Comparative Investigation on Chlorobenzene Oxidation by Oxygen and Ozone over a MnOx/Al2O3 Catalyst in the Presence of SO2

Exceptional Resistance to Chlorine-Induced Photocatalytic Poisoning via Vacuum UV Irradiation

Catalyst deactivation poses a significant challenge in environmental remediation, especially for the photocatalytic oxidation of chlorinated volatile organic compounds (Cl-VOCs). In this study, a functional flower-like TiO2@Mn/rGO (FTMG) catalyst coupled with a vacuum ultraviolet (VUV) lamp was used as a novel photocatalytic oxidation (VUV-PCO) system for chlorobenzene (CB) oxidation. In this system, more than 80% of CB was efficiently oxidized at a high w8 hly space velocity of 600,000 gcat-1 h-1, which was a 6.5-fold increase compared to conventional UV-PCO, and no catalytic deactivation over 1300 min of reaction. Notably, the COx selectivity consistently reached 100%. These outstanding performances were attributed to the synergy of direct VUV photolysis and gas-solid interface photocatalysis. Importantly, the C-Cl bond of CB was efficiently cleaved by VUV photolysis, generating •Cl as the oxidant. Ozone (O3) generated from VUV photolysis was efficiently adsorbed on oxygen vacancies and Mn (Ov + Mn) adjacent sites on FTMG. These adsorbed O3 rapidly captured the photogenerated electrons, thereby effectively preventing Cl reduction and avoiding catalyst deactivation. This study sheds light on the unique dechlorination reaction and Cl-poisoning-resistance mechanism in the VUV-PCO system, offering a novel strategy to boost the catalytic oxidation of Cl-VOCs.

Selective recovery of manganese from spent ternary lithium-ion batteries for efficient catalytic oxidation of VOCs: Unveiling the mechanism of activity Enhancement in recycled catalysts

With the widespread application of ternary lithium-ion batteries (TLBs) in various fields, the disposal of spent TLBs has become a globally recognized issue. This study proposes a novel method for reutilizing metal resources from TLBs. Through selective oxidation, manganese in a leaching solution of TLBs was converted into MnO2 with α, γ, and δ crystal phases (referred to as T-MnO2) for catalytic oxidation of volatile organic compounds (VOCs), while efficiently separating manganese from high-value metals such as nickel, cobalt, and lithium, achieving a manganese recovery rate of 99.99%. Compared to similar MnO2 prepared from pure materials, T-MnO2 exhibited superior degradation performance for toluene and chlorobenzene, with T90 decreasing by around 30 °C. The acidic synthesis environment provided by the leaching solution and the doping of trace metals altered the physicochemical properties of T-MnO2, such as increased specific surface area, elevated surface manganese valence, and improved redox performance and oxygen vacancy properties, enhancing its catalytic oxidation capacity. Furthermore, the degradation pathway of toluene on T-γ-MnO2 was inferred using thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) and in-situ DRIFTs. This study provides a novel approach for recycling spent TLBs and treating VOCs catalytically.

Bioanode boosts efficacy of chlorobenzenes-powered microbial fuel cell: Performance, kinetics, and mechanism

Microbial fuel cell (MFC) is a promising device for water decontamination and energy generation. However, the correlation between power generation and pollutant degradation has not been clarified. Herein, a ruthenium-activated carbon (Ru-AC) bioanode was constructed for chlorobenzenes (CBs) treatment. The pollutant tolerance was improved by Ru-AC anode, and the minimum removal efficiencies of CB and ortho-dichlorobenzene (o-DCB) reached 75.1 % and 69.3 %, respectively, which were considerably higher than those of other MFCs (16.3 %-39.7 %). Correspondingly, the maximum output voltage reached 360.7 mV for the Ru-AC anode, whereas the values obtained from others reached 45.2-149.6 mV. Interaction models were introduced to quantify the relationship between power generation and pollutant degradation. The conversion of highly toxic chlorophenols to organic acids could be accelerated by boosting the mass and electron transfer, thereby simultaneously enhancing CBs removal and power generation. This work provided important insights into pollutant-powered MFC development.

Efficient Ozone Elimination Over MnO2 via Double Moisture-Resistance Protection of Active Carbon and CeO2

The widespread ozone (O3) pollution is extremely hazardous to human health and ecosystems. Catalytic decomposition into O2 is the most promising method to eliminate ambient O3, while the fast deactivation of catalysts under humid conditions remains the primary challenge for their application. Herein, we elaborately developed a splendidly active and stable Mn-based catalyst with double hydrophobic protection of active carbon (AC) and CeO2 (CeMn@AC), which possessed abundant interfacial oxygen vacancies and excellent desorption of peroxide intermediates (O22-). Under extremely humid (RH = 90%) conditions and a high space velocity of 1200 L h-1 g-1, the optimized CeMn@AC achieved nearly 100% O3 conversion (140 h) at 5 ppm, showing unprecedented catalytic activity and moisture resistance toward O3 decomposition. In situ DRIFTS and theory calculations confirmed that the exceptional moisture resistance of CeMn@AC was ascribed to the double protection effect of AC and CeO2, which cooperatively prevented the competitive adsorption of H2O molecules and their accumulation on the active sites of MnO2. AC provided a hydrophobic reaction environment, and CeO2 further alleviated moisture deterioration of the MnO2 particles exposed on the catalyst surface via the moisture-resistant oxygen vacancies of MnO2-CeO2 crystal boundaries. This work offers a simple and efficient strategy for designing moisture-resistant materials and facilitates the practical application of the O3 decomposition catalysts in various environments.

