Chlorinated Volatile Organic Compounds Research Articles

Effect of support structure of Pt/Silicaite-1 catalyst on non-thermal plasma (NTP) assisted chlorobenzene degradation and PCDD/Fs formation

Development of efficient catalysts for non-thermal plasma (NTP) assisted catalysis to mitigate the formation of harmful by-products is a significant challenge in the degradation of chlorinated volatile organic compounds (Cl-VOCs). In this study, catalytically active Pt nanoparticles supported on non-porous SiO2 and silicalite-1 zeolites (S1) with different pore structure were comparatively investigated for catalytic chlorobenzene degradation under NTP condition. It was shown that the pore structure could significantly impact the metal size and metal dispersion rate. Pt supported on modified S1 hierarchical meso-micro-porous silicalite-1 (Pt/D-S1) exhibited the smallest particle size (∼6.19 nm) and the highest dispersion rate (∼1.87). Additionally, Pt/D-S1 demonstrated superior catalytic performance compared to the other catalysts, achieving the highest chlorobenzene conversion and COx selectivity at about 80% and 75%, respectively. Furthermore, the pore structure also affected the formation of by-products according to the findings from GC-MS analysis. Pt/SiO2 generated a total of 18 different species of organic compounds, whereas only 12 species of organic by-products were identified in the Pt/D-S1 system (e.g. polychlorinated compounds like 3,4 dichlorophenol were exclusively identified in Pt/SiO2). Moreover, dioxin-like polychlorinated biphenyl and other chlorinated organic compounds, which have potential to form highly toxic dioxins, were detected in the catalysts. HRGC-HRMS confirmed and quantified the 17 different dioxin/furans formed on Pt/SiO2 (25,100 ng TEQ kg−1), Pt/S1 (515 ng TEQ kg−1) and Pt/D-S1 (367 ng TEQ kg−1). The correlation between synthesis-structure-performance in this study provides insights into the design of catalysts for deep oxidation of Cl-VOCs in NTP system.

Unveiling the Function of Oxygen Vacancy on Facet-Dependent CeO2 for the Catalytic Destruction of Monochloromethane: Guidance for Industrial Catalyst Design.

Secondary pollution remains a critical challenge for the catalytic destruction of chlorinated volatile organic compounds (CVOCs). By employing experimental studies and theoretical calculations, we provide valuable insights into the catalytic behaviors exhibited by ceria rods, cubes, and octahedra for monochloromethane (MCM) destruction, shedding light on the elementary reactions over facet-dependent CeO2. Our findings demonstrate that CeO2 nanorods with the (110) facet exhibit the best performance in MCM destruction, and the role of vacancies is mainly to form a longer distance (4.63 Å) of frustrated Lewis pairs (FLPs) compared to the stoichiometric surface, thereby enhancing the activation of MCM molecules. Subsequent molecular orbital analysis showed that the adsorption of MCM mainly transferred electrons from the 3σ and 4π* orbitals to the Ce 4f orbitals, and the activation was mainly caused by weakening of the 3σ bonding orbitals. Furthermore, isotopic experiments and theoretical calculations demonstrated that the hydrogen chloride generated is mainly derived from methyl in MCM rather than from water, and the primary function of water is to form excess saturated H on the surface, facilitating the desorption of generated hydrogen chloride.

Phosphotungstic Acid as a Dechlorination Agent Collaborates with CeO2 for Synergistic Catalytic Elimination of NOx and Chlorobenzene.

The development of efficient technologies for the synergistic catalytic elimination of NOx and chlorinated volatile organic compounds (CVOCs) remains challenging. Chlorine species from CVOCs are prone to catalyst poisoning, which increases the degradation temperature of CVOCs and fails to balance the selective catalytic reduction of NOx with the NH3 (NH3-SCR) performance. Herein, synergistic catalytic elimination of NOx and chlorobenzene has been originally demonstrated by using phosphotungstic acid (HPW) as a dechlorination agent to collaborate with CeO2. The conversion of chlorobenzene was over 80% at 270 °C, and the NOx conversion and N2 selectivity reached over 95% at 270-420 °C. HPW not only allowed chlorine species to leave as inorganic chlorine but also enhanced the Bro̷nsted acidity of CeO2. The NH4+ produced in the NH3-SCR process can effectively promote the dechlorination of chlorobenzene at low temperatures. HPW remained structurally stable in the synergistic reaction, resulting in good water resistance and long-term stability. This work provides a cheaper and more environmentally friendly strategy to address chlorine poisoning in the synergistic reaction and offers new guidance for multipollutant control.

