The concepts of surface coordination number n, and of surface redox couples MO(n)/MO(n + 1) presented previously, are exploited to explain experimental results. Two cases are considered: reactions of chemical gaseous species such as CO, CO2, H-2, H2O, N2O, propene and methanol on the surface of the oxides NiO, TiO2, and Cr2O3, in the absence of oxygen: activated catalytic reactions of oxygen on reductive species such as CO, H-2, C2H6, and CH3OH. The knowledge of the potential of surface redox couples permits a rationalization of the study of these reactions. The efficiency of the two concepts is obvious in many cases. For example, the origin of an athermal oxidative process occurring for the oxidations of CO or H-2 on TiO2 is easily understood. as well as those of the poisoning of the catalysts or of the inactivity of a surface saturated by oxygen. In addition, the study of chemical reactions on the oxides confirms and completes the theoretical approach used. Particularly, the existence of the surface states, which are postulated in the case of Cr2O3, is corroborated by experimental observations concerning the number of surface states and the value of the chemical potentials. Even though the theory is based upon thermodynamical and structural data, it also leads to a better understanding of kinetic features.
