ABSTRACT
Historically, oxide catalysts have been used primarily for vapor phase reactions in the petroleum and petrochemical industries. Recent work, however, has shown that these catalysts can also be effective in promoting a number of synthetically useful reactions. While simple oxides show activity for some oxidations they are more commonly used as solid acids or bases. Oxide catalysts fall into two general categories. They are either electrical insulators or they can act as semiconductors. Insulator oxides are those in which the cationic material has a single valence so they have stoichiometric M:O ratios. Many oxide catalysts are materials having two or more cationic components. If the oxides are crystalline the crystal structure can determine the oxide composition. The catalytic activity of many mixed oxide catalysts is also related to the presence of similar defect sites in the solid.
