Oxidation Of Dichloromethane Research Articles

Catalytic abatement of dichloromethane over transition metal oxide catalysts: Thermodynamic modelling and experimental studies

Dichloromethane (DCM) is a noxious chemical that is widely used in industry. The current work focuses on the catalytic abatement of DCM from industrial effluents to minimize its harmful effects to the environment and human wellbeing. Three transition metal oxide catalysts (V, Cu and Mn) supported on γ-Al2O3 were synthetized for total oxidation of DCM in presence of steam. Thermodynamic modelling was used to reveal information related to the stability of the used transition metal oxides in the abatement conditions. The results showed that with 10 wt-% CuO and 10 wt-% V2O5 containing catalysts 100% conversion of DCM together with 90% HCl yield and insignificant by-product formation can be achieved at temperature around 500 °C. According to modelling, V2O5 should be stable at the conditions of DCM oxidation, while CuO would be more stable at higher temperature level (decomposition of CuCl2 starts at 300 °C). MnCl2 remains stable until 800 °C, which leads to deactivation of MnO2 catalyst. Presence of steam inhibits the poisoning of the materials by chlorine based on thermodynamic calculation. XRF analysis supports the results of thermodynamic modelling – used MnO2 and CuO catalysts contain chlorine, which was not detected in case of V2O5/Al2O3. CuO/γ-Al2O3 seems to be a good alternative to noble metal catalysts for the total oxidation of dichloromethane when used in the presence of steam and the temperatures above 300 °C to minimize Cl-poisoning. The outcomes of this study showed that the prepared metal oxides are promising catalysts to minimize pollution caused by chlorinated volatile organic compounds.

Catalytic Oxidation of Chlorinated Organics over Lanthanide Perovskites: Effects of Phosphoric Acid Etching and Water Vapor on Chlorine Desorption Behavior.

In this article, the underlying effect of phosphoric acid etching and additional water vapor on chlorine desorption behavior over a model catalyst La3Mn2O7 was explored. Acid treatment led to the formation of LaPO4 and enhanced the mobility of lattice oxygen of La3Mn2O7 evidenced by a range of characterization (i.e., X-ray diffraction, temperature-programmed analyses, NH3-IR, etc.). The former introduced thermally stable Brönsted acidic sites that enhanced dichloromethane (DCM) hydrolysis while the latter facilitated desorption of accumulated chlorine at elevated temperatures. The acid-modified catalyst displayed a superior catalytic activity in DCM oxidation compared to the untreated sample, which was ascribed to the abundance of proton donors and Mn(IV) species. The addition of water vapor to the reaction favored the formation and desorption of HCl and avoided surface chlorination at low temperatures. This resulted in a further reduction in reaction temperature under humid conditions ( T90 of 380 °C for the modified catalyst). These results provide an in-depth interpretation of chlorine desorption behavior for DCM oxidation, which should aid the future design of industrial catalysts for the durable catalytic combustion of chlorinated organics.

Phosphate-Functionalized CeO2 Nanosheets for Efficient Catalytic Oxidation of Dichloromethane.

Tuning the nature and profile of acidic and basic sites on the surface of redox-active metal oxide nanostructures is a promising approach to constructing efficient catalysts for the oxidative removal of chlorinated volatile organic compounds (CVOCs). Herein, using dichloromethane (DCM) oxidation as a model reaction, we report that phosphate (PO x) Brønsted acid sites can be incorporated onto a CeO2 nanosheet (NS) surface via an organophosphate-mediated route, which can effectively enhance the CeO2's catalytic performance by promoting the removal of chlorine poisoning species. From the systematic study of the correlation between PO x composition, surface structure (acid and basic sites), and catalytic properties, we find that the incorporated Brønsted acid sites can also function to decrease the amount of medium-strong basic sites (O2-), reducing the formation of chlorinated organic byproduct monochloromethane (MCM) and leading to the desirable product, HCl. At the optimized P/Ce ratio (0.2), the PO x-CeO2 NSs can perform a stable DCM conversion of 65-70% for over 10 h at 250 °C and over 95% conversion at 300 °C, superior to both pristine and other phosphate-modified CeO2 NSs. Our work clearly identifies the critical role of acid and basic sites over functionalized CeO2 for efficient catalytic CVOCs oxidation, guiding future advanced catalyst design for environmental remediation.

