Jing-Lin Liu

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 HCHO in Air over MnOx at Room Temperature

Abstract The complete oxidation of HCHO in air with O 3 over MnO x catalysts at room temperature was studied. The MnO x catalysts were prepared by a redox method. The catalysts showed amorphous patterns in X-ray diffraction characterization. Formaldehyde in simulated air containing 137 mg/m 3 HCHO with 56% relative humidity (RH, 25 °C) was totally oxidized to CO 2 by 642 mg/m 3 O 3 over the MnO x catalysts at GHSV (gas hourly space velocity) = 2 × 10 5 h −1 . The formaldehyde conversion and CO 2 selectivity were maintained at ∼ 100% during 150 min time-on-stream. The effect of the molar ratio of O 3 to HCHO was also investigated. At a O 3 to HCHO molar ratio of 2:3, which was significantly lower than the stoichiometric ratio, a CO 2 selectivity of 100% was still achieved. No byproduct was detected during HCHO oxidation with O 3 over the MnO x catalysts using an online Fourier transform infrared spectrometer.

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.

Temporal evolution characteristics of an annular-mode gliding arc discharge in a vortex flow

An annular-mode gliding arc discharge powered by a 50 Hz alternating current (ac) supply was studied in a vortex flow of dry and humid air. Its temporal evolution characteristics were investigated by electrical measurement, temporally resolved imaging, and temporally resolved optical emission spectroscopic measurements. Three discharge stages of arc-ignition, arc-gliding, and arc-extinction were clearly observed in each half-cycle of the discharge. During the arc-gliding stage, the intensity of light emission from the arc root at the cathode was remarkably higher than that at other areas. The spectral intensity of N2(C3Πu−B3Πg) during the arc-ignition stage was much higher than that during the arc-gliding stage, which was contrary to the temporal evolutions of spectral intensities for N2+(B2Σu+−X2Σg+) and OH(A2Σ+−X2Πi). Temporally resolved vibrational and rotational temperatures of N2 were also presented and decreased with increasing the water vapor content.

Ozone catalytic oxidation of benzene over AgMn/HZSM-5 catalysts at room temperature: Effects of Mn loading and water content

Abstract The effects of Mn loading and water content on AgMn/HZSM-5 (AgMn/HZ) catalysts were investigated in the ozone catalytic oxidation (OZCO) of benzene in a continuous air flow at room temperature. The catalytic activity is closely related to the Mn loading, and the AgMn/HZ catalyst with 2.4 wt% Mn (AgMn/HZ(2.4)) had the highest activity and stability in benzene oxidation as a result of its large surface area and high MnO x dispersion. Temperature-programmed desorption of the used catalysts demonstrated that 2.4 wt% was also the optimal Mn loading for suppressing the accumulation of benzene and HCOOH over the catalyst surface after benzene oxidation. For AgMn/HZ catalysts with Mn loadings ≤ 2.4 wt%, O 3 decomposition to active oxygen species (O*) plays the most important role in benzene oxidation; however, benzene activation is the crucial step for benzene oxidation by O 3 over AgMn/HZ catalysts with Mn loadings > 2.4 wt%. The AgMn/HZ(2.4) catalyst was then used to perform OZCO of benzene in a humid stream. Compared with dry gas, water vapor greatly enhanced the activity and stability of the AgMn/HZ(2.4) catalyst, and 0.1–0.2 vol% was the optimal water content for benzene oxidation.

Effect of O2/CH4 ratio on the optimal specific-energy-input (SEI) for oxidative reforming of biogas in a plasma-shade reactor

In a novel plasma-shade reactor for oxidative reforming of biogas (CH4/CO2 = 3/2), the effects of specific-energy-input (SEI) on CH4 and CO2 conversions and energy cost of syngas were investigated at O2/CH4 ratios ranged from 0.42 to 0.67. At each of O2/CH4 ratios, V-shape profiles of energy cost of syngas increasing with SEI were observed, reaching the lowest value at the optimal SEI (Opt-SEI). With the increase of O2/CH4 ratio, the Opt-SEI decreased significantly. Moreover, at the Opt-SEI, O2 and CH4 conversions and dry-basis concentration of syngas increased and energy cost of syngas decreased greatly with the increase of O2/CH4 ratio.

