Abstract
Our recent works on syntheses of solid superacids, sulfate-metal oxides and tungsten or molybdenum oxide supported on zirconia, and on their catalytic action are reviewed. Solid superacids with an acid strength of up to Ho ≦ −16.04 are obtained by adsorbing sulfate ion onto hydroxides or amorphous oxides of Fe, Ti, Zr, Hf, Sn, and Si followed by calcination in air above 500°C; a superacid of Al 2O 3 is prepared from the crystallized oxide. Superacids by metal oxides themselves with an acid strength of up to Ho ≦ −14.52 are synthesized in the same manner as that of the sulfate superacid by supporting ZrO 2 with WO 3 or MoO 3. Surface areas of the superacids are much larger compared with those of the oxides without sulfate, tungsten or molybdenum oxide. The superacids are satisfactorily active in a heterogeneous system for reactions which are generally catalyzed by strong acid. Structure of acid sites is discussed on the basis of the results of XPS, IR, and XRD spectra.
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