Nitrate Species Research Articles

Improvements to the representation of BVOC chemistry–climate interactions in UKCA (v11.5) with the CRI-Strat 2 mechanism: incorporation and evaluation

Abstract. We present the first incorporation of the Common Representative Intermediates version 2.2 tropospheric chemistry mechanism, CRI v2.2, combined with stratospheric chemistry, into the global chemistry–climate United Kingdom Chemistry and Aerosols (UKCA) model to give the CRI-Strat 2 mechanism. A rigorous comparison of CRI-Strat 2 with the earlier version, CRI-Strat, is performed in UKCA in addition to an evaluation of three mechanisms, CRI-Strat 2, CRI-Strat and the standard UKCA chemical mechanism, StratTrop v1.0, against a wide array of surface and airborne chemical data. CRI-Strat 2 comprises a state-of-the-art isoprene scheme, optimized against the Master Chemical Mechanism v3.3.1, which includes isoprene peroxy radical isomerization, HOx recycling through the addition of photolabile hydroperoxy aldehydes (HPALDs), and isoprene epoxy diol (IEPOX) formation. CRI-Strat 2 also features updates to several rate constants for the inorganic chemistry, including the reactions of inorganic nitrogen and O(1D). The update to the isoprene chemistry in CRI-Strat 2 increases OH over the lowest 500 m in tropical forested regions by 30 %–50 % relative to CRI-Strat, leading to an improvement in model–observation comparisons for surface OH and isoprene relative to CRI-Strat and StratTrop. Enhanced oxidants also cause a 25 % reduction in isoprene burden and an increase in oxidation fluxes of isoprene and other biogenic volatile organic compounds (BVOCs) at low altitudes with likely impacts on subsequent aerosol formation, atmospheric lifetime, and climate. By contrast, updates to the rate constants of O(1D) with its main reactants relative to CRI-Strat reduces OH in much of the free troposphere, producing a 2 % increase in the methane lifetime, and increases the tropospheric ozone burden by 8 %, primarily from reduced loss via O(1D)+H2O. The changes to inorganic nitrogen reaction rate constants increase the NOx burden by 4 % and shift the distribution of nitrated species closer to that simulated by StratTrop. CRI-Strat 2 is suitable for multi-decadal model integrations and the improved representation of isoprene chemistry provides an opportunity to explore the consequences of HOx recycling in the United Kingdom Earth System Model (UKESM1). This new mechanism will enable a re-evaluation of the impact of BVOCs on the chemical composition of the atmosphere and further probe the feedback between the biosphere and the climate.

Molecular and Functional Characteristics of DNA Polymerase Beta-Like Enzymes From Trypanosomatids.

Trypanosomatids are a group of primitive unicellular eukaryotes that can cause diseases in plants, insects, animals, and humans. Kinetoplast genome integrity is key to trypanosomatid cell survival and viability. Kinetoplast DNA (kDNA) is usually under attack by reactive oxygen and nitric species (ROS and RNS), damaging the DNA, and the cells must remove and repair those oxidatively generated lesions in order to survive and proliferate. Base excision repair (BER) is a well-conserved pathway for DNA repair after base damage, single-base loss, and single-strand breaks, which can arise from ROS, RSN, environmental genotoxic agents, and UV irradiation. A powerful BER system has been described in the T. cruzi kinetoplast and it is mainly carried out by DNA polymerase β (pol β) and DNA polymerase β-PAK (pol β-PAK), which are kinetoplast-located in T. cruzi as well as in other trypanosomatids. Both pol β and pol β-PAK belong to the X-family of DNA polymerases (pol X family), perform BER in trypanosomatids, and display intrinsic 5-deoxyribose phosphate (dRP) lyase and DNA polymerase activities. However, only Pol β-PAK is able to carry out trans-lesion synthesis (TLS) across 8oxoG lesions. T. cruzi cells overexpressing pol β are more resistant to ROS and are also more efficient to repair 8oxoG compared to control cells. Pol β seems to play a role in kDNA replication, since it associates with kinetoplast antipodal sites in those development stages in trypanosomatids which are competent for cell replication. ROS treatment of cells induces the overexpression of pol β, indicating that plays a role in kDNA repair. In this review, we will summarize the main features of trypanosomatid minicircle kDNA replication and the biochemical characteristics of pol β-like enzymes and their involvement in BER and kDNA replication. We also summarize key structural features of trypanosomatid pol β compared to their mammalian (human) counterpart.

