Xiao-Song Li

Enhanced effect of water vapor on complete oxidation of formaldehyde in air with ozone over MnOx catalysts at room temperature.

At room temperature, the enhanced effect of water vapor on ozone catalytic oxidation (OZCO) of formaldehyde to CO2 over MnOx catalysts and the reaction stability was reported. In a dry air stream, only below 20% of formaldehyde could be oxidized into CO2 by O3. In humid air streams (RH≥55%), ∼100% of formaldehyde were oxidized into CO2 by O3 and the reaction stability was significantly enhanced. Meanwhile, in situ Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectra of OZCO of HCHO demonstrate that the amount of both monodentate and bidentate carbonate species on MnOx, in the dry stream, increased gradually with time on stream (TOS). However, in the humid stream, almost no accumulation of carbonate species on the catalysts was observed. To clarify the enhanced mechanism, formaldehyde surface reactions and CO2 adsorption/desorption on the fresh, O3 and O3+H2O treated MnOx catalysts were examined comparatively.

Atmospheric-pressure plasma CVD of TiO 2 photocatalytic films using surface dielectric barrier discharge

Surface dielectric barrier discharge (DBD) was used for atmospheric-pressure plasma CVD of TiO2 films from TiCl4 and O2 for the first time. Under this experiment, the deposition rate was estimated at 22 nm min −1 by scanning electron microscope observation and the as-deposited TiO2 films were amorphous as evidenced by Raman analysis. The photocatalytic application of TiO2 films in removing HCHO from simulated air was examined in a continuous flow reactor. The TiO2 films after calcination at 350 or 450 ◦ C were notably photocatalytically active for complete oxidation of formaldehyde to an innocuous product (CO2), which was consistent with the results of Raman analysis. Using the TiO2 films, an extremely harmful by-product, CO, was not detected from photocatalytic oxidation of HCHO in a simulated air stream. (Some figures in this article are in colour only in the electronic version)

Modulating effects of the low-frequency source on ion energy distributions in a dual frequency capacitively coupled plasma

With the energy resolved quadrupole mass spectrometer and hybrid simulation, the influence of low-frequency (LF) source parameters on the ion energy distributions (IEDs) of argon ions impinging on the grounded electrode was studied, both experimentally and numerically, in a dual frequency capacitively coupled plasma. It was shown that for decreasing LF or increasing LF power, the high energy peak in IEDs shifts toward the high energy region significantly. The simulation results were in general agreement with the experimental data.

Determination of vibrational and rotational temperatures in a gliding arc discharge by using overlapped molecular emission spectra

Vibrational and rotational temperatures were simultaneously determined in a kilohertz alternating current (ac) gliding arc discharge by using overlapped emission spectra of N2(C 3Πu–B 3Πg) with OH(A 2Σ+–X 2Πi) and with . The simulated emission spectra of OH(A 2Σ+–X 2Πi) and were largely overlapped by radiation transition bands of N2(C 3Πu–B 3Πg) when the rotational temperature was elevated from 500 K to 2500 K. The temporally resolved vibrational and rotational temperatures in a discharge voltage period suggested that the rotational temperature from OH(A 2Σ+–X 2Πi) was remarkably larger than that from N2(C 3Πu–B 3Πg) and . The ratio of number densities of excited electronic states was also determined based on the overlapped emission spectra.

Ozone catalytic oxidation of adsorbed benzene over AgMn/HZSM-5 catalysts at room temperature

To provide insight into the mechanism of plasma catalytic oxidation of adsorbed benzene in a cycled storage–discharge (CSD) plasma catalytic process, ozone catalytic oxidation (OZCO) of adsorbed benzene over the AgMn/HZSM-5 (AgMn/HZ) catalyst at room temperature was studied. The properties of the AgMn/HZ catalyst were compared with those of HZ, Mn/HZ, Ag/HZ catalysts in investigations of the TPD of adsorbed benzene, the product distribution and O3 decomposition in OZCO of adsorbed benzene, and TPO and TPD of the used catalysts. For the AgMn/HZ catalyst, the adsorption capacity and the adsorption strength of benzene were significantly improved as compared to HZ, Ag/HZ and Mn/HZ. Adsorbed benzene is oxidized completely to CO2 by O3 catalyzed by Ag on HZ. MnOx, on the other hand, further speeds up the OZCO rate of benzene adsorbed on Ag/HZ.

