Plasma assisted Cu-Mn mixed oxide catalysts for trichloroethylene abatement in moist air

Degradation of o-dichlorobenzene by DBD-NTP co-modified titanium gel catalyst

In order to study the degradation process of dioxins in industrial flue gas, the decomposition of o-dichlorobenzene (o-DCB) in a DBD plasma catalytic reactor was investigated. The results showed that an NTP-catalyzed system, especially using the CuMnTiOx catalyst, had better o-DCB degradation performance compared to plasma alone. The combination of the CuMnTiOx catalyst with NTP can achieve a degradation efficiency of up to 97.2% for o-DCB; the selectivity of CO and CO2 and the carbon balance were 40%, 45%, and 85%, respectively. The dielectric constant and electrical property results indicated that the surface discharge capacity of the catalysts played a major role in the degradation of o-DCB, and a higher dielectric constant could suppress the plasma expansion and enhance the duration of the plasma discharge per discharge cycle. According to the O1s XPS and O2-TPD results, the conversion of CO to CO2 follows the M-v-K mechanism; thus, the active species on the catalyst surface play an important role. Moreover, the CuMnTiOx and NTP mixed system exhibited excellent stability, which is probably because Cu doping improved the lifetime of the catalyst. This work can provide an experimental and theoretical basis for research in the degradation of o-DCB by plasma catalyst systems.

Recent advances in the control of volatile organic compounds emissions from indoor wood-based panels: A comprehensive review

Wood-based panels provide efficient alternatives to materials such as plastics derived from traditional petroleum sources and thereby help to mitigate greenhouse gas emissions. Unfortunately, using indoor manufactured panel products also results in significant emissions of volatile organic compounds including olefins, aromatic and ester compounds, which negatively affect human health. This paper highlights recent developments and notable achievements in the field of indoor hazardous air treatment technologies to guide future research toward environmentally friendly and economically feasible directions that may have a significant impact on the improvement of human settlements. Summarizing and synthesizing the principles, advantages, and limitations of different technologies can assist policymakers and engineers in identifying the most appropriate technology for a particular air pollution control program based on criteria such as cost-effectiveness, efficiency, and environmental impact. In addition, insights into the development of indoor air pollution control technologies are provided and potential areas for innovation, improvement of existing technologies, and development of new technologies are identified. Finally, the authors also hope that this sub-paper will raise public awareness of indoor air pollution issues and promote a better understanding of the importance of indoor air pollution control technologies for public health, environmental protection, and sustainable development.

Catalytic Properties of the Spinel-Like CuxMn3−xO4 Copper Manganese Oxides—An Overview

Copper manganese oxide spinels and related (multiphase) materials with the formula CuxMn3−xO4 are the active catalysts in a wide variety of industrially important processes due to their great diversity in their phase relations, metal ion valence/site distribution, and chemical properties. In this review, we summarize the preparation methods and their effects on the composition, properties, and catalytic properties of various CuxMn3−xO4 catalysts with various Cu/Mn ratios. The main summarized catalytic reactions are the oxidation of carbon monoxide, nitrogen oxide, and hydrogen sulfide and the oxidative removal of organic solvents such as benzene, toluene, and xylene from the air. Some industrially important reactions (steam reforming of methanol or synthesis gas) and the manufacture of organic chemicals (methyl formate, propylene oxide, and benzyl alcohol) catalyzed by CuxMn3−xO4 spinels are also reviewed.

A critical review on plasma-catalytic removal of VOCs: Catalyst development, process parameters and synergetic reaction mechanism

It is urgent to control the emission of volatile organic compounds (VOCs) due to their harmful effects on the environment and human health. A hybrid system integrating non-thermal-plasma and catalysis is regarded as one of the most promising technologies for VOCs removal due to their high VOCs removal efficiency, product selectivity and energy efficiency. This review systematically documents the main findings and improvements of VOCs removal using plasma-catalysis technology in recent 10 years. To better understand the fundamental relation between different aspects of this research field, this review mainly addresses the catalyst development, key influential factors, generation of by-products and reaction mechanism of VOCs decomposition in the plasma-catalysis process. Also, a comparison of the performance in various VOCs removal processes is provided. Particular emphasis is given to the importance of the selected catalyst and the synergy of plasma and catalyst in the VOCs removal in the hybrid system, which can be used as a reference point for future studies in this field.

Activation and characterization of environmental catalysts in plasma-catalysis: Status and challenges

Plasma-catalysis has attracted great attentions in environmental/energy-related fields, but the synergetic mechanism still suffers intractable defects. Key issues are that what kind of catalysts are applicable for plasma system, how are they activated in plasma, and how to characterize them in plasma. This review systematically gives a comprehensive summarization of the selection of catalysts and its activation mechanism in plasma, based on the character of plasma, including physical effects containing the enhancement of discharge intensity and adsorption of reactants, and the utilization of plasma-generated active species such as·O, heat, O₃, ultraviolet light and e* . Focus is given to the illumination of the activation mechanisms of catalysts when placed in plasma zone. Subsequently, the novel characterization techniques for catalysts, which may associate properties to performance, are critically overviewed. The challenges and opportunities for the activation and characterizations of catalysts are proposed, and future perspectives are suggested about where the efforts should be made. It is expected that a bridge between catalysts design and character of plasma can be built to shed light on the synergetic mechanism for plasma-catalysis and design of new plasma-catalysis systems.

