Enhanced (photo)catalytic activity of Wells-Dawson (H6P2W18O62) incomparison to Keggin (H3PW12O40) heteropolyacids for 2-propanoldehydration in gas-solid regime

tCatalytic and photocatalytic 2-propanol dehydration to propene at atmospheric pressure and a tem-perature range of 60-120oC were carried out in gas-solid regime by using bare and supported KegginH3PW12O40(PW12) and Wells-Dawson H6P2W18O62(P2W18) heteropolyacids (HPAs). Binary materialswere prepared by impregnation of the HPAs on commercial SiO2and TiO2. The Wells-Dawson was in anycase more active than the Keggin heteropolyacid and the differences were enhanced when the supportedsamples were used. In particular, Wells-Dawson HPA supported on TiO2and under irradiation showedthe highest activity. The HPA species played the key role both in the catalytic and photo-assisted reac-tions. The acidity of the cluster accounts for the catalytic role, whereas both the acidity and the redoxproperties of the HPA species were responsible for the increase of the reaction rate in the photo-assistedcatalytic reaction. The estimated apparent activation energy resulted always lower for the photocatalyticprocess than for the catalytic one.