Showing papers on "NOx published in 2016"

Impact of nitrogen oxides on the environment and human health: Mn-based materials for the NOx abatement

Abstract: An overview is given of the impact of nitrogen oxides on the environment and human health including the low-temperature selective catalytic reduction of NOx by ammonia (NH3-SCR) over manganese-based materials. The review gives a comprehensive overview of NH3-SCR chemistry including the impacts of NOx, stringent regulations, limitations on NOx emissions and aspects of the reaction mechanism over Mn-based catalysts using isotopic labeled and in situ FT-IR studies. The review attempts to correlate catalyst activity and stability with the acidity, manganese oxidation state, surface texture, and structural morphology. Prospectively, low-temperature SCR of NOx over Mn-based catalysts opens up novel views to mitigate NOx and help us design the next generation industrial catalysts.

Manganese oxide-based catalysts for low-temperature selective catalytic reduction of NOx with NH3: A review

Abstract: Selective catalytic reduction (SCR) technology has been widely used for the removal of NOx from flue gas. However, it is still a challenge to develop novel low-temperature catalysts for SCR of NOx, especially at temperatures below 200 °C. This paper reviewed the recent progress on the Mn-based catalysts for low-temperature SCR de-NOx with NH3. Catalysts were divided into four categories, single MnOx, Mn-based multi-metal oxide, Mn-based multi-metal oxide with support, and Mn-based monolith catalyst. In the section of single MnOx, the effects of several factors, such as Mn oxidation state, crystallization state, specific surface area and morphology on catalytic activity were systematically reviewed. In the section of multi-metal oxide catalysts, the various roles played by the components of catalysts were intentionally summarized from four aspects, improving de-NOx efficiency, enhancing N2 selectivity, improving resistance to SO2 and H2O, extending operation temperature window, respectively. Moreover, the newly emerging morphology-dependent nanocatalysts were highlighted at the end of this section. In the introduction of supported metal oxide catalysts, the effects of supports were systematically analyzed according to their types, such as Al2O3, TiO2, carbon materials, etc. Considering the actual operation, Mn-based monolith catalysts were also introduced with regard to monolith supports, such as ceramics, metal wire mesh, etc. Subsequently, NH3-SCR mechanisms at low temperature, including E-R and L-H mechanisms, were discussed. At last, the perspective and the future direction of low-temperature SCR of NOx were proposed.

Selective Transformation of Various Nitrogen-Containing Exhaust Gases toward N2 over Zeolite Catalysts.

Abstract: In this review we focus on the catalytic removal of a series of N-containing exhaust gases with various valences, including nitriles (HCN, CH3CN, and C2H3CN), ammonia (NH3), nitrous oxide (N2O), and nitric oxides (NOx), which can cause some serious environmental problems, such as acid rain, haze weather, global warming, and even death. The zeolite catalysts with high internal surface areas, uniform pore systems, considerable ion-exchange capabilities, and satisfactory thermal stabilities are herein addressed for the corresponding depollution processes. The sources and toxicities of these pollutants are introduced. The important physicochemical properties of zeolite catalysts, including shape selectivity, surface area, acidity, and redox ability, are described in detail. The catalytic combustion of nitriles and ammonia, the direct catalytic decomposition of N2O, and the selective catalytic reduction and direct catalytic decomposition of NO are systematically discussed, involving the catalytic behaviors as ...

