FISCHER-TROPSCH SYNTHESIS: MOSSBAUER STUDIES OF PRETREATED ULTRAFINE IRON OXIDE CATALYSTS

Mossbauer spectroscopy indicates that a 24 hour pretreatment in CO at 260°C and 8 atm. in a tetralin solvent almost completely converts ultrafrne iron oxide (about 3 nm) to iron carbide. However, pretreatment in hydrogen under the same conditions resulted in reduction of about 33% of the iron to metallic Fe; the remainder was Fe3O4Exposure of the CO pretreated catalyst to a 1:1 H2/CO synthesis gas resulted in the gradual reoxidation of the carbides to Fe304During the first 2 hours of exposure of the H2 pretreated sample to synthesis gas, the metallic Fe was converted to iron carbides. Further exposure of the H2 pretreatment sample to synthesis gas did not result in a composition change of the catalyst. Therefore, it is concluded that iron carbides with different oxidation characteristics were formed in these two cases.