Oxidation Of Trichloroethylene Research Articles

Operando investigation of catalytic trichloroethylene combustion over metal-doped CeO2 nanorods

The remediation of chlorinated volatile organic compounds is an intractable issue for it typically requires high temperatures and generates undesirable byproducts. This work utilized a series of representative transition metals (i.e., Cr, Cu, V) to modify the morphology, surface oxygen, and acidity of the CeO2 nanorods for trichloroethylene (TCE) treatment. A spectroscopic operando DRIFT − online GCMS reactor was introduced to examine the catalytic performance and elucidate the reaction pathway. Among them, Cr-CeO2 exhibited 50 % (T50) and 90 % (T90) TCE conversions with no byproduct at 171 °C and 241 °C, respectively. The performances of Cu-CeO2 (T90 = 391 °C), V-CeO2 (T90 = 423 °C) and CeO2 (T90 = 494 °C) were inferior to Cr-CeO2 (T90 = 241 °C), with obvious C2Cl4 generated in the TCE oxidation. It reveals that TCE adsorbed on Cr-CeO2 is dechlorinated on acidic sites and oxidized to carbonate/formate intermediates by the surface oxygen then facilely to generate carbon oxides, while TCE is adsorbed as chlorinated species (CH2ClCH2O−) on the other three catalysts which occupy the surface and require higher temperature to be oxidized. The abundant medium-strong acidic sites and surface oxygen species of Cr-CeO2 nanorods are responsible for the low-temperature activation via C-Cl cleavage on acidic sites and fast oxidation of hydrocarbon intermediates in the TCE oxidation, respectively.

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.

Kinetics of Hydroxyl Radical Production from Oxygenation of Reduced Iron Minerals and Their Reactivity with Trichloroethene: Effects of Iron Amounts, Iron Species, and Sulfate Reducing Bacteria.

Reactive oxygen species generated during the oxygenation of different ferrous species have been documented at groundwater field sites, but their effect on pollutant destruction remains an open question. To address this knowledge gap, a kinetic model was developed to probe mechanisms of •OH production and reactivity with trichloroethene (TCE) and competing species in the presence of reduced iron minerals (RIM) and oxygen in batch experiments. RIM slurries were formed by combining different amounts of Fe(II) and sulfide (with Fe(II):S ratios from 1:1 to 50:1) or Fe(II) and sulfate with sulfate reducing bacteria (SRB) added. Extents of TCE oxidation and •OH production were both greater with RIM prepared under more reducing conditions (more added Fe(II)) and then amended with O2. Kinetic rate constants from modeling indicate that •OH production from free Fe(II) dominates •OH production from solid Fe(II) and that TCE competes for •OH with Fe(II) and organic matter (OM). Competition with OM only occurs in experiments with SRB, which include cells and their exudates. Experimental results indicate that cells and/or exudates also provide electron equivalents to reform Fe(II) from oxidized RIM. Our work provides new insights into mechanisms and environmental significance of TCE oxidation by •OH produced from oxygenation of RIM. However, further work is necessary to confirm the relative importance of reaction pathways identified here and to probe potentially unaccounted for mechanisms that affect abiotic TCE oxidation in natural systems.

Enhanced catalytic performance of CuCr/ZSM-5 catalyst by chemical vapour deposition for trichloroethylene oxidation

ABSTRACT The CuCr mixed oxides catalysts supported on ZSM-5 zeolite (CuCr/ZSM-5) were synthesized via metal organic chemical vapour deposition (MOCVD) method for catalytic oxidation of trichloroethylene (TCE). SEM, XRD, BET, H2-TPR, NH3-TPD and XPS were tested. The active components were dispersed uniformly over the surface of ZSM-5 zeolite. The catalytic experimental results exhibited that the CuCr/ZSM-5 exhibited the best catalytic performance for TCE oxidation with 90% of TCE at 338°C and the concentration of C2Cl4 decreased compared with Cu/ZSM-5 and Cr/ZSM-5. The possible reason is that CuCr/ZSM-5 has superior reducibility, higher Cu2+ surface concentration as well as more surface oxygen.