Effect of support structure of Pt/silicaite-1 catalyst on non-thermal plasma (NTP) assisted chlorobenzene degradation and PCDD/Fs formation

Development of efficient catalysts for non-thermal plasma (NTP) assisted catalysis to mitigate the formation of harmful by-products is a significant challenge in the degradation of chlorinated volatile organic compounds (Cl-VOCs). In this study, catalytically active Pt nanoparticles supported on non-porous SiO2 and silicalite-1 zeolites (S1) with different pore structure were comparatively investigated for catalytic chlorobenzene degradation under NTP condition. It was shown that the pore structure could significantly impact the metal size and metal dispersion rate. Pt supported on modified S1 hierarchical meso-micro-porous silicalite-1 (Pt/D-S1) exhibited the smallest particle size (∼6.19 nm) and the highest dispersion rate (∼1.87). Additionally, Pt/D-S1 demonstrated superior catalytic performance compared to the other catalysts, achieving the highest chlorobenzene conversion and COx selectivity at about 80% and 75%, respectively. Furthermore, the pore structure also affected the formation of by-products according to the findings from GC-MS analysis. Pt/SiO2 generated a total of 18 different species of organic compounds, whereas only 12 species of organic by-products were identified in the Pt/D-S1 system (e.g. polychlorinated compounds like 3,4 dichlorophenol were exclusively identified in Pt/SiO2). Moreover, dioxin-like polychlorinated biphenyl and other chlorinated organic compounds, which have potential to form highly toxic dioxins, were detected in the catalysts. HRGC-HRMS confirmed and quantified the 17 different dioxin/furans formed on Pt/SiO2 (25,100 ng TEQ kg-1), Pt/S1 (515 ng TEQ kg-1) and Pt/D-S1 (367 ng TEQ kg-1). The correlation between synthesis-structure-performance in this study provides insights into the design of catalysts for deep oxidation of Cl-VOCs in NTP system.

Fundamental insights and recent advances in catalytic oxidation processes using ozone for the control of volatile organic compounds

The development of technologies for highly efficient treatment of emissions containing low concentrations of volatile organic compounds (VOCs) remains an important challenge. Catalytic oxidation with ozone (catalytic ozonation) is useful for the oxidative decomposition of VOCs, particularly aromatic compounds, under ambient temperature conditions. Only inexpensive transition metal oxides are required as catalysts, and Mn-based catalysts are widely used for catalytic ozonation. This review describes the oxidation reaction mechanisms, reaction pathways of aromatic hydrocarbons, and dependence of the catalytic ozonation activity on the reaction conditions. The reasons why Mn oxides are effective in catalytic ozonation are also explained. The structure of the catalytic active sites and the types of supporting materials contributing to the reaction are also discussed in detail, with the aim of establishing a VOC control technology. In addition, recent progress in catalytic oxidation processes using ozone as an oxidant has been outlined, focusing on catalyst materials and reaction conditions.

Homogeneous and heterogeneous atmospheric ozonolysis of chlorobenzene:Mechanism, kinetics and ecotoxicity assessment

The reactions between chlorobenzene(CB) and ozone have been studied comprehensively in this paper. Chlorobenzene is a commonly found chlorinated aromatic volatile organic compound(VOC), and its emission into the atmosphere can cause harm to the ecosystem and human health. The frequent occurrence of mineral particles from sandstorms exerts a significant influence on the atmospheric chemistry of the troposphere. Mineral particles are abundant in SiO2 and Al2O3 content. Therefore, we investigated the homogeneous and heterogeneous reaction processes of CB and ozone in the atmosphere by using density functional theory (DFT) method at the M06-2X/6-311++g(3df,2p)//M06-2X/6-31+g(d,p) level. The atmospheric fate, reaction rate and toxicity evaluation of CB ozonation were studied in the gas-phase section. Toxicity evaluation results showed that ozonation of CB could effectively reduce its toxicity. For the heterogeneous process, we simulated three types of SiO2 clusters and nine types of (Al2O3)n clusters, and studied the configurations of CB adsorbed on the cluster surfaces. We found that adsorption of CB on the SiO2 clusters was achieved through hydrogen bonding, while adsorption of CB on the Al2O3 clusters was achieved through both hydrogen bonding and metal bonding. The energy for CB adsorption on the (Al2O3)n cluster surface was higher than that for the SixOy(OH)z cluster surface, and both types of clusters exhibited efficient adsorption of CB. As the SixOy(OH)z clusters grew larger, the rates for the reactions between O3 and CB increased. CB travelled long distances along the Al2O3 clusters, leading to an extended influence range.

