Oxidation Of Chlorobenzene Research Articles

Synergistic Promotion Effect between NO x and Chlorobenzene Removal on MnO x-CeO2 Catalyst.

Developing new technologies for the simultaneous removal of NO x and dioxins from metallurgical facility and waste incinerator emissions remains challenging. Here, we present a new synergistic improvement effects of NO x and chlorobenzene (CB) on the MnO x-CeO2 catalyst. CB promoted both the NO x conversion and N2 selectivity below 300 °C during the NO x reduction process, in which the MnO x-CeO2 catalyst caused the undesired side reactions due to the over-oxidation of NH3. Meanwhile, NO x and NH3 promoted the CB oxidation activity above 100 °C in the presence of O2. On the basis of the diffuse reflectance infrared Fourier transforms and kinetic studies, the promotion was due to the separation of the MnO x-CeO2 catalyst into different temperature windows: NO x reduction at 100-200 °C and CB oxidation at 200-300 °C. The side reactions mainly occurred above 200 °C, which is suppressed by the coverage and activation of CB on catalyst surface.

MnOx-CeO2 catalysts for effective NOx reduction in the presence of chlorobenzene

The catalytic performance of MnOx-CeO2 for the simultaneous NOx reduction and chlorobenzene (CB) oxidation was investigated. The MnOx(0.4)-CeO2 solid composition exhibited excellent catalytic activity due to the formation of MnyCe1-yO2-δ solid solution and the good balance between redox properties and surface acidity compared to pure ceria. The presence of CB improved both the NOx conversion and N2 selectivity in the range of 200–300 °C. Furthermore, the activity temperature window for NOx reduction was broadened when CB was introduced into the flue gas, and the CB oxidation ability was also enhanced in the presence of O2 and NH3/NO.

One-pot synthesis of monolithic Mn-Ce-Zr ternary mixed oxides catalyst for the catalytic combustion of chlorobenzene

Mn-based catalysts have been widely investigated for the disposal of chlorinated volatile organic compounds (CVOCs), due to their excellent catalytic performances. In this study, Ce-Zr co-modified monolithic Mn-based oxide catalysts were synthesized by one-pot solution combustion method. All the samples were tested with chlorobenzene (CB), as a model molecule of CVOCs. The Mn-Ce-Zr catalyst retained high surface area, small particle size and high redox properties, and exhibited superior catalytic activity with T90% at 390 °C. The superior catalytic activity of Mn-Ce-Zr catalyst originated from the larger specific surface area, the higher Mn4+ cation and surface oxygen contents, as well as the greater oxygen mobility and manganese reducibility. The catalytic activity declined slightly during the life test and the reduced activity could be partially regenerated by introducing water vapor. H2-TPR results indicated that the blockage of active sites by strongly adsorbed chlorine species contributed to the deactivation. By-products generated during CB oxidation included phenol, 2-butene, 2-butenal, acetone, trichloromethane, etc., no highly toxic polychlorinated aromatic compounds were detected. CB oxidation was initiated by CCl bond cleavage followed with ring-open reactions. This work developed a monolithic Mn-Ce-Zr ternary mixed oxides catalyst with striking activity and stability and provided some insightful understandings for designing industrial catalysts.

Correction to Catalytic Oxidation of Chlorobenzene over Mn xCe1- xO2/HZSM-5 Catalysts: A Study with Practical Implications.

Correction to Catalytic Oxidation of Chlorobenzene over Mn xCe1- xO2/HZSM-5 Catalysts: A Study with Practical Implications.

Manganese-Doped CeO₂ Nanocubes for Catalytic Combustion of Chlorobenzene: An Experimental and Density Functional Theory Study.

Manganese oxide (MnOx) supported on CeO2 nanocubes (MnOx/CeO2) were synthesized and tested for the catalytic combustion of chlorobenzene (CB), which was taken as a model compound of chlorinated volatile organic compounds (CVOCs). The catalytic activity tests demonstrated that MnOx/CeO2 nanocube catalysts exhibited a catalytic activity significantly better than that of bare CeO2 nanocubes, indicating MnOx plays a significant role for CB oxidation. To illustrate the effect of MnOx on the CeO2 nanocubes, experimental and theoretical methods such as density functional theory (DFT) calculations were carried out. Experimental characterization testified that the introduction of MnOx to CeO2 nanocubes brought the facile reduction of cerium species, larger amount of Oα species and oxygen vacancies, which lead to the enhanced catalytic performance of MnOx/CeO2 nanocube. Furthermore, DFT calculations clearly validated that MnOx/CeO2 (100) models could form the oxygen vacancies more easily, and CB molecules were preferentially adsorbed on the MnOx/CeO2 (100) models than on the CeO2 (100) models, which facilitated the easier formation of C-O* bond; this facile bond formation enabled faster CB decomposition into COx, thereby a higher CB conversion on the MnOx/CeO2 (100) could be found. Therefore, the vital role of MnOx can be successfully elucidated by both experimental and theoretical methods. Hence, this finding can be utilized for enhanced catalytic performance of CeO2 nanocube catalysts for the CVOCs elimination.

