Chlorinated Volatile Organic Compounds Research Articles

An alternative generic groundwater-to-indoor air attenuation factor for application in commercial, industrial, and other nonresidential settings

ABSTRACT The default groundwater-to-indoor air attenuation factor (AF) of 10−3 (0.001) to assess the vapor intrusion (VI) pathway and generate VI screening levels for groundwater was developed by the United States Environmental Protection Agency (EPA) based on chlorinated volatile organic compound (VOC) indoor air and groundwater data collected in residential buildings and compiled in EPA’s 2012 VI database. In their VI guidance published in 2015, EPA recognized that this default AF may be overly conservative for nonresidential buildings. In 2015, the Department of Defense (DoD) began developing a first-of-its-kind VI database to assess AFs at commercial and industrial buildings at DoD installations and support the development of alternative generic AF values. This database was expanded in 2019 to include 76 buildings at 22 DoD installations across the United States and is comparable in size to the EPA VI database. The DoD database includes chlorinated VOC data from groundwater and indoor air samples collected from multiple sampling zones within these buildings. Empirical groundwater-to-indoor air AFs were calculated using similar screening methods employed by EPA, including a source strength screen, to filter out potential background source contributions unrelated to VI. Analysis of indoor air-groundwater data pairs found that there is more attenuation occurring from groundwater to indoor air in DoD commercial and industrial buildings relative to residential buildings and that the DoD buildings’ AFs are one to four orders of magnitude lower than EPA’s residential-based default of 10−3. The results support the use of a generic groundwater AF of 10−4 (0.0001) to support VI assessment and develop groundwater screening levels specific to large commercial and industrial buildings as an alternative to the residential default AF. Implications: The use of groundwater-to-indoor air attenuation factors (AFs) is a key component of vapor intrusion (VI) pathway assessments and VI screening-level development for groundwater. Currently, the United States Environmental Protection Agency (EPA) and many state regulatory agencies use a default groundwater AF of 10−3 (0.001) based on chlorinated volatile organic compound (VOC) data collected in residential buildings. VI assessment data collected at Department of Defense (DoD) installations indicate that there is significantly more groundwater-to-indoor air attenuation occurring at DoD commercial and industrial buildings. For that reason, the default AF of 10−3 results in groundwater screening levels that are overestimating VI-related risks in these types of building. The DoD data support the use of a generic groundwater AF of 10−4 (0.0001) for conducting VI assessment and developing groundwater screening levels at large commercial and industrial buildings.

Visible Light‐Driven Degradation of Trichloroethylene in Aqueous Phase with Vanadium‐Doped TiO2 Photocatalysts

The development of photocatalyzed water remediation strategies using visible (solar) light to mineralize volatile chlorinated organic compounds (VCOCs) is a long standing, not yet fully achieved goal. Herewith, a facile route is presented to synthesize vanadium‐doped TiO2 photocatalysts using a one‐step hydrothermal method. Different characterization methods are employed to investigate the physicochemical properties of as‐prepared V‐doped TiO2 samples, indicating the mixed phases of anatase, rutile, and brookite in the crystal structure addition to the mesoporous framework. The nature of the vanadium species at the TiO2 surface is assessed by X‐ray photoelectron and emission spectroscopy. The aerobic photodegradation of a common VCOC, trichloroethylene, using V‐doped catalysts is demonstrated to be much more effectively than with undoped TiO2. Importantly, the herein described V‐doped photocatalysts show high activity both under ultraviolett and visible light irradiation. Moreover, these V‐doped TiO2 photocatalysts are robust under the reaction conditions, being recyclable for at least four consecutive runs without any activity loss.

Enhanced activity of CuOy/TNTs doped by CeOx for catalytic ozonation of 1,2-dichloroethane at normal temperatures: Performance and catalytic mechanism