Why do models overestimate surface ozone in the Southeast United States

Abstract: . Ozone pollution in the Southeast US involves complex chemistry driven by emissions of anthropogenic nitrogen oxide radicals (NOx ≡ NO + NO2) and biogenic isoprene. Model estimates of surface ozone concentrations tend to be biased high in the region and this is of concern for designing effective emission control strategies to meet air quality standards. We use detailed chemical observations from the SEAC4RS aircraft campaign in August and September 2013, interpreted with the GEOS-Chem chemical transport model at 0.25° × 0.3125° horizontal resolution, to better understand the factors controlling surface ozone in the Southeast US. We find that the National Emission Inventory (NEI) for NOx from the US Environmental Protection Agency (EPA) is too high. This finding is based on SEAC4RS observations of NOx and its oxidation products, surface network observations of nitrate wet deposition fluxes, and OMI satellite observations of tropospheric NO2 columns. Our results indicate that NEI NOx emissions from mobile and industrial sources must be reduced by 30–60 %, dependent on the assumption of the contribution by soil NOx emissions. Upper-tropospheric NO2 from lightning makes a large contribution to satellite observations of tropospheric NO2 that must be accounted for when using these data to estimate surface NOx emissions. We find that only half of isoprene oxidation proceeds by the high-NOx pathway to produce ozone; this fraction is only moderately sensitive to changes in NOx emissions because isoprene and NOx emissions are spatially segregated. GEOS-Chem with reduced NOx emissions provides an unbiased simulation of ozone observations from the aircraft and reproduces the observed ozone production efficiency in the boundary layer as derived from a regression of ozone and NOx oxidation products. However, the model is still biased high by 6 ± 14 ppb relative to observed surface ozone in the Southeast US. Ozonesondes launched during midday hours show a 7 ppb ozone decrease from 1.5 km to the surface that GEOS-Chem does not capture. This bias may reflect a combination of excessive vertical mixing and net ozone production in the model boundary layer.

Enhanced photocatalytic oxidation of NO over g-C3N4-TiO2 under UV and visible light

Abstract: In this work, graphitic carbon nitride-titanium dioxide (g-C3N4-TiO2) was successfully prepared by a facile calcination route utilizing commercial P25 and melamine as the precursors. The as-prepared g-C3N4/TiO2 photocatalysts were characterized systematically to elucidate their morphological structure and physico-chemical properties. The photocatalytic performance of g-C3N4-TiO2 composites was investigated for the removal of NOx in air. At the optimal g-C3N4 content (∼15 wt%, labeled as M400), the conversion of NOx was 27%, which is higher than that of pure P25 (17%) and g-C3N4 (7%) under visible light. The activity of M400 was also enhanced under UV light. However, a mechanically mixed g-C3N4 and TiO2 sample (with the content of g-C3N4 the same as M400, labeled as M0 + g-C3N4) did not improve the conversion of NOx. Therefore, the interaction of g-C3N4 and P25 is important for the activity. EPR results indicated that O2− is the main active species for NO oxidation to NO3− under visible and UV light, which is responsible for the difference in activity between M400 and M0 + g-C3N4. The present study can improve our understanding of NO removal on the photocatalyst surface and the mechanism for the activity enhancement by the formation of g-C3N4-TiO2.

MOF-74 as an Efficient Catalyst for the Low-Temperature Selective Catalytic Reduction of NOx with NH3.

Abstract: In this work, Mn-MOF-74 with hollow spherical structure and Co-MOF-74 with petal-like shape have been prepared successfully via the hydrothermal method. The catalysts were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry–mass spectrum analysis (TG-MS), N2 adsorption/desorption, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). It is found that MOF-74(Mn, Co) exhibits the capability for selective catalytic reduction (SCR) of NOx at low temperatures. Both experimental (temperature-programmed desorption, TPD) and computational methods have shown that Co-MOF-74 and Mn-MOF-74 owned high adsorption and activation abilities for NO and NH3. The catalytic activities of Mn-MOF-74 and Co-MOF-74 for low-temperature denitrification (deNOx) in the presence of NH3 were 99% at 220 °C and 70% at 210 °C, respectively. It is found that the coordinatively unsaturated metal sites (CUSs) in M-MOF-74 (M = Mn and Co) played important role...

