Production of Reactive Oxygen Species and Application for NOx Control

Current gas ionization discharge techniques used in the removal of NOx from waste gases require large plasma sources, have high energy consumption, and may feature low NOx removal rates. We develop a system to generate reactive oxygen species through a strong ionization discharge, which is injected into a flow of simulated waste gas. The relative proportions and temperatures of input gases were controlled and the rate of consumption by reactive species was monitored. HNO₃ oxidization products of NOx were also collected and measured. The molar ratio of reactive oxygen species to NO was optimized to improve the rate of NOx removal. A input gas temperature of 58–60 °C was also found to be optimal. The O₂ volume fraction has almost no influence on NOx removal, while H₂O volume fractions above 6 %, gave rise to NOx removal rates of 97.2 %. The present study addresses disadvantages of current gas ionization discharge and requires no catalyst, reducing agent or oxidant.     

Abatement of Gaseous Xylene Using Double Dielectric Barrier Discharge Plasma with In Situ UV Light: Operating Parameters and Byproduct Analysis

Ultraviolet (UV) light with a wavelength of 254 nm was applied to a double dielectric barrier discharge (DDBD) system to decompose of gaseous xylene. The results show that a significantly synergistic effect can be achieved with the introduction of UV light into the DDBD system. When UV light is applied, the system show a 21.8 % increase in its removal efficiency for xylene at 35 kV with an ozone concentration close to 971 ppmv. The CO _x (x = CO₂ and CO) selectivity of outlet gas rises from 6.54 to 76.2 %. The optimal synergetic effect between UV light and DDBD can be obtained at a peak voltage of 30 kV. The system is robust for humidity, which only slightly reduces the xylene removal efficiency at a high peak voltage (30–35 kV). With the increase of gas flow rate, the removal efficiency for xylene decreases due to a reduced residence time. In addition, the products of xylene degradation were also analyzed. The major products of the degradation were found to be CO₂ and H₂O while byproducts such as O₃ and HCOOH were observed as well.     

On the mechanism of the OH initiated oxidation of acetylene in the presence of O2 and NO x

The mechanism of the oxidation of acetylene, in the presence of O₂ and NO _x , has been studied. Different levels of theory have been tested for the first step of the mechanism: the acetylene + OH radical reaction. Based on these results the meta-hybrid functional MPWB1K has been chosen for modeling all the other steps involved in the oxidation of acetylene. Different reaction paths have been considered and the one leading to glyoxal formation and OH regeneration is predicted to be the main channel, independently of the presence of NO _x . Two different mechanisms were modeled to account for formic acid formation, both of them involving cyclic intermediates. According to the computed activation free energies, the three-membered intermediate seems to be more likely to occur than the four-membered one. However, reaction barriers are very high and only a very small proportion of formic acid is expected to be formed through such intermediates. In the presence of NO _x , considered in this work for the first time, the main product of the tropospheric oxidation of acetylene is also expected to be glyoxal.     

Point and Multipoint to Plane Barrier Discharge Process for Removal of NOx from Engine Exhaust Gases: Understanding of the Reactional Mechanism by Isotopic Labeling

An experimental study on the removal of NO_x in a simulated vehicle exhaust gas has been carried out using point to plane and multipoint to plane DBD corona reactors. Hydrocarbon (C₃H₆) and NO_x by-products were systematically investigated with a Gas Chromatography coupled to a Mass Spectrometry (GC/MS). NO_x (NO and NO₂) and CO output were also monitored with a gas analyzer in order to complete the mass balance. ¹⁸O tracer technique analyzes is applied to investigate the mechanism of propylene decomposition. From the plasma chemical reaction pathway proposed, it is apparent that the oxygen activation is one of the important steps for initiating the oxidation processes and the R-NO_x formation. We present data for the reaction of the (N₂/O₂/C₃H₆/CO₂NO/H₂O system in the corona discharge reactors mentioned above. This system has been shown to generate a significant amount of aldehyde. CH₃NO₂ and CH₃ONO₂ are the main R-NO_x compounds produced. Reactant composition and discharge energy densities (controlled by a numerical oscilloscope) were the operating parameters under study in wet and dry air mixture. Water vapors played an important role in NO_x removal (especially in NO₂ removal) via the reaction forming HNO₃. Therefore, in wet-gas mixture supplied reactors the highest removal rates of NO_x were as high as 30%, while in dry-gas only 15%. Different dielectric materials such as Al₂O₃/SiO₂ and TiO₂ on Al₂O₃/SiO₂ support have been used.     

