Complete Oxidation of Volatile Organic Compounds (Vocs) Using Plasma-Driven Catalysis and Oxygen Plasma

Kim et al. 46

Complete Oxidation of Volatile Organic Compounds (VOCs) Using Plasma-Driven Catalysis and Oxygen Plasma

H.H. Kim*, A. Ogata, S. Futamura National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

Abstract ⎯ The decomposition of volatile organic compounds (VOCs) was investigated using a flow-type plasma-driven catalysis (PDC) system and a cycled system. In the flow-type PDC reactor a trade-off relation was observed between the formation of nitrogen oxides and the decomposition of VOCs. Complete decomposition of VOC to CO2 was achieved with the cycled system without forming CO, aerosol, and any nitrogen oxides. The oxygen-partial pressure dependence of different catalysts on the decomposition of benzene and toluene was investigated. The influence of VOC concentration and the temperature of oxygen plasma on the equivalent energy in the cycled system will be also discussed.

Keywords ⎯ Nonthermal plasma, plasma-driven catalysis (PDC), VOC, oxygen plasma, enhancement factor

Ⅰ. INTRODUCTION factors to be solved before the industrial use of the NTPs for the abatement of VOCs are the reduction of energy Volatile organic compounds (VOCs) have high vapor consumption (i.e. high energy efficiency), less NOx pressure under normal conditions, so they can be easily formation) and good material balance. One of the vaporized into the atmosphere. Two important VOCs- remarkable recent trends in the NTP application for air related environmental issues in urban area are the pollution control is the combination of NTP with catalyst photochemical smog and the secondary aerosol in either configuration of single-stage [6-8] or two-stage formation. Many of VOCs are known as carcinogenic, [9-11]. The authors have been investigated the teratogenic and mutagenic. The key driving force of decomposition of VOCs using a plasma-driven catalysis environmental market is the environmental policy of (PDC) system, and demonstrated the effectiveness of the government (i.e. policy-driven market) rather than PDC in terms of energy efficiency, product selectivity technology or demand (technology/demand-driven and carbon balance [12-15]. market). Emission standards and regulations are getting Table 1 summarizes the differences between the stringent in many countries over the world. There is, conventional NTP alone processes and the PDC system. therefore, an urgent need to develop more effective and Both the plasma alone and the PDC system are not inexpensive techniques for the treatment of VOCs. influenced by gas hourly space velocity (i.e. residence In Japan, new regulation of VOC emission has been time) because the characteristic time of plasma chemical started in April 2006 to achieve 30% reduction of the reactions is usually much more shorter than the gas total VOCs emission by 2010 compared to that of 2000 residence time. One important characteristics of the PDC (1.85 million tons/ year). More accelerated movements system that we focused on in this work is the influence of towards the reduction of toxic chemicals have been oxygen partial pressure on the decomposition efficiency noticed by European Union (EU, REACH; registration, [16]. In contrast to the plasma alone processes, the evaluation and authorization of chemicals) and United decomposition efficiency of VOC linearly increased with Nations (UN, GHS; globally harmonized system of oxygen partial pressure in the PDC reactor packed with 2 classification and labeling of chemicals). The upcoming wt% Ag/TiO2 catalyst. In addition to the decomposition new regulations of REACH may bring out big change on efficiency, the selectivity of CO2 also remarkably many industrial fields (especially for chemical industry) enhanced with oxygen partial pressure. On the other over the world. Generally, the approaches toward the hand, this strong influence of oxygen partial pressure on pollution control can be divided into two major groups of the decomposition efficiency of VOC is not observed in source reduction and end-of-pipe (EOP) treatment. The the NTP alone processes regardless of the type of plasma source reduction includes the modification of process, reactors [17-19]. Based on the highly oxygen partial changing chemicals to safer ones, and recycling before pressure-dependent property of the PDC system, a cycled they are released to the open air. While the source system of adsorption and the decomposition of adsorbed reduction approach is expected to be main stream in the VOCs using oxygen plasma has been proposed. The future, significant time and investments will be required expected advantages of this cycled process include high to meet the stringent upcoming regulations through the energy efficiency, high CO2 selectivity and no formation source reduction technology alone. From a practical of nitrogen oxides. viewpoint, the EOP treatment is more reasonable way to In this work, the decomposition of benzene and toluene meet the environmental goals at present stage. was investigated using a flow-type PDC reactor and a The nonthermal plasmas (NTPs) have been cycled system. The oxygen partial pressure-dependent investigated for the removal of a wide range of air characteristics of different catalysts (~ 4 wt% Ag/TiO2 pollutants during the last two decades [1-5]. Three key and 0.5 wt% Pt/γ-Al2O3) were evaluated using a new parameter of enhancement factor. The optimum range of Corresponding author: Hyun-Ha Kim plasma-catalyst process according to the gas flow rage e-mail address: [email protected] and the concentration of VOCs will be also discussed. Originally presented at ISNTPT-5, June 2006 Revised: October 29, 2006, Accepted: January 23, 2007 47 International Journal of Plasma Environmental Science & Technology Vol.1, No.1, MARCH 2007