Alkali Potassium Induced HCl/CO2 Selectivity Enhancement and Chlorination Reaction Inhibition for Catalytic Oxidation of Chloroaromatics

Industrial combustion of chloroaromatics is likely to generate unintentional biphenyls (PCBs), polychlorinated dibenzo- p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). This process involves a surface-mediated reaction and can be accelerated in the presence of a catalyst. In the past decade, the effect of surface nature of applied catalysts on the conversion of chloroaromatics to PCBs/PCDD/PCDF has been well explored. However, studies on how the flue gas interferent components affect such a conversion process remain insufficient. In this article, a critical flue gas interferent component, alkali potassium, was investigated to reveal its effect on the chloroaromatics oxidation at a typical solid acid-base catalyst, Mn xCe1- xO2/HZSM-5. The loading of alkali potassium was found to improve the Lewis acidity of the catalyst (by increasing the amounts of surface Mn4+ after calcination), which thus promoted the CO2 selectivity for catalytic chlorobenzene (CB) oxidation. The KOH with a high hydrophilicity has favored the adsorption/activation of H2O molecules that provided sufficient hydroxyl groups and possibly induced a hydrolysis process to promote the formation of HCl. The K ion also served as a potential sink for chorine ions immobilization (via forming KCl). Both of these inhibited the formation of phenyl polychloride byproducts, thereby blocking the conversion of CB to chlorophenol and then PCDDs/PCDFs, and potentially ensuring a durable operation and less secondary pollution for the catalytic chloroaromatics combustion in industry.

Catalytic Oxidation of Chlorobenzene over Ruthenium-Ceria Bimetallic Catalysts

A series of Ru-based mono and bimetallic materials were prepared and evaluated in the catalytic oxidation of chlorobenzene. Among the different Ru-based catalysts, 1Ru/TiO2(P25) was the most active catalyst and contributed the lowest complete oxidation temperature, suggesting that commercial P25 TiO2 was the best support for Ru catalysts. After ceria oxides were introduced into the Ru catalytic system, the catalytic activity of 1Ru-5Ce/TiO2(Rutile) dramatically improved and that of P25 supported catalysts was decreased. Comparing the chlorobenzene consumption rates for 1Ru/TiO2 and 1Ru-5Ce/TiO2 at 280 °C, it could be concluded that monometallic Ru catalytic system was appropriate for P25 support, and the Ru-Ce bimetallic catalytic system was suitable for the rutile TiO2 support. At 280 °C, for 1Ru-5Ce/TiO2(Rutile) and 1Ru-5Ce/TiO2(P25), the chlorobenzene conversion was stabilized at approximately 91% and 86%, respectively. According to the physicochemical properties of the catalysts as characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and Hydrogen temperature programmed reduction (H2-TPR), it can be concluded that (a) electrophilic Oads species play an important role in VOCs oxidation; (b) abundant RuO2 nanoparticles on the surface of 1Ru-5Ce/TiO2(Rutile) result in higher catalytic activity and stability; and (c) dispersion is not the major factor for the catalytic activity, rather the unique structure greatly facilitated the catalytic activity and stability.

Uranium oxide catalysts: environmental applications for treatment of chlorinated organic waste from nuclear industry

ABSTRACTHuge amounts of nuclear waste, including depleted uranium, significantly contribute to the adverse environmental situation throughout the world. An approach to the effective use of uranium oxides in catalysts for the deep oxidation of chlorine-containing hydrocarbons is suggested. Investigation of the catalytic activity of the synthesized supported uranium oxide catalysts doped with Cr, Mn and Co transition metals in the chlorobenzene oxidation showed that these catalysts are comparable with conventional commercial ones. Physicochemical properties of the catalysts were studied by X-ray diffraction, temperature-programmed reduction with hydrogen (H2-TPR), and Fourier transform infrared spectroscopy. The higher activity of Mn- and Co-containing uranium oxide catalysts in the H2-TPR and oxidation of chlorobenzene in comparison with non-uranium catalysts may be related to the formation of a new disperse phase represented by uranates. The study of chlorobenzene adsorption revealed that the surface oxygen is involved in the catalytic process.