Potentiometric NOx sensor based on stabilized zirconia and NiCr2O4 sensing electrode operating at high temperatures

The two types of electrochemical sensors using stabilized zirconia and the oxide sensing electrode (SE) were developed for NO_x detection at high temperatures. For the mixed-potential-type sensor, NiCr₂O₄ was found to give fairly excellent NO_x sensing characteristics in air among several spinel-type oxides tested. This NO_x sensor provided a linear correlation between EMF and the logarithm of NO or NO₂ concentration in the range 25–436 ppm and in the temperature range 550–650°C. With fixed bias voltage being applied between the SE (oxide) and the counter (Pt) electrode (CE), the EMF between SE and the reference (Pt) electrode (RE) was measured as a sensing signal. The NiCr₂O₄-attached tubular device was found to provide selective response to NO over NO₂ if SE was polarized at +175 mV versus RE. It was also found that this device gave selective response to NO₂ over NO, if SE was polarized at −250 mV versus CE. The new design of the planar device was proposed to avoid the cross-sensitivities to the others gases usually coexisting in car exhausts.     

Evaluation of kinetic stability against CO2 and conducting property of BaCe0.9−xZrxY0.1O3−δ

In order to prepare high proton conducting oxide with high chemical stability against CO₂ at 600–800 °C, preparation of BaCe_0.9?xZr_xY_0.1O_3?δ was examined. Almost single-phase could be prepared for the specimens with x = 0.0–0.2 by Pechini method. Reaction kinetics between BaCe_0.9?xZr_xY_0.1O_3?δ and CO₂ could be explained by Jander model. With increasing Zr content up to 0.2, apparent rate constant determined from Jander plot decreased by about one order, showing improvement of kinetic stability against CO₂. It was also clarified that influence of partial Zr substitution on electrical property was slight, leading to the conclusion that BaCe_0.7Zr_0.2Y_0.1O_3?δ exhibited both high kinetic stability against CO₂ and relatively high proton conduction.     

Gas-phase conversion of the U(VI), Sr,Mo, and Zr compounds in nitrating atmosphere

The gas-phase conversion of U₃O₈, MoO₃, SrO, and their mechanical mixtures, and also of ZrO₂ into water-soluble compounds in the atmosphere of (NO _x  + vapor H₂O) or HNO₃ (vapor) was studied. In the course of gas-phase conversion, U₃O₈ and SrO transform into water-soluble compounds (nitrates, hydroxonitrates), whereas MoO₃ and ZrO₂ undergo no changes. The principal possibility of separating U from Mo and Zr by gas-phase conversion of the oxides in the atmosphere of (NO _x  + vapor H₂O) or HNO₃ (vapor) was demonstrated.     

A study of non-isothermal kinetics of limestone decomposition in air (O2/N2) and oxy-fuel (O2/CO2) atmospheres

The non-isothermal experiments of limestone decomposition at multi-heating rates in O₂/N₂ and O₂/CO₂ atmospheres were studied using thermogravimetry. The limestone decomposition kinetic model function, kinetic parameters of apparent activation energy (E), and pre-exponential factor (A) were evaluated by Bagchi and Malek method. The results shown that in 20 % O₂/80 % N₂ atmosphere, the limestone decomposed slowly following the contracting sphere volume model controlled by boundary reaction (spherical symmetry) in two stages, and the E increased by about 50 kJ mol^?1 in the second decomposition stage. But in 20 % O₂/80 % CO₂ atmosphere, the presence of high-concentration CO₂ significantly inhibited the limestone decomposition, and made the decomposition process occur at high temperature with a rapid rate; the decomposition kinetics was divided into three stages, the first stage was an accelerated decomposition process following the Mampel Power law model with the exponential law equation, the second stage followed the nth order chemical reaction model as an α–t deceleration process, and the third stage belonged to the random nucleation and nuclei growth model with the Avrami–Erofeev equation. And with the heating rate increasing, the reaction order n showed a slight rise tendency. The E was about 1,245 kJ mol^?1 in 20 % O₂/80 % CO₂ atmosphere, but was only about 175 kJ mol^?1 in 20 % O₂/80 % N₂ atmosphere. The E and A increased markedly in the O₂/CO₂ atmosphere.     

