Superacids by Metal Oxides

Although the sulfate superacids are stable enough because of preparatory heat treatment at elevated temperatures, elimination of the sulfate is sometimes observed during reaction as a result of catalyst deactivation, especially in a solid-liquid system. It is hoped to synthesize superacids with the system of metal oxides. We have succeeded in preparing another type of superacid, not containing any sulfate ion but consisting of metal oxides, which can be used at temperatures over 800°C (188-192). 

The catalysts were quite effective for the benzoylation of toluene with benzoic anhydride and for the reaction of pentane the maximum activity was observed with calcination at surprisingly high temperatures of 800-850°C for both reactions. The Si02-Al203 catalyst was totally inactive under the same conditions. The catalyst treated at 800°C was active for 

Superacid sites were not created by impregnation of the molybdate on the crystallized oxide, but rather on the hydroxide, as was observed in the case of the W03 catalyst. The XRD pattern of the inactive material prepared from the crystallized oxide was also completely different from that prepared from the hydroxide, as shown in Fig. 15, i.e., monoclinic for the former and tetragonal for the latter (191). 

Specific surface areas of the W03 and MoO, catalysts are shown in Table XI. It is noteworthy that the areas of both catalysts are large compared with those of the oxides without tungsten, and compared to molybdenum oxides, as was observed with the sulfate superacids, especially in the case of calcination at 800°C. 

The S04/Zr02-I catalyst with the highest acidity, prepared by calcination 

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