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The effects of initial water content on steam reforming of aliphatic hydrocarbons such as methane, propane, and neopentane with nonthermal plasma were analyzed in terms of substrate conversion, carbon recovery, and product selectivity. It was found that water addition increased CO2 yield despite a decrease in substrate conversion. The number of carbon atoms in the substrate hydrocarbon affected the additive effect due to the insufficient supply of oxygen atoms from water. Plausible reaction pathways for the conversion of substrate to COx are proposed to explain the relative concentrations of COx species; these pathways involved different precursors for CO and CO2.

The reaction behavior of mixed dichloromethane (CH2Cl2) and toluene in nonthermal plasma was investigated with a ferroelectric packed-bed reactor. The decomposition efficiencies of 109 ppm CH2Cl2 and 100 ppm toluene were not affected by mixing in the presence of O2. In the decomposition of CH2Cl2 and toluene, CO2 selectivity increased with O2 content. The higher the COx yield, the lower the CO2 selectivity. In N2, cyanides were detected as byproducts from CH2Cl2 and toluene, organic chlorides from CH2Cl2, and benzene from toluene. However, no mixing effect was observed in the byproduct formation. The number and amounts of the byproducts decreased with an increase of O2 content in the background gas. In the presence of O2, formic acid was transiently formed from CH2Cl2, but its amount decreased with the increase in reactor energy density. No oxygen-containing byproducts were newly detected.

Surface discharge plasma reactors (SDRs) have been shown to be effective in removing a wide range of pollutants. In this study, the effectiveness of a SDR for the removal of propane and propene from an atmospheric pressure air stream was investigated. For an input energy of 100 J L-1, the conversions were found to be 16% and 68% for propane and propene, respectively. The total carbon recovery was found to increase with increasing specific input energy (SIE) for both hydrocarbons. FTIR analysis showed that CO and CO2 are the major end-products, and GC-MS identified formic acid as a significant byproduct. The effect of initial propane concentration was also investigated. The reaction chemistry involved in the oxidative plasma conversion of propane and propene is discussed.

In this work, comprehensive investigation was done on the oxygen partial pressure-dependent behavior of the various catalysts using a flow-type plasma-driven catalyst (PDC) reactor. These data provide a useful guideline for the optimization of the cycled system using adsorption and the O 2 plasma-driven catalysis of adsorbed volatile organic compounds (VOCs). The potentials of the tested catalysts for the cycled system were evaluated based on the enhancement factor and the adsorption capability. All the tested materials (TiO 2 , γ-Al 2 O 3 , zeolites) exhibited positive enhancement factor, while negative values with the dielectric-barrier discharge (DBD) plasma alone. TiO 2 catalysts showed the highest enhancement factor of about 100 regardless of the type of metal catalysts and their supporting amount. Based on the experimental findings in this study and the literature information, a plausible mechanism of plasma-driven catalysis of VOCs was suggested.

In this work, a nonthermal plasma was applied to the TiO 2 -supported gold nanoparticle catalysts (Au/TiO 2 ) for the catalyst regeneration and the enhancement of catalytic activity for CO oxidation. Exposure to the 100 ppm toluene or C 3 H 6 resulted in rapid deactivation of the Au/TiO 2 catalyst. Oxygen plasma and O 3 injection were found to be effective in the regeneration of the deactivated Au/TiO 2 catalysts. The adsorbed toluene or C 3 H 6 preferentially decomposed to CO 2 regardless of the regeneration method. Direct application of nonthermal plasma greatly enhanced the CO oxidation not only over the completely deactivated Au/TiO 2 catalysts, but also over the Au/TiO 2 catalysts prepared by the impregnation method, which showed no catalytic activity without plasma.

A nonthermal, atmospheric pressure, packed-bed plasma reactor has been used to study the effect of temperature on the plasma−catalytic destruction of toluene and benzene in air. The plasma reactor was packed with BaTiO3 beads to which TiO2, γ-Al2O3, and Ag, Pt, or Pd impregnated catalysts were added. The reactor can be heated up to ∼500 °C, and the destruction efficiencies for toluene and benzene were determined for plasma alone, catalyst alone, and the combined plasma−catalyst configuration. Comparisons have been made to determine the relative contributions of the catalyst and plasma and to discover any synergistic effects. Plasma−catalysis shows greater destruction than catalysis alone with increasing temperature for both benzene and toluene. Catalysis alone has a threshold temperature of ∼300 °C for the destruction of toluene and benzene, but plasma−catalysis with Pd- and Pt-impregnated alumina achieves >95% destruction at this temperature and has a threshold of ∼100 °C. Toluene is more easily destroye...

