The Pt-catalyzed reduction of NO by propene exhibits strong electrochemical promotion by spillover Na supplied from a β′′-alumina solid electrolyte. In the promoted regime, rate increases by an order of magnitude are achievable. At sufficiently high loadings of Na the system exhibits poisoning, and excursions between the promoted and poisoned regimes are fully reversible. Reaction kinetic data obtained as a function of catalyst potential, temperature, and gas composition indicate that Na increases the strength of NO chemisorption relative to propene. This is accompanied by weakening of the N-O bond, thus facilitating NO dissociation, which is proposed as the critical reaction-initiating step. The dependence of N 2 /N 2 O selectivity on catalyst potential is in accord with this view: Na pumping to the Pt catalyst favors N 2 production at the expense of N 2 O. X-ray photoelectron spectroscopic (XPS) data confirm that electrochemical promotion of the Pt film does indeed involve reversible pumping of Na to or from the solid electrolyte. They also show that under reaction conditions the promoter phase consists of a mixture of sodium nitrite and sodium nitrate and that the promoted and poisoned conditions of the catalyst correspond to low and very high loadings of these sodium compounds. Under all reaction conditions, a substantial fraction of the promoter phase is present as 3D crystallites.

The electrochemical promotion (EP) of propene combustion has been studied over a platinum film catalyst supported on sodium β‘ ‘-alumina. Fully reversible promotion and poisoning are observed as a function of catalyst potential (i.e., sodium coverage), the precise behavior being dependent on reactant partial pressures. A model based on a Langmuir−Hinshelwood mechanism and Na-modified chemisorption of the reactants accounts for all the results:  Na enhances the chemisorption of oxygen and inhibits the chemisorption of propene. The formation, chemical identity, stability, and electrochemical decomposition of the Na surface compounds produced in the promoted and poisoned regimes were explored using postreaction XPS, AES, and, for the first time, postreaction Na K edge XAFS. These results indicate that thick layers consisting of sodium carbonate are responsible for catalyst poisoning. The promoter phase consists of smaller amounts of sodium carbonate, and much of this material is present as three-dimensional crystallites. These promoter and poisoning phases are stable at reaction temperature, but rapidly destroyed by electropumping Na away from the catalyst surface. Their direct participation in the electrochemically promoted reaction is thereby demonstrated.

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Nickel oxide (NiO) was screen printed onto the surfaces of 3 and 8 mol% yttria-stabilized zirconia (YSZ) dense pre-fired substrates and then heat treated at temperatures from 13501 to 15501C. The effect of NiO was dependent on the yttria content of the substrate. In 3 mol% YSZ, it was found to alter the phase composition from predominantly tetragonal with a small amount of cubic phase to one consisting of approximately equal amounts of cubic and monoclinic phase. The cubic grains were much larger than the monoclinic ones and contained more nickel. Furthermore, nickel was observed to migrate through the thickness of the tile, a distance of approximately 200 lm. In the 8 mol% YSZ substrates, the phase composition was unaltered, although large grains developed under the printed NiO layer and the nickel migration was confined to the extent of these large grains.(2) Phase Analysis Small sections, approximately 8 mm  8 mm in size, were cut from the samples for X-ray diffraction (XRD) analysis. For the J. Hellmann-contributing editor Based in part on the thesis submitted by P. M. Delaforce for the degree of Doctor

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