Oxidation Of Trichloroethylene Research Articles

Ce-modified zeolite BEA catalysts for the trichloroethylene oxidation. The role of the different and necessary active sites

This paper reports the activity of different Ce-BEA zeolites for the catalytic oxidation of trichloroethylene and it is focused on determining the nature of the catalyst active sites. The study was made by using a microporous zeolite BEA, two types of desilicated BEA zeolites and mildly steamed desilicated BEA zeolites. The catalysts were prepared by introducing Ce to the zeolites with incipient wetness impregnation and their structural, textural, and acidic properties were established. The evolution of TCE conversion was correlated with the physicochemical properties of the zeolites. It is shown that highly developed mesopore surface area, well-dispersed cerium species and a high number of Brønsted sites results in the highest activity. The activity and selectivity of the Ce-loaded zeolites were found to be dependent on the number of high strength Brønsted acid centres. The hierarchical materials with a higher density of hydroxyls showed higher yields to HCl while the formation of chlorine was prevented.

Alloying of gold with palladium: An effective strategy to improve catalytic stability and chlorine-tolerance of the 3DOM CeO2-supported catalysts in trichloroethylene combustion

The three-dimensionally ordered macroporous (3DOM) CeO2-supported Au–Pd alloys (xAuPdy/3DOM CeO2, x is the total loading (wt%) of Au and Pd, and y is the Pd/Au molar ratio) were synthesized using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The samples were characterized by a number of analytical techniques, and their catalytic performance was evaluated for the combustion of trichloroethylene (TCE). It is found that the xAuPdy/3DOM CeO2 samples displayed a good-quality 3DOM architecture, and the noble metal nanoparticles (NPs) with a size of 3–4 nm were uniformly dispersed on the skeleton surface of 3DOM CeO2. Among all of the samples, 2.85AuPd1.87/3DOM CeO2 exhibited the highest catalytic activity, with the temperature at a TCE conversion of 90% (T90%) being 415 °C at a space velocity of 20,000 mL/(g h). Furthermore, the 2.85AuPd1.87/3DOM CeO2 sample possessed the lowest apparent activation energy (33 kJ/mol), excellent catalytic stability, and good moisture- and chlorine-tolerant behaviors. Alloying of Au with Pd changed the pathway of TCE oxidation and reduced formation of perchloroethylene. We conclude that the excellent catalytic performance for TCE combustion of 2.85AuPd1.87/3DOM CeO2 was associated with the highly dispersed AuPd1.87 alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd1.87 NPs and 3DOM CeO2 as well as the high-quality 3DOM structure and high surface acidity.

Catalytic oxidation of tricholoethylene over Cr/ZSM‐5/PSSF zeolite membrane catalysts prepared by chemical vapor deposition

AbstractBACKGROUNDChemical vapor deposition (CVD) is a promising catalyst preparation method owing to high dispersion and small particles of metallic oxides. Besides, the ZSM‐5 zeolite membrane is used to treat volatile organic compounds (VOCs) due to relatively high contact efficiency, lower bed pressure drop and mass transfer resistance than granular ZSM‐5, giving good stability of the metal catalysts. However, Cr modified ZSM‐5 zeolite membrane prepared by CVD for trichloroethylene (TCE) catalytic oxidation was still not well‐studied. In the present study, a series of Cr(x)/ZSM‐5/PSSF (x = 1, 3, 5 and 7) catalysts with different Cr loadings was prepared by CVD and further characterized by nitrogen gas (N2) adsorption and desorption, X‐ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature‐programmed desorption (NH3‐TPD) and X‐ray photoelectron spectroscopy (XPS), as well as catalytic performance for TCE oxidation.RESULTSThe results showed that the Cr2O3 species were uniformly dispersed on the surface of ZSM‐5/PSSF, and that the Cr(1)/ZP catalyst exhibited the best catalytic activity for TCE oxidation owing to more Cr6+ species and adsorbed oxygen. It also demonstrated that the Cr(1)/ZP catalyst shows superior catalytic performance for TCE oxidation, giving a T90 that is about 62 °C (c.15%) lower than 1% Cr/ZSM‐5 particle catalyst. Furthermore, it exhibited an excellent stability after online testing at 440 °C for 30 h, and then dropped from 91% to 62% after 95 h, finally remaining at 62% after 120 h.CONCLUSIONThe study demonstrated that Cr/ZSM‐5 zoelite membrane catalysts prepared by CVD show better catalytic behavior and stability for catalytic oxidation of TCE than Cr/ZSM‐5 zoelite catalysts. © 2019 Society of Chemical Industry

