Plasma-catalytic System Research Articles

A plasma-catalytic system with MgO/NiO/Ni cathode for SF6 degradation

In this work, a plasma-catalytic system in DC discharge with MgO/NiO/Ni (MNN) cathode is proposed for the degradation of SF6 greenhouse gas. The discharge power with MNN cathode is significantly increased compared with Ni cathode due to its good electron emission characteristics, and an effective and stable SF6 degradation performance is achieved in this multi-needle plate discharge system. Besides, surface discharge occurs on the MNN cathode in addition to the needle tips, which is believed to be conducive to the catalytic decomposition of SF6 on the MgO surface. Nontoxic products of MgF2 and MgSO4 are detected on the MgO layer after discharge from various characterizations (XRD, XPS, FTIR and Raman, etc.), suggesting that there is a series of catalytic reactions between SF6/intermediates and MgO. The addition of appropriate O2 (O2:SF6 = 1:1) in the background is not only conducive to the defluorination decomposition of SF6 in ionization region, but also O atom generated from O2 discharge promotes the formation of MgF2 and MgSO4, thus resulting in an effective SF6 degradation performance. Then, the possible degradation mechanism of SF6 in gas phase and on the MgO layer is discussed and the possible degradation pathways are proposed. This research first demonstrates the effectiveness of enabling degrading SF6 gases in a plasma-catalytic system with MNN cathode.

Enhanced degradation of tetracycline by gas-liquid discharge plasma coupled with g-C3N4/TiO2

Plasma-catalysis is considered as one of the most promising technologies for antibiotic degradation in water. In the plasma-catalytic system, one of the factors affecting the degradation effect is the performance of the photocatalyst, which is usually restricted by the rapid recombination of electrons and holes as well as narrow light absorption range. In this research, a photocatalyst g-C3N4/TiO2 was prepared and coupled with gas-liquid discharge (GLD) to degrade tetracycline (TC). The performance was examined, and the degradation pathways and mechanisms were studied. Results show that a 90% degradation rate is achieved in the GLD with g-C3N4/TiO2 over a 10 min treatment. Increasing the pulse voltage is conducive to increasing the degradation rate, whereas the addition of excessive g-C3N4/TiO2 tends to precipitate agglomerates, resulting in a poor degradation efficiency. The redox properties of the g-C3N4/TiO2 surface promote the generation of oxidizing active species (H2O2, O3) in solution. Radical quenching experiments showed that ·OH, hole (h +), play important roles in the TC degradation by the discharge with g-C3N4/TiO2. Two potential degradation pathways were proposed based on the intermediates. The toxicity of tetracycline was reduced by treatment in the system. Furthermore, the g-C3N4/TiO2 composites exhibited excellent recoverability and stability.

Cobalt catalysts for COx-free hydrogen production: Effect of catalyst type on ammonia decomposition in gliding discharge plasma reactor

Hydrogen is considered the cleanest, most environmentally friendly fuel and energy carrier required for the gradual decarbonisation of many industrial sectors. Using ammonia as a Cox-free source of hydrogen is the most reasonable and most applicable method. This paper studies the properties and activity of cobalt catalysts in the ammonia decomposition reaction using a plasma-catalytic system. The effect of catalyst type (supported versus bulk) was evaluated. The catalysts were examined using XRD, STEM-EDX, and sorption techniques (N2 physisorption, TGA-TPR, H2-TPD, CO2-TPD) to reveal the influence of physicochemical properties of these two types of catalysts on the efficiency of NH3 decomposition in the plasma-catalytic process using a gliding discharge plasma. The results disclose that the supported-type catalyst (Ba-Co/CeO2) decomposed NH3 more effectively than the bulk-type catalyst (Co/Ce/Ba). At discharge power of 300 W and flow rate of 180 dm3 h–1 of NH3:N2 mixture (50/50 vol%), the ammonia conversion over the Ba-Co/CeO2 catalyst was 70%, whereas over the Co/Ce/Ba catalyst it was only 21%. The favourable performance of the supported-type catalyst was attributed to a more thermally stable surface area compared with the bulk-type catalyst. Smaller and more stable cobalt nanoparticles (NPs) with numerous weak hydrogen adsorption sites were also seen. Meanwhile, the strong basic sites were generated, improving the electron-donating ability of the surface active sites. High ammonia conversion and relatively low-energy consumption of the plasma-catalytic ammonia decomposition over Ba-Co/CeO2 make it suitable for practical hydrogen production applications, such as fuel cells and hydrogen storage.