Plasma TABLE 1. Catalyst COMPARASION OF THE NTP ALONE AND THE PDC VOCs CO2, H2O Parameter Plasma alone PDC

First-order Zeroth-order Kinetics* η (%) = (-exp-{1 k ⋅SIE)} k E ⋅SIE E η (%) = ×100 (a) Flow-type PDC system C ×100 0 Adsorption mode GHSV No influence No influence Adsorbent/Catalyst O2 content No influence Large influence VOCs Clean gas Carbon balance Poor Good Aerosol Yes No IP vs DRE Highly related Unrelated

* The rate constant kE is referred to as energy constant. The unit for first-order and zeroth-order are LJ-1 and Cycled operation ppm·J-1L, respectively. Regeneration mode

Oxygen Ⅱ. EXPERIMENTAL CO , H O A. Reactor and Method 2 2

Figure 1 shows the conceptual diagrams of (a) the (b) Cycled system flow-type PDC reactor and (b) the cycled system for the complete destruction of VOCs. In the flow-type PDC Fig. 1. Schematic diagram of (a) the flow-type PDC reactor reactor, catalysts are packed inside the reactor and and (b) the cycled system for the total destruction of VOCs. In directly activated by a plasma application. There is a the cycled system plasma is only applied in the regeneration trade-off relation between the degree of VOCs mode, but not in the adsorption mode decomposition and the NOx formation. So the All the used catalysts were pellet type and their size were determination of the maximum applicable specific input in range of 1.6 mm – 3.2 mm. Benzene and toluene were energy (SIE) is important in the flow-type PDC reactor. used as model compounds of VOCs. Their On the other hand, nitrogen oxides are formed in the concentrations were adjusted by changing either the cycled system because the plasma is only turned on temperature of water bath or the N flow rate purging the under oxygen environment. The cycled process is based 2 bubbler. Temperature was measured near the plasma on the highly oxygen content-dependent behavior of the zone at the outlet of the reactor using a fiberoptic PDC system for the decomposition of benzene [16]. In thermometer (Anrits Co., AMOTH FX 8500). The the adsorption mode, VOCs was removed by adsorption temperature sensor was covered with insulating materials, without plasma application. When the catalyst bed which enables us to avoid interruption during the reached a saturated adsorption, then the catalyst bed temperature measurement. purged with oxygen before applying oxygen plasma to decompose the adsorbed VOCs. For the measurement B. Electrical Measurement purpose, the regeneration mode was operated with oxyge flow of 5~8 L/min. A small additional PDC reactor was Discharge power of the PDC reactor was measured set downstream of the main PDC reactor to decompose using the automated V-Q Lissajous program (Insight Co. the desorbed VOC just after the O plasma was turned on. 2 ver 1.71) [15]. A condenser (about 100 nF) was In practical case, it will be beneficial to operate the connected in series to the ground line of the plasma regeneration mode in closed system after purging the reactor. The charge Q (i.e. time-integrated current) was catalyst bed with oxygen. Since the main goal of the measured with a 10:1 voltage probe. Specific input current work is to find the dependence of various energy (P/Q ) is the ratio of discharge power (P in watt) catalysts on the oxygen partial pressure, most of the f dis to gas flow rate (Q in L/min). experiments were done with the flow-type PDC reactor f at 100 oC. The flow-type system consisted of the PDC P (J/L) SIE (J/L) dis ×= 60 (1) reactor (quartz tube of 13 mm in inner diameter and Q 200 mm in effective length), AC power supply, and f measurement system. In the case of cycled system, the In the case of the cycled operation equivalent specific adsorption mode was operated at room temperature. The input energy (SIEeq) was introduced to evaluation the regeneration mode was operatured at room temperature energy consumption. or 100 oC to see the temperature influence on the energy T )(P Avedis Oxy (2) efficiency. A Fourier transform infrared (FITR) SIEeq (J/L) ××= 60 )(Q T spectrometer (Perkin Elmer, Spectrum One) was used for Ads f Ads the gas measurements of both the reactants and products. Kim et al. 48

