Studies of the Acidity and Ionic Conductivity of Silica-Supported Heteropoly Compounds. II. Acidity and Catalytic Activity of Supported Heteropoly Compound Catalysts

Article abstract of DOI:10.1246/bcsj.63.2071

The acidity function, H₀, of silica-supported heteropoly compounds (HPC) such as H3PMo12O40, H3PW12O40, and their sodium, potassium, ammonium, cesium, and bismuth oxide salts has been examined in connection with their catalytic activity for the dehydration of t-butyl alcohol(TBA).The values of H₀ for the respective catalysts have been determined spectrophotometrically utilizing adsorbed dicinnamylideneacetone (DCA) as a probe molecule.A linear relationship has been established between the amount of HPC supported (log m) and its H₀.Also, for the dehydration of TBA in the liquid-phase all plots of log k'₁ vs.H₀ fall on a straightline with a slope of -1, independent of the kind of catalyst.In this case k'₁ is the apparent rate constant of the dehydration of liquid TBA.On the other hand, for the gas-phase dehydration of TBA the plots yield straight lines with different slopes, depending on the type of catalst.The dependence of the catalytic activity on the H₀ supports the previous conclusion that the dehydration of liquid and gaseous TBA proceeds through pseudo-liquid and outer-surface mechanisms, respectively.