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Large-scale electric discharges events called high energy arcing faults (HEAF) have been reported in a nonnegligible number at nuclear power stations (NPSs) worldwide. If a HEAF occurs, the pressur...

The present study experimentally investigated the performance and emission characteristics of the diesel engine with hydrogen added to the intake air at late diesel-fuel injection timings. The diesel-fuel injection timing and the hydrogen fraction in the intake mixture were varied while the available heat produced by diesel-fuel and hydrogen per second of diesel fuel and hydrogen was kept constant at a certain value. NO showed minimum at specific hydrogen fraction. The maximum rate of incylinder pressure rise also showed minimum at 10 vol. % hydrogen fraction. However, it is desirable to set the maximum rate of incylinder pressure rise less than 0.5 MPa/deg. to realize low level of combustion noise and NO emission. We attempt to reduce further NO and smoke emissions by EGR. As the result, in the case of the diesel-fuel injection timing of −2 °. ATDC with 3.9 vol. % hydrogen addition, the smoke emission value was 0%, NO emission was low, the cyclic variation was low, and the maximum rate of incylinder pressure rise was acceptable under a nearly stoichiometric condition without sacrificing indicated thermal efficiency.

Roles of CO 2 and H 2 O as oxidants are discussed based on the data on the substrate conversions and the product distributions in the nonthermal plasma reforming of aliphatic hydrocarbons such as methane, propane, and neopentane from 303 K to 433 K. Only small effects of initial concentrations of hydrocarbons and types of oxidants are observed on hydrocarbon conversions, and the initial chemical interaction between hydrocarbons and the oxidants unlikely occurs. CO 2 and H 2 O have shown the comparable oxidation powers in the hydrocarbon reforming. Two molar excess of CO 2 or H 2 O to methane is required to oxidize methane carbon atoms to CO and CO 2 , and larger amounts of CO 2 or H 2 O for propane and neopentane. The different natures of CO 2 and H 2 O are reflected in the synthesis gas composition as in the ordinary catalytic reforming processes at higher temperatures: higher H 2 yields and higher H 2 to CO ratios on addition of H 2 O.

Steam reforming of aliphatic hydrocarbons such as methane, ethane, propane, and neopentane was investigated with two types of barrier discharge plasma reactors. With a ferroelectric packed-bed reactor ( FPR) in N/sub 2/, almost the same conversions were obtained for ethane, propane, and neopentane, but methane was less reactive than these hydrocarbons. Hydrogen gas yield decreased in the order: methane/spl ap/ethane>propane>neopentane. The molar ratio of H/sub 2/ to CO {[H/sub 2/]/[CO]} exceeded 3.5 for all the hydrocarbons. [H/sub 2/]/[CO] did not change in the range of H/sub 2/O content from 0.5% to 2.5%. At the volumetric ratio of H/sub 2/O to Hydrocarbon=2.0, carbon balances were poor for ethane, propane, and neopentane, but almost all of the carbon atoms in the reacted methane were recovered as CO and CO/sub 2/. The mole fractions of CO and CO/sub 2/ depended on the chemical structures of the substrate hydrocarbons. It is considered that the water-gas-shift reaction proceeds backward for the reaction systems of the hydrocarbons with higher hydrogen atom densities per molecule. FPR maintained the same performance for 10 h in the steam reforming of methane. The efficiency of a silent discharge plasma reactor was much lower than that of FPR.

Methods for hybridization of silent discharge plasma and catalysts in different forms are presented, and their synergy in benzene decomposition is discussed. TiO2 deposition on the inside wall of the coaxial type of the silent discharge plasma reactor promotes benzene decomposition in air and increases CO2 yield. TiO2–silica gel granules housed inside of the punched internal electrodes also facilitate the oxidative decomposition of benzene. Comparison of the TiO2 surface before and after the reactions by FTIR suggests that the positive effect of TiO2 can be ascribed to the active oxygen species generated on its surface. Replacement of TiO2–silica gel by MnO2 also promotes the oxidative decomposition of benzene in silent discharge plasma. Ozone, which is generated from gaseous oxygen, is decomposed by MnO2, but not by TiO2. Catalytic effects of TiO2 and MnO2 can be ascribed to formation of active oxygen species on their surfaces and that of the triplet oxygen atom from ozone on the MnO2 surface. It has been shown that both of TiO2 and MnO2 can sustain their catalytic activities in silent discharge plasma.

