Nitrate Species Research Articles

The Direct Partial Oxidation of Methane to Dimethyl Ether over Pt/Y2 O3 Catalysts Using an NO/O2 Shuttle.

Using a mixture of NO + O2 as the oxidant enabled the direct selective oxidation of methane to dimethyl ether (DME) over Pt/Y2 O3 . The reaction was carried out in a fixed bed reactor at 0.1 MPa over a temperature range of 275-375 °C. During the activity tests, the only carbon-containing products were DME and CO2 . The DME productivity (μmol gcat -1 h-1 ) was comparable to oxygenate productivities reported in the literature for strong oxidants (N2 O, H2 O2 , O3 ). The NO + O2 mixture formed NO2 , which acted as the oxygen atom carrier for the ultimate oxidant O2 . During the methane partial oxidation reaction, NO and NO2 were not reduced to N2 . In situ FTIR showed the formation of surface nitrate species, which are considered to be key intermediate species for the selective oxidation.

The Direct Partial Oxidation of Methane to Dimethyl Ether over Pt/Y2O3Catalysts Using an NO/O2Shuttle

AbstractUsing a mixture of NO + O2as the oxidant enabled the direct selective oxidation of methane to dimethyl ether (DME) over Pt/Y2O3. The reaction was carried out in a fixed bed reactor at 0.1 MPa over a temperature range of 275–375 °C. During the activity tests, the only carbon‐containing products were DME and CO2. The DME productivity (μmol gcat−1 h−1) was comparable to oxygenate productivities reported in the literature for strong oxidants (N2O, H2O2, O3). The NO + O2mixture formed NO2, which acted as the oxygen atom carrier for the ultimate oxidant O2. During the methane partial oxidation reaction, NO and NO2were not reduced to N2. In situ FTIR showed the formation of surface nitrate species, which are considered to be key intermediate species for the selective oxidation.

Characterization of the sensitive material for a resistive NOx gas dosimeter by DRIFT spectroscopy

Resistive NOx gas dosimeters measure continuously the integrated NOx concentration, i.e., the NOx dose. The impedance of potassium-manganese based NOx storage catalyst films decrease at 350 °C linearly with the NOx dose. The slope of the signal is proportional to the actual NOx concentration. The dosimeter principle is based on the sorption of NOx on the sensitive material. During NOx absence, the sensor signal remains constant, i.e. no desorption occurs. When a certain sorption state is reached, the sorbed species has to be desorbed thermally. To study the sorption processes on the NOx storage material, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) was used. Different material compositions were investigated by DRIFTS on powdered catalysts and operando DRIFTS on NOx dosimeters themselves. On Al2O3 (catalyst support) no NOx sorbs. Manganese addition (Mn-Al2O3) leads to few detectable nitrites on Aluminum-sites during NOx exposure. On Potassium-loaded alumina (K-Al2O3), nitrites and nitrates form. The comparison of NO2 and NO proves that NO2 is sorbed directly as nitrate species and NO cannot be strongly sorbed as nitrate on K-Al2O3. The complete material composition K/Mn-Al2O3 shows strong nitrate bands during NO and NO2 exposure. An interplay of potassium and manganese when forming nitrates was found. Operando DRIFTS confirms the direct relation between formed nitrates and complex impedance. Furthermore, it is proven that during thermal regeneration, sorbed nitrites and nitrates desorb completely and the sensor signal returns to its initial value. On the whole, the sorption behavior of the powders and the dosimeter behavior can be explained.

New insights into MnCe(Ba)Ox/TiO2 composite oxide catalyst: Barium additive accelerated ammonia conversion

MnCeOx/TiO2 has been widely used in selective catalytic reduction (SCR) of NOx at low temperature. However, it is often poisoned in the presence of water vapor and sulfur dioxide. In this work, the promotion mechanism of Ba modification was investigated. Results show that the doped BaO reacts with CeO2 and forms BaCeO3. This unique perovskite structure of BaCeO3 significantly enhances NO oxidation and NH3 activation of MnCeOx/TiO2 catalyst so that the NO conversion and the resistances to SO2 improve. It is found that Ba species obviously promotes the NO adsorption ability and improve the redox properties of MnCeOx/TiO2 catalyst. While the acid properties of the catalyst are inhibited by Ba modification and among which Lewis acid sites are dominant for both MnCeOx/TiO2 and MnCe(Ba)Ox/TiO2 catalysts. Furthermore, in situ DRIFT experiments reveal that the NO reduction upon MnCeOx/TiO2 and MnCe(Ba)Ox/TiO2 catalysts follows both E-R and L-H mechanisms, in which L-H is preferred. Ba species enhances the formation of active nitrate species, which accelerates the NO reduction through L-H mechanism. It is interesting that although Ba species weakens the NH3 adsorption, it induces the ammonia conversion to coordination ammonia, which in turn accelerates the catalytic reaction.