Catalytic ozonation mechanism over M1-N3C1 active sites

The structure-activity relationship in catalytic ozonation remains unclear, hindering the understanding of activity origins. Here, we report activity trends in catalytic ozonation using a series of single-atom catalysts with well-defined M1-N3C1 (M: manganese, ferrum, cobalt, and nickel) active sites. The M1-N3C1 units induce locally polarized M - C bonds to capture ozone molecules onto M atoms and serve as electron shuttles for catalytic ozonation, exhibiting excellent catalytic activities (at least 527 times higher than commercial manganese dioxide). The combined in situ characterization and theoretical calculations reveal single metal atom-dependent catalytic activity, with surface atomic oxygen reactivity identified as a descriptor for the structure-activity relationship in catalytic ozonation. Additionally, the dissociation barrier of surface peroxide species is proposed as a descriptor for the structure-activity relationship in ozone decomposition. These findings provide guidelines for designing high-performance catalytic ozonation catalysts and enhance the atomic-level mechanistic understanding of the integral control of ozone and methyl mercaptan.

Current status and future challenges of chlorobenzenes pollution in soil and groundwater (CBsPSG) in the twenty-first century: a bibliometric analysis

The global industrial structure had undertaken significant changes since the twenty-first century, making a severe problem of chlorobenzene pollution in soil and groundwater (CBsPSG). CBsPSG receives increasing attention due to the high toxicity, persistence, and bioaccumulation of chlorobenzenes. To date, despite the gravity of this issue, no bibliometric analysis (BA) of CBsPSG does exist. This study fills up the gap by conducting a BA of 395 articles related to CBsPSG from the Web of Science Core Collection database using CiteSpace. Based on a comprehensive analysis of various aspects, including time-related, related disciplines, keywords, journal contribution, author productivity, and institute and country distribution, the status, development, and hotspots of research in the field were shown visually and statistically. Moreover, this study has also delved into the environmental behavior and remediation techniques of CBsPSG. In addition, four challenges (unequal research development, insufficient cooperation, deeply mechanism research, and developing new technologies) have been identified, and corresponding suggestions have been proposed for the future development of research in the field. Afterwards, the limitations of BA were discussed. This work provides a powerful insight into CBsPSG, enabling to quickly identify the hotspot and direction of future studies by relevant researchers.

Three-dimensional porous CuO-modified CeO2-Al2O3 catalysts with chlorine resistance for simultaneous catalytic oxidation of chlorobenzene and mercury: Cu-Ce interaction and structure

Chlorine poisoning effects are still challenging to develop efficient catalysts for applications in chlorobenzene (CB) and mercury (Hg⁰) oxidation. Herein, three-dimensional porous CuO-modified CeO₂-Al₂O₃ catalysts with macroporous framework and mesoporous walls prepared via a dual template method were employed to study simultaneous oxidation of CB and Hg⁰. CuO-modified CeO₂-Al₂O₃ catalysts with three-dimensional porous structure exhibited outstanding activity and stability for simultaneous catalytic oxidation of CB and Hg⁰. The results demonstrated that the addition of CuO into CeO₂-Al₂O₃ can simultaneously enhance the acid sites and redox properties through the electronic inductive effect between CuO and CeO₂ (Cu²⁺+Ce³⁺↔Cu⁺+Ce⁴⁺). Importantly, the synergistic effect between Cu and Ce species can induce abundant oxygen vacancies formation, produce more reactive oxygen species and facilitate oxygen migration, which is beneficial for the deep oxidation of chlorinated intermediates. Moreover, macroporous framework and mesoporous nanostructure dramatically improved the specific surface area for enhancing the contact efficiency between reactants and active sites, leading to a remarkable decrease of byproducts deposition. CB and Hg⁰ had function of mutual promotion in this reaction system. In tune with the experimental results, the possible mechanistic pathways for simultaneous catalytic oxidation of CB and Hg⁰ were proposed.

Boosting Ozone Catalytic Oxidation of Toluene at Room Temperature by Using Hydroxyl-Mediated MnOx/Al2O3 Catalysts

Ozone catalytic oxidation (OZCO) has gained great interest in environmental remediation while it still faces a big challenge during the deep degradation of refractory volatile organic compounds (VOCs) at room temperature. Hydroxylation of the catalytic surface provides a new strategy for regulating the catalytic activity to boost VOC degradation. Herein, OZCO of toluene at room temperature over hydroxyl-mediated MnO_x/Al₂O₃ catalysts was originally demonstrated. Specifically, a novel hydroxyl-mediated MnO_x/Al₂O₃ catalyst was developed via the in situ AlOOH reconstruction method and used for toluene OZCO. The toluene degradation performance of MnO_x/Al₂O₃ was significantly superior to those of most of the state-of-the-art catalysts, and 100% toluene was removed with an excellent mineralization rate (82.3%) and catalytic stability during OZCO. ESR and in situ DRIFTs results demonstrated that surface hydroxyl groups (HGs) greatly improved the reactive oxygen species generation, thus dramatically accelerating the benzene ring breakage and deep mineralization. Furthermore, HGs provided anchoring sites for uniformly dispersing MnO_x and greatly enhanced toluene adsorption and ozone activation. This work paves a way for deep decomposition of aromatic VOCs at room temperature.

