We have studied the activity of various ferric-sulfide-based catalysts in model hydrogenation and cracking reactions under conditions typical of direct coal liquefaction (DCL). The catalysts used were mixtures of FeS2 (pyrite, PY) and nonstoichiometric FeSx (pyrrhotite, PH) obtained by high-temperature disproportionation of ferric sulfide in a nitrogen atmosphere or a hydrogen atmosphere. The structural changes in the catalyst were also examined, both before and after the model reactions. The cracking functionality of the catalysts was studied by using cumene, and the hydrocracking functionality was studied by using diphenylmethane. Phenanthrene was used as a model compound for hydrogenation and hydrogen shuttling. Phenanthrene hydrogenation was studied in the presence of H-2(g), and hydrogen shuttling was studied when a hydrogen donor (tetralin) was present in the absence of H-2(g). All the model reactions were performed under conditions typical of DCL : 400 degrees C and 1000 psig for 30 min. The surface and bulk of the catalysts were characterized by Auger electron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and atomic absorption spectroscopy. The performance of the catalysts was found to vary with the type of reaction, the initial ratio of FeSx to FeS2 (PH/PY) found in the catalyst, and the catalyst age. Catalysts freshly prepared in a nitrogen atmosphere were most active for model hydrogenation and hydrocracking runs. Catalysts freshly prepared in hydrogen were most active in shuttling. In all cases, catalytic cracking was negligible. Aging was found to reduce the activity of the catalyst. After the exposure of the catalyst to H-2(g) at 315 degrees C, the ratio PH/PY increased, but only limited changes in the PH/PY ratio were noted in a helium atmosphere. The surface uniformity of the catalyst was reduced after the catalyst reacted in H-2(g) or He(g). A simple model was developed to explain these changes in the surface and bulk of the catalysts. The model incorporates the hydrogenation of PY to PH and the removal of elemental S to form H2S. The further interaction of H2S with the catalyst surface makes it nonuniform, with S-deficient and S-rich sites. In the absence of hydrogen, surface reconstruction involves elemental S (from the disproportionation of the ferric sulfide) interacting with PH to form PK with a larger value of x, or PY in the limit.