i m p r c g n a t i o n o r k n e a d i n g , i t was found t h a t t h e f o r m e r method i s more f a v o r a b l e and t h a t t h e d i f f e r e n t optimum Co/!40 r a t i o f o r b o t h methods c x i s t s . The m e c h a n i c a l s t r e n g t h measured f o r t h e Coo-and/or No03-supportcd c a t a l y s t s s u g g e s t s t h a t t h e dominating f a c t o r s t o a f f e c t t h e s t r e n g t h r ~ o u l d he t h e p a r t i c l e s i z e , t h e s u r f a c e a r e a , t h e adsorbed water c o n t e n t , t h e d i s p e r s e d s t a t e of t h e i n g r e d i e n t s and s o o n . INTRODUCTION E x t e n s i v c works [ l - 5 1 on t h c a c t i v i t y o f MoOp-CoO-Al203 flowever, o n l y
d c s i i 1f u r i za t on c a t a l y s t h a v e been d e v e l o p e d .
a fcw p a p e r s t r i e d t o c l a r i f y t h c r e l a t i o n s h i p b e t w e e n t h e s t r u c t u r e o r s u r f a c e p r o p e r t i e s and t h e p r e p a r a t i o n c o n d i t i o n s , nd t h i s h a s n o t y e t heen f u l l y u n d e r s t o o d . I n t h e p r e s e n t p a p e r i t was shown t h a t t h e s o l i d - s t a t e r e a c t i o n o c c u r s between c o h a l t o x i d e and molybdenum o x i d e t o form c o h a l t molybtlate and t h e e x c e s s o x i d e s which e x i s t s a b o v e t h e s t o i c h i o m e t r i c r a t i o o f 1 : 1 i s i n t h e same s t a t e a s was c a l c i n e d w i t h a l u m i n a [ 6 , 7 ] , w h i l e t h e u n r e a c t e d o x i d e
372
changes to Co30b or MOO^-^. From the measurements of the catalytic activity for hydrodesulfurization, it was elucidated that the activity of the catalysts prepared by the method similar to the practical procedure depends considerably upon the preparation methods and upon the amount of cobalt and molybdenum supported on alumina [S]. The mechanical strength varied with the supported amount of cobalt and molybdenum and with the calcination temperature. EXPERIMENTAL Starting materials were cobalt salt, molybdenum salt, =-alumina and y-alumina, the last one being prepared in our laboratory [9] or obtained commercially, The solid-state reaction was followed by the high-temperature X-ray diffraction apparatus. The catalysts used for measurement of the catalytic activity were prepared both by impregnation and kneading methods, the latter being common to the sample for measurement of the mechanical strength. Impregnation was carried out as follows; aqueous solutions of ammonium paramolybdate and cobalt nitrate were mixed, while pelletized alumina was added to this solution and dried. The disoarsed state of the individual component, cobalt and molybdenum, was investigated by means of an electron mjcroprobe X-ray analyser. The initial catalytic activity for hydrodesulfurization of atmospheric distilled khafji residue was determined by a semi-batch reactor system under the standard conditions, temperature of 4 O O 0 C , hydrogen pressure of 100 kg/cm2and hydrogen flcw rate of 3@n/hr for 9 0 min. The mechanical strength of extruded pellets prepared by kneading method was calculated from the value obtained by compression in the direction of radial axis. EXPERIMENTAL RESULTS AND DISCUSSION When the mixture of alumina and cobalt salt was calcined in the temperature range between 500 and 9 0 0 O C , the
373
formation o f cobalt aluminate begins at temperature higher than 8 5 0 O C , while at lower temperature the oxidation or reduction of cobalt oxide occurs, as in the case of cobalt oxide without alumina [ 6 ] . The X-ray pattern of the calcined products is shown in Fig 1 (a).
>
1
I
4 3
4 1
4
f 1 1
a
8 1
4
2
1 I
diffraction pattern of the mixture of oxides at a MoO,/a-A120~ ratio of 2/1 after heated at 650OC for 2 hr. l-MoO,, 2-M04011, 3-M0s0zaS4-
In the case of the mixture of alumina and molybdenum oxide, the reduction of molybdenum trioxide occurs in the temperature range of 600 6 0 0 and 700'C to form M ooOOl ~, n, as ,a , M002,76 MOO^,,^ and MOO^.^^, as shown in Fig l(b) [7]. When the mixture of alumina and molybdenum and cobalt 500 and 8 O O 0 C , salts was calcined in the temperature ranged 500 the formation of cobalt molybdate begins at temperature
374
higher than 500°C. Cobalt molybdate has 3 polymorphic modifications, that is, the solvated cobalt molybdate by coprecipitation, the low-temperature and the high-temperature modifications as described in detail ( 3 , 10, 111. When the mixtures of cobalt oxide,molybdenum trioxide and a - or y alumina with a molar ratio of 1:l:l were calcined the hightemperature X-ray diffraction patterns, shown in Fig. 2(a) and (b), were obtained.