The direct molecular oxygen partial oxidation of CH4 to dimethyl ether without methanol formation over a Pt/Y2O3 catalyst using an NO/NO2 oxygen atom shuttle

The direct partial oxidation of CH4 to dimethyl ether (DME) on a Pt/Y2O3 catalyst was studied using a mixture of NO and O2 as the oxidant. The reaction was carried out in a fixed bed reactor at 0.1 MPa and 275–400 °C using 20% CH4, 1% NO, and 1% O2 in inert gas. No methanol was detected in the effluent and a contact time study demonstrated that DME was a primary product. The DME productivities were comparable to the oxygenate (methanol, formaldehyde) productivities obtained with stronger oxidants such as N2O, H2O2, and O3. The presence of Pt and the NO + O2 gas mixture was necessary for DME formation; without NO only CO2 was produced. During the methane partial oxidation reaction NO and NO2 were not reduced to N2, indicating that they worked as a shuttle to transfer oxygen from O2 to CH4. In situ Fourier transform infrared showed the formation of a bridged nitrate species on the Pt/Y2O3 catalyst which was associated with the reaction of CH4. A comprehensive study of this bridged nitrate species indicated they were formed on yttria sites close to Pt and were likely responsible for the formation of DME. The characterization of catalysts using X-ray diffraction showed that the Pt was highly dispersed and CO uptake measurements indicated a particle size of ~3 nm. Analysis by X-ray absorption fine structure measurements showed the presence of Pt oxide with Pt-O and Pt-Pt bonds.

Promotional role of Mo on Ce0.3FeOx catalyst towards enhanced NH3-SCR catalytic performance and SO2 resistance

The SO2 resistance of low temperature NH3-SCR in non-electric power industries has always been the bottleneck of this technology. Herein, a series of Mo-modified Ce0.3FeOx catalysts (MoaCe0.3FeOx) were synthesized by an easy to scale-up, environment-friendly two-step solid interface reaction and applied to the treatment of flue gas from the glass industry. Incorporation of Mo into Ce0.3FeOx catalyst could not only remarkably expand the operation temperature window in both low and high temperature regions, but also maintain high catalytic activity (>85% NOx conversion) under 65 h long stability test conditions even with the coexistence of H2O and SO2. The two-step interface reaction over MoaCe0.3FeOx provided an increased specific surface area and more amorphous structure, forming highly dispersed MoO3 species on the surface of the catalyst which serves as a sacrificial site to react with SO2. The process of redox reaction has been greatly improved due to the facilitated electron transfer between Fe2+ and Ce4+ as well as more oxygen vacancies and active oxygen. The enhanced presence of NH4+ could react with gaseous NO species via Eley–Rideal (E–R) mechanism due to the lack of nitrate species (greatly inhibited) while the NH4NO3 was not generated during the reaction which is responsible for excellent low temperature SCR performance as well as high N2 selectivity. Furthermore, less sulfate species and no bulk sulfate were formed, which indicated that the doping of Mo could effectively reduce the basic sites and delay the irreversible deactivation as well as reduce catalyst sulphation. The above features provide a strategy for design and development of non-vanadium-based catalysts with low temperature SO2 resistance in non-electric power industries with high NOx emission concentrations.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.

A comparative study of silver- and palladium-exchanged zeolites in propylene and nitrogen oxide adsorption and desorption for cold-start applications