Oxidation of TCE by Combining Perovskite-Type Catalyst With DBD

A novel hybrid system constituting of La-Mn-based perovskite-type catalyst with nonthermal plasma (NTP) is developed and evaluated for the removal of trichloroethylene (TCE) from gas streams. Ce and Ni were used as promoter for modification LaMnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> because addition of Ce and Ni could enhance redox property and activity of catalyst. First, the activities of various perovskites including LaMnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ce <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ce <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> were evaluated for TCE removal via catalysis, and the results indicate that La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ce <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> has the highest activity for TCE removal among three perovskites prepared. The three perovskites are individually combined with NTP to form various plasma catalysis systems for TCE removal. Experimental results indicate that 100% TCE removal efficiency can be achieved with plasma catalysis (La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ce <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) when the system is operated with the applied voltage of 16 or 17 kV. On the other hand, the highest TCE removal efficiency achieved with NTP alone is 73.2% with the applied voltage of 17 kV. In addition, CO2 mineralization efficiencies achieved with plasma catalysis combined with La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ce <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (31.1%-46.6%) are significantly higher than that of NTP alone (8.4%-13.1%). It is worth noting that concentrations of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> generated with plasma catalysis are significantly lower than that of NTP alone, implying that formation of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> could be effectively decomposed as plasma catalysis is applied for TCE removal. Overall, perovskite-type catalyst can be integrated with NTP to form plasma catalysis system for effective removal of TCE from gas streams.

Three-dimensionally ordered macroporous Cr2O3−CeO2: High-performance catalysts for the oxidative removal of trichloroethylene

Abstract Three-dimensionally ordered macroporous (3DOM) CeO2, 3DOM Cr2O3, 3DOM xCr2O3−CeO2 (x (the weight percentage of Cr2O3) = 3.5, 5.5, and 8.0 wt%), and 5.5 wt% Cr2O3/3DOM CeO2 samples were prepared using the polymethyl methacrylate (PMMA)-templating and incipient wetness impregnation methods, respectively. A number of techniques were used to characterize physicochemical properties of the materials, and their catalytic activities were evaluated for the oxidation of trichloroethylene (TCE). These samples possessed a good-quality 3DOM structure and a surface area of 35−47 m2/g. The 3DOM 5.5Cr2O3−CeO2 sample performed the best (the temperature at TCE conversion = 90% = 255 °C at a space velocity of 20,000 mL/(g h)). Effects of water vapor and carbon dioxide on activity of the 5.5Cr2O3−CeO2 sample were also examined. It is observed that partial deactivation induced by H2O introduction of the 5.5Cr2O3−CeO2 sample was reversible, while that induced by CO2 addition was irreversible. Based on the activity data and characterization results, it is concluded that the good catalytic activity and thermal stability of 3DOM 5.5Cr2O3−CeO2 was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Cr2O3 and CeO2. We believe that the 3DOM 5.5Cr2O3−CeO2 catalyst is promising in the application for oxidative removal of chlorinated volatile organic compounds.

Influence of the synthesis method on the catalytic activity of mayenite for the oxidation of gas-phase trichloroethylene

Catalytic oxidation of trichloroethylene (TCE) in heterogeneous phase (gas-solid) is an effective strategy for the conversion of this pollutant in less harmful compounds, namely CO2, CO and HCl. In this work, we have studied the use of mayenite, a cost-effective material, as an active catalyst for the TCE conversion. In particular, we have assessed the influence of the mayenite synthesis method (hydrothermal, sol-gel and ceramic) on the reaction performance. The materials have been characterized by different techniques, such as XRD, N2-sorption (BET), TPR, Raman spectroscopy, FESEM-EDX and TEM. The analysis of the light-off curves and product distribution, has shown that the use of the hydrothermal method for the mayenite synthesis results in the most active and selective catalyst. This has been related with a higher surface area and with a higher concentration of oxygen anions in the mayenite prepared by this method. It has been found that the presence of water in the stream do not influence the catalytic performance of the material. A mechanism for the reaction and for the partial deactivation of the catalyst has been proposed.

