The Acidity and Basicity of Bi2O3-based Binary Oxides

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Abstract
The numbers of both acidic and basic sites in a series of Bi2O3-XnOm binary oxides, with different kinds and amounts of the second component, XnOm, were systematically determined by means of the adsorption of NH3 and CO2 from the gas phase, using the static method. Pure Bi2O3 has both acidic and basic sites, much like TiO2, SnO2, and Fe2O3, and it is more basic than these oxides. The generation of an unexpectedly high acidity or basicity was not observed in the combination of Bi2O3 with 11 kinds of oxides, and the acid-base properties of the binary oxides can be understood in terms of the nature of the second component. The order of ability for the promotion of the acidity and the diminution of the basicity is: MoO3, SO3, WO3>V2O5, P2O5>Sb2O4>TiO2, SnO2, Fe2O3. The addition of K2O decreases the acidity and increases the basicity. The relationship between the acid-base properties and the catalytic activities for the isomerization of 1-butene, the dehydration and dehydrogenation of 2-propanol, and the oxidative decomposition of formic acid was investigated. It was proposed that the basic sites of the Bi2O3based mixed oxides originate from Bi2O3 and that the nature remains approximately the same, regardless of any change in the kind and amount of the second component. However, the acidic sites are generated by the combination with second component; therefore, the nature varies widely depending on the nature of the second component.