Achieving efficient and stable catalysts with chlorine resistance is of great importance for chlorinated volatile organic compounds (CVOCs) degradation. This study developed catalysts containing abundant CeOCu bonds anchored on titanium nanotubes (TNTs) to form strong electronic metal–metal interaction (EMMI) coordination structure for efficiently catalytic ozonation of 1,2-dichloroethane (1,2-DCE). The occurrence of EMMI resulted in the formation of electron-poor/rich centers and a high proportion of weak-acidity sites over Ce-Cu/TNTs catalysts. Among various catalysts, 1Ce1Cu/TNTs exhibited the optimum catalytic performance with 92.5 % of 1,2-DCE conversion and 85.4 % of CO2 selectivity, the long-term stability of 24 h and the good water resistance to 50 % relative humidity (RH). Importantly, the XPS results and DFT calculations suggested Ce drove the Cl atom off Cu species, thus alleviating the chloridion deposit on Cu sites, accelerating the migration of chlorine and offering more redox sites for O3 activation. Electron paramagnetic resonance (EPR) and radical quenching tests identified that •OH was a key reactive oxygen species to achieve efficient degradation of 1,2-DCE. The possible reaction pathways for the catalytic ozonation of 1,2-DCE included three parts, including O3 activation, 1,2-DCE preliminary degradation and deep oxidation, which obeyed the L-H mechanism.

Experiment and Molecular Mechanism of Two Chlorinated Volatile Organic Compounds in Ionic Liquids

The structure–property relationship between ionic liquids (ILs) and two chlorinated volatile organic compounds (CVOCs), dichloromethane (DCM) and 1,2-dichloroethane (DCE), was systematically investigated. The suitable IL was screened using the COSMO-RS model, and 1-ethyl-3-methylimidazolium acetate [EMIM][Ac] was considered the optimal absorbent to capture the two CVOCs. The vapor–liquid equilibrium experiment demonstrates that the addition of the IL significantly reduces the vapor pressures of the IL + DCM (or DCE) systems. The structure of ILs on the absorption performance was investigated by absorption capacity experiments. Then, the absorption mechanism was investigated through QC calculations and wavefunction analysis. The consistency between the experiments and the molecular mechanism reveals that the formation of the hydrogen bond between the IL and CVOC enhances the absorption process.

Formation of PCDD/Fs, PCBs and HCl during catalytic combustion of chlorobenzene over supported transition metal (Cr, V and Cu) oxide catalysts

As an efficient scheme, catalytic combustion can be used to eliminate chlorinated volatile organic compounds (CVOCs). To avoid the formation of more toxic by-products, it is essential to reveal the relationship between the chlorine-containing products and redox properties of catalyst. In the present study, the activity for chlorobenzene (CB) oxidation, HCl production, and formation of by-products polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs)were investigated over γ-Al2O3-supported transition metal (Cr, V and Cu) oxide catalysts. The results showed that the 10Cr-Al catalyst with relatively high specific surface areaand more oxygen absorbed than other catalysts exhibited higher catalytic oxidation activity for CB. The temperatures needed for 90% conversion of CB (T90) were 331, 353 and 386 °C for 10Cr-Al, 10V-Al and 10Cu-Al, respectively. The amount and type of acid sites on the surface of catalysts play an important role in the distribution of products and by-products. It was found that the increase of acid sites and the presence of Brønsted acid (B-acid) significantly improve the HCl selectivity of catalysts. More HCl was formed on the 10V-Al catalyst with B-acid sites. Meanwhile PCDD/Fs and PCBs detected in the by-products had a tight relationship with the acidity sites and redox performance of the catalyst. The yields of ∑PCDD/Fs and ∑PCBs were the largest on 10V-Al at T10, reaching 25.60, 66.93 mmol/mol CB, respectively. The obtained results provided theoretical support for the subsequent development of CVOCs catalytic oxidation catalysts and the control of toxic by-products.

A Systematical Comparison of Catalytic Behavior of NM/γ-Al2O3 (NM = Ru, Rh, Pt, Pd, Au, Ir) on 1,2-Dichloroethane Oxidation: Distributions of By-Products and Reaction Mechanism

Understanding the reaction path and mechanism of chlorinated volatile organic compound (CVOC) destruction is important for designing efficient catalysts, especially for the application of noble metal-based materials. Herein, several typical noble metals, Ru, Rh, Pt, Pd, Au, and Ir, supported on γ-Al2O3 catalysts were synthesized by the hydrazine hydrate reduction method for 1,2-dichloroethane (1,2-DCE) elimination. Various character measurements were conducted, and the results suggest that the high-valence state of noble metals is beneficial for the 1,2-DCE reaction as it enables the enhancement of the mobility of the surficial active oxygen species of catalysts. Among the noble metals, Ru/γ-Al2O3 expresses superior catalytic reactivity, with a 90% pollutant conversion rate at 337 °C, and competitive CO2 selectivity, 99.15% at the temperature of total oxidation. The distribution of by-products and the degradation routes were analyzed online by GC-ECD and in situ diffuse reflectance infrared spectroscopy, which may provide helpful insight for the future application of noble metal-based catalysts for CVOC elimination in industrial fields.