Cycled storage-discharge (CSD) plasma catalytic removal of benzene over AgMn/HZSM-5 using air as discharge gas

Cycled storage-discharge (CSD) plasma catalytic removal of benzene (C6H6) using air as the discharge gas over AgMn/HZSM-5 (AgMn/HZ) catalyst is reported in this study. The properties of AgMn/HZ catalyst were compared with HZ, Mn/HZ, and Ag/HZ catalysts in investigations of C6H6 storage capacity and plasma catalytic oxidation of stored C6H6. Among HZ, Mn/HZ and Ag/HZ catalysts, the AgMn/HZ catalyst possessed the highest breakthrough capacity of C6H6, which is almost twice than that of the unsupported HZ zeolite. For the AgMn/HZ catalyst, stored C6H6 is oxidized completely to CO2 due to the promoting effect of Ag and MnOx. On the other hand, this accelerates the oxidation rate of stored C6H6 during plasma oxidation of stored C6H6. The effects of discharge parameters on plasma oxidation of stored C6H6 over the AgMn/HZ catalyst are discussed. During the CSD process, under conditions of ∼20000 mL h−1 g−1 space velocity, 6 W of input power, 0.4 vol% of absolute humidity and 24 min of discharge, the stored C6H6 conversion increased rapidly with cycle number during the first three cycles and nearly all stored C6H6 could be oxidized into CO2 thereafter. In addition, CO2 selectivity was maintained at around 100% and only a small amount of N2O (40–50 ppm) was detected during all five cycles. Temperature-programmed desorption of adsorbed C6H6 on the used AgMn/HZ catalyst indicates that the minor Ag sites, which are highly active, cannot be renewed by the air plasma, but the major Ag sites, which are normally active, are renewable. This explains the variation of stored C6H6 conversion with cycle number.

A novel process of ozone catalytic oxidation for low concentration formaldehyde removal

Abstract To reduce energy costs, minimize secondary pollution from undecomposed ozone, and improve the efficiency of ozone use, a novel process of cycled storage-ozone catalytic oxidation (OZCO) was employed to remove formaldehyde (HCHO) at low concentrations in air. We applied Al2O3-supported manganese oxide (MnOx) catalysts to this process, and examined the HCHO adsorption capacity and OZCO performance over the MnOx catalysts. Owing to the high dispersion of MnOx and low oxidation state of manganese, the MnOx/Al2O3 catalysts with a manganese acetate precursor and 10%-Mn loading showed good performance in both storage and OZCO stages. The presence of H2O led to a decrease of the HCHO adsorption capacity owing to competitive adsorption between moisture and HCHO at the storage stage; however, high relative humidity (RH) favored complete conversion of stored HCHO to CO2 at the OZCO stage and contributed to an excellent carbon balance. Four low concentration HCHO storage-OZCO cycles with a long HCHO storage period and relatively short OZCO period were successfully performed over the selected MnOx/Al2O3 catalyst at room temperature and a RH of 50%, demonstrating that the proposed storage-OZCO process is an economical, reliable, and promising technique for indoor air purification.

In Situ Regeneration of Au Nanocatalysts by Atmospheric-Pressure Air Plasma: Regeneration Characteristics of Square-Wave Pulsed Plasma

Atmospheric-pressure air plasma, powered by alternating current (AC) sine-wave high voltage, can in-situ regenerate deactivated Au nanocatalysts during CO oxidation, but it needs high-humidity air as the discharge gas. To overcome the limitation on humidity for in-situ regeneration of air plasma, a square-wave pulsed plasma is applied in this work. Differently from the AC plasma, the pulsed plasma exhibits excellent regeneration performance at any humidity. Further, surface carbonate decomposition, nitrogen oxides poisoning species and electric discharge of the pulsed plasma regeneration are investigated. For the pulsed plasma regeneration at any humidity, the evolution of CO2 concentration with the regeneration time almost keeps the same profile, featuring zero-order kinetics for the carbonate decomposition; on the other hand, whether in the gas phase or on the catalyst surface, there are no formation of poisoning nitrogen oxides. The pulsed plasma at any humidity has the powerful ability in carbonate decomposition and simultaneously prevents the formation of poisoning nitrogen oxides, which is ascribed to its highly centralized energy deposition with high instantaneous power and long interval of instantaneous power. For practical application, normal air is also confirmed to be qualified for the pulsed plasma regeneration.

Ozone catalytic oxidation for ammonia removal from simulated air at room temperature

Ozone catalytic oxidation (OZCO) for removing ammonia from simulated air over the AgMn/HZSM-5 (AgMn/HZ) catalyst with high ammonia conversion and high N2 selectivity at room temperature is reported for the first time. HZ, Ag/HZ, Mn/HZ and AgMn/HZ catalysts were compared in the OZCO reactions of gaseous and adsorbed NH3. In OZCO of gaseous NH3, N2 was the major product and N2O was the minor product. NH3 conversion dropped quickly with time-on-stream (TOS) over HZ and Ag/HZ catalysts while it remained almost constant at a high level over Mn/HZ and AgMn/HZ catalysts during the entire test. N2 selectivity of the AgMn/HZ catalyst was higher than that of the Mn/HZ catalyst. When the initial concentration of NH3 was 521 ppmv and the ratio of initial concentration of O3 to NH3 was 1.73, 99% NH3 conversion with 94% N2 selectivity was obtained over the AgMn/HZ catalyst at room temperature and 150 000 ml g−1 h−1 gas hourly space velocity (GHSV). Finally, the pathways for OZCO of NH3 were proposed for the four catalysts based on the comparative investigation of the gaseous products and surface species during OZCO of adsorbed and gaseous NH3.