Catalytic Oxidation of Trichloroethylene over RuO2 Supported on Ceria-zirconia Mixed Oxide

Ru/Ce-Zr catalysts were prepared by impregnation of Ru on the hydrothermally synthesized Ce-Zr mixed oxide with different molar ratio of Ce/Zr. The resultant products were systematically characterized by inductively coupled plasma(ICP), X-ray diffraction(XRD), scanning electron microscopy(SEM)/energy dispersive spectrometry(EDS), H2-temperature programmed reduction(H2-TPR), NH3-temperature programmed desorption(NH3-TPD) and X-ray photoelectron spectroscopy(XPS). It was proved by H2-TPR and NH3-TPD that the introduction of Ru can improve the activity of oxygen of catalysts and the presence of Zr contributes to the increments of acid properties of catalysts. When the molar ratio of Ce-Zr was 8:4, the quantity of Ru was 0.9%(mass ratio), and the calcined temperature of catalysts was at 400 °C, the removal rate of 90% for trichloroethylene(TCE) was reached at 250 °C for 5360 mg/m3 TCE and the stability of the catalysts was investigated under the condition. The results showed that the high removal rate can be maintained for at least 90 h, which is promising for industrial application.

A Novel Synthetic Route to Prepare High Surface Area Mayenite Catalyst for TCE Oxidation

Mayenite (Ca12Al14O33) was synthesized by a novel route based on the use of polymethyl methacrylate (PMMA) as a soft templating agent. The material was tested for the total oxidation of trichloroethylene in the gas phase and the catalytic performance was analysed when using different initial amounts of PMMA in the catalyst synthesis. The results were compared with those obtained with a mayenite synthetized by a classical hydrothermal method. The highest activity in terms of TCE conversion was achieved in the presence of mayenite prepared using 10% w/w of PMMA; its activity was also higher than that of the hydrothermal mayenite. The surface area and the number of superoxide anions (O2−) seem to be the main properties determining the catalytic activity of the material.

Evaluation of LaBO3 (B=Mn, Cr, Mn0.5Cr0.5) perovskites in catalytic oxidation of trichloroethylene

In this study, La–Mn–Cr perovskite-type catalysts were synthesized as LaMnO3,LaCrO3, and LaMn0.5Cr0.5O3 by a microwave-assisted gel-combustion method. They were then calcined at 600oC for 5h in air. X-ray diffraction (XRD) analysis indicated that the crystalline perovskite phase is the dominant phase formed in all the synthesized samples. The scanning electron microscopy (SEM) analysis showed that the perovskites have a full spongy and porous structure. The specific surface area (BET) analysis showed a specific surface area of about 12.4-26.8 m2/g, and the highest specific surface area belonged to the LaMn0.5Cr0.5O3 perovskite. Moreover, the highest oxygen mobility revealed by the temperature-programmed desorption of oxygen (O2–TPD) analysis was related to the LaMn0.5Cr0.5O3 sample. The catalytic activity of the synthesized perovskites in catalytic oxidation of 1000 ppm trichloroethylene (TCE) in air was investigated at different temperatures. The substituted perovskite (LaMn0.5Cr0.5O3) with the highest BET specific surface area and the highest oxygen mobility yielded the best catalytic performance among the probed perovskites.

AuPd/3DOM TiO2 Catalysts: Good Activity and Stability for the Oxidation of Trichloroethylene

Three-dimensionally ordered macroporous (3DOM) TiO2-supported AuPd alloy (xAuyPd/3DOM TiO2 (x = 0.87–0.91 wt%; y = 0.51–1.86)) catalysts for trichloroethylene (TCE) oxidation were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The as-prepared materials possessed a good-quality 3DOM structure and a surface area of 49–53 m2/g. The noble metal nanoparticles (NPs) with a size of 3–4 nm were uniformly dispersed on the surface of 3DOM TiO2. The 0.91Au0.51Pd/3DOM TiO2 sample showed the highest catalytic activity with the temperature at a TCE conversion of 90% being 400 °C at a space velocity of 20,000 mL/(g h). Furthermore, the 0.91Au0.51Pd/3DOM TiO2 sample possessed better catalytic stability and moisture-resistant ability than the supported Au or Pd sample. The partial deactivation induced by H2O introduction of 0.91Au0.51Pd/3DOM TiO2 was reversible, while that induced by CO2 addition was irreversible. No significant influence on TCE conversion was observed after introduction of 100 ppm HCl to the reaction system over 0.91Au0.51Pd/3DOM TiO2. The lowest apparent activation energy (51.7 kJ/mol) was obtained over the 0.91Au0.51Pd/3DOM TiO2 sample. The doping of Au to Pd changed the TCE oxidation pathway, thus reducing formation of perchloroethylene. It is concluded that the high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd NPs and 3DOM TiO2 as well as more amount of strong acid sites were responsible for the good catalytic activity, stability, and water- and HCl-resistant ability of 0.91Au0.51Pd/3DOM TiO2. We believe that 0.91Au0.51Pd/3DOM TiO2 may be a promising catalyst for the oxidative elimination of chlorine-containing volatile organics.