Simultaneous Photocatalytic Abatement of NO and SO2: Influence of the TiO2 Nature and Mechanistic Insights

Background: TiO2 is currently being incorporated into several construction materials, such as cement and asphalt because this photocatalyst can act as a passive system to reduce the concentration of typical urban pollutants like NOx and SO2 under solar illumination. Objective: In order to get further insights on the possible influence of the interaction between common pollutants, the present work investigates the mechanism of NOx photo-oxidation in the presence of SO2 traces over TiO2 samples of different textural and morphological characteristics. Methods: The performance for the photo-oxidation of NOx and SO2 in a dry air stream over TiO2 samples, both commercial and lab-prepared by hydrothermal and thermal methods, was evaluated by means of FTIR analyses of the gas phase. These materials were characterized by XRD, N2 adsorption isotherms, and DR UV-vis spectroscopy. Mechanistic studies were performed by in situ DRIFT under UV irradiation. Results: Photocatalytic tests showed a very efficient removal of the two selected pollutants using most of the TiO2 samples. In the case of SO2, elimination of these molecules is due not only to photocatalytic oxidation but also to a significant extent, to adsorption. Although in shorter periods, no byproducts are generated, following irradiation for several hours, the production of NO2 progressively increases and reaches 100 % selectivity over some photocatalyst. In situ DRIFTS analyses show the evolution of the surface composition and reveal the formation of the different types of surface nitrates with different symmetry. Under these operating conditions, a minor amount of sulfates are also formed. Conclusions: The presence of a low concentration of SO2 does not appear to be detrimental for NO removal. NO2 formation is delayed on the TiO2 samples with high specific surface area, which also tend to be more active. The spectroscopic results confirm the involvement of surface hydroxyls in the formation of adsorbed nitrate species.

Towards improved models for indoor air chemistry: A Monte Carlo simulation study

Model predictions are sensitive to a number of complex and often coupled input parameters. Some of these parameters have a wide range of acceptable values from literature and therefore choosing the appropriate value is non-trivial. In this paper, we use the INdoor Detailed Chemical Model (INDCM) to perform a Monte Carlo analysis, in which a wide but realistic range of model input parameter values is stochastically varied over 1000 model runs. The model output defines the likely range of the model performance, and directly correlates input parameter values with predicted indoor air species concentrations. The air exchange rate or the ozone deposition velocity onto internal materials such as painted walls, control the predicted concentrations of ozone, hydroxyl and peroxy radicals and peroxyacetyl nitrate species for our study conditions. The transmission of UV light from outdoors showed the strongest Spearman's rank positive correlation coefficients with predicted hydroxyl radical (0.92), and organic nitrate (0.95) concentrations. The deposition rate of ozone onto painted walls shows the strongest negative correlations with 4-oxopentanal (−0.86) and acetic acid (−0.83). Reducing the uncertainty around transmission of UV light indoors and ozone deposition rates onto surfaces reduces the model uncertainty by up to 70–80% for ozone and hydroxyl radical concentrations. Some species concentrations showed complex relationships with the various input parameters. For instance, maximum isoprene concentrations decreased with air exchange rate, but minimum isoprene concentrations were largely invariant. Emissions from human breath ensured that isoprene was always present in our model runs. However, its removal rate varied with the air exchange rate, which affected the concentrations of ozone and hydroxyl radicals (which can both chemically remove isoprene), and the direct removal rate by ventilation. Finally, we used our results to understand the 95% confidence bounds around our median predicted concentrations. For hydroxyl radicals, these were ±60% of the median value.

