Ternary Pt<Subscript>45</Subscript>Ru<Subscript>45</Subscript>M<Subscript>10</Subscript>/C (M=Mn,Mo and W) catalysts for methanol and ethanol electro-oxidation

Ternary Pt₄₅Ru₄₅Mn₁₀/C, Pt₄₅Ru₄₅Mo₁₀/C and Pt₄₅Ru₄₅W₁₀/C catalysts were synthesized and physical and electrochemical properties were characterized. Particle sizes of the catalysts were determined by X-ray diffraction to be 3.9, 4.8 and 4.6 nm for the Mn, Mo and W incorporated catalysts, respectively. Electrochemically active surface areas were calculated from CO stripping results, which were 17.7, 17.2 and 15.7 m²/g _catal for the Pt₄₅Ru₄₅Mn₁₀/C, Pt₄₅Ru₄₅Mo₁₀/C and Pt₄₅Ru₄₅W₁₀/C catalysts, respectively. In methanol electro-oxidation, the Pt₄₅Ru₄₅W₁₀/C catalyst showed highest mass and specific activities of 2.78 A/g _cat. and 177 mA/m², respectively, which were 22 and 100% higher than those of commercial PtRu/C. In the case of ethanol electro-oxidation, the Pt₄₅Ru₄₅Mo₁₀/C catalyst exhibited highest mass and specific activities of 4.8 A/g _catal and 280 mA/m², respectively. Specific activity of the Pt₄₅Ru₄₅Mo₁₀/C catalyst was 56% higher than that of the commercial PtRu/C.     

Electrocatalytic oxidation of ethanol on Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript>(<Emphasis Type="Italic">x</Emphasis>)</Subscript>O<Subscript>2</Subscript> electrodes in acid medium

The electrochemical oxidation of ethanol at Sn_(1−x)Ir _x O₂ electrodes (with x = 0.01, 0.05, 0.1 and 0.3) was studied in 0.1 mol L⁻¹ HClO₄ solution. Electrolysis experiments were carried out and the reaction products were analyzed by Liquid Chromatography. It was found that the amounts of the reaction products depended on the composition of the electrode. In situ infrared reflectance spectroscopy measurements were performed to identify the adsorbed intermediates and to postulate a reaction mechanism for ethanol electrooxidation on these electrode materials. As evidence, acetaldehyde and acetic acid were formed through a successive reaction process. Carbon dioxide was also identified as the end product, showing that the cleavage of the carbon–carbon bond occurred. These results indicate that the synthesized catalysts are able to lead to the total combustion of organic compounds. Analysis of the water bending band at different potentials illustrated its role at the electrode interface.     

Electrochemical oxidation of an acid dye by active chlorine generated using Ti/Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> electrodes

The generation of active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L⁻¹) and a low current density (5 mA cm⁻²) it was possible to produce up to 60 mg L⁻¹ of active chlorine on a Ti/Sn_0.99Ir_0.01O₂ anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm⁻² and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 × 10⁻⁴ mol L⁻¹. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.     

Promoting Effect of Triglyme on Lean NO<Subscript>x</Subscript> Reduction Over Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Abstract  

The highly oxygenated hydrocarbon triethylene glycol dimethyl ether or triglyme (CH₃O–(C₂H₄O–)₃CH₃) was found to efficiently reduce NO_x under lean conditions over Ag/Al₂O₃, but gave a low NO_x conversion over Cu-ZSM-5. Furthermore, triglyme showed an extraordinary promoting effect when added together with propene as reducing agent for NO_x over Ag/Al₂O₃ at low temperature. This is most likely due to that triglyme promotes the activation of propene.     

Synergism Between Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Au/TiO<Subscript>2</Subscript> in the Low Temperature Oxidation of Propene

CO impedes the low temperature (<170 °C) oxidation of C₃H₆ on supported Pt. Supported Au catalysts are very effective in the removal of CO by oxidation, although it has little propene oxidation activity under these conditions. Addition of Au/TiO₂ to Pt/Al₂O₃ either as a physical mixture or as a pre-catalyst removes the CO and lowers the light-off temperature (T ₅₀) for C₃H₆ oxidation compared with Pt catalyst alone by ~54 °C in a feed of 1% CO, 400 ppm C₃H₆, 14% O₂, 2% H₂O.     