Electron transfer enhancing the Mn(II)/Mn(III) cycle in MnO/CN towards catalytic ozonation of atrazine via a synergistic effect between MnO and CN

In this study, manganese oxide (MnO) dispersed on CN (Mn-nCN) was fabricated as a catalyst in heterogeneous catalytic ozonation (HCO), achieving excellent catalytic performance on refractory organic pollutant degradation via the synergistic effects between MnO and CN. The study demonstrated that the C-N-Mn and C-O-Mn bonds constructed in the catalyst linking MnO and CN created the synergistic effects which could overcome typical problems, such as metal leaching etc. The C-N-Mn and C-O-Mn bonds could promote electron transfer from cation-π reactions to form electron-rich Mn(II) sites and electron-poor CN sites. The electron-rich Mn(II) sites as active sites supplied electrons to ozone which then further evolved into reactive oxygen species (ROS). The electron-poor CN sites captured electrons from the pollutant intermediate radicals to electron-rich Mn(II) sites via cation-π reactions with the help of C-N-Mn and C-O-Mn bonds, which promote the redox reactions of Mn. The surface hydroxyl groups also participated in ozone decomposition and ROS production. Additionally, ^•OH was the dominant ROS of the Mn-nCN HCO processes. This study presents the excellent HCO performance of Mn-nCN, as well as provides views on the electron transfer route between the catalyst, pollutant and ozone, which is crucial for the design of the catalyst.

Recent advances in the abatement of volatile organic compounds (VOCs) and chlorinated-VOCs by non-thermal plasma technology: A review

Most of the volatile organic compounds (VOCs) and especially the chlorinated volatile organic compounds (Cl-VOCs), are regarded as major pollutants due to their properties of volatility, diffusivity and toxicity which pose a significant threat to human health and the eco-environment. Catalytic degradation of VOCs and Cl-VOCs to harmless products is a promising approach to mitigate the issues caused by VOCs and Cl-VOCs. Non-thermal plasma (NTP) assisted catalysis is a promising technology for the efficient degradation of VOCs and Cl-VOCs with higher selectivity under relatively mild conditions compared with conventional thermal catalysis. This review summarises state-of-the-art research of the in plasma catalysis (IPC) of VOCs degradation from three major aspects including: (i) the design of catalysts, (ii) the strategies of deep catalytic degradation and by-products inhibition, and (iii) the fundamental research into mechanisms of NTP activated catalytic VOCs degradation. Particular attention is also given to Cl-VOCs due to their characteristic properties of higher stability and toxicity. The catalysts used for the degradation Cl-VOCs, chlorinated by-products formation and the degradation mechanism of Cl-VOCs are systematically reviewed in each chapter. Finally, a perspective on future challenges and opportunities in the development of NTP assisted VOCs catalytic degradation were discussed.

Catalytic ozonation of dichloromethane at low temperature and even room temperature on Mn-loaded catalysts

Five Mn-loaded catalysts were synthesized on γ-Al2O3, TiO2, ZrO2, nano γ-Al2O3 and nanoZrO2 supports. The catalytic ozonation of DCM (dichloromethane) was evaluated under industrial conditions (i.e., temperature, O3 input, H2O and SO2 content). According to results, >90% DCM conversion without O3 residue was achieved for all samples at 120 °C and an O3/DCM ratio of 6. At 20-120 °C, the highest Mn3+ content, abundant surface oxygen species and more weak acid sites led to the best performance of Mn/nanoAl2O3 (M/A-II). At 20 °C and 120 °C, 80% and 95% DCM can be degraded respectively on M/A-II at 20 °C with matched surface oxygen species and acidity. An O3/DCM ratio of 6 was optimal for performance and economy. For the effects of complex exhaust, both H2O and SO2 deactivated M/A-II. The H2O-induced deactivation was recoverable and also removed surface-deposited chlorine-containing species, enhancing the HCl selectivity. Finally, the Cl equilibrium of the reaction was comprehensively analyzed.

Low-Temperature Catalytic Ozonation of Multitype VOCs over Zeolite-Supported Catalysts

Volatile organic compounds (VOCs) are an important source of air pollution, harmful to human health and the environment, and important precursors of secondary organic aerosols, O₃ and photochemical smog. This study focused on the low-temperature catalytic oxidation and degradation of benzene, dichloroethane, methanethiol, methanol and methylamine by ozone. Benzene was used as a model compound, and a molecular sieve was selected as a catalyst carrier to prepare a series of supported active metal catalysts by impregnation. The effects of ozone on the catalytic oxidation of VOCs and catalysts' activity were studied. Taking benzene as a model compound, low-temperature ozone catalytic oxidation was conducted to explore the influence of the catalyst carrier, the active metal and the precious metal Pt on the catalytic degradation of benzene. The optimal catalyst appeared to be 0.75%Pt-10%Fe/HZSM(200). The catalytic activity and formation of the by-products methylamine, methanethiol, methanol, dichloroethane and benzene over 0.75%Pt-10%Fe/HZSM(200) were investigated. The structure, oxygen vacancy, surface properties and surface acidity of the catalysts were investigated. XRD, TEM, XPS, H₂-TPR, EPR, CO₂-TPD, BET, C₆H₆-TPD and Py-IR were combined to establish the correlation between the surface properties of the catalysts and the degradation activity.

