Showing papers on "NOx published in 2013"

Improvement of Activity and SO2 Tolerance of Sn-Modified MnOx–CeO2 Catalysts for NH3-SCR at Low Temperatures

Abstract: The performances of fresh and sulfated MnOx–CeO2 catalysts for selective catalytic reduction of NOx by NH3 (NH3-SCR) in a low-temperature range (T < 300 °C) were investigated. Characterization of these catalysts aimed at elucidating the role of additive and the effect of sulfation. The catalyst having a Sn:Mn:Ce = 1:4:5 molar ratio showed the widest SCR activity improvement with near 100% NOx conversion at 110–230 °C. Raman and X-ray photoelectron spectroscopy (XPS) indicated that Sn modification significantly increases the concentration of oxygen vacancies that may facilitate NO oxidation to NO2. NH3-TPD characterization showed that the low-temperature NH3-SCR activity is well correlated with surface acidity for NH3 adsorption, which is also enhanced by Sn modification. Furthermore, as compared to MnOx–CeO2, Sn-modified MnOx–CeO2 showed remarkably improved tolerance to SO2 sulfation and to the combined effect of SO2 and H2O. In the presence of SO2 and H2O, the Sn-modified MnOx–CeO2 catalyst gave 62% and ...

In Situ-DRIFTS Study of Selective Catalytic Reduction of NOx by NH3 over Cu-Exchanged SAPO-34

Abstract: The intrinsic mechanism of the selective catalytic reduction (SCR) reaction over a Cu-exchanged SAPO-34 catalyst at low temperature was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), coupled with mass spectrometry to measure inlet and outlet gas concentrations. The evolution of the surface intermediates, as well as the reactivity of NH3 with surface NOx species and NOx with surface NH3 species, was evaluated. In terms of NOx adsorption, surface nitrates and nitrites are the main NOx adsorption species at low temperature. When NO was exposed to the sample with NH3 preadsorbed, surface NH3 was not reactive because of the low surface coverage of nitrates and nitrites. However, the reactivity is significantly enhanced by the inclusion of O2 in the feed, which promotes an increase in the concentration of surface nitrates and nitrites. DRIFTS results also reveal that the low temperature SCR reaction involves the formation of an NH4NO3 intermediate and its subsequent red...

NO x emissions in China: historical trends and future perspectives

Abstract: . Nitrogen oxides (NOx) are key pollutants for the improvement of ambient air quality. Within this study we estimated the historical NOx emissions in China for the period 1995–2010, and calculated future NOx emissions every five years until 2030 under six emission scenarios. Driven by the fast growth of energy consumption, we estimate the NOx emissions in China increased rapidly from 11.0 Mt in 1995 to 26.1 Mt in 2010. Power plants, industry and transportation were major sources of NOx emissions, accounting for 28.4%, 34.0%, and 25.4% of the total NOx emissions in 2010, respectively. Two energy scenarios, a business as usual scenario (BAU) and an alternative policy scenario (PC), were developed to project future energy consumption. In 2030, total energy consumption is projected to increase by 64% and 27% from 2010 level respectively. Three sets of end-of-pipe pollution control measures, including baseline, progressive, and stringent control case, were developed for each energy scenario, thereby constituting six emission scenarios. By 2030, the total NOx emissions are projected to increase (compared to 2010) by 36% in the baseline while policy cases result in reduction up to 61% in the most ambitious case with stringent control measures. More than a third of the reduction achieved by 2030 between least and most ambitious scenario comes from power sector, and more than half is distributed equally between industry and transportation sectors. Selective catalytic reduction dominates the NOx emission reductions in power plants, while life style changes, control measures for industrial boilers and cement production are major contributors to reductions in industry. Timely enforcement of legislation on heavy-duty vehicles would contribute significantly to NOx emission reductions. About 30% of the NOx emission reduction in 2020 and 40% of the NOx emission reduction in 2030 could be treated as the ancillary benefit of energy conservation. Sensitivity analysis was conducted to explore the impact of key factors on future emissions.