Catalytic oxidation of benzene with ozone was carried out over Mn ion-exchanged zeolites at 343 K. Benzene was oxidized on Mn-Y to form CO x without the release of organic byproducts, whereas formic acid was formed with supported manganese oxide catalysts, Mn/SiO 2 and Mn/SiO 2 –Al 2 O 3 . Mn-Y showed higher activity and selectivity to CO 2 than other zeolite catalysts, Mn-β, Mn-MOR, and Mn-ZSM-5. Linear relationship was observed between benzene consumption, CO x formation and ozone consumption. Formic acid adsorbed on Mn-Y catalyst was completely oxidized to CO 2 with ozone at around 343 K.

The effect of water vapor on catalytic oxidation of benzene with ozone was studied over alumina-supported manganese oxides. Water vapor suppressed catalyst deactivation by inhibiting the build-up of organic byproducts on the catalyst surface, including formic acid and strongly bound surface formates. FTIR spectroscopic studies revealed that the surface formates were not completely oxidized with ozone in the absence of water vapor, whereas their oxidation with ozone was promoted by addition of water vapor.

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.

This paper presents the effect of different catalysts on the decomposition of benzene and toluene using flow-type plasma-driven catalyst (PDC) system. Three representative materials of titanium dioxide, two types of gamma-alumina and two zeolites were tested. Several types of metal catalysts (Ag, Ni, Pt, Pd) and their loading amount were also investigated for the optimization of the PDC system. Three key factors of energy consumption, carbon balance and safety of products were emphasized in evaluating the performance of different catalysts. The type of catalysts greatly influenced on the carbon balance, CO2 selectivity, ozone formation, while no much difference was observed in the degree of enhancement in energy efficiency. Pt/gamma-Al2O3 catalyst was found to be effective in enhancing the CO2 selectivity. The CO2 selectivity increased as Ag-loading amount on TiO2 catalyst increased. The 4.0 wt% Ag/TiO2 catalyst was effective in suppressing the formation of NO2 and N2 O. Zeolites showed comparable decomposition efficiency and good carbon balance, while the CO2 selectivity was poor compared to the other catalysts. Mechanical mixing of 2.0 wt% Ag/H-Y zeolite with Pt/gamma-Al2O3 was effective in enhancing the CO 2 selectivity without changing other performance

Role of the TiO 2 catalyst under plasma discharge was investigated on the decomposition of CClF 3 in Ar at atmospheric pressure. It was found that the removal rate of CClF 3 increased using a plasma reactor packed with TiO 2 compared with a conventional reactor. Carbon oxides and hydrogenated compound were detected even in the absence of oxygen and hydrogen sources. In order to clarify the sources of these products, we tried the measurement of chemical species desorbed from TiO 2 by plasma discharge, resulting that molecular oxygen and hydrogen were detected in the gas phase. From these findings, it was suggested that the lattice oxygen and the surface OH on the metal oxides could be activated directly by plasma discharge.

Toluene was decomposed in a surface-discharge plasma reactor and the combined effect of zeolite in the plasma reactor was studied. The decomposition of toluene and the product compositions depended on the reactor configuration and the capacity of zeolite to adsorb toluene. Toluene adsorbed on the zeolite (micro-pores) was not properly decomposed in the head of the plasma (P1), while it was readily decomposed not only in the tail of the plasma (P2) but also in the second reactor (P3) out of the plasma region because the oxidation of adsorbed toluene was enhanced by ozone as well as by atomic oxygen species derived from the plasma region. The synergistic effect of zeolite was attributed to its capacity to adsorb toluene and the cyclic plasma operation, which reduced the input energy.