Thermal analysis and calorimetry in the study of materials and processes for fundamental sciences and various applications in Central and Eastern Europe

We investigated the influence of B substitution for Al₂W₃O₁₂ on thermal changes of UV–Vis and Raman spectra, and colors. First, B-substituted Al₂W₃O₁₂ powder was synthesized by a solid-state reaction method. Single-phase Al_2?xB_xW₃O₁₂ powders with x = 0, 0.10 and 0.20 were successively prepared. B substitution promoted thermal changes of the UV–Vis spectra, resulting in a more pronounced color change of Al₂W₃O₁₂ in the range of 30–150 °C. Raman spectra of the Al_2?xB_xW₃O₁₂ powders with x = 0 and 0.20 indicated that the lattice vibrations of Al_2?xB_xW₃O₁₂ with x = 0.20 were larger than those of Al₂W₃O₁₂. The thermal change of the color phase (ΔE) in the range 30–150 °C of Al₂W₃O₁₂ was increased by B substitution. The color of the B-substituted Al₂W₃O₁₂ powders changed reversibly from pale white at 30 °C to light yellowish green at 150 °C.     

Shielded Sliding Discharge-Assisted Hydrocarbon Selective Catalytic Reduction of NOx over Ag/Al2O3 Catalysts Using Diesel as a Reductant

The nonthermal plasma generated in a shielded sliding discharge reactor was used to reform diesel for the hydrocarbon-selective catalytic reduction (HC-SCR) of NO_x on Ag/Al₂O₃ catalysts. Compared with raw diesel, the reformed diesel enhanced the NO_x reduction efficiency, mitigated hydrocarbon poisoning of the catalyst and reduced the fuel penalty for the HC-SCR reaction. The NO_x conversion values obtained with a commercial Ag/Al₂O₃ catalyst exceeded that of a 2.0 wt% Ag/Al₂O₃ catalyst prepared by wet impregnation. A significant amount of NH₃ was produced as a by-product during the HC-SCR reaction, which suggests that further NO_x conversion enhancement can be achieved by placing a second NH₃-SCR catalyst in series with the Ag/Al₂O₃ catalyst.     

By-Products NOx Control and Performance Improvement of a Packed-Bed Nonthermal Plasma Reactor

NO_x are main toxic by-products in the effluent gas whendecomposing volatile organic compounds in air by a packed-bed plasmareactor. Several types of materials such as 13X zeolite, BaTiO₃and Pd/Pt catalysts have been selected to be packed in the reactor, andmethane decomposition and NOx by-products in discharged gases areinvestigated at different range of reaction temperature and dischargeenergy density at atmospheric pressure. The ratios of methane decompositionpercentage/NO_x concentration are used to assess these packed bedmaterials and reaction conditions. The results show that usingPd/-Al₂O₃ with lower percentage Pd as packedbed, and discharging with lower discharge density at higher reactiontemperature can reduce NO_x output effectively and greatly improveperformance of the reactor.     

NOx-Sorbing Metal Oxides, MnOx–CeO2. Oxidative NO Adsorption and NOx–H2 Reaction

(n)MnO_x–(1?n)CeO₂ binary oxides have been studied for the sorptive NO removal and subsequent reduction of NO_x sorbed to N₂ at low temperatures (≤150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO^? ₃) and/or nitrite (NO^? ₂) species on the surface depending on temperature, O₂ concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NO_x toward H₂ was examined for MnO_x–CeO₂ impregnated with Pd, which is known as a nonselective catalyst toward NO–H₂ reaction in the presence of excess oxygen. The Pd/MnO_x–CeO₂ catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H₂ at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnO_x–CeO₂ surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H₂–O₂ combustion, H₂–NO reaction was suppressed to a certain extent in the presence of O₂. Nevertheless, Pd/MnO_x–CeO₂ attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H₂, and 6% O₂ in He at as low as 150 °C, compared to ca. 30% conversion for Pd/γ–Al₂O₃ at the same temperature. The combination of NO_x-sorbing materials and H₂-activation catalysts is expected to pave the way to development of novel NO_x-sorbing catalysts for selective deNO_x at very low temperatures.     

