Characterization of acidic and redox properties of Ce–Mo–O catalysts for the selective oxidation of toluene

The surface acidic and redox properties of CeO2, MoO3, mechanically mixed CeO2–MoO3 and co-precipitated Ce–Mo–O catalysts were characterized by using microcalorimetric adsorption of ammonia and isopropanol (IPA) probe reaction, and the surface properties of these catalysts were correlated with their selectivity for the oxidation of toluene to benzaldehyde and benzoic acid. With the presence of O2, IPA converted to propylene and diisopropyl ether on acidic sites while converted to acetone on redox sites. It was found that CeO2 exhibited mainly the redox property while MoO3 the surface acidity. The IPA probe reaction showed that the mechanically mixed CeO2–MoO3 exhibited the surface acidic property, similar to that of MoO3, indicating that the surface of CeO2 might be covered by MoO3 in the mixture upon the calcination at 773 K. On the other hand, the co-precipitated Ce–Mo–O catalyst showed the equivalent acidic and redox properties, and thereby the selectivity to benzaldehyde was greatly enhanced on it as compared to the other catalysts studied in this work.