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1.
J Hazard Mater ; : 124203, 2020 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-33268207

RESUMO

Plasma catalysis technology has been demonstrated to be effective for the decomposition of volatile organic compounds (VOCs). It is highly desired to explore the effect of supports on VOCs oxidation processes during plasma catalysis. In this work, four supports of SiO2, ZSM-5-300, ZSM-5-38 and γ-Al2O3 loading with transition metal oxides were used to decompose toluene at room temperature. It was found that toluene decomposition with 1 wt%Mn/γ-Al2O3 was highest, which was strongly proportional to the ozone decomposition ability of the catalyst. The plasma catalytic decomposition of toluene over 1 wt% MnO2 on different supports were characterized using in situ plasma diffuse reflectance infrared Fourier transform spectrometer. The results showed that 1 wt%Mn/γ-Al2O3 could further catalyze toluene to carbonate and bicarbonate via the breakage of C-C bonds from benzoic acid, while that was difficult for 1 wt% Mn/SiO2, 1 wt%Mn/ZSM-5-300 and 1 wt%Mn/ZSM-5-38. The reaction mechanism of toluene decomposition on different catalysts were proposed.

2.
Phys Chem Chem Phys ; 22(34): 19349-19358, 2020 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-32822443

RESUMO

A kinetic study revealed that a Ni/Al2O3 catalyst exhibited a drastic increase in CH4 and CO2 conversion under nonthermal plasma when lanthanum was added to the Ni/Al2O3 catalyst as a promoter. For a better fundamental understanding of the plasma and catalyst interfacial phenomena, we employed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under plasma-on conditions to elucidate the nonthermal plasma-enabled reaction enhancement mechanisms. Compared with thermal catalysis, plasma-activated CO2 shows a 1.7-fold enhancement for bidentate (1560 and 1290 cm-1) and monodentate carbonate (1425 and 1345 cm-1) formation on La. Moreover, new peaks of bicarbonate (1655 cm-1) and bridge carbonate (1720 cm-1) were formed due to nonthermal plasma interactions. CO2-TPD study after thermal- and plasma-activated CO2 treatment further confirmed that plasma-activated CO2 enhances bidentate and monodentate carbonate generation with a 1.5-fold promotion at high temperature (500 °C). XRD and EDS analyses suggest that atomic-scale interaction between CO2-La and CHx-Ni is possible over the complex La-Ni-Al oxide; vibrationally excited CO2-induced carbonates provide the key to enhancing the overall performance of CH4 dry reforming at low temperature.

3.
J Hazard Mater ; 396: 122730, 2020 09 05.
Artigo em Inglês | MEDLINE | ID: mdl-32344365

RESUMO

Plasma-catalytic oxidation of particulate matter (PM) has potential applications for diesel exhaust cleaning. There is a grand requirement to explore the mechanism of carbonaceous PM oxidation for the development of plasma catalysts. Herein, Au/γ-Al2O3 was used to catalyze the gasification of the graphitic carbon. A modified diffuse reflectance infrared Fourier transform spectrometer equipped with a mass spectrometer was originally utilized to in situ characterize the surface intermediates of graphite on Au/γ-Al2O3 and the gaseous products during the discharges processes in the O2-He balanced gases. It was found that O atoms and O3 play important roles in the formation of surface oxygen complexes (SOCs) and facilitate the gasification of SOCs to CO2 in the presence of Au/γ-Al2O3. The findings are helpful to understand the plasma-catalytic oxidation mechanism of PM and further develop efficient plasma catalysts.

4.
Chemosphere ; 247: 125863, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-31972485

RESUMO

Plasma-catalysis technologies (PCTs) have the potential to control the emissions of volatile organic compounds, although their low-energy efficiency is a bottleneck for their practical applications. A plasma-catalyst reactor filled with a CeO2/γ-Al2O3 catalyst was developed to decompose toluene with a high-energy efficiency enhanced by the elevating reaction temperature. When the reaction temperature was raised from 50 °C to 250 °C, toluene conversion dramatically increased from 45.3% to 95.5% and the energy efficiency increased from 53.5 g/kWh to 113.0 g/kWh. Conversely, the toluene conversion using a thermal catalysis technology (TCT) exhibited a maximum of 16.7%. The activation energy of toluene decomposition using PCTs is 14.0 kJ/mol, which is far lower than those of toluene decomposition using TCTs, which implies that toluene decomposition using PCT differs from that using TCT. The experimental results revealed that the Ce3+/Ce4+ ratio decreased and Oads/Olatt ratio increased after the 40-h evaluation experiment, suggesting that CeO2 promoted the formation of the reactive oxygen species that is beneficial for toluene decomposition.


