Polymer electrolyte fuel cells (PEFCs) are clean and highly efficient energy sources without emission of global warming CO2 gas, and have been developed as electric power sources in fuel cell vehicles (FCVs). One of the most important issues in the development of PEFCs is currently a drastic reduction of Pt usage by an improvement in the activity for oxygen reduction reaction at the Pt cathode catalyst. To improve the activity of the Pt catalyst, we have so far developed core-shell catalysts using Pt monolayer shell covered on Au or Pd core materials. In this review article, a novel preparation method for Pt monolayer formation on non-Pt core nanoparticles that is suitable for mass production of the core-shell catalysts, and the results on the activity and durability of the resulting core-shell catalysts are overviewed. The potentials and difficulties of the core-shell catalysts for use in practical FCVs are discussed.
From the viewpoint of environmental protection, residential fuel cell systems are expected to be widely used. Pt-Ru/C catalyst is usually used as anode catalyst for fuel cell, CO strongly adsorbed on Pt is removed by oxidation to CO2. Since CO adsorbed on Pt reacts with OH adsorbed on Ru, Pt-Ru bonding on the surface of Pt-Ru particle is active site for CO oxidation via bifunctional mechanism or water-gas shift reaction. Enthalpy of homo bonding such as Pt-Pt or Ru-Ru is lower than that of Pt-Ru. Pt and Ru atoms are randomly distributed and number of Pt-Ru bonding is theoretically maximum for the Pt-Ru catalyst prepared by rapid quenching method. Hydrogen oxidation reaction effectively proceeds even in the presence of high concentration of CO.
Solid oxide fuel cells (SOFCs) can directly convert the chemical energy of various fuels to electric power with unmatched energy conversion efficiency. The oxide ion conductivity of LaGaO3 doped with Sr and Mg (LSGM) is introduced and application of LSGM to low temperature SOFCs is explained. Power density at lower temperature was dramatically increased by application of LSGM film manufactured with laser ablation techniques. By application of a suitable buffer layer, the cell using LSGM thin film electrolyte had reasonable power density (0.2 W cm−2) at 773 K. Ce0.6Mn0.3Fe0.1O2 (CMF) oxide had high activity for the anodic reaction and insertion of a CMF layer much improved the maximum power density (0.17 W cm−2 at 673 K). Oxide anode consisting of Ce0.6Mn0.3Fe0.1O2 (CMF)-La0.6Sr0.4Fe0.9Mn0.1O3 (LSFM) (=12.5 : 87.5 wt%) enabled the use of dry hydrocarbon for fuel with almost no coke deposition.
Solid oxide fuel cells (SOFCs) have high conversion efficiency and excellent fuel flexibility for various fuels. The possibility of internal reforming of methane and other hydrocarbons for power generation has been investigated. Fuel flexibility is important for high conversion efficiency and simplified generation systems. Carbon deposition may cause deterioration. Deposition of carbon was effectively avoided by steam and CO2 formed by power generation. Another approach to avoid carbon deposition is to design catalysts less active for carbon formation. The deposition rates were significantly affected by types of metal and oxide in the cermet material and were related to the ionic/electronic conductivities of oxides and dissolution of carbon in the metal species. Extensive dilution of hydrocarbon fuel with water may lead to extremely high water concentrations in the downstream region of the fuel cell under discharge condition. High water content damages the Ni surface and catalytic activity by strong adsorption of water. Reconstruction and analyses of three-dimensional microstructures by focused ion beam-scanning electron microscopy were effective to clarify the degradation of the fuel electrode.
Ni/perovskite-type oxide catalyst (Ni/La0.7Sr0.3AlO2.85: LSAO) shows high catalytic activity and low carbon formation during the steam reforming of aromatic hydrocarbons because of the high mobility of lattice oxygen in the support. The reaction mechanisms of the catalyst were investigated by characterizations and catalytic activity tests for steam reforming of various hydrocarbons including toluene, methylcyclohexane, and n-heptane. The catalytic performance was affected by the reactant structure, as revealed by Arrhenius plots and FT-IR analyses. Adsorption state and stability of reaction intermediates were very important factors in the catalytic activity for steam reforming.
Chemical materials such as alkaline, surfactants, and polymers are widely used for the chemical EOR to reduce the trapped oil saturation in the reservoirs. Parameters such as surfactant adsorption and surfactant loss affect the performance of the mentioned EOR method. In this paper an attempt is made to enhance the performance of the surfactant flooding by application of nanoparticles. A series of core flooding tests were completed for sandstone core samples under reservoir conditions to study the effect of a novel application of nanoparticles to alter the properties of the surfactant in chemical flooding EOR processes. Sodium dodecyl sulfate (SDS) is widely used for the EOR approach. Silica nanoparticles were used to change the surfactant adsorption on the rock surfaces. The results showed that the addition of hydrophilic nanoparticles reduces the surfactant adsorption on the rock and improves the performance of the surfactant flooding which increases the oil recovery.
Al2O3-supported Co and Mo catalysts were prepared by the sol-gel method, in which Co and/or Mo species were added at the hydrolysis of Al tri-s-butoxide. XRD patterns, N2 adsorption and desorption, amounts of NO adsorption and NO species by FT-IR were measured to characterize the catalysts. Catalysts with active components Co and Mo separately supported by the sol-gel method had higher activity for hydrodesulfurization of dibenzothiophene. Mo-Co/Al2O3, in which Mo species was supported on Co/Al2O3 by the sol-gel method, showed the highest activities at lower temperature, indicating that the Co species was effectively dispersed on Al2O3 during the preparation of Co/Al2O3. Catalysts in which Co and Mo species were simultaneously supported had lower activity, indicating that both Co and Mo species were dispersed and reduced interaction between Co and Mo. Co-Mo/sol-gelAl2O3, with the Co species supported on Mo/sol-gelAl2O3, showed the highest activity among sol-gelAl2O3 supported CoMo catalysts, indicating that the Mo species was effectively dispersed during the preparation of Mo/sol-gelAl2O3. Biphenyl was selectively obtained. NO adsorption measurement showed that the amount of NO adsorbed was almost same for Mo-Co/Al2O3 sulfided once or twice. In contrast, sol-gelCoMo/Al2O3, with the Co and Mo added simultaneously by the sol-gel method, showed significant decrease in NO adsorption after second sulfiding, which would be related to the lower stability of sol-gelCoMo/Al2O3 prepared by the sol-gel method. Al2O3-supported Co-Mo catalysts prepared using the sol-gel method had relatively high surface areas (282-544 m2/g) and relatively smaller pore sizes (3.7-6.3 nm).
A new approach to non-catalytic biodiesel production under supercritical conditions of t-butyl methyl ether (MTBE) using a novel spiral reactor is proposed. Previously, canola oil was reacted with MTBE under supercritical conditions to generate fatty acid methyl esters (FAME) and glycerol t-butyl ether (GTBE). To conduct this reaction more effectively, a novel spiral reactor that could also serve as heat exchanger was employed in this study. Using a pressure of 10 MPa and an oil-to-MTBE molar ratio of 1 : 40, experiments were performed at 250-400 °C over 6-30 min. Complete conversion to FAME (FAME yield of 1.00 mol/mol) was rapidly achieved in 20 min at 385 °C. The results revealed that the spiral reactor is superior to a conventional reactor because of the improved FAME yield and thermal efficiency.