The effective combination of plasma energy and solid surface properties, such as catalysis and adsorption, was investigated using packed-bed type catalyst–hybrid and adsorbent–hybrid reactors that were packed with a mixture of BaTiO 3 pellets and other ceramic pellets (catalyst or adsorbent). The plasma reactor that employed catalysts indicated improvement in CO 2 selectivity and suppression of N 2 O formation compared with the reactor that was packed with BaTiO 3 alone. It was also found that the catalysts and adsorbents in the plasma reactor were useful in enhancing energy efficiency. Furthermore, the catalyst and adsorbent positions in the plasma reactor were very important for induction of surface reactions on the packed materials.

Nitroaldol reaction of a nitro compound with a carbonyl compound was carried out over a variety of solid base catalysts to elucidate the activity-determining factors in the nature of the catalysts and in the nature of nitro and carbonyl compounds. Among the catalysts examined, MgO, CaO, Ba(OH) 2 , KOH/alumina, KF/alumina, Sr(OH) 2 , hydrotalcite, and MgCO 3 exhibited high activity for nitroaldol reaction of nitromethane with propionaldehyde, the activities being in this order. Over these catalysts, the yields exceeded 20% at a reaction temperature of 313 K and a reaction time of 1 h. Mg(OH) 2 , γ-alumina, SrO, Ca(OH) 2 , BaCO 3 , SrCO 3 , BaO, and La 2 O 3 exhibited moderate activites; the yield were in the range 20–2%. CaCO 3 , ZrO 2 , and ZnO scarcely showed the activity. It is suggested that strongly basic sites are not required for the reaction because the abstraction of a proton from a nitro compound is easy. The reactivities of the nitro compounds were nitroethane > nitromethane > 2-nitropropane, and those of carbonyl compounds were propionaldehyde>isobutyraldehyde>pivalaldehyde>acetone>benzaldehyde>methylpropionate. On the basis of IR study of adsorbed reactants and the reactivities of the reactants, the reaction mechanisms are proposed. The reaction proceeds by the nucleophilic addition of the carbanion formed by the abstraction of a proton from nitro compounds to the cationic species formed by the adsorption of carbonyl compounds on the acidic sites (metal cations). The nitroaldol reaction of nitromethane with propionaldehyde over MgO was scarcely poisoned by carbon dioxide and water; nitromethane is so acidic that it is able to be adsorbed on the catalyst on which carbon dioxide or water was preadsorbed.

Catalytic effects of metal oxides in nonthermal plasma chemical processing of hazardous air pollutants (HAPs) are discussed, relevant to their activities for the oxidation of HAPs in nonthermal plasma media and their selective control of active oxygen species derived from background O2. In ferroelectric packed-bed reactors, the oxidation power of barium titanate (BaTiO3) is not strong enough to oxidize HAPs and their carbon intermediates to CO2. Only nitrous oxide (N2O) was formed from background N2 and lattice oxygen atoms in BaTiO3. The catalytic effect of BaTiO3 is negligible under aerated conditions. On the other hand, ozone (O3) is formed from background O2 in much higher concentrations in a silent discharge plasma reactor. Manganese dioxide (MnO2)-catalyzed decomposition of O3 promotes decomposition of benzene, which is less reactive than trichloroethylene and tetrachloroethylene. The acceleration of benzene consumption rate is ascribed to the promotion of its oxidative decomposition by the triplet oxygen atom. Catalytic control of in situ active oxygen species could be one of the most effective approaches to increase the energy efficiency of the nonthermal plasma reactor and to achieve the complete oxidation of the carbon atoms in HAPs.