Cometabolic decomposition of trichloroethylene by recombinant hydroxyquinol 1,2-dioxygenase

Trichloroethylene (TCE) is known to microbially decomposed by a cometabolic process. In this study, a dioxygenase for the ring cleavage of benzenetriols was used to catalyze the cometabolic oxidation of TCE. Hydroxyquinol 1,2-dioxygenase (HQD) was obtained in vitro using a recombinant technique, and its catalytic function and products in the TCE cometabolic transformation were identified. The HQD (CphA-I) was cloned from Pseudarthrobacter chlorophenolicus A6, overexpressed, and purified using Ni2+-nitrilotriacetic acid (Ni2+-NTA) affinity chromatography, and soluble form of enzymes with 34 kDa protein size were effectively achieved with a high expression rate (4,177 μg/mL). TCE was effectively decomposed by CphA-I, and the specific activity was 5.1 U/mg-protein. The Hill equation was found to describe well the kinetics of TCE decomposition by CphA-I, which were determined as: vmax = 1.06 mM/min, KM = 1.44 mM, and nH = 2.41. This indicates that CphA-I has at least three cooperative binding sites for TCE decomposition, further accentuating the high affinity between the enzyme and the substrate. Glyoxylate and chloral hydrate were identified as the primary decomposition products from TCE cometabolic oxidation. This suggested that CphA-I exhibited a cometabolism catalytic function similar to those of methane monooxygenase and toluene dioxygenase. These results are expected to provide fundamental information for the enzymatic remediation of organic contaminants.

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

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

Photo-assisted reductive cleavage and catalytic hydrolysis-mediated persulfate activation by mixed redox-couple-involved CuFeS2 for efficient trichloroethylene oxidation in groundwater

Persulfate (PS, S2O82−) activation through transition metal sulfides (TMS) has gained increasing attention since it can decompose a wide variety of refractory halogenated organic compounds in groundwater and wastewater. However, the processes of PS activation by TMS and particularly the formation of •OH radical under anoxic and acidic conditions (pH ∼2.8) remain elusive. Herein, by employing mixed redox-couple-involved chalcopyrite (CuFeS2) (150 mg/L) nanoparticles for PS (3.0 mM) activation, 96% of trichloroethylene was degraded within 120 min at pH 6.8 under visible light irradiation. The combination of experimental studies and theoretical calculations suggested that the Cu(I)/Fe(III) mixed redox-couple in CuFeS2 plays a crucial role to activate PS. Cu(I) acted as an electron donor to transfer electron to Fe(III), then Fe(III) served as an electron transfer bridge as well as a catalytic center to further donate this received electron to the O–O bond of PS, thus yielding SO4•− for trichloroethylene oxidation. Moreover, for the first time, •OH radicals were found to form from the catalytic hydrolysis of PS onto CuFeS2 surface, where S2O82− anion was hydrolyzed to yield H2O2 and these ensuing H2O2 were further transformed into •OH radicals via photoelectron-assisted O–O bond cleavage step. Our findings offer valuable insights for understanding the mechanisms of PS activation by redox-couple- involved TMS, which could promote the design of effective activators toward PS decomposition for environmental remediation.

RuO2 nanoparticles-accommodated graphitic carbon nitride for significant enhancement in photocatalytic oxidation of trichloroethylene