Optimizing the CeO2-MnO2 interface via H2O2 etching for surface lattice oxygen activation in the plasma catalytic degradation of trimethylamine

Trimethylamine (TMA) is a nitrogen-containing malodorous gas that is toxic and hazardous to humans. Plasma catalysis is a promising technique for removing low-concentration malodorous gases. CeO2/MnO2 nanowires with different Ce–Mn contact interfaces prepared by impregnation, physical mixing, and H2O2 etching were investigated for TMA degradation in a plasma catalytic system. The CMO-H sample prepared by H2O2 etching achieved a removal efficiency of 100% at 98 J/L, demonstrating the highest activity. Characterization revealed that H2O2 etching led to the uniform formation of CeO2 nanoparticles on MnO2, promoting the transfer of electrons between Ce and Mn species. Surface lattice oxygen and high-valent manganese were confirmed to be the main active species, consistent with the Mars van Krevelen mechanism. Density functional theory calculations confirmed that the CMO-H sample exhibited the lowest oxygen vacancy formation energy. In situ plasma diffuse reflection infrared transform spectroscopy analysis and gas chromatography-mass spectrometry results showed the possible degradation pathway of TMA. In summary, the H2O2 etching process optimized CeO2-MnO2 interactions and improved the utilization of lattice oxygen active sites, enhancing the catalytic degradation of TMA and providing new insights into the design of an efficient plasma catalytic system for environmental remediation.

Degradation of n-hexane by the high-throughput double dielectric barrier discharge: Influencing factors, degradation mechanism and pathways

The emission of volatile organic compounds (VOCs) is known to be a source of various environmental problems. N-hexane is a saturated aliphatic hydrocarbon that is a major precursor of ozone. For the decomposition of n-hexane, a novel double dielectric barrier discharge (DDBD) reactor design is developed and tested on a pilot scale. The factors influencing the plasma degradation of n-hexane have been thoroughly investigated. The degradation efficiency, carbon balance and nitrogen oxide concentration were measured and analysed. Through experiments, it was found that the maximum removal of n-hexane at an initial concentration of 2000 ppm and a flow rate of 5 L/min was 1544 ppm. The associated energy efficiency reached 67.71 ppm/J. The excited states of oxygen and nitrogen (O2+, O(3 s5S-3p5P), N2(C3Πu-B3Πg), N2+(B2Σu+-X2Σg+)) during n-hexane degradation were observed. Possible degradation pathways of n-hexane are proposed, and it is revealed that the active species play an important role in the formation of oxygen and nitrogen-containing volatile organic by-products. The results show that the pilot-scale design of the DDBD system provides a feasible way for the industrial treatment of n-hexane, and provides fundamental insights into the mechanism of plasma catalytic system operation.