Promotional effect of doping Cu into cerium-titanium binary oxides catalyst for deep oxidation of gaseous dichloromethane

In recent years, significant effort has been made in the development of novel catalysts for the total oxidation of chlorinated volatile organic compounds. In this work the catalytic activity of Cu doped cerium-titanium binary oxides for the oxidation of dichloromethane (DCM) have been studied for the first time. Combining catalysts characterization and activity data, it was found that Cu ions can uniformly disperse into titanium dioxide to form solid solution and induce the creation of additional surface oxygen species on the catalysts surface, while moderate amount of Ce ions are still needed for the activation of CCl. Detailed analysis of the in-situ FTIR experiment results revealed that the surface oxygen species, especially the hydroxyl groups associated with Cu ions, can promote the deep oxidation of the intermediate species formed in the nucleophilic substitution process occurred on the active sites of catalysts surface. The sample with the Cu/Ce molar ratio of 1:3 obtained a better CO2 selectivity than that reached with cerium-titanium binary oxides. Meanwhile, according to element balance analysis, removal of chlorine from the catalyst surface was also promoted by Cu doping.

Total Oxidation of Dichloromethane over Silica Modified Alumina Catalysts Washcoated on Ceramic Monoliths

Silica modified alumina was used in this study for coating of a cordierite monolith substrate with two different channel densities. The performance of the prepared monolith catalysts was evaluated in catalytic total oxidation of dichloromethane before and after Pt impregnation. The characteristics similar to the powder form catalysts were kept rather successfully after washcoating the monolith as evidenced by electron microscopy (FESEM) and N2 physisorption. A dichloromethane (DCM) conversion of higher than 80% at 500 °C was reached over all the catalysts with 200 cpsi. The maximum conversion was obtained with the catalyst containing 10 mol % of silica. The total amount of major byproducts (CO, CH3Cl and CH2O) were slightly decreased by increasing the silica loading, and remarkably after Pt impregnation. After impregnation of Pt, the HCl yields were increased for two samples with the higher loading of silica (10 and 15 mol %) and reached the maximum when silica loading was 10%. Even though Pt impregnation did not significantly affect the DCM conversion, it improved the selectivity. Comparison between the two substrates (200 and 600 cpsi) evidenced that the key parameters of the monolith influencing the DCM oxidation are low value of open fraction area, hydraulic diameter, thermal integrity factor and high value of mechanical integrity factor and geometric surface area.

Mineralization of dichloromethane using solar-oxidation and activated TiO2: Pilot scale study

The oxidation of gaseous dichloromethane (DCM) by advanced oxidation technology, advanced solar oxidation technology, biological treatment, and the combination of solar advanced oxidation technology and biological treatment were investigated in a pilot study. The effects of the inlet concentration of DCM, flow rate, and relative humidity on the percentage DCM removal were recorded. Photolysis and photocatalytic oxidation using TiO2 does not result in the complete removal of DCM, while ozone, ozone/solar-hν and TiO2/ozone/solar-hν can completely remove DCM from the gas stream. Combined photocatalytic oxidation processes enhance the process efficiency and reduce both ozone demand and the energy requirements needed to completely remove DCM. Through a combination of processes, ozone, solar photons, and hydroxyl radicals oxidize DCM, generating byproducts that are water soluble and more biodegradable than the original DCM, providing the possibility for it to be combined with subsequent biological treatment. The decomposition of DCM was affected by the inlet flow rate, gas relative humidity, and gas flow rate with high percentage DCM removal achieved at low flow rate, DCM initial concentration up to 200 mg/m3, and humidity around 40%. The kinetics of DCM oxidation in different processes were successfully modeled to pseudo-first order or second-order kinetics. The kinetic analysis showed that the choice of oxidation process greatly affected the kinetic constants of DCM conversion, and RH 40% could cause faster oxidation. The results support the use of solar oxidation, not only for the mineralization of DCM, but also as a pretreatment before biodegradation.