Methane selective oxidation on metal oxide catalysts at low temperatures with O2 using an NO/NO2 oxygen atom shuttle

Methane oxidation using O2 over transition metal oxides often requires severe conditions (>500 °C) to achieve detectable conversion. In this study, NO was used to transfer oxygen atoms from O2, through the facile gas-phase formation of NO2 at moderate conditions (0.1 MPa and 300–400 °C), to oxidize methane over silica-supported transition metal oxides (VOx, CrOx, MnOx, NbOx, MoOx, and WOx). In situ infrared spectroscopy measurements indicated that the reaction likely proceeded by the formation of surface monodentate nitrate intermediates. These nitrate species were formed by the interaction between adsorbed NO2 and the supported metal oxides. During the reaction, the oxides of vanadium, molybdenum, and tungsten formed formaldehyde and CO2, whereas the oxides of chromium, manganese, and niobium produced only CO2. These results are consistent with the known hydrocarbon oxidation chemistry of the metal oxides. Contact time measurements on VOx/SiO2 indicated that formaldehyde was a primary product and CO2 was the final product; conversely, analogous measurements on MnOx/SiO2 showed that CO2 was the sole product. The formaldehyde production rate on VOx/SiO2, MoOx/SiO2, and WOx/SiO2, based on surface sites measured by high temperature oxygen chemisorption, compared favorably to oxygenate production rates for stronger oxidants (N2O and H2O2) reported in the literature.

Isotopic study of the influence of oxygen interaction and surface species over different catalysts on the soot removal mechanism

In order to improve the catalytic formulations for soot removal in after-treatment emission control technologies for gasoline and diesel engine vehicle, an isotopic study was approached using transitory labeled oxygen response method over model catalysts that allows the unraveling of soot oxidation mechanism. Ce-based materials promote oxygen exchange associated with the high population of lattice oxygen species (O2-) denoted as OI type. The incorporation of praseodymium produces a Pr3+ enrichment that decrease the energy for oxygen release and increase oxygen mobility through surface and subsurface oxygen centers (OII type) depending on the synthesis procedure. For PtBaK catalyst, OIII species are responsible for oxygen exchange. Gas-solid reaction between soot and gas phase molecular oxygen is responsible for direct uncatalyzed soot oxidation. For ceria containing catalysts, low-temperature soot removal takes place through the intervention of lattice atomic species and superoxide species. For DPNR model catalyst, PtBaK/Al2O3, the soot elimination occurs with the intervention of OIII type centers. In the presence NO, the assisted and cooperative mechanism due to NO2 and the intervention of the adsorbed nitrate species on the trimetallic catalyst enhances soot removal capacity.

Effects of atmosphere composition during direct ultraviolet-light patterning of solution-deposited In2O3 thin film transistors

Sol-gel synthesis is widely used to fabricate metal oxide thin films by solution, but it requires high-temperature thermal annealing to fully convert precursors to metal oxides. Exposure to Ultraviolet (UV) light before thermal annealing of precursor films has been shown to reduce the conversion temperature, with the added benefits of film patterning when done through a shadow mask and improved device performance. However, the mechanism by which UV exposure under different atmospheric compositions affects the properties of metal oxide films after thermal annealing has not been investigated. Here, we control the atmospheric composition during UV-patterning—prior to high-temperature thermal annealing—of In2O3 sol-gel films which serve as the semiconductor in thin-film transistors. Despite all films being annealed at 250°C in air after UV patterning, films exposed to UV under oxygen-containing atmospheres have higher metal-oxygen-metal bonding and exhibit higher transistor mobility compared to the films exposed to UV under N2 atmosphere. The origin of the effect of atmospheric composition on mobility is studied through X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy and is revealed to be the result of the reformation of the nitrate species in the films under more oxidizing atmospheres during UV exposure. These nitrates can be completely removed by thermal annealing, facilitating more complete metal-oxygen-metal bond formation, which is reflected in higher OI XPS signal and transistor mobility. In contrast, films processed under N2 atmosphere during UV exposure contain nitrite species that cannot be removed by thermal annealing, resulting in less metal-oxygen-metal bond formation and lower mobility.