Silver and palladium ion-exchanged BEA zeolites (Si/Al = 12.5) and silver ion-exchanged ZSM-5 zeolites (Si/Al = 15) were studied for their ability to adsorb and desorb propylene and NO under simulated diesel exhaust conditions. The adsorption experiment results demonstrated the excellent ability of bare BEA zeolites to adsorb propylene, but only a small amount of NO. The presence of H2O inhibited the adsorption of both C3H6 and NO. Ion-exchanging BEA zeolites with Ag (1.2 and 5.1 wt.% Ag/BEA) attenuated the inhibiting effect of H2O on C3H6 adsorption, while NO storage remained inhibited. Adsorption experiments indicated that C3H6 and NO competed with each other for Pd sites with C3H6 showing stronger adsorption compared to NO, whereas Ag sites preferentially adsorbed C3H6. DRIFTS data indicated the formation of nitrate, formate and acetate species on Ag and Pd, while C3H6 and NO adsorption was also observed on the zeolite hydroxyl groups in the absence of H2O. However, the C3H6 and NO adsorption on the zeolite hydroxyl groups was significantly inhibited in the presence of H2O. Additionally, nitrosyl, acrolein and carbonate species were formed over 1.0 wt.% Pd/BEA. The effluent analysis during the temperature-programmed desorption in the DRIFTS reactor revealed that adsorbed C3H6 and NO reacted during the release to form oxidation reaction byproducts. The 1.0 wt.% Pd/BEA zeolite showed the greatest oxidation ability during desorption with the majority of stored C3H6 converted to CO2.

MnO2-supported catalytic bodies for selective reduction of NO with NH3: Influence of NO2 and H2O

Catalytic bodies based on MnO2, TiO2 and sepiolite showed an improved behavior for selective reduction of NOx with NH3 at low temperatures. In this work, the influence of Mn %wt and NO2 and/or water vapor presence was assessed. The materials were prepared by wet equilibrium impregnation of the pre-shaped support. All the catalysts exhibited the characteristic diffraction peaks of TiO2-anatase, hexagonal MnO2and anhydrous sepiolite. According to SEM-EDX, MnO2 was preferentially deposited over TiO2.The optimum nominal content of Mn was 7.5 %wt, what may be related to an appropriate particle dispersion that confers the suitable properties: lower acid strength, and better redox properties with improved reducibility. This catalyst was then evaluated under NO2 and/or H2O presence. NO2 improved the catalytic response and the best result was obtained with 1:1 NO2:NO ratio showing 90 % NOx conversion and 97 % N2 selectivity at very low temperature, 110 °C. A higher amount of NH4NO3 seems to be formed with the increase in the NO2/NO ratio causing a modification of N2 selectivity.Although water presence affected the performance, mainly at low temperatures, the catalyst showed good resistance to water vapor at temperatures above 180 °C maintaining good activity (90 % of NO conversion and 96 % of N2 selectivity). When NO2 was co-added to the feed, a beneficial effect was again observed with 91 % of NOx and 95 % of N2 selectivity converted at 143 °C.At low temperatures, deactivation has to do with a competitive effect of H2O with NOx towards the adsorption centers, which decreases the concentration of nitrate species adsorbed on the surface. However, the adsorption of ammonia was less affected.7.5 Mn catalyst is a highly efficient system to work in real conditions, where there is water in gas stream. In this situation, co-feeding NO2 improves activity.

PM dispersion during stable winter episodes in tehran and effect of governmental emission regulations

Tehran is one of the most polluted cities in Middle East which during winter extremely high levels of particulate matter (PM) occurs due to frequent stable weather episodes. This study aims to identify major sources of PM and quantify effectiveness of possible control measures and strategies during these episodes. The Brute Force Method (BFM) with Community Multiscale Air Quality model (CMAQ) was implemented to estimate the contributions from major local anthropogenic sources on PM levels. In this regard several scenarios including the effect of existing governmental policies and regulations to upgrade vehicles emission standards were investigated. Emission due to the existing condition and future scenarios were estimated and effect of them on concentrations were modeled. Major local contributors were found to be transportation, energy and residential sources with the contributions of 64%, 15%, and 11%, respectively. The major governmental regulation to upgrade vehicles standard could led up to average of 35% PM concentration reduction during these stable weather episode. It is estimated that a set of scenarios could result in a goal of about 10% reduction in overall pollutant emissions, including both primary PM and precursor pollutants such as sulfate, nitrate and ammonium species. Our results show primary pollutants reduction led to average 8.4% reduction in aerosol levels, whereas precursor gaseous reduction could led to less than 1% PM concentration reduction. The results emphasize the need for control strategies focusing on primary particulate emission and transportation source.

Advancing Target Identification of Nitrated Phospholipids in Biological Systems by HCD Specific Fragmentation Fingerprinting in Orbitrap Platforms.