Dichloromethane oxidation over FexZr1-x oxide catalysts

FexZr1-x-S mixed oxide catalysts were prepared by precipitation of FeSO4 and ZrOCl2, and used in catalytic oxidation of dichloromethane (DCM). Analyses by a series of characterization technologies reveal that Fe-O-Zr solid solution with tetragonal ZrO2 or α-Fe2O3 structure can be formed, dependent on Fe/Fe + Zr ratio. Residual SO42− species obtained from FeSO4 precursor exist in a form of bridged bidentate complex with Zr4+ or Fe3+ ion, which increases acidity significantly. FexZr1-x-S catalysts with Fe/Fe + Zr of 0.2–0.5 possess high contents of both SO42− and surface oxygen, and are highly active in catalytic combustion of DCM with T90 below 320 °C and TOFs at 200 °C of 0.98–1.89 μmol/(m2 min). Another test shows that the activity for the other CVOVs oxidation over Fe0.5Zr0.5-S is 1,2-dichloroethane > dichloromethane > trichloroethylene > 1,2-di chlorobenzene. Because the substitution of Cl species for surface oxygen is retarded, high stable activity maintains within reaction temperatures for at least 80 h. In situ FT-IR indicates that DCM is adsorbed and activated mainly through the formation of chloromethyl sulfate, which is oxidized quickly into formate ion. The synergism between SO42- complex anchoring on Zr-O-Fe solid solution and surface oxygen obtained from Fe2O3 cluster or nano-particles promotes the oxidation of formate.

Bimodal mesoporous TiO2 supported Pt, Pd and Ru catalysts and their catalytic performance and deactivation mechanism for catalytic combustion of Dichloromethane (CH2Cl2)

Pt-, Pd-, and Ru-doped bimodal mesoporous TiO2 catalysts were prepared by wet impregnation and applied to the catalytic combustion of dichloromethane (DCM). The Pd/TiO2 and Ru/TiO2 catalysts exhibited excellent catalytic activity. Total oxidation of DCM was obtained at 335°C with less undesired CO and byproducts (CxHyClz). A certain decrease in the selectivity of the Pd/TiO2 catalyst was observed in a long-term stability test, whereas Ru/TiO2 displayed appreciable stability. Pt/TiO2 was easily deactivated and showed the poorest performance for DCM decomposition. Deactivation of the catalysts was related to the deposition of carbon species and chlorine poisoning, whereby the active sites for DCM decomposition were occluded. Furthermore, the adsorption of chlorine species could change the chemical states of the Pd or Pt species and generate inactive species. Deactivation of the Ru/TiO2 catalyst was inhibited to some extent as carbon and chlorine species could be removed by RuO2. Moreover, the larger pore-size distribution of Ru/TiO2 was favorable for the desorption of by-products during DCM oxidation.

Combining transcriptomics and PBPK modeling indicates a primary role of hypoxia and altered circadian signaling in dichloromethane carcinogenicity in mouse lung and liver

