Akira Morikawa

Active and selective catalysts for the synthesis of C2H4 and C2H6 via oxidative coupling of methane

Active and selective catalysts for oxidative coupling of methane were tested over many metal oxides (30 oxides) under the experimental conditions chosen (T = 973 K, PO2 = 0.4 kPa, PCH4 = 18.2 kPa, PHe = 82.7 kPa). In general, the oxides of rare earth elements showed higher C2-selectivity (C2H6 + C2H4) than 80%. Among the various metal oxides tested, Sm2O3 was the most active and selective catalyst in the formation of C2-hydrocarbons (selectivity 93%). No appreciable decrease in activity and selectivity was observed after the experiments for 180 h at 973 K. The kinetic studies on the reaction over Sm2O3 were carried out under different experimental conditions. Relative rates of reactions of CH4, C2H6, and C2H4 suggest that the overall reaction of CH4 proceeds as follows: The apparent activation energies for each path can be put in order as EII > EI > EV > EIII. Therefore, the C2-selectivity and the ratio of C2H4C2H6 increase as the reaction temperatures were raised. The pressure effects on the rate of reaction observed showed that the C2-selectivity becomes better when PO2PCH4 decreases. For example, at 18.2 kPa of PCH4, the C2-selectivity approached 100% when the mole percentage of oxygen in reactants decreased to 1.6%.

Hydrogen from water by reduced cerium oxide

A fundamental behavior of the CeO/sub 2/ in its reduction by hydrogen and carbon monoxide and in the oxidation by water and carbon dioxide is described. It is believed that CeO/sub 2/ works as an oxidation catalyst by its redox mechanism. The effects of solid additives on the rates of reduction and oxidtion of the oxide are also described briefly.

Decomposition of water by cerium oxide of δ-phase

Reduced cerium dioxide (CeO2−x) can reduce water, producing hydrogen at ⩾298 K. Kinetic studies were focused on the stoichiometric reaction of δ-phase cerium oxide (CeO1.818) with water vapor. Different activation energies of 18.1 and 33.4 kJ mol−1 were observed for the reactions at the temperature ranges above and below ca. 453 K, respectively. Rate equations observed in the two temperature ranges were also different. These results strongly suggest that the rate-determining steps are different between the two temperature ranges. Rapid oxygen exchange observed between H218O and lattice oxygen in cerium oxide of δ- phase at ⩾ 298 K indicated that neither the adsorption of water molecules not the diffusion of oxygen ions in the bulk of the oxide can be the rate-determining step. H2D2 exchange occurred rapidly at 373 K compared to the rate of water decomposition, suggesting that the recombination of hydrogen atoms on the surface is not rate- determining either. A tentative reaction mechanism was proposed to explain the results of the kinetic studies. The rate-determining step at high temperatures (>453 K) is the reduction of OH− by the six-coordinated Ce3+ which is present in the nonstoichiometric cerium oxide, while that at low temperatures (<453 K) is the subsequent reduction of H+ by the seven-coordinated Ce3+.

Oxidative couplings of methane, ethane, and propane with sodium peroxide at low temperatures

Abstract Partial oxidations of CH 4 , C 2 H 6 , and C 3 H 8 proceeded over sodium peroxide at low temperatures (600–650 K). The only partial oxidation product from CH 4 was ethane, a coupling product. The quantity of its formation depended on the second order of the methane pressure. The products from C 2 H 6 were ethylene and butane. The formation rate of ethylene depended on the first order but that of butane depended on the second order of the ethane pressure. In the case of C 3 H 8 , the products were C 6 alkanes, C 4 alkanes, ethylene, and traces of propylene. The formation rates of C 6 and C 4 alkanes depended on the second order but those of ethylene and propylene depended on the first order of the propane pressure. The activation energies for the conversions of CH 4 (127 kJ mol −1 ) were considerably larger than those of C 2 H 6 (83) and C 3 H 8 (89). The transition state of CH 4 in its activation is suggested to be different from those of C 2 H 6 and C 3 H 8 . The presence of gaseous oxygen decreased the selectivities to the coupling products and to the dehydrogenation products, although the rates of conversion of alkanes were not affected by gaseous oxygen. These observations suggest that the activation of alkanes is caused only by peroxide anions, but the selectivities to further reactions of the surface alkyl groups formed are affected strongly by the presence of gaseous oxygen.

One-step oxidation of benzene to phenol applying a fuel cell system

Abstract The fuel cell system, [ O 2 , Benzene, FeCl 3 (FeSo 4 , CuCl 2 , CuSO 4 or SnCl 2 ) in HCl or H 2 SO 4 aq., Pd (or Au)/Nafion-H/Pt, H 2 ], produced phenol selectively while continously generating electricity. The system reduces Fe III to Fe II or Cu II to Cu I and forms H 2 O 2 as well. Thus, the fuel cell system generates Fentons type reagents continously, producing phenol.