Nitrated phospholipids have recently been detected in vitro and in vivo and associated with beneficial health effects. They were identified and quantified in biological samples by lipidomics methodologies using liquid chromatography-collision-induced dissociation (CID) tandem mass spectrometry (MS/MS) acquired with the linear ion trap mass spectrometer. Only a few studies have used higher-energy collision dissociation (HCD)-MS/MS in high-resolution Orbitraps to characterize nitrated phosphatidylserines and nitrated cardiolipins, highlighting the marked differences in the fragmentation patterns when using CID or HCD fragmentation methods. In this study, we aimed to evaluate the fragmentation of nitrated phosphatidylcholine and nitrated phosphatidylethanolamine species under HCD-MS/MS. We studied the effect of normalized collision energy (NCE) in the fragmentation pattern to identify the best acquisition conditions and reporter ions to detect nitrated phospholipids. The results showed that the intensity of the typical neutral loss of nitrous acid (HNO2) diminishes with increasing NCE, becoming non-detectable for a higher NCE. Thus, the loss of HNO2 could not be the most suitable ion/fragment for the characterization of nitrated phospholipids under HCD. In HCD-MS/MS new fragment ions were identified, corresponding to the nitrated fatty acyl chains, NO2-RCOO−, (NO2-RCOOH-H2O + H)+, and (NO2-RCOOH + H)+, suggested as potential reporter ions to detect nitrated phospholipids when using the HCD-MS/MS lipidomics analysis.

In-Situ DRIFT Spectroscopy on a Resistive NOx Dosimeter – How Can the Non-Linear Electrical Behavior be Explained?

Introduction The detection of low NOx concentrations is still on focus for air-quality monitoring. The direct detection of the total dose of NOx is beneficial since the air pollution limits are given as hourly and annual mean values. A gas dosimeter for direct detection of the dose of NOx was presented in [1,2]. In the so-called sorption phase, NOx molecules are adsorbed on the functional film and the electrical properties, e.g. the resistance, change. During this phase, the characteristic sensor curve corresponds to the correlation between NOx dose and resistance change. The sensor curve is linear until a certain loading state is reached. As soon as the characteristic curve gets non-linear, described often as saturation of the NOx adsorption [1], the regeneration of the sensor is necessary. During the thermally induced regeneration, the sorbed NOx species is desorbed from the surface. Afterwards, a new sorption cycle can begin.For further understanding of the sensing mechanism and the effects of non-linearity, NOx dosimeters are investigated by in-situ DRIFT (Diffuse Reflectance Infrared-Fourier-Transformed)-Spectroscopy [3]. The electrical sensor signal and the formation of adsorbed species are investigated in-situ directly on the dosimeter. The non-linear behavior of the electrical properties occurring at a certain sensor signal will be investigated at various film thicknesses [4] and will be combined with the sorption properties of the material. Materials and Methods As functional material potassium-permanganate impregnated on lanthanum-stabilized alumina powder (K/Mn-La-Al2O3) [1] is investigated. It is applied by screen-printing on an alumina substrate equipped with interdigitated Au electrodes and fired at 650 °C. Different layer thicknesses of the functional film are achieved by several screen printing steps. The sensors are mounted in a gas purgeable in-situ DRIFTS cell (see Fig. 1) [3] and heated by an integrated platinum heating structure to 350 °C. They are exposed to synthetic air (20 % O2 and 2 % humidity in N2 balance) and varying ppb NOx concentrations are added. The NOx concentration is analyzed by a chemiluminescence detector (CLD). The electrical behavior of the sensor is measured by impedance spectroscopy (f = 200 Hz, U eff = 200 mV) and the resistance R can be calculated since the R||C equivalent circuit is valid. The sensor signal is defined as the relative resistance change (R-R 0/R 0), with R 0 being the resistance in base gas and R the resistance during NOx exposure. At the same time, Drift-spectra of the sensor are measured by a FTIR Spectrometer and the absorbance -log(I/I 0), with the intensity I 0 in base gas and the intensity I during NOx adsorption, is calculated. The sensors are regenerated by heating up to 650 °C. Results and Discussion An in-situ DRIFTS result during exposure to three peaks of 50 ppb NOx with NOx pauses in-between is shown in Fig. 2. The NOx dose in ppm∙s is calculated by integrating the CLD NOx signal. The dose increases linearly during NOx exposure and stays constant during dosing pauses. The sensor signal shows the same behavior: ΔR/R 0 increases linearly when 50 ppb NOx are present and stays constant during NOx absence. The calculated absorbance shows a clear peak at a wave number of 1370 cm-1 occurring during NOx exposure. It can be attributed to the formation of nitrates on potassium sites of K/Mn-La-Al2O3 and is characteristic for the sorption phase [3]. The calculated peak area A E of this nitrate peak is presented in Fig. 2, too. The peak area A E and therefore the amount of formed nitrates increases linearly during NOx addition and remains constant during NOx pauses. The electrical properties of the dosimeter can be related directly to the NOx dose and to the formed nitrates. One important point is, that all curves increase linearly during NOx exposure and no saturation effects can be observed for the sensor signal and the nitrate formation. In Fig. 3, the sensor is exposed to three peaks of 390 ppb NOx. ΔR/R 0 gets non-linear after reaching 40 %, the sensor seems to saturate. The slope during NOx exposure is non-linear and the signal in NOx pauses decreases. In contrast, A E behaves almost linear. It is assumed that the electrically observed non-linearity cannot be explained by a saturation of the adsorption capability of K/Mn-La-Al2O3. It seems that the NOx adsorption capability is not exhausted, but the electrical properties show a saturation effect. Conclusions The results show that the sensor behaves like a dosimeter with linear characteristics between NOx dose, sensor signal and formed nitrate species until a certain sensor signal of around 40 % is reached. At higher relative resistance changes, the electrical signal becomes non-linear, whereas the adsorption capability itself, i.e. the nitrate formation, remains linear and the NOx adsorption on K/Mn-La-Al2O3 is not saturated. This behavior will be investigated by in-situ DRIFTS in dependence on the film thickness.

