S.G. Neophytides

Solid electrolyte aided study of the mechanism of CO oxidation on polycrystalline platinum

The mechanism of CO oxidation on polycrystalline Pt at atmospheric pressure has been investigated by combining kinetic and simultaneous potentiometric studies in a gradientless reactor containing one or two polycrystalline Pt films supported on stabilized zirconia. The initial oxidation state of the catalyst was found to have an important effect both on the steady-state behavior and on the waveform of rate and emf oscillations. A simple kinetic model where both oxygen adsorption and surface reaction are rate limiting is found to describe semiquantitatively the steady-state kinetic and potentiometric results both on preoxidized and on prereduced surfaces. The oscillatory behavior of the system was studied in detail by simultaneous mass spectroscopic monitoring of the concentrations of O/sub 2/ and CO/sub 2/. The kinetic and potentiometric results suggest strongly that the oscillations are caused by periodic formation and consumption of surface PtO/sub 2/. The formation of PtO/sub 2/ is verified by a series of surface CO-O/sub 2/ titration experiments. The experiments with two polycrystalline films show that oscillation synchronization occurs via the gas phase as the two films exposed to the same gaseous environment exhibit synchronous oscillations in the surface oxygen activity.

Non-faradaic electrochemical modification of catalytic activity: 2. The case of methanol dehydrogenation and decomposition on Ag

Abstract It was found that the catalytic activity and selectivity of polycrystalline Ag for the dehydrogenation and decomposition of CH 3 OH can be markedly affected by electrochemically pumping oxygen anions from the catalyst surface via stabilized zirconia solid electrolyte cells. The steady-state increases in catalytic rates are typically a factor of 20 higher than the rate of O 2− transfer from the catalyst surface. Oxygen anion pumping causes up to sixfold increases in the rates of production of H 2 CO, CO, and CH 4 and induces significant changes in product selectivity. Over a wide range of conditions the rates of the catalytic reactions increase exponentially with catalyst-solid electrolyte interface overpotential η, which is proportional to the induced change in catalyst work function. The phenomena are reversible and show that catalyst work function and catalytic activity and selectivity can be varied deliberately by adjusting the catalyst potential. The observed non-Faradaic rate enhancement for this catalytic system can be interpreted by taking into account the decrease in catalyst work function with decreasing catalyst potential and the consequent changes in the strength of chemisorptive bonds.

Non-faradaic electrochemical modification of catalytic activity III. The case of methanol oxidation on Pt

Abstract It was found that the catalytic activity and selectivity of polycrystalline Pt for the oxidation of methanol to formaldehyde and Co 2 can be dramatically and reversibly affected when oxygen anions O 2− 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 H 2 CO and CO 2 formation, are typically 10 3 –10 4 higher than the rate of O 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 H 2 CO 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.

Catalysis, Electrocatalysis and Electrochemical Promotion of the Steam Reforming of Methane over Ni Film and Ni-YSZ Cermet Anodes

AbstractThe 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

The effect of catalyst-electrode potential and work function on the chemisorptive bond of oxygen on Pt interfaced with YSZ

P_{CH_4 }

Underpotential deposition of hydrogen on MoPt4 intermetallic phase in acid solution: temperature dependence

and

Thermal desorption study of Oxygen adsorption on Pt, Ag & Au films deposited on YSZ

P_{H_2 O}