Based upon the interest in iron as a potential dispersed phase catalyst for synfuels production, the high-pressure hydrogenation of naphthalene in mineral oil and cyclohexane solvents was studied in trickle flow and vapor-phase reactors, respectively, with an unsupported iron oxide powder as catalyst. Several forms of iron catalyst were examined including the original iron oxide, hydrogen prereduced, and in-situ sulfided forms. A commercial Ni-Mo/Al2O3 catalyst was used for comparison. Iron oxide was not active for hydrogenation; however, in situ reduction by hydrogen yielded a remarkably active hydrogenation catalyst. The secondary hydrogenation reaction to form decalins from tetralin occurred only with the hydrogen reduced iron. Kinetic behavior was determined in the vapor phase at 6.9 MPa and at temperatures over a range of 160-300 degrees C. Trickle bed experiments showed the iron oxide catalyst to be much more rapidly deactivated than the baseline NiMo/Al2O3. In vapor-phase operation using reduced iron as catalyst, rapid deactivation occurred with a 2.0 wt % naphthalene feed, whereas little deactivation was found with a 0.2% feed. Transport limitations found with NiMo/Al2O3 catalyst extrudates were consistent with estimated effectiveness factors, and were eliminated by crushing the extrudates to 40-50 mesh. Sulfur rapidly poisoned the hydrogenation function of the iron catalyst with the order of decreasing activity being Fe much greater than FeSx or Fe2O3. A proposed Langmuir-Hinshelwood rate expression, which reduced to a first-order dependence on both naphthalene and hydrogen, was found to satisfactorily fit the data. Although the reduced iron catalyst exhibited high hydrogenation activity under certain conditions, its propensity toward deactivation and poisoning would limit its application in direct coal liquefaction.