Catalytic ozonation of toluene over amorphous Cu-Mn bimetallic oxide: Influencing factors, degradation mechanism and pathways

Herein, amorphous catalysts were employed to investigate the catalytic ozonation system, revealing the degradation mechanism and influencing factors (O₃ concentration, temperature, and humidity) for toluene catalytic ozonation. Cu_0.2MnO_x exhibited the highest toluene oxidized and excellent stability (∼85% at 60 h) based on the suitable value of O_ads/O_lat and potent synergy between Cu with Mn. To explore the effect of factors, the change of fresh and post-reaction samples was compared as revealed in the relevant characterization results (SEM, XRD, BET, XPS, TGA), DRIFTS and GC-MS identified the intermediates and byproducts. The results show that appropriate temperature (100 °C) and O₃ concentration (2100 ppm) can effectively enhance the number of reactive oxygen species. Although H₂O can increase the production of ·OH to promote degradation, it is easier to quench the active sites on the surface of amorphous catalysts. During the reaction, the main role of Cu in Cu-Mn bimetallic oxides is adsorption of toluene and O₃, formation of benzoic acid, and oxidation of short-chain products. As for the adjacent Mn, it works on the cleavage of O-O in O₃ and the ring-opening of benzene. Then, the mainly catalytic ozonation pathway of toluene was proposed and followed the order: toluene, benzoic acid, benzene, maleic anhydride, short-chain carbon species, CO₂, and H₂O.

The Study of Thermal Stability of Mn-Zr-Ce, Mn-Ce and Mn-Zr Oxide Catalysts for CO Oxidation

MnO_x-CeO₂, MnO_x-ZrO₂, MnO_x-ZrO₂-CeO₂ oxides with the Mn/(Zr + Ce + Mn) molar ratio of 0.3 were synthesized by coprecipitation method followed by calcination in the temperature range of 400-800 °C and characterized by XRD, N₂ adsorption, TPR, TEM, and EPR. The catalytic activity was tested in the CO oxidation reaction. It was found that MnO_x-CeO₂, MnO_x-ZrO₂-CeO₂, MnO_x-ZrO₂ catalysts, calcined at 400-500 °C, 650-700 °C and 500-650 °C, respectively, show the highest catalytic activity in the reaction of CO oxidation. According to XRD and TEM results, thermal stability of catalysts is determined by the temperature of decomposition of the solid solution Mn_x(Ce,Zr)_1-xO₂. The TPR-H₂ and EPR methods showed that the high activity in CO oxidation correlates with the content of easily reduced fine MnO_x particles in the samples and the presence of paramagnetic defects in the form of oxygen vacancies. The maximum activity for each series of catalysts is associated with the start of solid solution decomposition. Formation of active phase shifts to the high-temperature region with the addition of zirconium to the MnO_x-CeO₂ catalyst.

Catalytic Oxidation of NO by Ozone over Mn-Ce/Al2O3/TiO2 Catalyst

In this study, Mn-Ce/Al2O3/TiO2 catalyst prepared by impregnation method was used for synergistic O3 oxidation NO. The catalyst prepared by impregnating Al2O3/TiO2 at a Mn:Ce molar ratio of 4:1 showed the best catalytic activity. The catalyst performance showed that when the molar ratio of Mn:Ce was 4:1 and the volume ratio of O3:NO was 1:4, the removal rate of NO could reach 63%, which could increase the removal rate by 40% compared with that of NO oxidized by O3 alone. BET, XRD, and TEM characterization results showed that when the molar ratio of Mn:Ce was 4:1, the catalyst specific surface area, and pore capacity were the largest. A large amount of MnOx and CeOx were distributed on the catalyst surface. The XPS analysis showed that the oxidation-reduction and oxygen vacancy of Mn (IV)/Mn (III)/Mn (II) and Ce (IV)/Ce (III), had a synergistic effect on the decomposition of O3 into reactive oxygen species(O*), thus improving the catalytic capacity of Mn-Ce/Al2O3/TiO2 catalyst for O3. The O2-TPD analysis showed that the oxygen vacancies and oxygen species in the catalyst could be used as the active point of decomposition of O3 into O*. The experimental results show that the prepared catalyst can significantly improve the efficiency of ozone oxidation of NO and reduce the amount of ozone. The catalyst can be applied to ozone oxidation denitrification technology.

