Magneto-chemical character studies of iron-moly and iron-cobalt-moly catalysts

Iron, cobalt and molybdenum compounds are extensively used for the conversion of coal to liquid fuels. To examine the correlations between catalytic, magnetic, and spectroscopic properties, we investigated the Zero-field Nuclear Magnetic Resonance spectra of cobalt. Mossbauer spectra of iron, FTIR spectra and magnetic character of the composite for a series of Fe/MoO₃ and Fe/Co/MoO₃ catalysts with different inter-metallic ratios and metal loadings. All the precursors are paramagnetic according to the magnetization data. Mossbauer results show that in the precursors Fe is in Fe³⁺ state. FTIR spectra reveal bands due to monodentate and bidentate structures of Fe-MoO₃ and Co-MoO₃. NMR spectra support these findings indicating strong inter-metallic interaction between Co and MoO₃. FTIR results show that exposure to CO or syngas (CO+H₂), leads to dissociation of metal-MoO₃ structures and Mossbauer data shows the presence of excess lattice charge with iron in the Fe²⁺ state. Only a minute portion of the composite gets reduced to metallic state. Cobalt seems to form cobalt carbonyl structures, while carbide formations seem to occur with iron. Lack of free metal sites seems to be the reason for the poor conversion of CO observed in the catalytic runs