(a1 (b1 Fig. 2.X-ray diffraction patterns of the mixture of oxides at a MoO~/CoO/a-A120~(a) or y-AlzO, (b) ratio of l/l/l, 20 min. after indicated temperatures were reached. 1 - COO, 2 - CO,O*, 3 - MOO,, 4 - COh1004, 5 - “ - A 1 ~ 0 3 ,6 MosO11,7
-
N0170s7.
It was observed that a low-temperature modification of cobalt molybdate appeared on cooling to room temperature independent of the sort of alumina used. When the composition deviated from the stoichiometric ratio or the reaction did not proceed completely, the oxide of ingredient, cobalt o r molybdenum, was shown t o undergo the changes as described
375
above and c o b a l t a l u m i n a t e could n o t be formed t i l l 8 5 O o C i n t h e presence of e x c e s s c o b a l t o x i d e .
2
L
6
8 1 0 1 2 M O 011w t %I
tL
1
F i g . 3. R e l a t i o n between d e s u l f u r i z a t i o n a c t i v i t y and MOOS c o n c e n t r a t i o n a t v a r i o u s c o n c e n t r a t i o n s of COO. 1 - COO 3.7-3.9 w t % impregnated w i t h homemade Y - A l z O , . 2 - COO 4.0-4.3 wtib kneaded w i t h homemade y - A l i O 3 . 3 - COO 2.6-3.3 w t % impregnated w i t h commercial Y - A l z O 3 , 4 - COO 3.0-3.1 w t S kneaded w i t h commercial y-AlzOa 6): A f t e r t r e a t e d w i t h ammoniacal s o l u t i o n .
In Fig. 3, t h e d e s u l f u r i z a t i o n a c t i v i t y f o r t h e c a t a l y s t s prepared by impregnation and kneading methods, s u p p o r t i n g v a r i o u s c o n c e n t r a t i o n s o f c o b a l t o x i d e , were p l o t t e d a g a i n s t molybdenum t r i o x i d e c o n c e n t r a t i o n s . The r e s u l t s c l e a r l y i n d i c a t e t h a t t h e impregnated c a t a l y s t s e x h i b i t e d h i g h e r c a t a l y t i c a c t i v i t i e s t h a n t h e kneaded ones and t h a t t h e d i f f e r e n t optimum Co/Mo r a t i o e x i s t s f o r b o t h p r e p a r a t i o n methods. The p l o t s f o r t h e c a t a l y s t s from which f r e e molybdenum t r i o x i d e was e x t r a c t e d w i t h aqueous ammonia i n d i c a t e t h a t n e c e s s a r y amount of c o b a l t oxide/molybdenum t r i o x i d e i s found f o r b o t h methods r e g a r d l e s s of t h e combined s t a t e of molybdenum t r i o x i d e . I t was found by an e l e c t r o n microprobe X-ray a n a l y s i s t h a t t h e d i s p e r s i o n of c o b a l t tended t o be more inhomogeneous t h a n t h a t of molybdenum when t h e c a t a l y s t s were p r e p a r e d by impregnation method, a s shown i n F i g . 4 .
376
F i g . 4 . L i n e p r o b e s o f Co, Mo and A 1 of an i m p r e g n a t e d c a t a l y s t of 9 . 6 M O O S - 3.18 COO - y-AlrO3 ( W t t ) .
100
100 0 100 Oirtancr from c m t r r rlfl
200
T h i s r e s u l t s u g g e s t s t h a t t h e u n i f o r m i t y of i m p r e g n a t e d components s h o u l d b e a s s u r e d when t h e c a t a l y t i c a c t i v i t y i s e s t i m a t e d i n terms of t h e Co/Mo c o m p o s i t i o n . F i g . 5 . R e l a t i o n between c o m p r e s s i v e s t r e n g t h and M O O 3 concentration a t various calcination temperatures. 0 : 50, 0 : 1 2 0 , 0 : 3 0 0 , A: 450, 0 : 650, x : 900(°C)
The r e l a t i o n s b e t w e e n t h e m e c h a n i c a l s t r e n g t h and t h e c o n t e n t o f molybdenum t r i o x i d e o r c o b a l t o x i d e a t v a r i o u s c a l c i n a t i o n temperatures,respectively,were o b t a i n e d , a s e x e m p l i f i e d i n F i g . 5 and F i g . 6 . The c o n t e n t o f molybdenum t r i o x i d e showed l i t t l e i n f l u e n c e o n t h e m e c h a n i c a l s t r e n g t h w h i l e t h e c o b l a t o x i d e c o n t e n t up t o 2 % i n c r e a s e d t h e s t r e n g t h , t h i s b e i n g a l m o s t c o n s t a n t i n f u r t h e r a d d i t i o n . The a d s o r b e d water reduced t h e compressive s t r e n g t h a s p r e s e n t e d i n Table 1. The s t r e n g t h o f t h i s c a t a l y s t a f t e r u s e i n t h e d e s u l f u r i z a t i o n r e a c t i o n f o r 400 h o u r s remained o n l y 12-13%
377
Fig. 6. Relation between compressive strength and COO concentration at various calcination temperatures. The same temperatures indicated as in Fig. 5 .
