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1.
A. C. Kaloyannis C. A. Pliangos D. T. Tsiplakides I. V. Yentekakis S. G. Neophytides S. Bebelis C. G. Vayenas 《Ionics》1995,1(5-6):414-420
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.
Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995 相似文献
2.
《Surface science》1992,262(3):L111-L117
High spatial resolution Auger electron spectra and scanning Auger microscope (SAM) images of supported metal catalysts have been obtained in a UHV scanning transmission electron microscope. Ag/α-Al2O3 was used as a model catalyst system, where silver was evaporated, in situ, onto polycrystalline alumina carriers. Silver particles, as small as 2 nm in diameter, were clearly revealed in SAM images with high contrast. On large islands, an edge resolution < 3 nm was achieved. Information about surface and bulk properties of supported catalysts can be extracted from images formed with different signals generated from the same area which are obtained simultaneously. 相似文献
3.
The influence of the spacing between active metal particles placed on the supported metal catalyst on the kinetics of the catalytic reaction with spillover was investigated. The 2A+B2→2AB reaction, modelling the CO oxidation on Pd/Al2O3 catalyst, was studied using Dynamic Monte Carlo simulations. It was shown that there exists an optimal spacing, that provides the maximum reaction rate. It was postulated that this optimum is a consequence of both competition and cooperative effects occurring between metal particles. 相似文献
4.
Electrochemical catalysts were used for environmental applications, such as the clean production of energy from propane and
propene combustion, the elimination of VOC's like propene and the NOx abatement All the selected electrochemical catalysts
were composed of a Pt film deposited on YSZ, NASICON or CGO. It was found that all these chemical reactions can be electropromoted.
Moreover, the reaction rates can be in-situ tuned by applying a polarisation. Furthermore, the selectivity of Pt-based electrochemical
catalysts can be modified in order to avoid the formation of pollutant. Finally, EPOC can improve the lifetime of a catalyst
by inhibiting its poisoning by carbonaceous species.
Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004. 相似文献
5.
The effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect) or Electrochemical Promotion
(EP) was used to promote the methane oxidation reaction to CO2 and H2O over Pd polycrystalline films interfaced with yttria-stabilized zirconia in galvanic cells of the type: CH4, O2, CO2, Pd/YSZ/Au, CH4, O2, CO2
It was found that by applying positive potentials or currents and thus, supplying O2− onto the catalyst surface, up to 90-fold increases in CH4 oxidation catalytic rate can be obtained. The induced changes in catalytic rate were two orders of magnitude higher than
the corresponding rate of ion transfer to the catalyst-electrode surface, i.e. faradaic efficiency Λ values above 100 can
be attained. The reaction exhibits electrophobic behavior under the experimental conditions of the investigation. The results
can be rationalized on the basis of the theoretical considerations invoked to explain NEMCA behavior, i.e. the effect of changing
work function on chemisorptive bond strengths of catalytically active electron donor or acceptor adsorbates.
Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998. 相似文献
6.
We experimentally report a magnetic plasmonic metamaterial, which is constructed with a metal ring-shaped disk array supported by a dielectric layer on a metal film for high sensitive refractive index sensing. An ultrasensitive refractive index sensitivity of about 1842?nm per refractive index unit is achieved through the reflection spectrum measurement. We attribute the high sensitivity to greatly enhanced electric field intensity and its large spatial overlapping with the surrounding medium to sense. The present plasmonic structure provides an effective way for high sensitive chip-based biochemical sensors and integrated devices. 相似文献
7.
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.
Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994. 相似文献
8.
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.
Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995 相似文献
9.
The electrochemical promotion of the ammonia decomposition reaction over Fe catalyst films interfaced with K2YZr(PO4)3, a K+-conductor, and CaZr0.9In0.1O3−a, a H+-conductor, was investigated at temperatures 500–600 °C. At the higher temperatures, the catalytic rate was found to decrease
significantly and reversibly upon decreasing the catalyst potential, VWR, i.e., upon pumping K+ or H+ to the Fe surface. The effect of potassium was more pronounced than that of protons leading to almost complete poisoning
of the reaction. At the lower temperatures, it was found that electrochemical supply of moderate amounts of potassium causes
an enhancement in the catalytic rate while higher amounts poison the reaction.