Efficient catalytic degradation of VOCs using Mn-based hydrotalcite-like compounds coupled with non-thermal plasma

Aiming to discover a novel catalyst that exhibits a high synergistic effect with plasma technology for the degradation of volatile organic compounds (VOCs), we employed manganese-based layered double hydroxides (LDHs), which are referred to as MMn-LDHs (M=Ni, Co, Fe). Comprehensive physicochemical characterization via catalyst characterization techniques such as XRD, SEM, XPS, BET, confirmed the successful synthesis of the catalysts. These analyses revealed excellent crystallinity, distinctive lamellar structure, and remarkable thermal stability for three synthesized catalysts. The experimental results demonstrate that post non-thermal plasma (post-NTP) catalytic system has significantly improved the degradation efficiency, CO2 selectivity, and carbon balance for toluene, while notably suppressing the formation of by-products (e.g., NOx and O3) compared to the NTP alone system. Among the three MMn-LDHs, NiMn-LDHs exhibited the best performance in the post-NTP-catalytic system, achieving a toluene degradation rate of 95.87%, a CO2 selectivity of 57.41%, a carbon balance of 79.86%, and an energy efficiency of 3.19 g·kWh−1 at a specific energy density (SED) of 930.45 J/L. The catalytic degradation mechanism of toluene was proposed based on a combination of catalyst characterization techniques, plasma emission spectroscopy, and gas chromatography-mass spectrometry (GC-MS). The findings revealed that plasma discharge generated a substantial amount of free radicals and active species, thereby promoting the decomposition of toluene. Subsequently, the residual toluene and intermediate products were adsorbed onto the catalysts, where they underwent further reacted with the abundant hydroxyl radicals and activate metal species on the catalyst surface, ultimately decomposing into CO2 and H2O. Additionally, the interaction of ozone with LDHs facilitated the generation of reactive oxygen species, consequently accelerating the decomposition of organic intermediates, formation of CO2, and the enhancement of toluene mineralization. The finding in this work offer valuable theoretical support for the plasma-catalytic degradation of VOCs.

Dielectric barrier discharge plasma-coupled rare-earth modified Er3+-BiOI catalytic materials for degradation of organic pollutant benzohydroxamic acid in mineral beneficiation waster: Performance, degradation pathway, and its mechanism

A dielectric barrier Discharge (DBD) plasma catalytic system for synergistic degradation of benzohydroxamic acid (BHA) was established. A series of Er3+-BiOI samples doped with rare earth elements (Er3+) were prepared by the hydrothermal synthesis method. The characterization showed that Er3+-BiOI had a microglobular structure assembled by nanosheets, and the specific surface area of Er3+-BiOI was larger than that of pure BiOI. The degradation performance showed that in the DBD/Er3+-BiOI system, the highest BHA degradation efficiency reached 96.3 % with 4 % Er3+. Compared with the DBD-BiOI system and the single DBD system, the degradation efficiency of BHA increased by 9.1 % and 17.5 %, respectively. Meanwhile, the kinetic constants and cofactors were also the highest, at 3.36 and 2.88 times the DBD-BiOI system, respectively. The radical capture experiments showed ∙OH, ∙O2−, and cavities play a key role in the degradation of BHA, while O3, H2O2, e−, and H+ promote the degradation of BHA. The intermediates in the degradation of BHA were determined by LC-MS, and the possible degradation pathways of BHA were predicted. Finally, the degradation mechanism of BHA in the DBD/4 % Er3+-BiOI system was proposed.

Boosting toluene mineralization and ozone decomposition in plasma catalytic system by regulating the oxygen vacancy over Ag-based catalyst

Incomplete mineralization and high outlet ozone concentration are two urgent issues that need to be overcome in plasma catalytic systems for the purification of volatile organic compounds (VOCs). Herein, we attempted to address these issues by coupling Ag/ZSM-5 catalyst reduced by hydrogen at different temperatures with a dielectric barrier discharge (DBD) reactor during toluene degradation. The catalyst characterization (including XRD, UV–vis, XPS, XAFS, Raman, EPR) combined with density functional theory (DFT) calculations indicated that hydrogen reduction lowered the energy between metal ions and oxygen, generating more oxygen vacancies and facilitating the transition from Ag ions to Ag0. The abundant vacancies influenced the electron properties in the adjacent atoms, making them catalytically active and thereby promoting the adsorption and activation of CO and O3. Thus, the mineralization rate and O3 decomposition performance were significantly enhanced for the hydrogen-reduced Ag/ZSM-5 catalysts. Moreover, the L-H, E-R and MVK mechanisms were first experimentally verified in plasma catalytic system by changing the background atmosphere during toluene adsorption and discharge degradation stages. This study provides insights into the rational design of highly effective catalysts in a plasma catalytic system for the removal of VOCs.

