The selective ring opening (SRO) of naphthalene over a series Of MO2C/HY catalysts with 7-27 wt% MO2C, is reported. Pulsed adsorption and temperature programmed desorption of n-propyl amine showed that increased Mo2C content of the Mo2C/HY catalysts significantly decreased the amount and strength of the catalyst acid sites, especially the Bronsted acid sites necessary for SRO. Carbon deposition was the main cause of catalyst deactivation and thermogravimetric analysis of the used catalysts indicated that accumulation of carbonaceous species over the surface of the acidic HY support with time-on-stream led to deactivation of the Mo2C/HY catalysts, whereas no significant carbon deposition occurred on the Mo2C. Catalyst activity tests showed a synergistic effect between the Mo2C and the acidic support (HY) that was not readily obtained with a mechanical mixture of the two catalyst components. (c) 2007 Elsevier B.V. All rights reserved.