The effect of the reactor configuration and several key parameters such as the gas temperature, humidity, and flow rate on the corona discharge plasma in honeycomb monoliths was investigated. The AC ...corona discharge-based plasma reactor consisted of two parallel electrodes (perforated disk/wire-mesh) placed at both ends of the honeycomb monolith. Although the wire-mesh electrode offers increased sharpness, the perforated disk electrode, where the corona discharge started at the sharp edges of the holes, produced more discharge power because of the larger effective electrode area. Loading a small amount of metal onto the monolith was found to increase the discharge power significantly. Coating the monolith with a zeolite such as ZSM-5 (Si/Al: 23.9) led to a decrease in the discharge power because of its hydrophobic nature and large surface area. The result also revealed that the operating temperature, the humidity of the feed gas, and the gas velocity were key factors affecting the discharge performance. The discharge power was inversely proportional to the temperature. On the other hand, the use of a high-velocity feed gas with high water vapor content was found to be particularly advantageous for obtaining high discharge power.
Display omitted
•A honeycomb plasma reactor for practical-environmental applications.•Successful generation of large-volume air plasma in commercial monoliths.•Enhancing discharge power by metal-coating over commercial monolith.•Increase in discharge power with increasing either air flow rate or humidity.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The removal of NO x over a Ag/γ-Al2O3 catalyst coupled with gliding arc plasma at low temperatures is demonstrated. Specifically, n-heptane (the reducing agent) was pretreated by exposure to gliding ...arc plasma (the outlet gas temperature of 73.4 °C) before injecting into the simulated diesel exhaust gas and passing it through the catalyst zone. As a result of the plasma treatment, the feed gas consisted of oxygenated hydrocarbons (OHCs), which serve as reducing agents, instead of only n-heptane without plasma treatment. Consequently, the NO x removal efficiency increased substantially by approximately 10% at temperatures of 165–225 °C owing to the presence of the OHCs. The dependence of the NO x removal efficiency on typical reducing agents was examined; these results agreed with our hypothesis that aldehyde derivatives were more effective than the parent compound (n-heptane) for NO x removal at low temperatures. However, enhancement of the NO x removal efficiency after plasma pretreatment was not observed at high plasma discharge power. This is because NO x is formed from the air and a significant amount of n-heptane is completely oxidized to CO2 when the gliding arc plasma is operated at high power. Besides, the plasma treatment of n-heptane did not improve the NO x removal under high operating temperature conditions at which the catalyst itself exhibits high catalytic activity. This led us to surmise that boosting the effectiveness of the OHCs generated during plasma pretreatment would require the ratio of the exhaust gas flow rate to the reducing agent flow rate to be high, which is challenging to realize in laboratory-scale experiments. This method would lower the energy consumption of the plasma stage.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
The high removal efficiency of NO x from diesel engine exhaust gas at low temperatures remains challenging due to the poor activity of catalysts under this condition. This work investigated the ...effectiveness of gliding arc plasma in the NO x removal over the Ag/γ-Al2O3 catalyst with n-heptane as a reducing agent source for NO x reduction. The plasma conjugated with the catalyst was performed like an injection method, i.e., a small part flow (1/26) that consisted of n-heptane was reformed to H2 and oxygenated hydrocarbons (OHCs) by gliding arc plasma before mixing it with the gas containing NO x . Then, the overall gas was passed through the catalyst stage at various temperatures from 127 to 253 °C. The experimental data revealed that NO x removal efficiency significantly increased with plasma treatment. The enhancement by plasma treatment increased with temperature from 127 to 226 °C, but the enhancement reduced at a temperature of 253 °C. The result came from formation of H2 and OHCs in the treated plasma gas, which reactivated NO x removal over the catalyst at low temperatures. Moreover, the enhanced NO x removal efficiency in a wide low-temperature range is obtained due to considerable hydrogen formation by the gliding arc plasma. To sum up, the highest NO x removal efficiency was 68.5% under a temperature of 226 °C and specific energy input of 34.6 J/L, while it was 20.3% for the catalyst alone; in other words, the removal efficiency increased by 48.1% with using plasma under these conditions. Owing to its low energy consumption, high-throughput gas treatment, and effectiveness at low temperatures, the technology is promising in practical applications for refining diesel exhaust gases.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Display omitted
•In-plasma is superior to injected-plasma catalysis for NOx removal at low temperatures.•Significant synergy between plasma and catalyst for NOx removal at low temperatures.•NOx ...removal efficiency up to 70% by assisting plasma at 200–250 °C temperature.•Energy delivery through plasma is better than a thermal process for NOx removal.•Injected-plasma catalysis has potential applications in circumstantial high-throughput gas.
