Showing papers on "NOx published in 2014"

Novel Mn–Ce–Ti Mixed-Oxide Catalyst for the Selective Catalytic Reduction of NOx with NH3

Abstract: Mn-Ce-Ti mixed-oxide catalyst prepared by the hydrothermal method was investigated for the selective catalytic reduction (SCR) of NOx with NH3 in the presence of oxygen. It was found that the environmentally benign Mn-Ce-Ti catalyst exhibited excellent NH3-SCR activity and strong resistance against H2O and SO2 with a broad operation temperature window, which is very competitive for the practical application in controlling the NOx emission from diesel engines. On the basis of the catalyst characterization, the dual redox cycles (Mn4+ + Ce3+ Mn3+ + Ce4+, Mn4+ + Ti3+ Mn3+ + Ti4+) and the amorphous structure play key roles for the high catalytic deNO(x) performance. Diffuse reflectance infrared Fourier transform spectroscopy studies showed that the synergetic effect between Mn and Ce contributes to the formation of reactive intermediate species, thus promoting the NH3-SCR to proceed.

In situ DRIFTS and temperature-programmed technology study on NH3-SCR of NOx over Cu-SSZ-13 and Cu-SAPO-34 catalysts

Abstract: In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS), temperature-programmed desorption (TPD), and temperature-programmed surface reactions (TPSR) were employed to investigate the adsorption and reactive properties of Cu-SSZ-13 and Cu-SAPO-34 zeolite catalysts; these fully formulated washcoat cordierite monoliths were hydrothermally treated at 750 °C in the simulated feed gases. The intrinsic mechanism and reasons for the differences in NH3-SCR activity were proposed based on the characterization results. The in situ DRIFTS and TPD results showed that ammonia could adsorb on both the Lewis and Bronsted acidic sites on these two catalysts; the ammonia on the Bronsted acidic sites might be active in the NH3-SCR reaction. For the different NOx adsorption processes, the total NOx desorption levels followed the following sequence: NO

High winter ozone pollution from carbonyl photolysis in an oil and gas basin

Abstract: Data from the oil- and gas-producing basin of northeastern Utah and a box model are used to assess the photochemical reactions of nitrogen oxides and volatile organic compounds that lead to excessive atmospheric ozone pollution in winter. The US experience with air quality degradation from shale gas extraction presents a measurement and modelling framework relevant to similar developments in other regions projected for the near future. High ozone mixing ratios have been observed in oil and gas producing basins in the United States during winter, but the underlying chemistry involved is not fully understood. This study presents a quantitative assessment of the underlying chemistry responsible for the winter ozone pollution events based on data from an oil and gas basin in Utah and a chemical 'box model' simulation. The results show that very high volatile organic carbon concentrations optimize the ozone production efficiency of nitrogen oxides with carbonyl photolysis as a dominant oxidant source. The United States is now experiencing the most rapid expansion in oil and gas production in four decades, owing in large part to implementation of new extraction technologies such as horizontal drilling combined with hydraulic fracturing. The environmental impacts of this development, from its effect on water quality1 to the influence of increased methane leakage on climate2, have been a matter of intense debate. Air quality impacts are associated with emissions of nitrogen oxides3,4 (NOx = NO + NO2) and volatile organic compounds5,6,7 (VOCs), whose photochemistry leads to production of ozone, a secondary pollutant with negative health effects8. Recent observations in oil- and gas-producing basins in the western United States have identified ozone mixing ratios well in excess of present air quality standards, but only during winter9,10,11,12,13. Understanding winter ozone production in these regions is scientifically challenging. It occurs during cold periods of snow cover when meteorological inversions concentrate air pollutants from oil and gas activities, but when solar irradiance and absolute humidity, which are both required to initiate conventional photochemistry essential for ozone production, are at a minimum. Here, using data from a remote location in the oil and gas basin of northeastern Utah and a box model, we provide a quantitative assessment of the photochemistry that leads to these extreme winter ozone pollution events, and identify key factors that control ozone production in this unique environment. We find that ozone production occurs at lower NOx and much larger VOC concentrations than does its summertime urban counterpart, leading to carbonyl (oxygenated VOCs with a C = O moiety) photolysis as a dominant oxidant source. Extreme VOC concentrations optimize the ozone production efficiency of NOx. There is considerable potential for global growth in oil and gas extraction from shale. This analysis could help inform strategies to monitor and mitigate air quality impacts and provide broader insight into the response of winter ozone to primary pollutants.

