Abstract
The influence of the concentration of Cs and the ratio of Mo/Nb in materials with Csx(Mo,Nb)5O14 (x=0, 0.47, 0.53, 0.86, and 1.2) stoichiometry on their electronic properties was elucidated by performing alternating current measurements at various partial oxygen pressures and temperatures. All materials feature mainly ionic conductivity rather than electronic one at 523K. The ionic contribution decreases in favor of a rising electronic type for most of the materials with further increase in temperature. Upon cesium promotion, the total conductivity generally increases, while the electronic conductivity changes from the n- to the p-type. The individual differences in the electronic properties of the investigated catalysts were related to their activity and selectivity in the oxidative dehydrogenation of C2–C4 alkanes. It appears that the n-type conductivity is crucial for high catalytic activity. Mechanistic investigations on the two best-performing catalyst systems, Mo1.6Nb3.4Om and Mo2.3Nb2.7Om, in the oxidative dehydrogenation of ethane disclosed, that secondary (non-selective) oxidation reactions are inhibited progressively with rising contributions of the n-type conductivity.
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