Synthesis and Application to Shape Selective Reaction of Microporous Heteropoly Compounds

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Recently porous heteropoly compounds were synthesized from H_3PW_<12>O_<40> and Cs^+, and showed shape selective catalysis. Interestingly, the pore dimension of the acidic Cs salts varied from micropores to mesopores by changing the content of Cs. We have studied the catalysis of these porous heteropoly compounds as water tolerant catalysts and shape selective catalysts.Adsorption of various molecules having different molecular size was measured under the relative pressure of 0.2. Cs2.5 and Pt-Cs2.5 adsorbed appreciably all the molecules. However, only N_2 (3.6*) was adsorbed on Pt-Cs2.1 and Pt-Cs2.1, but benzene (5.9*), 2,2-dimethylpropane (6.2*), CCl_4 (6.9*) and 1,3,5-trimethylbenzene (7.5*) were not adsorbed indicating that both Cs2.1 and Pt-Cs2.1 possess the pore widths of 3.6-5.9*. Isotherm of N_2 revealed that Cs2.5 and Pt-Cs2.5 were mesoporous.Hydrolysis of 2-mehtylphenyl acetate was performed at 343K.Cs2.5 was far superior in the activity to other oxide catalysts such as H-ZSM-5, mordenite, SO_4^22-/ZrO_2, Nb_2O_5 and SiO_2-Al_2O_3., showing that Cs2.5 is a promising water-tolerant solid acid. For hydration of 2,3-dimethyl-2-butene, the order of activity (in the unit of catalyst weight) was Cs2.5>H-ZSM-5>>Nb_2O_5-SiO_2-Al_2O_3-SiO_2-TiO_2 (-0). This also support the efficient catalytic function of Cs2.5 as a water-tolerant solid acid.Pt-Csx catalyzed the hydrogenation of alkenes and complete oxidation of alkanes. The activity (per unit weight) for the hydrogenation of ethylene was Pt-Cs2.1 : Pt-Cs2.5=0.5 : 1.0. On the other hand, the activity of Pt-Cs2.1 was less than 1% that of Pt-Cs2.5. Since cyclohexene was not adsorbed on Pt-Cs2.1, this result shows that Pt-Cs2.1 is an efficient shape selective catalyst. Furthermore, Pt-Cs2.1 exhibited shape selectivity for the oxidation of alkanes.