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+H-2), 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.

Transition metals copper and cobalt play vital roles in the conversion of syngas (CO + H-2) to liquid fuels. Catalytic studies reveal that product selectivity is governed by intermetallic ratios and method of preparation. Perturbations in metallic charge distribution and morphological changes in metal crystallites could influence both catalytic and magnetic behavior of the catalyst. To examine the correlations between catalytic and magnetic properties, we investigated the Zero-field NMR and Magnetization character of a series of supported and unsupported Cu-Co catalysts in the range 0.2 < Cu/Co < 8.0. Significant shifts of NMR lines of cobalt occur in samples for Cu/Co > 1, indicating strong interactions between Cu and Co. Chromia serves as a neutral support inhibiting inter-metallic interactions, while titania supported catalysts exhibit strong metal-support interaction (SMSI). Cu-Co-Cr2O3 catalysts show three distinct regions of magnetization character similar to the three regions of selectivity. Magnetic moment of the composite is very low for Cu/Co < 1.5 (hydrocarbons), appreciably increases for 1.5 < Cu/Co < 5.0 (mixed alcohols), and drops again when Cu/Co > 5.0 (methanols).

To examine the relation between catalytic and magnetic properties, the zero-field NMR spectra and hysteresis loops of cobalt supported on silica, alumina, magnesia, titania, and ZSM-5 with and without the promoter thoria were investigated. Cobalt was incorporated on the support by simple physical admixture of precipitated cobalt and support, and by aqueous impregnation technique. Our studies indicate that the particle sizes are consistently lower in the presence of thoria. Of all the catalysts examined, the Co/Th/TiO2 catalyst exhibits a high saturation magnetization value—about 20% higher than pure cobalt. In addition, the NMR spectrum of the aqueous impregnation Co/TiO2 catalyst is distinctly different from the rest. All the NMR lines are shifted to a higher frequency by about 4 MHz. These two features—enhancement of the magnetic moment of cobalt atoms and increases in the hyperfine field at the Co nucleus—clearly indicate that there occurs strong metal-support interaction between cobalt and titania support. The higher hydrocarbon yields observed by the earlier investigators with Co/TiO2 catalysts might be related to this phenomenon.

Co-ZSM-5 and Co-ThO2-ZSM-5 are promising bifunctional zeolite catalysts used for the conversion of synthesis gas to gasoline range hydrocarbons. Previous catalytic tests have shown that small amounts of the promoter thoria (0.4 wt%) significantly increase the liquid hydrocarbon yields. Zero-field nuclear magnetic resonance studies were undertaken to ascertain the effect of thoria upon the magnetic and structural nature of these catalysts. In Co-ZSM-5, NMR lines corresponding to fcc and hcp phases were found. When the promoter thoria was added, there was a systematic absence of the hcp line before use as catalyst. The change in catalytic behavior can be related to the changes in crystallite species and crystallite size.

The Co-ZSM-5 and Co-ThO2-ZSM-5 catalysts are a particularly promising group of bifunctional zeolite catalysts used for the conversion of synthesis gas to gasoline-range hydrocarbons. Catalytic properties of these materials, such as activity and selectivity, depend upon the amount of the cobalt on the medium-pore zeolite ZSM-5, as well as upon the presence of promoters such as ThO2. These studies were undertaken to ascertain the effect of thoria upon the magnetic and structural nature of these catalysts. Zero-field nuclear magnetic resonance measurements have been made on a series of zeolite cobalt and cobalt-thoria catalysts with three different concentrations of Co (3, 6, and 9 wt. %). The catalysts were prepared by making physical admixtures of precipitated cobalt, or cobalt-thoria, and ZSM-5. The amount of thoria introduced ranged from 0.5 to 1.5 wt. %. After reduction of the catalyst samples, the normal metallic cobalt resonance line at 213.0 MHz (fcc) and the fault lines at 215.5 and 218.6 MHz were observed. In the unpromoted catalysts, a line at 210.7 MHz, which is lower than the fcc line frequency, and another line at 221.6 MHz, which is higher than the hcp line frequency, were observed. When the promoter thoria was added, there was a systematic absence of the hcp line in the unused catalyst. Previous catalytic tests had shown that small amounts of the promoter thoria (0.4 wt. %) significantly increase the liquid hydrocarbon yields. The change in catalytic behavior can be related to the changes in crystallite species and crystallite size.