The study reports, for the first time, electrochemical promotion over a Fe catalyst and shows that K+-conductors can also be used to induce the effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA).
The effect of backspillover potassium ions and protons on the catalytic activity is discussed in terms of the theory of electrochemical
promotion by considering the effect of varying catalyst work function on the coverages and chemisorptive bond strengths of
NH3, N and H. The results show the possibility of using electrically promoted catalyst pellets to alter the performance of industrial
reactions.
Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997. 相似文献
10.
V. Roche E. Siebert M. C. Steil J. P. Deloume C. Roux T. Pagnier R. Revel P. Vernoux 《Ionics》2008,14(3):235-241
Electrochemical catalysts based on LSM deposited on YSZ were used for propane deep oxidation. Electrochemical characterizations
such as impedance spectroscopy and current–overpotential measurements were performed. Different thicknesses of LSM films were
catalytically characterized and EPOC experiments were carried out on those electrochemical catalysts. It was found that the
reaction rates can be in situ tuned by applying an anodic polarization but with weak promotional effects. The faradaic efficiency
decreased as the applied potential, the temperature, and the thickness of the catalyst increased.
Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007. 相似文献
11.
12.
B. Béguin F. Gaillard M. Primet P. Vernoux L. Bultel M. Hénault C. Roux E. Siebert 《Ionics》2002,8(1-2):128-135
The reduction of NO by C3H6 in the presence of oxygen, is of great environmental importance. Platinum-based catalysts are very active but not selective
towards N2 production and mainly convert NO into N2O, which participates to the greenhouse effect. Moreover, their operating temperature window is quite narrow. Electrochemical
promotion was used to improve platinum catalytic behaviour. Platinum was deposited on YSZ (Y2O3 — stabilised ZrO2), an O2-conductor. It was found that a negative current increased the rate of NO reduction and CO2 formation. This rate enhancement was non-Faradaic with an apparent Faradaic efficiency (Λ) close to 180 indicating the manifestation
of a NEMCA effect. However, the current application had no effect on the N2 selectivity
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001. 相似文献
13.
The reaction of ethanol oxidation has been examined over a Pt polycrystalline film deposited on an yttria stabilized zirconia
(YSZ) electrochemical reactor. Experiments were carried out at 325 °C at atmospheric total pressure and under open and closed
circuit conditions. It was found that the electrochemically-induced change in the catalytic rate of ethanol consumption is
four orders of magnitude higher than the rate of ion transport through the solid electrolyte. The galvanostatic transient
behavior of the consumption rates of ethanol and oxygen and of the formation rates of carbon dioxide and acetaldehyde have
been also recorded.
Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000. 相似文献
14.
M. Marwood S. Balomenou A. Tsiliras C. A. Cavalca C. Pliangos C. G. Vayenas 《Ionics》1998,4(3-4):207-214
In this paper we discuss the first attempts to induce the effect of Electrochemical Promotion or Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) on highly dispersed catalyst-electrodes systems which can compete in terms of dispersion and surface area with industrial catalysts. Three systems are discussed:
- Electrochemical promotion of C2H4 oxidation on electronically isolated Pt catalysts on Y2O3-stabilized-Zirconia (YSZ) where NEMCA is induced via potential application between two terminal Au electrodes also supported on the solid electrolyte (bipolar design).
- Electrochemical promotion of C2H4 oxidation on a finely dispersed Pt catalyst deposited on a Au electrode which is supported on YSZ.
- Induction of NEMCA during CH3OH oxidation on Pt without external voltage application by utilizing the potential difference developed between the catalyst and a catalytically inert counter electrode.
15.
