Plasma-catalysis for VOCs decomposition: A review on micro- and macroscopic modeling

Enhanced plasma-driven H2S removal from natural gas via TiO2-coated dielectric surface modification

The efficient removal of H2S impurities from natural gas is critical for improving gas quality and reducing maintenance costs. This study explores the integration of dielectric barrier discharge (DBD) plasma with TiO2 to decompose H2S effectively. Results show that the presence of TiO2 significantly improve H2S removal and energy efficiency compared with the plasma-only condition. However, the TiO2-coated system achieves a much higher H2S removal rate (5.4 mmol/h/gTiO2), which was 27 times that of TiO2-packed system, minimizing TiO2 usage. Moreover, coated TiO2 inhibits methane conversion, preserving the primary components of natural gas. Discharge analysis reveals that packing TiO2 increases the reduced electric field and enhances mean electron energy, while coating further promotes filamentary discharge. Density functional theory (DFT) calculations confirm that defect-rich TiO2, formed under plasma conditions, plays a crucial role in facilitating H2S decomposition. A plausible reaction pathway for plasma-driven H2S decomposition with coated TiO2 is proposed. This study demonstrates the potential of DBD-coupled coated catalyst technology for efficient H2S removal, offering a scalable solution for industrial gas purification.

Electro-stimulated biodegradation of dimethyl disulfide: Insights from biofilm spatial structure and key functional genes

As a typical sulfur-containing volatile organic compound, dimethyl disulfide (DMDS) is known for its high toxicity and resistance to degradation, necessitating efficient control in environmental media. To address the limitations of biological treatment in degradation capacity, this study employs electro-stimulation to promote DMDS elimination by a porous polyaniline@carbon nanotube bioanode developed on graphite sheet (PANI@CNT/GS). Compared with the unmodified GS bioanode, the PANI@CNT/GS bioanode demonstrates significant advantages in biofilm activity, redox property, and DMDS degradation efficiency. Kinetics analysis shows that the maximum degradation rate of the PANI@CNT/GS bioanode was 0.60 mM h-1, which is 1.36 times higher than that of the control. Characterization results reveal that the highly active biofilms in PANI@CNT/GS bioanode possess 1.40 times the amount of living cells and a 12.5% increase in thickness, contributing to the notable enhancement in DMDS degradation capacity. Additionally, functional gene annotation indicates that the PANI@CNT/GS electrode facilitates the motility and activity of microbial cells and enriches the genes encoding key enzymes involved in DMDS metabolism. This work validates the feasibility of electro-stimulation for enhancing DMDS degradation and further provides in-depth insights into the process intensification mechanism from the perspectives of biofilm spatial structure and key functional genes.

Complete degradation of polystyrene microplastics through non-thermal plasma-assisted catalytic oxidation

In this study, a two-stage system, involving plasma degradation coupled with plasma-assisted catalytic oxidation, was developed for the degradation of polystyrene microplastics (PS-MPs) at low temperatures. The dielectric barrier discharge (DBD) plasma contributed reactive oxygen species (ROS) for the degradation of PS-MPs, and the plasma-assisted Hopcalite catalyst selectively facilitated the final oxidation of by-products to CO2. Within 60 min, the conversion rate of PS-MPs to CO2, α(CO2), reached an impressive 98.4 %, indicating nearly complete and harmless degradation. It was found that relying solely on the thermal activation induced by plasma heating was insufficient for achieving complete conversion, emphasizing the multifaceted synergy of plasma-catalysis. Subsequently, the cycling experiments revealed that the assistance of plasma enhanced the deactivation resistance and stability of the catalyst. When dealing with PS-MPs at a concentration of 5 wt%, the plasma-assisted Hopcalite still exhibited 93.2 % α(COx) and 99.5 % relative CO2 content after 10 cycles. Additionally, characterization of the plasma-modified Hopcalite using various techniques suggested an enhancement in surface-adsorbed oxygen species. On the other hand, the packed catalyst improved the uniformity of the discharge plasma, while micro-discharges within the pores could further facilitate the oxidation reaction. This work provides new insights into the comprehensive treatment of MP pollution.

Selective catalytic oxidation of DMF over Cu-Ce/H-MOR by modulating the surface active sites

Selective catalytic oxidation of the hazardous DMF exhaust gas presents a significant challenge in balancing oxidation activity and products selectivity (CO, NOx, N2, etc.). It is found that Cu/H-MOR demonstrates superior performance for DMF oxidation compared to CuO on other supports (γ-Al2O3, HY, ZSM-5) in terms of product selectivity and stability. The geometric and electronic structures of CuO active sites in Cu/H-MOR have been regulated by CeO2 promoter, leading to an increase in the ratio of active CuO (highly dispersed CuO and Cu+ specie). As a result, the oxidation activity and stability of the Cu/H-MOR catalyst were enhanced for DMF selective catalytic oxidation. However, excessive CuO or CeO2 content led to decreased N2 selectivity due to over-high oxidation activity. It is also revealed that Ce3+ species, active CuO species, and surface acid sites play a critical role in internal selective catalytic reduction reaction during DMF oxidation. The 10Cu-Ce/H-MOR (1/4) catalyst exhibited both high oxidation activity and internal selective catalytic reduction activity due to its abundance of active CuO specie as well as Ce3+ species and surface acid sites. Consequently, the 10Cu-Ce/H-MOR (1/4) catalyst demonstrated the widest temperature window for DMF oxidation with high N2 selectivity. These findings emphasize the importance of surface active sites modification for DMF selective catalytic oxidation.