Facile fabrication of three-dimensional MnO2 for trichloroethylene degradation by plasma catalysis

Non-thermal plasma (NTP) coupled with catalyst is a cutting-edge technique for the abatement of chlorinated volatile organic compounds (Cl-VOCs), which are typically chemically stable, highly toxic and non-biodegradable. In this study, different morphologies of 3D MnO2 catalysts were fabricated facilely through a hydrothermal method and coupled with NTP for trichloroethylene (TCE) degradation. Among the various catalysts tested, MnO2 IV exhibited the highest TCE degradation performance, with removal efficiency, mineralization and energy yield ranging from 44.3% to 94.8%, 28.9% to 90.1% and 5.76 to 2.31 g/kWh, respectively, at voltage levels between 7 and 11 kV. The relationship between the physicochemical properties of the catalysts and their degradation performance was established through various characterization methods. The exceptional catalytic efficiency of MnO2 IV can be ascribed to its hierarchical flower-like structure, the greatest specific surface area (120 m2/g), the weakest Mn-O bonds, increased lattice defects and oxygen vacancies, and lower H2 reduction temperature. These characteristics facilitate enhanced transfer, adsorption, and utilization of reactive oxygen species in NTP on the surface of MnO2 IV, promoting the deep oxidation of TCE. The optimization of operational parameters was achieved using response surface methodology, with results indicating that the applied voltage exerted the greatest influence on both the mineralization rate and energy yield. The optimal operating conditions were determined, with initial TCE concentration, applied voltage, and gas flow rate values identified as 393 ppm, 7.3 kV, and 0.83 L/min, respectively. Lastly, the TCE degradation mechanism in the NTP-MnO2 catalyst system was hypothesized based on the identification of various plasma reactive species and organic intermediates. This study provides new insights for the improvement of the VOCs oxidation performance in plasma catalytic system.

Pulsed gas–liquid discharge plasma catalytic degradation of bisphenol A over graphene/CdS: process parameters optimization and O3 activation mechanism analysis

In the present work, pulsed gas–liquid hybrid discharge plasma coupled with graphene/CdS catalyst was evaluated to eliminate bisphenol A (BPA) in wastewater. The optimization of a series of process parameters was performed in terms of BPA degradation performance. The experimental results demonstrated that nearly 90% of BPA (20 mg l−1) in the synthetic wastewater (pH = 7.5, σ = 10 μS m−1) was degraded by the plasma catalytic system over 0.2 g l−1 graphene/CdS at 19 kV with a 4 l min−1 air flow rate and 10 mm electrode gap within 60 min. The BPA removal rate increased with increasing the discharge voltage and decreasing the initial BPA concentration or solution conductivity. Nevertheless, either too high or too low an air flow rate, electrode gap, catalyst dosage or initial solution pH would lead to a decrease in BPA degradation. Moreover, optical emission spectroscopy was used to gain information on short-lived reactive species formed from the pulsed gas–liquid hybrid discharge plasma system. The results indicated the existence of several highly oxidative free radicals such as ·O and ·OH. Finally, the activation pathway of O3 on the catalyst surface was analyzed by density functional theory.