A novel application of a geotechnical soil stabilization technology for improved delivery of remedial amendments

AbstractAccelerating the remediation of contaminants that have diffused into low‐permeability (low‐k) geologic units such as silts and clays is a key need for the groundwater remediation industry. Injection‐based remedial technologies are often ineffective because the injected amendments are more likely to influence transmissive media (sands and sandy silts) and generally do not penetrate low‐k units. While some emerging technologies are now being tested, they are often expensive or have other technical limitations (e.g., installation depth and rate of amendment emplacement). To address the problem of treating contaminants in low‐k media, a geotechnical technology called the “Grout Bomber” (Keller North America) was repurposed for an environmental application to emplace ~800 vertical “reaction columns” containing zero valent iron (ZVI), sand, and neat vegetable oil for the treatment of chlorinated volatile organic compounds (CVOCs) in lean clays and sandy clays. The reaction columns were closely‐spaced (2–3 ft apart) to greatly accelerate the back diffusion of CVOCs from the low‐k media to the reaction columns where contact with ZVI and vegetable oil promotes abiotic and biotic reductive dechlorination of CVOCs, respectively. Overall, 35 tons of ZVI were emplaced into the 5200 cubic yard (yd3) (~4000 m3) source zone during the project. Key benefits of this technology include rapid installation (average of 107 reaction columns per day), ease of remediation amendment mixing, consistent amendment dosing, and relatively low unit installation costs ($71 per cubic yard of treatment zone). It should be emphasized that this application of the Grout Bomber relies on diffusion of contaminants into the reaction columns from the surrounding low‐k media—a process that occurs slowly over years to decades. A planning‐level model showed that installation of closely spaced vertical reaction columns in a TCE‐laden clay unit reduced the time to achieve maximum contaminant levels from greater than 500 years to approximately 26 years. Groundwater monitoring confirmed the establishment of a concentration gradient between the reaction columns which promotes diffusion of CVOCs toward the reaction columns. The presence of dissolved acetylene and gaseous “higher coupling” products (>C3) provide further evidence of ongoing abiotic reductive dechlorination within the reaction columns.

Simultaneously Constructing Active Sites and Regulating Mn-O Strength of Ru-Substituted Perovskite for Efficient Oxidation and Hydrolysis Oxidation of Chlorobenzene.

Chlorinated volatile organic compounds (CVOCs) are a class of hazardous pollutants that severely threaten environmental safety and human health. Although the catalytic oxidation technique for CVOCs elimination is effective, enhancing the catalytic efficiency and simultaneously inhibiting the production of organic byproducts is still of great challenge. Herein, Ru-substituted LaMn(Ru)O3+ δ perovskite with Ru-O-Mn structure and weakened Mn-O bond strength has been developed for catalytic oxidation of chlorobenzene (CB). The formed Ru-O-Mn structure serves as favorable sites for CB adsorption and activation, while the weakening of Mn-O bond strength facilitates the formation of active oxygen species and improves oxygen mobility and catalyst reducibility. Therefore, LaMn(Ru)O3+ δ exhibits superior low-temperature activity with the temperature of 90% CB conversion decreasing by over 90°C compared with pristine perovskite, and the deep oxidation of chlorinated byproducts produced in low temperature is also accelerated. Furthermore, the introduction of water vapor into reaction system triggers the process of hydrolysis oxidation that promotes CB destruction and inhibits the generation of chlorinated byproducts, due to the higher-activity *OOH species generated from the dissociated H2 O reacting with adsorbed oxygen. This work can provide a unique, high-efficiency, and facile strategy for CVOCs degradation and environmental improvement.

