Catalytic effect of iron on decomposition of carbon monoxide: I. carbon deposition in H 2 -CO Mixtures
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A N D J. V. VINTERS
Hematite o r e reduced with hydrogen was used as a c a t a l y s t in the p r e s e n t investigation of the r a t e of decomposition of carbon monoxide in H~-CO m i x t u r e s . It was found that the amount of carbon deposited f r o m purified carbon monoxide was d i r e c t l y p r o p o r t i o n a l to the amount of porous iron c a t a l y s t p r e s e n t in the s y s t e m . However, this s i m p l e r e l a t i o n did not hold for H~-CO m i x t u r e s . During carbon deposition the porous iron granules d i s i n t e g r a t e d and were d i s p e r s e d evenly in the carbon deposit. The deposit consisted of graphite, cementite and iron, with c e m e n t i t e / i r o n r a t i o i n c r e a s i n g as m o r e soot accumulated. When most of the i r o n was converted to cementite, carbon deposition ceased. A s m a l l amount of hydrogen enhanced m a r k e d l y the r a t e of decomposition of carbon monoxide. Indications a r e that hydrogen a d s o r b e d on iron c a t a l y z e s the decomposition of carbon monoxide, 2CO ~ C + COa, in addition to the o c c u r r e n c e of the second r e a c t i o n Ha+CO~ C +HaO.
T H E c a t a l y t i c decomposition of carbon monoxide in the p r e s e n c e of iron yielding graphite and cementite has been a subject of much study. This i n t e r e s t s t e m s f r o m the o c c u r r e n c e of carbon deposition in many p r o c e s s e s in which carbon monoxide is a r e a c t a n t , e . g . , b l a s t furnace, d i r e c t reduction p r o c e s s e s , Stelling p r o c e s s , F i s c h e r * T r o p s c h p r o c e s s , nuclear r e a c t o r s and p r o c e s s e s for the production of carbon black. As e a r l y as 1903, Schenck and c o w o r k e r s 1'2 found that soot f o r m a t i o n from carbon monoxide (Boudouard reaction) was c a t a l y z e d by the p r e s e n c e of m e t a l l i c iron and to a l e s s e r extent by oxides. Since those e a r l y days of r e s e a r c h much has been published in the t e c h nical l i t e r a t u r e and in patents on c a t a l y s t s and c a t a l y tic r e a c t i o n s Involving decomposition of carbon monoxide. R e f e r e n c e s to e a r l y work on this subject a r e given in an annotated bibliography by Donald. s Howe v e r , in r e l a t i o n to the p r e s e n t work it is d e s i r a b l e to state the s a l i e n t f e a t u r e s of the findings of some p r e vious i n v e s t i g a t o r s . Byrom 4 a p p e a r s to be the f i r s t to d i s c o v e r that iron exposed to a b l a s t furnace top gas at 550 to 650~ is converted to cementite (FesC), together with some p y r r h o t t t e (FeS), without the formation of f r e e carbon. Subsequently, C a r p e n t e r and Smith s found that both f r e e carbon and cementite f o r m e d when purified c a r bon monoxide r e a c t e d with e l e c t r o l y t i c iron. The absence of f r e e carbon in B y r o m ' s e x p e r i m e n t s was a t tributed to the p r e s e n c e of sulfur b e a r i n g s p e c i e s in the b l a s t furnace g
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