Preparation of solid superacid catalysts

Abstract

Our recent works on preparation of solid superacid catalysts, sulfate-metal oxides and tungstate-, molybdate-, or borate-metal oxides, ate reviewed. Superacids with an acid strength of up to Ho ≦-16.04 are obtained by adsorbing sulfate ion onto amorphous oxides of Fe, Ti, Zr, Hf, Sn, and Si followed by calcination in air at above 500°C; a superacid of Al2O3 is prepared from the crystallized oxide. Superacids by metal oxides with an acid strength of up to Ho ≦-14.52 are synthesized in the same manner as those of the sulfate superacids by supporting ZrO2 with WO3 (13 wt% W) or MoO3 (6 wt% Mo): impregnation of amorphous ZrO2 with aqueous ammonium metatungstate or molybdic acid dissolved in ammonia water, followed by evaporation of water and calcination in air at 800-850°C. Similar superacids are prepared by impregnation of amorphous oxides of Sn, Ti, and Fe with ammonium metatungstate and calcination in air, the maximum activity for reaction of isopentane being observed with calcination at 1000°C for the Sn base material and 700°C for those of Ti and Fe; borate supported on zirconia also shows superacidity, though weak in strength.