A Chemiresistor Sensor Based on Zn2SnO4-RGO Hybrids for High Selectivity to ppb-level Oxidizing Gas Under Humidity Conditions

Highly selective oxidizing gas sensors are of great importance for environmental pollution monitoring. In this work, Zn2SnO4 nanoparticles (NPs) and reduced graphene oxide (Zn2SnO4-RGO) hybrids were developed as a high-performance gas sensing materials for the detection of ppb-levels of oxidizing gases (NO2 and O3). The structural, morphological and compositional properties of the Zn2SnO4-RGO hybrids were systematically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), which demonstrated the successful anchoring of Zn2SnO4 NPs on RGO nanosheets. The obtained Zn2SnO4-RGO hybrids exhibited outstanding sensing performance for detecting oxidizing gases (NO2 and O3) with very low cross sensitivities to reducing gases, such as C2H5OH, CH3COCH3 and CO (Fig. 1a). The Zn2SnO4-RGO based sensors exhibited high response values of up to 3.50 for 500 ppb NO2, which is higher than that for detection of 500 ppb O3 (1.78) at 30 °C under 50% relative humidity (RH). Moreover, the NO2 sensing performances of Zn2SnO4-RGO-based sensors were investigated under various RH. In all cases, the sensors based on RGO and Zn2SnO4-RGO hybrids presented p-type behavior. In Fig. 1b and c, the sensors based on Zn2SnO4-RGO hybrids also exhibited high response values of up to 3.62 for 1 ppm NO2 at 50°C in 80% RH, which is much higher than that of pure RGO (1.31). The excellent sensing performances are mainly ascribed to the synergetic effect of Zn2SnO4 NPs and RGO. Furthermore, the surface reaction between Zn2SnO4-RGO hybrids and NO2 can be concluded from Operando diffuse reflectance infrared Fourier transformed spectroscopy (Operando DRIFT). NO2 is a highly electrophilic molecule and can directly capture free electrons from Zn2SnO4-RGO hybrids. The formation of NO3 -, NO and NO2 - can contribute to the decreased resistance of the sensor based on Zn2SnO4-RGO hybrids by loss of electrons as described in the chemical reaction [1,2], as shown in Fig.1d. The DRIFT spectrum of Zn2SnO4-RGO hybrids show absorption peaks at 1367 cm−1, 1535 cm−1 and 1735 cm−1 (Fig. 1e),which could be assigned to the n3 stretching vibration of nitrate species (NO3 -) [3], the NO vibration band of the bridging bidentate nitrate [4] and the formation of nitrite species (NO2 -) [5], respectively. This work is meaningful to design RGO-based sensors for detecting oxidizing gases.

