Yanqun Zhu

Catalytic oxidation of NO by O2 over CeO2–MnOx: SO2 poisoning mechanism

The catalytic oxidation of NO by O2 was performed over a series of CeO2–MnOx catalysts with different molar ratios of Mn/Ce, which were prepared by the sol–gel method. The highest NO conversion efficiency reached 96% over the catalyst with a 0.4 Mn doping value at 238 °C. The possible reaction pathways of the catalytic oxidation process were proposed according to several characterization measurements. NO was adsorbed on the catalyst surface to form nitrates and then decomposed into NO2. However, the catalyst was completely deactivated under an atmosphere of SO2. NO conversion efficiency dramatically declined from 92% to 22% within only 400 min. Comparing the BET, TPR, TPD, XRD, XPS, FTIR, and TGA results of fresh and poisoned catalysts, the catalyst deactivation could be mainly attributed to manganese sulfate formation on the catalyst surface, which could only slightly decompose. The active sites for NO adsorption were occupied. Finally, the oxidation of NO to NO2 was terminated due to lack of nitrates, which are intermediates for NO oxidation.

Development of Catalyst-Sorbents for Simultaneous Removal of SO2 From Flue Gas by Low Temperature Ozone Oxidation

One technological process employing ozone and heterogeneous catalyst-sorbents was proposed for removal of SO2 from flue gas. The catalyst-sorbents were developed and tested especially for adsorption and oxidation of SO2. Alternative catalyst-supporters including γ-Al2O3, permutite, silica gel, activated carbon and diatomite combined with different metal oxides (MnO2, Cr2O3, Fe2O3, CuO, CoO and NiO) were evaluated and tested. It was found that γ-Al2O3 doped with MnO2 can be considered as removal-effective sorbent for adsorption and oxidation of SO2. The synergetic effect between ozone and catalyst was found to be dominated. Effects of catalyst preparation parameters like calcination temperature, metal loaded and reaction temperature, etc. were investigated based on the MnO2/Al2O3 catalyst-sorbents. Results show that γ-Al2O3 combined with 8% Mn, calcinated under 573 K and reacted at 413 K are the optimal parameters for removal of SO2. Extra NO in flue gas can slightly enhance the capture efficiency of SO2.

Ozone Production with Dielectric Barrier Discharge from Air: The Influence of Pulse Polarity

ABSTRACT This research aims to study the effects of different pulse modes of the power supply on ozone production from air. Single positive, negative as well as the bipolar voltage pulses (positive–negative and negative–positive) with a repetition rate of 300 Hz have been applied to coaxial dielectric barrier discharge arrangement. Results reveal that at fixed specific input energy (SIE), which is defined as the ratio of power to gas flow rate, the ozone generation efficiencies for different pulse modes are in the sequence of positive > positive–negative > negative–positive > negative, and the difference between positive and positive–negative pulse becomes considerable with SIE higher than 500 J/L. Results also reveal that the maximum NO2 concentration is obtained at 400 J/L. Moreover, utilizing bipolar pulse can reduce N2O production with SIEs higher than 250 J/L and hinder NO2 production with SIEs higher than 350 J/L.

Catalyst tolerance to SO2 and water vapor of Mn based bimetallic oxides for NO deep oxidation by ozone

Improving the catalyst stabilities under different conditions (water vapor, SO2, both water vapor and SO2) is important for industrial applications regarding catalytic NO deep oxidation by ozone. In this paper, Ce–Mn/SA and Fe–Mn/SA catalysts were selected to investigate the stabilities. The results showed that the Ce–Mn/SA exhibited excellent stability and resistance to SO2, while the Fe–Mn/SA only displayed excellent stability without moisture and SO2. Almost a 50% drop in efficiency was observed after deactivation by water vapor and water vapor together with SO2 for the two catalysts. The Fe–Mn/SA displayed inferior resistance to SO2. After stability testing with water vapor, the surface area, pore volume, and average pore diameter all decreased. The low adsorption energy of the H2O molecule resulted in the superior adsorption of water vapor, which occupied large amounts of active sites. XPS results showed that the ratio of Mn4+ and chemisorbed oxygen decreased after deactivation. Mn4+ favors NO oxidation, while Mn3+ is favorable for ozone decomposition. Therefore, better performance in NO deep oxidation by ozone requires relative balance distribution between Mn4+ and Mn3+. Interestingly, the TPD results showed that the NO desorption peak was unaffected and even increased a lot after water vapor stability testing. This could be attributed to the nitrates, formed by the N2O5 and H2O in liquid phase, that were adsorbed on the catalyst surface prior to NO, which contributes to a bigger NO desorption peak with lower NO adsorption ability. The trace of sulfate formed after SO2 stability testing was verified from TPD and TGA results, but it was not observed from the FTIR spectra, indicating the sulfate species formed during the ozonation process may not exist on the catalyst surface.