Applicability of nonthermal plasma (NTP) to chemical reactions such as removal of hazardous air pollutants (HAPs), hydrogen production from small molecules, and hydrocarbon reforming is discussed on the basis of NTP-generating methods, the physicochemical nature of NTP, the reaction behavior of N2, O2, volatile organic compounds, and nitrogen oxides, and synergistic effects of NTP and catalysts/photocatalysts. Plasma-generating methods greatly affect the mean electron temperature and the distribution of active species formed in NTP. Hybridization of NTP with catalysts/photocatalysts is mandatory to increase the energy efficiency of the reaction system. Issues for practical application of NTP is discussed, using HAPs control as an example. The results of the authors' feasibility study indicate that the scale-up merit of the NTP reactor depends on the plasma-generating method.

Catalytic behaviors of solid base catalysts for mixed Tishchenko reactions were investigated to elucidate the activity- and selectivity-determining factors in active sites of the catalysts and molecular structures of the reactants. A mixture containing equal amounts of two kinds of aldehydes was allowed to react at 353 K. The aldehydes used were benzaldehyde, pivalaldehyde, and cyclopropanecarbaldehyde. For all the reactions, the catalytic activity of alkaline earth oxides increased in the order of BaO⪡MgO

Conjugate addition of methanol to 3-buten-2-one to form 4-methoxy-butan-2-one proceeds effectively over the solid base catalysts such as alkaline earth oxides, strontium hydroxide, barium hydroxide, and alumina supported potassium fluoride and hydroxide at a reaction temperature of 273 K. The catalytic activities of magnesium oxide, calcium oxide, and alumina supported KF catalyst were not much affected by exposure of the catalysts to carbon dioxide or air.

Flue gas desulfurization contributes much to the prevention of acid rain. In a dry-type flue gas desulfurization, promotive effect of NO on SO2 absorption is observed. To elucidate the reaction mechanisms for absorption of SO2 by a calcium compound in a dry-type flue gas desulfurization, the states of adsorbed SO2, NO, and NO2 on CaO and the reactivity of the adsorbed SO2 with NO, NO2, and O2 were studied by IR and temperature-programmed desorption (TPD). Sulfur dioxide (SO2) and NO2 were adsorbed on CaO mainly in the form of sulfite ion (SO32-) and nitrato (NO3) complex, respectively. Nitrogen oxide (NO) is adsorbed in the forms of nitrito (NO2) complexes, free nitro, and nitro or chelating nitro complexes. The sulfite ion reacts with the adsorbed species of NO to be oxidized to sulfate ion (SO42-) but reacts neither with the nitrato complex nor with O2. The nitrito complexes, free nitro, and nitro or chelating nitro complexes act as an oxidizing agent toward sulfite ion on CaO to form sulfate ion. The t...

Michael additions of nitromethane to α,β-unsaturated carbonyl compounds (methyl crotonate, butene-2-one, 2-cyclohexene-1-one, and crotonaldehyde) were carried out at 273 K or 323 K over solid base catalysts such as alumina-supported potassium fluoride and hydroxide, alkaline earth oxides and lanthanum oxide. For all Michael additions of nitromethane, KF/alumina and KOH/alumina exhibited high activities, while MgO and CaO exhibited no activity for methyl crotonate and butene-2-one, but low activities for 2-cyclohexene-1-one and crotonaldehyde. The SrO, BaO, and La2O3 exhibited practically no activities for all Michael additions examined. The reactivity of each α,β-unsaturated carbonyl compound is discussed on the basis of the surface properties of catalyst and the chemical properties of the α,β-unsaturated carbonyl compound.