Organic nitrate chemistry and its implications for nitrogen budgets in an isoprene- and monoterpene-rich atmosphere: constraints from aircraft (SEAC 4 RS) and ground-based (SOAS) observations in the Southeast US

Abstract: . Formation of organic nitrates (RONO2) during oxidation of biogenic volatile organic compounds (BVOCs: isoprene, monoterpenes) is a significant loss pathway for atmospheric nitrogen oxide radicals (NOx), but the chemistry of RONO2 formation and degradation remains uncertain. Here we implement a new BVOC oxidation mechanism (including updated isoprene chemistry, new monoterpene chemistry, and particle uptake of RONO2) in the GEOS-Chem global chemical transport model with ∼ 25 × 25 km2 resolution over North America. We evaluate the model using aircraft (SEAC4RS) and ground-based (SOAS) observations of NOx, BVOCs, and RONO2 from the Southeast US in summer 2013. The updated simulation successfully reproduces the concentrations of individual gas- and particle-phase RONO2 species measured during the campaigns. Gas-phase isoprene nitrates account for 25–50 % of observed RONO2 in surface air, and we find that another 10 % is contributed by gas-phase monoterpene nitrates. Observations in the free troposphere show an important contribution from long-lived nitrates derived from anthropogenic VOCs. During both campaigns, at least 10 % of observed boundary layer RONO2 were in the particle phase. We find that aerosol uptake followed by hydrolysis to HNO3 accounts for 60 % of simulated gas-phase RONO2 loss in the boundary layer. Other losses are 20 % by photolysis to recycle NOx and 15 % by dry deposition. RONO2 production accounts for 20 % of the net regional NOx sink in the Southeast US in summer, limited by the spatial segregation between BVOC and NOx emissions. This segregation implies that RONO2 production will remain a minor sink for NOx in the Southeast US in the future even as NOx emissions continue to decline.

Significant increase of summertime ozone at Mount Tai in Central EasternChina

Abstract: . Tropospheric ozone (O3) is a trace gas playing important roles in atmospheric chemistry, air quality and climate change. In contrast to North America and Europe, long-term measurements of surface O3 are very limited in China. We compile available O3 observations at Mt. Tai – the highest mountain over the North China Plain – during 2003–2015 and analyze the decadal change of O3 and its sources. A linear regression analysis shows that summertime O3 measured at Mt. Tai has increased significantly by 1.7 ppbv yr−1 for June and 2.1 ppbv yr−1 for the July–August average. The observed increase is supported by a global chemistry-climate model hindcast (GFDL-AM3) with O3 precursor emissions varying from year to year over 1980–2014. Analysis of satellite data indicates that the O3 increase was mainly due to the increased emissions of O3 precursors, in particular volatile organic compounds (VOCs). An important finding is that the emissions of nitrogen oxides (NOx) have diminished since 2011, but the increase of VOCs appears to have enhanced the ozone production efficiency and contributed to the observed O3 increase in central eastern China. We present evidence that controlling NOx alone, in the absence of VOC controls, is not sufficient to reduce regional O3 levels in North China in a short period.

Effect of nanofluid additives on performances and emissions of emulsified diesel and biodiesel fueled stationary CI engine: A comprehensive review

Abstract: This research paper reports the results of various researches carried out up to 2015 on the performance and emission characteristics of compression ignition (CI) engine using nano particles additives in diesel, biodiesel and water emulsified fuels. There are two methods of reducing the exhaust gas emission of the CI engine. First method is to reduce the emissions by using exhaust gas treatment devices like catalytic converter, diesel particulate filter. However, use of these devices affects the performance of CI engine. Second method to reduce emissions and improve performance of CI engine is the use of fuel additive. Main pollutants of CI engine are oxide of nitrogen (NOx) and particulate matter (PM). However, it is difficult to control NOx and PM simultaneously. Many researchers report that the best method to control the emissions and improve the performance is the use of nano particles additives and water emulsified fuels. This research paper also reports the biodiesel fuel as an alternative to diesel fuel by using various nano particle additives. Comparative studies of effects on various properties of diesel and biodiesel fuels without/with water contents and nano particles additives by previous researchers are done. Most of the researchers reported improved performance and reduction in emission characteristics with dosing of nano particles additives in diesel and biodiesel.