How do the main components influence the VOCs emission characteristics and formation pathways during moso bamboo heat treatment?

Bamboo heat treatment will cause plenty of release of volatile organic compounds (VOCs) into the atmosphere which are important precursors for ozone (O3) formation. In this study, dewaxed bamboo was heat-treated at 180 °C for 2 h to investigate the emission characteristics and the formation pathways of VOCs during heat treatment by removing different main components. The results showed that aldehydes (22.61%-57.54%) and esters (14.64%-38.88%) are the primary VOCs released during heat treatment. These compounds mainly originate from the degradation of hemicellulose, lignin, cellulose, and the linkage bonds between them in bamboo. During the bamboo heat treatment, the degradation of CO, CH, and CO bonds in hemicellulose results in the release of 5-hydroxymethylfurfural, 3-furfural, and 1-(+)-ascorbic acid 2,6-dihexadecanoate. The breakage of benzene ring group and the CO and CH bonds of lignin leading to the emission of VOCs including m-Formylphenol, Vanillin, and Syringaldehyde. The degradation of aliphatic CH, CC, and CO bonds in the amorphous region of cellulose contributes to an enhanced release of alcohols, olefins, and alkanes. It is calculated that acids (28.92%-59.47%), esters (10.10%-22.03%) and aldehydes (17.88%-39.91%) released during heat treatment contributed more to Ozone Formation Potential (OFP).

Effective reduction on flame soot via plasma coupled with carbon dioxide

This study explored the impact of non-thermal plasma and CO2 on the flame soot characteristics within the diffusion flames. We analyzed on flame structures that were diluted with either CO2 or N2, temperature distributions, and soot characteristics, both in the presence and absence of plasma. Due to the higher specific heat capacity of CO2 compared to N2, the optical observations consistently showed lower temperatures in flames diluted with CO2 as compared to those diluted with N2. The inclusion of plasma and carbon dioxide resulted in the lowest soot concentration, indicating that plasma coupled with CO2 has a synergistic inhibitory effect on soot emissions. The findings revealed that when CO2 was used to dilute the flames and the oxygen concentration was low, the soot nanostructure appeared amorphous. Raman results showed that the level of graphitization observed in soot particles from CO2 dilution flames was lower than that from N2 dilution flames. In the presence of plasma and CO2, the soot obtained exhibited the shortest fringe length and the highest fringe tortuosity. Significant correlations were observed between the nanostructure of soot and its reactivity. The combined application of plasma and CO2 proved to be effective in reducing the soot carbonization degree.

Size Effect of Platinum Nanoparticles over Platinum-Manganese Oxide on the Low-Temperature Oxidation of Toluene

The effect of size of Pt nanoparticles has an important influence on the performance of supported Pt-based catalysts for the elimination of toluene. Herein, uniform Pt nanoparticles with average sizes of 1.5, 2.0, 2.5, 2.9, and 3.6 nm were obtained and supported on manganese oxide octahedral molecular sieves (OMS-2), and their catalytic performances for toluene oxidation were evaluated. Benefiting from the moderate interfacial interaction between nanoparticles and manganese oxide support, Pt/OMS-2-3 with the Pt particle size of 3.0 nm showed the best catalytic performance owing to the highest content of Pt2+ species. It also facilitates the formation of more abundant Mnδ+ (Mn2+ and Mn3+) and oxygen vacancies than that of the other sizes of the OMS-2-supported Pt nanoparticles, which can be filled by a large amount of adsorbed oxygen and converted into reactive oxygen species. We further showed that the resulting surface synergetic oxygen vacancies (Pt2+-Ov-Mnδ+) play a decisive part in catalyzing the complete oxidation of toluene. The result will provide new insights for designing efficient Pt-based catalysts for deep purification of toluene.

The Removal of CH4 and NOx from Marine LNG Engine Exhaust by NTP Combined with Catalyst: A Review

Compared to diesel, liquefied natural gas (LNG), often used as an alternative fuel for marine engines, comes with significant advantages in reducing emissions of particulate matter (PM), SO_x, CO₂, and other pollutants. Promoting the use of LNG is of great significance for achieving carbon peaking and neutrality worldwide, as well as improving the energy structure. However, compared to diesel engines, medium- and high-speed marine LNG engines may produce higher methane (CH₄) emissions and also have nitrogen oxide (NO_x) emission issues. For the removal of CH₄ and NO_x from the exhaust of marine LNG engines, the traditional technical route of combining a methane oxidation catalyst (MOC) and an HN₃ selective catalytic reduction system (NH₃-SCR) will face problems, such as low conversion efficiency and high operation cost. In view of this, the technology of non-thermal plasma (NTP) combined with CH₄-SCR is proposed. However, the synergistic mechanism between NTP and catalysts is still unclear, which limits the optimization of an NTP-CH₄-SCR system. This article summarizes the synergistic mechanism of NTP and catalysts in the integrated treatment process of CH₄ and NO_x, including experimental analysis and numerical simulation. And the relevant impact parameters (such as electrode diameter, electrode shape, electrode material, and barrier material, etc.) of NTP reactor energy optimization are discussed. The work of this paper is of great significance for guiding the high-efficiency removal of CH₄ and NO_x for an NTP-CH₄-SCR system.