0
1
1
5
10
coo ‘I.
I 15
less independent of the composition. The behaviour o f the strength of the cobalt oxide-and/or molybdenum trioxidesupported catalysts might be affected with the particle size, the surface area, the adsorbed water content, the dispersed Table 1 Effects of
H20
adsorbed on compressive strength.
(wt % 1
coo
MOO 5 (wt 9 0 )
3
0
3
12
adsorbe (m mol/g)
1120
5
20.5
Compress ive strength (kg/cm2) 16
12
5
9
9
7 4
22
state of ingredients and so on. The dominating parameters, however, in this respect would require further investigations. REFERENCES 1. 2.
J. 11. Ashley and P. C. €1. Mitchel, J . Chem. S O C . Ser. A, (1958) 2 8 2 1 ; ibid., (1969) 2 7 3 0 . 0 . V. Krylov and L . Ya. Margolis, Kinet. katal., 11 (1970)
432.
378
J. M. J. G. Lipsch and G. C. A. Schuit, J. Catal., 1 5 (1969) 163, 174, 179. P. Ratnasamy, R. P. Mehrotra and A . V. Ramaswamy, ibid., 4. 26 (1972) 352; ibid., 32 (1974) 63. P. Ratnasamy, L. Rodrique and A . J. Leonard, J. Phys. 5. Chem., 77 (1973) 2242. T. Nishina, M. Yonemura and Y . Kotera, J. Inorg. Nucl. 6. Chem., 34 (1972) 3279. Y . Kotera and A . Ueno, Bull. Chem. SOC. Japan, 46 7. (1973) 3431. Y . Kotera, N. Todo, K. Muramatsu, K. Ogawa, M. Kurita, 8. T. Sato, M. Ogawa and T. Kabe, Kogyo Kagaku Zasshi, 74 (1971) 330. S. Yamadaya, K. Shimomura, T. Kinoshita and H. Uchida, 9. Kogyo Kagaku Zasshi, 73 (1970) 847. 10, J. Chojnacki and R. Kozlowski, J. Solid State Chem., 11 (1974) 106. 11. P. Courtine, P. P. Cord, C. Pannetier, J. C. Daumas and P. Montarnall, Bull. SOC. Chin. France, 12 (1968) 4816.
3.
319
DISCUSSION P. MARS : 1) What is the temperature of calcination of the catalysts dealt with in figure 3 ? 2 ) The heterogeneity of the catalyst with respect to the Mo and especially Co concentration (figure 4) suggests that in the outer layer of the catalyst particles, CoMo04 (Co/Mo : 1/1) is present. May this compound already have been formed in the solution ? 3 ) Was this heterogeneity also present after testing the catalytic activity ? Y. KOTERA : 1) The catalyst was calcined at 3 3 O o C for 30 min and at 55OoC for 2 hrs. 2 ) The solvated modification of cobalt molybdate which is usually prepared by coprecipitation would not be formed in the mixed solution of cobalt and molybdenum salts. The high temperature modification is formed during calcination at temperatures higher than 45OoC. We assume that cobalt compounds in the outer layer would be cobalt oxide, and the high temperature modification of cobalt molybdate since the catalyst was calcined at 5OO0C as cited above. 3 ) The same relative intensities of heterogeneously supported impregnants were found after the reaction, as well as more prominent line probes of S, Nil or V deposited during the reaction. (N. Todo et al., Bull.Japan Petroleum Inst., 14,89, 1972). E.J. NEWSON : My question concerns the nice maxima for curves 1 and 3 in Figure 3 . The optimum Co/Mo ratio for these curves is 0.5 for curve 1 and 0 . 3 for curve 3 . Does this mean that the optimum for HDS of Khafjii atmospheric residuum is different to 0.2 as is well known in the literature for distillate HDS ?
Y. KOTERA : We used the atmospheric Khafjii residue mixed with 6 % light oil and the result obtained is shown in Figure 3 . We do not have other experimental data, and we would not like to speculate on the difference of Co/Mo ratio when a different kind of oil to be desulfurized is used. (See reference in answer to question of P. Mars).
P. BERNUSSET : My question concerns table I of your communication. Are the results expressing the effects of adsorbed H20 on crushing strength specific for catalysts prepared by knea,ding and, if s o , do you think it would be possible that the same behaviour occurs with pure carrier ? Y. KOTERA : The results obtained are not exclusively specific for the kneaded series of catalysts. The effect of water content in the alumina powder on the pellet strength has been studied in detail to find the maximum strength at the water content of about lo%, that is, in the range of 5-7 mol/g. However, it seems rather difficult to discriminate the effect of water adsorbed from that of impregnants on the mechanical strength of pure carrier. (J. Yamahaya et al., J. Catal., 19, 264, 1970). P. GRANGE
:
Do you think that there is no sublimation of Mooj at
high temperature ? Y. KOTERA : Molybdenum trioxide sublimates above 8OO0C and the amount of sublimation is negligible in the temperature range lower than 7 0 0 ' C . (7).