Catalytic oxidation of cyclohexane with ozone was carried out over alumina-supported manganese oxides at 295 K. The catalytic activities decreased steeply with time on stream, and then reached a steady state. At the steady state, the mole fractions of CO2 and CO were 90 and 10%, respectively, with the carbon balance of around 50%. The decomposition ratio was estimated to be 8–10, independent of Mn loadings and support materials. Partially oxidized compounds including alcohols, ketones, acid anhydrides and carboxylic acids were formed on the catalyst surface. These compounds were decomposed by ozone feed. On the other hand, highly resistant species containing C O, COO– and CH groups remained on the catalyst surface, which caused the gradual deactivation of the catalyst. The C O groups were decomposed at relatively lower temperatures ( 473 K) was necessary to decompose the COO– and CH groups.

In situ X-ray absorption fine structure spectroscopic studies were carried out to investigate the structural changes in manganese oxides supported on alumina in the catalytic decomposition of ozone at room temperature. In the ozone decomposition with water vapor, Mn atom was oxidized to higher oxidation state with the coordination of water to Mn site, which was caused by the cleavage of Mn–O–Al bond. The used catalyst was regenerated by the heat treatment in an O 2 flow at 723 K.

In the decomposition of hydrofluorocarbons such as HFC-32 and HFC-23 with silent discharge plasma or surface discharge plasma, MnO2, TiO2–SiO2, and AlPO4 show catalytic effects. MnO2 and TiO2–SiO2 promote the oxidative decomposition of HFCs and FC-14 in the presence of gaseous oxygen, while AlPO4 promotes the cleavage of C–F bonds in them.

The decomposition of volatile organic compounds (VOCs)—six aromatic compounds of benzene derivatives and formic acid—was investigated using a plasma-driven catalysis (PDC) system at atmospheric pressure. In the PDC reactor, the decomposition efficiency of VOCs was mostly determined by the specific input energy (SIE) and insensitivity to the gas hourly space velocity from 11 000 to 55 000 h−1. Formic acid (HCOOH) was formed as a common intermediate from the decomposition of the tested aromatic compounds. Formic acid was also found to be an important intermediate for CO2 formation. Except for styrene, all the tested VOCs indicated zero-order kinetics, which confirm the dominant role of the catalytic reaction in the decomposition of VOCs using the PDC reactor. A simple kinetic model represents well the observed zero-order kinetics with respect to the SIE. Unlike conventional plasma reactors, no correlation between the ionization potential and the decomposition was found with the PDC reactor. Continuous operation tests indicated stable performance without deterioration of catalytic activity over 150 h.

This paper describes the decomposition of gas-phase benzene using a plasma-driven catalyst (PDC) reactor packed with 1.0 wt.% Ag/TiO2 catalysts. The decomposition of benzene preferentially produced CO2 and CO, and formic acid as minor one. Carbon balance based on these products was satisfactory at around 100%. For the concentration lower than 110 ppm, the PDC reactor successfully decomposed benzene with specific input energy of around 130 J/l, where the formation of nitrogen oxides was small. The plasma-induced catalytic activity appeared only during plasma application and disappeared as the plasma was turned off. Thermal catalysis showed that temperature was not an important parameter in the decomposition of benzene using the PDC reactor. Comparison of the effects of dilution gases (Ar, N2) on the benzene decomposition revealed that the contribution of UV light from the plasma to the activation of Ag/TiO2 catalyst was negligible. The contribution of catalytic reaction became dominant as increasing specific input energy. The removed amount of benzene showed zero-order to the initial concentration of benzene and determined mostly by specific input energy to the PDC reactor.

This work presents a comparative assessment of five different types of plasma reactors (pulsed corona, dielectric-barrier discharge (DBD), surface discharge (SD), BaTiO/sub 3/ packed-bed reactor, and plasma-driven catalyst (PDC) reactor) using the decomposition of gas-phase benzene. The parameters used in the assessment include energy constant, carbon balance, product selectivity, and nanometer-sized aerosol formation. The DBD reactor, the pulsed corona reactor, and the SD reactor, where the gas-phase chemical reactions prevail, showed similar performance both in the decomposition efficiency and in the aerosol formation. Size distribution and number concentration of the aerosol formed in the SD and the pulsed corona were 10-80 nm and /spl sim/10/sup 5/ particles/cm/sup 3/, respectively. The PDC reactor showed the highest removal efficiency as well as the highest CO/sub 2/ yield. Carbon balances were strongly related to the nanometer-sized aerosol formation. Negligible amounts of aerosol were formed in the BaTiO/sub 3/ packed-bed reactor and the PDC reactor packed with Ag/TiO/sub 2/ catalyst.

