XPS study of the surface properties and Ni particle size determination of Ni supported catalysts

Abstract

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.