Application of plasma catalysis system for C4F8 removal.

Octafluorocyclobutane (C4F8) with a GWP100 (global warming potential) of 10,000 times of CO2 is listed as potent greenhouse gas. Therefore, development of effective control technologies for reducing C4F8 emissions has become an emerging issue to be addressed. In this study, decomposition of C4F8 was investigated via three systems including catalytic hydrolysis, non-thermal plasma, and plasma catalysis, respectively. Decomposition of C4F8 achieved with catalytic hydrolysis reaches the highest efficiency of 20.1%, being obtained with γ-Al2O3 as catalyst in the presence of 10% H2O(g) and operating temperature of 800 °C. For plasma-based system, the highest C4F8 conversion obtained with non-thermal plasma is 62% at a voltage of 23 kV. As for the plasma catalysis system, 100% C4F8 conversion efficiency can be achieved at an applied voltage of 22-23 kV. The effects of various parameters such as gas flow rate and C4F8 concentration on plasma-based system show that the plasma catalysis also has better resistivity for the high gas flow rate. The highest energy efficiency of 0.75 g/kWh is obtained for the gas flow rate of 500 mL/min, with the C4F8 conversion of 41%. The highest conversion 89% was achieved with the O2 content of 0.5%. Addition of Ar improves the performance of plasma-based system. When Ar is controlled at 20%, C4F8 conversions obtained with plasma catalysis reach 100% at applied voltage of 22-23 kV even in the presence of 5% O2. The main products of the C4F8 conversion include CO2, NOx, and COF2 when O2 is added into the system. As water vapor is added, HF is also formed. This study has confirmed that combined non-thermal plasma with catalyst system to convert C4F8 is indeed feasible and has good potential for further development.

Plasma catalytic oxidation of toluene over double perovskite-type oxide via packed-bed DBD.

Various perovskite-type catalysts including La2CoMnO6, LaCoO3, and LaMnO3 are first evaluated for the activities toward C7H8 removal. Experimental results indicate that double-type La2CoMnO6 shows better activity if compared with single perovskites due to high lattice oxygen content and good reducibility. Subsequently, perovskite catalysts are combined with plasma (NTP) to form in-plasma catalysis (IPC) and post-plasma catalysis (PPC) systems. The results indicate that IPC systems have better higher performance than that of NTP-alone and PPC. Especially, high C7H8 conversion (100%) and mineralization efficiency (96.8%) can be achieved with the applied voltage of 18 kV and temperature of 120 °C when La2CoMnO6 is integrated with NTP to form IPC system. Also, it owns the highest energy efficiency (0.14 g/kWh). It is concluded that IPC performance for C7H8 removal is closely related with the properties of catalyst surface. In addition, the kinetics of IPC systems are investigated by a simplified model, and the result indicates that IPC with La2CoMnO6 as catalyst has a higher overall energy constant. This study reveals that double-type La2CoMnO6 is of higher activity than single perovskites for C7H8 removal, and demonstrates that double-type La2CoMnO6 is of high potential to form plasma catalysis system for VOCs removal.

Storage and reduction of NOx by combining Sr-based perovskite catalyst with nonthermal plasma.

