Fluoride-promoted NiMo catalysts supported on alumina, carbon, and carbon-covered alumina have been investigated for their activity in cumene cracking, hydrocracking (reduced and sulfided forms), and thiophene HDS. The carbon-covered alumina was prepared by pyrolysis of cyclohexene over either γ-alumina or boehmite and the carbon deposition followed adsorption isotherm-type behavior. The cumene reaction studies indicate that the resulting support system successfully merges the properties of carbon and alumina, possessing improved dehydrogenation-hydrogenation functionality due to carbon and acidic properties due to alumina, such as the generation of Brønsted acidity upon fluoride impregnation. In the thiophene HDS reaction the catalyst activities followed the order Al 2O 3 > C-Al 220 3 > C, suggesting that alumina, and not carbon, is the superior HDS support at atmospheric H 2 pressure and at the metal loadings used in this study. Carbon deposition onto NiMoF/Al 2O 3 catalysts revealed that cyclohexene polymerization is promoted by the metal centers, resulting in multilayer islands on these sites, and not by the fluoride-associated Brønsted acid sites. However, the Brønsted acid sites do promote coke formation when the polymerization reaction is easier, such as for α-methylstyrene.