Mechanisms for Abiotic Dechlorination of Trichloroethene by Ferrous Minerals under Oxic and Anoxic Conditions in Natural Sediments.

Bench-scale experiments were performed on natural sediments to assess abiotic dechlorination of trichloroethene (TCE) under both aerobic and anaerobic conditions. In the absence of oxygen (<26 μM), TCE dechlorination proceeded via a reductive pathway generating acetylene and/or ethene. Reductive dechlorination rate constants up to 3.1 × 10-5 d-1 were measured, after scaling to in situ solid:water ratios. In the presence of oxygen greater than 120 μM, TCE dechlorination proceeded via an oxidative pathway generating formic/glyoxylic and glycolic/acetic acids, and oxidative dechlorination rate constants (again scaled to in situ conditions) up to 7.4 × 10-3 d-1 were measured. These rates correspond to half-lives of 60 and 0.25 years for abiotic TCE dechlorination under anaerobic and aerobic conditions, respectively, indicating the potentially large impact of aerobic TCE oxidation in the field. For both reductive and oxidative TCE dechlorination pathways, measured first-order rate constants increased with increasing ferrous iron content, suggesting the role of iron oxidation. Hydroxyl radical formation was measured and increased with increasing oxygen and ferrous iron content. Rate constants associated with TCE oxidation products increased with increasing hydroxyl radical generation rates, and were zero in the presence of a hydroxyl radical scavenger, suggesting that oxidative TCE dechlorination is a hydroxyl radical driven process.

Remediation of TCE-contaminated groundwater using KMnO4 oxidation: laboratory and field-scale studies.

The objectives of this study were to (1) conduct laboratory bench and column experiments to determine the oxidation kinetics and optimal operational parameters for trichloroethene (TCE)-contaminated groundwater remediation using potassium permanganate (KMnO4) as oxidant and (2) to conduct a pilot-scale study to assess the efficiency of TCE remediation by KMnO4 oxidation. The controlling factors in laboratory studies included soil oxidant demand (SOD), molar ratios of KMnO4 to TCE, KMnO4 decay rate, and molar ratios of Na2HPO4 to KMnO4 for manganese dioxide (MnO2) production control. Results show that a significant amount of KMnO4 was depleted when it was added in a soil/water system due to the existence of natural soil organic matters. The presence of natural organic material in soils can exert a significant oxidant demand thereby reducing the amount of KMnO4 available for the destruction of TCE as well as the overall oxidation rate of TCE. Supplement of higher concentrations of KMnO4 is required in the soil systems with high SOD values. Higher KMnO4 application resulted in more significant H+ and subsequent pH drop. The addition of Na2HPO4 could minimize the amount of produced MnO2 particles and prevent the clogging of soil pores, and TCE oxidation efficiency would not be affected by Na2HPO4. To obtain a complete TCE removal, the amount of KMnO4 used to oxidize TCE needs to be higher than the theoretical molar ratio of KMnO4 to TCE based on the stoichiometry equation. Relatively lower oxidation rates are obtained with lower initial TCE concentrations. The half-life of TCE decreased with increased KMnO4 concentrations. Results from the pilot-scale study indicate that a significant KMnO4 decay occurs after the injection due to the reaction of KMnO4 with soil organic matters, and thus, the amount of KMnO4, which could be transported from the injection point to the downgradient area, would be low. The effective influence zone of the KMnO4 oxidation was limited to the KMnO4 injection area (within a 3-m radius zone). Migration of KMnO4 to farther downgradient area was limited due to the reaction of KMnO4 to natural organic matters. To retain a higher TCE removal efficiency, continuous supplement of high concentrations of KMnO4 is required. The findings would be useful in designing an in situ field-scale ISCO system for TCE-contaminated groundwater remediation using KMnO4 as the oxidant.