Characterizations of a Plasma-Water System Generated by Repetitive Microsecond Pulsed Discharge with Air, Nitrogen, Oxygen, and Argon Gases Species

A non-thermal plasma-water system using a microsecond pulsed high-voltage power supply was investigated with air, nitrogen, oxygen, and argon gas feedings individually. Optical emission spectroscopy (OES) was utilized to characterize the primary active species inside the plasmas generated by different gas feedings. The OES method was also employed to estimate the neutral gas and electron temperatures. The pH and the oxidation-reduction potential (ORP) of plasma-activated water (PAW) were measured in the liquid phase. An ion chromatography system (ICS) was employed to present the PAW activity, such as nitrite and nitrate species. Moreover, hydrogen peroxide as a secondary active species inside the activated water, generated by the gases mentioned above, was measured by potassium permanganate titration. It was found that the gas species have a noticeable effect on the pH level as well as the ORP of PAW. In the cases of argon and oxygen plasmas, the pH level of PAW does not change significantly. In contrast, the pH values of PAW generated by air and nitrogen plasmas decline sharply during the treatment time. Moreover, the gas species have a significant impact on the concentrations of nitrite, nitrate, and hydrogen peroxide generated in PAW. The activated water generated by oxygen plasma provides the highest level of hydrogen peroxide. Although the consumed power of argon plasmas was half of the other plasma sources, it provides relatively high hydrogen peroxide contents compared to the nitrogen and air plasmas.

Acid modification enhances selective catalytic reduction activity and sulfur dioxide resistance of manganese-cerium-cobalt catalysts: Insight into the role of phosphotungstic acid

Improving the SO2 resistance of catalysts is crucial to driving commercial applications of Mn-based catalysts. In this work, the phosphotungstic acid (HPW) modification strategy was applied to improve the N2 selectivity, SO2 and H2O resistance of the Mn-Ce-Co catalyst, and further, the mechanism of HWP modification on enhanced catalytic performance was explored. The results showed that HPW-Mn-Ce-Co catalyst exhibits higher NOx conversion (~100% at 100–250 °C) and N2 selectivity (exceed 80% at 50–350 °C) due to more oxygen vacancies, greater surface acidity, and lower redox capacity. In situ diffused reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) reveal that HPW changed the reaction path of Mn-Ce-Co catalysts, promoted the adsorption and activation of NH3, and reduced the effect of SO2 on the active bidentate nitrate species, and thereby exhibiting good SO2 resistance. X-ray photoelectron spectrometer (XPS) and NH3 temperature-programmed desorption of (NH3-TPD) results show that HPW can inhibit the formation of metal sulfate, and SO2 can be combined with Ce species more easily. The generated Ce2(SO3)3 can not only protect Mn species but also increase the acid sites and weaken the poisoning effect of metal sulfate. This study provides a simple design strategy for the catalyst to improve the low-temperature catalytic performance and toxicity resistance.

Improved NOx Reduction over Phosphate-Modified Fe2O3/TiO2 Catalysts Via Tailoring Reaction Paths by In Situ Creating Alkali-Poisoning Sites.

The deactivation issue arising from alkali poisoning over catalysts is still a challenge for the selective catalytic reduction of NOx by NH3. Herein, improved NOx reduction in the presence of alkaline metals over phosphate-modified Fe2O3/TiO2 catalysts has been originally demonstrated via tailoring the reaction paths by in situ creating alkali-poisoning sites. The introduction of phosphate results in the partial formation of iron phosphate species and makes the catalyst to mainly exhibit the characteristics of FePO4, which is responsible for the widened temperature window and enhanced alkali resistance. The tetrahedral [FeO4]/[PO4] structures in iron phosphate act as the Brønsted acid sites to increase the catalyst surface acidity. In addition, the formation of an Fe-O-P structure enhances the redox ability and increases surface adsorbed oxygen. Furthermore, the created phosphate groups (PO43-) serving as alkali-poisoning sites preferentially combine with potassium so that iron species on the active sites are protected. Therefore, the enhanced NH3 species adsorption capacity, improved redox ability, and active nitrate species remaining in the phosphate-modified Fe2O3/TiO2 catalyst ensure the de-NOx activity after being poisoned by alkali metals through the Langmuir-Hinshelwood reaction pathway. Hopefully, this novel strategy could provide an inspiration to design novel catalysts to control NOx emission with extraordinary resistance to alkaline metals.