Low Temperature NO Storage of Zeolite Supported Pd for Low Temperature Diesel Engine Emission Control

Abstract: Pd supported on various zeolites has been found to be able to adsorb NO at temperatures below 200 °C with high storage efficiency and capacities in a gas feed which simulate diesel engine exhaust conditions. Highly dispersed Pd at the exchange sites of the zeolites are believed to be the active site for the low temperature NO storage. Different framework structures of the zeolites significantly affect not only the NO storage capacity but also the NOx desorption temperature. These materials show high potential for low temperature NOx emission control.

Abatement technologies for high concentrations of NOx and SO2 removal from exhaust gases: A review

Abstract: Nitrogen oxides (NOx) and sulfur dioxide (SO2) are the main air pollutants. Both of them are mostly formed during the process of fossil fuels combustion, while some processes generate very high concentrations of NOx and SO2. In this review the authors describe and summarize the currently used methods and the new techniques that are under investigation. They also give a detailed description of the regulations and sources of SO2 and NOx emissions, as well as their impact on human health and the environment. The authors focus primarily on the environmental protection technologies used in power plants, vehicles, ships, and the chemical industry.

Mechanism of arsenic poisoning on SCR catalyst of CeW/Ti and its novel efficient regeneration method with hydrogen

Abstract: Deactivation and regeneration of arsenic are studied on novel CeO2–WO3/TiO2 for selective catalytic reduction (SCR) of NOx with NH3. It is found that the activity and N2 selectivity of poisoned catalyst are inhibited immensely at the entire temperature range. The fresh, poisoned and regenerated catalysts are characterized using XRD, BET, XPS, H2-TPR, NH3-TPD, NO + O2-TPD, in situ Raman and in situ DRIFTS. The characterization results indicate that the poisoning of arsenic decrease BET surface area, surface Ce3+ concentration and the amount of Lewis acid sites and adsorbed NOx species but increase the reducibility and number of chemisorbed oxygen species. According to the in situ DRIFTS investigations, the adsorption of surface-adsorbed NH3 and NOx species is suppressed at low temperature, while the reactivity between surface-adsorbed NH3 and NO is prohibited at high temperature. A novel H2 reduction regeneration not only effectively removes arsenic from the poisoned catalysts, but promotes surface Ce3+/Ce4+ ratio and form new NOx adsorptive sites. However, it also affects the chemical properties of catalyst such as crystalline Ce2(WO4)3 forming, surface active oxygen species raise and loss of Bronsted acid sites.

Promotional effects of zirconium doped CeVO4 for the low-temperature selective catalytic reduction of NOx with NH3

Abstract: In this work, we developed a novel zirconium doped CeVO 4 to form Ce 1− x Zr x VO 4 ( x = 0.05, 0.10, 0.15, 0.20, 0.30, 0.50, 0.70, 0.80) solid solution as a low-temperature catalyst for the selective catalytic reduction (SCR) of NO x with NH 3 . The optimized catalysts showed excellent performance at low temperature. The light-off temperature (the temperature at which the conversion of NO reaches 50%) was down to about 125 °C, while the temperature window (the NO conversion is above 80%) ranged from 150 to 375 °C. The selectivity was kept close to 100% during the whole temperature range. Furthermore, the catalysts also exhibited good H 2 O/SO 2 durability and fascinating performance at high gas hourly space velocity of 400,000 h −1 . Hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, ammonia and nitrogen oxides temperature-programmed desorption and in-situ diffuse reflectance infrared Fourier transform experiments were performed to study the influence of Zr doping on the SCR performance. It was found that the introduction of Zr in CeVO 4 with a proper amount could significantly increase the surface area, oxidative ability, active oxygen species and especially surface acid sites of the catalysts, which were beneficial to the promotion of SCR performance.

Rapid cycling of reactive nitrogen in the marine boundary layer

Abstract: Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.

Prospects of 2nd generation biodiesel as a sustainable fuel - Part 2: Properties, performance and emission characteristics.

