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.

A membrane reactor containing different types of ZSM-5/porous SS membranes was used to perform the xylene isomerization reaction. The parent Na-ZSM-5 layer was synthesized by secondary growth on top of porous stainless steel tubes. The xylene isomerization reaction was carried out at different temperatures in the membrane reactor and in a fixed-bed reactor of identical geometry for comparison. Two different kinds of membranes were prepared by ion exchange: a Pt/H-ZSM-5 catalytic membrane and two Ba-ZSM-5 composites with different Ba 2+ concentration. The p-xylene production using 100% exchanged Ba-membrane was about 28% higher than the fixed-bed reactor at 370°C, when m-xylene was fed.

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Steady-state single-component and ternary mixture xylene permeation fluxes through Ba−ZSM-5/SS composite membranes were studied, as a function of temperature and pressure. The single p-xylene flux has a weak maximum, relative to temperature (100−400 °C). The flux magnitude and its maximum location are dependent on the extent of Ba-exchange. The o- and m-xylene fluxes steadily increase with temperature. The single permeation behavior is well-described by a model based on the contribution of different transport mechanisms:  Knudsen flux, surface diffusion, and activated gas translation diffusion. The comparisons between either the mixture permeation results or the pressure effect experiments and the simulated data reflect the existing adsorbate-framework interactions that are not easily contemplated by a macroscopic model.

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