Hydroisomerization of n-heptane and dehydration of 2-propanol on bulk and supported WO 2(H x) ac on TiO 2

Abstract

Characterization by XPS–UPS and XRD of commercial bulk WO 2 enabled us to identify the presence of four to five layers of WO 3 on the sample surface with an equal amount of W 5+, possibly W 20O 58 in the interface. The presence of these WO 3 and W 20O 58 on the WO 2 surface were not detected by XRD. Exposure of commercial bulk WO 2 to hydrogen at temperatures higher than 673 K results in the reduction of surface WO 3 to WO 2 and the formation of the bifunctional WO 2(H x ) ac phase on its surface. A complete conversion of surface WO 3 to WO 2(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 WO 2(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 WO 3 and WO 3/TiO 2 systems. Dehydration and dehydrogenation of 2-propanol were studied on these systems at 393 K reaction temperature.