PREPARATION OF SUPERACIDS BY METAL-OXIDES AND THEIR CATALYTIC ACTION

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 less-than-or-equal-to -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-degrees-C; a superacid of Al2O3 is prepared from the crystallized oxide. Superacids by metal oxides themselves with an acid strength of up to Ho less-than-or-equal-to -14.52 are synthesized in the same manner as that of the sulfate superacid by supporting ZrO2 with WO3 or MoO3. 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.