Degradation of chlorinated volatile organic compounds in waste gas by catalytic plasma system

Dichloromethane (DCM), one of the main components of chlorinated volatile organic compounds (Cl-VOCs), is recognized as extremely hazardous and severely affects human health and the environment. In this study, a self-designed Dielectric Barrier Discharge (DBD) reactor combined with different catalysts to treat the exhaust DCM gas containing ppm concentration levels. A plasma system can generate high-energy electrons and free radicals (such as hydroxyl radical (OH·), and superoxide radical (O2·)) to degrade DCM in the industrial exhaust gas into most HCl and CO2. The removal efficiency can achieve 98.7% under the conditions, a flow rate of 1042 mLmin−1, the residence time of 76.72 ms, concentration of DCM of about 1650 ppm, and specific input energy of 591 JL−1. Although the plasma was highly reactive, the selectivity of the desired products was low, and there were unwanted toxic byproducts such as CHCl3 (1.7%) and CCl4 (13.8%). Thus catalysts were loaded in the plasma discharging zone to enhance removal efficiency and change product distribution. The catalysts were conducive to producing water-soluble products such as HCl. At the same time, the formation of some unwanted byproducts, CHCl3 and CCl4, were also inhibited. We found that using 11.5 kVpp plasma operating voltage combined with 200 mg Co3O4/HZSM-5 can lower the DCM concentration of the outlet stream from 1650 ppm to 53 ppm. Under this condition, the removal efficiency was about 96.7%, attaining permitted emissions.

Research progress of molecular sieve supported catalysts in catalytic oxidation of chlorine-containing volatile organic compounds

Chlorinated Volatile Organic Compounds (CVOCs) come from a wide range of sources and are common precursors of PM2.5 and ozone pollution, which pose a serious threat to the environment and have adverse effects on human health. Catalytic degradation is one of the effective methods to solve CVOCs pollution, which has the advantages of low operating temperature, less chlorine-containing by-products and high degradation efficiency. The core of this technology is to design and develop catalyst materials with excellent stability and catalytic performance. At present, molecular sieve catalysts have attracted extensive attention because of their acidity and unique pore structure. In this paper, the current research status of catalysts supported by molecular sieve, such as noble metals, transition metal oxides and perovskites, and their activity, acidity, stability and selectivity in CVOCs catalytic reactions were summarized and analyzed, and the future development direction of CVOCs molecular sieve supported catalysts was prospected.

Chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane kinetics and equilibrium adsorption studies on selective macrocyclic adsorbents

Chlorinated volatile organic compounds (CVOCs) are often found in combination with 1,4-dioxane which has been used as a solvent stabilizer. It would be desirable to separate these compounds since biodegradation of 1,4-dioxane follows an aerobic pathway while anaerobic conditions are needed for biodegrading CVOCs. Conventional adsorbents such as activated carbon (AC) and carbonaceous resins have high adsorption capacities for 1,4-dioxane and CVOCs but lack selectivity, limiting their use for separation (Liu et al., 2019). In the current work, two macrocyclic adsorbents, β-CD-TFN and Res-TFN, were examined for selective adsorption of chlorinated ethenes in the presence of 1,4-dioxane. Both adsorbents exhibited rapid adsorption of the CVOCs and minimal adsorption of 1,4-dioxane. Res-TFN had a higher adsorption capacity for CVOCs than β-CD-TFN (measured linear partition coefficient, Kd 2140 -9750 L·kg−1 versus 192-918 L·kg−1 for 1,1, DCE, cis-1,2-DCE and TCE, respectively) and was highly selective for CVOCs(TCE Kd ∼117 Kd for 1,4-dioxane). By comparison, TCE and 1,4-dioxane adsorption on AC was approximately equal at 100 µg·L−1 and approximately 1/3 of the adsorption of TCE on the Res-TFN. The greater adsorption and selectivity of Res-TFN suggest that it can be used as a selective adsorbent to separate CVOCs from 1,4-dioxane to allow separate biodegradation.