Simultaneous soot combustion and NOx reduction over a vanadia-based selective catalytic reduction catalyst

Simultaneous NO_x reduction and soot combustion over a commercial vanadia-based selective catalytic reduction (SCR) catalyst were investigated. Carbon black was used as model soot. The impact of the contact intensity between carbon and catalyst was studied. The experiments appeared as promising results for the utilization of vanadia-based SCR catalysts in SCR on filter system as, in the SCR operating temperature range (250–400 °C), no significant impact of the presence of carbon black on NO_x reduction was observed. However, a decrease in the specific carbon oxidation rate was highlighted. This latter increases with the contact between carbon and catalyst and is attributed to a lack of NO₂, consumed by the fast SCR reaction. At temperatures greater than 400 °C, the contact between carbon particles and the SCR catalyst partially inhibits the NO_x reduction, whereas it exhibits a catalytic effect on the carbon oxidation rate. The tighter the contact between the two materials, the more significant is this behavior. A redox mechanism, which competes with the redox cycle of the SCR mechanism, was proposed. The impregnation of a V-based SCR catalyst with 2 wt % of calcium was also performed. A drastic loss of DeNO_x activity was observed, whereas the effect of the contact between carbon and catalyst was reduced.     

Catalytic epoxidation of alkenes over supported manganese oxide with hydrogen peroxide: effect of supports and manganese loading

Manganese oxides supported on γ-Al₂O₃, amorphous SiO₂, MCM-41, and TiO₂ prepared by an impregnation method were used as heterogeneous catalysts for epoxidation of alkenes with 30 % H₂O₂ in the presence of NaHCO₃ aqueous solution. The effect of support and manganese loading on their activity was studied. The 1.3-MnO _x /γ-Al₂O₃ exhibited superior epoxidazing activity of styrene, compared with other supported MnO _x . Hydrogen temperature-programmed reduction, UV–vis and ESR analyses suggested that Mn²⁺ (catalytic activity species) dominated in 1.3 % MnO _x /γ-Al₂O₃ due to a strong interaction between MnO _x and γ-Al₂O₃. Recycling studies showed the catalyst was a heterogeneous one and retained its activity after recycling four times.     

Preparation and characterization of an active catalyst

As an active catalyst to promote thermolysis of ammonium perchlorate (AP), potassium lead hexanitrocobaltate(II) complex (K₂Pb[Co(NO₂)₆]) was synthesized by the direct deposition method and inverse microemulsion method. Its submicron, size, cube morphology, and crystal structure were investigated by SEM, TEM, and XRD analysis, respectively. Thermal decomposition of K₂Pb[Co(NO₂)₆] was studied by the TG/DSC-IR online system and XRD analysis. The catalyst was decomposed at about 300 °C; its gaseous products were NO₂, NO, and N₂O and its solid products were Pb₃O₄, Co₃O₄, PbO, CoO, and KNO₂. Because thermal decomposition of the catalyst was synchronous with low temperature decomposition of AP, thermolysis of AP was promoted remarkably. In particular, the gaseous products (NO _x ) could directly oxidize the absorbed NH₃. As a result, compared to the data of pure AP, the integral heat of AP added 3.0 wt% of the catalyst multiplied by 280 %, the maximum rate of heat release increased by 634 %. The decomposition of catalyzed AP ended at about 317 °C, at which only less than 30 % of pure AP decomposed.     

Mixed matrix vanadium oxide catalytic nanocomposite membrane for styrene oxidation

Mesoporous nanocomposite membranes with vanadium oxide–carbon nanotubes (V_xO_y-CNTs) embedded in γ-Al₂O₃ were successfully synthesized using the dip coating method. The membranes were evaluated for styrene oxidation to determine the optimum styrene conversion and benzaldehyde selectivity. Several factors that influence the preparation of defect-free coatings, such as the type of binder, the binder addition time and surface support treatments, were investigated. The physico-chemical permeation properties of the membranes were characterized using scanning electron microscope, transmission electron microscope (TEM), X-ray Diffraction XRD, Nitrogen adsorption (BET) and Thermogravimetric TGA. Response surface methodology (RSM) was used to investigate the effects of oxidant (H₂O₂) concentration, temperature, contact time and catalyst loading on styrene conversion and the selectivity of benzaldehyde. Based on the RSM analysis, the optimal oxidation conditions included a reaction temperature of 45 °C, a differential pressure of 1.5 bars, a molar ratio of H₂O₂: styrene of 1.5:1 and a catalyst loading of 30 %. These conditions resulted in the maximal styrene conversion of 25.6 and 84.9 % benzaldehyde selectivity.     