Oxygen effect in NO direct decomposition over K/Co-Mg-Mn-Al mixed oxide catalyst–Temperature programmed desorption study

• The role of oxygen in NO decomposition was studied over Co-Mg-Mn-Al mixed oxide. • Transition metals in octahedral coordination represent sites for NO chemisorption. • Potassium ensures NO oxidation to surface nitrite intermediates. • Oxygen inhibition was ascribed to formation of stable surface nitrate species. Co-Mg-Mn-Al mixed oxide with or without K was prepared and characterized by XPS, TPR H 2 , TPD NO, TPD O 2 and TPD NO+O 2 . NO decomposition was performed over catalyst activated in different atmosphere (N 2 , He, O 2 ). Presence of oxygen during activation changed the course of surface stabilization but did not affect NO conversion achieved at steady state. O 2 desorbed as a reaction product does not affect the reaction rate for NO inlet concentration of 400 - 8000 ppm, but presence of O 2 in inlet gas mixture (0.05 - 3 mol.%) has significant inhibiting effect. Transition metals in octahedral coordination represent sites for NO chemisorption, while potassium ensures NO oxidation to surface nitrites, which are indispensable reactive species. Oxygen desorption was the slowest reaction step, while N 2 desorption was fast. Oxygen inhibition was ascribed to oxidation of NO* species on the octahedral Co 3+ and Mn 3+ to more stable surface nitrates making NO* species as limiting reactant.

Effects of Effluent Stream Composition and Competing Reactions Effect on Wastewater Nitrate Reduction in a Photoelectrochemical Device

More than 80% of nitrogen-contaminants are present in the form of nitrates in point sources of wastewater, including municipal wastewater effluents, ion-exchange brines, low-level nuclear wastes and in power generation. Wastewater nitrates represent an untapped source for the recovery of nutrients, value-added chemicals, and energy. Nitrates can be reduced to form ammonia, which can be used as a fertilizer or fuel, and nitrous oxide, which is a powerful oxidizer for the combustion and supercharging applications. Depending upon the source of the wastewater, the concentration of nitrates present in these streams can vary significantly. Ion-exchange brines and low-level nuclear wastes have large nitrate concentrations, on the order of > 0.1 M, whereas municipal and power generation effluents are more dilute (0.1 mM). However, the effect of varying contaminant concentrations and the competing redox reactions have not been quantified for these systems.In this study, a photoelectrochemical device is proposed to transform wastewater nitrates into ammonia, coupled with water oxidation. We expand on a previously developed numerical model to include the effects of the reacting nitrate species concentrations and the competing redox reactions on the solar-to-chemical efficiencies and nitrogen-removal rates. Notably, we implemented an equivalent circuit modeling approach to account for the influences of the competing reactions and the concentration-dependent mass-transfer limiting current densities. Model results predict that for a single light-absorber and a nitrate concentration of 100 mM, the optimal solar-to-chemical efficiency is 7% and the nitrogen recovery rate (as NH3) is 260 gN m-2 day-1. Oxygen reduction is more dominant as a competing reaction than hydrogen reduction at the cathode. However, this reduction is mass-transfer limited even while assuming an air-saturated (1 atm) device and therefore didn’t impact the performance significantly. Modeling results are complemented by experimental measurements of the effects of nitrate concentrations on the operating current densities and the rates of product formation with copper and platinum electrodes at the cathode and anode respectively.

Explanation of the Non-Linear Electrical Behavior of a Resistive NOx Dosimeter By Operando DRIFT Spectroscopy

