Chloride inhibition of ethanol electrooxidation at a platinum electrode in aqueous acid solution

The effect of adsorbed chloride ion on the electrooxidation of ethanol at a platinum electrode in 0.5 M H₂SO₄ at 25°C has been studied in order to determine if adsorbed species are important in this electrooxidation. The cyclic voltammogram for this system exhibits three anodic waves, one of which is unusual in that it occurs during the cathodic going potential sweep. The data indicate that adsorbed species are involved in all three waves. Mechanisms proposed in the literature for ethanol electrooxidation are discussed in terms of these results. The most likely mechanism for the first wave during the anodic going potential sweep includes a chemical reaction between chemisorbed CH₃?HOH and OH_(ads), while a reaction between CH₃CH₂OH_(ads) and PtO is involved in the second wave. The cathodic going potential sweep wave is acounted for by the electrooxidation of CH₃CH₂OH_(ads) on a surface free of oxide and chemisorbed species.     

Zur elektrooxidation zweiwertiger alkohole

The electrooxidation of aliphatic polyvalent alcohols is studied on Pt in H₂SO₄-medium under triangular potential sweep control. The anodic behaviour of the investigated organic substances is compared with that of the corresponding primary, secondary and tertiary monovalent analogues.The electrooxidation of the primary bivalent alcohols is characterized by higher cds in the double layer potential range and lower current densities in the oxygen region. The latter could be qualitatively explained on the basis of two schemes of adsorption of the organic molecule on the Pt surface. The exceptional behaviour of ethyleneglycol and glycerine can be explained as well. It is concluded that the presence of more than one OH-group does not require an essential change in the mechanism earlier accepted by the author.     

The influence of temperature and the role of chromium in the passive layer in relation to pitting corrosion of 316 stainless steel in NaCl solution

The electrochemical behaviour of 316 stainless steel was studied in nearly neutral electrolytes containing NaCl in the − 3 to 50°C temperature range, using potentiostatic and potentiodynamic techniques. Special attention was paid to both the current fluctuations previous to the irreversible breakdown of the passive film and to the breakdown potential. No pitting was observed at temperature lower than 0°C. In the 0–15°C range the breakdown potential shifts slightly in the negative direction. Between 15 and 25°C a remarkable decrease in the breakdown potential was observed whereas in the 25–50°C range it remained practically constant. The temperature dependence of the breakdown potential correlates closely with the temperature dependence of the Cr(III) to soluble Cr(VI) electrooxidation current. This suggests that the depletion of Cr(III) and surrounding water with increasing temperature decreases the capability of self-repair of the passive film. Conversely, the increase in temperature produces a thicker and more crystalline passive film which becomes more resistant to breakdown. As this effect is counterbalanced by the depletion of Cr(III) in the passive layer the breakdown potential in the 25–50°C range remains practically constant.     

Effect of pH Value and Temperatures on Performances of Pd/C Catalysts Prepared by Modified Polyol Process for Formic Acid Electrooxidation

The highly active Pd/C catalysts for formic acid electrooxidation have been prepared by a modified polyol process at different pH values of reaction solutions and different reducing temperatures, respectively. Their physical properties have been characterised by energy dispersive analysis of X‐ray, X‐ray diffraction and transmission electron microscopy. Their electrochemical performances for formic acid electrooxidation have been tested by cyclic voltammetry and amperometric i–t curves. The results of physical characterisations show that all the Pd/C catalysts present an excellent face centered cubic crystalline structure. Their particle sizes are decreasing firstly and then increasing with the increasing of the pH values of reaction solutions. The reducing temperatures also markedly affect the Pd particle sizes. And their nanoparticles have narrow size distributions and are highly dispersed on the surface of carbon support, and Pd metal loading in Pd/C catalyst is similar to the theoretical value of 20 wt.%. The results of electrochemical measurements present that the Pd/C catalyst prepared by waterless polyol process at the pH value of 10 and the reducing temperature of 120 °C has the smallest particle size of about 5.6 nm, and exhibits the highest catalytic activity (1172.0 A · g_Pd<?h‐2.85>^–1<?h.8>) and stability for formic acid electrooxidation.     

