•Industrial speciated VOCs emission inventory in China for 2010 was developed.•Reactivity-based (OFP-based) VOCs emission inventory was established.•OFP-based and mass-based characteristics by species and sources were different.•OFP-based top 15 species, top 10 sources and high-polluted regions were identified.•Three implications about reactivity-based strategies were proposed for more efficient O3 mitigation.Increasingly serious ozone (O3) pollution, along with decreasing NOx emission, is creating a big challenge in the control of volatile organic compounds (VOCs) in China. More efficient and effective measures are assuredly needed for controlling VOCs. In this study, a reactivity-based industrial VOCs emission inventory was established in China based on the concept of ozone formation potential (OFP). Key VOCs species, major VOCs sources, and dominant regions with high reactivity were identified. Our results show that the top 15 OFP-based species, including m/p-xylene, toluene, propene, o-xylene, and ethyl benzene, contribute 69% of the total OFP but only 30% of the total emission. The architectural decoration industry, oil refinery industry, storage and transport, and seven other sources constituted the top 10 OFP subsectors, together contributing a total of 85%. The provincial and spatial characteristics of OFP are generally consistent with those of mass-based inventory. The implications for O3 control strategies in China are discussed. We propose a reactivity-based national definition of VOCs and low-reactive substitution strategies, combined with evaluations of health risks. Priority should be given to the top 15 or more species with high reactivity through their major emission sources. Reactivity-based policies should be flexibly applied for O3 mitigation based on the sensitivity of O3 formation conditions.

Methanol synthesis from CO2 hydrogenation in a fixed-bed plug flow reactor was investigated over Cu–ZrO2 catalysts supported on CNTs bearing various functional groups. The highest methanol activity (turnover frequency 1.61 × 10−2 s−1, space time yield 84.0 mg gcat−1 h−1) was obtained over the Cu/ZrO2/CNTs catalyst (CZ/CNT-3) with CNTs functionalized by nitrogen-containing groups and Cu loading only about 10.3 wt% under the reaction conditions of 260 °C, 3.0 MPa, V(H2):V(CO2):V(N2) = 69:23:8 and GHSV of 3600 h−1. The catalysts were fully characterized by N2 physisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR) and temperature-programmed desorption of H2 (H2-TPD) techniques. The excellent performance of CZ/CNT-3 is attributed to the presence of nitrogen-containing groups on the CNTs surface, which increase the dispersion of copper oxides, promote their reduction, decreases the crystal size of Cu, and enhances H2 and CO2 adsorption capability, thus leading to good catalytic performance towards methanol synthesis.

Based on the important effect of catalyst on the plasma-catalytic system, various types of zeolites (5A, HZSM-5, Hβ, HY and Ag/HY) were chosen as catalysts to remove toluene under non-thermal plasma conditions in this work. The results showed that all the zeolites, with or without toluene adsorption abilities, significantly enhanced the toluene removal efficiency in the plasma discharge zone. Moreover, the carbon balance and CO2 selectivity showed the same tendency of Ag/HY > HY > Hβ (HZSM-5) > 5A, which was basically consistent with toluene adsorption ability, while being opposite to the ozone emission. Loading silver on the zeolite greatly decreased organic byproduct emission, and further improved the mineralization of toluene oxidation. At the same time, the intermediates including ring-opening products on the catalyst surface were identified, and the pathways of toluene decomposition were proposed.

MnOx(0.4)-CeO2 was investigated for soot oxidation assisted with a pulse dielectric barrier discharge (DBD). The catalysts were evaluated and characterized with TPO (temperature programmed oxidation), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The ignition temperature Ti for soot oxidation decreased from 240.8 to 216.4 °C with the increase of the pulse DBD frequencies from 50 to 400 Hz, lower than that of the case without pulse DBD present (253.4 °C). The results of XRD, Raman and XPS agreed well with the TPO activities of MnOx(0.4)-CeO2 towards soot oxidation. More solid solution of ceria and manganese, and surface reactive species including O2–, O− and Mn4+ were responsible for the enhancement of soot oxidation due to pulse DBD injection in the present study. For solid solution favors to the activation and transformation of those species, which are believed to be involved in the soot oxidation in a hybrid catalysis-plasma.Proposed pathway for soot oxidation over MnOx(0.4)- CeO2 catalysts assisted with pulse DBD (ads: adsorpted)

