The conversion of naphthalene, tetralin or decalin to ring-opened products over Mo2C/HY, Mg- or K-Mo2C/HY, and a commercial Pd/HY catalyst, is reported. Conversion of all reactants at 300 degrees C and 3 MPa was higher over the Pd/HY catalyst than the Mo2C/HY catalysts. Tetralin was the least reactive among the three model compounds over both Pd/HY and Mo2C/HY. With decalin as reactant, higher selectivity to C-10 products was obtained over the Mo2C/HY catalysts compared to the Pd/HY. The addition of K or Mg to Mo2C/HY improved the Mo2C dispersion while K also moderated the catalyst Bronsted acidity. The conversion of all three reactants was reduced by the addition of Mg or K to the Mo2C/HY, as was the carbon deposition. For all the studied catalysts, carbon deposition was lowest after reaction with decalin compared to naphthalene or tetralin. These results suggest that the deposited carbon has as its precursor, species that are derived from naphthalene or tetralin, rather than decalin, and the coke species are generated through bimolecular reactions on acid sites. Consequently, the catalysts with higher hydrogenation activity (Pd/HY and 1% K-7% Mo2C/HY) had lower deactivation rates. (C) 2011 Elsevier B.V. All rights reserved.