Ichiro Yamanaka

Decomposition of methane over supported-Ni catalysts: effects of the supports on the catalytic lifetime

Abstract Decomposition of methane into carbon and hydrogen over Ni catalysts supported on different supports was studied. The catalytic activities and the lifetimes of the catalysts for the reaction were examined and are discussed. Ni catalysts supported on SiO 2 , TiO 2 and graphite showed high activities and long lifetimes for the reaction, whereas the catalysts supported on Al 2 O 3 , MgO and SiO 2 ·MgO were inactive for the reaction. The relation between the catalytic performance of the supported-Ni catalysts and the structure or electronic state of Ni species is discussed on the bases of the results of X-ray diffraction (XRD) and Ni K-edge XANES/EXAFS. In the supported-Ni catalysts effective for the methane decomposition, Ni species were present as crystallized Ni metal particles. On the other hand, the Ni species on the inactive catalysts were present as nickel oxides mainly, suggesting the formation of a compound oxide between Ni and the supports. The catalytic performance of the Ni catalysts supported on silicas with different specific surface areas and pore structures indicated that the catalytic activity and lifetime for the methane decomposition depended significantly on the pore structures of the supports. The silica support with no pore structure was the most favorable one for enhancing the catalytic activity and lifetime of the supported-Ni catalysts.

One step synthesis of hydrogen peroxide through fuel cell reaction

The fuel cell system [O2, HCl aq. or H2SO4 aq., M(cathode)/Nafion—H/Pt(anode), H2] where M is Pt, Pd, Au, graphite or Au-mesh, cogenerates H2O2 and electricity. Current efficiency for the formation of H2O2 was 100% at the early stage of the reaction. However, the efficiency dropped sharply as H2O2 accumulated in the solution at cathode because of further electrochemical reduction and/or thermal decomposition of the H2O2. The rate of formation of H2O2 was controlled by mass transfer of oxygen. Thus, less active material such as graphite or Au-mesh was a better electrode for the synthesis of H2O2. The best conditions for the accumulation of H2O2 were as follows: M = Au-mesh, pH = 1.1 using HCl aq., pressure of hydrogen = 5 kPa, and pressure of oxygen ⩾ 101 kPa.

Production of hydrogen from methane without CO2-emission mediated by indium oxide and iron oxide

Abstract Production of hydrogen without CO 2 -emission and a safe storage method of hydrogen are expected for the fuel-cell era in the next century. In order to meet this expectation, the authors proposed a new method for the storage and production of hydrogen from methane mediated by indium and iron oxides. First, methane is decomposed into carbon and hydrogen on a Ni/SiO 2 catalyst at >673 K . The hydrogen is used for the reduction of metal oxides into reduced metal oxides. The reducing potential of hydrogen is preserved in the reduced oxides that can be stored under open-air at room temperature and transported safely. The contact of the reduced oxides with water vapor at 673 K quickly regenerates pure hydrogen without carbon oxides (CO,CO 2 ).

Dechlorination of chloroaromatics by electrocatalytic reduction over palladium-loaded carbon felt at room temperature

Abstract The selective dechlorination of various chloroaromatics in water-MeOH medium containing trifluoroacetic acid and tetraalkylammonium salts was successfully performed over Pd-loaded carbon felt cathode at room temperature. The reactivities of 2,4-dichlorophenyl derivatives varied in the order: 2,4 dichlorotoluene

Electrochemical cells as reactors for selective oxygenation of hydrocarbons at low temperature

Abstract New oxidation methods for the partial oxidation of alkenes at low temperatures (

Catalytic Behavior of Pd–Ni/Composite Anode for Direct Oxidation of Methane in SOFCs