Dechlorination of chlorobenzene on vanadium-based catalysts for low-temperature SCR.

Chlorobenzene (CB) inhibits SCR activity of V-based catalysts at low temperature, though the adsorption amount is small. NH3 adsorption increases due to the break in the C-Cl bond during CB oxidation. The dissociated Cl- ions provide extra Brønsted acid sites, leading to the formation of inactive NH4Cl. Ce and Mn improve dechlorination, forming more NH4Cl on the catalyst surface.

Catalytic Oxidation of Chlorobenzene over MnxCe1-xO2/HZSM-5 Catalysts: A Study with Practical Implications.

Industrial-use catalysts usually encounter severe deactivation after long-term operation for catalytic oxidation of chlorinate volatile organic compounds (CVOCs), which becomes a "bottleneck" for large-scale application of catalytic combustion technology. In this work, typical acidic solid-supported catalysts of MnxCe1-xO2/HZSM-5 were investigated for the catalytic oxidation of chlorobenzene (CB). The activation energy (Ea), Brønsted and Lewis acidities, CB adsorption and activation behaviors, long-term stabilities, and surficial accumulation compounds (after aging) were studied using a range of analytical techniques, including XPS, H2-TPR, pyridine-IR, DRIFT, and O2-TP-Ms. Experimental results revealed that the Brønsted/Lewis (B/L) ratio of MnxCe1-xO2/HZSM-5 catalysts could be adjusted by ion exchange of H• (in HZSM-5) with Mnn+ (where the exchange with Ce4+ did not distinctly affect the acidity); the long-term aged catalysts could accumulate ca. 14 organic compounds at surface, including highly toxic tetrachloromethane, trichloroethylene, tetrachloroethylene, o-dichlorobenzene, etc.; high humid operational environment could ensure a stable performance for MnxCe1-xO2/HZSM-5 catalysts; this was due to the effective removal of Cl• and coke accumulations by H2O washing, and the distinct increase of Lewis acidity by the interaction of H2O with HZSM-5. This work gives an in-depth view into the CB oxidation over acidic solid-supported catalysts and could provide practical guidelines for the rational design of reliable catalysts for industrial applications.

Photocatalytic degradation of volatile chlorinated organic compounds with ozone addition

Abstract The decomposition of hydrocarbons using combined advanced oxidation methods is largely considered owing to abundant production of OH radicals and the potential economic advantages. In this study, the synergetic effect of ozonation on photocatalytic oxidation of chloroform and chlorobenzene over expanded graphite-TiO2&ZnO Nano composite was investigated. The effect of introduced ozone concentration and residence time was also examined on removal efficiency. The results showed that the removal efficiency was significantly enhanced by the combined system resulting from the additional oxidation process causing active species to be increased. Increasing the introduced ozone concentration which generates more reactive compounds had a greater effect on the removal efficiency than that of residence time. However, from the mineralization point of view, the residence time had a dominant effect, and the selectivity towards CO2 was dramatically declined when the flow rate increased. Based on these results, the combined system is preferred due to higher removal efficiency and complete mineralization.

Atmospheric oxidation of halogenated aromatics: comparative analysis of reaction mechanisms and reaction kinetics.

Atmospheric transport is the major route for global distribution of semi-volatile compounds such as halogenated aromatics as well as their major exposure route for humans. Their major atmospheric removal process is oxidation by hydroxyl radicals. There is very little information on the reaction mechanism or reaction-path dynamics of atmospheric degradation of halogenated benzenes. Furthermore, the measured reaction rate constants are missing for the range of environmentally relevant temperatures, i.e. 230-330 K. A series of recent theoretical studies have provided those valuable missing information for fluorobenzene, chlorobenzene, hexafluorobenzene and hexachlorobenzene. Their comparative analysis has provided additional and more general insight into the mechanism of those important tropospheric degradation processes as well as into the mobility, transport and atmospheric fate of halogenated aromatic systems. It was demonstrated for the first time that the addition of hydroxyl radicals to monohalogenated as well as to perhalogenated benzenes proceeds indirectly, via a prereaction complex and its formation and dynamics have been characterized including the respective transition-state. However, in fluorobenzene and chlorobenzene reactions hydroxyl radical hydrogen is pointing approximately to the center of the aromatic ring while in the case of hexafluorobenzene and hexachlorobenzene, unexpectedly, the oxygen is directed towards the center of the aromatic ring. The reliable rate constants are now available for all environmentally relevant temperatures for the tropospheric oxidation of fluorobenzene, chlorobenzene, hexafluorobenzene and hexachlorobenzene while pentachlorophenol, a well-known organic micropollutant, seems to be a major stable product of tropospheric oxidation of hexachlorobenzene. Their calculated tropospheric lifetimes show that fluorobenzene and chlorobenzene are easily removed from the atmosphere and do not have long-range transport potential while hexafluorobenzene seems to be a potential POP chemical and hexachlorobenzene is clearly a typical persistent organic pollutant.