Stable kilohertz spark discharges for high-efficiency conversion of methane to hydrogen and acetylene

Stable kilohertz spark discharges with a unique waveform of discharge current were studied for high-efficiency conversion of methane to hydrogen and acetylene at atmospheric pressure for the first time. Discharge stability was confirmed by the concentration variation in the product streams with 220 min discharge time using pure methane as the feed gas. Utilizing the stable kilohertz spark discharges, the hydrogen concentration in the product stream could be as high as 72.1 vol% at an energy cost of 6.7 eV per H2 molecule produced and 81.5% of methane conversion. The acetylene concentration could reach 18.4 vol% at an energy cost of 21.2 eV per C2H2 molecule produced and 70.3% of methane conversion. For methane conversion ranging from 51.9% to 81.5%, the energy costs were 6.6‐10.7 eV per CH4 molecule converted, 4.4‐6.7 eV per H2 molecule produced and 16.9‐27.6 eV per C2H2 molecule produced. This study showed the high-concentration production of COx-free hydrogen and acetylene from methane at a low energy cost by stable kilohertz spark discharges. (Some figures in this article are in colour only in the electronic version)

A process for a high yield of aromatics from the oxygen-free conversion of methane: combining plasma with Ni/HZSM-5 catalysts

A process for a high yield of aromatics and co-produced hydrogen from the oxygen-free conversion of methane using a two-stage plasma-followed-by-catalyst (PFC) reactor at atmospheric pressure and low temperature is reported. Pure methane and a methane and hydrogen mixture as the feed gas for the two-stage PFC process were investigated, respectively. Using the methane and hydrogen mixture as the feed gas into the two-stage PFC reactor, Ni/HZSM-5 catalysts keep stable catalytic activity for a much longer on-stream time than that using pure methane as the feed gas. The maximum aromatic yield may be achieved using low Ni-loading Ni/HZSM-5 catalysts and at a suitable catalyst temperature.

Methane conversion in low-temperature plasma

The conversion of methane in electric discharges of different types and under electron beam irradiation are considered. The influence of nonequilibrium conditions of conversion in low-temperature plasma on the energy consumption, product composition, and selectivity is analyzed. The results of works on plasma pyrolysis, partial plasma oxidation, and steam and carbon dioxide reforming of methane in a low-temperature plasma are discussed. It is shown that the use of chain processes makes it possible to substantially reduce the power consumption for methane conversion by an electrophysical device.

Spatially resolved measurements of ion density and electron temperature in a dual-frequency capacitively coupled plasma by complete floating double probe technique

Spatially resolved measurements of the ion density and electron temperature in a dual-frequency capacitively coupled Ar discharge plasma are performed with a newly developed complete floating double probe. Axial and radial distributions of the ion density and electron temperature under various high-frequency (HF) power and gas pressure were studied in detail. Both the ion density and the electron temperature increased with increasing HF power. With increasing gas pressure from 1.3 to 9.3 Pa, the radial profile of ion density below the driven electrode experienced a change from “bimodal” to “unimodal” shape, with better uniformity being achieved at the optimal pressure of about 5 Pa. In addition, changing the axial profile of ion density was also observed with the peak shift toward the powered electrode at higher pressures. The measured results showed satisfying consistency with that of improved two dimensional fluid simulations.

Experimental investigation of ion energy distributions in a dual frequency capacitively coupled Ar/CF4 plasma

An energy resolved quadrupole mass spectrometer was adopted to determine ion energy distributions (IEDs) impinging on the ground electrode in a dual frequency (DF) capacitively coupled Ar/CF4 (95%/5%) plasma. The influences of discharge parameters, such as power of low frequency (LF power) source, frequency of LF source (LF frequency), and gas pressure, on IEDs of Ar+ and CF3+ were investigated. The enhancement in LF power, which hence means the increase in sheath potential, results in a significant shift in the IEDs of Ar+ and CF3+ toward higher energy area and then a broader energy width. However, the increase in LF frequency leads to narrow and unimodal IEDs, which is probably because the regime of DF CCP has changed during the process. The pressure has a remarkable effect on IEDs structure, i.e., the exhibited saddle-shaped structure of IEDs is obvious in a collisionless sheath at lower pressure but becomes eliminated in a collision sheath at higher pressure. The Ar+ IEDs have low energy regions becau...