Synchronously constructing the optimal redox-acidity of sulfate and RuOx Co-modified CeO2 for catalytic combustion of chlorinated VOCs

CeO2-based catalysts are highly active but easily deactivated for the catalytic combustion of chlorinated VOCs (CVOCs), and enhanced redox and acidity are also considered to be effective strategies. However, the screening of practicable modifiers and their preparation method to achieve the promotion and balancing of redox-acidity is still desired. In this work, sulfate and RuOx were simultaneously introduced into CeO2 by a simple co-precipitation method, and the optimal redox-acidity was constructed. The catalytic combustion of 1,2-dichloroethane (DCE) indicated that 2.5Ru-CeO2-S0.05 presented an outstanding oxidation activity and selectivity of chlorinated byproducts and superior cycle and long-term stability (at least 60 h at 280 °C), even in the presence of 5 % H2O. A series of control experiments, such as the introduction methods, the precursors and contents of Ru and sulfate, and their property characterization revealed that the bulk doping of Ru mainly contributed to the promoted activity and durability through more exposed Ce3+/4+ and oxygen vacancies and the rapid removal ability of the inorganic chlorine species via a semi-Deacon reaction pathway, as well as to the formation of chlorinated byproducts. Meanwhile, the synchronous introduction of sulfate as Brønsted acid sites efficiently inhibited these chlorinated byproducts, while its retained redox ability and the enhanced Lewis acid sites owing to the strong electron withdrawing of the sulfate also further promoted DCE oxidation. Moreover, 2.5Ru-CeO2-S0.05 showed a high activity and excellent durability for the catalytic oxidation of ethylene, vinyl chloride and their mixtures with 1,2-DCE. This work provided a demonstration for balancing the oxidation performance and acidity of CeO2-based catalysts, which contributed to the development of applicable catalysts for catalytic oxidation of CVOCs under actual working conditions.

Insights into Chlorobenzene Catalytic Oxidation over Noble Metal Loading {001}-TiO2: The Role of NaBH4 and Subnanometer Ru Undergoing Stable Ru0↔Ru4+ Circulation.

Catalytic combustion of ubiquitous chlorinated volatile organic compounds (CVOCs) encounters bottlenecks regarding catalyst deactivation by chlorine poisoning and generation of toxic polychlorinated byproducts. Herein, Ru, Pd, and Rh were loaded on {001}-TiO2 for thermal catalytic oxidation of chlorobenzene (CB), with Ru/{001}-TiO2 representing superior reactivity, CO2 selectivity, and stability in the 1000 min on-stream test. Interestingly, both acid sites and reactive active oxygen species (ROS) were remarkably promoted via adding NaBH4. But merely enhancing these active sites of the catalyst in CVOC treatment is insufficient. Continuous deep oxidation of CB with effective Cl desorption is also a core issue successfully tackled through the steady Ru0↔Ru4+ circulation. This circulation was facilitated by the observed higher subnanometer Ru dispersion on {001}-TiO2 than the other two noble metals that was supported by single atom stability DFT calculation. Nearly 88 degradation products in off-gas were detected, with Ru/{001}-TiO2 producing the lowest polychlorinated benzene byproducts. An effective and sustainable CB degradation mechanism boosted by the cooperation of NaBH4 enhanced active sites and Ru circulation was proposed accordingly. Insights gained from this study open a new avenue to the rational design of promising catalysts for the treatment of CVOCs.

Catalytic oxidation of dichloromethane over phosphate-modified Co3O4: Improved performance and control of byproduct selectivity by Co3O4 defects and surface acidity

The catalytic oxidation of chlorinated volatile organic compounds (CVOCs) is an important topic in environmental catalysis, but the design of highly effective catalysts remains challenging. In this work, phosphate – modified Co3O4 oxides gave higher activity, better durability and much lower selectivities to Cl-containing byproducts (e.g., CH3Cl and CHCl3) compared to the pristine Co3O4 in the catalytic oxidation of dichloromethane (CH2Cl2). Such phosphate modification created more oxygen vacancies on the Co3O4 and thus enhanced reducibility. On the other hand, the presence of phosphate generated abundant surface Brønsted acid sites and suppressed surface basicity. The improved performance was related to the promoted adsorption/activation of CH2Cl2 on the surface acid sites, and synergistically facile oxidation of the reactive intermediates by the oxygen species activated on the oxygen vacancies. Moreover, on the modified catalyst, the fast oxidation of the reaction intermediate (i.e., CH3O-) inhibited the formation of CH3Cl. Meanwhile, the low surface basicity of the catalyst was probably responsible to the low selectivity to CHCl3.