It is greatly desired to construct bifunctional photocatalysts to achieve extremely effective photocatalytic ability. Herein, RuO2 nanoparticles (10 nm), accommodated in porous g-C3N4 to construct mesoporous RuO2/g-C3N4 heterojunctions, were prepared utilizing a modified sol-gel process in the existence of soft surfactant. The synthesized RuO2/g-C3N4 heterostructures were employed as photocatalysts in the mineralization of trichloroethylene (TCE) in an aqueous solution through visible light. The synthesized RuO2/g-C3N4 nanocomposites exhibited superior photocatalytic performance with 100% degradation of TCE within 150 min. The photodegradation rate of TCE of RuO2/g-C3N4 photocatalyst was remarkably promoted, compared with g-C3N4 and RuO2. The rate constant of 3%RuO2/g-C3N4 was determined to be 0.0127 min−1, which was 4.88 and 6.68 times higher than RuO2 (0.0026 min−1) and g-C3N4 (0.0019 min−1). This magnificent photocatalytic ability of RuO2/g-C3N4 nanocomposites can be interpreted to highly crystalline RuO2 NPs with small size, enhanced electron and mass transfer, visible light harvest and heterojunction structure with a synergistic effect. Furthermore, the synthesized photocatalyst could be recycled for five cycles with insignificant remarkable diminish in its photocatalytic ability. Fortunately, the photocatalytic ability of RuO2/g-C3N4 nanocomposites for TCE mineralization exhibited varied advances by utilizing visible light at room temperature without the employ of any oxidant.

Development of novel persulfate tablets for passive trichloroethylene (TCE)-contaminated groundwater remediation

In this study, a biodegradable binder, hydroxypropyl methyl cellulose (HPMC), was used for the first time to mix with persulfate powder for developing novel persulfate-releasing tablets to remediate trichloroethylene (TCE)-contaminated groundwater. To obtain feasible parameters for the preparation of persulfate tablets, different pressures, HPMC/tablet mass ratios, and persulfate dosages were evaluated. The results showed that the persulfate tablet released 2868 mg-persulfate/day for 12 days under the optimal manufacturing parameters of HPMC/tablet mass ratio of 0.5 and pressure of 4.90 × 108 N/m2. Persulfate diffusion and gel layer erosion were dominant mechanisms for controlling the persulfate released in water. The persulfate release time and rate can be controlled by adjusting the persulfate dosage at the optimal HPMC/tablet ratio. In the column experiment, TCE with an initial concentration of 70 mg/L reached 55% removal efficiency by the tablet, which showed that the developed tablet was capable of degrading highly concentrated TCE. The results of electron spin resonance (ESR) spectroscopy showed that both SO4−· and ·OH were responsible for the oxidation of TCE. During 150 days of incubation, the biodegrading efficiency of HPMC by microbes in soil and activated sludge was 67% and 80%, respectively, under aerobic conditions, while 58% of HPMC was removed by soil bacteria under anaerobic conditions. The results showed that persulfate tablets could be used as a passive groundwater remediation system. There is no waste generated after persulfate is completely released during groundwater remediation. The developed persulfate tablets are environmentally friendly and meet the green remediation aspect.

Synergistic roles of Fe(II) on simultaneous removal of hexavalent chromium and trichloroethylene by attapulgite-supported nanoscale zero-valent iron/persulfate system

Synthesized attapulgite-supported nanoscale zero-valent iron (AT-nZVI) composite/persulfate (PS) systems were utilized to simultaneously remove hexavalent chromium (Cr(VI)) and trichloroethylene (TCE) from aqueous solutions. The structures of AT-nZVI before and after the reaction with Cr(VI)-TCE were characterized by TEM-EDS-Mapping, HR-TEM and HR-XPS with ion sputtering. The effects of initial Cr(VI), TCE and PS concentrations, and PS addition time intervals on Cr(VI)-TCE removal efficiencies were evaluated. Experimental results revealed that the AT-nZVI composites with 1 mM PS can effectively and simultaneously remove Cr(VI) and TCE with the removal efficiencies of Cr(VI) and TCE reaching 90.02% and 90.40% respectively. It is thought that PS promoted TCE oxidation and the reduction of Cr(VI), which was predominately controlled by Fe(II). TCE was mainly degraded by free radical oxidation resulting from the PS activation of AT-nZVI. The enhanced Cr(VI) removal was attributed to the exposed areas and available active sites of nZVI, and Fe(II) in the solution increased by PS-mediated processes of rapid corrosion and dissolution of nZVI. The dual roles of AT-nZVI as a activator for PS activation and reductant for Cr(VI) reduction in Cr(VI)-TCE removal were identified. This implies that AT-nZVI/PS can be utilized as potential remediation reagents for simultaneous removal of heavy metal and chlorinated solvents in groundwater frequently encountered in contaminated sites.