200 250

PDC reactor (1% Ag/TiO2) C) Benzene o 200 150

150 100 100 20%O -N 2 2 202 ppm (1%-Ag/TiO ) 50 2 20%O2-He 50 110 ppm (1%-Ag/TiO2)

60 ppm (1%-Ag/TiO2) Reactor outlet temperature ( temperature outlet Reactor

0 (ppm) benzene amount of Removed 0 0 50 100 150 200 250 0 100 200 300 Specific input energy (J/L) Specific input energy (J/L) 200 Fig. 2. Temperature increase in the PDC reactor as a function of Toluene specific input energy. 150 Here, (Pdis)Ave and (QAds)f indicate the average discharge power of oxygen plasma for the decomposition of adsorbed VOC and gas flow rate during the adsorption, 100 respectively. TOxy and TAds indicate the period of oxygen plasma and adsorption, respectively. 101 ppm (2%-Ag/TiO ) 50 2 145 ppm (2%-Ag/TiO ) Ⅲ. RESULTS AND DISCUSSION 2 150 ppm (0.5%-Pt/γ-Al O ) 2 3

Figure 2 shows the temperature increase as a function (ppm) amount of toluene Removed 0 of SIE at the outlet of PDC reactor packed with 1 wt% 0 100 200 300 Specific input energy (J/L) Ag/TiO2 catalysts. The real gas temperature inside the PDC reactor depends on the SIE and the position. There was a temperature gradient along with the flow direction, Fig. 3. The influence of VOCs concentration on their so the maximum temperature was measured at the outlet decomposition using flow-type PDC reactors. of the PDC reactor. The temperature data shown in Figure 2 indicate the maximum temperature found in the flow-type PDC reactors. As long as the NTP is applied in PDC reactor. A good linear function was obserbed air-like mixtures, the formation of NxOy is unavoidable between the temperature increase and the SIE. [20-22]. Although the flow-type PDC system can decompose 200 ppm of benzene or more, for example, complete conversion of VOCs is counterbalanced by the [Temp]outlet = [Temp]inlet + 0.35[SIE] (3) formation of nitrogen oxides. As was aslo reported on the Helium dilution test exhibited almost the same trend with decomposition of halomethanes using BaTiO3 packed bed reactor [23], the type of VOCs or the catalysts had the N2 dilution case. Considering the thermal no influence on the formation of NO and N O. In both decomposition of benzene on the Ag/TiO2 catalyst starts 2 2 above 200 oC [13], it is quite clear that the thermal cases of benzene and tolene, the formation of NO2 catalytic reaction play a minor role in the PDC reactor. increased qudratically, while the N2O exhibited a linear Figure 3 shows the decomposition of benzene and increase. The formation of NO2 became significant as the toluene using the flow-type PDC reactors. The SIE became larger than about 100 J/L. This observation decomposed amounts of benzene was found to be indicates that the flow-type PDC reactor should be determined by the SIE regardless of its inlet operated at SIE below about 100 J/L to suppress the concentration. Benzene of 110 ppm was completely formation of nitrogen oxides. The concentration of VOCs decomposed with about SIE of 120 J/L. The (benzene and toluene), which can be removed by the decomposition of toluene also showed a similar trend PDC reactors with SIE of about 100 J/L, may range