MnxOy/SBA-15 catalysts were prepared via the impregnation method and utilized for toluene removal in dielectric barrier discharge plasma at atmospheric pressure and room temperature. The catalysts were characterized by X-ray diffraction, N2 adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, and O2 temperature-programmed desorption methods. The characterization results indicated that manganese loading did not influence the 2D-hexagonal mesoporous structure of SBA-15. The catalyst had various oxidation states of manganese (Mn2+, Mn3+, and Mn4+), with Mn3+ being the dominant oxidation state. Toluene removal was investigated in the environment of pure N2 and 80 % N2 + 20 % O2 plasma, showing that the toluene removal efficiency and CO2 selectivity were noticeably increased by MnxOy/SBA-15, especially in the presence of 5 % Mn/SBA-15. This activity was closely related to the high dispersion of 5 % Mn on SBA-15 and the lowest reduction temperature exhibited by this catalyst. Mn loading increased the yield of CO2 in the N2 plasma and promoted the deep oxidation of toluene. During toluene oxidation, oxygen exchange might follow a pathway, wherein bulk oxygen was released from the MnxOy/SBA-15 surface; gas-phase O2 subsequently filled up the vacancies created on the oxide. Each of the manganese oxidation states played an important role; Mn2O3 was considered as a bridge for oxygen exchange between the gas phase and the catalyst, and Mn3O4 mediated transfer of oxygen between the catalyst and toluene.

To improve toluene removal efficiency and reduce byproducts, a TiO2/γ-Al2O3/nickel foam catalyst was combined in and after the non-thermal plasma (NTP), leading to a plasma-driven catalysis (PDC) and plasma-assisted catalysis (PAC) process, respectively. The addition of catalysis could significantly enhance the toluene destruction with an increased CO2 selectivity and carbon balance while the byproducts, such as O3 and organic compounds, were dramatically reduced. The PAC exhibited the highest efficiency in toluene destruction due to the formation of more atomic oxygen and hydroxyl radicals from O3 catalytic decomposition. The pathways of toluene destruction by NTP and plasma-catalysis were proposed according to the identified intermediates.Graphical abstractThe pathways of toluene destruction by energetic electrons are greatly different to that by O/OH, which accounts for much less byproducts in the plasma-catalysis process.Research highlights▶ The catalyst could significantly enhance the toluene destruction and reduce byproducts. ▶ The PAC process exhibited the highest efficiency in both toluene and O3 destruction. ▶ More reactive species from O3 catalytic decomposition is responsible for the increased activity. ▶ The pathways of toluene destruction in plasma-catalysis are greatly different to that in the NTP alone.

The contribution of UV light from plasma and an external UV lamp to the decomposition of toluene in a dielectric barrier discharge (DBD) plasma/UV system, as well as in a plasma/photocatalysis system was investigated. It was found that UV light from the DBD reactor was very weak. Its contribution to the removal of toluene in the plasma/photocatalysis system could be ignored. Whereas, the introduction of external UV light to the plasma significantly improves the removal efficiency of toluene by 20%. The removal efficiency of toluene in the plasma/photocatalysis system increased about 22% and 16% when compared with a plasma only system and plasma driven photocatalyst system, respectively. The increased toluene removal efficiency was mostly attributed to the contribution of the synergy between plasma and UV light, but not to the synergy between plasma and photocatalysis. The synergetic effect between plasma and photocatalysis was not significant.

The performance on toluene removal in a dielectric barrier discharge (DBD) type plasma system under different background gases, including N2, Ar, N2/Ar, and N2/O2 was studied at room temperature and atmospheric pressure. For comparison, another laboratory-scale plasma-catalysis system was set up and four kinds of metal oxides, i.e., copper oxide, iron oxide, cobalt oxide, and manganese oxide supported on alumina/nickel foam (NF), were used as catalysts. The reaction mechanism and dynamics analysis on toluene removal were suggested. In addition, the characterization of the catalysts was performed by BET, XRD, SEM, FT-IR, and EDS. It has been found that adding argon in the background gas could improve the toluene removal efficiency significantly in the plasma system. Combining plasma with catalyst in situ could improve the toluene removal efficiency, increase the carbon dioxide selectivity and suppress byproducts formation. In addition, manganese oxide/alumina/NF was confirmed as the most effective catalyst for toluene removal. The XRD and SEM results showed that the proportion of metal oxide increased while aluminate decreased after plasma application. The granularity of the grain on the catalyst surface became smaller and the distribution became more uniform after discharge. The results of FT-IR and EDS suggested that some organic compounds deposited on the catalysts after plasma reaction.

