Insights into the relationship between the catalytic oxidation performances of Ce-Pr mixed oxides and their semiconductive and redox properties

Abstract

The semiconductive and redox properties of different Ce1-xPrxO2-δ systems with x = 0, 0.2, 0.5, 0.8 and 1 were investigated by in situ electrical conductivity measurements and correlations with their catalytic behavior in the total oxidation of methane and the CO-PROX process were attempted. Thus, the electrical conductivity of the Ce1-xPrxO2-δ oxides was measured as a function of temperature and oxygen partial pressure, and was followed with time during sequential exposure to air and different gaseous mixtures containing CH4, CO or H2, in conditions close to those of their catalytic applications. All the solids showed both electronic and ionic conductivities, the total conductivity increasing continuously with the value of x. CeO2 appeared to be of n-type, while all the Pr-containing materials were p-type semiconductors in air. They kept their semiconductivity type under different gaseous atmospheres, except for Ce0.8Pr0.2O2-δ mixed oxide which switches from p-type to n-type passing through an NDC-like (Negative Differential Conductivity) state in the presence of CO and H2. The catalytic behavior of the Ce1-xPrxO2-δ oxides, which function during the catalytic oxidation reactions via a heterogeneous redox mechanism, was discussed for both processes studied in correlation with the electrical conductivity results.