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  • 1
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    Non-faradaic electrochemical modification of catalytic activity in solid electrolyte cells (1989)
    Springer
    Details
    Publication Date: 1989-07-01
    Print ISSN: 0947-8396
    Electronic ISSN: 1432-0630
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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  • 2
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    Methane to Ethylene with 85 Percent Yield in a Gas Recycle Electrocatalytic Reactor-Separator (1994)
    American Association for the Advancement of Science
    Details
    Publication Date: 1994-06-10
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science
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  • 3
    Electronic Resource
    Electronic Resource
    Non-faradaic electrochemical modification of catalytic activity in solid electrolyte cells (1989)
    Springer
    Applied physics 49 (1989), S. 95-103 
    Details
    ISSN: 1432-0630
    Keywords: 85.80 ; 82.20 ; 82.65 ; 73.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The catalytic activity and selectivity of metal catalysts used as electrodes in high temperature solid electrolyte cells can be altered dramatically and in a reversible manner. This is accomplished by electrochemically supplying oxygen anions onto catalytic surfaces via polarized metal-solid electrolyte interfaces. Oxygen anions, forced electrochemically to adsorb on the metal catalyst surface, alter the catalyst work function in a predictable way and lead to reaction rate increases as high as 4000%. Changes in catalytic rates typically exceed the rate of O2− transport to or from the catalyst surface by 102-3 · 105. Significant changes in product selectivity have been also observed. The case of several catalytic reactions in which this new phenomenon has been observed is presented and the origin of the phenomenon is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00615471
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  • 4
    Electronic Resource
    Electronic Resource
    Ethylene production from methane in a gas recycle electrocatalytic reactor separator (1995)
    Springer
    Ionics 1 (1995), S. 286-291 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It was found that methane can be oxidatively coupled to ethylene with an ethylene yield up to 85% and a total C2 hydrocarbon yield up to 88%, in a novel gas-recycle electrocatalytic reactor-separator where the recycled gas passes continuously through a molecular sieve trap in the recycle loop. The molecular sieve traps and thus protects a controllable percentage of ethylene and ethane produced during each gas cycle. These products are obtained by subsequent heating of the trap. In this way we have obtained, using the batch operating mode of the recycle reactor, ethylene yields up to 85%, i.e. 88% selectivity to ethylene at 97% CH4 conversion. Oxygen is supplied electrochemically to the Ag-Sm2O3 or Ag anode via a solid electrolyte, i.e. Y2O3-stabilized-ZrO2, which is a O2- conductor. The cathode is exposed to ambient air and the electrocatalytic reactor operates at 750–830 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02390209
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  • 5
    Electronic Resource
    Electronic Resource
    In situ controlled promotion of catalyst surfaces via solid electrolytes: Ethylene oxidation on Rh and propylene oxidation on Pt (1995)
    Springer
    Ionics 1 (1995), S. 159-164 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetics of C2H4 oxidation on Rh and C3H6 oxidation on Pt were investigated on polycrystalline metal films interfaced with ZrO2(8mol%Y2O3) solid electrolyte in galvanic cells of the type: $$\begin{gathered} C_2 H_4 ,O_2 ,Rh/YSZ/Pt,O_2 and \hfill \\ C_3 H_6 ,O_2 ,CO_2 ,Pt/YSZ/Au,C_3 H_6 ,O_2 ,CO_2 \hfill \\ \end{gathered} $$ It was found that by applying positive potentials and thus, supplying O2- to the catalyst surface, up to 100-fold increases in catalytic rate can be obtained (electrophobic NEMCA effect) for the case of C2H4 oxidation on Rh. For the case of C3H6 oxidation on Pt, up to 6-fold increases in catalytic rate were observed by negative potentials, i.e. removing of O2- from the catalyst surface (electrophilic NEMCA effect). The induced changes in catalytic rates for both reactions were found to be 103 to 5×104 higher than the rates of ion transfer to or from the catalyst-electrode surface. For both reactions it was found that varying the catalyst potential, and thus work function, causes pronounced changes in activation energy and preexponential factor, leading to an interesting demonstration of the well-known “compensation” effect. The results can be rationalized on the basis of the theoretical considerations invoked to explain previous NEMCA studies, i.e. the effect of changing work function on chemisorptive bond strengths of electron acceptor and electron donor adsorbates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02388675
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  • 6
    Electronic Resource
    Electronic Resource
    Electrochemical promotion of catalyst surfaces deposited on ionic and mixed conductors (1995)
    Springer
    Ionics 1 (1995), S. 414-420 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) or electrochemical promotion (EP) was investigated on Pt films deposited on Y2O3-stabilized-ZrO2 (YSZ), an O2− conductor, TiO2, a mixed conductor, and Nafion 117 solid polymer electrolyte (SPE), a H+ conductor and also on Pd films deposited on YSZ and β″-Al2O3 a Na+ conductor. Four catalytic systems were investigated, i.e. C2H6 oxidation on Pt/YSZ, C2H4 oxidation on Pd/YSZ and Pd/β″-Al2O3, C2H4 oxidation on Pt/TiO2 and H2 oxidation on Pt/Nafion 117 in contact with 0.1 M aqueous KOH solution. In all cases pronounced and reversible non-Faradaic electrochemical modification of catalytic rates was observed with catalytic rate enhancement up to 2000% and Faradaic efficiency values up to 5000. All reactions investigated exhibit a pronounced electrophobic behaviour which is due to the weakening of chemisorptive oxygen bond at high catalyst potentials. Ethane oxidation, however, also exhibits electrophilic behaviour at low potentials due to weakened binding of carbonaceous species on the surface. The general features of the phenomenon are similar for all four cases presented here showing that the NEMCA effect is a general, electrochemically induced, promoting catalytic phenomenon not depending on the reaction and the type of supporting electrolyte.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375285