with the benzene case. The inlet concentration had little below 100 ppm. Judging from the experimental results in influence on the decomposed amount of toluene. The key Figs 3 and 4 in terms of decomposition efficiency of factor determining the decomposed amount of tolune was VOC and the formation of nitrogen oxides, the optimum SIE. These simple relationship between the SIE and the concentration region of the flow-type PDC system ranges removed amount of VOCs render the SIE as designing below about 100 ppm. and scaling parameter of the PDC system. When the type Figure 5 shows the influence of oxygen partial and the concentration of VOC are given, one can easily pressure on the decomposition of benzene and toluene grasp how much energy is necessary to decompose it using the PDC reactors packed with different catalysts. using the flow-type PDC system. In the case of benzene removal using the TiO2 catalysts the decomposition efficiency increased linearly with Figure 4 shows the formation of NO2 and N2O during the decomposition of benzene and toluene using the oxygen partial pressure regardless of the loading amount 49 efficiency of VOCwith respect toO enhancement factoristh for the cycled system. Thephysicalmeaning ofthe ofcatalyst the potential the higher larger theEF value, Since the cycledsystem is efficiency of VOCs in oxygen andin air, respectively. decomposition ofbenzeneusingcycled system. the the cycledsystem. a very important factor determining the performance of indicate that theselection of catalyst having a large EF is decomposition was about 6.7. These results clearly the O the efficiency to respect VOC with of ofdecomposition ratio system. Theenhancement factor (EF) is defined as the cycled catalyststhe each for of potential the evaluate to pressure. An enhancement factor was newly introduced partial the with oxygen was increased also toluene degree of enhancement, the Although wt%). Ag(0~4 of Fig. 4. Formation of NO factor Pt/ factor with the benzene and toluene, respectively. Theenhancement catalyst were100 and 61 for the decomposition of given SIE. The enhancemen toluene (150 ppm). PDCreactors;(a)benzene (200using flow-type ppm),(b) Here, Figure 6 shows the required energy required thecomplete the for Figure 6 shows Concentration (ppmv) Concentration (ppmv) 120 150 120 150 30 60 90 30 60 90 2 0 0 ata rsuea h aeSE pressureatthepartial same SIE. EF = η 0 0 Oxygen Oxygen Oxygen2 and 2.0 % 2.0 % 1.0 % 0.5 % 0.3 % 0.1 0.5%-Pt/ 0 % 0 0.5%Pt/ 2% Ag/TiO Specific input energy input Specific (J/L) Specific input energy (J/L) energy input Specific − γ η ηη 2 100 100 -Al andN Air Air γ Ag/TiO γ -Al 2 O -Al ][O-][O indicate the decomposition indicatethe decomposition 2 3 Air2 2 O operated in pure oxygen, the the oxygen, in pure operated 2 e slope of decomposition decomposition of slope e 3 2 O 2 decomposition effciency of t factors with the Ag/TiO the with factors t × there was difference inthe O in the VOCs decomposition 3 catalystfortoluene 100 International (4) 2 partial pressure at partialpressure a 200 200 NO N Journal N 2 2 NO O 2 O 2 (b) (a) 300 300 of Plasma 2