Introduction To detect low NOx concentrations is still a 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 [1,2,3]. In the sorption phase, NOx molecules are adsorbed on the functional film and the electrical resistance changes. During this phase, the correlation between NOx dose and resistance change 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], sensor regeneration is necessary. During thermal regeneration, the sorbed NOx species is desorbed from the surface, and a new sorption cycle can begin.To further understand the sensing mechanism and the effects of non-linearity, NOx dosimeters are investigated by operando DRIFT spectroscopy [4]. The electrical sensor signal and the formation of adsorbed species are investigated operando on the dosimeter. The non-linear behavior of the electrical properties occurring at a certain sensor signal are investigated at various film thicknesses [5] and are combined with the sorption properties. Materials and Methods Potassium-permanganate impregnated on lanthanum-stabilized alumina powder (K/Mn-La-Al2O3) [1] serves as the functional material. 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 films are achieved by several screen-printing steps. The sensors are mounted in a gas purgeable operando DRIFTS cell (Fig. 1) [4] 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). NOx concentrations (ppb-range) are added and validated by a chemiluminescence detector (CLD). The sensor resistance is derived by impedance spectroscopy (f = 200 Hz, U eff = 200 mV) from an R||C equivalent circuit. 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. Simultaneous DRIFT spectra are obtained 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 operando 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 derived from the integration of the CLD NOx signal. The dose increases linearly during NOx exposure and remains 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 nitrate formation on potassium sites of K/Mn-La-Al2O3 and is characteristic for the sorption phase [4]. The calculated peak area A E of this nitrate peak is shown in Fig. 2, too. 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 resistance shows 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 operando DRIFTS in dependence on the film thickness.

Micro-structured Cu-ZSM-5 catalyst on aluminum microfibers for selective catalytic reduction of NO by ammonia

Selective catalytic reduction of NOx with NH3 (NH3-SCR) is one of the most efficient technologies to remove NOx emissions. The copper ion-exchanged zeolites with broad temperature windows and high N2 selectivity are very promising for this process. In this work, we synthesized a series of microfibrous-structured Cu-ZSM-5/Al-fiber catalysts for SCR reaction by changing the Si/Al molar ratios. The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NH3 adsorption results show that the Cu-ZSM-5/Al-fiber catalysts with higher Si/Al molar ratios have higher NH3 adsorption capacity. The subsequent NO adsorption results show that the amount of adsorbed bridged nitrates species is in accordance with the enhanced NOx degradation activity. At moderate temperature, Cu-ZSM-5/Al-fiber catalyst shows better NH3-SCR performance under higher gas hourly space velocity (GHSV), indicating microstructured Cu-ZSM-5 catalysts are more active at high-throughout conditions due to the enhanced mass transfer.

Impact of NOx and NH3 addition on toluene oxidation over MnOx-CeO2 catalyst

An increasing number of industries remove toluene from flue gas by the existing NH3-selective catalytic reduction (NH3-SCR) units. A thorough probe into the impact of NOx and NH3 addition on toluene oxidation is imperative but still lacks a unified understanding. In this work, NH3-SCR reactants are found to inhibit the toluene oxidation process over the MnOx-CeO2 catalyst below 200 °C. The competitive adsorption between NH3-SCR reactants and toluene, the NO2 adsorption state, and carbon deposition are emphasized to play important roles in this deactivation. Within the NO2 adsorption states, only the adsorbed NO2 can enhance the toluene oxidation. The formed nitrate species (NO3-) on the surface is inactive. NO2 adsorption is the weakest among the reactants with the smallest adsorption energy of −0.42 eV, restricting its promotion on toluene oxidation. NO and N2O are both demonstrated to be inefficient to oxidize toluene. Meanwhile, MnOx-CeO2 catalyst suffers from serious acetonitrile and benzonitrile poisoning. The amount of nitrile species accounts for ~95% of total carbon deposition, while no simple substance carbon (C) can be generated from CO disproportionation. Special care should be considered towards the formation of environmentally hazardous benzamide in the off-gas from the simultaneous NOx and toluene removal process.