Effect of ethanol–gasoline blend on NOx emission in SI engine

Abstract: The stricter worldwide emission legislation and growing demands for lower fuel consumption and anthropogenic CO2 emission require significant efforts to improve combustion efficiency while satisfying the emission quality demands. Ethanol fuel combined with gasoline provides a particularly promising and, at the same time, a challenging approach. Ethanol is widely used as an alternative fuel or an effective additive of gasoline due to the advantage of its high octane number and its self-sustaining concept, which can be supplied regardless of the fossil fuel. As a result, vast study has been carried out to study its effects on engine performance and emission. The first part of this article discusses prospect of fuel ethanol as a gasoline substitute. Then it discusses comparative physicochemical properties of ethanol and gasoline. The slight differences in properties between ethanol and gasoline fuels are enough to create considerable change to combustion system as well as behaviors of SI engines. These effects lead to several complex and interacting mechanisms, which make it difficult to identify the fundamentals of how ethanol affects NOx emission. After that, general NOx forming mechanisms are discussed to create a fundamental basis for further discussion. Finally, the article discusses different fuel composition, engine parameter and engine modification effects on NOx formation as well as mathematical approach for NOx prediction using ethanol.

Impacts of biodiesel combustion on NOx emissions and their reduction approaches

Abstract: Increasing energy demand and environment concerns have prompted an evolution of alternative fuel sources. As an alternative fuel source, biodiesel is attractive because it reduces engine emissions. However, biodiesel produces higher NOx emissions compared to ordinary diesel fuel. Previous researches have established many factors that cause biodiesel to produce elevated NOx emissions. This study reviews the impacts of biodiesel combustion on NOx emissions and their reduction approaches in diesel engines. The first part of this study recaps the NOx formation mechanisms for understanding the kinetics behind the NOx forming reactions. The second part describes the factors affecting on NOx emissions. This paper established that higher NOx emissions are produced for biodiesel combustion which influenced by several factors such as physicochemical properties and molecular structure of biodiesel, adiabatic flame temperature, ignition delay time, injection timing and engine load conditions etc. The final section discusses on the reduction of NOx emissions from biodiesel fuelled engines for both pre and post combustion techniques. The results of reduction approaches of the NOx emissions implies, exhaust gas recirculation (EGR) and retarded injection timing are effective as well as low cost techniques than others. Between these two techniques, EGR reduces the NOx emissions at 5–25% EGR rate adequately in biofuelled engine by controlling oxygen content and combustion peak temperature with slightly decreasing HC and CO emissions. However this technique shows few penalties on smoke and PM emissions as well as brake specific fuel consumption if not perfectly optimized.

Removal of NOx by photocatalytic processes

Abstract: The photocatalytic methods for nitrogen oxides removal were recently very intense areas of scientific research. Photo-deNOx processes offer interesting ways for abatement of these harmful gases. This review describes several methods for removing NO by photocatalytic reactions. These methods can be classified into three major groups: photo selective catalytic reduction (photo-SCR), photo-oxidation and photo-decomposition. The application of photocatalysts and photo-processes for NOx abatement in real-scale cases are presented. The fast-growing development of these methods is revealed by the large number of issued patents in photo-deNOx applications. The mechanism of NO creation and the traditional methods (primary and secondary) of NOx removal are summarized and discussed. A cooperative system that combines the traditional (thermal) process and a photo-process is then proposed for improving NOx removal efficiency.

Sulfate-nitrate-ammonium aerosols over China: response to 2000–2015 emission changes of sulfur dioxide, nitrogen oxides, and ammonia

Abstract: . We use a chemical transport model to examine the change of sulfate-nitrate-ammonium (SNA) aerosols over China due to anthropogenic emission changes of their precursors (SO2, NOx and NH3) from 2000 to 2015. From 2000 to 2006, annual mean SNA concentrations increased by about 60% over China as a result of the 60% and 80% increases in SO2 and NOx emissions. During this period, sulfate is the dominant component of SNA over South China (SC) and Sichuan Basin (SCB), while nitrate and sulfate contribute equally over North China (NC). Based on emission reduction targets in the 12th (2011–2015) Five-Year Plan (FYP), China's total SO2 and NOx emissions are projected to change by −16% and +16% from 2006 to 2015, respectively. The amount of NH3 emissions in 2015 is uncertain, given the lack of sufficient information on the past and present levels of NH3 emissions in China. With no change in NH3 emissions, SNA mass concentrations in 2015 will decrease over SCB and SC compared to their 2006 levels, but increase over NC where the magnitude of nitrate increase exceeds that of sulfate reduction. This suggests that the SO2 emission reduction target set by the 12th FYP, although effective in reducing SNA over SC and SCB, will not be successful over NC, for which NOx emission control needs to be strengthened. If NH3 emissions are allowed to keep their recent growth rate and increase by +16% from 2006 to 2015, the benefit of SO2 reduction will be completely offset over all of China due to the significant increase of nitrate, demonstrating the critical role of NH3 in regulating nitrate. The effective strategy to control SNA and hence PM2.5 pollution over China should thus be based on improving understanding of current NH3 emissions and putting more emphasis on controlling NH3 emissions in the future.

