15 Preparation and Properties of Cobalt Sulfide, Nickel Sulfide, and Iron Sulfide 1
D. M. PASQUARIELLO, R. KERSHAW, J. D. PASSARETTI , K. DWIGHT, and A. WOLD
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Department of Chemistry, Brown University, Providence, RI 02912
Co S , Ni S , and Fe S were prepared as single-phase polycrystalline materials by heating the appropriate metal sulfates in a controlled mixture of H and H S at low temperature. The products were characterized by x-ray diffraction, thermogravimetric analysis, and magnetic susceptibility measurement. The x-ray diffraction pattern and field dependent magnetic susceptibility of Fe S were affected by the thermal history of the sample. The observed differences can be related to the vacancy ordering associated with ferrimagnetic F e S . 9
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The t r a n s i t i o n metal sulfides CogSg, N 1 3 S 2 and FeySg have been i d e n t i f i e d as possible promotors i n hydrodesulfurization c a t a l y s t s . However, the actual catalysts are amorphous, and discrete sulfide phases have never been observed i n γ - Α ΐ 2 θ 3 supported systems within the composition range of commercial catalysts. Since the preparation of CogSg, Ni3S2,and FeySg i s d i f f i c u l t to achieve by direct combination of the elements, a low temperature synthesis involving the treatment of anhydrous sulfates i n a controlled H 2 / H 2 S atmosphere was developed at Brown University (1). Since magnetic s u s c e p t i b i l i t y appears to be capable of distinguishing the various members of the Fe-S, Co-S and Ni-S systems (2-4), i t was decided to characterize the low temperature single-phase products by magnetic s u s c e p t i b i l i t y measurements as well as x-ray d i f f r a c t i o n analysis. Delafosse, et a l . (S), have shown that sulfides of nickel and cobalt can be prepared by heating their anhydrous sulfates i n a stream of H 2 / H 2 S at low temperatures. However, the experimental conditions f o r obtaining pure N 1 3 S 2 and CogSg were not specified. It has been shown (2), (6) that both CogSg and N 1 3 S 2 permit l i t t l e variation from ideal stoichiometry. For both compounds, there i s no observable v a r i a t i o n i n the l a t t i c e parameter as determined from x-ray analyses, and magnetic measurements of CogSg have confirmed i t s narrow homogeneity range. 1
Current address: Exxon Research & Engineering Company, Annandale, ΝJ 08801 Author to whom correspondence should be directed.
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0097-6156/85/0279-0247$06.00/0 © American Chemical Society
In Solid State Chemistry in Catalysis; Grasselli, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
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S O L I D STATE C H E M I S T R Y IN CATALYSIS
S y n t h e t i c samples o f the low temperature phase o f FeySg have been p r e p a r e d by L o t g e r i n g (4) and magnetic measurements c o n f i r m e d the work o f o t h e r i n v e s t i g a t o r s (7-9) t h a t the spontaneous magnetism of FeySg r e p r e s e n t s a f e r r i m a g n e t i c s t r u c t u r e which i s based upon an o r d e r i n g o f i r o n v a c a n c i e s . T h i s can be r e p r e s e n t e d by the f o r m u l a Fe4[Fe3 Q ] S g . I f t h i s model i s c o r r e c t , then r a n d o m i z a t i o n o f the v a c a n c i e s s h o u l d a f f e c t markedly the observed magnetic b e h a v i o r .
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Experimental Section P r e p a r a t i o n o f Samples. The s u l f i d e s CogSg, N13S2, and FeySg were p r e p a r e d by t r e a t i n g p r e - d r i e d s u l f a t e s a l t s o f c o b a l t , n i c k e l , and i r o n w i t h a m i x t u r e H2 and H2S i n a v e r t i c a l r e a c t o r ( F i g u r e 1) a t 325°C f o r FeySg, and 525°C f o r CogSg and N13S2. C o b a l t and n i c k e l s u l f a t e s were d r i e d i n i t i a l l y a t 135°C.; p r e l i m i n a r y d r y i n g o f f e r r i c s u l f a t e was u n n e c e s s a r y . A f t e r placement o f the s u l f a t e i n the r e a c t o r t u b e , the system was purged w i t h n i t r o g e n , and a d r y i n g s t e p f o l l o w e d . A f t e r one hour o f d r y i n g under a n i t r o g e n f l o w , the d e s i r e d f l o w r a t e s f o r H2 and H2S were s e l e c t e d and a l l o w e d t o e q u i l i b r a t e . A t t h i s p o i n t , the temperature was e l e v a t e d t o ensure complete r e a c t i o n . For b o t h CogSg and N13S2, the r e a c t o r tube was removed from the furnace a t the end o f the r e a c t i o n and a i r quenched t o room t e m p e r a t u r e . The quenched samples o f FeySg were p r e p a r e d i n a s i l i c a r e a c t o r tube ( f i t t e d w i t h a V y c o r f r i t ) which was c o o l e d r a p i d l y w i t h i c e water a t the end o f the r e a c t i o n . An annealed sample o f FeySg was p r e p a r e d by h e a t i n g the quenched p r o d u c t i n a s e a l e d evacuated s i l i c a tube f o r two weeks a t 3 0 0 ° C . The tube was a l l o w e d t o r e a c h room temperature o v e r n i g h t . S l o w - c o o l e d samples o f FeySg were p r e p a r e d by l o w e r i n g the temperature o f the r e a c t o r from 325°C t o 175°C a t a r a t e o f l ° C / m i n . The r e a c t o r tube was then removed from the furnace and a l l o w e d t o r e a c h room t e m p e r a t u r e . For a l l the s y n t h e s e s , once the r e a c t o r tube reached room t e m p e r a t u r e , the system was purged w i t h n i t r o g e n b e f o r e the samples were removed. The e x p e r i m e n t a l c o n d i t i o n s f o r the p r e p a r a t i o n o f CogSg, N13S2, and FeySg are g i v e n i n T a b l e I . C h a r a c t e r i z a t i o n o f Samples. Powder d i f f r a c t i o n p a t t e r n s o f the samples were o b t a i n e d w i t h a P h i l i p s d i f f r a c t o m e t e r u s i n g monochromated h i g h - i n t e n s i t y CuKai r a d i a t i o n (λ = 1.5405A). F o r q u a l i t a t i v e i d e n t i f i c a t i o n o f the phases p r e s e n t , the p a t t e r n s were t a k e n from 12° < 2Θ
