Showing papers on "NOx published in 2011"

Effect of biodiesel on engine performances and emissions

Abstract: As a renewable, sustainable and alternative fuel for compression ignition engines, biodiesel instead of diesel has been increasingly fueled to study its effects on engine performances and emissions in the recent 10 years. But these studies have been rarely reviewed to favor understanding and popularization for biodiesel so far. In this work, reports about biodiesel engine performances and emissions, published by highly rated journals in scientific indexes, were cited preferentially since 2000 year. From these reports, the effect of biodiesel on engine power, economy, durability and emissions including regulated and non-regulated emissions, and the corresponding effect factors are surveyed and analyzed in detail. The use of biodiesel leads to the substantial reduction in PM, HC and CO emissions accompanying with the imperceptible power loss, the increase in fuel consumption and the increase in NOx emission on conventional diesel engines with no or fewer modification. And it favors to reduce carbon deposit and wear of the key engine parts. Therefore, the blends of biodiesel with small content in place of petroleum diesel can help in controlling air pollution and easing the pressure on scarce resources without significantly sacrificing engine power and economy. However, many further researches about optimization and modification on engine, low temperature performances of engine, new instrumentation and methodology for measurements, etc., should be performed when petroleum diesel is substituted completely by biodiesel.

Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies

Abstract: Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies Pascal Granger* and Vasile I. Parvulescu* Unit e de Catalyse et de Chimie du Solide, UMR CNRS 8181, University of Lille 1, 59655 Villeneuve d’Ascq, France Department of Organic Chemistry, Biochemistry and Catalysis, University of Bucharest, Romania, 412 Regina Elisabeta Boulevard, Bucharest 030016, Romania

Influence of sulfation on iron titanate catalyst for the selective catalytic reduction of NOx with NH3

Abstract: Iron titanate catalyst (FeTiOx) is a potential candidate for the substitution of conventional V2O5–WO3 (MoO3)/TiO2 and Fe/Cu-zeolite catalysts for the selective catalytic reduction (SCR) of NOx with NH3 because of its high SCR activity and N2 selectivity in the medium temperature range. Due to the presence of small amount of SO2 in typical diesel exhaust derived from combustion of sulfur-containing fuels, it is very important to investigate the influence of sulfation on SCR activity, catalyst structure and reaction mechanism. After sulfation under the SCR condition, the surface area and pore volume of FeTiOx catalyst decreased to a certain extent due to the formation of sulfate species. According to the characterizations of FeTiOx catalyst using X-ray diffraction, X-ray absorption fine structure spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy of SO2 + O2 treatment, the sulfate species mainly formed on iron sites in a chelating bidentate conformation, resulting in the enhancement of Bronsted acidity and Lewis acid strength simultaneously. NH3 adsorption was greatly enhanced in the high temperature range, while NOx adsorption was severely inhibited due to the stronger acidity of sulfate species. The operation temperature window of the sulfated catalyst shifted ca. 50 °C towards high temperature range accordingly. The reaction mechanism study shows that the Langmuir–Hinshelwood reaction pathway was cut off by the sulfation process, resulting in the activity loss at low temperatures; only Eley–Rideal reaction pathway between adsorbed NH3 species and gaseous or weakly adsorbed NO dominated in the SCR reaction, which made this catalyst resistant to SO2 poisoning at relatively high temperatures.

Nonlinear response of ozone to precursor emission changes in China: a modeling study using response surface methodology

Abstract: . Statistical response surface methodology (RSM) is successfully applied for a Community Multi-scale Air Quality model (CMAQ) analysis of ozone sensitivity studies. Prediction performance has been demonstrated through cross validation, out-of-sample validation and isopleth validation. Sample methods and key parameters, including the maximum numbers of variables involved in statistical interpolation and training samples have been tested and selected through computational experiments. Overall impacts from individual source categories which include local/regional NOx and VOC emission sources and NOx emissions from power plants for three megacities – Beijing, Shanghai and Guangzhou – were evaluated using an RSM analysis of a July 2005 modeling study. NOx control appears to be beneficial for ozone reduction in the downwind areas which usually experience high ozone levels, and NOx control is likely to be more effective than anthropogenic VOC control during periods of heavy photochemical pollution. Regional NOx source categories are strong contributors to surface ozone mixing ratios in three megacities. Local NOx emission control without regional involvement may raise the risk of increasing urban ozone levels due to the VOC-limited conditions. However, local NOx control provides considerable reduction of ozone in upper layers (up to 1 km where the ozone chemistry is NOx-limited) and helps improve regional air quality in downwind areas. Stricter NOx emission control has a substantial effect on ozone reduction because of the shift from VOC-limited to NOx-limited chemistry. Therefore, NOx emission control should be significantly enhanced to reduce ozone pollution in China.

