Comparison of activity in the 2-propanol dehydration of supported heteropolyacid (photo)catalysts at the gas-solid interface

Catalytic and photocatalytic tests for 2-propanol dehydration to propene were successfully carried out by using binary materials obtained by supporting a Keggin heteropolyacid H3PW12O40 (PW12) via impregnation method and/or solvothermal treatment. The supports used were commercial SiO2 (Mallinckrodt), TiO2 (Evonik P25) and multiwall carbon nanotubes (Sunnano) or home solvothermically prepared SiO2 and TiO2. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regime by using a continuous (photo)reactor working at atmospheric pressure and 80 °C. the reaction was also studied by performing FTIR spectra of the gas-phase over the HPA-support composites, where the 2-propanol had been previously adsorbed. Propene and diisopropyl ether were the main reaction products. For the continuous photo-assisted runs the reactor was also illuminated with UV light. The Keggin heteropolyacid species played a key role both for the catalytic and the photo-assisted catalytic reactions; indicating that the acidity of the cluster accounts for the catalytic role, whereas both the acidity of the cluster and the oxidant ability of PW12 were responsible for the increase of the reaction rate of the photo-assisted catalytic reaction. Moreover, the presence of a photoactive semiconductor support showed a beneficial effect to enhance the reactivity of the binary material. The increasing of the 2-propanol concentration in the secondary structure of PW12, i.e. in the pseudo-liquid phase, gave rise to an increase of the (photo)activity up to a maximum value above which a further absorption of the reagent cause a decrease. The apparent activation energy of 2-propanol catalytic and photocatalytic dehydration, determined in the range 60-120 °C, decreased in the presence of light for all of the (photo)catalysts used.