Toluene removal by sequential adsorption-plasma catalytic process: Effects of Ag and Mn impregnation sequence on Ag-Mn/γ-Al2O3

Bifunctional Cu-incorporated carbon nanospheres via in-situ complexation strategy as efficient toluene adsorbents and antibacterial agents

Carbon adsorbents have been widely used to remove indoor volatile organic compounds (VOCs), however, the proliferation of bacteria on the carbon adsorbents may deteriorate the indoor air quality and thus pose a serious threat to human health. Herein, we report the synthesis of antibacterial porous carbon spheres (carbonized aminophenol-formaldehyde resin, CAF) with well-dispersed Cu species via an in situ incorporation of Cu2+ during the polymerization of 3-aminophenol-formaldehyde resin followed by a thermal carbonization and reduction process. Compared with CAF, the Cu/CAF-x nanocomposites with Cu loading show a much higher specific surface area (>700 m2 g-1vs. 569 m2 g-1 for CAF). In addition, the pore size of Cu/CAF-x is ranging from 0.7 to 1.68 nm, which is exactly conducive to adsorb the toluene molecules. As a result, the toluene adsorption capacity is improved from 123.50 mg g-1 for CAF to >170 mg g-1 for Cu/CAF-x. More importantly, such adsorbents possess excellent antibacterial performance, the Cu/CAF-10 (10 wt% of Cu loading) with a concentration of 50 μg mL-1 can completely kill the E. coli within 30 min. Our work paves the way to the development of bifunctional adsorbents with both efficient VOCs adsorption and excellent antibacterial performance.

Removal of toluene via non-thermal plasma generated by applying rare-earth tungsten electrode and nanosecond pulsed power supply

The objective of this investigation is to evaluate the characteristics associated with degradation of toluene through the utilization of non-thermal plasma (NTP) generated via application of a low-work-function electrode and nanosecond pulsed power supply. Initially, a comparative analysis is made between toluene removal efficiency utilizing the low-work-function electrode and that achieved with the conventional stainless-steel electrode. The outcomes demonstrate that NTP generated by the low-work-function electrode exhibits markedly superior removal efficiency for toluene in comparison to the stainless-steel electrode operating at the same voltage. Subsequently, the impacts of voltage, pulse frequency, and initial concentration of toluene on the removal efficiency and production of by-products are investigated. It is found that as the voltage and frequency increase, the removal efficiency also increases, and a maximum toluene removal efficiency of 87.2% is achieved at a voltage of 12,000 V and pulse frequency of 2000 Hz. The removal efficiency first increases and then decreases with increasing toluene initial concentration. The investigation also finds that energy yield is negatively correlated with voltage and pulse frequency and positively correlated with the initial concentration. Finally, the reaction products were subjected to quantitative analysis using GC-MS. Based on the analysis results, potential reaction pathways are inferred.

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.

Gas-phase isopropanol degradation by nonthermal plasma combined with Mn-Cu/-Al2O3

In this study, the dielectric barrier discharge (DBD) induced by nonthermal plasma (NTP) technology was used for isopropanol (IPA) degradation. IPA, intermediate, final product, and ozone concentrations were analyzed using GC-MS, carbon dioxide detector, and ozone detector. The experimental flow rate and concentration were fixed to 1 L/min and 1200 ppm ± 10%, respectively. Different reaction procedures were proposed for self-made metal catalyst combined with a plasma system (plasma alone and γ-Al₂O₃ combined with plasma, Cu (5 wt%)/γ-Al₂O₃ combined with plasma, Mn (3 wt%)-Cu (5 wt%)/γ-Al₂O₃ combined with plasma). In addition, the effect of the carrier gas oxygen content (0%, 20%, and 100%) on IPA conversion and intermediate and carbon dioxide selectivity was also investigated. The results revealed that the Mn (F)-Cu/γ-Al₂O₃ combined with plasma exhibited more efficient IPA conversion. In the 100% oxygen environment, the IPA conversion rate increased from 79.32 to 99.99%, and carbon dioxide selectivity increased from 3.82 to 50.23%. IPA was completely converted after 60 min of plasma treatment with the acetone selectivity, carbon dioxide selectivity, and tail ozone concentration of 26.71% ± 1.27%, 50.23% ± 0.56%, and 1761 ± 11 ppm, respectively. This study proved that the current single planar DBD configuration is an effective advanced treatment technology for the decomposition of VOCs.

