Depolymerization of bituminous coal by conventional thermal reaction, both with and without a synthetic pyrite catalyst, and a superacid-catalyzed reaction using a mixture of hydrogen fluoride and boron trifluoride were examined to study differences between radical and ionic reactions in coal depolymerization. All reactions took place under hydrogen without any solvent. Depolymerization of bituminous Miike coal was comparatively homogeneous following the superacid-catalyzed reaction with HF/BF3, but was heterogeneous following the thermal reaction using the synthetic pyrite catalyst. Because a reaction temperature of 440 degrees C was required to cleave the linkages between the coal molecules, the thermal reaction probably promoted dealkylation (removal of alkyl side chains) as well as simultaneously promoting negative reactions such as condensation. In contrast, the superacid-catalyzed reaction at 150 degrees C predominantly promoted coal depolymerization and did not cause significant dealkylation, providing a highly soluble product. The synthetic pyrite catalyst accelerated deoxygenation of coal, resulting in higher extractability than that following the thermal reaction without a catalyst although the synthetic pyrite catalyst does not have substantial hydrogenation catalytic activity in the presence of gaseous hydrogen.