Catalytic performance and intermediates identification of trichloroethylene deep oxidation over Ru/3DOM SnO2 catalysts

SnO2 is widely used in catalysis owing to its oxygen vacancies, reducible oxygen species, and acidity. In this work, Ru nanoparticles (NPs) supported on three-dimensionally ordered macroporous (3DOM) SnO2 (xRu/3DOM SnO2, Ru loading (x) = 0.09–1.65 wt%) were fabricated via the polyvinyl alcohol-protected reduction routes, and their catalytic activities were determined for trichloroethylene (TCE) and/or toluene oxidation. It was shown that the 0.98Ru/3DOM SnO2 sample exhibited the best activity and good thermal stability, with the temperature (T90%) and apparent activation energy at a TCE (1000 ppmv) conversion of 90% being 300 °C and 44 kJ/mol at space velocity = 40,000 mL/(g h), respectively. Trichloromethane, carbon tetrachloride, tetrachloroethylene, and trichloroacetaldehyde hydrate were the main intermediates in TCE oxidation. The high catalytic performance of 0.98Ru/3DOM SnO2 was attributed to the presence of hydroxyl groups adsorbed at the oxygen vacancies, strong O2 adsorption ability, good low-temperature reducibility, and strong interaction between Ru NPs and 3DOM SnO2. In addition, a catalytic mechanism over xRu/3DOM SnO2 was proposed under dry and humid conditions. The introduction of H2O could block some of the reaction pathways from inhibiting the production of C2Cl4, reduce formation of some by-products (e.g., CH2Cl2, CH3COOH, and C2H2Cl2), promote removal of the chlorine species, and generate a greater amount of HCl and a smaller amount of Cl2. Furthermore, introducing toluene into the TCE stream could generate smaller amounts of organic chlorine by-products and greater amounts of inorganic chlorine products (HCl and Cl2). We are sure that this work can provide a guideline for the industrial application of supported Ru catalysts in the removal of Cl-containing volatile organic compounds.

Abiotic dechlorination in the presence of ferrous minerals

Laboratory batch experiments were performed to assess the reduction of trichloroethene (TCE) and oxygen via natural ferrous minerals. TCE reduction under anoxic conditions was measured via the generation of reduced gases, while oxygen reduction via the generation of hydroxyl radicals was measured as a surrogate for potential TCE oxidation. Results showed that TCE reduction under anoxic conditions was observed for ankerite, siderite, and illite, but not for biotite; acetylene was the primary identified dechlorination product. With the exception of biotite, first-order dechlorination rate constants increased with increasing ferrous content of the mineral, with rate constants ranging from 3.1 × 10−8 to 4.8 10−7 L g−1 d−1. Measured reduction potentials (mV vs SHE) ranged from −104 for illite to +84 for biotite. When normalizing measured first-order dechlorination rate constants to the estimated ferrous iron mineral specific surface area (where surface area was based on nitrogen adsorption analysis of the minerals), TCE dechlorination rate constants increased with increasing reduction potentials. Under oxic conditions, hydroxyl radicals were generated with each of the four minerals. However, mineral activity showed no readily apparent correlation to ferrous content or mineral surface area. In terms of TCE and oxygen reduced per mole of ferrous iron initially present in each mineral, illite was the most reactive of the four minerals. Together, these results suggest that several ferrous minerals may contribute to abiotic dechlorination in the natural environment, and (at least for TCE reduction under anoxic conditions) measurement of ferrous mineral content and reduction potential may serve as useful tools for estimating TCE first-order abiotic dechlorination rate constants.

