Search

Abstract: The effect of electrochemical promotion of catalysis on the SO2 oxidation reaction was investigated over thin (∼40nm) 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 30Lmin−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 30Lmin−1 which corresponds to 3×104 h−1 space velocity or 0.1s 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. [Copyright &y& Elsevier]

Cyclic voltammetry was used for the electrochemical study of a Ni thin film (∼880 nm) deposited on an yttria-stabilized zirconia (YSZ) solid electrolyte pellet at temperatures between 350 and 450°C at 20 kPa O2 and atmospheric pressure. NiO formed electrochemically by the O2-species supplied from the electrolyte upon anodic polarization, while it grew according to the parabolic growth law, in agreement with Wagner's oxidation theory of metals at high temperatures. A model for the NiO formation was proposed, where NiO is formed at the Ni/YSZ interface and grows by the outward diffusion of Ni2+ species through NiO, which is determined as the rate-limiting step. This implies the autoinhibition of NiO formation by its continuous growth. The above result agrees with Wagner's theory; however, a difference between the latter and the current model is the means of supplying oxygen for NiO formation. Also. O2 evolution reaction is not firmly affected by NiO formation because it is controlled by the electronic current. An apparent activation energy of the limiting Ni2+ diffusion step was calculated to be 35 kJ/mol under 400 mV and decreased with potential increase. [ABSTRACT FROM AUTHOR]

Abstract: A monolithic electropromoted reactor (MEPR) with up to 22 thin Rh/YSZ/Pt or Cu/TiO2/YSZ/Au plate cells was used to investigate the hydrogenation of CO2 at atmospheric pressure and temperatures 220–380°C. The Rh/YSZ/Pt cells lead to CO and CH4 formation and the open-circuit selectivity to CH4 is less than 5%. Both positive and negative applied potentials enhance significantly the total hydrogenation rate but the selectivity to CH4 remains below 12%. The Cu/TiO2/YSZ/Au cells produce CO, CH4 and C2H4 with selectivities to CH4 and C2H4 up to 80% and 2%. Both positive and negative applied potential significantly enhance the hydrogenation rate and the selectivity to C2H4. It was found that the addition of small (∼0.5kPa) amounts of CH3OH in the feed has a pronounced promotional effect on the reaction rate and selectivity of the Cu/TiO2/YSZ/Au cells. The selective reduction of CO2 to CH4 starts at 220°C (vs 320°C in absence of CH3OH) with near 100% CH4 selectivity at open-circuit and under polarization conditions at temperatures 220–380°C. The results show the possibility of direct CO2 conversion to useful products in a MEPR via electrochemical promotion at atmospheric pressure. [Copyright &y& Elsevier]

Abstract: The electrochemical promotion of catalysis (EPOC) was used to promote the selective reduction of NO by hydrocarbons in presence of oxygen using thin (∼40nm) porous Rh and Pt catalyst layers sputtered on the opposite surfaces of thin (0.25mm) solid electrolyte (YSZ) plates serving as electrocatalytic elements of a monolithic electrochemically promoted reactor (MEPR). Using 22 Rh/YSZ/Pt type cells it was found that the reduction of NO in presence of 1.1kPa O2 and 0.36kPa C2H4 can be efficiently electropromoted with 340% rate enhancement, reaching 95% NO conversion with 100% selectivity to N2 in the temperature range from 280 to 340°C. The apparent Faradaic efficiency is larger than unity for both the NO reduction and the C2H4 oxidation reaction. At elevated temperatures (≥300°C) and high reactant conversions it was found that after current interruption, the catalytic rates do not return to their initial values but remain in a new highly active steady state. It appears that this highly active state is not a genuine intrinsic permanent NEMCA state but is manifestation of steady-state multiplicity in the monolithic reactor resulting from near complete gaseous O2 consumption. Thus the low and high activity steady states corresponding to zero applied potential appear to correspond to high and low average in the reactor. The latter is the result of the near complete reactant conversion under the preceding electropromoted operation. These highly active permanent NEMCA states may be quite useful for practical applications. [Copyright &y& Elsevier]