A novel NOx storage and reduction (NSR) system is developed for NOx removal by integrating Sr-based perovskite catalyst with nonthermal plasma (NTP)-assisted process. In this hybrid system, Sr-based perovskite catalyst is applied for NOx adsorption in the lean-burn condition while NTP is used as a desorption-reduction step to convert NOx into N2 under rich-burn condition. Innovative Sr-based perovskites including SrKMnCoO4/BaO/Al2O3 (SKMCBA), SrKMnCeO4/BaO/Al2O3 (SKMCeBA), and SrKCoNiO4/BaO/Al2O3 (SKCNBA) are successfully prepared by impregnation method. Results indicate that SKMCBA possesses the highest NOx trapped (214 µmole NOx/gcatalyst) at 400 °C among 3 Sr-based perovskites investigated. High performance of SKMCBA for NOx adsorption is mainly attributed to the addition of Mn and Co which own good oxidation ability. Further, SKMCBA is combined with NTP-assisted process for NOx reduction. Result indicates that NOx conversion achieved with NTP-assisted process reaches 83% with the applied voltage of 18 kV and frequency of 10 kHz in the absence of reducing agent. Additionally, various reducing agents including hydrogen (H2), carbon monoxide (CO), and propene (C3H6) are introduced, individually, into the NTP reduction process, and the results indicate that performance of NSR with NTP can be effectively enhanced. Especially, 100% NOx conversion is achieved with H2-NTP. This study demonstrates that reduction of NOx via NTP-assisted process is promising.

Removal of VOCs from gas streams with double perovskite-type catalysts.

Double perovskite-type catalysts including La2CoMnO6 and La2CuMnO6 are first evaluated for the effectiveness in removing volatile organic compounds (VOCs), and single perovskites (LaCoO3, LaMnO3, and LaCuO3) are also tested for comparison. All perovskites are tested with the gas hourly space velocity (GHSV) of 30,000hr-1, and the temperature range of 100-600°C for C7H8 removal. Experimental results indicate that double perovskites have better activity if compared with single perovskites. Especially, toluene (C7H8) can be completely oxidized to CO2 at 300°C as La2CoMnO6 is applied. Characterization of catalysts indicates that double perovskites own unique surface properties and are of higher amounts of lattice oxygen, leading to higher activity. Additionally, apparent activation energy of 68kJ/mol is calculated using Mars-van Krevelen model for C7H8 oxidation with La2CoMnO6 as catalyst. For durability test, both La2CoMnO6 and La2CuMnO6 maintain high C7H8 removal efficiencies of 100% and 98%, respectively, at 300°C and 30,000hr-1, and they also show good resistance to CO2 (5%) and H2O(g) (5%) of the gas streams tested. For various VOCs including isopropyl alcohol (C3H8O), ethanal (C2H4O), and ethylene (C2H4) tested, as high as 100% efficiency could be achieved with double perovskite-type catalysts operated at 300-350°C, indicating that double perovskites are promising catalysts for VOCs removal.

Catalytic oxidation of trichloroethylene from gas streams by perovskite-type catalysts.

Three perovskite-type catalysts including LaMnO3, La0.8Ce0.2MnO3, and La0.8Ce0.2 Mn0.8Ni0.2O3 are prepared using citric acid sol-gel method and evaluated as catalyst for the oxidation of trichloroethylene (TCE) in air with temperature ranging from 100 to 600 °C. The physicochemical properties of three perovskite-type catalysts were characterized by SEM, EDS, XRD, BET, and XPS to investigate the relationship with catalytic activities. The results show that the removal efficiency of TCE achieved with La0.8Ce0.2Mn0.8Ni0.2O3 (the best one) reaches 100% at 400 °C and the mineralization efficiency reaches 100% at 600 °C. The enhanced activity can be attributed to the addition of Ce and Ni which increases the surface areas, active oxygen species, and the redox ability of the Mn4+/Mn3+ ratio on the catalyst surface. As La0.8Ce0.2Mn0.8Ni0.2O3 is applied for TCE oxidation, the main intermediate chlorinated byproduct detected is tetrachloroethylene (C2Cl4) which is generated by the reaction of TCE and chlorine (Cl2). The activation energy for the TCE oxidation with La0.8Ce0.2Mn0.8Ni0.2O3 catalyst is 51 kJ/mol using kinetic models of power-law type.

Combined fast selective reduction using Mn-based catalysts and nonthermal plasma for NOx removal.

