A Comparative Study on the Acidic Properties and Catalytic Activities of TiO2, SiO2, Al2O3, SiO2–Al2O3, SiO2–TiO2, Al2O3–TiO2, and TiO2–SiO2–Al2O3

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Abstract
Investigations are carried out to have a systematic comparison of the acidic properties and catalytic activities of single oxide TiO2, SiO2, Al2O3, their binary oxides and the ternary oxide TiO2–SiO2–Al2O3. The acidity distributions are measured by using butylamine titration technique and the test reactions selected for the catalytic activity measurements are alkylation of toluene with 2-propanol and the dehydration of 2-propanol. The single oxides have only low acid strength and are not at all active in catalyzing the alkylation reaction, but are marginally active in the dehydration of 2-propanol. However the binary oxides SiO2–TiO2 and Al2O3–TiO2 of 10% by weight of TiO2 are found to contain very strong acid sites Ho≤−8.2 and are highly active catalysts in both the test reactions. But TiO2–SiO2–Al2O3 of 10% by weight of TiO2 showed the highest acid amount and the highest activity in the aikylation and dehydration reactions compared to the binary oxides. The acid amount and the catalytic activity of the ternary oxide increased with the increase of TiO2 content upto 50 mol% of TiO2 and then decreased. The ternary oxide containing 80 mol% of TiO2 is rich in weak acid sites. The increase of TiO2 content does not affect the selectivity.