Evaluation of the Flexibility for Catalytic Ozonation of Dichloromethane over Urchin-Like CuMnOx in Flue Gas with Complicated Components

The evaluation of the poisoning effect of complex components in practical gas on DCM (dichloromethane) catalytic ozonation is of great significance for enhancing the technique's environmental flexibility. Herein, Ca, Pb, As, and NO/SO₂ were selected as a typical alkaline-earth metal, heavy metal, metalloid, and acid gas, respectively, to evaluate their interferences on catalytic behaviors and surface properties of an optimized urchin-like CuMn catalyst. Ca/Pb loading weakens the formation of oxygen vacancies, oxygen mobility, and acidity due to the fusion of Mn-Ca/Pb-O, leading to their inferior catalytic performance with poor CO₂ selectivity and mineralization rate. Noticeably, the presence of As induces excessively strong acidity, facilitating the inevitable formation of byproducts. Catalytic co-ozonation of NO/DCM is achieved with stoichiometric ozone addition. Unfortunately, SO₂ introduction brings irreversible deactivation due to strong competition adsorption and the loss of active sites. Unexpectedly, Ca loading protects active sites from an attack by SO₂. The formation of unstable sulfites and the released Mn-O structure offset the negative effect from SO₂. Overall, the catalytic ozonation of DCM exhibits a distinctive priority in the antipoisoning of metals with the maintenance of DCM conversion. The construction of more stable acid sites should be the future direction of catalyst design; otherwise, catalytic ozonation should be arranged together with post heavy metal capture and a deacidification system.

Catalytic ozonation of CH2Cl2 over hollow urchin-like MnO2 with regulation of active oxygen by catalyst modification and ozone promotion

This paper firstly reported efficient catalytic ozonation of CH₂Cl₂ (dichloromethane, DCM) at low temperature over hollow urchin-like MnO₂ with high chlorine resistance. Regulations on morphologies and Cu doping, as well as ozone promotion were conducted to optimize active oxygen of MnO₂ catalysts, contributing to excellent catalytic behaviors. Cu doping MnO₂ with hollow urchin-like morphology attained a stable 100% DCM conversion with O₃/DCM molar ratio of 10 at 120 °C. The ozone utilization rate, final products, and byproducts distribution were discussed. Abundant crystal defects, low-valance Mn/Cu, O_ads, and weak acidity, as well as better low temperature reducibility contributed to its superior performance. During DCM catalytic ozonation, DCM oxidation exhibited competitive effect on O₃ decomposition due to the occupation of intermediates (CH₂ClO₃·, O-CH₂Cl, and O-CH₂ -O) over active sites that should belong to O₃ originally. Nevertheless, O₃ decomposition exhibited synergistic effects on DCM oxidation with promotion on active oxygen. Density functional theory (DFT) calculations confirmed the positive effect on oxygen vacancy formation and O₃/DCM adsorption from Cu doping. The possible mechanism for DCM catalytic ozonation included four parts, including O₃/DCM adsorption, O₃ activation, DCM oxidation, and electron replenishment. This paper provides new insight for catalytic elimination of chlorinated alkanes at mild conditions.

Highly efficient catalytic ozonation for ammonium in water upon γ-Al2O3@Fe/Mg with acidic-basic sites and oxygen vacancies

Catalytic ozonation has prospects in the advanced treatment of nitrogen removal, and solid base MgO can efficiently catalyze the ozonation of ammonium nitrogen. However, it is necessary to improve the problem of easy loss, difficult recovery, and low percentage of gaseous products. Here, MgO, amorphous Fe2O3, and γ-Al2O3 were selected as doping components and supports, respectively, to prepare γ-Al2O3@Fe/Mg composite catalysts with abundant acidic-basic sites and oxygen vacancies. The results show that γ-Al2O3@Fe/Mg5 can efficiently catalyze the ozonation of ammonium nitrogen (98.73%) with 67.82% gaseous product selectivity under the conditions of initial pH = 7, catalyst dosage of 112.88 g/L, and ozone dosage of 2.4 mg/min. The doping of Fe2O3 and MgO with a weaker lattice oxygen binding energy improves the gaseous product selectivity. The mechanism of ammonium nitrogen removal for γ-Al2O3@Fe/Mg5 is revealed, especially the intrinsic contribution of acidic-basic sites and oxygen vacancies. The pH and active sites play different roles in ozone decomposition for NH4+ removal. Surface hydroxyl protonation on basic sites and oxygen vacancies and electron transfer on acidic sites are responsible for ozone decomposition to hydroxyl radicals. Moreover, γ-Al2O3@Fe/Mg5 exhibits good stability, few leaching ions, and can be settled in water for easy recovery. This study suggests that γ-Al2O3@Fe/Mg5 is a good candidate for the catalytic ozonation of ammonium nitrogen.