Catalytic combustion of 1,2-dichloroethane via C[sbnd]C/C[sbnd]Cl bond cleavage through core-shell structured CeO2@TiO2 catalyst with excellent catalytic performances

A highly representative chlorinated volatile organic compound (Cl-VOCs), including 1,2-dichloroethane (1,2-DCE), which is extremely hazardous to human health and the environment. Improving the catalytic activity is very important for catalytic degradation of 1,2-DCE. In the work, CeO2@TiO2 catalyst which has a core-shell structure were made by a simple two-step hydrothermal synthesis method for 1,2-DCE oxidation. CeO2@TiO2 catalysts show higher activity (T90=275 °C), better carbon dioxide yield (YCO2=89.54 %) and lower by-products production than primitive CeO2 and TiO2. Due to its core-shell structure, CeO2@TiO2 shows the appropriate oxidation and reduction ability and appropriate acidity distribution, the powerful relationship between Ce and Ti elements in CeO2@TiO2 leads to effectively generate activity Ce3+and oxygen, which is greatly great enhance the activity of CeO2@TiO2 in 1,2-DCE catalytic oxidation. Based on the analysis of 1,2-DCE degradation performance and physical and chemical attributes, it proposes a way to catalyze 1,2-DCE catalytic oxidation over CeO2@TiO2. In addition, CeO2@TiO2 has good stability, and adding water vapor over the CeO2@TiO2 during 1,2-DCE degradation to promote 1,2-DCE conversion. The findings of this study might offer some new suggestions for creating catalysts that will destroy Cl-VOCs in their preparation and design.

Efficient Catalytic Elimination of Chlorobenzene Based on the Water Vapor-Promoting Effect within Mn-Based Catalysts: Activity Enhancement and Polychlorinated Byproduct Inhibition.

Achieving no or low polychlorinated byproduct selectivity is essential for the chlorinated volatile organic compounds (CVOCs) degradation, and the positive roles of water vapor may contribute to this goal. Herein, the oxidation behaviors of chlorobenzene over typical Mn-based catalysts (MnO2 and acid-modified MnO2) under dry and humid conditions were fully explored. The results showed that the presence of water vapor significantly facilitates the deep mineralization of chlorobenzene and restrains the formation of Cl2 and dichlorobenzene. This remarkable water vapor-promoting effect was conferred by the MnO2 substrate, which could suitably synergize with the postconstructed acidic sites, leading to good activity, stability, and desirable product distribution of acid-modified MnO2 catalysts under humid conditions. A series of experiments including isotope-traced (D2O and H218O) CB-TPO provided complete insights into the direct involvement of water molecules in chlorobenzene oxidation reaction and attributed the root cause of the water vapor-promoting effect to the proton-rich environment and highly reactive water-source oxygen species rather than to the commonly assumed cleaning effect or hydrogen proton transfer processes (generation of active OOH). This work demonstrates the application potential of Mn-based catalysts in CVOCs elimination under practical application conditions (containing water vapor) and provides the guidance for the development of superior industrial catalysts.

Evaluating groundwater ecosystem dynamics in response to post in-situ remediation of mixed chlorinated volatile organic compounds (CVOCs): An insight into microbial community resilience, adaptability, and metabolic functionality for sustainable remediation and ecosystem restoration

The in-situ remediation of groundwater contaminated with mixed chlorinated volatile organic compounds (CVOCs) has become a significant global research interest. However, limited attention has been given in understanding the effects of these remediation efforts on the groundwater microbial communities, which are vital for maintaining ecosystem health through their involvement in biogeochemical cycles. Hence, this study aimed to provide valuable insights into the impacts of in-situ remediation methods on groundwater microbial communities and ecosystem functionality, employing high-throughput sequencing coupled with functional and physiological assays. The results showed that both bioremediation and chemical remediation methods adversely affected microbial diversity and abundance compared to non-polluted sites. Certain taxa such as Pseudomonas, Acinetobacter, and Vogesella were sensitive to these remediation methods, while Aquabacterium exhibited greater adaptability. Functional annotation unveiled the beneficial impact of bioremediation on the sulfur cycle and specific taxa such as Cellvibrio, Massilia, Algoriphagus, and Flavobacterium which showed a significant positive relationship with dark oxidation of sulfur compounds. In contrast, chemical remediation showed adverse impacts on the nitrogen cycle with a reduced abundance of nitrogen and nitrate respiration along with a reduced utilization of amines (nitrogen rich substrate). The findings of this study offer valuable insights into the potential impacts of in-situ remediation methods on groundwater microbial communities and ecosystem functionality, emphasizing the need for meticulous consideration to ensure the implementation of effective and sustainable remediation strategies that safeguard ecosystem health and function.