Synthesis and Evaluation of ABO3 Perovskites (A=La and B=Mn, Co) with Stoichiometric and Over-stoichiometric Ratios of B/A for Catalytic Oxidation of Trichloroethylene

In this contribution, perovskite catalysts (ABO3) were probed that site A and site B were occupied by lanthanum and transition metals of manganese or cobalt, respectively, with stoichiometric ratios as well as 20 % over-stoichiometric ratios of B/A. The perovskite samples were synthesized using a gel-combustion method and characterized by BET, XRD, SEM and O2-TPD analyses. After mounting in a fixed bed reactor, the catalysts were examined in atmospheric pressure conditions at different temperatures for oxidation of 1000 ppm trichloroethylene in the air. Evaluation of over-stoichiometric catalysts activity showed that the increased ratio of B/A in the catalysts compared to the stoichiometric one led to BET surface area, oxygen mobility, and consequently catalytic performance improvement. The lanthanum manganite perovskite with 20 % excess manganese yielded the best catalytic performance among the probed perovskites.

δ13C and δ37Cl Isotope Fractionation To Characterize Aerobic vs Anaerobic Degradation of Trichloroethylene

Trichloroethylene (TCE) is a carcinogenic organic chemical impacting water resources worldwide. Its breakdown by reductive vs oxidative degradation involves different types of chemical bonds. Hence, if distinct isotope effects are reflected in dual element (carbon and chlorine) isotope values, such trends could help distinguishing both processes in the environment. This work explored dual element isotope trends associated with TCE oxidation by two pure bacterial cultures: Pseudomonas putida F1 and Methylosinus trichosporium OB3b, where the latter expresses either soluble methane-monooxygenase (sMMO) or particulate methane-monooxygenase (pMMO). Carbon and chlorine isotope enrichment factors of TCE (e13C = −11.5, −2.4, and −4.2‰; e37Cl = 0.3, −1.3, and −2.4‰, respectively) differed strongly between the strains. The dual element isotope trend for strain F1 (e13C/e37Cl = −38) reflected, as expected, primary carbon and negligible chlorine isotope effects, whereas unexpectedly large chlorine isotope effects bec...

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

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

Au–pd bimetallic alloy nanoparticle-decorated BiPO4 nanorods for enhanced photocatalytic oxidation of trichloroethylene

Photocatalytic oxidation reactions are regarded as promising green synthesis methods for the photodegradation of volatile organic compounds such as trichloroethylene. However, low photocatalytic efficiency and selectivity limit practical application of the technique. We report the synthesis of novel hexagonal BiPO4/Au-Pd nanorods with diameters of 500nm that display excellent performance in degrading trichloroethylene under visible-light irradiation. With co-catalytic Au–Pd bimetallic alloy nanoparticles deposited on the nanorod surfaces, the photocatalytic activity is enhanced approximately 25 times compared to that of the BiPO4 nanorods. The dramatic enhancement of activity is attributed to the Au–Pd alloy nanoparticles effectively separating the oxidation and reduction sites, thereby promoting charge-separation efficiency and providing abundant catalytically active sites to enhance the reactivity of BiPO4. The excellent photocatalytic performance is also attributed to the moderated conduction band position and an optimum Au–Pd weight percentage. This material provides a promising strategy for degradation of volatile organic compounds.

Editor's Highlight: Collaborative Cross Mouse Population Enables Refinements to Characterization of the Variability in Toxicokinetics of Trichloroethylene and Provides Genetic Evidence for the Role of PPAR Pathway in Its Oxidative Metabolism.

Trichloroethylene (TCE) is a known carcinogen in humans and rodents. Previous studies of inter-strain variability in TCE metabolism were conducted in multi-strain panels of classical inbred mice with limited genetic diversity to identify gene-environment interactions associated with chemical exposure. To evaluate inter-strain variability in TCE metabolism and identify genetic determinants that are associated with TCE metabolism and effects using Collaborative Cross (CC), a large panel of genetically diverse strains of mice. We administered a single oral dose of 0, 24, 80, 240, or 800 mg/kg of TCE to mice from 50 CC strains, and collected organs 24 h post-dosing. Levels of trichloroacetic acid (TCA), a major oxidative metabolite of TCE were measured in multiple tissues. Protein expression and activity levels of TCE-metabolizing enzymes were evaluated in the liver. Liver transcript levels of known genes perturbed by TCE exposure were also quantified. Genetic association mapping was performed on the acquired phenotypes. TCA levels varied in a dose- and strain-dependent manner in liver, kidney, and serum. The variability in TCA levels among strains did not correlate with expression or activity of a number of enzymes known to be involved in TCE oxidation. Peroxisome proliferator-activated receptor alpha (PPARα)-responsive genes were found to be associated with strain-specific differences in TCE metabolism. This study shows that CC mouse population is a valuable tool to quantitatively evaluate inter-individual variability in chemical metabolism and to identify genes and pathways that may underpin population differences.