Plasma-assisted hydrocarbon selective catalytic reduction (HC-SCR) of NOx was investigated by a packed Ag/γ-Al2O3 catalyst in a dielectric barrier discharge reactor at low temperatures. The effect of plasma discharge on NOx removal was investigated with two methods for comparison, in- and injected-plasma catalysis systems. In-plasma catalysis comprised a plasma-catalytic discharge with the entire feed gas, and injected-plasma catalysis incorporated a part of feed gas consisting of dodecane pretreated with the plasma-catalytic discharge and mixed with the remaining gas before passing through the catalyst-alone stage. Here, using the surface response method with temperature and specific energy input (SEI) as independent variables, the results revealed that energy delivery through plasma gained more NOx removal efficiency than that by thermal catalyst process; a set of SEI and temperature is needed to obtain a similar level of NOx removal. There is a significant synergy between plasma and catalyst in in-plasma catalysis at low temperatures (≤250 °C) that increased NOx removal efficiency up to Δη = 50% (SEI = 137 J/L; T = 200 °C). In-plasma catalysis is superior to injected-plasma catalysis for enhancing the NOx removal and widening the temperature window of effective NOx removal owing to the plasma-catalytic interface in-plasma catalysis supplies. Interestingly, the results also revealed that the plasma in the catalyst for both methods did not always improve the NOx removal efficiency. The plasma had a negative effect on NOx removal at sufficient temperature and SEI. As a result, the in-plasma catalysis presented a high NOx removal efficiency; it can be higher than 70% at temperatures of 200–250 °C. However, injected-plasma catalysis has potential applications in circumstantial high-throughput gas due to low plasma energy consumption by adjusting the entire feed to plasma-treated gas ratio.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The effective removal of dilute ethylene in a novel honeycomb plasma reactor was investigated using a honeycomb catalyst (Pd/ZSM-5/monolith) sandwiched between two-perforated electrodes operating at ...ambient temperature. Herein, the dependence of catalyst performance on the binder fraction, catalyst preparation method, and catalyst loading was examined. Ethylene removal was carried out by a process comprising cycles of 30-min adsorption conjugated with 15-min plasma-catalytic oxidation. Interestingly, the performance of the cyclic process was superior to continuous plasma-catalytic oxidation and thermally activated catalyst in terms of energy conservation, i.e., ~36 compared to ~105 and ~300 J/L, respectively. Hence, the novel cyclic process can be considered advanced-oxidation technology that features room-temperature oxidation, offers low energy consumption, negligible hazardous by-products emissions such as NOx and O3. Moreover, the process operated under described conditions: low-pressure drop, ambient atmosphere, a mechanically stable system, and a simple reactor configuration, suggesting the practical applicability of this plasma process.
Display omitted
•Successful generation of stable plasma in practical-scale honeycomb monolith.•Uniform and robust catalyst washcoat deposited on honeycomb monolith at 8% binder.•High ethylene removal efficiency (~95%) with low energy input (~36 J/L).•Ethylene treatment under surrounding ambient conditions without toxic byproducts.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Display omitted
•Stable plasma generation in reactor configuration comprising multiple honeycomb monoliths.•Linear relationship between discharge power and increased number of monoliths.•High ...ethylene adsorption capacity in an open channeled monolith catalyst at humid conditions.•Higher ethylene removal efficiency with high energy yield at low energy requirement.•Simplified overall system and operation at atmospheric conditions.