In this study, the concept of fast SCR for NO reduction with NH3 as reducing agent is realized via the combination of nonthermal plasma (NTP) with Mn-based catalyst. Experimental results indicate that 10% wt. Mn-Ce-Ni/TiO2 possesses better physical and chemical properties of surface, resulting in higher NO removal efficiency if compared with 10% wt. Mn-Ce/TiO2 and 10% wt. Mn-Ce-Cu/TiO2. Mn-Ce-Ni/TiO2 of 10% wt. achieves 100% NOx conversion at 150 °C, while 10% wt. Mn-Ce/TiO2 and 10% wt. Mn-Ce-Cu/TiO2 need to be operated at a temperature above 200 °C for 100% NOx conversion. However, NO conversion achieved with 10% wt. Mn-Ce-Ni/TiO2 is significantly reduced as H2O(g) and SO2 are introduced into the SCR system simultaneously. Further, two-stage system (SCR with DBD) is compared with the catalyst-alone for NOx conversion and N2 selectivity. The results indicate that 100% NOx conversion can be achieved with two-stage system at 100 °C, while N2 selectivity reaches 80%. Importantly, NOx conversion achieved with two-stage system could maintain >95% in the presence of C2H4, CO, SO2, and H2O(g), indicating that two-stage system has better tolerance for complicated gas composition. Overall, this study demonstrates that combining NTP with Mn-based catalyst is effective in reducing NOx emission at a low temperature (≤200 °C) and has good potential for industrial application.

Catalytic removal of phenol from gas streams by perovskite-type catalysts.

Three perovskite-type catalysts prepared by citric acid method are applied to remove phenol from gas streams with the total flow rate of 300mL/min, corresponding to a GHSV of 10,000/hr. LaMnO3 catalyst is first prepared and further partially substituted with Sr and Cu to prepare La0.8Sr0.2MnO3 and La0.8Sr0.2Mn0.8Cu0.2O3, and catalytic activities and fundamental characteristics of these three catalysts are compared. The results show that phenol removal efficiency achieved with La0.8Sr0.2Mn0.8Cu0.2O3 reaches 100% with the operating temperature of 200°C and the rate of mineralization at 300°C is up to 100%, while the phenol removal efficiencies achieved with La0.8Sr0.2MnO3 and LaMnO3 are up to 100% with the operating temperature of 300°C and 400°C, respectively. X-ray photoelectron spectroscopy (XPS) analysis shows that the addition of Sr and Cu increases the lattice oxygen of La0.8Sr0.2Mn0.8Cu0.2O3, and further increases mobility or availability of lattice oxygen. The results indicate that La0.8Sr0.2Mn0.8Cu0.2O3 has the best activity for phenol removal among three catalysts prepared and the catalytic activity of phenol oxidation is enhanced by the introduction of Sr and Cu into LaMnO3. Apparent activation energy of 48kJ/mol is calculated by Mars-Van Krevelen Model for phenol oxidation with La0.8Sr0.2Mn0.8Cu0.2O3 as catalyst.

Desorption of isopropyl alcohol from adsorbent with non-thermal plasma.

Effective desorption of isopropyl alcohol (IPA) from adsorbents with non-thermal plasma is developed. In this system, IPA is effectively adsorbed with activated carbon while dielectric barrier discharge is applied to replace the conventional thermal desorption process to achieve good desorption efficiency, making the treatment equipment smaller in size. Various adsorbents including molecular sieves and activated carbon are evaluated for IPA adsorption capacity. The results indicate that BAC has the highest IPA adsorption capacity (280.31 mg IPA/g) under the operating conditions of room temperature, IPA of 400 ppm, and residence time of 0.283 s among 5 adsorbents tested. For the plasma desorption process, the IPA selectivity of 89% is achieved with BAC as N2 is used as desorbing gas. In addition, as air or O2 is used as desorbing gas, the IPA desorption concentration is reduced, because air and O2 plasmas generate active species to oxidize IPA to form acetone, CO2, and even CO. Furthermore, the results of the durability test indicate that the amount of IPA desorbed increases with increasing desorption times and plasma desorption process has a higher energy efficiency if compared with thermal desorption. Overall, this study indicates that non-thermal plasma is a viable process for removing VOCs to regenerate adsorbent.