Improving oxidation removal of toluene in plasma coupling perovskite catalysts system by constructing Au sites on a La0.5Ce0.5CoO3-δ

Plasma-catalysis technique is a promising approach to control air pollution caused by volatile organic compounds (VOCs). Perovskite-type oxides have excited much interest in constructing plasma-catalytic system for the oxidation removal of VOCs owing to their flexible electronic structure, alterable geometry, unique catalytic properties and high stability. However, the perovskites commonly suffer from low surface area and small amounts of active surface sites because of their high synthesis temperature, which limits the synergism between the perovskites and plasma and thus decreases the performance of plasma-catalytic oxidation of VOCs. Here we show that the oxidation removal of toluene (typical refractory VOCs) in the plasma-catalytic system is improved by constructing Au sites on a perovskite of La0.5Ce0.5CoO3-δ (Au/La0.5Ce0.5CoO3-δ). Compared with plasma-catalytic systems integrated by LaCoO3 or La0.5Ce0.5CoO3-δ, coupling the Au/La0.5Ce0.5CoO3-δ with plasma enables the boost of toluene conversion and CO2 selectivity, but suppresses the generation of secondary pollutants (O3 and NOx). The calculation of apparent activation energy (Ea) demonstrates that the plasma-catalytic system integrated by Au/La0.5Ce0.5CoO3-δ obtains lower Ea of 6.9 kJ/mol than those integrated by LaCoO3 (9.5 kJ/mol) and La0.5Ce0.5CoO3-δ (8.1 kJ/mol) as well as plasma alone (15.0 kJ/mol), confirming a favorable toluene oxidation process in the plasma coupling Au/La0.5Ce0.5CoO3-δ system. Catalyst characterizations, discharge diagnosis and density functional theory calculations suggest that depositing Au on the La0.5Ce0.5CoO3-δ render the favorable gas and surface reactions for toluene oxidation in the plasma-catalytic system and thus a strong synergism between the perovskites and plasma, by modulating the discharge mode and creating large numbers of highly active Auδ+-Oδ--Ce interfacial sites on the surface of La0.5Ce0.5CoO3-δ.

Plasma-catalytic CO2 methanation over NiFen/(Mg, Al)Ox catalysts: Catalyst development and process optimisation

Plasma-assisted catalytic carbon dioxide (CO2) methanation is a promising approach to valorise CO2 under mild conditions, and the system requires rational design regarding both catalysts and processes to advance it towards practical applications. Herein, the bimetallic NiFen/(Mg, Al)Ox catalysts were developed for plasma-catalytic CO2 methanation, and the effect of atomic ratio of Ni and Fe and reduction temperature on the catalysts was investigated systematically. The findings show that a higher reduction temperature was beneficial to the formation of Ni3Fe alloy and abundant surface oxygen vacancies, and increased CO2 adsorption ability. As a result, the NiFe0.1/(Mg, Al)Ox-800 catalyst led to a good catalytic performance in the plasma-assisted catalysis with about 84.7% CO2 conversion and 100% methane (CH4) selectivity. In addition, this study also employed response surface methodology (RSM) to explore the optimisation of plasma-catalytic CO2 methanation for the first time. Results from RSM show that in the plasma-catalytic system the selective CO2 hydrogenation to CH4 was favoured by higher applied voltage, lower gas flow rate and higher gas ratio (H2: CO2).

Investigation on removal of multi-component volatile organic compounds in a two-stage plasma catalytic oxidation system - Comparison of X (X=Cu, Fe, Ce and La) doped Mn2O3 catalysts