The decomposition of fluorocarbons (1%) in Ar was investigated using a surface discharge-type plasma reactor. To enhance the effectiveness of plasma chemical processing, we investigated the effects of catalysts and additives. The removal rate increased when the plasma reactor was packed with TiO 2 pellets as a catalyst. The catalytic effect seems to be derived from the direct activation of the TiO 2 surface by the plasma discharge, because significant UV emission and temperature increase were not observed in the plasma reactor. The removal rate was also enhanced when water vapor, oxygen, or hydrogen was added to the reactant. In addition, the presence of TiO 2 or the additional gases or both depressed byproduct formation. Analysis of the reaction products suggested that the catalysts and additives enhanced the process by preventing the recombination of decomposed fragments.

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.

Catalytic oxidation of benzene with ozone over alumina-supported manganese oxides was carried out at room temperature (295 K) to investigate the behavior of benzene oxidation and CO x formation. The ratio of the decomposition rate for ozone to that for benzene was found to be 6, independent of ozone concentration, reaction times, and the amount of Mn loading. A linear correlation was observed for the amount of ozone decomposed and that of CO x formed, whereas deviation from linearity was observed between the amount of ozone decomposed and that of benzene reacted. Carbon balance was in the range of 26–37% due to the formation of two types of intermediates, weakly bound compounds including formic acid and strongly bound surface formate and carboxylates. Catalyst was significantly deactivated due to the buildup of the intermediates on the catalyst surface during the course of benzene oxidation. The weakly bound compounds were removed by heat treatment at 573 K in the O2 flow. The strongly bound surface formate and carboxylates were oxidized to CO x by further heating up to 723 K. The deactivated catalyst was regenerated by the heat treatment.

We have observed significant enhancements in the rate and capacity of NO2 uptake caused by the injection of ozone over the zeolite H-ZSM-5, which has a high SiO2/Al2O3 ratio. We performed these experiments using a gas-flow system in which the profiles of NO2 adsorption and subsequent temperature-programmed desorption were measured by Fourier transform infrared spectroscopy. We interpret these results in two ways: either by assuming that fast surface reactions lead to N2O5 formation or by considering that ozone suppresses the blockage of the reactive Bronsted-acidic protons.

This paper describes the effects of electrode configuration and the loading amount of Ag catalyst on the decomposition of gas-phase benzene using plasma-driven catalyst (PDC) reactors. Modification of ground electrode brought out a great enhancement in the energy efficiency for benzene decomposition by reducing abnormal discharges outside the reactor tube. The data of carbon balance and the selectivity of CO2 indicated that the Ag catalyst played an important role in the decomposition of benzene, especially for the intermediates. The larger the Ag-loading amounts on the TiO2, the better the performance of benzene decomposition in terms of the carbon balance and the selectivity of CO2. Formation of NO2 and N2O indicated that the maximum specific input energy applicable to the PDC reactor should be determined not only by the decomposition efficiency but also by the formation of nitrogen oxides.

Photocatalytic oxidation of benzene in air at room temperature was studied in order to obtain the information on its reactivity on the photoirradiated TiO2 catalyst. The objective of this paper is to describe in detail the dependence of the rate for benzene photooxidation on humidity, initial benzene concentration, and incident light intensity, since they are important factors for construction of VOC control system utilizing solar energy. The reaction mechanism is also discussed to understand the decomposition behavior of benzene.Copyright © 2003 by ASME

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.

Catalytic oxidation of benzene and cyclohexane in the gas phase with ozone was carried out at room temperature. The catalytic activities of the oxides of Mn, Fe, Co, Ni, Cu and Ag for the reaction were compared.

