Dong Jun Koh

Oxidation of elemental mercury using atmospheric pressure non-thermal plasma

The oxidation of gas phase elemental mercury (Hg0) by atmospheric pressure non-thermal plasma has been investigated at room temperature, employing both dielectric barrier discharge (DBD) of the gas mixture of Hg0 and injection of ozone (O3) into the gas mixture of Hg0. Results have shown that the oxidative efficiencies of Hg0 by DBD and the injection of O3 are 59% and 93%, respectively, with energy consumption of 23.7 J L(-1). This combined approach has indicated that O3 plays a decisive role in the oxidation of gas phase Hg0. Also the oxidation of Hg0 by injecting O3 into the gas mixture of Hg0 proceeds with better efficiency than DBD of the gas mixture of Hg0. These results have been explained by the incorporation of the competitive reaction pathways between the formation of HgO by O3 and the decomposition of HgO back to Hg0 in the plasma environment.

Structure of MnZr mixed oxide catalysts and their catalytic properties in the CO hydrogenation reaction

MnZr oxide catalysts with varying MnZr ratio were prepared by a coprecipitation method. Their structure and catalytic properties were studied by means of N2 adsorption, XRD, TPR, and CO hydrogenation as a probe reaction. The precipitated MnZr mixed oxide was composed of a mixture of large particles of manganese oxide and small particles of zirconium oxide. Addition of Mn retarded the growth of fine particles of zirconium oxide. By calcination at high temperature, part of the manganese oxide forms a solid solution with zirconium oxide and deposits on the surface of zirconium oxide as a thin layer. The type of Mn present in the mixed oxide affected the selectivity pattern in the CO hydrogenation. The bulk Mn exhibited a high selectivity to isobutene, but products contained hydrocarbons higher than C5. Mn dispersed on the surface of zirconium oxide showed a similar selectivity pattern to bulk Mn, but hydrocarbon chain growth was limited to C4 or lower. The formation of a solid solution enhanced production of lower hydrocarbons, especially methane.

Removal mechanism of elemental mercury by using non-thermal plasma.

The removal mechanism of elementary mercury (Hg(0)) by non-thermal plasma (NTP) has been investigated, where dielectric barrier discharge and O(3) injection methods as oxidation techniques are employed, together with the analysis of mercury species deposited on the reactor surface using temperature-programmed desorption and dissociation (TPDD) and scanning electron microscopy-energy dispersive spectroscopy. The removal of Hg(0) by NTP is found to be time-dependent and proceed through three domains; the Hg(0) concentration just slightly decreases as soon as NTP is initiated and then becomes constant for several minutes (Region 1), thereafter starts to decrease rapidly for 1h (Region 2) and, after passing fall-off region, very slowly decreases for about 4h (Region 3). The deposited mercury species on the reactor surface were conglomerated like islands, rather than dispersed uniformly, and their ratio of Hg(0) to O composition is observed to be 1:2. Additionally, the new peak in TPDD spectra observed in the region of 260-380°C is proposed as HgO(3). These results lead us to conclude that the deposited mercury species by NTP have extra O atoms to oxidize the adsorbed Hg(0), resulting in the acceleration of removal rate as the oxidation of Hg(0) proceeds.

Effect of the catalyst supports on the removal of perchloroethylene (PCE) over chromium oxide catalysts

The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on TiO2, Al2O3, SiO2, SiO2–Al2O3 and activated carbon. The phase of chromium oxide on the catalyst surface is critical for the oxidation of PCE. The catalytic activity of PCE removal enhances as the formation of Cr(VI) species on the catalyst surface increases. The surface area and the type of the catalyst supports were also essential for high performance in the PCE oxidation. In addition, the structure of Cr(VI) on the catalyst surface also plays an important role for the decomposition of PCE. The polymerized Cr(VI) mainly formed by the interaction of metals with the support is the active reaction site for the present reaction system. CrOx/TiO2 reveals the strongest PCE removal activity among the catalysts examined in the present study.