Dichloromethane (DCM) is a lung and liver carcinogen in mice at inhalation exposures≥2000ppm. The modes of action (MOA) of these responses have been attributed to formation of genotoxic, reactive metabolite(s). Here, we examined gene expression in lung and liver from female B6C3F1 mice exposed to 0, 100, 500, 2000, 3000 and 4000ppm DCM for 90days. We also simulated dose measures - rates of DCM oxidation to carbon monoxide (CO) in lung and liver and expected blood carboxyhemoglobin (HbCO) time courses with a PBPK model inclusive of both conjugation and oxidation pathways. Expression of large numbers of genes was altered at 100ppm with maximal changes in the numbers occurring by 500 or 2000ppm. Most changes in genes common to the two tissues were related to cellular metabolism and circadian clock. At the lower concentrations, the changes in metabolism-related genes were discordant – up in liver and down in lung. These processes included organelle biogenesis, TCA cycle, and respiratory electron transport. Changes in circadian cycle genes – primarily transcription factors - showed strong concentration-related response at higher concentrations (Arntl, Npas2, and Clock were down-regulated; Cry2, Wee1, Bhlhe40, Per3, Nr1d1, Nr1d2 and Dbp) were up-regulated with similar directionality in both tissues. Overall, persistently elevated HbCO from DCM oxidation appears to cause extended periods of hypoxia, leading to altered circadian coupling to cellular metabolism. The dose response for altered circadian processes correlates with the cancer outcome. We found no evidence of changes in genes indicative of responses to cytotoxic, DNA-reactive metabolites.

Comparative study on the support properties in the total oxidation of dichloromethane over Pt catalysts

The aim of this work was to study the influence of the support oxide properties on the total oxidation of dichloromethane in moist conditions. The support materials γ-Al2O3, TiO2, CeO2 and MgO were synthesized by a sol-gel method followed by wet impregnation of Pt and characterized by different physico-chemical techniques. The conversion of DCM was higher than 90% at 500°C over impregnated and non-impregnated Al2O3, TiO2 and CeO2, even at high GHSV. CO, CH3Cl and CH2O were the major by-products observed and their amounts decreased after Pt impregnation. The CH3Cl formation was higher when Lewis acid sites were present while the existence of Brønsted sites promoted the CH2O formation. The complete conversion of DCM was achieved at around 450°C over the Al2O3 and Pt/Al2O3 and at 500°C for Pt/TiO2. These two catalysts exhibited the highest total acidities among the materials tested. The activity of Pt/Al2O3 remained the same also after 55h of testing, however, increase in Pt particle size and decrease in acidity were observed. Pt/CeO2 while being less active showed smallest amount of by-product formation during the whole temperature range used in light-off tests. This is most probably due to its easy reduction ability. The textural parameters of the supports did not appear to be the key parameters when considering the activity and selectivity of the catalysts.

Morphology-dependent properties of CeO2 nano-catalysts on CH2Cl2 oxidation

Morphology-dependent properties of CeO2 nano-catalysts on CH2Cl2 oxidation: a diagrammatic drawing of dichloromethane oxidation over CeO2 nanorods.

Highly active spinel type CoCr2O4 catalysts for dichloromethane oxidation

A series of spinel type CoCr2O4 catalysts calcined at different temperatures were prepared and tested for oxidation of dichloromethane (CH2Cl2). These catalysts were active for this reaction. The final products in the reaction were COx, HCl and Cl2, without the formation of Cl-containing organics. The best performance was obtained on a catalyst calcined at 400°C (CoCr2O4-4), with a T50 of 218°C and a T90 of 257°C, which was mainly due to the highest surface area of this catalyst (91.3m2g−1). Detailed quantitative analyses revealed that the catalytic behavior was synergistically governed by surface acidity and reducibility of the catalyst, as evidenced by ammonia temperature-programmed desorption and hydrogen temperature-programmed reduction results, respectively. Kinetic studies revealed similar activation energies (124.5–155.5kJmol−1) on these catalysts, implying the reaction might follow the same pathways on these catalysts. More importantly, in situ Fourier transform infrared spectroscopic investigation of the reaction revealed that formate species were the main reaction intermediates, which could be further oxidized to CO and CO2.

Remarkable enhancement of dichloromethane oxidation over potassium-promoted Pt/Al2O3 catalysts

A series of K-promoted Pt/Al2O3 catalysts were prepared by an incipient wetness impregnation method and tested for oxidation of dichloromethane (DCM). It was found that the activity was greatly enhanced by the modification of K, which depended on the K content in the catalyst. The T50 temperature on a 0.42K–2Pt/Al2O3 catalyst was 270°C, which was much lower than that on a K-free 2Pt/Al2O3 catalyst (400°C). The remarkable improvement of activity was attributed to the enhanced catalyst reducibility, by the generation of Pt–O–Kx (x≈2) surface species through an intimate interaction between K and Pt. The presence of such Pt–O–Kx species in the catalyst could significantly accelerate the decomposition of formate intermediates formed on Al2O3 surface and thus the overall reaction, as evidenced by the in situ Fourier transform infrared spectroscopic results.