Gas-solid heterogeneous photocatalytic oxidation of aromatic compounds in air was carried out at room temperature with a fixed bed flow reactor. The deposition of Rh on TiO2 catalyst improved the catalyst durability in benzene photooxidation. The Rh deposition reduced the amounts of carbonaceous materials on the catalyst surface that were the cause of catalyst deactivation. The highest reaction rate was obtained at the Rh loading of 0.5-1.0 wt %. The Rh/TiO2 catalyst was gradually deactivated in prolonged benzene photooxidation, due to the increasing amount of carbonaceous materials on the catalyst surface. XPS studies showed that the gradual deactivation was related to the changes in the oxidation state of the surface Rh metals. The catalysts were regenerated by the treatment of hydrogen reduction after the photoirradiation in humidified air, indicating that Rh(0) was essential for the improvement of the catalyst durability. The catalyst was also regenerated by the heat treatment in N2 flow instead of the hydrogen reduction. Rh deposition was also effective for the improvement of catalyst durability in toluene photooxidation.

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.

We investigated the chemical transformation of low concentrations (∼100 ppm) of chlorofluorocarbons (CFCs) in gaseous nitrogen by nonthermal plasma processing by assuming that this transformation occurs by the dominant mechanism of CFC dissociation. The calculated and experimental results indicate that the extent of CFC dissociation induced by energy transfer from electronically excited species is negligible. We suggest that dissociation by impact with high-energy plasma electrons is the process mainly responsible for the decomposition of CFC. We also discuss the possibility of optimizing this plasma process for environmental engineering in the semiconductor industry.

Photocatalytic oxidation of CO to CO2 was carried out with TiO2 and Pt/TiO2 catalysts at room temperature to investigate the effect of Pt deposition. The rate for CO photooxidation by Pt/TiO2 was higher than that by TiO2. The reaction rate increased with incident light intensity to the power of 0.7 for Pt/TiO2 and 0.5 for TiO2. The dependency of reaction rate on the concentration of CO and water vapor was explained in terms of Langmuir−Hinshelwood mechanism, where CO was more efficiently adsorbed on Pt sites compared with TiO2. On the basis of diffuse reflectance FTIR spectroscopic studies and CO photodesorption measurements, Pt on TiO2 acted as the active sites on which CO was chemically adsorbed and oxidized to CO2 on photoirradiation in the presence of O2.

Decomposition of gas-phase benzene was investigated using plasma-driven catalyst (PDC) reactors packed with TiO 2 , Pt/TiO 2 or Ag/TiO 2 . A conventional BaTiO 3 packed-bed plasma reactor was also used for comparison purpose. The PDC reactors were found to be more effective in both aspects of energy efficiency and the reduction of undesirable reaction products compared to those with the conventional BaTiO 3 packed-bed plasma reactor. Catalytic activity on the benzene decomposition was in order of Ag/TiO 2 > TiO 2 > Pt/TiO 2 among the test materials. Silver (Ag) catalyst was also found to be effective in enhancing the CO 2 selectivity.

The determination of the absolute configuration of chiral molecules is an important aspect of molecular stereochemistry. Vibrational circular dichroism (VCD) is the extension of electronic CD into the infrared region where fundamental vibrational transitions occur. VCD has a number of advantages over all previous methods of absolute configuration assignment. The absolute configuration and predominant solution-state conformation in CDCl(3) of the chiral lactone, 5-formyl-cis,cis-1,3,5-trimethyl-3-hydroxymethylcyclohexane-1-carboxylic acid lactone, 1, obtained by the comparison of measured and calculated VCD spectra, are reported. It is found that (-)-1 corresponds to the absolute configuration (1S,3S,5R)-1.

Gas–solid heterogeneous photocatalytic decomposition of benzene, toluene, cyclohexane and cyclohexene over TiO 2 was studied at room temperature, and their reactivities were compared. Catalyst deactivation was ascribed to the formation of the carbon deposits on TiO 2 surface, and the formation and decomposition behavior of the carbon deposits affected the decomposition rate. Deactivated TiO 2 catalysts were photochemically regenerated in the presence of water vapor, and the carbon deposits were decomposed to CO x .

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.

The novel synthetic method for dioxa-azawurtzitanes to selectively cap amino groups in amino acids or peptides is described. Mixing the CH(3)CN solution of cis,cis-1,3,5-triformyl-1,3,5-trimethylcyclohexane (2) with the aqueous solution of the equimolar amounts of glycine and NaHCO(3) yields glycine-containing dioxa-azawurtzitane 7-Na. Dioxa-azawurtzitane 7-Na almost quantitatively isomerizes to lactone-imine 9-Na through the hydride-transfer rearrangement in CH(3)CN/H(2)O. Lactone-imine 9-Na also isomerizes to lactam-aldehyde 12-Na in DMSO.