Catalytic destruction of chlorobenzene over K-OMS-2: Inhibition of high toxic byproducts via phosphate modification

In the process of catalytic destruction of chlorinated volatile organic compounds (CVOCs), the catalyst is prone to chlorine poisoning and produce polychlorinated byproducts with high toxicity and persistence, bringing great risk to atmospheric environment and human health. To solve these problems, this work applied phosphate to modify K-OMS-2 catalysts. The physicochemical properties of catalysts were determined by using X-ray powder diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), hydrogen temperature programmed reduction (H2-TPR), pyridine adsorption Fourier-transform infrared (Py-IR) and water temperature programmed desorption (H2O-TPD), and chlorobenzene was selected as a model pollutant to explore the catalytic performance and byproduct inhibition function of phosphating. Experimental results revealed that 1 wt.% phosphate modification yielded the best catalytic activity for chlorobenzene destruction, with the 90% conversion (T90) at approximately 247°C. The phosphating significantly decreased the types and yields of polychlorinated byproducts in effluent. After phosphating, we observed significant hydroxyl groups on catalyst surface, and the active center was transformed into Mn(IV)-O…H, which promoted the formation of HCl, and enhanced the dechlorination process. Furthermore, the enriched Lewis acid sites by phosphating profoundly enhanced the deep oxidation ability of the catalyst, which promoted a rapid oxidation of reaction intermediates, so as to reduce byproducts generation. This study provided an effective strategy for inhibiting the toxic byproducts for the catalytic destruction of chlorinated organics.

Vinyl chloride catalytic combustion on Pt/CeO2: Tuning Pt chemical state to promote Cl removing

Supported Pt catalysts usually produce chlorinated byproducts during chlorinated volatile organic compounds (CVOCs) combustion, the removal of formed surface chlorine species is the key to improve the activity, selectivity and stability. In this paper, the Pt chemical state is adjusted by the interaction between Pt and CeO2 through controlling the morphology of CeO2, which further affects the catalytic performance of VC combustion. For Pt/CeO2-octahedron, the weak interaction between Pt and CeO2 results in the formation of PtO2, facilities VC adsorption and C–Cl bonds cleavage and becomes a key active site to accommodate the dissociated Cl species. While the strong interaction leads to the formation of PtxCe1-xO2-σ solid solution on Pt/CeO2-rod has relative lower ability in Cl species removal compared with PtO2. Density functional theory (DFT) calculations also confirms that the introduced Pt species reduces the concentration of Cl species on the surface as well as the chlorinated-byproducts. Hence, Pt/CeO2-octahedron outperformed Pt/CeO2-rod and Pt/CeO2-cube with 90% VC conversion at 280 °C. Furthermore, under the same VC conversion (90%), the concentration of chlorinated byproducts on Pt/CeO2-octahedron was only 4% than that of Pt/CeO2-rod.

Complete oxidation of 1,2-dichloroethane over highly efficient Cu/Al-Ti composite metal oxide catalyst

Chlorinated volatile organic compounds (CVOCs) have received attention as hazardous air contaminants for decades, and a complete oxidation process of CVOCs using an efficient catalyst should be most effective to handle such hazardous materials. A series of CuOx-supported on Al-Ti mixed oxide catalysts were prepared by sol-gel method for the mixed oxide support and followed by wet impregnation method for the CuOx nanoparticles formation on the support. These Cu/Al-Ti composite catalysts were investigated for catalytic complete oxidation of 1,2-dichloroethane (DCE), which is one representative CVOCs. Through combining each transition metal components that having different catalytic properties with appropriate composition, excellent catalytic performances in terms of activity and selectivity for the catalytic oxidation of DCE were obtained on the resultant Cu/Al-Ti composite catalysts. The design strategy of composite catalyst studied in this work should suggest the way for efficient and sustainable removal of CVOCs using nonprecious catalytic materials.