NO reduction performance of Rh paste catalyst on YSZ under steady state and forced oscillation electropromotion conditions

The technique of cyclic voltammetry was applied in conjunction with on-line catalytic product analysis to investigate the electrochemical promotion of NO reduction by C₃H₆ in presence of O₂ on Rh catalyst-electrode films on YSZ at temperatures 350–490 °C. Cyclic linear potential sweep amperometry under catalytic reaction conditions leads to cyclic non-Faradaic electrochemical modifications in the CO₂ formation and NO reduction rates which are compared to those obtained under steady state potentiostatic operation.     

Nickel hydroxide electrocatalysts for alcohol oxidation reactions: An evaluation by infrared spectroscopy and electrochemical methods

We have investigated the electrochemical oxidation of four alcohols (methanol, 1-, 2- and tertiary butanol) at Ni hydroxide electrodes in alkaline electrolytes. In situ FTIR spectroscopy and electrochemical methods have been used to examine these oxidation reactions. Oxidation of the primary and secondary alcohols commences in the potential region where it is proposed that multi-layers of NiOOH are formed on the electrode surface; while no reaction occurs with tertiary butanol. Methanol oxidation occurs in two stages, with predominantly formate being formed in the potential window 0.36-0.44 V (vs. SCE), followed by further oxidation to carbonate at potentials above approx. 0.45 V. Butanoate is the only detected reaction product for 1-butanol electrooxidation in the potential range 0.36-0.5 V. The oxidation of 2-butanol is more complex. In the lower potential range (0.36-0.44 V) the major reaction product is butanone, which is further oxidised at higher potentials to either acetate or a mixture of propanoate and formate (or carbonate). In addition, rate constants have been determined for the first stage of the electrochemical oxidation of all the alcohols investigated.     

The electrochemical oxidation of aqueous phenol at a glassy carbon electrode

The electrooxidation of phenol is of interest as a model compound for the treatment of aqueous organic wastes. The effect of voltage, concentration and temperature on the electrochemical oxidation of acidic dilute aqueous solutions of phenol was studied. Electrolysis was carried out by recirculating phenol solutions through a flow-by electrochemical reactor employing a reticulated glassy carbon anode. Concentrations of phenol and some breakdown products were monitored using HPLC analysis. Increased voltage was found to shift the product distribution to favour more oxidized products but also to increase electrode corrosion and decrease current efficiency. Higher phenol concentrations (over the range of 5-20 mmol/L) showed a shift in product distribution to favour less oxidized, mostly insoluble products. Elevated temperatures (about 50°C and higher) showed a marked ability to reduce electrode passivation and increase the phenol oxidation rate.     

The influence of temperature on the pitting corrosion of copper

The influence of temperature on pitting corrosion of copper in borate—boric acid buffer (ph 9.00) + x M sodium chloride (0.0 < x < 0.5) is studied in the 0–50°C range, through the change in the breakdown potential determined at a low sweep rate and the passivity current measured at a constant potential. As the temperature rises, the breakdown potential decreases in the 0–15°C range and increases in the 25–50°C range. These results are explained in terms of opposite effects caused by temperature rise, namely the increase in the rate of reactions involved in passivity breakdown and the increase in the protective characteristics of the passive layer.     

Synthesis of alcohols from CO and H2 on a Fe/A1203 catalyst at 8-30 bars pressure

We have investigated the effect of the temperature and pressure on the activity and selectivity in the production of alcohols and hydrocarbons from CO/H₂ on supported iron catalysts. The tests were performed in a differential microreactor in the 8-30 bars range and between 200 and 275°. The results show that pressure increases the rate of production of hydrocarbons and alcohols. At low temperatures (200-225°), a high methanol selectivity is observed, up to 40%. Homologous linear alcohols are also obtained and their yield is increased upon raising the reaction temperature. However the alcohol-selectivity diminishes on account of a higher conversion into hydrocarbons. The influence of temperature upon the relative hydrocarbon and alcohol formation as well as the Schulz-Flory distributions suggest that a comlmon precursor exists between hydrocarbons and higher alcohols (C₃-C₁₁). Furthermore, the enhancement of the production of n pentanol-1 by adding n-butene-1 to the H₂/CO mixture indicates that CO insertion in a metal-alkyl like bond must occur during the synthesis, and probably constitutes the reaction pathway to alcohols. That supposes the existence of a molecularly adsorbed CO which supposedly is stable at the prevailing pressures. The presence of adsorbed CO also explains the observed methanol selectivity.     