Mn2O3-X catalysts (X = Cu, Fe, Ce and La) were prepared based on γ-Al2O3 for the mixture degradation of muti-component volatile organic compounds (VOCs) composed of toluene, acetone, and ethyl acetate. The catalysts were characterized, and the density functional theory (DFT) simulation of ozone adsorption on Mn2O3-X were carried out to investigate the influence of adsorption energy on catalytic performance. The results showed that the removal efficiency (RE) of each VOC component was similarly improved by Mn2O3-X catalysts, and the greatest increase in VOCs' removal efficiency was obtained (7.8% for toluene, 86.2% for acetone, and 82.5% for ethyl acetate) at a special input energy (SIE) of 700 J L−1 with Mn2O3–La catalyst. Characterization results demonstrated that Mn2O3–La catalyst had the highest content of low valence Mn elements and the greatest Oads/Olatt ratio, as well as the lowest reduction temperature. Mn2O3–La catalyst also presented superior catalytic effect in improving carbon balance (CB) and CO2 selectivity (SCO2). The CB and SCO2 were increased by 47.7% and 12.61% respectively with Mn2O3–La at a SIE of 400 J L−1 compared with that when only γ-Al2O3 was applied. The DFT simulation results of ozone adsorption on Mn2O3-X catalysts indicated that the adsorption energy of catalyst crystal was related to the catalytic performance of the catalyst. The Mn2O3–La/γ-Al2O3 catalyst, which had the highest absolute value of adsorption energy, presented the best performance in improving VOCs’ RE.

Plasma-Catalytic CO2 Reforming of Toluene over Hydrotalcite-Derived NiFe/(Mg, Al)O x Catalysts.

The removal of tar and CO2 in syngas from biomass gasification is crucial for the upgrading and utilization of syngas. CO2 reforming of tar (CRT) is a potential solution which simultaneously converts the undesirable tar and CO2 to syngas. In this study, a hybrid dielectric barrier discharge (DBD) plasma-catalytic system was developed for the CO2 reforming of toluene, a model tar compound, at a low temperature (∼200 °C) and ambient pressure. Periclase-phase (Mg, Al)O x nanosheet-supported NiFe alloy catalysts with various Ni/Fe ratios were synthesized from ultrathin Ni-Fe-Mg-Al hydrotalcite precursors and employed in the plasma-catalytic CRT reaction. The result demonstrated that the plasma-catalytic system is promising in promoting the low-temperature CRT reaction by generating synergy between DBD plasma and the catalyst. Among the various catalysts, Ni4Fe1-R exhibited superior activity and stability because of its highest specific surface area, which not only provided sufficient active sites for the adsorption of reactants and intermediates but also enhanced the electric field in the plasma. Furthermore, the stronger lattice distortion of Ni4Fe1-R provided more isolated O2- for CO2 adsorption, and having the most intensive interaction between Ni and Fe in Ni4Fe1-R restrained the catalyst deactivation induced by the segregation of Fe from the alloy to form FeO x . Finally, in situ Fourier transform infrared spectroscopy combined with comprehensive catalyst characterization was used to elucidate the reaction mechanism of the plasma-catalytic CRT reaction and gain new insights into the plasma-catalyst interfacial effect.

Overcoming energy mismatch of metal oxide semiconductor catalysts for CO2 reduction with triboelectric plasma

The activities of semiconductor-based catalytic reactions are limited by mismatch between energy bandgaps of semiconductors and redox potentials of inert small molecules, especially for stable molecules, such as CO2. Herein, a triboelectric plasma catalytic system using metal oxide catalysts has been developed, which reduces CO2 to CO at room temperature and atmospheric pressure. Among the various metal oxide semiconductors, TiO2 catalyst exhibited the best activity, reaching a production rate of 0.14mmol·gcat−1·h−1, and an energy efficiency of 5.3 % for the conversion of electrical to chemical energy. In triboelectric plasma, CO2 molecules were pre-activated to form the transient CO2− anions, and the limiting step of electron transfer between TiO2 and CO2 was avoided, overcoming the energy mismatch between catalyst and CO2. The energy barrier of CO2 dissociation was markedly reduced to 0.18 eV. This work provides an effective strategy to overcome the energy bandgap restriction inherent in semiconductor-based catalytic reactions.

