XPS and UPS characterization of partially reduced MoO3 by hydrogen at different temperatures enabled us to define the metallic character of MoO2 Hydrogen dissociation by this state results in the formation of Bronsted acidic group(s) Mo-OH as characterized by O 1s and catalytic properties. A bifunctional MoO2(H-x)(ac) phase is formed on the outermost sample surface layer. Two hydrocarbons were studied: methylcyclohexane (MCH) and n-heptane (nC7). The catalytic behavior of MCH on this system shows two different pathways depending on the reaction temperature. A selectivity close to 95% in dimethyl and ethyl-cyclopentanes (DMCP and EtCP) products were obtained at temperatures between 493 and 573 K. At higher temperatures up to 653 K, toluene is the major dehydrogenation product. The general tendency of this catalytic system seems to behave as a bifunctional; to confirm this hypothesis, an acid-supported catalyst, i.e. sulfated zirconia-supported Pt-Ir, was tested under the same experimental conditions. The possible formations of dimethyl or ethylcyclopentanes as intermediate products in the catalytic reaction of n-heptane have been explored using both catalysts. (C) 2004 Elsevier B.V. All rights reserved.