ACTIVE-SITE OF IRON-BASED CATALYST IN COAL-LIQUEFACTION

Catalytic activity for coal liquefaction of sulfate-promoted iron oxid e was investigated by a high-pressure differential thermal analysis te chnique and an autoclave test, It was found by X-ray photoelectron spe ctrometry that the main component of the catalyst was iron oxide, but this included 1.1 wt % sulfur, A particular finding from these experim ents was that the catalyst showed sufficiently high activity for coal liquefaction without added sulfur and the activity was comparable to t he activities of the catalyst with sulfur and FeS2 catalyst in a range of temperatures between 375 and 450 degrees C. This was very interest ing because the sulfate-promoted iron oxide catalyst showed significan tly high activity without addition of a promoter, To find possible rea sons, temperature-programmed desorption profiles of hydrogen (TPRD) of these catalysts were measured, The sulfate-promoted iron oxide cataly st showed clear TPRD profiles in a wide range of temperatures between 100 and 350 degrees C. In contrast, FeS did not show any TPRD profile, However, after oxidation of FeS with air at elevated temperatures, it did show TPRD profiles, although these were weak, This suggests that surface-sulfate species can activate hydrogen molecules. It is well-kn own that sulfur or sulfides are easily oxidized with water or air. It is also well-known that much water is included in the coal liquefactio n system, Therefore, the catalysts used in coal liquefaction are alway s exposed to oxidative agents in the reaction system, Therefore, it wa s concluded that an active site in working states for coal liquefactio n was sulfate species formed during the process on the surface of the iron-based catalysts in the coal liquefaction.