采用原子尺度的模拟方法,探讨了在零偏压下扫描隧道显微镜(STM)针尖调制的金属表面岛上原子运动及岛边的层间质量输运. 研究结果显示STM的移动对岛上及岛边的原子扩散有重要的影响. 针尖与吸附原子的交互作用及岛和基体中强的形状变化影响了岛上吸附原子的跳跃扩散及岛边的跳下扩散和交换扩散过程. 研究发现,通过调节针尖与基体的垂直距离及针尖与吸附原子的水平距离,可以降低岛上吸附原子的跳跃扩散能垒及岛边的跳下扩散和交换扩散能垒,从而实现薄膜由三维生长模式向二维生长模式的转变.
关键词:
扫描隧道显微镜
原子运动
质量输运 相似文献
16.
Tungsten and molybdenum oxide bronzes of the general formulas AxMO3 and AxM6O17 (A=K, Li, Na; M=W, Mo) are well known as electrode materials with good response to pH changes. However, there is also a high
cross sensitivity to other ions, e.g. Na+ or Li+. Currently, the synthesis of tailored materials for special applications is the priority task. Preparation routes such as
fused salt electrolysis, solid state reactions in vacuum or hydrothermal synthesis were studied. New compounds of the general
formula LixMo1−yWyO3 and also AxWO3 (A = bi- or trivalent) have a high technological potential. Preliminary experiments have shown that some of these new materials
possess properties of reference electrodes within a restricted pH range. To prepare electrodes, usually single crystals are
required. This is adverse because of high operating expense of single crystal synthesis. In some cases it is also possible
to use polycrystalline materials for the preparation.
Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002. 相似文献
17.
Electrochemical activities of Pt-Ru-Co and Pt-Ru-Ni electrocatalysts supported by a carbon fiber web
Jihye KimBeta Zenia Poliquit Ho-Seong NamSang Hern Kim Yong Min LeeKwang Man Kim Jang Myoun Ko 《Current Applied Physics》2012,12(1):254-258
Dynamic cyclic voltammetry is performed as functions of cycle number and potential window for the electrodeposition of Pt-Ru-Co and Pt-Ru-Ni catalysts on a carbon fiber (CF) web. Surface morphologies of the electrodeposited catalysts are observed by a scanning electron microscope. The electrochemical activity in methanol oxidation is examined by the cyclic voltammetry using a mixed aqueous solution of methanol as an electrolyte component. As the cycle number increases, both the current density and the amount of the electrodeposited metallic particles on the CF web are increased. The Pt-Ru-Ni/CF catalyst prepared in the potential range of −0.6 to 0.2 V and from the 1:2:2 mixed solution of H2PtCl6, RuCl3·3H2O, and Ni(NO3)2·6H2O, respectively, shows the higher current density, corresponding to the higher catalytic activity. 相似文献
18.
A. A. Sinchenko Yu. I. Latyshev S. G. Zybtsev I. G. Gorlova P. Monceau 《JETP Letters》1996,64(4):285-291
Nonlinear effects at the interface between a normal metal and the quasi-one-dimensional conductor with a charge-density wave
K0.3MoO3 are investigated experimentally. It is found that the scattering of the normal carriers with energy E less than the Peierls gap Δp gives rise to an excess resistance of the N-CDW boundary. The character of the scattering is similar to Andreev reflection.
In contrast to superconductors, however, the sign of the charge of the reflected particle does not change.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 259–264 (25 August 1996) 相似文献
19.
We demonstrate the existence of a bound optical mode supported by a slot in a thin metallic film deposited on a substrate, with slot dimensions much smaller than the wavelength. The modal size is almost completely dominated by the near field of the slot. Consequently, the size is very small compared with the wavelength, even when the dispersion relation of the mode approaches the light line of the surrounding media. In addition, the group velocity of this mode is close to the speed of light in the substrate, and its propagation length is tens of micrometers at the optical communication wavelength. 相似文献