Evaluation of Graphene/WO<Subscript>3</Subscript> and Graphene/CeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Structures as Electrodes for Supercapacitor Applications

The combination of graphene with transition metal oxides can result in very promising hybrid materials for use in energy storage applications thanks to its intriguing properties, i.e., highly tunable surface area, outstanding electrical conductivity, good chemical stability, and excellent mechanical behavior. In the present work, we evaluate the performance of graphene/metal oxide (WO₃ and CeO _x ) layered structures as potential electrodes in supercapacitor applications. Graphene layers were grown by chemical vapor deposition (CVD) on copper substrates. Single and layer-by-layer graphene stacks were fabricated combining graphene transfer techniques and metal oxides grown by magnetron sputtering. The electrochemical properties of the samples were analyzed and the results suggest an improvement in the performance of the device with the increase in the number of graphene layers. Furthermore, deposition of transition metal oxides within the stack of graphene layers further improves the areal capacitance of the device up to 4.55 mF/cm², for the case of a three-layer stack. Such high values are interpreted as a result of the copper oxide grown between the copper substrate and the graphene layer. The electrodes present good stability for the first 850 cycles before degradation.     

Reductive amination of ethanol to ethylamines over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Ni(x)/Al₂O₃ (x=wt%) catalysts with Ni loadings of 5–25 wt% were prepared via a wet impregnation method on an γ-Al₂O₃ support and subsequently applied in the reductive amination of ethanol to ethylamines. Among the various catalysts prepared, Ni(10)/Al₂O₃ exhibited the highest metal dispersion and the smallest Ni particle size, resulting in the highest catalytic performance. To reveal the effects of reaction parameters, a reductive amination process was performed by varying the reaction temperature (T), weight hourly space velocity (WHSV), and NH₃ and H₂ partial pressures in the reactions. In addition, on/off experiments for NH₃ and H₂ were also carried out. In the absence of NH₃ in the reactant stream, the ethanol conversion and selectivities towards the different ethylamine products were significantly reduced, while the selectivity to ethylene was dominant due to the dehydration of ethanol. In contrast, in the absence of H₂, the selectivity to acetonitrile significantly increased due to dehydrogenation of the imine intermediate. Although a small amount of catalyst deactivation was observed in the conversion of ethanol up to 10 h on stream due to the formation of nickel nitride, the Ni(10)/Al₂O₃ catalyst exhibited stable catalytic performance over 90 h under the optimized reaction conditions (i.e., T=190 °C, WHSV=0.9 h^?1, and EtOH/NH₃/H₂ molar ratio=1/1/6).     

Effect of Cu promoter and alumina phases on Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for propane dehydrogenation

We investigated the effects of different Cu weight ratio on θ or γ-Al₂O₃ which were impregnated with platinum in terms of catalytic activity for propane dehydrogenation and physicochemical properties. 1.5 wt% Pt, 0-10 wt% Cu catalyst supported on θ-Al₂O₃ or γ-Al₂O₃ was prepared by incipient wetness co-impregnation. Enhanced Pt dispersion by increasing Cu contents in γ-Al₂O₃ supported catalyst was confirmed via XRD and XPS. Pt and CuO was separated in Pt-Cu/θ-Al₂O₃, but Pt-Cu alloy was identified after reduction treatment. Also, adding Cu in Pt/Al₂O₃ makes catalyst’s acidity lower and this property led to increased propylene yield in propane dehydrogenation. However, Pt₃Cu was not good for yield of PDH, which was confirmed in Pt-10Cu/θ-Al₂O₃ through XRD.     

Еlectrochemical hydriding/dehydriding of nanocrystalline Mg<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni (<Emphasis Type="Italic">x</Emphasis> = 0, 0.1, 0.3)

The electrochemical hydriding/dehydriding under galvanostatic conditions of nanostructured Mg_2-x Sn _x Ni (x = 0,0.1,0.3) were studied at different temperatures in the range 28–45 °C. The discharge capacity, cycle life and electrochemical impedance of the alloys were found to depend on the presence of Sn. Tin decreases the maximum electrochemical capacity, but essentially improves the cycle life of Mg₂Ni. Intensive corrosion of surface Mg was found to take place during the first 2–3 charge/discharge cycles to a much larger extent for Mg₂Ni, compared to the tin containing alloys. Sn decreases the electron density around the Mg atoms and therefore impedes magnesium oxidation. It was also found that Sn hampers charge transfer but reduces the hydrogen diffusion resistance in Mg₂Ni based alloys.     

Low-temperature CO oxidation of Pt/Al<Subscript>0.1</Subscript>Ce<Subscript>0.9</Subscript>O<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> catalysts: Effects of supports prepared with different precipitants

We prepared 0.1Al-0.9Ce supports using various precipitants such as NH₄OH, KOH, NaOH, K₂CO₃, and Na₂CO₃ to prepare Pt-based CO oxidation catalysts. Of the studied catalysts, the Pt/0.1Al-0.9Ce_NH₄OH catalyst showed the optimum activity for CO oxidation. Catalysts prepared with carbonate-form precipitants revealed relatively lower activity than carbonate-free precipitants. A temperature at 50% CO conversion of all samples was observed in the low-temperature region in the presence of water vapor because of the promotional effect of the water-gas shift reaction. Several characterization results revealed that catalytic activity was related to oxygen capacity and Pt dispersion was attributable to precipitant nature.     

