Hydration of α-pinene over hydrophobic zeolites in 1,4-dioxane-water and in water

Acid catalyzed hydration of α-pinene in the presence of water was conducted over MFI, BEA, MOR and FAU type zeolites with various SiO2/Al2O3 molar ratios and over many other catalysts. Except for MFI, the catalytic activity of all zeolites increased and, then, fell down with increasing SiO2/Al2O3 ratio. Analysis of water adsorption isotherm and NH3-TPD revealed explicitly that, at high Al content, the crowded water molecules on an acid site inhibit the adsorption of α-pinene while, at low Al content, only a small number of water are competing with α-pinene to adsorb on an active site. The catalytic activity per acid site of all zeolites increased monotonously with increasing hydrophobicity.