Semiconducting catalysts adsorption

The adsorption of oxygen on certain semiconductors, such as NiO and Cu20 was studied in fair detail. The activation energies, heats of adsorption and kinetic laws for oxygen sorption on simple semiconducting catalysts are summarized in Table VI. 

Hydrocarbons are sorbed on semiconducting catalysts either weakly—reversibly, or strongly—irreversibly. The ratio of weak to strong adsorption is a function of temperature and the chemical composition of the catalyst. 

The layer is thought to be doped with interstitial silver atoms which act as electron donors and endow the layer with n-type semiconducting properties. The work function of such a catalyst falls progressively, up to 7 mol % addition of barium. The authors have argued that this effect will favour the adsorption of the more strongly polarized oxygen species, i.e. atomic rather than molecular oxygen, which results in the observed loss of selectivity and increase in activity. 

The objectives of this work are to study the influence of gold particles on the properties of typical catalyst supports, namely MgO and TiO. Gold has been chosen because of its relatively low catalytic activity except for oxygen transfer reactions (4). MgO, an insulator, and TiO, a semiconducting material, are widely used as catalyst supports, and for both of them metal-support interactions have been reported in the literature. Our study places main emphasis on the role of gold on thermal stability, phase transformations, solid-phase oxygen exchange activity, and adsorption characteristics of the oxides. 

The above discussion of CO oxidation and N2O decomposition is, however, designed mainly to show the type of situation which can occur when either of two related properties may appear to determine catalyst activity. Probably in these reactions semiconductivity is of primary importance and electronic configuration of secondary importance, both because oxygen adsorption is likely to involve simple formation of negative ions and is therefore governed by boundary-layer considerations and also because a correlation of activity with electron configuration is not, in fact, so successful as one with semiconductivity. 

---