Tailoring the electrochemical charge storage properties of carbonaceous support by redox properties of heteropoly acids: where does the synergy come from?

Journal of Solid State Electrochemistry - The synergistic effects between two Keggin-type heteropoly acids (HPAs) and carbon surface were examined and elucidated. An improved high rate capability...     

Effect of silver modification on structure and catalytic performance of Ni-Mg/diatomite catalysts for edible oil hydrogenation

Silver modified Mg-Ni/diatomite materials with ratios of SiO₂/Ni = 1.07 and Mg/Ni = 0.1, differing in Ag content (Ag/Ni = 0.025 and 0.1) were prepared by the precipitation–deposition method. The effects of silver presence and content on the structure, morphology, texture and H₂-adsorption capacity of the obtained precursors were studied by X-ray diffraction, scanning electron microscopy, Hg-porosimetry and H₂-chemisorption techniques. The catalytic performance of the corresponding catalysts in the soybean oil hydrogenation was investigated. The increase of the silver loading resulted in the development of macroporosity and increase in the total sample porosity. The decrease of both H₂-adsorption capacity and hydrogenation activity are related to the metallic silver covering and blocking effects on the Ni²⁺ species, thus hampering the access of hydrogen. The decrease of hydrogenation activity and favorable limiting of cis–trans isomerization on the silver modified catalyst are explained by Horiuti–Polanyi mechanism based on the assumption that hydrogenation and isomerization proceed at the same active metallic nickel sites via half-hydrogenated intermediates.It was shown that the adjustment of the catalyst composition by changing the content of silver modifier offers the possibility to control the total amount of solid fat content, stearic acid and detrimental trans fatty acids in the hydrogenated derivatives. The catalyst with higher silver content is proposed as a promising candidate for selective edible oil hydrogenation catalyst.     

Breakdown Voltage Distributions in Ne-Filled Diode at 1.33 mbar with Corona Appearance in Pre-breakdown Regime

The electrical breakdown of a gas subject to an up-ramping external voltage is studied, experimentally and theoretically, under conditions leading to the appearance of a positive corona at the anode in the pre-breakdown regime. Experimentally, voltage ramps with various rates k in the interval ranging from 0.3 V/s to 26 kV/s are applied to the diode, with the histogram of breakdown voltages being recorded for each rate. The theoretical model gives attention to the pre-breakdown multiplication causing the corona, which tends to reduce the statistical time delay $t_{S}$ before the primary electron is released and hence to make $t_{S}$ comparable to the formative time $t_{F}$ . The multiplication being therefore expected to affect the voltage dependence of the electron yield, a nonlinear equation relating the yield to the overvoltage is introduced. The resulting theoretical expression for the breakdown voltage distribution agrees well with the experimental histograms. Especially noteworthy is the good agreement with the low-voltage tail of the distribution, a segment of the data that has challenged previous theoretical analyses of the problem.