Oxidation of trichloroethylene by the hydroxyl radicals produced from oxygenation of reduced nontronite

Reduction by Fe(II)-bearing silicate minerals has been proposed as an important mechanism for the attenuation of chlorinated hydrocarbons (CHCs) in anoxic subsurfaces. The redox condition of subsurface often changes from anoxic to oxic due to natural processes and human activities, but little is known about the transformation of CHCs induced by Fe(II)-bearing silicate minerals under oxic conditions. This study reveals that trichloroethylene (TCE) can be efficiently oxidized during the oxygenation of reduced nontronite at pH 7.5, whereas the reduction was negligible under anoxic conditions. The maximum oxidation of TCE (initially 1 mg/L) attained 89.6% for 3 h oxygenation of 2 g/L nontronite with 50% reduction extent. TCE oxidation is attributed to the strongly oxidizing hydroxyl radicals (OH) produced by the oxygenation of Fe(II) in nontronite. Fe(II) on the edges is preferentially oxygenated for OH production, and the interior Fe(II) serves as an electron pool to regenerate the Fe(II) on the edges. Oxidation of TCE could be sustainable through chemically or biologically reducing the oxidized silicate minerals. Our findings present a new mechanism for the transformation of CHCs and other redox-active substances in the redox-fluctuation environments.

Chemical oxidation of benzene and trichloroethylene by a combination of peroxymonosulfate and permanganate linked by in-situ generated colloidal/amorphous MnO2

The present study demonstrates the effectiveness of a novel oxidant system, namely the combined use of peroxymonosulfate (PMS) and permanganate (CUPP), for the degradation of benzene and trichloroethylene (TCE) in simulated groundwater. The CUPP process exhibited favorable oxidizing capability because the in-situ generated colloidal and amorphous MnO2 linked the two oxidants. Compared with the separate use of permanganate or peroxymonosulfate, the CUPP process showed much better efficiency for the removal of refractory benzene. According to the electron paramagnetic resonance analysis and PMS-activating experiments, both colloidal and amorphous MnO2 (AM-MnO2) triggered the radical-mediated oxidation, but the AM-MnO2-activated PMS showed an adsorption-dependent oxidizing capability. For the CUPP process, higher temperatures promoted the initial degradation rate of benzene, but did not change its final removal efficiency. The degradation of benzene was mostly associated with the activated PMS, and the intermediates also competed with TCE for KMnO4. The KMnO4 component played a more important role than PMS for the removal of TCE. For an aqueous mixture of 0.3mM benzene and TCE, the combination of 2.4mM PMS and 1.8mM KMnO4 was optimal, achieving removal efficiencies higher than 85% for both pollutants. Regarding the degradation of benzene, chloride ions had a concentration-dependent effect, and bicarbonate ions and dihydrogen phosphate showed different levels of retarding effect. The CUPP is envisaged to be used as a remedial reagent for the in-situ chemical oxidation of groundwater contaminants.

Total oxidation of trichloroethylene over mayenite (Ca12Al14O33) catalyst

The catalytic oxidation of gaseous trichloroethylene (TCE), mediated by a cost effective mayenite support, was studied in a fixed bed reactor. Mayenite was synthetized by using hydrothermal method and characterized before and after catalytic oxidation experiments by using XRD, N2-sorption (BET), SEM-EDX, TEM and FTIR; the reaction products were analyzed by means of GC–MS, IC and a IR-based CO2 probe. The results showed that mayenite promoted the total oxidation of TCE in the temperature range 300–500°C, where TCE was quantitatively converted in CO2 and chlorine. The mayenite catalyst showed high recyclability and could be used for several reaction cycles without any loss of activity and selectivity. Owing to its characteristics, mayenite was found to be a promising catalyst for the TCE total conversion and remediation.