Performance of co-doped Mn-Ce catalysts supported on cordierite for low concentration chlorobenzene oxidation

The catalytic activity for low concentration chlorobenzene oxidation was measured with Mn-Ce/cordierite and Mn-Co-Ce/cordierite catalysts with different mole ratios, which were prepared by a sol-gel method and characterized using XRD, BET, SEM Raman, H2-TPR and XPS. The results demonstrated that part of the manganese and cobalt could be incorporated into the lattice of CeO2 to form a solid solution phase. Among all of the catalysts synthesized, Mn8Co1Ce1/cordierite presented the best activity and stability. When the concentration of chlorobenzene was 500ppm, and the GHSV was 15000h−1, the complete combustion temperature (T90%) of chlorobenzene was 325°C. In addition, there was almost no change in the conversion of chlorobenzene during the long-term reaction at 350°C. These results were primarily attributed to the synergistic effect of ceria, manganese and cobalt, which can promote the formation of more lattice defects, more oxygen vacancies and smaller crystallite sizes.

Mechanism study on catalytic oxidation of chlorobenzene over MnxCe1-xO2/H-ZSM5 catalysts under dry and humid conditions

Developments on advanced catalysts for catalytic oxidation of chlorinated hydrocarbons still encounter bottlenecks in Cl deactivation, low HCl and CO2 selectivity, toxic by-products generation, etc. In this paper, a well-reported MnxCe1-xO2 catalyst was selected as active phase to access the role of H-ZSM5 in catalytic oxidation of chlorobenzene (CB) under both dry and humid conditions. The HCl and CO2 production, by-products generation and CB oxidation routes variation were evaluated by using a range of analytical techniques including XRD, BET, GC/MS, in situ DRIFT, Ion Chromatography, etc. It was noted that the presence of H-ZSM5 could induce ca. 90% CB conversion at ca. 230°C. However, only 20% CB was converted into CO2. There were nearly 25 by-products being detected in the off-gas. In situ DRIFT analyses revealed that under dry condition, the H-ZSM5 could promote Cl dissociation from the aromatic ring of CB, which transferred the CB into cyclohexanone or benzoquinone species, hence facilitating CB ring-opening process. Under humid condition, the presence of H2O could not only protect the active sites of Mn0.8Ce0.2O2 from accumulated chlorine poisoning but also act as H and OH radical source to deeply oxidize CB, promoting the HCl and CO2 production over the MnxCe1-xO2/H-ZSM5 catalyst.

Mineralization of chlorobenzene in aqueous medium by anodic oxidation and electro-Fenton processes using Pt or BDD anode and carbon felt cathode

This study focuses on the in situ destruction of pesticide chlorobenzene (CB) by using two electrochemical advanced oxidation processes, namely anodic oxidation and electro-Fenton. Influence of several operating parameters such as applied current, catalyst concentration and supporting electrolytes was assessed to optimize oxidation and mineralization of CB. Kinetics study showed that CB is quickly oxidized by OH following a pseudo first-order reaction kinetics. The rate constant of oxidative degradation of CB by hydroxyl radicals was determined by competition kinetics method and found to be 4.35×109M−1s−1. The quasi complete mineralization (95% TOC removal) of 0.1mM CB aqueous solution was achieved at 4h treatment. Formation and evolution of aromatic and aliphatic (short-chain carboxylic acids) intermediates during treatment were monitored by HPLC analysis and a mineralization pathway was proposed. The results obtained highlight the great efficiency of electro-Fenton process in effective destruction of a very persistent pollutant such as CB that can be extrapolated to other toxic/persistent organic pollutants.

