C. Cavalca

University of Patras, Rhion, West Greece, Greece

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Publications (11)29.76 Total impact

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    ABSTRACT: The effect of electrochemical promotion of catalysis on the SO2 oxidation reaction was investigated over thin (40 nm) Pt catalyst electrodes interfaced with YSZ, in a monolithic electrochemically promoted (MEP) reactor equipped with five or twenty-two electrocatalytic plates. A mildly oxidizing gas mixture was used at temperatures from 330 to 370 °C and flowrates between 1 and 30 L min−1. It was found that positive potential application, i.e. O2− supply to catalyst surface, can cause an increase of up to 200% in the catalytic oxidation rate of SO2 with Faradaic efficiency values up to 30 at flowrates as high as 30 L min−1 which corresponds to 3 × 104 h−1 space velocity or 0.1 s residence time. The results show the strong potential of MEP reactors for practical applications of the electrochemical promotion of catalysis (EPOC) effect, in gas treatment units and chemical synthesis and destruction processes.
    Applied Catalysis B Environmental 04/2011; 103(3-4):336-342. DOI:10.1016/j.apcatb.2011.01.040 · 6.01 Impact Factor
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    ABSTRACT: The performance of a monolithic electropromoted reactor was investigated under high gas flow rates, for the oxidation of ethylene utilizing thin (40nm) tailor-structured highly porous skeletal Pt catalyst-electrodes coated on Y2O3-stabilized-ZrO2 (YSZ). Electrochemical enhancement was observed at gas flow rates as high as 25Lmin−1 and mean gas residence times as low as 0.15s. This is a promising step for the practical utilization of the electrochemical promotion of catalysis. An interesting feature of the skeletal Pt catalyst-electrodes is the appearance of a sharp rate maximum upon anodic current interruption which appears to be related to their dendritic structure and enhanced capacity for promoter storage.
    Journal of Applied Electrochemistry 08/2008; 38(8):1171-1176. DOI:10.1007/s10800-008-9533-3 · 2.15 Impact Factor
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    ABSTRACT: 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 C2H4 oxidation on porous Pt paste catalyst-electrodes deposited on YSZ. It was found that the catalytic rate enhancement ρ is up to 400 for thinner (0.2 μm) Pt films (40,000% rate enhancement) and gradually decreases to 50 for thicker (1 μm) films. The results are in good qualitative agreement with model predictions describing the diffusion and reaction of the backspillover O2) species which causes electrochemical promotion.
    Topics in Catalysis 09/2006; 39(1-2):97-100. DOI:10.1007/s11244-006-0042-5 · 2.22 Impact Factor
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    ABSTRACT: The effect of catalyst film thickness on the magnitude of the effect of electrochemical promotion was investigated for the model catalytic reaction of C2H4 oxidation on porous Pt paste catalyst-electrodes deposited on YSZ. It was found that the catalytic rate enhancement ρ is up to 400 for thinner (0.2 μm) Pt films (40,000% rate enhancement) and gradually decreases to 50 for thicker (1 μm) films. The Faradaic efficiency Λ was found to increase moderately with increasing film thickness and to be described semiquantitatively by the ratio 2Fro/I0, where ro is the unpromoted rate and I0 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 O2- species, which causes electrochemical promotion.
    Topics in Catalysis 07/2006; 38(1-3):157-167. DOI:10.1007/s11244-006-0081-y · 2.22 Impact Factor
  • C. A. Cavalca · G. L. Haller
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    ABSTRACT: The influence of Na on benzene hydrogenation over Pt has been investigated. The amount of Na interacting with the Pt catalyst was reversibly changed by electrochemically pumping the Na from β″Al2O3, a solid electrolyte which was both the Pt support and the source of the Na. The kinetics of the reaction are affected in a way that indicates an electronic effect of Na on benzene adsorption. The reaction can be completely inhibited at apparently low coverages of Na relative to the total surface area measured by oxygen chemisorption which may imply that only a small fraction of this surface is active for benzene hydrogenation on Pt/β″Al2O3.
    Journal of Catalysis 07/1998; 177(2):389-395. DOI:10.1006/jcat.1998.2060 · 6.07 Impact Factor
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    ABSTRACT: 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: 1. Electrochemical promotion of C(2)H(4) oxidation on electronically isolated Pt catalysts on Y(2)O(3)-stabilized- Zirconia (YSZ) where NEMCA is induced via potential application between two terminal Au electrodes also supported on the solid electrolyte (bipolar design). 2. Electrochemical promotion of C(2)H(4) oxidation on a finely dispersed Pt catalyst deposited on a Au electrode which is supported on YSZ. 3. Induction of NEMCA during CH(3)OH oxidation on Pt without external voltage application by utilizing the potential difference developed between the catalyst and a catalytically inert counter electrode. In all cases significant non faradaic behavior has been obtained. The underlying catalytic/electro-catalytic phenomena are discussed together with some of the engineering challenges for potential practical applications.
    Ionics 05/1998; 4(3-4):207-214. DOI:10.1007/BF02375947 · 1.84 Impact Factor