Identification of the active sites on CeO2–WO3 catalysts for SCR of NOx with NH3: An in situ IR and Raman spectroscopy study

Abstract: A series of CeO2–WO3 (WxCe) catalysts were prepared for the SCR of NOx with NH3. Among the three representative samples, the W1Ce catalyst exhibited great activity during SCR reaction and a large amount of N2 from NH3 oxidation, whereas the W0.05Ce catalyst yielded more NO from NH3 oxidation than the W3Ce at high temperature. Three types of metal oxide species (isopolytungsten species, Ce2(WO4)3 compounds and crystalline WO3) were observed on the catalyst surfaces with increased WO3 loading. CeO2, rather than WO3 or Ce2(WO4)3, presented favorable reducibility behavior. Furthermore, CeO2 with intrinsic oxygen vacancies and unsaturated Wn+ cations of crystalline WO3 provided Lewis acid sites; meanwhile, the W O W or W O modes of Ce2(WO4)3 provided Bronsted acid sites. Based on the Raman spectra, the W O species of the [WO4] or [WO6] units could be the active sites. The results suggest a reaction mechanism consisting of two independent cycles, denoted as a redox cycle due to the excellent oxygen storage capability and reducibility of cubic fluorite CeO2 (for NH3 activation) and an acid site cycle, resulting from Bronsted acid sites formed on the W O W species of Ce2(WO4)3 (for NH3 adsorption). Surface nitrate species cannot be involved directly in SCR reaction with gaseous NH3; additionally, the adsorbed NO2 demonstrated activity over the W1Ce catalyst at 200 °C.

A study on the effects of promising edible and non-edible biodiesel feedstocks on engine performance and emissions production: A comparative evaluation

Abstract: Global energy demand is increasing due to the population growth and industrialization. In order to fulfill the energy demand with considering global concern, it is necessary to find out alternative fuel sources. Biodiesel is one of the best choices because of its immense potential to be part of energy mix in the near future as well as the capability of reducing greenhouse gas emissions. This paper aims to provide information to the engineers, industrialists and researchers who are interested on biodiesel. The paper presents a comprehensive review on the impact of potential biodiesel feedstocks (edible and non-edible) on engine performance and exhaust emissions including details of engine and operating condition. A large number of literatures from highly rated journals in scientific indexes are reviewed including the most recent publications. Most of the authors showed that using biodiesel from various feedstocks in diesel engines slightly lowered brake power and brake thermal efficiency but increases BSFC than diesel fuel. It was also reported that biodiesel significantly reduced the PM, HC, CO and CO 2 emissions but gives slightly higher NOx emissions. It was shown that NOx can be reduced by some approaches such as blending with additives and EGR technique. The study concluded that biodiesel can be used in compression ignition engine with no or minor engine modification. Finally biodiesel can be used as a substitute of diesel fuel to fulfill the energy demand, reduce dependency on fossil fuel as well as the exhaust emissions of the engine.

Exhaust emissions with ethanol or n-butanol diesel fuel blends during transient operation: A review

Abstract: The present work reviews the literature concerning the effects of alcohol/diesel blends on the exhaust emissions of diesel engines operating under transient conditions, i.e., acceleration, load increase, starting and transient/driving cycles. Two very promising alcohols are covered in this survey, namely ethanol and n-butanol. The analysis focuses on all regulated exhaust pollutants, i.e., particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons (HC), with results for unregulated emissions, carbon dioxide and combustion noise radiation also included. The main mechanisms of exhaust emissions during transients are identified and discussed, with respect to the fundamental aspects of transient operation and the differing properties of alcohols relative to the reference diesel oil. Based on the published studies up today, summarization of emissions data and cumulative trends are presented, for the purpose of quantifying the alcohol blends benefits or penalties on the regulated emissions during various driving cycles. Particularly for the emitted PM and smoke, a statistically significant correlation with the oxygen content exists (R2=0.85 and 0.95, respectively). A similar correlation holds true for the heavy-duty, engine-dynamometer data of engine-out CO. Finally, a detailed list is provided that summarizes the main data from all studies published so far.

