The role of TiO2 layers deposited on YSZ on the electrochemical promotion of C2H4 oxidation on Pt (original) (raw)
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The effect of catalyst film thickness on the electrochemical promotion of ethylene oxidation on Pt
Topics in Catalysis, 2006
The effect of catalyst film thickness on the magnitude of the effect of electrochemical promotion of catalysis (EPOC or NEMCA effect) was investigated for the model catalytic reaction of C 2 H 4 oxidation on porous Pt paste catalyst-electrodes deposited on YSZ. It was found that the catalytic rate enhancement q is up to 400 for thinner (0.2 lm) Pt films (40,000% rate enhancement) and gradually decreases to 50 for thicker (1 lm) films. The results are in good qualitative agreement with model predictions describing the diffusion and reaction of the backspillover O 2) species which causes electrochemical promotion.
Journal of Catalysis, 2004
The oxidation of CO by gaseous 18 O 2 was investigated on electropromoted Pt films deposited on Y 2 O 3 -stabilized ZrO 2 (YSZ) and on nanodispersed Pt/YSZ catalysts under high vacuum and under atmospheric pressure conditions. For both catalyst systems and in both cases it was found that the temperature dependence of the catalytic oxidation rate can be correlated directly with the corresponding TPD spectra of 18 O 2 , 16 O 18 O, and 16 O 2 and that lattice oxygen plays a key role in the oxidation reaction, acting both as a reactant and as a sacrificial promoter. For both systems the results confirm the sacrificial promoter model of electrochemical promotion and metal-support interactions with O 2− -conducting supports. This mechanism contains as limiting cases the promoted Langmuir-Hinshelwood and the Mars-van Krevelen mechanisms, which predominate at low and high temperatures, respectively. (C.G. Vayenas).
Topics in Catalysis
The combined promotional effect of electrochemically-supplied O 2− and chemically-supplied Na + promoters, was studied for the case of CO oxidation on Pt/YSZ. Four different sodium coverages (0.16, 1.6, 8 and 40%) were loaded onto the catalyst surface and the catalytic behaviour was compared with a nominally 'clean' catalyst under a wide range of reactants' ratios under open-circuit and polarised conditions. Sodium generally increased oxygen adsorption by lowering the work function of the catalyst. However, sodium promoted the catalytic rate only at coverages up to 1.6% and worked synergistically with O 2− promoting species to an increased overall promotion of the catalytic rate. At higher sodium coverages, i.e. θ Na ≥ 8%, the catalytic behaviour was strongly affected by the interactions between the sodium species, the catalyst, the reactants and oxygen ions promoting species. The postulated formation of stable sodium oxide species on the catalyst pores reduced the active catalytic area which resulted in poisoning the catalytic rate and suppressing EPOC effect, respectively. It is suggested that these stable sodium oxide species which also induced a permanent EPOC effect by oxygen storage, were formed by the migrated oxygen ions.
Materials Science Forum, 1991
It was found that the catalytic activity and selectivity of polycrystalline Pt for the oxidation of methanol to formaldehyde and CO2 can be dramatically and reversibly affected when oxygen anions 02-are electrochemically pumped to or from the Pt catalyst surface. The experiments were conducted using a stabilized zirconia solid electrolyte at temperatures 600 to 900 K. The steady state increases in the catalytic rates of H2CO and CO2 formation, are typically 103-104 higher than the rate of 0 2-transport to or from the catalyst surface. Over a wide range of experimental conditions the catalytic rates depend exponentially on the catalyst-solid electrolyte overpotential, which is proportional to the induced change in catalyst work function. The product selectivity to H2CO can be varied between 35 and 60% by controlling the catalyst potential. The phenomena are reversible and show that catalyst work function and catalytic activity and selectivity can be varied at will by adjusting the catalyst potential. As in previous studies of non-Faradaic electrochemical modification of catalytic activity one can interpret the observed behaviour by taking the change in catalyst work function with changing catalyst potential and the concomitant changes in the strength of chemisorptive bonds into account. ~:~ 1991 Academic Pres~, Inc.
Topics in Catalysis, 2006
The effect of catalyst film thickness on the magnitude of the effect of electrochemical promotion was investigated for the model catalytic reaction of C 2 H 4 oxidation on porous Pt paste catalyst-electrodes deposited on YSZ. It was found that the catalytic rate enhancement q is up to 400 for thinner (0.2 lm) Pt films (40,000% rate enhancement) and gradually decreases to 50 for thicker (1 lm) films. The Faradaic efficiency L was found to increase moderately with increasing film thickness and to be described semiquantitatively by the ratio 2Fr o /I 0 , where r o is the unpromoted rate and I 0 is the exchange current of the catalyst-electrolyte interface. The results are in good qualitative agreement with model predictions describing the diffusion and reaction of the backspillover O 2species, which causes electrochemical promotion.
Catalytic study and electrochemical promotion of propane oxidation on Pt/YSZ
Journal of Catalysis, 2005
The Pt-catalyzed oxidation of propane was studied in an oxygen ion conducting solid electrolyte cell at 623-773 K and atmospheric total pressure. Under open circuit, the solid electrolyte potentiometry (SEP) technique was used to monitor the thermodynamic activity of oxygen adsorbed on the catalyst surface during reaction. Reaction kinetics and SEP measurements were combined to elucidate the reaction mechanism. Under certain conditions, sustained oscillations in the reaction rate and the surface oxygen activity were observed. The reaction exhibited a strong non-Faradaic modification of catalytic activity (NEMCA) effect. By varying the potential of the Pt catalyst, the rate of propane oxidation could be reversibly enhanced by up to a factor of 1400. At positive potentials, the reaction exhibited a pronounced electrophobic NEMCA enhancement. At negative potentials, the reaction also exhibited a strong electrophilic enhancement, indicating that the promoting effect is of the "inverted volcano" type. 2005 Elsevier Inc. All rights reserved.
Applied Catalysis B: Environmental, 2010
The electrochemical promotion of ethylene oxidation on Pt was investigated using Pt(1 1 1) thin film model catalyst-electrodes deposited on top of YSZ(1 1 1) single crystals. This is the first study involving a thin epitaxial and well-characterized catalyst system. The nearly covering Pt films were prepared by pulsed laser deposition (PLD) and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). In order to explore the influence of potentially catalytic active impurities, samples with and without FeO x dopants on the Pt catalyst surface were investigated. A major result is that most of the samples showed unequivocal electrochemical promotion of catalytic activity (EPOC). The Faradaic efficiency values are typically 2.5-77 which is considerably smaller than those reported for usually investigated macroscopically porous paste electrodes ( max = 3 × 10 5 ). This fact can be attributed to the much shorter three-phase boundary (tpb) length of the catalyst films. The iron-doped samples showed a permanent effect (P-EPOC). The results are discussed in terms of morphology changes and iron-doping effects. A short survey of EPOC studies using different catalyst/electrolyte preparation techniques is given.