Atmospheric peroxyacetyl nitrate (PAN): a global budget and source attribution

Abstract: . Peroxyacetyl nitrate (PAN) formed in the atmospheric oxidation of non-methane volatile organic compounds (NMVOCs) is the principal tropospheric reservoir for nitrogen oxide radicals (NOx = NO + NO2). PAN enables the transport and release of NOx to the remote troposphere with major implications for the global distributions of ozone and OH, the main tropospheric oxidants. Simulation of PAN is a challenge for global models because of the dependence of PAN on vertical transport as well as complex and uncertain NMVOC sources and chemistry. Here we use an improved representation of NMVOCs in a global 3-D chemical transport model (GEOS-Chem) and show that it can simulate PAN observations from aircraft campaigns worldwide. The immediate carbonyl precursors for PAN formation include acetaldehyde (44% of the global source), methylglyoxal (30%), acetone (7%), and a suite of other isoprene and terpene oxidation products (19%). A diversity of NMVOC emissions is responsible for PAN formation globally including isoprene (37%) and alkanes (14%). Anthropogenic sources are dominant in the extratropical Northern Hemisphere outside the growing season. Open fires appear to play little role except at high northern latitudes in spring, although results are very sensitive to plume chemistry and plume rise. Lightning NOx is the dominant contributor to the observed PAN maximum in the free troposphere over the South Atlantic.

Study on using hydrogen and ammonia as fuels: Combustion characteristics and NOx formation

Abstract: This paper evaluates the potential of hydrogen (H-2) and ammonia (NH3) as carbon-free fuels The combustion characteristics and NOx formation in the combustion of H-2 and NH3 at different air-fuel equivalence ratios and initial H-2 concentrations in the fuel gas were experimentally studied NH3 burning velocity improved because of increased amounts of H-2 atom in flame with the addition of H-2 NH3 burning velocity could be moderately improved and could be applied to the commercial gas engine together with H-2 as fuels H-2 has an accelerant role in H-2-NH3-air combustion, whereas NH3 has a major effect on the maximum burning velocity of H-2-NH3-air In addition, fuel-NOx has a dominant role and thermal-NOx has a negligible role in H-2-NH3-air combustion Thermal-NOx decreases in H-2-NH3-air combustion compared with pure H-2-air combustion NOx concentration reaches its maximum at stoichiometric combustion Furthermore, H-2 is detected at an air-fuel equivalence ratio of 100 for the decomposition of NH3 in flame Hence, the stoichiometric combustion of H-2 and NH3 should be carefully considered in the practical utilization of H-2 and NH3 as fuels H-2 as fuel for improving burning performance with moderate burning velocity and NOx emission enables the utilization of H-2 and NH3 as promising fuels Copyright (C) 2014 John Wiley & Sons, Ltd

DRIFT Study of CuO–CeO2–TiO2 Mixed Oxides for NOx Reduction with NH3 at Low Temperatures

Abstract: A CuO–CeO2–TiO2 catalyst for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperatures was prepared by a sol–gel method and characterized by X-ray diffraction, Brunner–Emmett–Teller surface area, ultraviolet–visible spectroscopy, H2 temperature-programmed reduction, scanning electron microscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The CuO–CeO2–TiO2 ternary oxide catalyst shows excellent NH3-SCR activity in a low-temperature range of 150–250 °C. Lewis acid sites generated from Cu2+ are the main active sites for ammonia activation at low temperature, which is crucial for low temperature NH3-SCR activity. The introduction of ceria results in increased reducibility of CuO species and strong interactions between CuO particles with the matrix. The interactions between copper, cerium and titanium oxides lead to high dispersion of metal oxides with increased active oxygen and enhanced catalyst acidity. Homogeneously mixed metal oxides facilita...

Novel V2O5–CeO2/TiO2 catalyst with low vanadium loading for the selective catalytic reduction of NOx by NH3

Abstract: The effect of Ce on the activity and alkali resistance of V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NOx by NH3 has been investigated It was found that the addition of Ce not only reduced the vanadium loading of V2O5/TiO2 but also enhanced its activity and alkali resistance The NOx conversion over 05%V2O5-5%CeO2/TiO2 was much higher than that over 1%V2O5/TiO2 catalyst Based on the catalyst characterization, the redox cycle (V4+ + Ce4+ V5+ + Ce3+) can account for the excellent NH3-SCR catalytic performance of 05%V2O5-5%CeO2/TiO2 catalyst In situ diffuse reflectance infrared transform spectroscopy (DRIFTS) measurements revealed that the role of Ce on the V2O5-CeO2/TiO2 catalyst was to contribute to the formation of NO2 and monodentate nitrate species, both of which were reactive intermediates for the NH3-SCR of NOx (C) 2014 Elsevier BV All rights reserved