The remarkable oxidation of trichloroethylene in a post-plasma-catalytic system over Ag-Mn-Ce/HZSM-5 catalysts

The degradation of trichloroethylene (TCE) is of paramount importance due to its harmful effect on human health and the environment. In this study, a remarkable oxidation of the toxic TCE was achieved by using a hybrid system integrating a corona discharge reactor and a series of Ag-Mn-Ce/HZSM-5 catalysts. The combination of plasma and catalysis significantly promoted TCE oxidation compared with the plasma alone system. A maximum TCE removal efficiency (100 %) and an energy yield of 204 g·kWh−1 were obtained in the plasma-catalytic system by using the Ag4MnCeOx/HZSM-5 (4 wt% Ag loading) catalyst in dry air with a weight hourly space velocity of 200000 mL·g−1·h−1. In contrast, the plasma alone system showed only a removal efficiency of 34.8 % and an energy yield of 83 g·kWh−1 under the same conditions. By adding Ag, the surface adsorbed oxygen was activated and the reducibility of catalyst was promoted, which enhanced oxygen mobility and improved the oxidation of TCE. Furthermore, relative humidity (RH) had an important effect on TCE oxidation. The highest CO2 selectivity (71.86 %) and CO selectivity (22.21 %) were obtained at an RH of 20 %. The decomposition pathway of TCE in the post-plasma-catalytic system was proposed. This study is expected to provide a feasible method for the control of chlorine-containing waste gas.

Enhanced activity of plasma catalysis for trichloroethylene decomposition via metal-support interaction of Si[sbnd]O[sbnd]Co/Mn bonds over CoMnOX/ZSM-5

Metal-support interaction has a substantial influence on catalyst activity while little attention has been paid to it in the plasma catalytic system. Herein, the effect of support on the activity of CoMnOX-based catalysts was investigated for trichloroethylene removal by plasma catalysis, and CoMnOX/ZSM-5 exhibited the highest mineralization rate (36.93−94.24 %), HCl and Cl2 yield (19.66−94.37 %), energy yield (63.29–29 g/kWh), as well as the lowest export ozone concentration (18.72–108.83 mg/m3) under 6–10 kV. The excellent catalytic activity of CoMnOX/ZSM-5 was ascribed to the formation of abundant defects and oxygen vacancies, which was induced by the SiOCo/Mn hybridization promoting Co/MnO bonds cleavage. CoMnOX/ZSM-5 also exhibited superior adsorption ability, large amount of Co3+, Mn4+ and adsorbed oxygen species, high reducibility and suitable acidity. Moreover, CoMnOX/ZSM-5 maintained superior water-resistant ability and high catalytic activity after 50 h operation. The proposed TCE degradation mechanism suggested that the contribution of plasma active oxygen species was involved in TCE oxidation and oxygen cycle of catalyst. This work provides a novel strategy to design catalysts in plasma catalytic system.

Cycled Storage-Discharge Plasma Catalytic Degradation of Toluene Using Metal Oxide Loaded MS-13X and Glass Beads Packed Bed Dielectric Barrier Discharge Reactor

In this study, a cycled storage-discharge (CSD) plasma catalytic system packed with MOx/MS-13X (M = Cu, Mn, or Cu–Mn) and glass beads was investigated for the abatement of toluene in dry air. The total amount of adsorbed toluene, the catalytic performance of MOx/MS-13X, the energy cost, and the energy yield of the CSD plasma catalysis process were investigated for the different metal-loaded MS-13X samples under study. The metal loading on MS-13X enhanced the mineralization efficiency and reduced the energy cost to remedy 1 m3 of air when compared to unloaded MS-13X. The lowest energy cost (0.25 kWh <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{m}^{-3}$ </tex-math></inline-formula> ) and the highest energy yield (4.37 g/kWh) were obtained using CuMnOx/MS-13X as an adsorbent and catalyst. The influence of the amount of toluene initially adsorbed on CuMnOx/MS-13X on the mineralization efficiency of the CSD plasma catalysis process was studied. The highest COx selectivity (82%) was obtained for the adsorption of 0.23 mmol/g of toluene on CuMnOx/MS-13X, which corresponded to an adsorption time of 2 h. The stability and regenerability of the CuMnOx/ MS-13X catalyst were examined during four cycles of CSD plasma catalytic abatement of 0.23 mmol/g of adsorbed toluene by comparing: 1) the amount of adsorbed toluene; 2) breakthrough time; 3) carbon balance; and 4) the bulk and surface properties of fresh and nonthermal plasma (NTP) regenerated CuMnOx/ MS-13X. The crystallinity, textural properties, elemental composition of the CuMnOx/MS-13X zeolite, and the oxidation state of the metals loaded on the zeolite did not change upon NTP exposure during four cycles of CSD plasma catalysis. Moreover, in this work, NTP exposure also showed to be successful in the regeneration of the CuMnOx/MS-13X zeolite for the CSD plasma catalytic abatement of toluene.