Mechanism Study of NO Catalytic Oxidation over MnOx/TiO2 Catalysts

Abstract: The MnOx/TiO2 catalysts have been proved very active in the catalytic oxidation of NO to NO2, but the mechanism of this heterogeneous reaction was still not clear. In this study, through a systematic in situ diffuse reflectance infrared Fourier transform spectroscopy investigation, the main pathway of NO oxidation over MnOx/TiO2 was revealed. Experimental results indicated that the NO was first coordinated to Mn sites, forming nitrosyls, which were readily oxidized to nitrates by lattice oxygen, and then the nitrates were decomposed to NO2 at high temperatures. However, when SO2 was present, the formation of nitrates was significantly hindered because the SO2 would permanently occupy the active Mn sites as sulfates. We believe that this revealed the mechanism of NO oxidation and SO2 deactivation would provide useful guidance for the development of better catalysts toward fast selective catalytic reduction, NOx storage-reduction, continuously regenerating trap, and NOx wet scrubbing.

Particulate emissions from biodiesel vs diesel fuelled compression ignition engine

Abstract: Studies conducted over the last decade have well established a direct relationship between deteriorating human health and diesel engine exhaust. Biodiesel has shown a lot of promise in terms of both its relatively higher combustion efficiency and lower harmful emissions. Biodiesel has the potential to replace a significant amount of the petroleum used to power diesel engines. The emissions from biodiesel are different than petroleum-based diesel and it is important to understand how they are different with respect to the levels emitted and the combustibility of the particulates. One of the major pollutants emitted from engine exhaust is particulate matter (PM). PM emitted from tailpipes contains a variety of toxic contaminants either embedded or adsorbed on its surface. This study provides a one to one comparison between PM emitted from a mid-size engine running on petroleum-based diesel versus biodiesel. The key physical and chemical parameters analyzed include metals, benzene soluble organic fraction, elemental and organic carbon fractions, particle morphology, particle number and size distribution. This is the first study of its kind where various aspects of the PM emitted from a biodiesel-operated engine have been extensively studied. The major results from the study showed that metals that come from engine wear are not present in biodiesel exhaust particulate due to its self lubricating properties. Samples collected of mineral diesel exhaust are relatively darker in color and stickier than biodiesel exhaust. Biodiesel and its blends gave more benzene soluble organic fraction (BSOF) in engine exhaust particulate matter than mineral diesel at all operating conditions. B100 gave higher number of smaller particles in its exhaust than mineral diesel; comprehensively all size particles were also higher in case of B100. Peak particle concentrations for biodiesel were shifted towards smaller size particles. As load increases, B20 emission performance in terms of particle concentrations improves very rapidly and even surpasses mineral diesel emission performance. Scanning electron microscope (SEM) images for B100 and B20 showed granular structure particulates with bigger grain size compared to mineral diesel. Among B100, B20 and mineral diesel, total particle accumulation was maximum for mineral diesel.

CeO2–WO3 Mixed Oxides for the Selective Catalytic Reduction of NOx by NH3 Over a Wide Temperature Range

Abstract: A series of cerium-tungsten oxide catalysts was prepared by the co-precipitation method and was evaluated for the selective catalytic reduction of NO x by ammonia (NH3-SCR) over a wide temperature range. These catalysts were characterized by BET, XRD, XPS and H2-TPR analyses. The experimental studies demonstrated that, among cerium-tungsten oxides, CeO2–WO3 with a Ce/W molar ratio of 3/2 exhibited the best activity toward NH3-SCR reactions, N2 selectivity and SO2 durability over a broad temperature range of 175–500 °C at a space velocity of 47,000 h−1. The strong interaction between Ce and W could be the main factor leading to the high activity of the CeO2–WO3 mixed oxide catalyst. A series of cerium-tungsten oxide catalysts was prepared by the co-precipitation method and was evaluated for the selective catalytic reduction of NO x by ammonia (NH3-SCR) over a wide temperature range. These catalysts were characterized by BET, XRD, XPS and H2-TPR analyses. The experimental studies demonstrated that, among cerium-tungsten oxides, CeO2–WO3 with a Ce/W molar ratio of 3/2 exhibited the best activity toward NH3-SCR reactions, N2 selectivity and SO2 durability over a broad temperature range of 175–500 °C at a space velocity of 47,000 h−1. The strong interaction between Ce and W could be the main factor leading to the high activity of the CeO2–WO3 mixed oxide catalyst.