Selective synthesis of ethylene by partial oxidation of methane over LiCl–Sm2O3

Methane is partially oxidised over LiCl–Sm2O3 catalyst to give C2-compounds (ethylene and ethane) in 7.2–19.9% C2-yield at 750 °C, with a high C2H4:C2H6 ratio.

Photocatalytic decomposition of dinitrogen oxide on Cu-containing ZSM-5 catalyst

Photodecomposition of dinitrogen oxide (N2O) into N2 and O2 on Cu-exchanged ZSM-5 zeolite (ion-exchange degree, 145 %), degassed at 723 K, proceeds catalytically at 278 K. The dependence of the decomposition rate on the wavelength of the irradiated light reveals the importance of the excitation of monovalent Cu ions (<300 nm) in the photocatalytic decomposition of N2O. The rate of decomposition can be expressed by the rate equation: r=a[N2O]//([N2O]+b[O2]½), where a and b are constants, and a is proportional to the light intensity.The desorption of O2 from the surface is not a rate-determining step in the photodecomposition or the thermal decomposition of N2O on the zeolite which occurs with an apparent activation energy of 37 ± 3 kJ mol–1.

Specific catalysis of the cis-trans isomerization of olefins by sulfur dioxide adsorbed on various metal oxides and zeolites

Abstract SO 2 adsorbed on solids inactive for the n -butene isomerization, such as NaX zeolite, porous Vycor glass, or silica gel, catalyzes selectively the cis-trans isomerization of 2-butenes at room temperature. On solids active for the reactions, such as γ-Al 2 O 3 , NiO, or α-Fe 2 O 3 , SO 2 poisons the double-bond migration, whereas it enhances the cis-trans isomerization. It was confirmed that the adsorbed SO 2 catalyzes neither the hydrogenation of cis -2-butene nor the hydrogen exchange reactions in the systems of C 2 H 4 -C 2 D 4 , cis -2-butene-C 2 D 4 , or cis -2-butene-deuterium, which was examined on NaX zeolite. The catalysis specific to the geometrical isomerization by adsorbed SO 2 was also observed in the case of 1,3-pentadiene. The formation of the polysulfone between SO 2 and 2-butenes was confirmed on MnO 2 and PbO 2 . These catalysts show very high catalytic activity also for the geometrical isomerization of 2-butenes in the presence of SO 2 . The kinetic data on the geometrical isomerization of 2-butene and 1,3-pentadiene catalyzed by SO 2 are well interpreted by the mechanism that the cis-trans isomerization is accompanied by the copolymerization of SO 2 with olefin, i.e., addition and elimination of 2-butenes at the terminal of the polysulfone cause the isomerization of 2-butenes { cis - or trans -2-butenes + · SO 2 [CH(CH 3 )CH(CH 3 )SO 2 ] n ⇆ · CH(CH 3 )CH(CH 3 )SO 2 [CH(CH 3 )CH(CH 3 ) SO 2 ] n }. It is suggested that the polymerization may be initiated by the SO 2 -olefin (1:1) charge transfer complex such as the one confirmed on the porous Vycor glass.

KINETIC-STUDY OF THE PARTIAL OXIDATION OF METHANE OVER FE2(MOO4)3 CATALYST

The product distributions for partial oxidation of methane over Fe2(MoO4)3 catalyst are compared with those for partial oxidation of methanol in the presence and absence of methane over the same catalyst under similar reaction conditions. The results suggest that CH3OH is the precursor of HCHO which is the main product of partial oxidation of methane by oxygen over Fe2(MoO4)3. The consecutive oxidation of HCHO leads to the formation of CO, the main by-product, and CO2. The presence of abundant methane improves the selectivity to HCHO.The results of kinetic studies on methane oxidation are analysed in terms of the Eley–Rideal model in which the rate-determining step is the activation of methane by the dissociatively adsorbed oxygen. The absence of C2 hydrocarbons in the products suggests that the reaction intermediate is either the surface CH3 species or the methoxide, formed from the reaction of CH4 with the adsorbed oxygen. The mechanism for the formation of HCHO and CO is also discussed on the basis of the results of partial oxidation of methane and methanol.

Reproducible hydrogen production from water by indium oxide

Indium oxide, In/sub 2/O/sub 3/, is proposed as a potential oxide for hydrogen production by a two-step water decomposition process. In/sub 2/O/sub 3/ was reduced by hydrogen at 673/sup 0/K, and the water vapor was condensed at 77/sup 0/K in a U-shaped trap. The reduced oxide was then brought into contact with water vapor with production of H/sub 2/. The reduction and oxidation occurred smoothly and reproducibly at 673/sup 0/K. (BLM)