Plasma-catalytic oxidation of chlorobenzene over Co-Mn/TiO2 catalyst in a dielectric barrier discharge reactor with the segmented electrodes

Plasma-assisted catalytic oxidation of chlorinated volatile organic compounds (CVOCs) over Co-Mn/TiO2 catalyst was performed in a dielectric barrier discharge (DBD) reactor having two segmented electrodes. The combination of DBD reactor with segmented electrodes and Co-Mn/TiO2 catalyst remarkably enhanced the removal efficiency of chlorobenzene (CB) and selectivity of CO2. The segmented discharge reactor with Co-Mn/TiO2 catalyst presented the best performance with 96.3 % of removal efficiency and 69.0 % of CO2 selectivity at discharge voltage of 17 kV compared with the traditional plasma-only and other plasma-catalytic reactors. Results from discharge characteristics analysis showed that the addition of segmented electrodes and the catalysts could improve the plasma characteristics and greatly boost the specific energy density (SED) at the same voltage, resulting in the generation of more high-energy electrons and chemical active species which favor the oxidation of CB. Although the segmented electrodes facilitated the generation of O3, the Co-Mn/TiO2 catalyst boosted the decomposition of O3 to generate active oxygen species (O* and O2). The synergistic effect of introducing segmented electrodes and the Co-Mn/TiO2 catalyst into the DBD reactor at alternate voltages of 13 and 15 kV could promote the deep oxidation of intermediate products thereby bringing less effects on the catalyst surface, leading to a stable and high performance in CB removal. Furthermore, a plausible decomposition mechanism of CB destruction in the DBD reactor having segmented electrode over Co-Mn/TiO2 catalyst was proposed according to the identification of gaseous intermediates based on GC-MS analysis.

Unveiling the lead resistance mechanism and interface regulation strategy of Ru-based catalyst during chlorinated VOCs oxidation

Maintaining stable catalytic performance for chlorinated volatile organic compounds (CVOCs) oxidation in Pb-containing scenarios is an intractable challenge for the industrial application of Ru-based catalysts. Herein, we systematically investigated the effect of Pb poisoning on the activity over various Ru-based catalysts during the CVOCs oxidation and explored the possible Pb resistance mechanism. The source of high Pb resistance was clarified from two aspects: (1) oxygen vacancies on supports (CeO2 or TiO2) captured Pb and firmly locked it in lattice, namely strong capture effect; and (2) the formation of stable Ru-O-M (M = Ce and/or W) bonds weakened the affinity between active Ru sites and Pb, ensuring the preferential deposition of Pb at oxygen vacancies. With the synergistic effect of above factors, the intrinsic activity (mainly strong acidity) of Ru sites in Ru/CeO2 and RuW/TiO2 catalysts was retained, which ensured the efficient dissociation of C-Cl bond and oxidation of CB.

Recent Advances of Chlorinated Volatile Organic Compounds' Oxidation Catalyzed by Multiple Catalysts: Reasonable Adjustment of Acidity and Redox Properties.

The severe hazard of chlorinated volatile organic compounds (CVOCs) to human health and the natural environment makes their abatement technology a key topic of global environmental research. Due to the existence of Cl, the byproducts of CVOCs in the catalytic combustion process are complex and toxic, and the possible generation of dioxin becomes a potential risk to the environment. Well-qualified CVOC catalysts should process favorable low-temperature catalytic oxidation ability, excellent selectivity, and good resistance to poisoning, which are governed by the reasonable adjustment of acidity and redox properties. This review overviews the application of different types of multicomponent catalysts, that is, supported noble metal catalysts, transition metal oxide/zeolite catalysts, composite transition metal oxide catalysts, and acid-modified catalysts, for CVOC degradation from the perspective of balance between acidity and redox properties. This review also highlights the synergistic degradation of CVOCs and NOx from the perspective of acidity and redox properties. We expect this work to inspire and guide researchers from both the academic and industrial communities and help pave the way for breakthroughs in fundamental research and industrial applications in this field.