Effective Model of NOx Adsorption and Desorption on PtPd/CeO2-ZrO2 Passive NOx Adsorber

An effective model for describing NOx adsorption and desorption on a PtPd/CeO2-ZrO2 passive NOx adsorber is presented. The kinetic parameters are evaluated from the available experimental data obtained during NOx adsorption/desorption experiments including CO2 and H2O in the feed, performed at 80, 120 and 160 °C both in the presence and in the absence of reducing agents (CO or C2H4 ). The model describes the temperature dependence of the NOx adsorption rate and capacity, the impact of CO, and dynamics of the NOx desorption events. The model predicts formation of nitrites, nitrates, and additional storage enabled in the presence of CO. Thermal decomposition of the stored NOx species results in two main desorption peaks. Nitrites are desorbed at lower temperatures while nitrates are thermally more stable. The evolution of nitrite and nitrate species in the model corresponds with the measured DRIFTS spectra of the catalyst surface. The presence of CO significantly improves the rate of NOx adsorption and storage efficiency at low temperatures, most probably due to reduction of oxidic Pt and Pd nanoparticles. The developed model captures well the observed trends and can be utilized for simulations of PNA performance under real operating conditions.

An efficient and sulfur resistant K-modified activated carbon for SCR denitrification compared with acid- and Cu-modified activated carbon

In this work and for the first time, an alkali metal potassium (K) as a promoter was loaded on an activated carbon (AC) to be used for selective catalytic reduction of NO from industrial flue gas. The denitrification activity of K-modified AC samples was investigated and compared with those of acid- and Cu-modified AC samples. The three modifications can enhance the denitrification activity of AC samples. To investigate the enhanced mechanisms of denitrification and SO2 resistance, various AC samples were characterized by SEM, EDX, XRF, ICP, XRD, N2 physisorption, H2-TPR, XPS, in situ DRIFTS and TPD. For the acid modification, the content of phenolic hydroxyl increases and then promotes the adsorption of NH3. For the loading of Cu, the appearance of Cu2+/Cu+ sites with high catalytic activity promotes NH3 and NO adsorption and changes the reaction pathway. For the loading of K, the adsorption capacity for NO increases nearly 12 times higher than that on Raw-AC, of which 85.0% is chemical adsorption. Moreover, three kinds of active nitrate species additionally forms, including nitro compounds, monodentate nitrate and nitrous oxide, which promote the denitrification reaction path. AC-Cu has poor sulfur resistance due to the sulfation of Cu, while AC-K show good sulfur resistance due to the enhanced adsorption of NO. The catalytic dissociation activity of N2O on AC-K makes the formation and decomposition of N2O into a dynamic equilibrium. As a result, AC-K has a high N2 selectivity, while AC-Cu has poor N2 selectivity.

Source assessment of atmospheric fine particulate matter in a Chinese megacity: Insights from long-term, high-time resolution chemical composition measurements from Shanghai flagship monitoring supersite

Here we present a long-term, hourly resolution dataset (from January 2014 to April 2015) of secondary inorganic aerosol (SIA) matter, organic matter (OM) and black carbon (BC) as PM2.5 chemical components in China. Seasonally differentiated weekly diurnal profiles of major particulate species were investigated in conjunction with potential source contribution function (PSCF) analysis. The average concentration of PM2.5 was 48.3 ± 35.1 μg m−3, in which OM was the major constituent (29.7 ± 13.9%), followed by sulfate (25.1 ± 8.1%), nitrate (18.5 ± 8.3%), ammonium (13.3 ± 3.8%), and other trace species (6.8 ± 4.0%). Interestingly, unlike other PM species, OM concentrations kept very similar level among different seasons, indicating on-road traffic is a stable source of PM2.5. Besides, a persistently strong particulate OM pollution belt was found along the lower reaches of Yangtze River. Significant enhancement of SIA (mainly nitrate) was coincided with high PM2.5 mass loading. Source apportionment were conducted and found the overwhelming dominance of long-range transport of the pollutants from north China. Using a case study, we further integrate Weather Research and Forecasting (WRF) meteorological modeling and lidar observation to better understand the evolution process of a typical pollution episode. Our assessment of the extremely large datasets derived from Shanghai supersite demonstrated the online instrumentation as a robust and credible alternative to filter-based sampling techniques for long-term PM2.5 monitoring and characterization in heavily polluted areas.