Combining nonthermal plasma with perovskite-like catalyst for NOx storage and reduction.

A new NOx storage and reduction (NSR) system is developed for NOx removal by combining perovskite-like catalyst with nonthermal plasma technology. In this hybrid system, catalyst is mainly used for oxidizing NO to NO2 and storing them, while nonthermal plasma is applied as a desorption-reduction step for converting NOx into N2. An innovative catalyst with a high NOx storage capacity and good reduction performance is developed by successive impregnation. The catalysts prepared with various metal oxides were investigated for NOx storage capacity (NSC) and NOx conversion. Characterization of the catalysts prepared reveals that addition of cobalt (Co) and potassium (K) considerably increases the performance for NSC. Results also show that SrKMn0.8Co0.2O4 supported on BaO/Al2O3 has good NSC (209 µmol/gcatalyst) for the gas stream containing 500 ppm NO and 5 % O2 with N2 as carrier gas. For plasma reduction process, NOx conversion achieved with SrKMn0.8Co0.2O4/BaO/Al2O3 reaches 81 % with the applied voltage of 12 kV and frequency of 6 kHz in the absence of reducing agents. The results indicate that performance of plasma reduction process (81 %) is better than that of thermal reduction (64 %). Additionally, mixed gases including 1 % CO, 1 % H2 and 1 % CH4, and 2 % H2O(g) are simultaneously introduced into the system to investigate the effect on NSR with plasma system and results indicate that performance of NSR with plasma can be enhanced. Overall, the hybrid system is promising to be applied for removing NOx from gas streams. Graphical abstract ᅟ.

Enhancement of nitric oxide decomposition efficiency achieved with lanthanum-based perovskite-type catalyst.

UNLABELLED: Direct decompositions of nitric oxide (NO) by La0.7Ce0.3SrNiO4, La0.4Ba0.4Ce0.2SrNiO4, and Pr0.4Ba0.4Ce0.2SrNiO4 are experimentally investigated, and the catalysts are tested with different operating parameters to evaluate their activities. Experimental results indicate that the physical and chemical properties of La0.7Ce0.3SrNiO4 are significantly improved by doping with Ba and partial substitution with Pr. NO decomposition efficiencies achieved with La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4 are 32% and 68%, respectively, at 400 °C with He as carrier gas. As the temperature is increased to 600 °C, NO decomposition efficiencies achieved with La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4, respectively, reach 100% with the inlet NO concentration of 1000 ppm while the space velocity is fixed at 8000 hr(-1). Effects of O2, H2O(g), and CO2 contents and space velocity on NO decomposition are also explored. The results indicate that NO decomposition efficiencies achieved with La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4, respectively, are slightly reduced as space velocity is increased from 8000 to 20,000 hr(-1) at 500 °C. In addition, the activities of both catalysts (La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4) for NO decomposition are slightly reduced in the presence of 5% O2, 5% CO2, or 5% H2O(g). For durability test, with the space velocity of 8000 hr(-1) and operating temperature of 600 °C, high N2 yield is maintained throughout the durability test of 60 hr, revealing the long-term stability of Pr0.4Ba0.4Ce0.2SrNiO4 for NO decomposition. Overall, Pr0.4Ba0.4Ce0.2SrNiO4 shows good catalytic activity for NO decomposition. IMPLICATIONS: Nitrous oxide (NO) not only causes adverse environmental effects such as acid rain, photochemical smog, and deterioration of visibility and water quality, but also harms human lungs and respiratory system. Pervoskite-type catalysts, including La0.7Ce0.3SrNiO4, La0.4Ba0.4Ce0.2SrNiO4, and Pr0.4Ba0.4Ce0.2SrNiO4, are applied for direct NO decomposition. The results show that NO decomposition can be enhanced as La0.7Ce0.3SrNiO4 is substituted with Ba and/or Pr. At 600 °C, NO decomposition efficiencies achieved with La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4 reach 100%, demonstrating high activity and good potential for direct NO decomposition. Effects of O2, H2O(g), and CO2 contents on catalytic activities are also evaluated and discussed.