Electrochemical characterization of the Pt/β′′–Al2O3 system under conditions of in situ electrochemical modification of catalytic activity for propane combustion

Linear sweep and cyclic voltammetry were used for electrochemical characterization of the Pt/sodium-β′′-Al₂O₃ system and investigation of the phases formed upon electrochemical pumping of sodium ions to the Pt catalyst-electrode under conditions of propane combustion or under mixtures of O₂ or CO₂ with helium, at temperatures between 320 and 480 °C. The number, position and magnitude of the peaks in the obtained voltammograms were found to depend on gas phase composition, temperature, and pre-scan (initial polarization) conditions. The results showed that under conditions of propane combustion more than one sodium phases can be formed as a result of electrochemical pumping of sodium ions to the Pt catalyst. The related electrochemical reactions and the identity of these sodium phases, which correspond mainly to carbonate or bicarbonate phases but also to oxide phases, are discussed on the basis of the obtained results and those of former studies.     

New insight into the kinetics of diisocyanate‐alcohol reactions by high‐performance liquid chromatography and mass spectrometry

The uncatalyzed reactions of 2,4‐TDI (2,4‐ toluenediisocyanate ) and MDI (4,4 ′ ‐ diphenylmethane‐diisocyanate ) with alcohols including butan‐1‐ol, butan‐2‐ol, diethylene glycol monomethylether (DEGME) were studied by high ‐ performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI‐MS). The reactions were carried out at different temperatures from 22°C to 75°C using high molar ratios of alcohols to diisocyanates. It was found that the first isocyanate group of the MDI reacts about 1.5 times faster with the alcohols than the second one. The relative reactivities of the isocyanate groups (para and ortho) of 2,4‐TDI as a function of the temperature was also deduced. From the temperature dependence of the rate constants the apparent activation energies were determined. Furthermore, the dependence of the apparent rate constant on the concentration of alcohols was also investigated and a mechanism was proposed for the reaction of diisocyanates with alcohols. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42127.     

Semiconductor-conductor transition of pristine polymer-derived ceramics SiC pyrolyzed at temperature range from 1200°C to 1800°C

This paper studies the effect of pyrolysis temperature on the semiconductor-conductor transition of pristine polymer-derived ceramic silicon carbide (PDC SiC). A comprehensive study of microstructural evolution and conduction mechanism of PDC SiC pyrolyzed at the temperature range of 1200°C-1800°C is presented. At relatively lower pyrolysis temperatures (1200°C-1600°C), the carbon phase goes through a microstructural evolution from amorphous carbon to nanocrystalline carbon. The PDC SiC samples behave as a semiconductor and the electron transport is governed by the band tail hopping (BTH) mechanism in low pyrolysis temperature (1300°C); by a mixed mechanism driven by band tail hopping and tunneling at intermediate temperature (1500°C). At higher pyrolysis temperatures (1700°C-1800°C), a percolative network of continuous turbostratic carbon is formed up along the grain boundary of the crystallized SiC. The samples demonstrate metal-like conductive response and their resistivity increases monotonically with the increasing measuring temperature.     

Electrochemical investigation of Pd nanoparticles and MWCNTs supported Pd nanoparticles-coated electrodes for alcohols (C1–C3) oxidation in fuel cells

Incorporation of palladium nanoparticles (PdNPs) and multi-walled carbon nanotubes (MWCNTs) into chitosan-coated glassy carbon (GC) electrode for alcohols (methanol, ethanol, and isopropanol) electrooxidation has been studied. PdNPs–chitosan and MWCNTs–PdNPs–chitosan nanocomposites are successfully prepared and characterized by transmission electron microscopy images and UV–Vis spectroscopy. Based on the results, PdNPs–chitosan nanocomposite indicates high electrochemical activity and excellent catalytic characteristic for alcohol (C₁–C₃) electrooxidation on a GC electrode in an alkaline medium. The current density of the alcohols oxidation at GC–PdNPs–chitosan electrode is investigated in optimized conditions and compared with that obtained at the GC-modified electrode by Pd with different polymers. Also, our results show that the dispersion of Pd nanoparticles on the MWCNTs significantly improved the performance of the PdNPs/chitosan composite for electrooxidation of the C₁–C₃ alcohols.     