higher the benzene concentration, the larger theSIE The concentration. inlet onthe largely depended benzene nbt ae. in bothcases. catalysts. Adsorption mode was operated at room temperature decomposition of (a) benzene and (b)toluene. system. TheSIE conventional NTPalone proce the PDC system [10, 11]. In the zeroth-order kinetics, the the kinetics, 11]. system zeroth-order PDC [10, the the In results can be explained by the zeroth-order kinetics of the complete decomposition of adsorbed benzene. These benzene to CO Oxygen plasma completely oxidized the adsorbed benzene using the cycled sy Fig. 6. Therequired energy for the complete decomposition of Fig. 5. The influence of O Environmental Decomposition efficiency (%) SIEeq (J/L) Toluene decomposition efficiency (%) 100 100 25 50 75 100 200 300 400 40 60 80 20 0 0 0 0 204060801000 0 Science 04 60 40 20 eq Oxygen partial pressure (%) 2 Oxygen partial pressure(%) , which is impossible the, isimpossible with which Benzene concentration (ppm) forthe decomposition ofadsorbed 2wt%Ag/TiO (120 J/L) & 100 Technology 2 stem with2.0 wt% Ag/TiO 2 sses or thesses orflow-typePDC partial pressure on the Vol.1, 100 RT 0.5wt%Pt/ 200 Ag 4.0% (136 J/L) Ag 4.0% (168 J/L) Ag 2.0% (169 J/L) Ag 1.0% (165 J/L) Ag 0.5% (158 J/L) Ag 0.3% (158 J/L) Ag 0.1% (194 J/L) 0% Ag (120 J/L) o No.1, C Ag/TiO γ -Al 0100 80 MARCH 2 2 O 3 (b) (a) 300 eq 2007 for

Kim et al. 50

10,000 NTP process. Since the NTP is an energy-dependent Thermal Oxidation Adsorption process, the overall efficiency is mostly determined by + the energy input to the system rather than the residence Thermal/CAT Oxidation time (i.e. reactor size). Therefore, the [C] is more 1,000 Catalytic Oxidation Condensation important factor than the Qf in the plasma process. The Biofiltration upper concentration limit may depend on the gas flow rate, the type of VOCs, and NOx formation as well. Up Adsorption to medium scale application, NTP process can be applied 100 for the three-digit concentration (roughly less than 200 Nonthermal ppm). At large scale, where the flow rate exceeds about

Concentration (ppm) Concentration 3 Afterburner Plasma 200 m /min, the optimum concentration may be reduced 10 to two-digit range. In contrast to the important role of

10 100 1,000 catalyst type on the CO2 selectivity, the type of catalyst 3 had little influence on the decomposition efficiency in Gas flow rate (m /min) the flow-type PDC reactors [12]. On the other hand, the Fig. 7 Flow rate (Qf) versus concentration map for the optimum cycled system is expected to have higher concentration range of nonthermal plasma for the control of VOCs. The ● limit than that of the flow-type PDC system due to the marks in the figure indicate the data of the commercialized adsorption. This adsorption step may also render the plasma-catalyst systems for the removal of VOC and odor. cycled system effective because there is a large variation of VOCs concentration over the operation period in amount of VOC decomposition is determined by SIE many chemical facilities. rather than the concentration of benzene. These observations indicated that the cycled system is more effective in treating dilute VOCs than the high Ⅳ. CONCLUSION concentration. Our preliminary data indicated that the SIEeq to achieve complete decomposition of 60 ppm and The decomposition of benzene and toluene has been 205 ppm benzene were about 150 J/L and 310 J/L, investigated using the flow-type PDC reactor and the respectively. It should be noted that these values are the cycled system. The key findings in this study can be required energy for the total oxidation of benzene to CO2, summarized as follows. which is impossible with the flow-type PDC reactors. 