Fe–Ce–Mn/ZSM-5 catalysts were prepared and performance of catalysts in NO selective catalytic reduction by NH3 was tested in the temperature range of 100–500 °C. NO conversion reached 96.6% and 98.1% at 200 °C and 300 °C respectively at a GHSV of 30,000 h−1. In situ diffuse reflectance infrared transform spectroscopy (DRIFTS) study was carried out for revealing the reaction mechanism. Two possible reaction pathways were proposed. One was that NO2 could react with NH4+ on Bronsted acid sites and the formed NO2[NH4+]2 would react with NO, producing N2 and H2O. Another way was that NH3 was adsorbed and then reacted with NO or HNO2. Possible intermediate NH4NO2 and NH2NO were unstable and would decompose into N2 and H2O. The addition of Mn in Fe–Ce–Mn/ZSM-5 catalysts could contribute to provide more Bronsted acid sites which was beneficial for the adsorption of NH3. The addition of both Fe and Ce could obviously increase the conversion of NO to NO2. Introduction of Fe increased the oxidation of NH3 slightly and the addition of Ce increased the oxidation of NH3 significantly. The combination of manganese, iron and cerium could significantly enhance the low temperature SCR activity.Graphical abstractDownload high-res image (360KB)Download full-size imageHighlights► Over 95% of NO conversion was obtained on Fe–Ce–Mn/ZSM-5 at lower temperature. ► Addition of Mn could contribute to provide more Bronsted acid sites. ► Addition of both Fe and Ce could increase the conversion of NO to NO2. ► Addition of Ce increased the oxidation of NH3 significantly. ► Two possible reaction pathways involved with NO2[NH4+]2 and NH2NO were proposed.

Viscose-based activated carbon fibers (VACF) were treated by oxygen plasma modification (OPM) and nitric acid modification (NAM) respectively, and then supported with vanadium oxide. The activities of the catalysts were tested in a laboratory-scale unit measuring significant NO conversions in the selective catalytic reduction (SCR) of NO with NH3 at low temperature (120–240 °C). The attention was focused on the OPM or NAM on the VACF surface property and the relationship between the surface property and the loading of the vanadium oxide as well as the activities of the catalysts. The textural characteristics were analyzed by SEM, nitrogen adsorption. The surface chemical functional groups were analyzed by X-ray photoelectron spectroscopy (XPS). The results showed that after OPM or NAM, the VACF surface became rougher and a considerable amount of deposition with limited depths appeared on the VACF surface, the average micropore width was slightly enlarged, the pore size distributions of the VACF became wider. XPS revealed that the OPM and NAM could increase the oxygen functional groups on the VACF surface which contributed to a higher vanadium loading and dispersion. OPM or NAM made VACF loaded with vanadium oxide exhibit high activity and made VACF a promising support for SCR at low temperature.

The use of non-thermal plasma (NTP) technology for volatile organic compounds (VOCs) control has been limited because of its drawbacks. Although the combination of catalysis in plasma can avoid some of the limitations, there are still disadvantages such as the O3 byproduct. In this study, catalysts were combined in the post-plasma. It is found that not only O3 is efficiently eliminated, but also the removal of toluene is greatly enhanced due to O3 decomposition. The effect of catalysts, humidity and the initial O3 concentration on simultaneous catalytic removal of toluene and O3 was studied. Results show that the performance of catalysts for toluene conversion is closely related to that for O3 decomposition. The increase of O3 concentration benefits toluene conversion, whereas water has a negative effect on the toluene conversion. Catalytic ozonation is mainly responsible for the toluene decomposition in the post-plasma.