Synthesis and fabrication of (1 − x)ZnAl2O4–xSiO2 thin films to be applied as patch antennas

Zinc aluminate compounds have been dispersed in silica matrix prepared by sol-gel method with different compositions for (1 ? x)ZnAl₂O₄–xSiO₂. Continuous stirring of ethylene glycol solution contained zinc nitrate, aluminium nitrate and silicon dioxide to produces gel precursor. Structural and morphological studies of (1 ? x)ZnAl₂O₄–xSiO₂ thin films were examined by field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) analysis. The FESEM images showed the spherical structures with porosity for (1 ? x)ZnAl₂O₄–xSiO₂ thin films. XRD analysis indicated that the crystallite size for (1 ? x)ZnAl₂O₄–xSiO₂ increased from 39.79 to 44.34 nm. Fourier transform infra-red analysis showed that the existence of H₂O molecules and the presence of nitrate group within the samples. Dielectric permittivity (ε _r ) of (1 ? x)ZnAl₂O₄–xSiO₂ samples were measured within frequency range from 1 Hz to 1 MHz. The dielectric permittivity, ε _r decreased as frequency was applied to the sample. The performance of the patch antenna can be measured using return loss analysis. The highest result shows that the patch antenna resonated at frequency 3.46 GHz and gives ?14.25 dB return loss bandwidth.     

NO x storage properties of hollandite-type K x Ga x Sn8−x O16

The interaction of NO, NO+O₂ and NO₂ with K _x Ga _x Sn_8?x O₁₆ powder, including potassium ions, has been investigated by temperature-programmed desorption. In the case of NO+O₂, NO _x storage rapidly increased with increasing concentration of O₂ and the main peak has high intensity with a maximum around 600°C. These results indicate that K _x Ga _x Sn_8?x O₁₆ has NO _x storage ability with high thermal stability and is one of the promising catalysts for NO _x storage reduction.     

Promotion of Non-thermal Plasma on Catalytic Reduction of NOx by C3H8 Over Co/BEA Catalyst at Low Temperature

The effects of non-thermal plasma on selective catalytic reduction of NO_x by C₃H₈ (C₃H₈-SCR) over Co/BEA catalyst were investigated over a wide range of reaction temperatures (473–773 K). The significant synergistic effect between non-thermal plasma and catalytic reduction by C₃H₈ was exhibited at low temperatures from 473 to 673 K. The synergetic effect diminished with increasing temperature. The NO_x removal efficiency of non-thermal plasma facilitated C₃H₈-SCR hybrid system increased significantly with the increase in NO₂/NO ratio from 0.13 to 1.06 when the specific input energy increased from 0 to 136 J L^?1. The oxidation performance of NO to NO₂ was significantly enhanced by C₃H₈ in the plasma reactor. Results of CO₂/CO ratio and CO₂ selectivity suggested that adding non-thermal plasma improved CO₂ selectivity of C₃H₈-SCR. 200 ppm SO₂ slightly inhibited NO_x conversion of the non-thermal plasma facilitated C₃H₈-SCR hybrid system at below 673 K, whereas it exhibited no obvious effect at over 673 K. Non-thermal plasma was more selective toward NO oxidation than SO₂ oxidation in the presence of C₃H₈. The non-thermal plasma facilitated C₃H₈-SCR hybrid system could be used stably in durability tests with several hundreds ppm of SO₂.     

The Cu(I)- and HNO<Subscript>3</Subscript>-catalyzed oxidation of substituted toluenes to the benzoic acid based on NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> recycling

Based on the recycling of NO _x , the Cu(I)- and HNO₃-catalyzed oxidation of 2-chloro-4-(methylsulfonyl)toluene to 2-chloro-4-(methylsulfonyl)benzoic acid has been developed with an excellent yield of 84.2% and a purity of 99.7%. The optimized reaction conditions (160 °C, oxygen pressure 1.5 MPa, HNO₃ concentration 25 wt%, HNO₃: substrate 0.5:1) use 1.0 mol% CuI as catalyst. The dosage of HNO₃ in the new process is only 25% of the stoichiometric amount and 12.5% of the amount of the traditional process. The NO _x emission is 5% amount of the traditional process. The oxidation of several additional toluene derivatives with comparable yields demonstrates the generality to these reaction conditions.