Supported H3PW12O40 for 2-propanol (photo-assisted) catalytic dehydration in gas-solid regime: the role of the support and of the pseudo-liquid phase in the (photo)activity

Abstract

Catalytic and photocatalytic 2-propanol dehydration was carried out by using a supported Keggin heteropolyacid H3PW12O40(PW12). Binary materials were prepared by impregnation and/or solvothermal treatment by using commercial supports: SiO2(Mallinckrodt), TiO2(Evonik P25) and multiwall carbon nanotubes (Sunnano) or home solvothermically prepared SiO2and TiO2. All the materials have beencharacterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM) coupled withEDX microanalysis, specific surface area measurements, diffuse reflectance spectroscopy (DRS), FTIR and Raman spectroscopy. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regime by using a continuous (photo)reactor working at atmospheric pressure and 80◦C. FTIR spectra of the gas-phase over the PW12-support composites, where 2-propanol had been previously adsorbed, were recorded. Propene and diisopropyl ether were the main reaction products. For the continuous photo-assisted runsthe reactor was also illuminated with UV light. The apparent activation energy of 2-propanol catalytic and photocatalytic dehydration was determined in the range 60–120◦C.The irradiance increased significantly the dehydration reaction rate. Important differences were observed between the different supported materials. The Keggin heteropolyacid species played a keyrole both for the catalytic and the photo-assisted catalytic reactions; in fact, the acidity of the cluster accounts for the catalytic role, whereas both the acidity of the cluster and the oxidant ability of PW12wereresponsible for the increase of the reaction rate of the photo-assisted catalytic reaction. Moreover, thephoto-generated electrons on the solid semiconductor conduction band can account for a further increase of the reaction rate, when the heteropolyacid was supported on TiO2. Formation of a pseudo-liquid phase played an important role to determine the (photo)activity