Insight into modified CeMn based catalysts for efficient degradation of toluene by in situ infrared

Trace activated carbon (AC) and diatomaceous earth (DE) were used as structural promoters to be incorporated into Ce-Mn-based solid-solution catalysts by the redox precipitation method. The modified catalysts exhibit superior reducibility, with abundant Ce3+, Mn3+and reactive oxygen species, which are facilitated to the migration of oxygen and the generation of oxygen vacancies. In particular, the catalytic combustion temperatures of 90 % toluene (3000 ppm) on Ce1Mn3Ox-AC/DE were 84 °C (dry) and 123 °C (10 vol% H2O), respectively. The role of lattice oxygen and adsorbed oxygen was revealed by in situ DRIFTS. Additionally, in situ DRIFTS was employed to verify that the degradation of toluene by Ce1Mn3Ox-AC/DE satisfied the Langmuir-Hinshelwood (L-H) mechanism and the Mars-Van Krevelen (MvK) mechanism. The possible reaction pathway was elucidated (toluene → benzyl alcohol → benzoic acid → maleic anhydride → CO2 + H2O). Furthermore, final products attributed to toluene oxidation were detected by in situ DRIFTS at 50 °C in the absence of oxygen, confirming that the catalyst possessed outstanding performance at low temperatures beyond mere adsorption.

Biomimetic Light-Driven Aerogel Passive Pump for Volatile Organic Pollutant Removal

Inspired by the solar-light-driven oxygen transportation in aquatic plants, a biomimetic sustainable light-driven aerogel pump with a surface layer containing black manganese oxide (MnO₂ ) as an optical absorber is developed. The flow intensity of the pumped air is controlled by the pore structure of nanofilbrillated cellulose, urea-modified chitosan, or polymethylsilsesquioxane (PMSQ) aerogels. The MnO₂ -induced photothermal conversion drives both the passive gas flow and the catalytic degradation of volatile organic pollutants. All investigated aerogels demonstrate superior pumping compared to benchmarked Knudsen pump systems, but the inorganic PMSQ aerogels provide the highest flexibility in terms of the input power and photothermal degradation activity. Aerogel light-driven multifunctional gas pumps offer a broad future application potential for gas-sensing devices, air-quality mapping, and air quality control systems.

Degradation of toluene by pulse-modulated multistage DBD plasma: Key parameters optimization through response surface methodology (RSM) and degradation pathway analysis

In the present work, a pulse-modulated high-frequency (HF) dielectric barrier discharge (DBD) plasma has been employed and utilized to evaluate the feasibility of toluene degradation in a multistage rod-type reactor at room temperature. Experimental result indicates that the energy consumption is significantly reduced and heating effect can be effectively suppressed when the DBD plasma is ignited in pulse-modulated mode instead of continuous mode. The response surface methodology (RSM) based on central composite design (CCD) model has been proposed to evaluate the contribution of key operating parameters including duty cycle and modulation frequency. The proposed model offers a good fit for actal data. The contribution of the modulation frequency is observed to be more dominant compared to the duty cycle for both the degradation efficiency and the energy yield. According to the results provided by the proposed model, the toluene degradation efficiency of 62.9 % and the energy yield of 0.90 g/kWh are obtained under the optimal conditions of 400 Hz modulation frequency and 56 % duty cycle. The effect of initial toluene concentration and gas flow rate have also been investigated. Increasing toluene initial concentration and gas flow rate are found to be unfavorable for the degradation of toluene, however, which are of benefit to the energy yield. A long-time experiment to assess the stability of pulse-modulated DBD has been successful performed. The possible pathways in plasma degradation of toluene is proposed based on the intermediates identification using GC-MS and FTIR.

Plasma-catalytic destruction of xylene over Ag-Mn mixed oxides in a pulsed sliding discharge reactor

Plasma-assisted catalytic degradation of xylene was performed in a pulsed sliding dielectric barrier discharge (SLDBD) reactor based on three-electrode geometry over Ag-Mn bimetallic oxides catalysts at room temperature. Experimental results showed that more active species were distributed uniformly in the SLDBD plasma than traditional surface dielectric barrier discharge (SDBD), contributing to higher degradation and energy performance. The xylene degradation efficiency and energy yield in the SLDBD reactor driven by both +pulse (+18 kV) and -DC (-10 kV) were 40% and 2.3 g/kWh higher, respectively, than in the SDBD reactor energized by +pulse alone. The combination of SLDBD plasma with catalysts significantly improved the xylene degradation efficiency and CO₂ selectivity than the plasma-only system. The incorporation of Ag into Mn oxide further enhanced its catalytic activity for xylene degradation, and the catalytic activity of Ag-Mn oxides was closely correlated with the Ag/Mn molar ratio. Ag-Mn/γ-Al₂O₃ (1:2) presented the best performance in plasma-catalysis process, with 91.5% of degradation efficiency and 80.1% of CO₂ selectivity at 4.6 W. The higher proportion of surface O_ads and better reducibility through the interaction between Ag and Mn species can explain the excellent reactivity of Ag-Mn/γ-Al₂O₃ (1:2).