Synergistic catalytic removal of NOx and chlorinated organics through the cooperation of different active sites

The synergistic removal of NOx and chlorinated volatile organic compounds (CVOCs) has become the hot topic in the field of environmental catalysis. However, due to the trade-off effects between catalytic reduction of NOx and catalytic oxidation of CVOCs, it is indispensable to achieve well-matched redox property and acidity. Herein, synergistic catalytic removal of NOx and chlorobenzene (CB, as the model of CVOCs) has been originally demonstrated over a Co-doped SmMn2O5 mullite catalyst. Two kinds of Mn-Mn sites existed in Mn-O-Mn-Mn and Co-O-Mn-Mn sites were constructed, which owned gradient redox ability. It has been demonstrated that the cooperation of different active sites can achieve the balanced redox and acidic property of the SmMn2O5 catalyst. It is interesting that the d band center of Mn-Mn sites in two different sites was decreased by the introduction of Co, which inhibited the nitrate species deposition and significantly improved the N2 selectivity. The Co-O-Mn-Mn sites were beneficial to the oxidation of CB and it cooperates with Mn-O-Mn-Mn to promote the synergistic catalytic performance. This work paves the way for synergistic removal of NOx and CVOCs over cooperative active sites in catalysts.

Deep Oxidation of Chlorinated VOCs by Efficient Catalytic Peroxide Activation over Nanoconfined Co@NCNT Catalysts.

The catalytic removal of chlorinated VOCs (CVOCs) in gas-solid reactions usually suffers from chlorine-containing byproduct formation and catalyst deactivation. AOP wet scrubber has recently attracted ever-increasing interest in VOC treatment due to its advantages of high efficiency and no gaseous byproduct emission. Herein, the low-valence Co nanoparticles (NPs) confined in a N-doped carbon nanotube (Co@NCNT) were studied to activate peroxymonosulfate (PMS) for efficient CVOC removal in a wet scrubber. Co@NCNT exhibited unprecedented catalytic activity, recyclability, and low Co ion leakage (0.19 mg L-1) for chlorobenzene degradation in a very wide pH range (3-11). The chlorobenzene removal efficiency was kept stable above 90% over Co@NCNT, much higher than that of nonconfined Co@NCNS (45%). The low-valence Co NPs achieved a continuous electron redox cycling (Co0/Co2+ → Co3+ → Co0/Co2+) and greatly promoted the O-O bond dissociation of PMS with the least energy (0.83 eV) inside the channel of Co@NCNT to form abundant HO• and SO4•-. Thus, the deep oxidation of chlorobenzene was achieved without any biphenyl byproducts from the coupling reaction. This study provided a new avenue for designing novel nanoconfined catalysts with outstanding activity, paving the way for the deep oxidation of CVOC waste gas via AOP wet scrubber.

Decomposition mechanism of Cl-VOCs on Cu- and Fe-modified activated carbon in an O2-free atmosphere: The oxidation pathway and product distribution

Activated carbon exhibits a high adsorption capacity for chlorinated volatile organic compounds (Cl-VOCs), while the desorption of Cl-VOCs is not desirable in the thermal regeneration progress of activated carbon. Chlorobenzene was selected as the model substance to explore whether Cl-VOCs can be oxidized as expected in the regeneration atmosphere of O2-free at the temperature range of 150–450 °C. The modification of activated carbon by Cu or Fe has been shown to considerably improve the decomposition activities. According to the breakthrough curves and detection results from XPS and in situ DRIFTS, the decomposition mechanism of C6H5Cl on Cu and Fe active sites is illustrated. The adsorbed C6H5Cl is firstly dechlorinated to form C6H6 and *Cl, and then it was found there are two pathways for the C6H6 oxidation. C6H6 is indirectly oxidized to form C6H5OH and benzoquinone species, or directly ring-opened to generate ethylene and 1,3-butadiene, and further oxidized to produce CO2, CO and H2O. The C6H6 oxidation is determined by the decomposition of acetate on Cu/AC, but the decomposition of benzoquinone and maleate on Fe/AC. The Fe3O4 and Fe2O3 active sites have a higher dechlorination activity but accelerate the deposition of FeCl2, FeCl3 and organic Cl-containing components. The CuO active center has a higher oxidation performance with a higher CO2 selectivity. About 83.0–83.5% of adsorbed chlorobenzene has been oxidized, and the main Cl-containing product is HCl accounting for approximately 77.8–81.0%, a small amount of Cl forms polychlorinated organic compounds or metal chlorides occupying 2.0–5.7%. As the regeneration temperature decreases, the total amount of Cl-containing species is reduced due the lower oxidation and dechlorination activity of catalysts. The decomposition products of Cl-VOCs in the thermal regeneration process of activated carbon were clarified and quantified, which provides a theoretical basis to control Cl-VOCs in regeneration gas.