Low temperature oxidation of CO over supported PdCl2-CuCl2 catalysts

PdCl2-CuCl2 catalyst supported on activated carbon was examined for the low temperature oxidation of CO. The catalyst developed in the present study was active and stable at ambient conditions if water were existing in the feed gas stream. The addition of Cu(NO3)2 into the PdCl2-CuCl2 catalyst significantly enhanced the CO oxidation activity. X-ray diffraction study revealed that the role of Cu(NO3)2 was to stabilize active Cu(II) species, Cu2Cl(OH)3, on the catalyst surface which maintains the redox property of palladium. When HC1 and SO2 were also existing in the feed, they easily inactivated the catalyst. It was found that HC1 and SO2 inhibited the formation of active Cu(II) species on the catalyst surface.

A pilot plant study for selective catalytic reduction of NO by NH3 over mordenite-type zeolite catalysts

Abstract The copper-ion-exchanged synthetic mordenite and natural zeolite catalysts washcoated on a honeycomb reactor have been examined in a pilot plant for the selective catalytic reduction of NO by NH 3 . The catalyst life and the cause of the catalyst deactivation were mainly investigated for the design of the commercial reactor to remove NO x from a sintering plant at the steel mill.

Preparation and Fischer—Tropsch reaction of highly-reduced cobalt clusters in cobalt-exchanged zeolite

Abstract Impregnation of 3–5 M NaOH solution into cobalt ion-exchanged Y zeolite using the incipient wetness method enables the preparation of highly reduced cobalt clusters entrapped inside zeolite pores after the catalyst is reduced with hydrogen gas. TEM and ferromagnetic resonance experiments reveal that the cobalt clusters are extremely small and uniform in size. Reaction measurements on these catalysts show an enhanced production of linear forms of hydrocarbons such as 1-olefins and n-paraffins. The catalysts also exhibit a bimodal distribution in the selectivity pattern in which one maximum is observed at C6 with another at C16. The formation of high-order linear hydrocarbons above C10 is attributed to an increased chance for the chain growth owing to a hold-up effect of reaction intermediates, especially 1-olefins, which are accumulated deep inside zeolite pores during the reaction. The accumulated amount of hydrocarbon products, ranging from C1–C18, was found to be 2.3×10−3 mol/g cat (about 10 vol.% of total pore volume in zeolite crystallite when the average density is assumed to be that of C12) after reaction for 10 h. The formation of hydrocarbon isomers is related with acidic sites on the exterior surface of the zeolite particle.

Preparation of zeolite-entrapped iron clusters by alkali injection followed by reduction with dihydrogen gas

An alkali injection method was used to promote the formation of reduced iron clusters in zeolite Y. By injecting NaOH solution into the pores of iron ion-exchanged zeolite, the iron ions were exchanged back with the injected sodium ions to be precipitated as hydroxide forms. Reduction of these precipitates in hydrogen gas yielded reduced iron clusters inside the zeolite. All preparation procedures should be performed under oxygen-free atmosphere since the reexchange of the injected sodium ions with Fe3+ ions was much more difficult than that with the Fe3+ ions. Mössbauer spectra and ferromagnetic resonance spectra of the reduced catalysts revealed that the iron clusters were extremely small and uniform in size.

Average 120-kW MPC modulator for plasma de-NO/sub x//de-SO/sub x/ system

The pulsed corona discharge process shows the encouraging results for the removal of NO/sub x/ and SO/sub x/ gases based on small-scale experiments. The lifetime and the reliability of the system are major difficulties to realize this newly developed technology because the downtime for maintenance affects the plant availability. The combination of a high power solid-state switch with a magnetic pulse compressor (MPC) is a suitable scheme to meet these requirements. An average 120-kW MPC modulator has been constructed and tested with a plasma reactor for an industrial incinerator plant. The plasma reactor has wire-plate electrodes and can treat the gas of 50000 Nm/sup 3//Hr. This modulator can generate 150 kV pulses with 500 nsec (FWHM) pulse width, and 300 Hz repetition rate. This paper presents design details and the operational characteristics of the MPC modulator.