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Substituent effects relevant to coal chemistry were studied using polyfunctional aromatic compounds in catalytic reactions under coal liquefaction conditions. The compounds utilized were nhexyldibenzothiophene (I), 6-methyl-9-(l-methylethyl)dibenzothiophen-4-ol (II), and 4-methoxy-6-methyl-9-(l-methylethyl)dibenzothiophene (III). Reactions were performed in the presence of an H donor at temperatures of 350-430 °C; catalysts utilized in this study consist of carbon black, iron oxides (magnetite and ferrihydrite, activated by methylene chloride), and a complex iron-sulfur catalyst system. For all the catalysts studied, the presence of phenol or alkoxy groups on an alkylated aromatic ring system was found to enhance considerably the tendency for cleavage of the C-C bond connecting an alkyl group to the ring, as compared to compounds without phenol or alkoxy groups. Other reactions occurring with these models are dehydroxylation (or demethoxylation), isomerization of the starting material, and hydrogenation. The time dependence of the catalytic conversion of II is presented as an illustration of the contrasting behavior of the carbon and iron catalysts.

Fine-particle (6-8 nm) iron-sulfur systems with complex chemical compositions are formed when a 3-nm iron oxide is heated with sulfur in the presence of 9,10-dihydrophenanthrene for 1 h. These systems form small-particle pyrrhotite when heated at 320 °C. The fine-particle pyrrhotites are very active hydrocracking catalysts but agglomerate rapidly during reaction at 320 °C.