Effect of external axial magnetic field on a helium atmospheric pressure plasma jet and plasma-treated water

Potential in biomedical-related applications by atmospheric pressure plasma-treated water gradually increased recently. In order to enhance the generation of reactive species in atmospheric pressure plasma in regards to liquid treatment, this study aims to investigate the effect of external axial magnetic field on a helium atmospheric pressure plasma jet (APPJ) and plasma-irradiated water. Magnetic field strength up to 2.0 T was generated by an electromagnet in Helmholtz configuration. The dielectric barrier discharge-based APPJ is driven by 4.4 slm helium and sinusoidal 30 kHz, 10 k signals. Plasma was mainly characterized by optical emission where vibrational and rotational temperature was estimated by nitrogen second positive system, and electron temperature and density by emission intensity line ratio method. Representative reactive species of nitrite, nitrate, and hydrogen peroxide concentration in the plasma-treated water were also quantified. Results of vibrational temperature and electron density showed a first drop then rise trend which partially corresponds to the reactive species in the plasma-treated water. No significant changes were found in rotational temperature, while electron temperature monotonically increased with the magnetic field.

Selective catalytic reduction of NO by methane over Co,H-SSZ-13 catalysts: Types and catalytic functions of active Co sites

Co-SSZ-13 zeolite catalysts were prepared by solid-state ion exchange with CoCl2 salt for the selective catalytic reduction of NO with methane (CH4/NO–SCR). Fresh catalysts contained hard-to-reduce lattice Co2+/[Co-OH]+ ions and showed activity proportional to the concentration of these species. The NO conversion was accompanied by steam-generating methane oxidation. Under the arising hydrothermal conditions, a fraction of Co ions transformed into Co-oxo species especially in catalysts of high Co content (Co/AlF > 0.3), resulting in boosted activity in NO2-forming catalytic NO oxidation. The increased NO2 concentration brought about higher concentration of surface cobalt nitrate species responsible for the rate-determining methane activation, so the overall rate of the NO–SCR reaction was also accelerated. Steam admixed to the feed decreased the conversion of methane more significantly than that of NO. Its observed high hydrothermal stability renders the Co-SSZ-13 catalyst a very promising candidate for the CH4/NO–SCR reaction.

Fischer-Tropsch synthesis: Direct cobalt nitrate reduction of promoted Co/Al2O3 catalysts

Direct reduction of cobalt nitrate versus conventional calcination/reduction treatment was conducted using alumina with identical methodology as previously applied to SiO2 and TiO2. Similar BET surface areas, pore volumes and pore size distributions were obtained for the activated calcined and uncalcined catalysts indicating no significant difference in morphological properties. However, the reducibility slightly increases and Co crystallite size is smaller for activated uncalcined samples. Reduction phenomena were analyzed by TPR-MS and TPR-EXAFS/XANES. Combining these techniques allows an explanation of the complex phenomena occurring during the direct reduction of cobalt nitrate, as both nitrate decomposition and cobalt oxide reduction are involved. Cobalt nitrate species are converted to CoOx intermediates. These species are oxidized by NOX (from nitrate decomposition) to Co3O4 spinel, which is converted to CoO prior to Co0 formation. Noble metals (Pt, Re, Ru and Ag) improve cobalt oxide reducibility, especially for the final reduction step (i.e., CoO to Co0). The effect of direct nitrate reduction on FT activity was investigated using a 1 L CSTR. Activated unpromoted and Pt-promoted uncalcined catalysts achieved higher initial and steady-state CO conversions in comparison to the corresponding calcined catalysts. The best performance was achieved with direct reduction of uncalcined 0.5 %Pt-25 %Co/Al2O3.

In-situ DRIFTs study on different exposed facets of VOx-MnOx/CeO2 catalysts for low-temperature NH3-SCR

In order to achieve the low-temperature (200–250°C) NH3-SCR, highly dispersed VOx-MnOx/CeO2 catalysts with different exposed facets were produced. The NH3-SCR performance results indicate that the NO conversion over VOx-MnOx/CeO2-R with preferentially exposed {110} facets can achieve NO conversion >95% over a wide temperature span of 220–330°C. From the in-situ DRIFTs, gaseous NH3 and NO are favorable to be absorbed on the surface of the VOx-MnOx/CeO2-R catalyst with preferentially exposed {110} facets, which improves the efficiency of NO conversion. The mechanism study via in-situ DRIFTs demonstrates that the well dispersed vanadium species on CeO2{110} absorb NH3 to generate NH3(L) and NH+ 4(B) species, which in turn become highly reactive toward bridging nitrate and bidentate nitrate species to form N2 and H2O according to the Langmuir-Hinshelwood mechanism.