Alumina-supported KF (KF/alumina) catalysts containing different amounts of KF were characterized by XRD, XRF, XPS, and 19 F MAS NMR to elucidate the catalytically active sites, whose appearance varies much with the pretreatment temperature. The reactions examined are double bond isomerization of 1-butene and 1-pentene, Tishchenko reaction of pivalaldehyde, and Michael addition of nitromethane to butene-2-one. The pretreatment temperature range in which the catalysts exhibited the activities depends on the loading of KF. For the double bond isomerization and Tishchenko reaction, the catalysts loaded with 1.2 and 4.6 mmol KF/g-catalyst exhibited the activities only in the pretreatment temperature range 573–873 K, and the catalyst loaded with 8.2 mmol KF/g-catalyst (Fluka-KF/alumina) exhibited the activities in the range 473–773 K. For the Michael addition, the activity of Fluka-KF/alumina did not vary much with the pretreatment temperature, though the maximum activity was obtained when the sample was pretreated at 623 K. Although the main species containing F was K 3 AlF 6 formed by the reaction of KF with alumina, which was observed by both XRD and 19 F MAS NMR, it was not related to the formation of active sites. The surface species relevant to the catalytic activities, in particular for the double bond isomerization and Tishchenko reaction, is the F − containing species which gives a peak at −150 ppm in 19 F MAS NMR.

Effects of hydrogen and hydrogen sulfide on the activity of Pt/WO3-ZrO2 for cumene cracking and hydrogenation were studied to find the way for controlling the acidic function and metallic function of a solid acid supported metal catalyst. Introduction of hydrogen sulfide suppressed only the hydrogenation activity, but did not affect the cracking activity, indicating that hydrogen sulfide suppresses the metallic function without changing the acidic function.

Cyanoethylation of alcohols with acrylonitrile to form 3-alkoxypropanenitriles proceeds effectively over solid base catalysts such as alkaline metal oxides and hydroxides, lanthanum oxide, and alumina supported potassium fluoride and hydroxide at a reaction temperature below 323 K. The order of the reactivity of alcohols varied with the types of catalyst. With magnesium hydroxide and calcium hydroxide, the reactivity of alcohol decreased: methanol>ethanol>2-propanol, while with the alkaline earth oxides, lanthanum oxide, and alumina supported KOH and KF, the reactivity order was opposite. The reactivity orders are interpreted by the acidity of alcohol combined with the basic strength of the catalysts. The catalytic activity of solid base catalysts were scarcely affected by exposure of the catalyst to air before use for the reaction.

Dimerization of methyl crotonate was studied for active solid base catalysts as well as for elucidation of the reaction mechanisms on the solid base catalysts. Among various types of solid base catalysts, MgO showed a higher activity than those of the other solid base catalysts, such as CaO, SrO, BaO, ZrO 2 , La 2 O 3 , KF/alumina, KOH/alumina and K-X zeolite. Dimerization of methyl crotonate proceeds over MgO by Michael addition, which is initiated by abstraction of an allylic hydrogen of methyl crotonate by the basic site on the catalyst to form allylic carbanion. The anion attacks a second methyl crotonate molecule at the β-position to form a methyl diester of 3-methyl-2-vinylglutaric acid which undergoes double bond migration to form the final products: the methyl diesters of (E)-2-ethylidene-3-methylglutaric acid and methyl diesters of (Z)-2-ethylidene-3-methylglutaric acid. The active sites of MgO are discussed on the basis of the product distribution that varies with the pretreatment temperature of the catalyst.

All the alkaline earth oxides exhibit activities for double, bond isomerization of 5-vinylbicyclo[2.2.1]hept-2-ene (VBH) to 5-ethylidenebicyclo[2.2.1]hept-2-ene (EBH) at a reaction temperature of 273 K. The order of the activity on the basis of unit weight of catalyst was CaO>MgO>SrO>BaO when compared under optimum pretreatment conditions. The E/Z ratio in the products is determined by the reaction temperature regardless of the type of catalyst; the ratios were 82/18 and 88/12 for the reaction temperatures of 323 and 273 K, respectively.

KF/alumina catalyst exhibits activity for double bond isomerization of 1-pentene at 273 K when pretreatedin vacuo in the temperature range 573–673 K, while the activity for Michael addition of nitromethane to butene-2-one does not change much with the pretreatment temperature.

A series of ethylene-bridged [2.2.l]metacyclophanes has been synthesized. It was found out that they can adopt a new type of “inward-folded” conformation depending on the substituent of the one aromatic ring. This conformer exhibited different reactivities from another “inward-folded” one of the non-bridged [2.2.l]metacyclophanes.

