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Mossbauer spectroscopy, XAFS spectroscopy, and a number of complementary techniques have been used to investigate the structure and size dispersion of a variety of ultrafine iron-based DCL catalysts. In the as-prepared state, iron that was chemically incorporated into the coal exhibited an FeOOH structure, while iron catalysts prepared separately had the Fe203 structure. The Mossbauer spectra exhibited pronounced superparamagnetic relaxation effects. The relaxation spectra could be analyzed at several temperatures to determine size distributions for the catalyst particles. The resulting size distributions were in the nanometer range and agreed reasonably well with size information obtained by SQUID magnetometry, STEM, and XRD. Radical structure functions (RSF) derived from the XAFS spectra of the catalysts confirmed the Mossbauer structural identifications and also exhibited significant size effects. While the interatomic distances determined from the RSF were close to those of the bulk phases, the coordination numbers of the iron neighbor shells were significantly decreased. The origins of this effect are (i) iron atoms on or near the surface of fine particles have fewer iron neighbors at distances of 3-4 A and (ii) the electron mean free path is decreased for very small particles, causing an apparent decrease in coordination numbers. During DCL, the highly dispersed ferric iron rapidly reacts with H2S to form pyrrhotite (Fei_*S). If insufficient sulfur is present in the reactor to convert all of the iron to pyrrhotite, the remainder is left in the form of a superparamagnetic oxide. An in situ XAFS study of the reactions of ultrafine Fe203 catalysts in a hydrogen donor solvent in the presence of elemental sulfur showed that conversion of a 30-A catalyst to pyrrhotite proceeded fairly rapidly at 110-180 °C, while the transformation of an F62O3 catalyst of larger particle size (>100 A) proceeded somewhat sluggishly at 250-320 °C.

The total conversion and the oil yield in liquefaction tests of iron ion-exchanged Black Thunder coal were found to increase by up to 23 and 18%, respectively, relative to the untreated coal. The ion-exchanged coal samples were prepared by stirring a slurry mixture of the coal and ferric acetate [Fe(OOCCH3)3] in a 10-L fermenter. The ion-exchange process, in which iron was exchanged primarily for calcium and magnesium, yielded a highly dispersed catalytic iron species for coal liquefaction. 57Fe Mossbauer and X-ray absorption fine structure (XAFS) spectroscopies and electron probe microanalysis (EPMA) X-ray mapping were used to characterize this iron species after the ionexchange process. The results indicate that the added iron is present in bimodal form. The majority of the iron is present as oxyhydroxide particles ranging from 25 to 100 A in diameter, while the smaller fraction is believed to be molecularly dispersed ferric ions held at ion-exchange (carboxyl) sites. With sufficient sulfur present in the system, the iron is rapidly transformed to pyrrhotite (Fei_*S) during liquefaction.indicate that the added iron is initially present in bimodal

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