Both the acidity and basicity of Fe2O3P2O5 and Fe2O3K2O, with different compositions, were directly measured by means of the adsorption of NH3, pyridine, CO2, and SO2 from the gas phase. With the addition of P2O5 or K2O, the acid-base properties of the Fe2O3-based catalysts vary as can be expected from the natures of P2O5 and K2O. The acidic character of Fe2O3P2O5 is fairly low compared with that of Fe2O3V2O5 and Fe2O3MoO3. The acidity data were confirmed by the catalytic activities for acid-catalyzed reactions such as isomerization of 1-butene and dehydration of isopropyl alcohol. Then, the acid-base properties of a series of ternary oxides, Fe2O3Bi2O3P2O5, with different Bi Fe compositions and a constant P2O5 content, P (Fe + Bi) = 1 10, were also determined. The Bi2O3P2O5 ( P Bi = 1 10) is far more basic and less acidic than the Fe2O3P2O5 ( P Fe = 1 10). With the substitution of Bi2O3 for Fe2O3, the acidity of the mixed oxides decreases and the basicity increases steadily. The vapor-phase oxidation of n-hexane, 1-butene, butadiene, methanol, and formic acid was carried out in an ordinary continuous-flow reactor. Then, the relationship between the catalytic behavior and the acid-base properties of the catalysts was investigated. The results support an earlier proposal that the oxidation activity and selectivity can be interpreted in terms of the acid-base properties of the metal oxide catalysts and the reactants. © 1979.