Solution-Combustion Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> as a Cathode Material for Lithium-Ion Batteries

A cathode material for lithium-ion batteries–LiNi_1/3Co_1/3Mn_1/3O₂–was prepared by solution combustion synthesis and characterized by XRD, SEM, and galvanostatic charge/discharge cycling. The sample calcined at 950°C for 10 h showed best charge/discharge performance. An initial discharge capacity (C) of 150.5 mA h g^–1 retained 95.7% of its value after 75 charge/discharge cycles at I_c = 14 mA g^–1 (0.2C rate), I_d = 70 mA g^–1 (0.5C rate).     

In Situ FT-IR Study of Diesel Hydrocarbon Oxidation Over Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst

Abstract  

The catalytic performance of Pt/Al₂O₃ for the total oxidation of a hydrocarbon mixture of n-decane and 1-methylnaphthalene was investigated by using in situ FT-IR spectroscopy. Although carbonate and/or carboxylate species were mainly detected under steady-state conditions, the formation of an acrylate species during the initial stage of the reaction was observed under transient conditions. Based on a comparison of the reaction and formation behavior of the acrylate species and CO₂ as a gaseous product, it was proposed that the total oxidation of the hydrocarbon mixture proceeds via the formation of an acrylate species as a reaction intermediate.     

CO oxidation from syngas (CO and H<Subscript>2</Subscript>) using nanoporous Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The concept of “waste-to-wealth” is spreading awareness to prevent global warming and recycle the restrictive resources. To contribute towards sustainable development, hydrogen energy is obtained from syngas (CO and H₂) generated from waste gasification, followed by CO oxidation and CO₂ removal. In H₂ generation, it is key to produce more purified H₂ from syngas using heterogeneous catalysts. In this respect, we prepared Pt/Al₂O₃ catalyst with nanoporous structure using precipitation method, and compared its catalytic activity with commercial alumina (Degussa). Based on the results of XRD and TEM, it was found that metal particles did not aggregate on the alumina surface and showed high dispersion. Optimum condition for CO conversion was 1.5 wt% Pt loaded on Al₂O₃ support, and pure hydrogen was obtained after removal of CO₂ gas.     

Preparation of Cu/ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst under microwave irradiation for slurry methanol synthesis

Cu/ZnO/Al₂O₃ catalysts with Cu/Zn/Al ratios of 6/3/1 were precipitated and aged by conventional and microwave heating methods and tested in the slurry phase reactor for methanol synthesis. The effect of technological condition of precipitation and aging process under microwave irradiation on the catalytic performance was investigated to optimize the preparing condition of Cu/ZnO/Al₂O₃ catalyst. The results showed that the microwave irradiation during precipitation process could improve the activity of the catalyst, but had little effect on the stability. While the microwave irradiation during aging process has a great benefit to both the activity and stability of the catalyst, the catalyst aged at 80°C for 1 h under microwave irradiation possessed higher methanol space time yield (STY) and more stable catalytic activity. The activity and stability of the catalyst was further enhanced when microwave irradiation was used in both precipitation and aging processes; the optimized condition for the catalyst precursor preparation was precipitation at 60°C and aging at 80°C under microwave irradiation.     

Simplified synthesis of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>-promoted hydrotalcite based on hydroxide-form precursors: Effect of Mg/Al/K<Subscript>2</Subscript>CO<Subscript>3</Subscript> ratio on high-temperature CO<Subscript>2</Subscript> sorption capacity

Hydrotalcite was synthesized from hydroxide-form precursors to prepare a novel high-temperature CO₂ sorbent, and the effect of Mg/Al ratio on CO₂ sorption was studied. To enhance the CO₂ sorption capacity of the sorbent, K₂CO₃ was coprecipitated during the synthetic reaction. X-ray diffraction analysis indicated that the prepared samples had a well-defined crystalline hydrotalcite structure, and confirmed that K₂CO₃ was successfully coprecipitated in the samples. The morphology of the hydrotalcite was confirmed by scanning electron microscopy, and N₂ adsorption analysis was used to estimate its surface area and pore volume. In addition, thermogravimetric analysis was used to measure its CO₂ sorption capacity, and the results revealed that the Mg: Al: K₂CO₃ ratio used in the preparation has an optimum value for maximum CO₂ sorption capacity.