Characterization by XPS-UPS and XRD of commercial bulk WO2 enabled us to identify the presence of four to five layers of WO3 on the sample surface with an equal amount of W5+, possibly W20O58 in the interface. The presence of these WO3 and W20O58 on the WO2 surface were not detected by XRD. Exposure of commercial bulk WO, to hydrogen at temperatures higher than 673 K results in the reduction of surface WO3 to WO, and the formation of the bifunctional WO2(H-x)(ac) phase on its surface. A complete conversion of surface WO3 to WO2(H-x)(ac) has been obtained following the exposure of the sample to hydrogen for at least 6 h at 773 K. A conversion of 52% of n-heptane at 573 K reaction temperature and a selectivity of 90% in isomerization products, mainly 2,3-MH and multibranched molecules were obtained. The isomerization products distribution is in agreement with the statistical and thermodynamic equilibrium of the methyl-shift mechanism. The stability of the active WO2(H-x)(ac) phase has been tested under prolonged exposure to hydrogen and the reaction mixture. Similar results were obtained in the case of bulk WO3 and WO3/TiO2 systems. Dehydration and dehydrogenation of 2-propanol were studied on these systems at 393 K reaction temperature. (C) 2003 Elsevier B.V. All rights reserved.