Adsorption Followed by Plasma Assisted Catalytic Conversion of Toluene into CO2 on Hopcalite in an Air Stream

The abatement of toluene was studied in a sequential adsorption-plasma catalysis (APC) process. Within this process, Hopcalite was used as bifunctional material: as adsorbent (storage stage) and as catalyst via the oxidation of adsorbed toluene (discharge stage). It was observed that the desorption and oxidation activity of the adsorbed toluene was significantly affected the process variables. In addition, the adsorption time influenced the CO2 selectivity and CO2 yield by changing the interaction between the catalyst and the plasma generated species. At least four APC sequences were performed for each examined condition suggesting that Hopcalite is very stable under plasma exposure during all the sequences. Consequently, these results could contribute to advance the plasma–catalyst system with an optimal VOC oxidation efficiency. The catalytic activity, amount of toluene adsorbed, amount of toluene desorbed and product formation have been quantified by FT-IR. Moreover, the catalyst was characterized by XRD, H2-TPR, N2 adsorption–desorption analysis and XPS. Hopcalite shows a good CO2 selectivity and CO2 yield when the APC process is performed with an adsorption time of 20 min and a plasma treatment with a discharge power of 46 W which leads to a low energy cost of 11.6 kWh·m−3 and energy yields of toluene and CO2 of 0.18 (±0.01) g·kWh−1 and 0.48 (±0.06) g·kWh−1 respectively.

Characteristics and mechanism of toluene removal from gas by novelty array double dielectric barrier discharge combined with TiO2/Al2O3 catalyst

A new reactor of array double dielectric barrier discharge (DDBD) combined with catalysis was prepared, and the effect of different factors on removal efficiency of toluene at pilot scale were investigated. The possible degradation mechanism was explored. The results indicate that the removal efficiency of toluene in the exhaust gas decreases with the increasing of the toluene initial concentration and the gas flow rate, but increases with the increasing of the specific energy density. When the air relative humidity is 55%, the removal efficiency of toluene is higher than that of the relative humidity by 85%. The results of XPS, FT-IR and GC-MS analysis show that the main intermediate products of removing toluene by DDBD combined with TiO₂/Al₂O₃ catalyst are phenol, benzaldehyde, benzyl alcohol, benzoic acid, N-benzyl formamide, dimethyl terephthalate, dimethyl isophthalate and other substances. There are five possible pathways to degrade toluene by DDBD combined with TiO₂/Al₂O₃.

Removal of benzene by non-thermal plasma catalysis over manganese oxides through a facile synthesis method

Three manganese oxide catalysts (MnO_x) were synthesized via a simple method, and then they were introduced into the non-thermal plasma (NTP) system for benzene removal. The XRD and EXAFS results showed the MnO_x were mainly in the Mn₃O₄ phase, and from the analysis of N₂ adsorption/desorption isotherms, we knew the MnO_x calcined at 250 °C (Mn250) had the largest surface area of 274.5 m² g^-1. Besides, Mn250 also exerted higher benzene adsorption capacity (0.430 mmol g^-1) according to C₆H₆-TPD. O₂-TPD indicated that Mn250 showed better oxygen mobility than Mn300. Moreover, by analyzing XPS results, it revealed that Mn250 exhibited rich abundant of surface adsorbed oxygen species (O_ads) and moderate ratio of Mn⁴⁺/Mn³⁺, and the reducibility temperature was also the lowest among all the MnO_x catalysts drawn by H₂-TPR profiles. As a result, Mn250 combined with NTP could remove 96.9% of benzene at a low input power of 3 W (benzene concentration 200 ppm, and GHSV 60,000 mL g_cat.^-1 h^-1), performing the best catalytic activity among the three catalysts and plasma only. Furthermore, the "NTP + Mn250" system also produced the highest CO₂ concentration and lowest CO concentration in downstream, and the residual O₃ after catalytic reaction was also the lowest, that is to say, the synergistic effect between NTP and Mn250 was more effective than other catalysts in benzene removal. Graphical abstract.

Removal of toluene by sequential adsorption-plasma oxidation: Mixed support and catalyst deactivation

A sequential adsorption-plasma oxidation system was used to remove toluene from simulated dry air using γ-Al₂O₃, HZSM-5, a mixture of the two materials or their supported Mn-Ag catalyst as adsorbents under atmospheric pressure and room temperature. After 120min of plasma oxidation, γ-Al₂O₃ had a better carbon balance (∼75%) than HZSM-5, but the CO₂ yield of γ-Al₂O₃ was only ∼50%; and there was some desorption of toluene when γ-Al₂O₃ was used. When a mixture of HZSM-5 and γ-Al₂O₃ with a mass ratio of 1/2 was used, the carbon balance was up to 90% and 82% of this was CO₂. The adsorption performance and electric discharge characteristics of the mixed supports were tested in order to rationalize this high CO_x yield. After seven cycles of sequential adsorption-plasma oxidation, support and Mn-Ag catalyst deactivation occurred. The support and catalyst were characterized before and after deactivation by SEM, a BET method, XRD, XPS and GC-MS in order to probe the mechanism of their deactivation. 97.6% of the deactivated supports and 76% of the deactivated catalysts could be recovered by O₂ temperature-programmed oxidation.