Tatsuya Takeguchi

Effect of the property of solid acid upon syngas-to-dimethyl ether conversion on the hybrid catalysts composed of Cu–Zn–Ga and solid acids

Abstract Syngas-to-dimethyl ether (STD) conversion was examined on various hybrid catalysts. The catalyst composed of a methanol-synthesis catalyst and a silica-rich silica–alumina showed high dimethyl ether (DME) yield (55.5%) with a good selectivity (93.5%). The effects of water on the acid property and on the reaction were examined. At atmospheric pressure, Lewis acid–base pairs were major active sites for methanol dehydration. At higher pressures, however, water formed by methanol dehydration was strongly adsorbed on Lewis acid sites, suppressing the DME formation. The solid-acid catalyst having Bronsted acid sites with moderate acid strength was the best catalyst for the STD process. Modification of the methanol-synthesis catalysts with Pd was effective to enhance the STD activity at low temperatures.

Fuel flexibility in power generation by solid oxide fuel cells

Power generation characteristics of solid oxide fuel cell (SOFC) with internal steam reforming of hydrocarbons were investigated. Steam reforming reaction over a Ni-YSZ cermet catalyst attained almost the equilibrium conversion and selectivity in the fixed bed reactor at 1000 °C. The conversion of internal reforming of hydrocarbons was incomplete because of the limited contact time with a thick layer of the Ni cermet electrode. Therefore, the fuel cell supplied with pre-reforming gas to the anode always gave rise to a lower terminal voltage because of the insufficient conversion of fuel compared with that supplied with post-reforming gas at a given current density. Methane internal reforming proceeded without deterioration with time, whereas the power generation with ethane and ethylene suffered from carbon deposition even at high steam-to-carbon ratio. Carbon deposition region and equilibrium partial pressure of oxygen in the C–H–O diagram were estimated from the thermodynamic data. The effect of the gas composition in the power generation characteristics, especially, difference in reactivity between H2 and CO, was investigated. The H2–H2O and CO–CO2 fuel systems led to almost the same open circuit voltage at the same H2/H2O and CO/CO2 ratios at 1000 °C, as expected from the thermodynamic equilibrium. The output voltage in a discharge condition was always higher for H2–H2O than for CO–CO2 at every current density.

Effective conversion of carbon dioxide and hydrogen to hydrocarbons

Abstract Recent studies on effective catalytic conversion of carbon dioxide to hydrocarbons were summarized. Firstly, requisites of catalyst structure to realize rapid methanation of carbon dioxide were investigated in detail. The support having a meso-macro bimodal pore structure was found to be superior for both diffusion rates of reactants and products and high dispersion of active catalyst substances, respectively. The Ni-based composite catalyst combined with a small amount of La2O3 and a very small amount of Ru exhibited a very high methanation rate. The role of Ru in the composite catalyst was elucidated as the portholes of hydrogen spillover for the active sites in Ni part. Next, CuZnCrAl mixed oxide catalysts were synthesized by the intrinsic uniform gelation method to synthesize methanol with a comparable reaction rate of syngas conversion to methanol. Furthermore, the performance of methanol synthesis catalyst was markedly improved by modification with Pd or Ag as anticipated an effect of spillover. Gasoline synthesis from carbon dioxide and hydrogen was firstly achieved by adopting a two-stage reactor connected in a series manner as follows; in the first reactor the modified methanol synthesis catalyst was packed, and in the second reactor an HFesilicate catalyst, which has the ZSM-5 (MFI) structure and the activity of methanol to gasoline conversion without acceptance of any effect from the unconverted hydrogen, was packed.

Layered perovskite oxide: a reversible air electrode for oxygen evolution/reduction in rechargeable metal-air batteries.

For the development of a rechargeable metal-air battery, which is expected to become one of the most widely used batteries in the future, slow kinetics of discharging and charging reactions at the air electrode, i.e., oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively, are the most critical problems. Here we report that Ruddlesden-Popper-type layered perovskite, RP-LaSr3Fe3O10 (n = 3), functions as a reversible air electrode catalyst for both ORR and OER at an equilibrium potential of 1.23 V with almost no overpotentials. The function of RP-LaSr3Fe3O10 as an ORR catalyst was confirmed by using an alkaline fuel cell composed of Pd/LaSr3Fe3O10-2x(OH)2x·H2O/RP-LaSr3Fe3O10 as an open circuit voltage (OCV) of 1.23 V was obtained. RP-LaSr3Fe3O10 also catalyzed OER at an equilibrium potential of 1.23 V with almost no overpotentials. Reversible ORR and OER are achieved because of the easily removable oxygen present in RP-LaSr3Fe3O10. Thus, RP-LaSr3Fe3O10 minimizes efficiency losses caused by reactions during charging and discharging at the air electrode and can be considered to be the ORR/OER electrocatalyst for rechargeable metal-air batteries.

Effect of precious metal addition to Ni-YSZ cermet on reforming of CH4 and electrochemical activity as SOFC anode

Abstract Various kinds of precious metals were added to the Ni-Y2O3-stabilized zirconia (Ni-YSZ) cermets, and the relation between steam reforming of CH4 and the electrochemical activity as a solid oxide fuel cell (SOFC) anode was investigated. Ru and Pt additions promoted the reforming and suppressed the coke depositions. The electrochemical activity of the SOFC anode was enhanced by the addition of Ru and Pt, indicating that these precious metals effectively functioned as the anode catalysts. The impedance related to gas diffusion was greatly reduced, indicating that stability of the anode catalyst of SOFC was considerably improved since coke was hardly deposited.