Dilute ethylene (C2H4) was removed in a novel plasma reactor comprising multiple honeycomb monoliths consisting of up to four PdO/ZSM-5/monolith catalysts. These monoliths were packed in a tubular reactor separated by mesh electrodes alternatively grounded or connected to a high voltage (HV) power source. The effect of the number of monoliths on the discharge power, adsorption, and removal of C2H4 was investigated. Additionally, the influence of the energy input, C2H4 inlet concentration, and gas flow rate on the C2H4 abatement was examined. The adsorption capacity, C2H4 conversion, and energy efficiency were observed to increase as the number of monoliths increased. The effect of the palladium (Pd) loading technique, namely ion exchange (IE), incipient wetness impregnation (IM), and combined IE-IM, IE followed by IM, on the C2H4 adsorption was also studied. The combined IE-IM method presented an exceptional adsorption capacity of ∼136 µmol/gcatalyst under humid conditions despite nonpolar nature of C2H4. C2H4 removal was performed via both continuous and cycled storage-discharge (CSD) plasma-catalytic oxidation processes. The CSD process was conducted in two ways: with intermittent C2H4 feed (CSD-IEF) and with maintained C2H4 feed (CSD-MEF), both comprising intermittent plasma discharge. Intriguingly, the performance of the CSD-MEF process was superior (56 J/L, 1.61 g/kWh) to that of the CSD-IEF (119 J/L, 0.98 g/kWh), and continuous process (∼228 J/L, 0.53 g/kWh) in terms of energy efficiency as well as the overall simplicity of the system.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A two-stage plasma catalyst system for high-throughput NOx removal was investigated. Herein, the plasma stage involved the large-volume plasma discharge of humidified gas and was carried out in a ...sandwich-type honeycomb monolith reactor consisting of a commercial honeycomb catalyst (50 mm high; 93 mm in diameter) located between two parallel perforated disks that formed the electrodes. The results demonstrated that, in the plasma stage, the reduction of NOx did not occur at room temperature; instead, NO was only oxidized to NO2 and n-heptane to oxygenated hydrocarbons. The oxidation of NO and n-heptane in the honeycomb plasma discharge state was largely affected by the humidity of the feed gas. Furthermore, the oxidation of NO to NO2 occurs preferably to that of n-heptane with a tendency of the NO oxidation to decrease with increasing feed gas humidity. The reason is that the generation of O3 decreases as the amount of water vapor in the feed gas increases. Compared to the catalyst alone, the two-stage plasma catalyst system increased NOx removal by 29% at a temperature of 200 °C and an energy density of 25 J/L.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
The effective removal of acetaldehyde by humidified air plasma was investigated with a high throughput of contaminated gas in a sandwiched honeycomb catalyst reactor at surrounding ambient ...temperature. Here, acetaldehyde at the level of a few ppm was successfully oxidized by the honeycomb plasma discharge despite the harsh condition of large water content in the feed gas. The conversion rate of acetaldehyde increased significantly with the presence of catalysts coating on the surface channels. The increased conversion rate was also obtained with a high specific energy input (SEI) and total flow rate. Interestingly, the conversion changed negligibly under the acetaldehyde concentration range from 5 to 20 ppm. However, the conversion rate decreased toward increased water amount in the feed gas. Notably, about 60% of acetaldehyde in the feed was oxidized under SEI of 40 J/L at water amounts ≤ 2.5%, approximately 0.5 g/kWh for acetaldehyde removal. Also, the plasma-catalyst reaction was superior to the thermal reactive catalyst for acetaldehyde removal in airborne pollutants. In comparison with other plasma-catalyst sources for acetaldehyde removal, the energy efficiency under the condition is comparable. Moreover, the honeycomb plasma discharge features high throughput, avoiding pressure drop, and straightforward reactor configuration, suggesting potential practical applications.
Display omitted
•Generation of large humid air plasma volume by a sandwich honeycomb plasma reactor.•Capable of practical plasma application for acetaldehyde removal in atmosphere.•Treating high throughput of simulated indoor emission of acetaldehyde.•High efficiency acetaldehyde removal although humid conditions.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A two-stage plasma catalyst system for high-throughput NO x removal was investigated. Herein, the plasma stage involved the large-volume plasma discharge of humidified gas and was carried out in a ...sandwich-type honeycomb monolith reactor consisting of a commercial honeycomb catalyst (50 mm high; 93 mm in diameter) located between two parallel perforated disks that formed the electrodes. The results demonstrated that, in the plasma stage, the reduction of NO x did not occur at room temperature; instead, NO was only oxidized to NO2 and n-heptane to oxygenated hydrocarbons. The oxidation of NO and n-heptane in the honeycomb plasma discharge state was largely affected by the humidity of the feed gas. Furthermore, the oxidation of NO to NO2 occurs preferably to that of n-heptane with a tendency of the NO oxidation to decrease with increasing feed gas humidity. The reason is that the generation of O3 decreases as the amount of water vapor in the feed gas increases. Compared to the catalyst alone, the two-stage plasma catalyst system increased NO x removal by 29% at a temperature of 200 °C and an energy density of 25 J/L.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
The dependence of the plasma discharge performance on the size of the honeycomb monolith in a sandwich-type honeycomb monolith plasma reactor operated under humidified air conditions was ...investigated. In addition, the effect of the feed gas temperature on the plasma discharge was also examined in the low-temperature range (25 °C-42 °C), which is similar to the typical temperature of the actual surrounding ambient air. The results showed that variation of the temperature significantly affects the discharge power, i.e., the discharge power decreases with increasing temperature. The results also indicated that, in the absence of the honeycomb monolith in the reactor, the plasma discharge did not occur inside the discharge zone created by two parallel perforated disks. However, when the honeycomb monolith was sandwiched between the two electrodes, the discharge developed between them because of the generated surface discharge spread through the honeycomb channels. Interestingly, a parallel relationship exists between monoliths with two different diameters in terms of their energy density and energy efficiency for O3 generation. These results suggest that the use of a monolith with a small diameter, instead of the original large commercial monolith, is sufficient when conducting research on the honeycomb discharge, as it facilitates experimental design.