Effects of hydrogen pressure on hydrogasification of Taiheiyo (Japan) coal

The non-isothermal hydrogasification of Taiheiyo coal is studied at hydrogen pressures up to 5 MPa and temperatures of 900 °C using a high-pressure thermobalance and tubular reactor. Gaseous products are analysed and liquid products obtained from the mass balance. Rates of formation of methane increased with temperature to two maxima, at 550 °C and at 750 °C. Corrections to rate are necessary because of appreciable weight losses. In the temperature range 650–800 °C the activation energy of methane formation is ≈ 115 kJ mol^?1. Below 55 °C, the pressure dependence of reaction is 0.3, becoming first order at higher temperatures. Rates of formation of methane and ethane indicate a similar mechanism of formation. Rates of formation of liquid hydrocarbons maximize at ≈ 450 °C and increase with hydrogen pressure.     

Conversion of isopropanol and mixed alcohols to hydrocarbons using HZSM‐5 catalyst in the MixAlco™ process. Part 2: Studies at 5000 kPa (abs)

This study employed HZSM‐5 (SiO₂/Al₂O₃ = 280 mol/mol) to produce hydrocarbons from reagent‐grade isopropanol and mixed alcohols made from lignocellulosic biomass (waste office paper and chicken manure) using the MixAlco? process. All studies were performed at P = 5000 kPa (abs). The experiments were conducted in two sets: (1) vary temperature (300–450°C) at weight hourly space velocity (WHSV) = 1.92 h^?1, and (2) vary WHSV (1.92–11.52 h^?1) at T = 370°C. For isopropanol at higher temperatures, the olefins undergo more cracking reactions to produce smaller molecules and more aromatics. At low temperatures, the molecules have less energy so they do not crack and therefore form larger molecules. At T = 300°C, the carbon distribution is bimodal at C9 and C12, which shows trimerization and tetramerization of propene. At 300°C, propene was the only gas produced, cracking did not occur and therefore preserved high‐molecular‐weight molecules. For mixed alcohols, higher temperatures show significant catalyst deactivation; however, isopropanol did not show any catalyst deactivation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1707–1715, 2016     

Evaluation of interactions of biopolymers using dynamic rheological measurements: Effect of temperature and blend ratios

Herein, a robust scheme is defined to elaborate interaction behavior of biopolymers and the effect of temperature on it using dynamic rheological measurements. As a case study, sage seed gum‐xanthan gum (SSG‐XG) interaction at different ratios (1‐0, 3‐1, 1‐1, 1‐3, 0‐1) and temperatures (10, 30, 50, 70, and 90 °C) were experimentally evaluated. SSG‐XG of 3‐1 showed the highest temperature tolerance of almost all rheological parameters and relaxation time in amplitude sweep and frequency sweep measurements, respectively. Higher elastic component and higher extent of temperature dependency of this parameter were observed with increasing SSG fraction. At high temperature, XG molecules in aqueous solution illustrated an ordered (helix) –disordered (coil) conformational transformation while SSG exhibited more rigidity at higher temperature. Only 3‐1 and 1‐1 SSG‐XG at 50 °C showed synergistic interaction of A_a (stiffness parameter) among all blends, which suggested the use of 3‐1 SSG‐XG blend in systems where enhanced structure at high temperature is desirable. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44414.     