Electrocatalysis of a Pd-Ni/composite anode (small amounts of Pd-Ni catalyst on a lanthanum chromite-based porous composite anode) for direct oxidation of dry methane in solid oxide fuel cells (SOFCs) was studied at 1073-1173 K. Synergy of Pd and Ni catalysts was observed for the direct oxidation of dry methane. Maximum power densities with the Pd-Ni/composite anode were 150 and 420 mW cm - 2 at 1073 and 1173 K, respectively. Carbon deposition on the Pd-Ni/composite anode was quite low under both open- and closed-circuit conditions. Therefore, stable power generation was performed under the closed-circuit condition, and no physical damage was observed for the cell under the open-circuit condition with dry methane. XRD analysis suggested the formation of Pd-Ni alloy on the composite anode. A suitable reaction scheme for the direct oxidation of dry methane over the Pd-Ni/composite anode was proposed on the basis of the kinetic experiment, the gasification experiment of the deposited carbon by steam, and impedance spectra. The decomposition of CH 4 to H 2 and C, and the gasification of C by H 2 O to H 2 and CO, are key reactions for the effective direct oxidation of dry CH 4 over the Pd-Ni/composite anode.

Partial oxidation of light alkanes by NOx in the gas phase

Partial oxidations of CH4, C2H6, C3H8, and iso-C4H10 with O2 were promoted by addition of NO in the gas phase. The addition of NO increased the conversion rate of alkanes and decreased the initiation temperatures for the reactions. Moreover, selectivities and yields to oxygenates, aldehydes, ketones and alcohols, were remarkably improved by the addition of NO. The maxima of one-pass yields of oxygenates were 7% for CH4, 11% for C2H6, 13% for C3H8, and 29% for iso-C4H10. It is suggested that NO2 produced from NO and O2 is the initiator for the oxidation of light alkanes. Alkyl nitrite was proposed as the reaction intermediate for the formation of oxygenates. The alkyl nitrite decomposes into oxygenates and NO that works as catalyst for the activation of O2 and the oxidation of alkanes.

The production of synthesis gas by the redox of cerium oxide

The oxidation of CH 4 with CeO 2 in the absence of gaseous oxygen (Step1) and subsequent reduction of CO 2 to CO or of H 2 O to H 2 (Step2) by the reduced cerium oxide, CeO 2−x , have been studied under atmospheric pressure at 673 to 1073K. The reaction of Step1 occurred at ≥873 K producing H 2 and CO with the ratio of 2. This synthesis gas was strongly suggested to be formed directly from CH 4 . Addition of Pt black (1 wt%) to CeO 2 remarkably enhanced this reaction. The reaction of Step2 proceeded at≥673K for both CO 2 and H 2 O. When the degree of reduction of the oxide in Step1 had been adjusted to ca. 10%, both CO 2 and H 2 O were stoichiometrically converted to CO and H 2 , respectively. If the degree of the reduction exceeded 10% in Step1, the carbon deposited on the CeO 2−x strongly retarded the formation of CO from CO 2 in Step2. However, the decomposition of H 2 O was not affected. Thus, it is suggested that the reoxidation of the reduced oxide (Step2) should be operated with H 2 O.

Oxidative coupling of methane applying a solid oxide fuel cell system

Abstract A fuel cell system using yttria-stabilized zirconia as a solid electrolyte was applied to the oxidative coupling of methane. The most active and selective catalyst was BaCO3 deposited on Au-electrode (anode). Optimum conditions for the reaction were examined. The pressure of methane at the anode and that of oxygen at the cathode should be high as much as possible. The optimum temperature was 1073 K. Several advantages of the method are described.

Pd‐Loaded Carbon Felt as the Cathode for Selective Dechlorination of 2,4‐Dichlorophenoxyacetic Acid in Aqueous Solution

Electrocatalytic reductive dehalogenation of 2,4-dichlorophenoxyacetic acid (2,4-D) to phenoxyacetic acid in aqueous solution containing MeOH, trifluoroacetic acid, and tetraalkylammonium salt was studied. A Teflon-made two-compartment flow-through cell with a permeable carbon felt cathode and a platinum foil anode was employed. Several noble metals were tested as electrocatalysts. Palladium-loaded carbon felt was found to be the most suitable significantly enhanced its electrocatalytic activity toward 2,4-D dechlorination. The reaction was hypothesized to proceed at carbon-palladium interface areas through 4-chlorine cleavage to form 2-chlorophenoxyacetic acid as the main reaction intermediate.