Catalysis by Doped Oxides

Abstract

The article discusses oxidation catalysis by substitutional cation doping of binary oxides. Substitutional cation doping is not the only possibility. One can imagine that replacing some anions with other anions may also be beneficial. There is evidence that the presence of small amounts of halogen in the feed or on the oxide surface improves its catalytic activity. It is very likely that doped oxide catalysts have been used before the concept was formulated explicitly. Most oxide catalysts have low levels of impurities that may be substitutional dopants. If they segregate at the surface, they can affect the catalytic activity without our knowledge even though their net concentration is very low. It is also possible that the 'as-prepared' catalyst is a doped oxide that, under reducing reaction conditions, is converted to very small metallic dopant clusters supported on the host oxide. The physical and chemical properties of such clusters are different from those of a bulk metal, and it is difficult to distinguish them from a doped oxide.