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    ABSTRACT: Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) have been recently used to study electrochemically controlled spillover and backspillover of oxygen and sodium on polycrystalline Pt films and Pt single crystals interfaced with O2− and Na+-conducting solid electrolytes. In this paper we summarize and compare the findings of these investigations which have elucidated the physicochemical origin of electrochemical promotion (NEMCA effect) and have provided concrete evidence that spillover-backspillover of atomic oxygen and sodium can take place over mm distances on metals interfaced with solid electrolytes.
    Studies in surface science and catalysis 12/1997; 112:39-47. DOI:10.1016/S0167-2991(97)80822-1
  • M. Makri · C.G. Vayenas · S. Bebelis · K.H. Besocke · C. Cavalca
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    ABSTRACT: Reversible electrochemically controlled dosing (back-spillover) of sodium on Pt(111) at atmospheric pressure was imaged via atomically resolved STM. The Pt(111) monocrystal was interfaced with a flat polycrystalline sample of β″-Al2O3, a Na+ conductor. Application of an electrical current between the Pt(111) monocrystal and a counterelectrode also in contact with the β″-Al2O3 Na+-conducting solid electrolyte causes reversible migration (back-spillover and spillover) of sodium, which forms a (12 × 12) hexagonal structure on the Pt(111) surface. In addition to explaining the phenomenon of electrochemical promotion in heterogeneous catalysis, these observations provide the first STM confirmation of spillover phenomena which play a key role in numerous catalytic systems.
    Surface Science 12/1996; 369(1-3-369):351-359. DOI:10.1016/S0039-6028(96)00911-9 · 1.87 Impact Factor
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    ABSTRACT: Solid electrolytes can be used as active catalyst supports to induce significant and reversible catalytic activity and selectivity enhancement via the effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect) or Electrochemical Promotion which has been recently reported for over fourty catalytic reactions. Atomically resolved Scanning Tunneling Microscopy was used to image the reversible electrochemically controlled dosing (backspillover) of sodium on Pt(111) interfaced to β″-Al2O3 at atmospheric pressure, which has been proposed as the cause of the NEMCA effect in the case of Na+ conductors. It was found that electrical current application between the Pt(111) monocrystal and a counter electrode also in contact with the β″-Al2O3 Na+-conducting solid electrolyte causes reversible migration (backspillover and spillover) of sodium which forms a (1212) hexagonal structure on the Pt(111) surface. In addition to explaining the phenomenon of Electrochemical Promotion in Heterogeneous Catalysis when using Na-β″-Al2O3 solid electrolyte these observations provide the first STM confirmation that: (i) spillover-backspillover phenomena can take place over enormous (~mm) atomic distances, and (ii) promoters can form ordered structures on catalyst surfaces under ambient conditions relevant to industrial practice.
    Ionics 05/1996; 2(3):248-253. DOI:10.1007/BF02376030 · 1.84 Impact Factor
  • L. Basini · C. A. Cavalca · G. L. Haller
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    ABSTRACT: During anodic current operation (I = 0.6 mu A) at 315 degrees C of a O-2, Pt/ZrO2 (8 mol % Y2O3/Ag, O-2 galvanic cell, we have detected Raman scattered photons from the Pt electrode. The corresponding bands have been assigned to the transient formation of Pt-O bonds with an unusually low vibrational frequency. The temporal evolution of the signals, at a constant value of current intensity, temperature, and oxygen flow conditions, has been related to the migration (spillover) of oxygen species from the solid electrolyte-metal-gaseous oxygen three-phase boundary zone onto the porous Pt electrode. These observation give direct information about oxygen atom motion which results from the O2- ions pumping toward the working electrode under conditions in which the non-Faradaic electrochemical modification of catalytic activity has been observed.
    The Journal of Physical Chemistry 10/1994; 98(42). DOI:10.1021/j100093a028 · 2.78 Impact Factor
  • C. A. Cavalca · G. Larsen · C. G. Vayenas · G. L. Haller
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    ABSTRACT: It was found that the catalytic activity and selectivity of Pt for the oxidation of methanol to formaldehyde and CO2 can be altered significantly and reversibly by depositing a Pt catalyst film on an yttria-stabilized zirconia (YSZ) disc and by applying current or potential between the catalyst film and a Ag film deposited on the other side of the O2--conducting YSZ disc. Both the catalyst film and the Ag counter and reference electrodes are exposed to the reacting CH3OH-O2 mixture. The observed increase in the rate of H2CO production was typically a factor of 100 higher than the rate of O2- supply to the catalyst with a concomitant 2-fold increase in selectivity. This demonstration of the effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) to reversibly modify catalyst activity and selectivity in a single-pellet flow reactor is a new result. It has considerable practical importance as it shows that the NEMCA effect can be utilized in conventional flow-type catalytic reactors. The present study has also shown the spontaneous generation of significant reaction-driven potential differences between the catalyst and the counter electrode. This observation is significant both for catalytic and also for sensor applications.
    The Journal of Physical Chemistry 06/1993; 97(23). DOI:10.1021/j100125a005 · 2.78 Impact Factor