Fuel injection strategies for performance improvement and emissions reduction in compression ignition engines—A review

Abstract: The call for reduction in pollution has been mandated by government′s policies worldwide. This challenges the engine manufacturer to strike an optimum between engine performance and emissions. However with growing technology in the field of fuel injection equipment, the task has become realizable. For past few years it has been the hot topic to improve combustion and emissions of compression ignition engines through optimizing the fuel injection strategies. Choosing between various injection strategies are potentially effective techniques to reduce emission from engines as injection characteristics have great influences on the process of combustion. For example, increasing the fuel injection pressure can improve the fuel atomization and subsequently improve the combustion process, resulting in a higher brake thermal efficiency, producing less HC, CO, PM emissions, but more NOx emission. Pilot injection help in reducing combustion noise and NOx emissions and immediate post injection may help in soot oxidation and late post injection helps in regeneration of diesel particulate filter. This article aims at a comprehensive review of various fuel injection strategies viz varying injection pressure, injection rate shapes, injection timing and split/multiple injections for engine performance improvement and emissions control. Although every strategy has its own merits and demerits, they are explained in detail, in view of helping researchers to choose the better strategy or combination for their applications.

Performance and emission characteristics of biodiesel from different origins: A review

Abstract: Alarming situation of world energy stimulated the researchers to look for new sources of fuel, which must be renewable, locally available and environmentally benign In this regard, the significance of biodiesel as technically and commercially viable alternative to fossil-diesel has led to intense research in the field Biodiesel is made from different feedstock depending on the availability This paper analyzes the performance and emission of biodiesel from different feedstock The main advantage of biodiesel is that it potentially reduces the key pollutants, carbon monoxide, unburnt hydrocarbons and particulate matters While several researchers have looked at the impact of biodiesel on these pollutants, only few publications discussed the effect of fatty acid composition on performance and emission characteristics An attempt has been carried out to discuss the effect of biodiesel in terms of performance and emissions based upon composition and properties of the respective biodiesel The results of the study show that different chemical compositions of biodiesel based upon their origin lead to variation in their properties and performance and emission characteristics Biodiesel produced from saturated feedstock reduce NOx emission and resistive to oxidation but exhibit poor atomization However, many further research needs to be carried out to understand the relationship between the type of biodiesel feedstock and performance and emission

Ceria added Sb-V2O5/TiO2 catalysts for low temperature NH3 SCR: Physico-chemical properties and catalytic activity

Abstract: A systematic investigation of the effect of ceria loading over Sb-V2O5/TiO2 catalysts was carried out for the selective catalytic reduction (SCR) of NOx by NH3. The various ceria loaded Sb-V2O5/TiO2 catalysts were prepared by deposition precipitation and impregnation methods. Addition of 10% ceria to Sb-V2O5/TiO2 catalyst significantly enhanced the NOx conversion at wide temperature range of 220–500 °C. The 10% ceria loaded Sb-V2O5/TiO2 catalyst showed superior N2 selectivity (>95%) throughout the reaction temperatures. The physicochemical characteristics of the obtained catalysts were thoroughly characterized by BET surface area, X-ray diffractometry (XRD), temperature programmed desorption (TPD) of NO, SO2 and NH3, H2- temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The XRD results indicated the active components of antimony and vanadia were homogeneously dispersed over CeO2/TiO2. It was found that the addition of 10% ceria to Sb-V2O5/TiO2 could enhance the total acidity and redox properties of the catalyst, which lead to show higher NOx conversions at wide temperature window. In XPS studies, increase in intensity of the chemisorbed mobile oxygen peak was observed for ceria loaded catalysts. In particular, the DRIFT spectra of ceria loaded Sb-V2O5/TiO2 catalysts showed abundant Bronsted acid sites at 1436 and 1673 cm−1 band, which are responsible for high NOx conversion. Furthermore, the results of NO and SO2 TPD of 10% ceria loaded Sb-V2O5/TiO2 catalyst showed enhancement of NO adsorption and SO2 inhibition properties, which is thought to play a significant role in long term stability of the catalyst during SO2 on–off study for 38 h at 240 °C.