1) The outlet temperature of the PDC reactor linearly One of the reasons for the larger SIEeq compared to that increased with the specific input energy. of the SIE with the flow-type PDC reactor is the use of 2) In the case of flow-type PDC reactors, a trade-off additional PDC reactor used in the regeneration mode relation was found between the formation of nitrogen [16]. This additional PDC reactor will not be necessary if oxides and the decomposition of VOCs. The the regeneration mode is operated in closed system, formation of NOx limits maximum applicable which may lead to the reduction of energy consumption. specific input energy to about 100 J/L in the Temperature during the regeneration mode did not affect flow-type PDC system. Therefere, the application of the SIEeq within the tested conditions. The data obtained o the flow-type PDC system may be limited to the at room temperature and 100 C fell on single line. processing of dilute VOCs (concentrations below 100 Further reduction of SIEeq can be possible by optimizing ppm). the plasma parameters of the regeneration mode and the 3) In the cycled system, the energy required for the use of proper adsorbent/catalyst. The key factor for the complete oxidation of benzene increased with the further enhancement and optimization of the cycled inlet concentration. The type of catalyst largely affect system is to seek proper catalyst materials having large the EF. Temperature did not influence on the required enhancement factor as well as a large adsorption energy of the oxygen plasma for the complete capability. decomposition of benzene. For practical point view, it is very important to know 4) The feasible Qf–[C] map of NTP technology was the advantages and the limitations of different VOCs presented based on the data of current study and the control technologies for the selection of best method for commercialized facilities. The energy-dependent a given condition. Figure 7 shows the cost-effective and characteristic of the NTP process may widen the technically feasible Q –[C] ranges for the major VOCs f optimum range of Qf, but limit the concentration. For control technologies together with the NTP technology. large-scale application, the optimum concentration The fundamental framework of this Qf–[C] map is based may reduced to 2-digit range. on the data reported by Dyer and Mulholland in 1994 [24], and later it was extended to the halogenated VOCs [25]. The solid circles in the figure indicate the ACKNOWLEDGMENT commercialized plasma-catalyst facilities in Japan. It is clear from the figure that each technology has This work was partly support by MEXT; Grand-in-Aid advantages and drawbacks according to the flow rate and for Young Scientist (A) (16681007). concentration. Generally, gas residence time is an important parameter determining the degree of removal REFERENCES efficiency in most of chemical reactors, so do in the [1] A. Mizuno, J. S. Clements, and R. H. Davis, "A method pollution control devices shown in Figure 7 except for for the removal of sulfur dioxide from exhaust gas 51 International Journal of Plasma Environmental Science & Technology Vol.1, No.1, MARCH 2007