Efficient gas phase VOC removal and electricity generation in an integrated bio-photo-electro-catalytic reactor with bio-anode and TiO2 photo-electro-catalytic air cathode

An efficient and cost-effective bio-photo-electro-catalytic reactor (BPEC) was developed, it combined bio-anode with TiO₂ photo-electro-catalytic air cathode and could remove rapidly model gas phase VOC ethyl acetate (EA) and generate electricity simultaneously. This BPEC system exhibited a synergistic effect between the photo-electro-catalysis and microbial fuel cell (MFC) bio-electrochemical process. Calculated kinetic constant of the BPEC system (0.085 min^-1) was twice the sum of those of photocatalysis (only electrolyte in the anode, without microbes, 0.033 min^-1) and MFC (no photocatalysis, 0.010 min^-1) systems. Compared to BPEC with proton exchange membrane (PEM) separator (59.6 mW/cm²), the system with polyvinylidene fluoride (PVDF) membrane had a higher EA degradation rate and power generation (92.8 mW/cm²). A lower external resistance resulted in a faster EA degradation rate. This report provides a new platform for treating other kinds of gas pollutants via integrated bio-electrochemical and gas-solid photo-electro-catalytic reactions, with energy generation and conversions.

Synergistically catalytic oxidation of toluene over Mn modified g-C3N4/ZSM-4 under vacuum UV irradiation

The process of vacuum ultraviolet (VUV)-assisted photocatalytic oxidation (PCO) has attracted great interest for volatile organic compounds (VOCs) degradation owing to its strong oxidation capability. However, the O₃ by-product from VUV irradiation causes secondary pollution and needs to be overcome. In this study, a multi-functional photocatalyst of Mn/g-C₃N₄/ZSM-4 was thus developed by a one-pot hydrothermal method, and then combined with VUV irradiation to eliminate O₃ byproduct as well as enhance toluene degradation via ozone-assisted catalytic oxidation (OZCO). Under VUV irradiation alone, 64% of toluene degradation was occurred but 51 ppm of O₃ was residual. In contrast, toluene degradation was enhanced to 96% over the Mn/g-C₃N₄/ZSM-4 while residual O₃ was decreased to 4 ppm. The enhanced performance was attributed to the synergistic PCO and OZCO, as the Mn modification can efficiently enhance the photocatalytic activity of g-C₃N₄ and trigger the catalytic ozonation simultaneously. The results of electron spin resonance (ESR) confirmed the generation of reactive species such as OH and O₂^- by VUV irradiation and then greatly enhanced after Mn/g-C₃N₄/ZSM-4 was added. Moreover, the possible mechanism of toluene degradation was also revealed through monitoring of reaction intermediate. Obviously, the process of Mn/g-C₃N₄/ZSM-4 cooperated well with VUV is promising for VOCs degradation.

Manganese oxide octahedral molecular sieve K-OMS-2 as catalyst in post plasma-catalysis for trichloroethylene degradation in humid air

The total oxidation of trichloroethylene (TCE) in air at low relative humidity (RH=10%) in the presence of CO2 (520ppmv) was investigated in function of energy density using an atmospheric pressure negative DC luminescent glow discharge combined with a cryptomelane catalyst positioned downstream of the plasma reactor at a temperature of 150°C. When using Non-Thermal Plasma (NTP) alone, it is found a low COx (x=1-2) yield in agreement with the detection of gaseous polychlorinated by-products in the outlet stream as well as ozone which is an harmful pollutant. Introduction of cryptomelane enhanced trichloroethylene removal, totally inhibited plasma ozone formation and increased significantly the COx yield. The improved performances of the hybrid system were mainly ascribed to the total destruction of plasma generated ozone on cryptomelane surface to produce active oxygen species. Consequently these active oxygen species greatly enhanced the abatement of the plasma non-reacted TCE and completely destroyed the hazardous plasma generated polychlorinated intermediates. The facile redox of Mn species associated with oxygen vacancies and mobility as well as the textural properties of the catalyst might also contribute as a whole to the efficiency of the process.