Enhanced Performance of Supported Ternary Metal Catalysts for the Oxidation of Toluene in the Presence of Trichloroethylene

Chlorinated volatile organic compounds (CVOCs), even in small quantities, can cause Pt-based catalyst poisoning. Improving the low-temperature chlorine resistance of catalysts is of vital importance for industrial application, although it remains challenging. Considering actual industrial production, a TiO2-supported ternary metal catalyst was prepared in this work to study the catalytic oxidation of multicomponent VOCs (toluene and trichloroethylene (TCE)). Among all of the samples, PtWRu/TiO2 and PtWCr/TiO2 exhibited the best catalytic performance for toluene oxidation. In the mixed VOC oxidation, the PtWCr/TiO2 sample showed the best catalytic activity for toluene combustion (a toluene conversion of 90% was achieved at 258 °C and a space velocity of 40,000 mL g−1 h−1, and the specific reaction rate and turnover frequency at 215 °C were 44.9 × 10−6 mol gPt−1 s−1 and 26.2 × 10−5 s−1). The PtWRu/TiO2 sample showed the best catalytic activity for TCE combustion (a TCE conversion of 90% was achieved at 305 °C and a space velocity of 40,000 mL g−1 h−1, and the specific reaction rate and turnover frequency at 270 °C were 9.0 × 10−6 mol gPt−1 s−1 and 7.3 × 10–5 s−1). We concluded that the ternary metal catalysts could greatly improve chlorine desorption by increasing the active lattice oxygen mobility and surface acidity, thus reducing chlorinated byproducts and other serious environmental pollutants. This work may serve as a reasonable design reference for solving more practical industrial production emissions of multicomponent VOCs.

FeMn/Al2O3 as a high-efficient and low-cost catalyst for chlorobenzene removal in a nonthermal plasma-catalysis reactor

Fe and Mn are the transition-metals that have advantages of low cost and easy availability. In order to high-efficient remove chlorinated volatile organic compounds (CVOCs), a series of high-efficient and low-cost FexMny/Al2O3 catalysts were synthesized by reflux-coprecipitation method, and the removal of chlorobenzene, a CVOCs model compounds, was studied in a nonthermal plasma coupled with FexMny/Al2O3 system at room temperature. The kinetic parameters of the chlorobenzene removal in the nonthermal plasma reactor coupled with FexMny/Al2O3 were obtained. Meanwhile, the reaction route of the chlorobenzene removal in the nonthermal plasma coupled with FexMny/Al2O3 reactor was revealed. The results indicated that the best conversion efficiency and the highest CO2 selectivity of the chlorobenzene removal in the plasma-Fe1Mn1/Al2O3 system were in sequence as 95.77% and 93.11%. Moreover, the positive synergy between the plasma and the FexMny/Al2O3 catalysts greatly reduced the activation energies of the chlorobenzene removal, and improved the chlorobenzene removal efficiency in the plasma-FexMny/Al2O3 system. Finally, the possible reaction routes of the chlorobenzene removal in the plasma-Fe1Mn1/Al2O3 system were proposed based on the intermediates identified by the GC/MS.

Oxy-Anionic Doping: A New Strategy for Improving Selectivity of Ru/CeO2 with Synergetic Versatility and Thermal Stability for Catalytic Oxidation of Chlorinated Volatile Organic Compounds.

Understanding the formation and inhibition of more toxic polychlorinated byproducts from the catalytic oxidation elimination of chlorinated volatile organic compounds (Cl-VOCs) and unveiling efficient strategies have been essential and challenging. Here, RuOx supported on CePO4-doped CeO2 nanosheets (Ru/Pi-CeO2) is designed for boosting catalytic oxidation for the removal of dichloromethane (DCM) as a representative Cl-VOC. The promoted acid strength/number and sintering resistance due to the doping of electron-rich and thermally stable CePO4 are observed along with the undescended redox ability and the exposed multi-active sites, which demonstrates a high activity and durability of DCM oxidation (4000 mg/m3 and 15,000 mL/g·h, stable complete-oxidation at 300 °C), exceptional versatility for different Cl-VOCs, alkanes, aromatics, N-containing VOCs, CO and their multicomponent VOCs, and enhanced thermal stability. The suppression of polychlorinated byproducts is determined over Ru/Pi-CeO2 and oxy-anionic S, V, Mo, Nb, or W doping CeO2, thus the oxy-anionic doping strategy is proposed based on the quenching of the electron-rich oxy-anions on chlorine radicals. Moreover, the simple mechanical mixing with these oxy-anionic salts is also workable even for other catalysts such as Co, Sn, Mn, and noble metal-based catalysts. This work offers further insights into the inhibition of polychlorinated byproducts and contributes to the convenient manufacture of monolithic catalysts with superior chlorine-poisoning resistance for the catalytic oxidation of Cl-VOCs.