Realizing Toluene Deep Mineralization by Coupling Nonthermal Plasma and Nitrogen-Enriched Hollow Hybrid Carbon

Achieving excellent efficiency to mineralize volatile organic compounds (VOCs) under nonthermal plasma catalysis (NTP-catalysis) systems tremendously relies on the catalyst design. Herein, we report a dual-template strategy for synthesizing a core-shell structured nitrogen-enriched hollow hybrid carbon (N-HHC) by a facile pyrolysis of a Mn-ZIF-8@polydopamine core-shell precursor. N-HHC exhibits a remarkable plasma synergy effect and superior degradation efficiency for toluene (up to 90% with a specific input energy of 281 J/L), excellent CO₂ selectivity (>45%), and byproduct-inhibiting capability. Such outstanding functionality of the developed N-HHC is uniquely attributed to its hollow multistage and channeling structure, high concentration of O₃-decomposing species (pyrrolic and oxide pyridinic-N), and abundant ZnO active sites. Shedding light on an efficient synthetic strategy for designing an advanced nanocatalyst with enhanced VOC destruction in the NTP-catalysis system, the present results could be extended to design other N-doped metal/metal oxide-decorated hollow porous carbons for environment-related applications.

Post-Plasma Catalysis for Trichloroethylene Abatement with Ce-Doped Birnessite Downstream DC Corona Discharge Reactor

Trichloroethylene (TCE) removal was investigated in a post-plasma catalysis (PPC) configuration in nearly dry air (RH = 0.7%) and moist air (RH = 15%), using, for non-thermal plasma (NTP), a 10-pin-to-plate negative DC corona discharge and, for PPC, Ce0.01Mn as a catalyst, calcined at 400 °C (Ce0.01Mn-400) or treated with nitric acid (Ce0.01Mn-AT). One of the key points was to take advantage of the ozone emitted from NTP as a potential source of active oxygen species for further oxidation, at a very low temperature (100 °C), of untreated TCE and of potential gaseous hazardous by-products from the NTP. The plasma-assisted Ce0.01Mn-AT catalyst presented the best CO2 yield in dry air, with minimization of the formation of gaseous chlorinated by-products. This result was attributed to the high level of oxygen vacancies with a higher amount of Mn3+, improved specific surface area and strong surface acidity. These features also allow the promotion of ozone decomposition efficiency. Both catalysts exhibited good stability towards chlorine. Ce0.01Mn-AT tested in moist air (RH = 15%) showed good stability as a function of time, indicating good water tolerance also.

The post plasma-catalytic decomposition of toluene over K-modified OMS-2 catalysts at ambient temperature: Effect of K+ loading amount and reaction mechanism

The present work is devoted to study the post plasma-catalytic (PPC) degradation of toluene using packed-bed discharge (PBD) plasma over K-modified manganese oxide octahedral molecular sieve (OMS-2) catalysts at ambient temperature. Compared to plasma alone, PPC can significantly improve the toluene degradation and mineralization performance simultaneously, and the generation of discharge byproducts and organic intermediates is suppressed. The catalytic capacity of OMS-2 for toluene degradation is greatly promoted by tuning potassium ions (K⁺) content in OMS-2 tunnel, which might be owing to the formation of more surface active oxygen species derived from weak Mn-O bonds, plenty of oxygen vacancies, as well as more superior low-temperature reducibility. Highest toluene degradation efficiency (89.4%) and CO_x selectivity (88.9%) can be achieved in plasma-catalysis system over K-modified OMS-2 sample with K/Mn molar ratio of 2 at the SIE of 658 J/L. A long-term stability test has also been successfully carried out to evaluate the stability of K-modified OMS-2 with the assistance of plasma. Possible reaction mechanism for plasma-catalytic degradation of toluene on K-modified OMS-2 catalyst has been proposed based on the plasma diagnosis, catalysts characterization, and organic intermediates identification. This work aims to gaina deeperunderstandingof plasma-catalytic degradation mechanism and provides an environmentally friendly and energy-efficient method for practical volatile organic compounds (VOCs) abatement in PPC process.