Abstract: Increased global warming and declining fossil fuel reserves have stimulated the researchers to look for new sources of fuel, which should be renewable, locally available and environmentally benign. Biodiesel has been receiving increasing attention because of the relevance it gains from the rising petroleum price and its environmental advantages. This paper reviews and highlights several aspects of non-edible oils which are termed as 2nd generation biodiesel, such as the biodiesel’s physico-chemical properties, and its effect on engine performances and emissions. In addition, the effect of biodiesel on engine power, fuel economy and emissions including regulated and non-regulated, and the corresponding effect factors are surveyed and analysed in detail. It is found from the review that the biodiesel fuel properties vary depending on the sources of feedstocks which have considerable impact on engine performances and emissions characteristics. The use of biodiesel leads to the substantial reduction in key pollutants namely particulate matter (PM), hydrocarbon (HC), and carbon monoxide (CO) emissions accompanying with the imperceptible power loss, slight increase in fuel consumption and slight increase in NOx emission on conventional diesel engines with no or fewer modification. This review introduces a potential guideline on further research for improving engine performance and emission characteristics using different 2nd generation biodiesels and their blends. The study provides a comparative baseline to make an easy comparison among the biodiesels in respect of fuel properties, engine performance and emission features.

Low temperature plasma-catalytic NOx synthesis in a packed DBD reactor: Effect of support materials and supported active metal oxides

Abstract: The direct synthesis of NOx from N2 and O2 by non-thermal plasma at an atmospheric pressure and low temperature is presented, which is considered to be an attractive option for replacement of the Haber-Bosch process. In this study, the direct synthesis of NOx was studied by packing different catalyst support materials in a dielectric barrier discharge (DBD) reactor. The support materials and their particle sizes both had a significant effect on the concentration of NOx. This is attributed to different surface areas, relative dielectric constants and particles shapes. The nitrogen could be fixed at substantially lowered temperatures by employing non-thermal plasma-catalytic DBD reactor, which can be used as an alternative technology for low temperature synthesis. The γ-Al2O3 with smallest particles size of 250–160 μm, gave the highest concentration of NOx and the lowest specific energy consumption of all the tested materials and particle sizes. The NOx concentration of 5700 ppm was reached at the highest residence time of 0.4 s and an N2/O2 feed ratio of 1 was found to be the most optimum for NOx production. In order to intensify the NOx production in plasma, a series of metal oxide catalysts supported on γ-Al2O3 were tested in a packed DBD reactor. A 5% WO3/γ-Al2O3 catalyst increased the NOx concentration further by about 10% compared to γ-Al2O3, while oxidation catalysts such as Co3O4 and PbO provided a minor (∼5%) improvement. These data suggest that oxygen activation plays a minor role in plasma catalytic nitrogen fixation under the studied conditions with the main role ascribed to the generation of microdischarges on sharp edges of large-surface area plasma catalysts. However, when the loading of active metal oxides was increased to 10%, NO selectivity decreased, suggesting possibility of thermal oxidation of NO to NO2 through reaction with surface oxygen species.

Tropospheric ozone change from 1980 to 2010 dominated by equatorward redistribution of emissions

Abstract: Ozone is an air pollutant and a greenhouse gas. Simulations with a global chemistry transport model reveal that the spatial distribution of ozone precursor emissions dominates the global ozone burden, and that emissions in the tropics matter most. Ozone is an important air pollutant at the surface1, and the third most important anthropogenic greenhouse gas in the troposphere2. Since 1980, anthropogenic emissions of ozone precursors—methane, non-methane volatile organic compounds, carbon monoxide and nitrogen oxides (NOx)—have shifted from developed to developing regions. Emissions have thereby been redistributed equatorwards3,4,5,6, where they are expected to have a stronger effect on the tropospheric ozone burden due to greater convection, reaction rates and NOx sensitivity7,8,9,10,11. Here we use a global chemical transport model to simulate changes in tropospheric ozone concentrations from 1980 to 2010, and to separate the influences of changes in the spatial distribution of global anthropogenic emissions of short-lived pollutants, the magnitude of these emissions, and the global atmospheric methane concentration. We estimate that the increase in ozone burden due to the spatial distribution change slightly exceeds the combined influences of the increased emission magnitude and global methane. Emission increases in Southeast, East and South Asia may be most important for the ozone change, supported by an analysis of statistically significant increases in observed ozone above these regions. The spatial distribution of emissions dominates global tropospheric ozone, suggesting that the future ozone burden will be determined mainly by emissions from low latitudes.