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  • 7
    Electronic Resource
    Electronic Resource
    Electrochemical promotion in emission control catalysis (1995)
    Springer
    Ionics 1 (1995), S. 29-31 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electrochemical promotion for the catalytic reduction of NO by CO and of NO by ethylene over a Pt catalyst are reported for the first time. Both reactions are of importance in the catalytic control of automotive emissions and both exhibit strong rate enhancement when Na is pumped to the Pt catalyst electrode from a β″ solid electrolyte. Complementary data obtained with a Pt(111)/Na model system indicate that electrochemically-pumped Na acts by inducing dissociation of chemisorbed NO, which is the reaction initiating step.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02426005
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  • 8
    Electronic Resource
    Electronic Resource
    Electrochemical promotion of environmentally important catalytic reactions (1995)
    Springer
    Ionics 1 (1995), S. 366-376 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The performance of conventional heterogeneous metal catalysts may be enhanced by the addition of so-called promoter species that are used to modify the intrinsic metal surface chemistry with respect to activity and/or selectivity. Electrochemical methods provide an alternative, radically different and uniquely efficacious method of catalyst promotion. Substantial and reversible changes in catalyst perfomance can be induced by back-spillover ions pumped from a solid electrolyte to the surface of a catalytically active electrode: one hasin situ control of the working catalyst. Studies of the electrochemical promotion of NO reduction over Pt films supported on β″-alumina (a sodium ion conductor) demonstrate that major enhancements in activity are possible when Na is pumped to the catalyst surface. We have examined the NO+CO reaction and the reaction of NO with propene. Both reactions are relevant to control of automotive and other emissions, and both exhibit strong electrochemical promotion. By simulating lean-burn engine conditions, we have also demonstrated that EP of a Pt catalyst very substantially enhances the ability of NO to oxidise propene in an oxygen-rich atmosphere. 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 CO or propene, a process that is accompanied by weakening of the N-O bond, thus facilitating NO dissociation, which is the critical reaction-initiating step. XP spectroscopy under the appropriate conditions of temperature and catalyst potential confirms that the mode of operation of the elctrochemically promoted Pt film does indeed involve reversible pumping of Na to or from the solid electrolyte.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375278
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  • 9
    Electronic Resource
    Electronic Resource
    Catalysis, electrocatalysis and electrochemical promotion of the steam reforming of methane over Ni film and Ni-YSZ cermet anodes (1995)
    Springer
    Ionics 1 (1995), S. 491-498 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetics of the steam reforming reaction of CH4 were investigated at temperatures 750 to 950°C under both open-circuit and closed-circuit conditions on Ni-YSZ (Yttria Stabilized Zirconia) solid oxide fuel cell (SOFC) anodes and polycrystalline Ni film SOFC anodes of measured Ni surface area. It was found that the rate of methane reforming on the Ni surface exhibits a Langmuir-Hinshelwood type dependence on $$P_{CH_4 }$$ and $$P_{H_2 O}$$ which results from competitive adsorption of carbonaceous species and oxygen or OH. Consequently the rate is maximized for intermediate $$P_{CH_4 }$$ to $$P_{H_2 O}$$ ratios. The reaction kinetics are affected significantly by cell current and potential under closed-circuit conditions. Over a rather wide range of operating conditions the observed rate changes are Faradaic, which implies negligible variation in the catalytic properties of the Ni surface with potential. At lower temperatures, however, and particularly under conditions of carbon deposition, the rates of CO, H2, CO2 and, more importantly, carbon formation exhibit pronounced non-Faradaic (NEMCA), or electrochemical promotion, behaviour. Some non-Faradaic behaviour is also observed for higher H2O to CH4 ratios but in this case the effect of applied potential is reproducible but not readily reversible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375296
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  • 10
    Electronic Resource
    Electronic Resource
    Electrochemical vs. conventional promotion: A new tool to design effective, highly dispersed conventional catalysts (1998)
    Springer
    Ionics 4 (1998), S. 148-156 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Pt-group metals exhibit strong Electrochemical Promotion (EP) by sodium during reactions related to emission control catalysis, such as NO reduction by hydrocarbons. Close similarities are found between electrochemically promoted catalysts and catalysts conventionally promoted and highly dispersed on large surface area supported materials. These similarities include (i) overall kinetic behaviour and (ii) the dependence of the activity and selectivity on Na loading. For example, using both methods of Na-promotion, the catalytic reduction of NO by propene exhibited rate enhancements by up to an order of magnitude accompanied by very pronounced increases of the system selectivity towards N2. Among other things, our results serve to validate further the interpretation offered for the EP (or NEMCA) phenomenon. More importantly, they demonstrate that the insight obtained from EP studies can be used to design successfully effective catalyst formulations that were previously untried, thus opening up new areas for investigation in the frontiers between catalysis and electrochemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375793
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