Total oxidation of dichloromethane and ethanol over ceria–zirconia mixed oxide supported platinum and gold catalysts

Ce0.5Zr0.5O2 prepared by sol–gel method was used as a support for platinum and gold catalysts that were tested in total oxidation of dichloromethane and ethanol. It was shown that the deposition of platinum and gold on Ce0.5Zr0.5O2 support enhanced the reducibility of surface ceria. This phenomenon was more pronounced for platinum catalysts. Introduction of both noble metals led to the decrease of catalysts’ acidity. In total oxidation of dichloromethane, the noble metal catalysts showed lower catalytic performance compared to parent Ce0.5Zr0.5O2, due to lower amount of acid sites that act as chemisorption sites for chlorinated compounds. On the other hand, platinum catalysts exhibited significantly enhanced selectivity to CO2 in comparison with the Ce0.5Zr0.5O2 support. In total oxidation of ethanol, the deposition of platinum on Ce0.5Zr0.5O2 resulted in a significant increase in catalytic performance, while the introduction of gold had only a minor effect. Moreover, the positive effect of higher noble metal loading on catalytic performance was more pronounced for Pt catalysts. For all investigated catalysts, the temperature of the H2-TPR peak corresponding to the reduction of surface ceria correlated with their catalytic performance. The influence of Pt loading on the mechanism of ethanol oxidation was revealed. Based on the concentration profiles of individual by-products/products detected by on-line FTIR analysis, the possible pathways of their formation were suggested. Both noble metal catalysts exhibited higher selectivity to CO2 than the pristine Ce0.5Zr0.5O2.

Total Oxidation of Dichloromethane Over Metal Oxide Catalysts

Three different transition metals (V, Mn and Cu) supported on TiO2, MgO and CeO2, were investigated for their performances in dichloromethane oxidation (500 ppm, 704,867 h−1) in moist conditions as a model reaction for the destruction of chlorinated volatile organic compounds. The catalysts were prepared by sol–gel method followed by wet impregnation of V, Mn or Cu precursors. The activities were evaluated in the temperature range from 100 to 500 °C with 5 °C min−1 temperature rise. The orders of activity and selectivity to HCl of the catalysts is CuTi > VMg > CuCe > CuMg. A correlation between acidic properties of support and performances was observed as the activity of copper catalysts followed the acidity order of supports.

Oxidation of dichloromethane over Pt, Pd, Rh, and V2O5 catalysts supported on Al2O3, Al2O3–TiO2 and Al2O3–CeO2

Pt, Pd, Rh and V2O5 metallic monolith catalysts supported on Al2O3, Al2O3–TiO2 and Al2O3–CeO2 were examined in the oxidation of dichloromethane (DCM). To improve the selectivity towards HCl and to prevent catalysts’ deactivation, the water amount in the feed gas mixture was adjusted to 1.5wt.%. All tested catalysts showed high activity in DCM oxidation and high selectivity towards HCl formation. Over Pt/Al2O3 and Rh/Al2O3, the 100% DCM conversions were reached at 420°C and 440°C and the maximum HCl yields detected were 92% and 93%, respectively. Addition of CeO2 to the Al2O3 support affected the activity only a little, while somewhat more visible enhancement was seen with the addition of Pt, Pd, Rh and V2O5. However, more positive effect on the HCl and/or CO2 yield was observed. Results showed that high acidity together with increased reducibility leads to an active catalyst for DCM oxidation. After the 40.3h stability test no obvious change in the Pt/Al2O3 catalysts’ performance was seen. Characterization showed no carbonaceous species on the catalyst's surface, but instead, some chlorine was detected on the surface that at this point did not affect the catalyst's activity or selectivity. The DCM decomposition seems to proceed on the catalyst surface via detaching the chlorine atoms before the breakage of the hydrogen bonds, hence following the order of the lowest bond energy in each step.