A tale of two pollutants: The mutual promotion mechanism of synergistic catalytic elimination of Hg0 and chlorobenzene on V2O5–WO3/TiO2 catalyst

The co-benefit of Hg0 or chlorinated volatile organic compounds (CVOCs) oxidation can be achieved by using vanadium-based catalysts in the selective catalytic reduction (SCR) unit. However, there is no research on the synergistic catalytic elimination of Hg0 and chlorobenzene (CB) in vanadium-based catalysts. Herein, the reaction mechanism of catalytic elimination of Hg0 and CB on vanadium-based catalysts was systematically analyzed and discussed for the first time. It is surprisingly observed that there is a synergistic effect between chlorobenzene catalytic oxidation (CBCO) and Hg0 oxidation. That is, CB could enhance Hg0 oxidation by providing active chlorine species, while the presence of Hg0 could also promote CBCO and reduce the formation of polychlorinated byproducts due to the consumption of chlorine species in the Hg0 oxidation reaction according to Le Chatelier’s principle. This synergistic effect was conducive to maintaining the physical structure and electronic properties of the catalyst and weakening the deposition of elements chlorine and mercury on the catalyst surface, promoting the re-exposure of active centers. This work provides unique insights for synergistic catalytic elimination of Hg0 and CB, and is expected to guide the prospective application on vanadium-based catalysts for multipollutant control.

Cometabolism of Chlorinated Volatile Organic Compounds and 1,4-Dioxane in Groundwater.

This article provides an overview of the bioremediation of groundwater plumes containing admixtures of chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane. The remediation of these plumes has historically focused on the reductive dechlorination of the CVOCs. Many of the remaining plumes are relatively large, and contaminant concentrations are diluted below the concentrations that can sustain reductive dechlorination. Cometabolic processes can decrease contaminant concentrations below the thresholds needed to support direct metabolism but typically require the addition of a substrate, such as high-purity propane. Relatively intensive site characterization and monitoring is necessary to implement bioremediation.

Highly efficient MnOx catalysts derived from Mn-MOFs for chlorobenzene oxidation: The influence of MOFs precursors, oxidant and doping of Ce metal

In this research, we introduce a simple, effective, and eco-friendly approach for preparing MnOx materials with a hierarchical porous structure and apply it to the catalytic oxidation of chlorobenzene. In this method, different Mn-based MOFs are used as templates, and MnOx materials with various morphologies and structures are prepared through an alkaline hydrolysis-oxidation method. Different Mn-MOF precursors, oxidants and doping of different metals have a considerable influence on the structural morphology of the obtained MnOx materials. Through adjusting the structural morphology, it is conducive to transfer, diffusion and enrichment of chlorobenzene during the reaction process, and improving the reaction activity. MnO2-74 catalyst derived from Mn-MOF-74 in the presence of H2O2 showed the best catalytic activity (T90 = 174 °C). The exceptional catalytic efficiency is attributed to its large specific surface area, mesoporous structure, better low-temperature reducibility, sufficient acidic sites, and enhanced oxygen activation ability. The primary cause of the decrease in catalytic activity is the existence of surface carbon and inorganic chlorine on the catalyst. This green, efficient, and economical preparation method introduces a novel strategy for the traditional derivatization of MOFs to prepare metal oxide materials for the catalytic oxidation of chlorinated volatile organic compounds (CVOCs).

A Monte‐Carlo Chemical Budget Approach to Assess Ambient Groundwater Flow in Bedrock Open Boreholes

AbstractIn low‐permeability rocks, ambient groundwater flow in open boreholes may go undetected using conventional borehole‐flowmeter tools and alternative approaches may be needed to identify flow. Understanding ambient flow in open boreholes is important for tracking of cross contamination in groundwater. Chlorinated volatile organic compound (CVOC) concentrations from three open boreholes set in a crystalline‐rock aquifer (two of three open boreholes) and a siltstone aquifer (one of three open boreholes) were examined using a new approach and associated software program called the AFCE (Aqueous‐Flow‐Concentration‐Estimator). The program allows comparison of coupled chemical datasets through a Monte‐Carlo simulation and a chemical‐budget approach to assess ambient groundwater flow in open boreholes. The coupled datasets required for the comparison include aqueous CVOC concentrations from groundwater samples from (1) discrete fractures, such as those measured from temporary deployment of straddle‐borehole packer assemblies; and (2) the concentration of the open borehole (wellbore) water, as measured by a vertical profile of passive samplers from within the same open borehole. Because results from the passive samplers represent a composite mixture of the results from the discrete samples under ambient groundwater‐flow conditions, potentially at unknown proportions, the comparison between coupled datasets affords the ability to discern likely water contributions of CVOC from discrete fractures (or fracture zones), and which fractures may be dominating the water chemistry of the open borehole.