Synthesis, characterization, and photocatalytic activity of porous La–N–co-doped TiO2 nanotubes for gaseous chlorobenzene oxidation

The photocatalytic oxidation of gaseous chlorobenzene (CB) by the 365nm-induced photocatalyst La/N–TiO2, synthesized via a sol–gel and hydrothermal method, was evaluated. Response surface methodology (RSM) was used to model and optimize the conditions for synthesis of the photocatalyst. The optimal photocatalyst was 1.2La/0.5N–TiO2 (0.5) and the effects of La/N on crystalline structure, particle morphology, surface element content, and other structural characteristics were investigated by XRD (X-ray diffraction), TEM (Transmission Electron Microscopy), FTIR (Fourier transform infrared spectroscopy), UV–vis (Ultraviolet–visible spectroscopy), and BET (Brunauer Emmett Teller). Greater surface area and smaller particle size were produced with the co-doped TiO2 nanotubes than with reference TiO2. The removal of CB was effective when performed using the synthesized photocatalyst, though it was less efficient at higher initial CB concentrations. Various modified Langmuir-Hinshelwood kinetic models involving the adsorption of chlorobenzene and water on different active sites were evaluated. Fitting results suggested that competitive adsorption caused by water molecules could not be neglected, especially for environments with high relative humidity. The reaction intermediates found after GC–MS (Gas chromatography–mass spectrometry) analysis indicated that most were soluble, low-toxicity, or both. The results demonstrated that the prepared photocatalyst had high activity for VOC (volatile organic compounds) conversion and may be used as a pretreatment prior to biopurification.

The promotional effect of MoO3 doped V2O5/TiO2 for chlorobenzene oxidation

A series of V2O5–MoO3/TiO2 catalysts prepared by an impregnation method was investigated on their catalytic performance of chlorobenzene oxidation. This study demonstrated that MoO3 is a dopant, which can improve catalyst redox properties and enhance chlorobenzene oxidation catalytic activity at low temperature. Compared to V2O5–TiO2 and V2O5–WO3/TiO2 catalysts, V2O5–MoO3/TiO2 catalysts showed outstanding activity on chlorobenzene oxidation, which is due to the promoting influence of MoO3. For excellent catalytic performance and good N2 selectivity with water, the V2O5–MoO3/TiO2 catalysts may have promising commercial potential for the synergetic control of dioxins and NOx emitted from stationary sources.

Performance of platinum and gold catalysts supported on ceria–zirconia mixed oxide in the oxidation of chlorobenzene

Monometallic noble metal catalysts supported on ceria–zirconia mixed oxide were prepared by impregnation and tested in the oxidation of chlorobenzene (100ppm in air). With the pure ceria–zirconia support, 27% conversion was achieved at 400°C and only incomplete oxidation to carbon monoxide was evidenced. The introduction of gold and especially platinum significantly improved the efficiency of the catalyst. The catalytic performance increased with increasing noble metal content. The catalyst with 1wt.% of Pt achieved 97% conversion of chlorobenzene already at 350°C and complete oxidation to CO2 with only traces of by-products was detected. Platinum catalysts were more efficient than gold ones, which was ascribed to their superior redox properties. On the other hand, the lower acidity of platinum catalysts was not detrimental for their catalytic performance.

Kinetics and mechanism study on catalytic oxidation of chlorobenzene over V2O5/TiO2 catalysts

In this article, we present a detailed study combining the kinetic studies and in-situ FTIR experiments to investigate the oxidation behavior of chlorobenzene over V2O5/TiO2 catalysts. The catalytic data show the 3–5wt.% V2O5/TiO2 catalysts are best fit for the oxidation of chlorobenzene. The calculated apparent reaction orders are about 0.6 and 0.2, respectively. The results of in-situ FTIR provided mechanism insights into the catalytic reaction, which supports the following proposal: (i) a nucleophilic substitution on VO species and (ii) attacking by surface oxygen through a electrophilic substitution, then (iii) followed by the cracking of ring structure, and further oxidation of the resulting species to form final products. The above results further suggest that the nucleophilic substitution process and surface reaction are kinetically significant steps for chlorobenzene oxidation, determining the overall rate of the reaction. Furthermore, 1,2-dichlorobenzene, 1,3-dichlorobenzene and 1,2,4-trichlorobenzene as additional reactants were tested together with chlorobenzene in binary mixtures to examine their competition reactions.

Enhancement of resistance to chlorine poisoning of Sn-modified MnCeLa catalysts for chlorobenzene oxidation at low temperature

The Sn-modified MnCeLa catalysts show significantly higher resistance to chlorine poisoning than MnCeLa catalysts at different temperatures.