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.

Pt/TiO2 was active for the oxidation of CO to CO2 in the dark at ambient temperature after UV irradiation. Pure TiO2 was inactive and the presence of Pt supported on TiO2 was indispensable for the reaction. Based on the ESR study, it was found that Pt deposited on TiO2 stabilized the O− and O3− species photoformed on the TiO2, and they were responsible for the CO oxidation.

Photocatalytic oxidation of benzene in gas phase was carried out with a flow reactor at room temperature. In a humidified airstream ([H2O] = 2.2%), benzene was quantitatively decomposed to CO2 over UV-irradiated 1.0 wt %-Pt/TiO2 catalyst. When the benzene conversion was decreased, the selectivity to CO2 was decreased, while that to CO was increased. As the amount of Pt loaded on the TiO2 catalyst was increased, the rate of the CO photooxidation was increased, while that of benzene photooxidation was almost unchanged. These findings showed that the photooxidation of benzene to CO2 over Pt/TiO2 catalyst proceeded by the two sequential steps: (i) benzene was decomposed to CO2 and CO with the selectivities of 94% and 6%, respectively, and (ii) CO was subsequently oxidized to CO2. The rate of CO photooxidation over Pt/TiO2 catalyst was greatly decreased by the presence of benzene in the reaction gas stream. The complete oxidation of benzene to CO2 could be also achieved by using the hybrid catalysts comprising pure TiO2 and platinized TiO2.

The performance of three different types of plasma reactors such as ferroelectric packed-bed (FPR), pulsed corona (PCR), and silent discharge (SDR) were compared in the decomposition of trichloroethylene (Cl/sub 2/C=CHCl, TCE), bromomethane (CH/sub 3/Br), and tetrafluoromethane (CF/sub 4/). Irrespective of reactors, hazardous air pollutant (HAP) reactivity in dry N/sub 2/ decreased in the order: TCE>CH/sub 3/Br>CF/sub 4/. Similar byproducts were obtained with any of the above reactors, and similar trends were observed in the HAP decomposition rate-retarding effect by water. Only for SDR, TCE decomposition was accelerated by O/sub 2/ in the background gas. The most plausible active oxygen species is considered to be the triplet oxygen atom. In the reaction systems where chemically induced decomposition of HAPs can occur, as in the case of TCE, PCR is expected to exceed FPR and SDR in performance. In the cases of CH/sub 3/Br and CF/sub 4/, residence time has been the most important factor governing their decomposition rates, and FPR and SDR have shown higher performance than PCR.

A hybrid system comprising a silent discharge plasma reactor (SDR) and manganese oxide (MnO/sub 2/) catalyst was used for the decomposition of benzene in air. The benzene conversion was greatly enhanced by combining MnO/sub 2/ with the SDR in the latter part. The MnO/sub 2/ catalyst decomposed benzene by using ozone (O/sub 3/) that was formed in the SDR as the oxidant precursor. With an increase in the amount of water vapor in air, the benzene conversion was decreased, due to the deactivation of high-energy electrons, the diminished formation of O/sub 3/ in SDR, and decreased activity of MnO/sub 2/ for the benzene oxidation with O/sub 3/. The only products of the reaction were CO/sub 2/ and CO. The carbon mass balance was not perfect due to the deposition of intermediates on MnO/sub 2/ during the reaction. The intermediates were subsequently decomposed to CO/sub 2/ and CO by MnO/sub 2/ in the presence of O/sub 3/. In dry air, the selectivities to CO/sub 2/ and CO were 70% and 30%, respectively, and were almost independent of specific energy density. The CO/sub 2/ selectivity was improved to 90% by humidifying the background air.

