ACIDIC PROPERTIES AND CATALYTIC ACTIVITIES OF TIO2-SIO2-AL2O3 AND MOO3-SIO2-AL2O3 SYNTHESIZED BY HOMOGENEOUS COPRECIPITATION

The physicochemical characteristics, acidic properties and catalytic activities of the title ternary oxides synthesized by homogeneous coprecipitation have been studied. The test reactions selected are alkylation of toluene with 1-propanol and 2-propanol and the dehydration of these alcohols. Surface area, porosity and acid strength of these ternary oxides are lower whereas total acid amount values are higher compared to the previously studied TiO2-SiO2-Al2O3 and MoO3-SiO2-Al2O3 catalysts prepared by heterogeneous coprecipitation. Increase in the pH of coprecipitation from 7 to 12 decreases the acid amount whereas increase in calcination temperature enhances the acid strength. Catalytic activity of both ternary oxide catalysts are found to be high for the dehydration reaction and only moderate for the alkylation. In other words, the dehydration of 2-propanol is catalyzed even by the weakest acid sites and that of 1-propanol by weak and strong acid sites and the alkylation of toluene by only strong acid sites. Nearly 92% of the total acid amount of an unused sample as well as its catalytic activities are shown by both ternary oxides subjected to five successive regeneration cycles.