utilizing pulsed streamer corona for electron energization," [14] H. H. Kim, A. Ogata, and S. Futamura, "Atmospheric IEEE Trans. Ind. Applicat., vol. 22, pp. 516-522, 1986. plasma-driven catalysis for the low temperature [2] L. A. Rosocha and R. A. Korzekwa, "Advanced oxidation decomposition of dilute aromatic compounds," J. Phys. D: and reduction processes in the gas phase using Appl. Phys., vol. 38, pp. 1292-1300, 2005. non-thermal plasmas," J. Adv. Oxid. Technol., vol. 4, pp. [15] H. H. Kim, A. Ogata, and S. Futamura, "Effect of 247-264, 1999. different catalysts on the decomposition of VOCs using [3] T. Yamamoto, K. Ramanathan, P. L. Lawless, D. S. Ensor, flow-type plasma-driven catalysis," IEEE Trans. Plasma J. R. Newsome, N. Plaks, and G. H. Ramsey, "Control of Sci., vol. 34, pp. 984-995, 2006. volatile organic compounds by an ac energized [16] H. H. Kim, S. M. Oh, A. Ogata, and S. Futamura, ferroelectric pellet reactor and a pulsed corona reactor," "Decomposition of gas-phase benzene using IEEE Trans. Ind. Applicat., vol. 28, pp. 528-534, 1992. plasma-driven catalyst reactor: Complete oxidation of [4] C. M. Nunez, G. H. Ramsey, W. H. Ponder, J. H. Abbott, adsorbed benzene using oxygen plasma," J. Adv. Oxid. L. E. Hamel, and P. H. Kariher, "Corona destruction: An Technol., vol. 8, pp. 226-233, 2005. innovative control technology for VOCs and air toxics," J. [17] Z. Falkenstein, "Effects of the O2 concentration on the Air & Waste Manage. Assoc., vol. 42, pp. 242-247, 1993. removal efficiency of volatile organic compounds with [5] H. H. Kim, "Nonthermal plasma processing for air dielectric barrier discharges in Ar and N2," J. Appl. Phys., pollution control: A historical review, current issues, and vol. 85, pp. 525-529, 1999. future prospects," Plasma Process. Polym., vol. 1, pp. [18] C. Fitzsimmons, F. Ismail, J. C. Whitehead, and J. J. 91-110, 2004. Wilman, "The chemistry of dechloromethane destruction [6] A. Ogata, K. Yamanouchi, K. Mizuno, S. Kushiyama, and in atmospheric-pressure gas streams by a dielectric T. Yamamoto, "Decomposition of benzene using packed-bed plasma reactor," J. Phys. Chem. A, vol. 104, alumina-hybrid and catalyst-hybrid plasma reactors," pp. 6032-6038, 2000. IEEE Trans. Ind. Applicat., vol. 35, pp. 1289-1295, 1999. [19] H. R. Snyder and G. K. Anderson, "Effect of air and [7] A. Rousseau, O. Guaitella, L. Gatilova, F. Thevenet, C. oxygen content on the dielectric barrier discharge Guillard, J. Ropcke, and G. D. Stancu, "Photocatalyst decomposition of chlorobenzene," IEEE Trans. Plasma activation in a pulsed low pressure discharge," Appl. Phys. Sci., vol. 26, pp. 1695-1699, 1998. Lett., vol. 87, pp. 221501, 2005. [20] A. Rousseau, A. Dantier, L. Gatilova, Y. Ionikh, J. [8] K. Hensel, Y. Matsui, S. Katsura, and A. Mizuno, Ropcke, and Y. Tolmachev, "On NOx production and "Generation of microdischarges in porous materials," Czec. volatile organic compound removal in a pulsed microwave J Phys., vol. 54, pp. C683-C689, 2004. discharge in air," Plasma Sources Sci. Technol., vol. 14, pp. [9] H. Einaga and S. Futamura, "Catalytic oxidation of 70-75, 2005. benzene with ozone over alumina-supported manganese [21] Y. Ionikh, A. V. Meshchanov, J. Ropcke, and A. oxides," J. Catal., vol. 227, pp. 304-312, 2004. Rousseau, "A diode laser study and modeling of NO and [10] Y. Xi, C. Reed, Y. K. Lee, and S. T. Oyama, "Acetone NO2 formation in a pulsed DC air discharge," Chem. Phys., oxidation using ozone on managanese oxide catalysts," J. vol. 322, pp. 411-422, 2006. Phys. Chem. B, vol. 109, pp. 17587-17595, 2005. [22] U. Kogelschatz and P. Baessler, "Determination of [11] K. P. Francke, H. Miessner, and R. Rudolph, "Cleaning nitrous oxide and dinitrogen pentoxide concentrations in of air streams from organic pollutants by plasma-catalytic the output of air-fed ozone generators of high power oxidation," Plasma Chem. Plasma Proc., vol. 20, pp. density," Ozone Sci. Eng., vol. 9, pp. 195-206, 1987. 393-403, 2000. [23] A. M. Harling, J. C. Whitehead, and K. Zhang, "NOx [12] H. H. Kim, H. Kobara, A. Ogata, and S. Futamura, formation in the plasma treatment of halomethanes," J. "Comparative assessment of different non-thermal plasma Phys. Chem. A, vol. 109, pp. 11255-11260, 2005. reactors on energy efficiency and aerosol formation from [24] J. A. Dyer and K. Mulholland, "Toxic air emissions what decomposition of gas-phase benzene," IEEE Trans. Ind. is the full cost to your business?," Chemcial Engineering, Applicat., vol. 41, pp. 206-214, 2005. vol. Feb., pp. 4-8, 1994. [13] H. H. Kim, S. M. Oh, A. Ogata, and S. Futamura, [25] R. A. Keller and J. A. Dyer, "Abating halogenated "Decomposition of gas-phase benzene using VOCs," Chemical Engineering, vol. Jan, pp. 100-105, plasma-driven catalyst (PDC) reactor packed with Ag/TiO2 1998. catalyst," Appl. Catal. B: Environ., vol. 56, pp. 213-220, 2005.