Engineering Platinum Catalysts via a Site-Isolation Strategy with Enhanced Chlorine Resistance for the Elimination of Multicomponent VOCs

Pt-based catalysts can be poisoned by the chlorine formed during the oxidation of multicomponent volatile organic compounds (VOCs) containing chlorinated VOCs. Improving the low-temperature chlorine resistance of catalysts is important for industrial applications, although it is yet challenging. We hereby demonstrate the essential catalytic roles of a bifunctional catalyst with an atomic-scale metal/oxide interface constructed by an intermetallic compound nanocrystal. Introducing trichloroethylene (TCE) exhibits a less negative effect on the catalytic activity of the bimetallic catalyst for o-xylene oxidation, and the partial deactivation caused by TCE addition is reversible, suggesting that the bimetallic, HCl-etched Pt₃Sn(E)/CeO₂ catalyst possesses much stronger chlorine resistance than the conventional Pt/CeO₂ catalyst. On the site-isolated Pt-Sn catalyst, the presence of aromatic hydrocarbon significantly inhibits the adsorption strength of TCE, resulting in excellent catalytic stability in the oxidation of the VOC mixture. Furthermore, the large amount of surface-adsorbed oxygen species generated on the electronegative Pt is highly effective for low-temperature C-Cl bond dissociation. The adjacent promoter (Sn-O) possesses the functionality of acid sites to provide sufficient protons for HCl formation over the bifunctional catalyst, which is considered critical to maintaining the reactivity of Pt by removing Cl and decreasing the polychlorinated byproducts.

Abatement of chlorobenzene by plasma catalysis: Parameters optimization through response surface methodology (RSM), degradation mechanism and PCDD/Fs formation

Dielectric barrier discharge coupled with 10 wt% Co/γ-Al₂O₃ catalyst was developed to degrade chlorobenzene in this study. The effects of experimental parameters including applied voltage, flow rate, initial chlorobenzene concentration, and their interactions on the chlorobenzene degradation performance were investigated by the response surface methodology integrated with a central composite design. Results indicated that applied voltage was the most significant parameter affecting the mineralization rate and the concentration of ozone generated, while energy yield was mainly determined by initial chlorobenzene concentration. As a key precursor of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorophenols were found during the identification of the intermediates produced during chlorobenzene degradation through GC-MS. Furthermore, HRGC-HRMS was used to detect the remaining byproducts on the catalyst surface after 3 and 10 h discharge time, and three types of PCDD/Fs (2,3,7,8-TCDF, 1,2,3,4,6,7,8-HCDF and OCDD) were detected after 10 h of discharge. The degradation mechanism of chlorobenzene was analyzed based on these detected intermediates, and the possible formation mechanisms of the three PCDD/Fs were proposed for the first time in plasma catalytic degradation of chlorobenzene.

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

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

Biotemplate Fabrication of Hollow Tubular CexSr1-xTiO3 with Regulable Surface Acidity and Oxygen Mobility for Efficient Destruction of Chlorobenzene: Intrinsic Synergy Effect and Reaction Mechanism

Developing economic and applicable catalysts with elegant chlorine resistance and organic byproduct inhibition capability is of great significance for chlorinated volatile organic compounds (Cl-VOCs) eco-friendly purification. Here, ternary Ce_xSr_1-xTiO₃ catalysts with tunable surface acidity and oxygen species mobility were creatively fabricated using the hollow tubular-structured fruit hair of Platanus (FHP; a widespread greenery waste) as the scaffolding biotemplate. It is shown that the oxygen vacancy (O_v) triggered by the presence of Ce can optimize the synergy between the Lewis acid sites (LAS) and Brønsted acid sites (BAS). High concentration of O_v and BAS promotes the C-Cl cleavage of chlorobenzene (CB) and accelerates the desorption of Cl^• radicals as inorganic chlorine. Simultaneously, the strong electron transfer within Ti-Ce-Sr linkage increases the acidity of LAS, resulting in the superior reducibility of Ce_0.4Sr_0.6TiO₃ and facilitating the deep oxidation of dechlorination intermediates. Additionally, the spatial confinement of the tubular structure remarkably accelerates the CB flow rate and reduces the residence time of byproducts over the prepared catalysts. Owing to these, CB can be efficiently destructed over Ce_0.4Sr_0.6TiO₃ with selectivity of CO₂ and inorganic chlorine dramatically enhanced, respectively, approximately 16 and 21 times at 275 °C compared to those of pure SrTiO₃. The present work provides a feasible and promising strategy for engineering efficient catalysts for heterogeneous thermocatalytic reactions for industrial-scale Cl-CVOC destruction.

Catalytic Decomposition of Residual Ozone over Cactus-like MnO2 Nanosphere: Synergistic Mechanism and SO2/H2O Interference

Ground-level ozone is an irritant and is harmful to human respiratory and nervous systems. Thus, four manganese oxides with different crystals were hydrothermally synthesized to decompose residual ozone (deO₃) in an ozone synergistic-oxidation system. Among them, a cactus-like MnO₂-IV nanosphere exhibited the highest deO₃ activity, with excellent tolerance to water vapor and SO₂/H₂O, which could maintain >88% deO₃ efficiency in the high-humidity and sulfur-containing conditions. It benefits from the unique morphology, high specific surface area, superior redox properties, oxygen chemisorption capabilities, abundant surface-active hydroxyl species, and low valence Mn species. More importantly, the detailed interference mechanism of O₂/O₃/H₂O/SO₂ molecules on MnO₂-IV was revealed utilizing in situ diffused reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy. H₂O generally caused recoverable deactivation, but that caused by SO₂ was irreversible. The synergistic effect of SO₂/H₂O promoted the formation of an unstable sulfate species, thereby deepening the deactivation but inhibiting the irreversible poisoning. Finally, nine specific steps to decompose ozone via surface-active hydroxyl/intermediates were established.

