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Mg−Mo−O catalysts have been investigated with different techniques (XRD, XPS, IR, and EPR spectroscopies) in order to explain the difference in catalytic behavior in the oxidative dehydrogenation of propane to propene. The active site would be a coordinatively unsaturated form of Mo5+. The active Mo5+ could be generated on the surface by propane reduction. The slight excess of MoO3 which is necessary for the catalyst to become an active one probably contributes to the formation of Mo5+.

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The surface properties of Ni/MgAl2O4 catalysts doped with Ce or Pr were analyzed by XPS after treatment in an inert and reductive atmosphere at 400 °C. The Ce‐promoted solids presented the Ce3+/Ce4+ couple on the surface even after treatment in a reductive atmosphere, H2(5%)/Ar. The promotion effect of Ce on these solids could be associated with their participation on the carbon deposition‐removal mechanism. Pr‐doped catalysts showed a very high concentration of Pr3+ under a reductive atmosphere and the redox behavior associated with the carbon removal could be partially inhibited or become slower. The size of the Ni0 particles after both an inert and a reductive atmosphere was estimated by XPS intensity ratio using the model proposed by Davis. The results obtained from the Davis model showed that an important increase occurred in Ni particle size after treatment in H2(5%)/Ar for the Pr‐promoted solids. The metal sintering under reductive atmosphere could be the reason for the higher loss of activity of the Pr‐doped solids under reforming conditions. Copyright © 2014 John Wiley & Sons, Ltd.

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