Autothermal reforming of methane over Ni catalysts supported over CaO–CeO2–ZrO2 solid solution

Abstract Ni catalysts supported on various solid solutions of ZrO2 with alkaline earth oxide and/or rare earth oxide were synthesized. The catalytic activities were compared for partial oxidation of methane and autothermal reforming of methane. For partial oxidation of methane, the Ni catalyst supported on a CaO–ZrO2 solid solution showed a high activity. Incorporation of CaO in the ZrO2 matrix was effective for increasing the reduction rate of the NiO particles and for decreasing the coke formation. On the other hand, the Ni particles supported on the CaO–CeO2–ZrO2 solid solution had a strong interaction with the support, and the Ni particles showed high activity and stability for autothermal reforming of methane.

Structure and function of Cu-based composite catalysts for highly effective synthesis of methanol by hydrogenation of CO2 and CO

Abstract A highly effective catalytic conversion of CO 2 and CO into methanol has been investigated by the multi-functional catalysts composed of CuZn oxides as the main components with the modification of a low concentration of precious metals and gallium oxide. The desired reduced state of the catalyst metal oxides for exhibiting the optimum catalytic performance could be controlled by both the hydrogen spillover through the precious metal parts and the inverse-spillover from the Ga parts. As a result, an extraordinary high space-time yield of methanol, 1300 g/1 · h, could be realized under conditions of 270°C, 80 atm, SV 18800 h −1 with 22.0% CO 2 conversion to methanol. Furthermore, the catalyst also exhibited a very high performance in CO hydrogenation, and gave a space-time yield of methanol as high as 6340 g/l · h under conditions of 270°C, 80 atm, SV 37 600 h −1 with 39.4% CO conversion to methanol.

HYDROGENATION OF CARBON DIOXIDE TO C1-C7 HYDROCARBONS VIA METHANOL ON COMPOSITE CATALYSTS

Abstract Hydrocarbon synthesis from CO 2 and H 2 , via methanol, was studied. Composite catalysts consisting of a low-temperature methanol synthesis catalyst and typical H-ZSM-5 were adopted. Syngas conversion was studied for comparison. Mixing H-ZSM-5 with the methanol synthesis catalyst promoted methanol conversion to hydrocarbons. It markedly affected the rate of syngas conversion, since the equilibrium between syngas and methanol was shifted. However, the rate of CO 2 hydrogenation was not affected. For this reason, it was considered that methanol was formed via CO as the intermediate in CO 2 hydrogenation on the composite catalyst, and consequently the selectivity to methanol was considerably low. Therefore, the effect of H-ZSM-5 was reduced. Nevertheless, hydrocarbons containing 71.8% C 2 -C 7 in addition to 28.2% methane could be obtained on a catalyst of mixed Pd-Na-modified Cu-Cr-Zn oxides and the H-ZSM-5.

Effective conversion of carbon dioxide to gasoline

Abstract As one of the powerful contributions to reduce the CO2 accumulation in atmosphere, catalytic conversion of CO2 into gasoline was studied by one-pass operation using seriesly connected two-stage reactor. In the first reactor CO2 was converted to methanol on a catalyst of mixed metal oxides composed of CuZnCrAlOxides, which was prepared by an intrinsic uniform gelation method. The total reaction mixture come out from the first reactor was directly introduced to a seriesly connected second reactor, in which a protonated HFesilicate crystalline catalyst having pentasil pore opening structure was packed. As this HFesilicate catalyst did not accept any unfavorable reaction even coexistence of unconverted hydrogen, the methanol formed in the first reactor was successfully converted into gasoline with about 50% in selectivity. The other products were still light olefins, which are intermediate compounds for gasoline production, therefore, more additional gasoline synthesis will be expected by circulation of those olefins.

Effect of reduction–oxidation treatment on the catalytic activity over tin oxide supported platinum catalysts

Abstract In precious metal-oxide catalyst system, the support materials strongly affect the catalytic activity. Especially the term of strong metal–support interaction is well known: Tauster et al. reported that partially reducible oxide such as titanium oxide could modify the chemisorption of H2 and CO [S.J. Tauster, S.C. Fung, R.L. Garten, J. Am. Chem. Soc. 100 (1978) 170; S.J. Tauster, S.C. Fung, J. Catal. 55 (1978) 29; S.J. Tauster, S.C. Fung, R.T.K. Baker, J.A. Horsley, Science 211 (1978) 1121.]. It was also demonstrated that this interaction could modify the catalytic activity of precious metals in different reactions. Accordingly, elucidating these phenomena will be the useful guide for the development of new class of active catalysts. Thus, we had focused on the chemical interaction between platinum and oxide and reported several results. Tin oxide supported platinum catalysts were heat-treated under oxidizing or reducing atmospheres at various temperatures, and their catalytic activity for methane combustion and electrochemical oxidation of CO was investigated. The resulting catalysts exhibited the peculiar microstructure and catalytic activity because of the metal–support interaction.