Cyanoethylation of methanol with acrylonitrile to form 3-methoxypropanenitrile proceeds effectively over solid basic catalysts such as alkaline earth oxides and hydroxides, and alumina supported potassium fluoride and hydroxide at a reaction temperature of 323 K. The catalytic activity of magnesium oxide was scarcely affected by exposure of the catalyst to air before use for the reaction.

Synthesis gas was produced from CO 2 and H 2 O with nonthermal plasma. A ferroelectric packed-bed reactor worked much better than a silent discharge plasma reactor. CO 2 and H 2 O competitively reacted to give CO and H 2 , respectively. Arbitrary molar ratios of H 2 to CO were obtained by controlling that of H 2 O to CO 2 . Energy conversion efficiency decreased with water content, and its maxima were observed in its functions of reactor energy density.

Hydrogen generation from water, methane, and methanol was investigated with different types of nonthermal plasma reactors under different conditions. With a ferroelectric packed-bed reactor in N/sub 2/, hydrogen gas yield decreased in the order: methanol > methane > water. A similar trend was observed with a silent discharge plasma reactor, but H/sub 2/ yields were much lower with the latter reactor. At fixed specific energy densities, higher H/sub 2/ yields were obtained at higher gas flow rates in the reactions of the above substrates. The initial water concentration was optimized at ca. 2.0% to obtain the highest rate for H/sub 2/ formation. Under the same conditions, H/sub 2/ yield decreased in the order: Ar>N/sub 2/>air/spl ap/O/sub 2/. The ferroelectric packed-bed reactor could be operated continuously for 10 h without any decrease in its performance in the H/sub 2/ generation from water.

Reactions of alcohols with ethyl acetate (transesterification) and propylene oxide were investigated by use of a variety of solid base catalysts to elucidate the activity determining factors of the catalyst in relation with type of alcohol. Solid base catalysts examined were alkaline earth oxides, hydroxides, and carbonates, alumina supported KF and KOH, rare earth oxide, zirconium oxide, etc. Reaction rate of the alcoholysis of ethyl acetate varies with the combination of type of alcohol and basic strength of solid base catalyst. Over strongly basic catalysts such as CaO, SrO, BaO, 2-propanol reacted much faster than methanol. On the other hand, over weakly basic catalysts such as alkaline earth hydroxides, methanol reacted faster than 2-propanol. 2-Methyl-2-propanol reacted only over strongly basic catalysts, and much slower than methanol and 2-propanol. Alcoholysis with propylene oxide was catalyzed only by strongly basic catalysts such as alkaline earth oxides, and KF/alumina, alkaline earth hydroxides scarcely showed activity. γ-Alumina, however, showed a high activity, though the selectivity of products was different from those for alkaline earth oxides. Reactives of alcohols with propylene oxide were in the order, methanol>ethanol>2-propanol>2-methyl-2-propanol, regardless of the type of catalyst. One of the characteristic features observed for both alcoholyses is that the catalysts are tolerant to air exposure, which is caused by strong adsorptivity of alcohol competitive to that of carbon dioxide and water.

Nonthermal plasma steam reforming of methane was carried out with two different types of reactors such as ferroelectric packed-bed (FPR) and silent discharge (SDR) in a flow reaction system. The yields of hydrogen and carbon monoxide were much higher with FPR than with SDR under the same conditions. FPR could be operated continuously for 10 h without any decrease in the yields of hydrogen and carbon monoxide.

Nonthermal plasma chemical decomposition of water was carried out with two different types of reactors such as ferroelectric packed-bed (FPR) and silent discharge (SDR) to explore the possibility of hydrogen generation in a flow reaction system. When FPR was used, the H2 yield in this reaction reached 63% at 150 kJ L−1 of supplied specific energy density in N2. On the other hand, the H2 yield was much lower with SDR than with FPR under the same conditions.

A series of ethylene-bridged [2.2.l]metacyclophanes has been synthesized. It was found out that they can adopt a new type of “inward-folded” conformation depending on the substituent of the one aromatic ring. This conformer exhibited different reactivities from another “inward-folded” one of the non-bridged [2.2.l]metacyclophanes.