Heterogeneous photochemical conversion of chlorobenzene on γ-Al2O3: A chamber experiment study

Atmospheric photochemical conversion of chlorinated volatile organic compounds (CVOCs) is crucial for secondary aerosol formation and tropospheric chlorine chemistry. However, their corresponding conversion pathways and the reaction products are lack of sufficient exploration. Herein, the photochemical conversion of chlorobenzene (CB) on the mineral γ-Al2O3 particulates was chosen as a model reaction to unveil the atmospheric chemistry of CVOCs. Chamber experiments were performed to determine the decay rates of CB with/without SO2 or NH3 under light irradiation. Reaction products were evaluated, along with the in situ diffuse reflectance infrared Fourier transform spectroscopy measurements, to explore the CB conversion pathways under different conditions. We showed that the CB could be greatly degraded by γ-Al2O3 under light irradiation, and the added SO2 significantly inhibited this conversion owing to surface acidification. However, the presence of NH3 was shown to facilitate the CB conversion by immobilizing Cl− as NH4Cl, and recovering surface oxygen vacancies for oxygen activation. In particular, we found that polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) could be generated from the photochemical CB conversion over γ-Al2O3, regardless of SO2 or NH3 coexistence, indicating a potential origin of PCDD/Fs on the atmospheric particulates from the heterogeneous photochemical CVOC conversion.

Pr-modified vanadia-based catalyst for simultaneous elimination of NOx and chlorobenzene

The V2O5/TiO2 catalyst is the most concerned NH3-SCR catalytic system for simultaneous removal of NOx and chlorinated volatile organic compounds (Cl-VOCs). There is an urgent need to develop a vanadia-based catalyst with low vanadium loading and excellent low-temperature catalytic performance. In this work, the Pr and W co-doped vanadia-based catalysts were prepared by a simple impregnation method. After the doping of Pr and W, the vanadia-based catalyst exhibited the excellent catalytic activity for NOx reduction and chlorobenzene (CB) oxidation. The more abundant polymeric vanadyl species and crystalline V2O5 were observed on the PrV5W/Ti catalyst, which are contributing to NH3-SCR and CB oxidation activity. The redox capability and the amount of surface-active adsorbed oxygen of vanadia-based catalyst were improved markedly, thus promoting NH3-SCR and CB oxidation reaction on PrV5W/Ti. This catalyst is promising to be used in the muti-pollutant control reaction of NOx and VOCs.

Catalytic performance of Nb2O5 modified Ru/CeO2 for dichloromethane oxidation

1 ​wt% Ru/5 ​wt% Nb2O5/CeO2 (RuNbCe) catalyst was synthesized via the incipient wetness impregnation method, and measured for the catalytic oxidation of dichloromethane (DCM). The physicochemical properties of catalysts were determined used various characterization techniques. Compared with 1 ​wt% Ru/CeO2, 5 ​wt% Nb2O5/CeO2, CeO2, 1 ​wt% Ru/xNb2O5/CeO2 (x ​= ​1 ​wt%, 2 ​wt%, and 3 ​wt%) and 1 ​wt% Ru/yMOn/CeO2 (M ​= ​Co, Cr, Fe, Mg, Cu; y ​= ​5 ​wt%), the addition of 5 ​wt% Nb2O5 obviously improved the catalytic performance of 1 ​wt% Ru/CeO2, with the T90% and apparent activation energy (Ea) being 287 oC and 43.5 ​kJ/mol, respectively, and less formation of polychlorinated byproducts at space velocity (SV) ​= ​15,000 ​mL ​g‒1 ​h‒1. The RuNbCe catalyst showed good thermal and hydrothermal stability, as well as HCl-resistance performance. We deduced that the higher oxidation performance of the RuNbCe catalyst may be attributed to the suitable acidic sites, good redox capacity, high surface adsorbed oxygen species concentration, and the strong interaction among Ru, Nb2O5 and CeO2. The RuNbCe catalyst has the potential to be applied for the elimination of chlorinated volatile organic compounds (CVOCs).

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.