Assuntos
Poluentes Atmosféricos/análise , Gases em Plasma/química , Tolueno/análise , Compostos Orgânicos Voláteis/análise , Óxido de Alumínio/química , Catálise , Cério/química , Temperatura Alta , Modelos Teóricos , Oxirredução
5.
J Hazard Mater ; 373: 698-704, 2019 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-30959283

RESUMO

The plasma-catalytic oxidation of methane (CH4) is a potential reaction for controlling CH4 emissions at low temperatures. However, the mechanism of the CH4 plasma-catalytic oxidation is still unknown, which inhibits the further optimization of the oxidation process. Herein, a CH4 oxidation mechanism over an Au/γ-Al2O3 catalyst was proposed based on our experimental findings. CH4 is first decomposed to CH3 and H by the discharge, and a fraction of the CH3 is adsorbed on γ-Al2O3 surface for deep oxidation. The oxygen atoms produced by the discharge react with H2O to yield surface reactive OH groups that contribute to the CH3 oxidation. Oxygen atoms also promote the release of H2O from the surfaces of the γ-Al2O3 and Au/γ-Al2O3 and especially promote CO2 desorption from the surface of the Au/γ-Al2O3. When γ-Al2O3 was used as the catalyst, the CO2 selectivity was only 15 vol.%, and the CH4 conversion decreased after 7 h of plasma-catalytic oxidation. In contrast, when Au/γ-Al2O3 was used, the CO2 selectivity was 80 vol.%, long-term CH4 conversion was obtained. Experimental results revealed that Au was beneficial for the decomposition of surface carbonate species into gaseous CO2, whereas the carbonate species accumulated on γ-Al2O3 when Au was absent.

6.
J Hazard Mater ; 363: 10-15, 2019 02 05.
Artigo em Inglês | MEDLINE | ID: mdl-30300773

RESUMO

Carbon oxidation has two stages, the first is the formation of surface oxides and the second is the gasification of the surface oxides to CO2. Calcium carbonate (CaCO3) was used to catalyze the gasification of the surface oxides. The catalytic effect of on graphite oxidation and its catalytic mechanism were studied by using thermogravimetric technique and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). It was found that characteristic temperature (T50) of graphite oxidation with CaCO3 was 946 K, 113 K lower than that of graphite only. DRIFTS analysis results show that surface oxides (adsorbed CO2 and carbonate CO32-) were formed on the graphite surface at a temperature above 473 K, carbonate products on graphite surface disappeared when CaCO3 was present; formation of CO32- on CaCO3 surface was confirmed, this CO32- may be more easily gasified into gaseous CO2. The kinetic analysis results showed that CaCO3 promoted graphite oxidation has an activation energy of 74.3 kJ mol-1, far lower than that of graphite (148 kJ mol-1).

7.
J Hazard Mater ; 347: 150-159, 2018 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-29306216

RESUMO

A dielectric barrier discharge (DBD) catalyst hybrid reactor with CeO2/γ-Al2O3 catalyst balls was investigated for benzene decomposition at atmospheric pressure and 30 °C. At an energy density of 37-40 J/L, benzene decomposition was as high as 92.5% when using the hybrid reactor with 5.0wt%CeO2/γ-Al2O3; while it was 10%-20% when using a normal DBD reactor without a catalyst. Benzene decomposition using the hybrid reactor was almost the same as that using an O3 catalyst reactor with the same CeO2/γ-Al2O3 catalyst, indicating that O3 plays a key role in the benzene decomposition. Fourier transform infrared spectroscopy analysis showed that O3 adsorption on CeO2/γ-Al2O3 promotes the production of adsorbed O2- and O22‒, which contribute benzene decomposition over heterogeneous catalysts. Nano particles as by-products (phenol and 1,4-benzoquinone) from benzene decomposition can be significantly reduced using the CeO2/γ-Al2O3 catalyst. H2O inhibits benzene decomposition; however, it improves CO2 selectivity. The deactivated CeO2/γ-Al2O3 catalyst can be regenerated by performing discharges at 100 °C and 192-204 J/L. The decomposition mechanism of benzene over CeO2/γ-Al2O3 catalyst was proposed.

8.
J Hazard Mater ; 347: 48-57, 2018 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-29289765

RESUMO

Non-thermal plasma technology has great potential in reducing polycyclic aromatic hydrocarbons (PAHs) emission. But in plasma-alone process, various undesired by-products are produced, which causes secondary pollutions. Here, a dielectric barrier discharge (DBD) reactor has been developed for the oxidation of naphthalene over a TiO2/diatomite catalyst at low temperature. In comparison to plasma-alone process, the combination of plasma and TiO2/diatomite catalyst significantly enhanced naphthalene conversion (up to 40%) and COx selectivity (up to 92%), and substantially reduced the formation of aerosol (up to 90%) and secondary volatile organic compounds (up to near 100%). The mechanistic study suggested that the presence of the TiO2/diatomite catalyst intensified the electron energy in the DBD. Meantime, the energized electrons generated in the discharge activated TiO2, while the presence of ozone enhanced the activity of the TiO2/diatomite catalyst. This plasma-catalyst interaction led to the synergetic effect resulting from the combination of plasma and TiO2/diatomite catalyst, consequently enhanced the oxidation of naphthalene. Importantly, we have demonstrated the effectiveness of plasma to activate the photocatalyst for the deep oxidation of PAH without external heating, which is potentially valuable in the development of cost-effective gas cleaning process for the removal of PAHs in vehicle applications during cold start conditions.