Investigation of Cu-Mn catalytic ozonation of toluene: Crystal phase, intermediates and mechanism

The effect of different crystal phases, i.e. spinel phase (CuMn₂O₄) and amorphous phase (Cu_0.2MnO_x), was explored in Cu-Mn catalytic ozonation of toluene. The toluene removal efficiency followed the order of Cu_0.2MnO_x (91.2%) ˃ CuMn₂O₄ (74.5%) ˃ commercial catalyst Cu_0.3MnO_x (70.3%) in 130 min, and the higher CO₂ yield (67.6%) could be also observed using Cu_0.2MnO_x. In order to investigate the effect of phases on the toluene degradation pathway, the intermediates and byproducts were identified by DRIFTS, GC-MS, and TOF-SIMS. No obvious difference was observed in the distribution of byproducts, except for the quantities, suggesting the discrepancy of oxidation rate. On the other hand, the catalysts were characterized before and after the ozonation process by TEM, BET, XPS, XRD, EPR, TGA, and TPR. It was proposed that for amorphous catalysts, the oxygen vacancy (V_o) helped the chemisorption of toluene, and adjacent Mn reacted as the main active site for the ozonation process. While, the redox pair of Cu⁺/Mn⁴⁺ and Cu²⁺/(Mn³⁺, Mn²⁺) in the spinel phase plays an important role in the generation of oxygen vacancies for O₃ decomposition.

Advanced catalytic ozonation for degradation of pharmaceutical pollutants-A review

Various chemical treatment techniques are involved in removing refractory organic compounds from water and wastewater using the oxidation reaction of hydroxyl radicals (^•OH). The use of catalysts in advanced catalytic ozonation is likely to improve the decomposition of molecular ozone to generate highly active free radicals that facilitate the rapid and efficient mineralization and degradation of numerous organics. For the degradation of toxic organic pollutants in wastewater, the advanced catalytic ozonation process has been widely applied in recent years. Low utilization efficiency of ozone and ineffective mineralization of organic contaminants by ozone can be remedied with advanced catalytic ozonation. Advanced catalytic ozonation has gained popularity because of these merits. However, homogeneous catalytic ozonation has the disadvantage of producing secondary contaminants from the addition of metallic ions. Heterogeneous catalytic ozonation can overcome this drawback by utilizing metals, metallic oxides, and carbon materials as a catalyst of efficacy and stability. This review discusses various aspects of catalytic ozonation in wastewater treatment of pharmaceutical pollutants, application of catalytic ozonation process in typical wastewater, and prospects in advancing the techniques in heterogeneous catalytic ozonation.

Catalytic ozonation of VOCs at low temperature: A comprehensive review

VOCs abatement has attracted increasing interest because of the detrimental effects on both atmospheric environment and human beings of VOCs. The assistance of ozone has enabled efficient VOCs removal at low temperature. Thereby, catalytic ozonation is considered as one of the most feasible and effective methods for VOCs elimination. This work systematically reviews the emerging advances of catalytic ozonation of different VOCs (i.e., aromatic hydrocarbons, oxygenated VOCs, chlorinated VOCs, sulfur-containing VOCs, and saturated alkanes) over various functional catalysts. General reaction mechanism of catalytic ozonation including both Langmuir-Hinshelwood and Mars-van-Krevelen mechanisms was proposed depending on the reactive oxygen species involving the reactions. The influence of reaction conditions (water vapor and temperature) is fully discussed. This review also introduces the enhanced VOCs oxidation via catalytic ozonation in the ozone-generating systems including plasma and vacuum ultraviolet. Lastly, the existing challenges of VOCs catalytic ozonation are presented, and the perspective of this technology is envisioned.

Recent Progress of Thermocatalytic and Photo/Thermocatalytic Oxidation for VOCs Purification over Manganese-based Oxide Catalysts

Volatile organic compounds (VOCs) are one of the main sources of air pollution, which are of wide concern because of their toxicity and serious threat to the environment and human health. Catalytic oxidation has been proven to be a promising and effective technology for VOCs abatement in the presence of heat or light. As environmentally friendly and low-cost materials, manganese-based oxides are the most competitive and promising candidates for the catalytic degradation of VOCs in thermocatalysis or photo/thermocatalysis. This article summarizes the research and development on various manganese-based oxide catalysts, with emphasis on their thermocatalytic and photo/thermocatalytic purification of VOCs in recent years in detail. Single manganese oxides, manganese-based oxide composites, as well as improving strategies such as morphology regulation, heterojunction engineering, and surface decoration by metal doping or universal acid treatment are reviewed. Besides, manganese-based monoliths for practical VOCs abatementare also discussed. Meanwhile, relevant catalytic mechanisms are also summarized. Finally, the existing problems and prospect of manganese-based oxide catalysts for catalyzing combustion of VOCs are proposed.