Catalytic oxidation of dichloromethane over Pt/CeO2–Al2O3 catalysts

A series of CeO2–Al2O3 catalysts with different CeO2 contents were prepared by a co-precipitation method, and supported Pt/CeO2–Al2O3 catalysts were also prepared by an impregnation method. These catalysts were tested for catalytic oxidation of dichloromethane (CH2Cl2). It was found that these catalysts were active for the reaction, with a 100% conversion of CH2Cl2 obtained at 410°C over a catalyst with 15% of CeO2. Various characterization results such as ammonia temperature programmed desorption, hydrogen temperature programmed reduction suggested that the catalytic behaviors were synergistically influenced by surface acidity and redox property of the catalysts. An optimal combination of surface acidity and redox property in the catalyst resulted in a high activity. Moreover, the addition of Pt could further enhance the activity, due to the promotion of surface acidity by the introduction of chlorine species in the catalyst during the preparation using H2PtCl6 as the precursor and reducibility of the catalyst probably via the formation of Ce–Pt–O solid solution.

Total oxidation of model volatile organic compounds over some commercial catalysts

Commercial VOC oxidation catalysts can be used as comparative materials during development of new or improved catalysts. The objective of this study was to investigate physicochemical properties of EnviCat® commercial catalysts and their performance in total oxidation of three model compounds (dichloromethane, toluene and ethanol) at laboratory scale. The reactivity of model VOC was decreasing in the order ethanol>toluene>dichloromethane. The Cu–Mn/Al catalyst was found to be the most active and selective catalyst in ethanol oxidation. In oxidation of dichloromethane, the Pt–Pd/Al–Ce catalyst with 0.10wt% Pt+Pd was the most active, while the most selective one (giving the highest HCl yield) was the Pt–Pd/Al catalyst containing 0.24wt% Pt+Pd. In toluene oxidation, the Pt–Pd/Al catalyst with 0.24wt% Pt+Pd possessed the highest activity; the selectivity to CO2 was 100% for all investigated catalysts. Obtained results showed that the performance of commercial catalysts in laboratory scale tests can be different from that declared by catalyst supplier. A possible difference in catalytic performance at industrial and laboratory scale should be taken into account when industrial catalysts are used in laboratory scale tests.

Bifunctional mechanism of dichloromethane oxidation over Pt/Al2O3: CH2Cl2 disproportionation over alumina and oxidation over platinum

The catalytic oxidation of dichloromethane (DCM, 1000ppm) in wet air was carried out in a fixed bed reactor over a range of Pt/γ-Al2O3 catalysts. The dichloromethane oxidation occurs following a bifunctional mechanism. DCM is disproportionated over γ-Al2O3 into a 1/1/3molar mixture of CO, CH3Cl, and HCl; the DCM transformation is followed by CH3Cl and CO oxidation into CO2. A mechanism of DCM disproportionation is proposed involving, as intermediates, formate species as well as alumina hydroxyl groups formed by water adsorption.

Preparation and characterisation of chromium-doped cobalt oxide spinel thin films

Thin films of cobalt-based oxide spinel were prepared by pulsed spray evaporation chemical vapour deposition (PSE-CVD), and doping with chromium was systematically investigated up to a Cr/Co ratio of 0.096, corresponding to a stoichiometry of Co3−x Cr x O4 with x = 0.00–0.26. The effect of doping concentration on the structure, assessed by X-ray diffraction and Raman scattering, and on the optical and electrical properties of the oxide films was investigated. Single-phase spinel could be preserved for stoichiometries below x = 0.22. The influence of Cr-doping on the band gap energies and on the electrical conductivity was determined, and the obtained results were exploited to discuss the cationic site occupations. The influence of Cr doping was complemented by the investigation of the surface catalytic reactivity towards the oxidation of dichloromethane.