Direct N2O decomposition over La2NiO4-based perovskite-type oxides.

Direct decomposition of N2O by perovskite-structure catalysts including La2NiO4, LaSrNiO4, and La0.7Ceo.3SrNiO4 was investigated. The catalysts were prepared by the Pechini method and characterized by x-ray diffraction (XRD), BETI scanning electron microscopy (SEM), and 02-TPD. Experimental results indicate that the properties of La2NiO4 are significantly improved by partially substituting La with Sr and Ce. N2O decomposition efficiencies achieved with LaSrNi04 and La0.7Ce0.3SrNiO4 are 44 and 36%, respectively, at 400 degrees C. As the temperature was increased to 600 degrees C, N2O decomposition efficiency achieved with LaSrNiO4 and La0.7Ce0.3SrNiO4 reached 100% at an inlet N2O concentration of 1000 ppm, while the space velocity was fixed at 8,000 hr(-1). In addition, effects of various parameters including oxygen, water vapor and space velocity were also explored. The results indicate that N2O decomposition efficiencies achieved with LaSrNiO4 and La0.7Ce0.3SrNiO4 are not significantly affected as space velocity is increased from 8,000 to 20,000 hr(-1), while La0.7Ce0.3SrNiO4 shows better tolerance for O2 and H2O(g). On the other hand, N2 yield with LaSrNiO4 as catalyst can be significantly improved by doping Ce. At a gas hour space velocity of 8000 hr(-1) and a temperature of 600 degrees C, high N2O decomposition efficiency and N2 yield were maintained throughout the durability test of 60 hr, indicating the long-term stability of La0.7Ce0.3SrNiO4 for N2O decomposition.

Removal of formaldehyde over Mn(x)Ce(1)-(x)O(2) catalysts: thermal catalytic oxidation versus ozone catalytic oxidation.

Mn(x)Ce(1)-(x)O(2) (x: 0.3-0.9) prepared by Pechini method was used as a catalyst for the thermal catalytic oxidation of formaldehyde (HCHO). At x=0.3 and 0.5, most of the manganese was incorporated in the fluorite structure of CeO(2) to form a solid solution. The catalytic activity was best at x=0.5, at which the temperature of 100% removal rate is the lowest (270°C). The temperature for 100% removal of HCHO oxidation is reduced by approximately 40°C by loading 5wt.% CuO(x) into Mn(0.5)Ce(0.5)O(2). With ozone catalytic oxidation, HCHO (61 ppm) in gas stream was completely oxidized by adding 506 ppm O3over Mn(0.5)Ce(0.5)O(2) catalyst with a GHSV (gas hourly space velocity) of 10,000 hr⁻¹ at 25°C. The effect of the molar ratio of O(3) to HCHO was also investigated. As O(3)/HCHO ratio was increased from 3 to 8, the removal efficiency of HCHO was increased from 83.3% to 100%. With O(3)/HCHO ratio of 8, the mineralization efficiency of HCHO to CO(2) was 86.1%. At 25°C, the p-type oxide semiconductor (Mn(0.5)Ce(0.5)O(2)) exhibited an excellent ozone decomposition efficiency of 99.2%, which significantly exceeded that of n-type oxide semiconductors such as TiO(2), which had a low ozone decomposition efficiency (9.81%). At a GHSV of 10,000 hr⁻¹, [O(3)]/[HCHO]=3 and temperature of 25°C, a high HCHO removal efficiency (≥ 81.2%) was maintained throughout the durability test of 80 hr, indicating the long-term stability of the catalyst for HCHO removal.