Probing the effects of plasma-induced surface species in ring-opening process of toluene decomposition via plasma-excited TPD and in situ DRIFTS

Aromatic ring-opening process is considered as the rate-determining step for catalytic toluene decomposition. However, the ring-opening pathway has not been fully revealed, especially the effect of the surface species in plasma catalytic hybrid system. Herein, a series of Mn based catalysts (with the low Mn content of 1 wt %), Mn/γ-Al2O3, Au-Mn/γ-Al2O3 and Ag-Mn/γ-Al2O3, were used to clarify the mechanism of plasma catalytic toluene degradation by a closely combined temperature-programmed desorption (TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Effects of plasma on surface oxygen species were investigated by a comparison study of O2-TPD and plasma-excited O2-TPD. A strong interaction between plasma and Ag-Mn/γ-Al2O3 could make better use of plasma-induced active oxygen species (i.e. O3, O*, O2* etc.) and considerably increase the amount of chemically adsorbed oxygen. Moreover, modified NH3-TPD experiments proved that O2 excited by plasma would greatly change the surface acidity of Ag-Mn/γ-Al2O3, resulting in the desorption activation energy (Ed) of toluene increasing to 19.5 kJ/mol. Finally, possible ring-opening mechanisms over different catalysts were proposed after the evolution of typical intermediates being systematically analyzed by in situ DRIFTS. It was found that the toluene ring-opening reaction on different catalysts might be selectively started at hydroquinone. The present work could provide both a more detailed toluene ring-opening process and new insights into the understanding of the plasma exciting effect on the surface species in VOCs decomposition.

Plasma-Catalytic Reforming of Naphthalene and Toluene as Biomass Tar over Honeycomb Catalysts in a Gliding Arc Reactor.

Biomass gasification is a promising and sustainable process to produce renewable and CO2-neutral syngas (H2 and CO). However, the contamination of syngas with tar is one of the major challenges to limit the deployment of biomass gasification on a commercial scale. Here, we propose a hybrid plasma-catalytic system for steam reforming of tar compounds over honeycomb-based catalysts in a gliding arc discharge (GAD) reactor. The reaction performances were evaluated using the blank substrate and coated catalytic materials (γ-Al2O3 and Ni/γ-Al2O3). Compared with the plasma alone process, introducing the honeycomb materials in GAD prolonged the residence time of reactant molecules for collision with plasma reactive species to promote their conversions. The presence of Ni/γ-Al2O3 gave the best performance with the high conversion of toluene (86.3%) and naphthalene (75.5%) and yield of H2 (35.0%) and CO (49.1%), while greatly inhibiting the formation of byproducts. The corresponding highest overall energy efficiency of 50.9 g/kWh was achieved, which was 35.4% higher than that in the plasma alone process. Characterization of the used catalyst and long-term running indicated that the honeycomb material coated with Ni/γ-Al2O3 had strong carbon resistance and excellent stability. The superior catalytic performance of Ni/γ-Al2O3 can be mainly ascribed to the large specific surface area and the in situ reduction of nickel oxide species in the reaction process, which promoted the interaction between plasma reactive species and catalysts and generated the plasma-catalysis synergy.