Unexpected increase in low-temperature NH3-SCR catalytic activity over Cu-SSZ-39 after hydrothermal aging

The control of nitrogen oxides (NOx) from heavy-duty diesel vehicles is becoming increasingly urgent due to its detrimental effects on the environment. Cu-SSZ-39, with its exceptional NH3-SCR activity and hydrothermal stability, has attracted more and more attention in the field of diesel vehicle emission control. In this work, an unexpected phenomenon was observed for Cu-SSZ-39 after hydrothermal aging. Generally, the hydrothermal aging process causes deterioration of the catalytic performance of catalysts. However, a remarkable increase in low-temperature NH3-SCR catalytic activity was observed in Cu-SSZ-39 after it was exposed to 850 ℃ hydrothermal aging conditions for 16 h. EPR, DRIFTS, H2-TPR, UV–vis and XANES were utilized to detect the changes in Cu species. It was determined that a portion of the Cu2+ ions near double six-membered rings (d6r) transformed into CuxOy species after hydrothermal treatment. These CuxOy species facilitated the production of nitrate species which were critical intermediates in the NH3-SCR process, resulting in an increase in low-temperature catalytic activity.

Comparative Numerical Study of PM2.5 in Exit-and-Entrance Areas Associated with Transboundary Transport over China, Japan, and Korea

We report the results of year-long PM2.5 (particulate matter less than 2.5 µm in diameter) simulations over Northeast Asia for the base year of 2013 under the framework of the Long-range Transboundary Air Pollutants in Northeast Asia (LTP) project. LTP is a tripartite project launched by China, Japan, and Korea for cooperative monitoring and modeling of the long-range transport (LRT) of air pollutants. In the modeling aspect in the LTP project, each country’s modeling group employs its own original air quality model and options. The three regional air quality models employed by the modeling groups are WRF-CAMx, NHM-RAQM2, and WRF-CMAQ. PM2.5 concentrations were simulated in remote exit-and-entrance areas associated with the LRT process over China, Japan, and Korea. The results showed apparent bias that remains unexplored due to a series of uncertainties from emission estimates and inherent model limitations. The simulated PM10 levels at seven remote exit-and-entrance sites were underestimated with the normalized mean bias of 0.4 ± 0.2. Among the four chemical components of PM2.5 (SO42−, NO3−, organic carbon (OC), and elemental carbon (EC)), the largest inter-model variability was in OC, with the second largest discrepancy in NO3−. Our simulation results also indicated that under considerable SO42− levels, favorable environments for ammonium nitrate formation were found in exit-and-entrance areas between China and Korea, and gas-aerosol partitioning for semi-volatile species of ammonium nitrate could be fully achieved prior to arrival at the entrance areas. Other chemical characteristics, including NO3−/SO42− and OC/EC ratios, are discussed to diagnose the LRT characteristics of PM2.5 in exit-and-entrance areas associated with transboundary transport over China, Japan, and Korea.

PSMA-Targeted Therapeutics: A Tale About Law and Economics.