Dynamic mechanical and impact properties of PP/SEBS blend

Studies on impact behaviour of the blend of isotactic polypropylene (PP) with styrene-b-ethylene-co-butylene–b-styrene triblock copolymer (SEBS) in the composition range 0–25 wt % SEBS at three temperatures, viz., ambient, ?30°C, and ?190°C, are presented. Dynamic mechanical properties on a torsion pendulum in the temperature range ?100?100°C are also studied for this blend at various compositions. Scanning electron microscopic studies of the impact-fractured surfaces are presented to illustrate the differences in the mode of fracture at the three temperatures of impact tests. Choice of the three temperatures for impact tests was such that the effect of shear yielding mechanism of toughening of PP at ambient temperature remains suppressed at ?30°C, whereas at the lowest temperature (i.e., ?190°C) the elastomeric role of the inclusion SEBS is suppressed. The observed considerably large difference in impact toughening at ambient temperature and at ?;30°C seems not entirely accountable by the prevalence of shear yielding or crazing mechanisms in the respective temperature regions. A third mechanism, viz., viscoelastic energy dissipation, is invoked to account for the observed large difference of impact toughening at these two upper temperatures. Correlation of peak area of dynamic mechanical loss peaks occurring below the impact test temperature with the impact strength is also shown. This suggests greater significance of viscoelastic energy dissipation mechanism in the toughening of this blend at ambient temperature than at ?30°C.     

A method for rough estimation of the catalyst surface area in a fuel cell

A method for a rough estimation of the catalyst surface area in a fuel cell is developed. It is based on the deconvolution of experimental CO oxidation data by use of a mathematical model. The kinetic parameters of the model are determined by fitting the experimental curves. The experimental data are collected at different sweep rates (2–100 mV s⁻¹) and at different temperatures (room −60.0 °C). The model can predict the sweep rate dependence of the CO oxidation onset potential, the peak current, the peak potential and the peak broadness. The model is further used for the prediction of the baseline in the presence of CO and for calculation of the CO charge consumed up to half peak potential. It is obtained that the latter value is constant at different sweep rates and that the baseline deviates from linearity already at low sweep rates (2 mV s⁻¹), but not very significantly (2.0% in comparison to 8.8% at 100 mV s⁻¹, based on calculated CO charge). It is suggested that lower sweep rates should be used for experimental surface area determination.     

Fabrication of manganese oxide electrodes by radio frequency sputtering for electrochemical capacitors

Manganese oxide thin films were sputtered on graphite foils by radio frequency (RF) sputtering. At the 1,000th cycle of potential cycling, maximum mass specific capacitance of 341 F g^?1 was obtained in 0.5 M LiCl and with optimum sputtering conditions (5 sccm of oxygen, 20 mTorr, and 70 W) as well as annealing temperature (150 °C). These show its high electrochemical stability and good mass specific capacitance at a higher sweep rate of 100 mV s^?1. In addition, the higher the volume flow rates of oxygen, the larger the amount of trivalent manganese oxide and the higher the surface roughness, the higher the mass specific capacitance at lower volume flow rates of oxygen, but the amounts of trivalent manganese oxide were almost the same and the mass specific capacitance decreased due to decreasing surface roughness at higher volume flow rates of oxygen. Furthermore, the geometric specific capacitance increases with increasing sputtering pressure and power.     

Temperature dependence of the electrochemical corrosion characteristics of carbon steel in a salty soil

The electrochemical corrosion characteristics of carbon steel in a salty soil at different temperatures were studied by measurements and analyses of potentiodynamic polarization curves, linear polarization resistance and electrochemical impedance spectroscopy. The results showed that the mass-transfer of dissolved oxygen plays an essential role in carbon steel corrosion, and the whole corrosion process is mix-controlled by both activation and mass-transfer steps. Passivity can be developed on carbon steel in the soil at low temperatures. With the increase of temperature, the passive current density increases and the passive potential range decreases. When temperature is elevated to a certain value, 50 °C in this system, passivity cannot be maintained and the steel is dominated by an active dissolution status. Anodic Tafel slope decreases continuously with the increase in temperature, which is mainly due to the enhanced electrode reaction rate at an elevated temperature. Simultaneously, cathodic Tafel slope increases with temperature continuously due to the decrease of the solubility of dissolved oxygen in soil. Since the diffusion activation energy is generally much smaller than the reaction activation energy, the effect of temperature on diffusion is far less than that on electrode reaction rate.