Simultaneous removal of toluene and styrene by non-thermal plasma-catalysis: Effect of VOCs interaction and system configuration

Toluene and styrene were two typical aromatic VOCs which were commonly used and coexistence in the exhaust gases from industrial manufacturing. Their simultaneous removal performances under non-thermal plasma (NTP) and NTP-catalysis were carried out and compared by a single stage coaxial dielectric barrier discharge (DBD) reactor. The effects of VOCs mixture, humidity, materials filling in the discharge zoon on the removal efficiency, CO_x selectivity, byproducts types and their emission levels were deeply investigated to explore the degradation mechanism and coexistence effect. Experimental results showed that the toluene removal was significantly inhibited when treated together with styrene under plasma treatment. But that of styrene was hardly affected at the same conditions. It was found that benzaldehyde as the primary organic byproducts from styrene consumed the oxidizing particles (O and ^. OH), limiting the conversion of toluene. The introduction of Cu-doped MnO₂ materials significantly improved the VOCs removal performance with nearly 100% conversion to CO_x at a discharge power less than 30 W, as well as O₃ generation from more than 1.2 mg L^-1 by NTP to 1.6 × 10^-3 mg L^-1 by NTP-catalysis. With the help of in situ FT-IR, it was believed that catalysts not only accelerated the adsorption and degradation of pollutants but also utilized ozone to involve this process. At last, a plausible explanation on binary coexistence effect under different conditions had been suggested and discussed.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.

MnOx-CuOx cordierite catalyst for selective catalytic oxidation of the NO at low temperature

Low-value solid waste cordierite honeycomb ceramics were used as carrier of SCO denitration catalyst, and the active component was supported by the impregnation method to improve the performance of the catalyst. Firstly, the effect of calcination conditions on the denitration performance of the Mn-loaded cordierite catalyst was studied for the cordierite-loaded active component MnO_X. Secondly, the preferred catalyst was reloaded with another active component to further improve its denitration performance; the bimetal ratios were affected by the denitration performance, which was, finally, characterized by XRD, XPS, and SEM. The result shows the following: (1) Mn-loaded cordierite prepared at 450 °C for 3 h has a good denitration effect; (2) the MnO_X-CuO_X/CR catalyst is superior to MnO_X-FeO_X/CR, MnO_X-CoO_X/CR, and MnO_X-CeO_X/CR; (3) the MnO₂ crystal form in the single metal-supported catalyst plays a major role, and Cu₂Mn₃O₈ in the bimetallic catalyst affects the performance and activity of the catalyst. Graphical abstract.

Effect of calcium addition in plasma catalysis for toluene removal by Ni/ZSM-5 : Acidity/basicity, catalytic activity and reaction mechanism

The effect of Ca modification on the Ni/ZSM-5 catalyst for efficient toluene oxidation was studied in a plasma-catalytic system. The Ni/ZSM-5 and Ca-Ni/ZSM-5 catalysts were prepared by a wet impregnation method and characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Pyridine-FTIR spectroscopy and temperature programmed desorption of ammonia (NH₃-TPD). Among the catalysts tested, the Ca-Ni/ZSM-5 sample showed the best potential for toluene conversion (90.2%) and CO₂ selectivity (70.7%). Pyridine-FTIR spectra and NH₃-TPD results proved that the introduction of Ca and Ni onto ZSM-5 caused a decrease in the strong and weak acidic sites. In addition, gas chromatography/mass spectrometry (GC-MS) result showed that the Ca-Ni/ZSM-5 catalyst reduced the production of undesirable byproducts (such as p-nitrotoluene and methyl benzoate). Calcium in the Ni/ZSM-5 system influenced the acidity and other surface characteristic of the catalyst, as well as directly impacting the reactive plasma species and the intermediates. Finally, possible reaction mechanisms in the plasma catalysis of toluene were also proposed.

Degradation of gas-phase o-xylene via combined non-thermal plasma and Fe doped LaMnO3 catalysts: Byproduct control

A series of Fe doped LaMnO₃ catalysts were prepared to control the production of byproducts such as O₃, N₂O, and CO, during the degradation of volatile organic compounds with a non-thermal plasma. Eliminating these potentially toxic byproducts will make non-thermal plasma technologies applicable for a wider range of commercial applications. The modified LaMnO₃ catalysts are combined in NTP-catalysis reactor with optimal configuration. Experimental results show that doping Fe on LaMnO₃ catalysts can not only enhance the oxidation of o-xylene, but also lower the emission levels of byproducts. LaMn_0.9Fe_0.1O₃ catalyst shows the best catalytic activity among the formulations tested herein. In addition to the strong mineralization of 88.1 %, the catalyst has the highest performance for o-xylene conversion (91.3 %), O₃ inhibition efficiency (84.9 %), and N₂O inhibition efficiency (61.2 %) due to the strong concentration of active oxygen species on the surface of the catalyst. Moreover, the high reducibility of Fe³⁺ demonstrated with H₂-TPR (hydrogen temperature-programed reduction) further enhances the removal of O₃ by oxygen species exchange between Mn³⁺/Mn⁴⁺ and Fe²⁺/Fe³⁺.