1482 Introduction: Thorium-227 (227Th) offers a longer half-life, 18.7 days, than other Targeted Alpha Therapy (TAT) agents currently being evaluated clinically such as actinium-225 (t1/2= 9.9 days) and astatine-211 (t1/2= 7.2 hours). This physical characteristic favors its use with biomolecules that have slower pharmacokinetics like monoclonal antibodies. Utilizing 227Th is also advantageous due to the 5 alpha emissions occurring during decay. Hydroxypyridinonate (HOPO) derivatives have been shown to be effective decorporation agents for actinides owing to their hard oxygen donor atoms and strong complexation. Therefore, utilizing these molecules as chelators for potential nuclear medicine agents should allow for radiometals to be effectively sequestered by the ligand. The biological chemistry of thorium is similar to calcium in that the unbound radiometal tends to localize in bone. Consequently, it is pivotal to establish a thorium complex that possesses high stability and thwarts bone uptake. Methods: 227Th received from Oak Ridge National Laboratory was purified from its daughters on a MP1 BioRad resin. The purified thorium was then complexed to the 3,4,3-(LI-1,2-HOPO) ligand by adding the radiometal to a 0.1 M acetate solution containing the ligand (0.08 mM) for 1 hour at 50 °C and was purified using Chelex resin column. The biological distribution of the 227Th-HOPO complex was compared to the “bare” 227Th (227Th-nitrate in 0.1 M HCl/ 5 M acetate solution) in male CD1 mice (n=3) injected with 1 μCi of either construct. At the prescribed time points (15 m, 1 h, 3 h, 6 h, 24 h, 3 d, 7 d, 14 d, 21 d, and 28 d) the organs of interest were harvested and counted using a gamma counter calibrated for 227Th. The biodistribution data was used to calculate the residence time in each organ and was then entered into the OLINDA software to produce the effective dose in rem/mCi. Terminal SPECT/CT imaging of 227Th-nitrate and 227Th-HOPO was obtained in representative mice at 20 min post injection of 15 µCi. Results: The biodistribution results for the 227Th-nitrate species shows clearance through the kidneys (%ID/g = 26.3 ±5.3, 1-day p.i.). Also, substantial localization in the bone as expected is observed. At 15 minutes p.i. the %ID/g in the bone is 7.1 ± 3.9 and gradually increases through the 7-day timepoint, %ID/g- 28.8 ± 12.8, ending the study 28 days p.i with an accumulation of 33.6 ± 17.5 %ID/g. Conversely the 227Th-HOPO species appears to clear through the hepatobiliary tract with accumulation in the gallbladder (54.2 ± 27.7 %ID/g, 1-hour p.i.) and the intestines (29.5 ± 2.2 %ID/g, 1-hour p.i.). Most significantly the bone localization is relatively low and remains constant, approximately 1.5 %ID/g, through all timepoints. The low bone uptake is also reflected in the dosimetry where the effective dose in the bone for 227Th-nitrate and 227Th-HOPO is 1680 rem/mCi and 192 rem/mCi respectively. The effective dose of the 227Th-HOPO species is at least 1 order of magnitude lower than the nitrate species in all organs. Conclusion: We have shown that the 227Th-HOPO complex is stable in vivo and facilitates rapid elimination from the body which results in lower dose to organs, specifically the bone. The stability of the 227Th-HOPO complex suggests that it has potential for use in TAT. Acknowledgments: This work has been funded by BNL LDRD 21-00 and Seed grant under B&R code YN0100000. We would also like to thank all those who assisted with the project.

Cerium-tungsten oxides supported on activated red mud for the selective catalytic reduction of NOx

Activated red mud (RM) has been proved to be a promising base material for the selective catalysis reduction (SCR) of NOx. The inherent low reducibility and acidity limited its low–temperature activity. In this work, molybdenum oxide, tungsten oxide, and cerium oxide were used to reconfigure the redox sites and acid sites of red mud based catalyst. When activated red mud was reconfigured by cerium-tungsten oxide (Ce–W@RM), the NOx conversion kept above 90% at 219–480 °C. The existence of Ce3+/Ce4+ redox electron pairs provided more surface adsorbed oxygen (Oα) and served as a redox cycle. Positive interactions between Ce, W species and Fe oxide in red mud occurred, which led to the formation of unsaturated chemical bond and promoted the activation of adsorbed NH3 species. WO3 and Ce2(WO4)3 (formed by solid–state reaction between Ce and W species) could provide more Brønsted acid sites (W–O modes of WO3, WO or W–O–W modes of Ce2(WO4)3). CeO2 species could provide more Lewis acid sites. The Langmuir–Hinshelwood (L-H) routes and Eley-Rideal (E-R) routes occurred in the low-temperature SCR reaction on the Ce–W@RM surface. NH4+ species on Brønsted acid sites, NH3 species on Lewis acid sites, bidentate nitrate and bridging nitrate species were key active intermediates species.

Role of silicotungstic acid on the catalytic performance over CeO2‐HSiW catalysts for selective catalytic reduction of NOx with NH3

The CeO2 modified by silicotungstic acid (impregnation method [SiW/CeO2] and one pot method [CeO2‐Si‐W]) was investigated in the NH3‐SCR reaction. The surface nitrate species and surface acid sites were improved by the introduction of silicotungstic acid into CeO2, which stopped forming stable nitrate, and then improved the N2 selectivity. The interaction between Ce and W species existed and caused the formation of Ce2(WO4)3 at CeO2‐Si‐W, resulting in the abundance of unsaturated W=O, which contributed to the generation of Brønsted acid sites and was responsible for the superior SCR performance. Thus, CeO2‐Si‐W exhibited the best NOx conversion and nearly 100% NOx conversion was obtained at 225–450°C.