Nonthermal plasma chemical decomposition of bromomethane (CH3Br) was investigated with a coaxial type packed-bed plasma reactor. It has been demonstrated that plasma chemical processing is an effective approach to decompose CH3Br in a wide concentration range. It has been shown that CH3Br decomposition reactivity depends on reactor operating factors such as background gas, O2 concentration, and humidification. Higher decomposition efficiencies can be obtained in dry N2. However, organic byproducts such as BrCN are concurrently produced under deaerated conditions. Water suppresses CH3Br decomposition and also affects the yields of COx (CO and CO2) and organic byproducts due to the involvement of some active species generated from water. The presence of O2 retards CH3Br decomposition by quenching high-energy electrons, while it suppresses organic byproducts and improves COx yield. The reacted carbons in CH3Br are recovered as COx almost quantitatively in air. Higher CO2 selectivities cannot be achieved by increasing O2 concentration. NOx formation, which is accompanied by CH3Br decomposition, can be effectively suppressed by decreasing O2 concentration down to 2%. Furthermore, reaction mechanisms are discussed by comparing the reactivities of CH3Br and its congeners.

The proximity effect in the Swern oxidation of cis,cis-1,3,5-tris(hydroxymethyl)-1,3,5-trimethylcyclohexane (4) with TFAA was examined. The oxidation reaction of triol 4 with DMSO, TFAA, and relatively small amounts of triethylamine gave 5-formyl-cis,cis-1,3,5-trimethyl-3-hydroxymethylcyclohexane-1-carboxylic acid hemiacetal (7a) as well as 1,7,9-trimethyl-3,5,12-trioxawurtzitane (6), 5-formyl-cis,cis-1,3,5-trimethyl-3-hydroxymethylcyclohexane-1-carboxylic acid lactone (5), and polymers of cis,cis-1,3,5-triformyl-1,3,5-trimethylcyclohexane (2). Hemiacetal 7a underwent novel solvent-dependent conversions to hemiacetal 7b, lactone 5, or 1,7,9-trimethyl-2-oxo-3,5-dioxatricyclo[5.3.1.04,9]undecane (8) via 5-formyl-cis,cis-1,3,5-trimethyl-3-hydroxymethylcyclohexane-1-carboxylic acid. In the cases of relatively large amounts of triethylamine, trialdehyde 2 was given in moderate yield.

Photocatalytic decomposition of benzene over TiO2 in the gas phase at room temperature was studied with a fixed-bed flow reactor. In a humidified airstream ([H2O]=2.2%), benzene was efficiently decomposed to CO2 and CO with the selectivities of 93 and 7%, respectively. The selectivities were almost independent of the benzene conversion, indicating that CO is not the intermediate of CO2 in the reaction. The selectivity of CO was in the range of 7–10% with varying concentration of O2, H2O, and benzene. The formation of phenol and brownish carbonaceous matter attributable to polymeric products was observed on the catalyst surface. In the absence of O2, benzene oxidation did not proceed at all, showing that O2 is essential for the reaction. The presence of H2O not only suppressed the formation of the carbon deposits on the catalyst surface, but also accelerated the decomposition of them to CO2 and CO. Diffuse reflectance IR study showed that the presence of H2O regenerated the surface hydroxyl groups of TiO2 which were consumed in the photoreaction. With increase in the benzene concentration, the benzene conversion was decreased and the amount of carbon deposits on the catalyst surface was increased.

Power consumption and byproducts analysis are two key issues that users must address in determining which nonthermal plasma technology is the most appropriate for certain applications. We compared the operating characteristics and power consumption for scaled-up nonthermal plasma devices: pulsed-corona, packed-bed, silent corona, and surface discharge plasma technologies. Advantages and disadvantages of each nonthermal plasma technology are discussed. Understanding of plasma chemistry or byproducts is also essential for the development of nonthermal plasma technologies. Plasma chemical reactions of trichloroethylene (TCE) and alkyl acetates were investigated using pulsed-corona and packed-bed reactors. The effects of excited electrons, background gas, moisture, and reactor-dependent phenomena on product distribution and chemical interaction were studied. The initial step of plasma chemical decomposition of TCE can be ascribed to the electron attachment (not to active oxygen species or OH radicals), followed by homolysis and/or heterolysis reactions. Extremely high decomposition of TCE was obtained in nitrogen. Byproduct formation was significantly suppressed under aerated conditions. Alkyl acetate decomposition was affected by reactor type and alkyl chain length.