9.
Environ Sci Pollut Res Int ; 24(19): 16195-16205, 2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-28540542

RESUMO

To reveal the seasonal variations and sources of PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) during haze and non-haze episodes, daily PM2.5 samples were collected from March 2015 to February 2016 in a mixed multi-function area in Hangzhou, China. Ambient concentrations of 16 priority-controlled PAHs were determined. The sums of PM2.5-bound PAH concentrations during the haze episodes were 4.52 ± 3.32 and 13.6 ± 6.29 ng m-3 in warm and cold seasons, respectively, which were 1.99 and 1.49 times those during the non-haze episodes. Four PAH sources were identified using the positive matrix factorization model and conditional probability function, which were vehicular emissions (45%), heavy oil combustion (23%), coal and natural gas combustion (22%), and biomass combustion (10%). The four source concentrations of PAHs consistently showed higher levels in the cold season, compared with those in the warm season. Vehicular emissions were the most considerable sources that result in the increase of PM2.5-bound PAH levels during the haze episodes, and heavy oil combustion played an important role in the aggravation of haze pollution. The analysis of air mass back trajectories indicated that air mass transport had an influence on the PM2.5-bound PAH pollution, especially on the increased contributions from coal combustion and vehicular emissions in the cold season.


Assuntos
Poluentes Atmosféricos/análise , Hidrocarbonetos Policíclicos Aromáticos/análise , China , Monitoramento Ambiental , Material Particulado , Estações do Ano , Emissões de Veículos
10.
Environ Sci Pollut Res Int ; 24(1): 135-145, 2017 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27475434

RESUMO

To investigate the characteristics of polycyclic aromatic hydrocarbons (PAHs) during haze episodes in warm seasons, daily PM2.5 and gaseous samples were collected from March to September 2015 in Hangzhou, China. Daily samples were further divided into four groups by the definition of haze according to visibility and relative humidity (RH), including non-haze (visibility, >10 km), light haze (visibility, 8-10 km, RH <90 %), medium haze (visibility, 5-8 km, RH <90 %), and heavy haze (visibility, <5 km, RH <90 %). Significantly higher concentrations of PM2.5-bound PAHs were found in haze days, but the mean PM2.5-bound PAH concentrations obviously decreased with the aggravation of haze pollution from light to heavy. The gas/particle partitioning coefficients of PAHs decreased from light-haze to heavy-haze episodes, which indicated that PM2.5-bound PAHs were restricted to adhere to the particulate phase with the aggravation of haze pollution. Absorption was considered the main mechanism of gas/particle partitioning of PAHs from gaseous to particulate phase. Analysis of air mass transport indicated that the PM2.5-bound PAH pollution in haze days was largely from regional sources but also significantly affected by long-range air mass transport. The inhalation cancer risk associated with PAHs exceeded the acceptable risk level markedly in both haze and non-haze days.


Assuntos
Poluentes Atmosféricos/análise , Hidrocarbonetos Policíclicos Aromáticos/análise , China , Monitoramento Ambiental , Temperatura Alta , Material Particulado/análise , Estações do Ano
11.
Anal Sci ; 24(2): 253-6, 2008 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-18270418

RESUMO

The removal properties of diesel exhaust particles (DEP) were investigated using an engine exhaust particle size spectrometer (EEPS), field emission-type scanning electron microscopy (FE-SEM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). DEP were treated using a dielectric barrier discharge (DBD) reactor installed in the tail pipe of a diesel engine, and a model DBD reactor fed with DEP in the mixture of N(2) and O(2). When changing the experimental parameters of both the plasma conditions and the engine load conditions, we obtained characteristic information of DEP treated with plasma discharges from the particle diameter and the composition. In evaluating the model DBD reactor, it became clear that there were two types of plasma processes (reactions with active oxygen species to yield CO(2) and reactions with active nitrogen species to yield nitrogen containing compounds). Moreover, from the result of a TOF-SIMS analysis, the characteristic secondary ions, such as C(2)H(6)N(+), C(4)H(12)N(+), and C(10)H(20)N(2)(+), were strongly detected from the DEP surfaces during the plasma discharges. This indicates that the nitrogen contained hydrocarbons were generated by plasma reactions.


Assuntos
Eletroquímica/instrumentação , Material Particulado/análise , Emissões de Veículos/análise , Eletroquímica/métodos , Microscopia Eletrônica de Varredura/instrumentação , Microscopia Eletrônica de Varredura/métodos , Nitrogênio/química , Oxigênio/química , Tamanho da Partícula , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Espectrometria de Massa de Íon Secundário/instrumentação , Espectrometria de Massa de Íon Secundário/métodos
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