Variations of ground-level O-3 and its precursors in Beijing in summertime between 2005 and 2011

Abstract: . Elevated ground-level ozone (O3), reflecting atmospheric oxidative capacity, are of increasing concern. High levels of total oxidants (Ox= O3 + NO2) have been persistently observed as a feature of Beijing's air pollution. Beijing is a well-known megacity requiring the enforcement of stringent air quality controls as rapid economic growth continues. To evaluate the effect of air quality controls in recent years, ground-based on-line measurements at an urban site were conducted in summer and the variations in O3 with simultaneous changes in NOx and volatile organic compounds (VOCs) between 2005 and 2011 were analyzed. Both NOx and total VOCs in Beijing decreased over the study period, 1.4 ppbv yr−1 and 1.6 ppbv yr−1, respectively. However, VOCs reactivity, in terms of OH loss rate, showed an indistinct statistical trend due to unsteady variations from naturally emitted isoprene, though some anthropogenic species showed decreasing trends, such as pentane, benzene and toluene. Meanwhile, daytime average O3 increased rapidly at an annual rate of 2.6 ppbv yr−1, around 5% yr−1 between 2005 and 2011. Considering the influence of NO titration effect and elevated regional ozone background in the North China Plain (NCP), the main reason for such an increase in oxidants was subject to "local" photochemistry. A simplified model was used to evaluate the effect of changes in the levels of ozone precursors on ozone production. We found that between 2001 and 2006, the production rate of total oxidants, P(Ox) increased rapidly due to increased VOC levels and decreasing NO2, while from 2006 to 2011 P(Ox) remained high, though decreased slightly as a consequence of the decrease in both VOC reactivity (−5% yr−1) and NOx (−4% yr−1). Observations have shown that Beijing's efforts to control air pollution were somehow effective in cutting ozone precursors, but still left higher ground-level ozone. We surmised that it resulted from potential contributions from OVOCs and regional transport near Beijing. Therefore, Beijing needs deeper cooperation with adjacent provinces to control ozone pollution together. To impel this kind of joint prevention and control program, ground-level ozone should become a mandatory index for air quality management, and a faster reduction of VOCs, especially reactive VOCs, in urban areas, should coordinate with national NOx emission control programs.

Investigation of emissions and combustion characteristics of a CI engine fueled with waste cooking oil methyl ester and diesel blends

Abstract: Biodiesel has been identified as a potential alternative fuel for CI engines because use of biodiesel can reduce petroleum diesel consumption as well as engine out emissions Out of many biodiesel derived from various resources, biodiesel from Waste Cooking Oil (WCO) can be prepared economically using usual transesterification process In the present study, in-depth research and comparative study of blends of biodiesel made from WCO and diesel is carried out to bring out the benefits of its extensive usage in CI engines The experimental results of the study reveal that the WCO biodiesel has similar characteristics to that of diesel The brake thermal efficiency, carbon monoxide, unburned hydrocarbon and smoke opacity are observed to be lower in the case of WCO biodiesel blends than diesel On the other hand specific energy consumption and oxides of nitrogen of WCO biodiesel blends are found to be higher than diesel In addition combustion characteristics of all biodiesel blends showed similar trends when compared to that of conventional diesel

The role of non-thermal plasma technique in NOx treatment: A review

Abstract: Non-thermal plasma (NTP) has been introduced over the past several years as a promising method for nitrogen oxide (NOx) removal. The intent, when using NTP, is to selectively transfer input electrical energy to the electrons, and to not expend this in heating the entire gas stream, which generates free radicals through collisions, and promotes the desired chemical changes in the exhaust gases. The generated active species react with the pollutant molecules and decompose them. This paper reviews and summarizes relevant literature regarding various aspects of the application of NTP technology on NOx removal from exhaust gases. A comprehensive description of available scientific literature on NOx removal using NTP technology is presented, including various types of NTP, e.g. dielectric barrier discharge, corona discharge and electron beam. Furthermore, the combination of NTP with catalyst and adsorbent for better NOx removal efficiency is presented in detail. The removal of NOx from both simulated gases and real diesel engines is also considered in this review paper. As NTP is a new technique and is not yet commercialized, there is a need for more studies to be performed in this field.