Glucose oxidase modified Fenton reactions for in-situ ROS generation and potential application in groundwater remediation

Catalyzed H2O2 propagations (CHP) have demonstrated great potential in the remediation of chlorinated aliphatic hydrocarbons (CAHs) like trichloroethene (TCE) contaminated groundwater. However, the importation of highly unstable H2O2 into subsurface environment remains challenging. In this work, the in-situ H2O2 generation reaction between glucose oxidase (GOD) and glucose was applied in combination with Fe(II) to form the modified Fenton system (GMFs) and its performance in TCE oxidative degradation was investigated. The influence of reactant concentration as well as environmental factors like temperature and pH on the kinetics of TCE oxidation in GMFs were studied. At optimized conditions, about 78% TCE were removed within 8 h in GMFs, which remained effective over the temperature range of 15–30 °C and pH range of 3.6–6.0 (in acetate buffer). The in-situ H2O2 and OH generation capacity of GMFs were further investigated to elucidate their functional mechanism on TCE oxidation. Intermediate and product analysis indicated the near-complete release of chloride ion by TCE oxidation with few organic chlorinated intermediates detected. This work reveals the potential of GMFs for CAHs contaminated groundwater remediation through in-situ generation of reactive oxygen species.

Catalytic activity and stability of Cu modified ZSM-5 zeolite membrane catalysts prepared by metal-organic chemical vapor deposition for trichloroethylene oxidation

In this work, the catalytic oxidation of trichloroethylene (TCE) was performed for the first time over the Cu modified ZSM-5 zeolite membrane catalysts prepared via metal-organic chemical vapor deposition (MOCVD). The results displayed that four Cu/ZSM-5/PSSF catalysts with different copper loadings were highly selective to HCl, while the 5Cu/Z (Cu/ZSM-5/PSSF catalyst with copper loading of 5%) exhibited the best catalytic behavior with 90% of TCE conversed at 490 °C, which decreased 36 °C compared with 0.5Cu/Z catalyst. The possible reasons are higher concentration of Cu2+ species and better dispersion of active species. Meanwhile, the stability test was performed on the 5Cu/Z catalyst for 50 h, and the 5Cu/Z catalyst started to deactivate gradually after 35 h due to the poison of Cl during the catalytic oxidation process. It has been shown that more Cu2+ species and better dispersion of active components are important to prepare a superior catalyst for CVOCs combustion.

A Bimetallic Fe-Mn Oxide-Activated Oxone for In Situ Chemical Oxidation (ISCO) of Trichloroethylene in Groundwater: Efficiency, Sustained Activity, and Mechanism Investigation.

Bimetallic Fe-Mn oxide (BFMO) has been regarded as a promising activator of peroxysulfate (PS), the sustained activity and durability of BFMO for long-term activation of PS in situ, however, is unclear for groundwater remediation. A BFMO (i.e., Mn1.5FeO6.35) was prepared and explored for PS-based in situ chemical oxidation (ISCO) of trichloroethylene (TCE) in sand columns with simulated/actual groundwater (SGW/AGW). The sustained activity of BFMO, oxidant utilization efficiency, and postreaction characterization were particularly investigated. Electron spin resonance (ESR) and radical scavenging tests implied that sulfate radicals (SO4•-) and hydroxyl radicals (HO•) played major roles in degrading TCE, whereas singlet oxygen (1O2) contributed less to TCE degradation by BFMO-activated Oxone. Fast degradation and almost complete dechlorination of TCE in AGW were obtained, with reaction stoichiometry efficiencies (RSE) of ΔTCE/ΔOxone at 3-5%, much higher than those reported RSE values in H2O2-based ISCO (≤0.28%). HCO3- did not show detrimental effect on TCE degradation, and effects of natural organic matters (NOM) were negligible at high Oxone dosage. Postreaction characterizations displayed that the BFMO was remarkably stable with sustained activity for Oxone activation after 115 days of continuous-flow test, which therefore can be promising catalyst for Oxone-based ISCO for TCE-contaminated groundwater remediation.