Diurnal and seasonal variability of surface ozone and NOx at a tropical coastal site: Association with mesoscale and synoptic meteorological conditions

Abstract: [1] Simultaneous measurements of near-surface ozone, NOx (NO + NO2), and meteorological parameters were carried out at the tropical coastal location of Trivandrum (8.55°N, 77°E) in India from November 2007 to May 2009. The data have been used to investigate the diurnal and seasonal patterns of ozone and its precursor, NOx, and also the interdependence of these two chemical species. The diurnal pattern is found to be closely associated with the mesoscale circulation (sea breeze and land breeze) and the availability of NOx. The daytime peak in ozone extends until the onset of land breeze, which brings in NOx for titration of ozone. Near-surface ozone concentration reaches peak values during the postmonsoon or winter months and shows minima during the summer or monsoon season. The high ozone concentration during winter is due to the presence of northeasterly winds that transport precursor gases to the site. The daytime concentration of ozone is found to be directly linked to the nighttime level of NOx. The present analysis reveals that one molecule of NOx or NO2 is responsible for the formation of about seven to nine molecules of ozone. A study of satellite-derived tropospheric ozone and total ozone has shown that tropospheric ozone contributes 8%–15% of total ozone over this site and near-surface ozone contributes 34%–83% of tropospheric ozone. The seasonal pattern of tropospheric column ozone is similar to that of tropospheric NO2.

Catalytic Performance, Characterization, and Mechanism Study of Fe2(SO4)3/TiO2 Catalyst for Selective Catalytic Reduction of NOx by Ammonia

Abstract: Iron oxides supported on TiO2 catalysts show good activity in selective catalytic reduction (SCR) of NOx by ammonia. In this work, Fe2(SO4)3/TiO2 and other catalysts containing iron and sulfates were prepared by the impregnation method, and their activities for SCR of NOx by ammonia were investigated. On Fe2(SO4)3/TiO2 catalyst, NOx conversion reached 98.0% in the temperature range of 350−450 °C, while yielding little N2O. Characterization results showed that α-Fe2O3 and sulfates were mainly formed on the Fe2(SO4)3/TiO2 catalyst. Iron oxide catalysts with sulfates [e.g., Fe2(SO4)3/TiO2] caused more dispersed iron phase, and the sulfation effect might have mostly occurred on iron oxides but not TiO2. In contrast, Fe(NO3)3 precursor supported on TiO2 without sulfates led to the Fe2O3 particle products, which physically connected to the surface of TiO2 and resulted in some agglomerations or heterogeneous distribution of Fe2O3 particles. In addition, sulfates played an important role in the SCR reactions, whi...

Effect of advanced aftertreatment for PM and NOx reduction on heavy-duty diesel engine ultrafine particle emissions.

Abstract: Four heavy-duty and medium-duty diesel vehicles were tested in six different aftertreament configurations using a chassis dynamometer to characterize the occurrence of nucleation (the conversion of exhaust gases to particles upon dilution). The aftertreatment included four different diesel particulate filters and two selective catalytic reduction (SCR) devices. All DPFs reduced the emissions of solid particles by several orders of magnitude, but in certain cases the occurrence of a volatile nucleation mode could increase total particle number emissions. The occurrence of a nucleation mode could be predicted based on the level of catalyst in the aftertreatment, the prevailing temperature in the aftertreatment, and the age of the aftertreatment. The particles measured during nucleation had a high fraction of sulfate, up to 62% of reconstructed mass. Additionally the catalyst reduced the toxicity measured in chemical and cellular assays suggesting a pathway for an inverse correlation between particle number and toxicity. The results have implications for exposure to and toxicity of diesel PM.