Ozone Production Influenced by Increasing Gas Pressure in Multichannel Dielectric Barrier Discharge for Positive and Negative Pulse Modes

ABSTRACT This paper describes the influence of gas pressure on the conversion of O2 to O3 and the ozone production efficiency in a multichannel dielectric barrier discharge (DBD) reactor utilizing positive and negative pulses. Results show that conversion of O2 to O3 is continuously enhanced by the increase of gas pressure (0.1–0.24 MPa) while the rising speed of oxygen conversion with the increasing gas pressure at fixed specific input energy is reduced above 0.15 MPa. The maximum ozone generation efficiency is increased with increasing gas pressure (0–0.2 MPa) while positive pulse exhibits higher energy efficiency. The maximum ozone generation efficiency is suppressed with further increase of gas pressure (0.2–0.24 MPa) while no significant difference in ozone generation efficiency is observed for two unipolar pulse modes. Results also show that 0.2 MPa is the optimal working gas pressure to obtain the maximum ozone generation efficiency and increasing gas pressure would lead to remarkable increase of ozone generation efficiency for ozone production at high energy densities in multichannel DBD.

Promotional effect of spherical alumina loading with manganese-based bimetallic oxides on nitric-oxide deep oxidation by ozone

ABSTRACT Nitric oxide (NO) deep oxidation to dinitrogen pentoxide (N 2 O 5 ) by ozone together with wet scrubbing has become a promising technology for nitrogen-oxide (NO x ) removal in industrial boilers. Catalysts were introduced to enhance the N 2 O 5 formation rate with less ozone injection and leakage. A series of monometallic catalysts (manganese, cobalt, cerium, iron, copper, and chromium) as prepared by the sol-gel method were tested. The manganese oxides achieved an almost 80% conversion efficiency at an ozone (O 3 )/NO molar ratio of 2.0 in 0.12 s. The crystalline structure and porous parameters were determined. The thermodynamic reaction threshold of NO conversion to N 2 O 5 is oxidation with an O 3 /NO molar ratio of 1.5. Spherical alumina was selected as the support to achieve the threshold, which was believed to improve the catalytic activity by increasing the surface area and the gas-solid contact time. Based on the manganese oxides, cerium, iron, chromium, copper, and cobalt were introduced as promoters. Cerium and iron improved the deep-oxidation efficiency compared with manganese/spherical alumina, with less than 50 mg/m 3 of outlet NO + nitrogen oxide, and less than 25 mg/m 3 of residual ozone at an O 3 /NO molar ratio of 1.5. The other three metal oxides inhibited catalytic activity. X-ray diffraction, nitrogen adsorption, hydrogen temperature-programmed reduction, and X-ray photoelectron spectroscopy results indicate that the catalytic activity is affected by the synergistic action of NO x oxidation and ozone decomposition.

Investigation on Removal of NOx and SO2 From Flue Gas by Combined Ozone With Absorption and By-Product Treatment

The combination of ozone with washing tower and an absorption products recovery system was utilized for removal of NOx and SO2 from flue gas. In our previous studies, more than 90% NO can be oxidized by ozone. In this study, three kinds of absorbents, Na2 SO3 , CaSO3 and Ca(OH)2 , were evaluated for simultaneous absorption of NO2 and SO2 in the wet scrubbing. It was found that NO2 absorption efficiency was increasing with S(IV). Effect of different concentration of CaSO3 on NO2 absorption was investigated. Results show that nearly 70% NO2 can be absorbed in calcium sulfite slurry. Furthermore, NO2 absorption efficiency is increasing to 85% in the sulfite with assistant of MnSO4 . In the meantime, the absorption efficiency of SO2 is always nearly 100%. A new system is built for recycling NO2 absorption products and purifying the waste water, which has the advantages of low investment and operating cost.Copyright