A process for heteroatom removal-enhancing hydrogenation of highly refractory aromatic ring structures that involves contacting a highly refractory structure having at least one aryl linkage connecting a first heteroaryl moiety and a moiety selected from the group consisting of an aryl moiety and a second heteroaryl moiety with supercritical water having a temperature of from about 400.degree. C. to about 600.degree. C. in the presence of from about 3.4 MPa to about 18.6 MPa of CO to produce lower molecular weight products having decreased aromatic and heteroatom content. The process has utility for producing more valuable lower molecular weight products having a reduced aromatic heteroatom content from starting materials that are highly refractory and widely considered to be difficult to upgrade such as coals and asphaltenes, and model compounds containing the biaryl linkages.