The influence of temperature on ozone production under varying NO x conditions – a modelling study

Abstract: . Surface ozone is a secondary air pollutant produced during the atmospheric photochemical degradation of emitted volatile organic compounds (VOCs) in the presence of sunlight and nitrogen oxides (NOx). Temperature directly influences ozone production through speeding up the rates of chemical reactions and increasing the emissions of VOCs, such as isoprene, from vegetation. In this study, we used an idealised box model with different chemical mechanisms (Master Chemical Mechanism, MCMv3.2; Common Representative Intermediates, CRIv2; Model for OZone and Related Chemical Tracers, MOZART-4; Regional Acid Deposition Model, RADM2; Carbon Bond Mechanism, CB05) to examine the non-linear relationship between ozone, NOx and temperature, and we compared this to previous observational studies. Under high-NOx conditions, an increase in ozone from 20 to 40 °C of up to 20 ppbv was due to faster reaction rates, while increased isoprene emissions added up to a further 11 ppbv of ozone. The largest inter-mechanism differences were obtained at high temperatures and high-NOx emissions. CB05 and RADM2 simulated more NOx-sensitive chemistry than MCMv3.2, CRIv2 and MOZART-4, which could lead to different mitigation strategies being proposed depending on the chemical mechanism. The increased oxidation rate of emitted VOC with temperature controlled the rate of Ox production; the net influence of peroxy nitrates increased net Ox production per molecule of emitted VOC oxidised. The rate of increase in ozone mixing ratios with temperature from our box model simulations was about half the rate of increase in ozone with temperature observed over central Europe or simulated by a regional chemistry transport model. Modifying the box model set-up to approximate stagnant meteorological conditions increased the rate of increase of ozone with temperature as the accumulation of oxidants enhanced ozone production through the increased production of peroxy radicals from the secondary degradation of emitted VOCs. The box model simulations approximating stagnant conditions and the maximal ozone production chemical regime reproduced the 2 ppbv increase in ozone per degree Celsius from the observational and regional model data over central Europe. The simulated ozone–temperature relationship was more sensitive to mixing than the choice of chemical mechanism. Our analysis suggests that reductions in NOx emissions would be required to offset the additional ozone production due to an increase in temperature in the future.

A review of the effect of the composition of biodiesel on NOx emission, oxidative stability and cold flow properties

Abstract: This paper will review and attempt to discover the ideal fatty acid composition of biodiesel which exhibits lower NO x emissions, better oxidative stability and cold flow properties. The physicochemical properties of biodiesel strongly depend on their fatty acid composition. A high percentage of unsaturated fatty acid in biodiesel is correlated with higher NO x emissions, poor oxidative stability and better cold flow properties. The presence of saturated fatty acids (SFA), in particular the long chain type, exhibits good oxidative stability and produces lower NO x emissions. SFA do however demonstrate poor cold flow properties. The polyunsaturated fatty acids (PUFA) exhibit better cold flow properties but produces higher NO x emissions and poorer oxidative stability. The ideal requirements of biodiesel properties impose contradictory conditions on the fatty acid composition of biodiesel. For example, coconut and palm kernel oils which have a high percentage of lauric fatty acid are reported to circumvent all three drawbacks of biodiesel. The monounsaturated fatty acids (MUFA), specifically oleic acids, a major component in almost all biodiesel, display the positive characteristics of both SFA and PUFA. Biodiesel properties can therefore be improved by using various remedial methods including genetic engineering, reformulated biodiesel and additives.