Keggin and Wells-Dawson supported heteropolyacids as heterogeneous (photo)catalysts for gas-solid 2-propanol dehydration

Catalytic and photocatalytic tests for 2-propanol dehydration to propene were successfully carried out by using binary materials obtained by supporting a Keggin or Wells-Dawson heteropolyacids via impregnation method to commercial SiO2 or 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. Propene and diisopropyl ether were the main reaction products. For the continuous photo-assisted runs the reactor was also illuminated with UV light. The 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 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 both PW12 and P2W18, 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 of the catalytic and photocatalytic dehydration has been determined in the range 60-120 °C for all of the (photo)catalysts used.