The reduction of NO by C2H4 in high excess of O2 and temperatures 200−300 °C was investigated using a monolithic electropromoted reactor (MEPR) with twenty-two Rh/YSZ/Pt parallel plate elements. It was found that at 220–240 °C and 10% O2 the selective catalytic reduction (SCR) of NO can be electropromoted by 450% with near 100% selectivity to N2 and ΛNO values up to 2.4. The corresponding rate enhancement ratio of complete C2H4 oxidation is up to 900% with Faradaic efficiency, $$ \Uplambda _{{{\text{CO}}_{2} }} $$ , values up to 350. The system appears promising for practical applications. [ABSTRACT FROM AUTHOR]

Abstract: The effect of “permanent electrochemical promotion of catalysis” (P-EPOC) was studied for the first time in the catalytic deep oxidation of C3H8 over a thin (∼150nm) sputtered Pt film on YSZ, under excess of oxygen at 350°C. Short positive potential application (+1V) resulted in a 5.6-fold increase of the catalytic rate, where C3H8 conversion reached 33%, while the apparent Faradaic efficiency was ∼330. After positive current interruption the catalytic rate remained in a highly active steady-state, determined by the total charge of the anodic polarization step. Restoration of the catalytic activity to the initial value occurred only by a similar negative potential imposition. This new stable steady-state after current interruption can be interpreted by storage of a non-reactive oxygen species upon anodic polarization at the proximity of the Pt/YSZ interface and subsequent enhanced migration of spillover Oδ− species from the electrolyte support to the Pt/gas interface under open-circuit conditions. [Copyright &y& Elsevier]

Abstract: The optimal amount of Nafion ionomer applied on IrO2 sputter-deposited electrodes on Ti covered carbon paper was investigated during low temperature PEM water splitting. Different Nafion ionomer loadings were applied on IrO2 electrodes and their performance towards the oxygen evolution reaction was evaluated. An optimum Nafion loading of 1.5mgcm−2 was found which gives a current density of 0.18Acm−2 at 1.75V and 60°C. The anode selectivity to O2 versus CO2 production was 100% and no signs of performance deterioration were observed over periods of several days. [Copyright &y& Elsevier]

The properties and structure of relevant interfaces involving molten alkali carbonates are studied using molecular dynamics simulation. Lithium carbonate and the Li/Na/K carbonate eutectic mixture are considered. Gas phases composed of pure CO 2 or a model flue gas mixture are analyzed. Similarly, the adsorption of these gas phases on graphene are studied, showing competitive CO 2 and N 2 adsorption that develops liquid-like layers and damped oscillation behavior for density. The interaction of the studied carbonates with graphene is also characterized by development of adsorption layers through strong graphene-carbonate interactions and the development of hexagonal lattice arrangements, especially for lithium carbonate. The development of molten salts-vacuum interfaces is also considered, analyzing the ionic rearrangement in the interfacial region. The behavior of the selected gas phases on top of molten alkyl carbonate is also studied, showing the preferential adsorption of CO 2 molecules when flue gases are considered.

A Diesel Particulate Filter (DPF) regeneration process was investigated during aftertreatment exhaust of a simulated diesel engine under the influence of a Diesel Oxidation Catalyst (DOC). Aerosol mass spectrometry analysis showed that the presence of the DOC decreases the Organic Carbon (OC) fraction adsorbed to soot particles. The activation energy values determined for soot nanoparticles oxidation were 97 ± 5 and 101 ± 8 kJ mol(-1) with and without the DOC, respectively; suggesting that the DOC does not facilitate elementary carbon oxidation. The minimum temperature necessary for DPF regeneration was strongly affected by the presence of the DOC in the aftertreatment. The conversion of NO to NO(2) inside the DOC induced the DPF regeneration process at a lower temperature than O(2) (ΔT = 30 K). Also, it was verified that the OC fraction, which decreases in the presence of the DOC, plays an important role to ignite soot combustion.