Heterogeneous Fenton oxidation of trichloroethylene catalyzed by sewage sludge biochar: Experimental study and life cycle assessment

Heterogeneous Fenton oxidation of trichloroethylene (TCE) catalyzed by sewage sludge biochar was studied. The highest TCE removal efficiency was 83% at pH 3.1, catalyzed by 300 W biochar. The biochars produced at higher microwave power levels provided better catalytic effect, due to higher iron contents and specific surface areas. Reactivity of sewage sludge biochar maintained after several uses, which provides an advantage for using as a permeable reactive barrier to remediate groundwater pollution. Chromium, copper, nickel, lead, and zinc were found in the leachate generated from sewage sludge biochar, and most of the concentrations were lower than the standards for non-drinking water use. Besides, copper, zinc, and iron were found in the reaction solutions of Fenton oxidation. Because of the highest dosage required for Fenton oxidation, the environmental impact caused by 200 W biochar is highest. The environmental impact caused by 300 W biochar is lowest. Among the four endpoint impact categories in the life cycle assessment (LCA), human health is the highest concern, whereas ecosystem quality is the least. According to experimental and LCA results, the optimum microwave power level would be 300 W. The primary impact source is microwave pyrolysis because of high energy usage.

3DOM CeO2-supported RuyM (M = Au, Pd, Pt) alloy nanoparticles with improved catalytic activity and chlorine-tolerance in trichloroethylene oxidation

The xRuyM/3DOM CeO2 catalysts are prepared using the PMMA-templating and PVA-protected reduction methods. The 0.93Ru2.87Pd/3DOM CeO2 exhibited excellent catalytic performance, hydrothermal stability, and chlorine-resistance for trichloroethylene oxidation.

Potential for co-metabolic oxidation of TCE and evidence for its occurrence in a large-scale aquifer survey

Trichloroethylene (TCE) is a groundwater pollutant that is prevalent worldwide. In contaminated groundwater, TCE can be biodegraded following either reductive dechlorination or aerobic co-metabolic oxidation. However, since the co-metabolic process is not accompanied by indicative and easily detectable transformation products, little is known about its prominence in the environment. To estimate the environmental importance of the oxidative process, a regional groundwater survey was conducted. In this survey, polluted water from 100 wells along the Israeli Coastal Aquifer was sampled. Geochemical data indicated oxic conditions prevailing in most sites. The sampled groundwater was used for microcosm experiments, functional gene analysis, and TCE compound-specific isotope analysis (δ13C and δ37Cl).Enrichments of methane and toluene oxidizers in microcosms indicated the high potential of the indigenous microbial community to co-metabolically oxidize TCE. This was further reinforced by the high abundance of mmoX and PHE functional genes quantified in some of the sites (yet lower abundance of TOD functional gene was found).Finally, compound-specific isotope analysis was used to assess the magnitude of TCE oxidation in practice. Applying the isotopic tool for scattered points on a regional scale demanded the consideration of a wide δ13C range of source TCE, hampering the ability to detect small shifts of a single permil. Thus, despite the high potential for the oxidation process, no evidence was attained for the natural occurrence of the process, and significant isotopic shifts were restricted to actively treated sites only. This limitation should be considered in future regional scale studies, in which no single source is defined.

Oxidative Degradation of Trichloroethylene over Fe2O3-doped Mayenite: Chlorine Poisoning Mitigation and Improved Catalytic Performance

Mayenite was recently successfully employed as an active catalyst for trichloroethylene (TCE) oxidation. It was effective in promoting the conversion of TCE in less harmful products (CO2 and HCl) with high activity and selectivity. However, there is a potential limitation to the use of mayenite in the industrial degradation of chlorinated compounds—its limited operating lifespan owing to chlorine poisoning of the catalyst. To overcome this problem, in this work, mayenite-based catalysts loaded with iron (Fe/mayenite) were prepared and tested for TCE oxidation in a gaseous phase. The catalysts were characterized using different physico-chemical techniques, including XRD, ICP, N2-sorption (BET), H2-TPR analysis, SEM-EDX, XPS FESEM-EDS, and Raman. Fe/mayenite was found to be more active and stable than the pure material for TCE oxidation, maintaining the same selectivity. This result was interpreted as the synergistic effect of the metal and the oxo-anionic species present in the mayenite framework, thus promoting TCE oxidation, while avoiding catalyst deactivation.

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.