Search

The role of the support in Rh-based catalysts for total oxidation of CH4was investigated using both amorphous SiO2and γ-Al2O3as well as ZSM-5 and SSZ-13 zeolites with varying SiO2/Al2O3ratios. The methane oxidation activity was measured in both the presence and absence of 5 vol% H2O and 20 ppm SO2. The support had a strong impact on Rh speciation (Rh2O3nanoparticlesvs.single Rh atom sites), which was important for the activity, as the nanoparticle sites were found to be far more active than the single atom sites. A 2 wt% Rh/ZSM-5(SiO2/Al2O3= 280) catalyst with Rh exclusively as Rh2O3nanoparticles was able to provide oxidation at a 75 °C lower temperature than an ion-exchanged 0.294 wt% Rh/ZSM-5(SiO2/Al2O3= 30) catalyst with Rh exclusively as single atoms despite a similar concentration of active sites in the two samples. All the catalysts were inhibited by the presence of water, but this inhibition was particularly strong for an amorphous SiO2support and for the most Al-rich zeolites and less severe for Si-rich zeolites. The inhibition from SO2was relatively stronger for the more Al-rich supports, which was attributed to an uptake of sulfur at Al sites that was detrimental to the performance of the active phase. In a realistic gas atmosphere containing both H2O and SO2, Si-rich ZSM-5(SiO2/Al2O3= 280) therefore emerged as the best support. This was because the low acidity ensured minimal loss of Rh to the less active single atom sites, avoidance of the detrimental sulfur uptake by the support seen for more Al-rich supports, and avoidance of the strong water-induced inhibition that occurs for amorphous SiO2and Al-rich zeolites.

The undesired oxidation of SO2 was studied experimentally at elevated pressures of up to 4.5 bar across two commercial vanadium-based (1.2 and 3 wt% V2O5) selective catalytic reduction (SCR) catalysts. This pressure range is of interest for preturbine SCR reactor configuration for NOx reduction on ships. The residence time in the catalyst was kept constant, independent on pressure, by adjusting the total flow rate. The conversion of SO2 was of the order 0.2–3% at temperatures of 300–400 °C and was independent of the pressure. Based on the measured conversion of SO2, the kinetics were fitted using an nth order rate expression. The reaction order of SO2 was found close to 1, and the reaction order of SO3 was found close to 0, also at increased pressures of up to 4.5 bar. The rate of SO2 oxidation was clearly promoted by the presence of 1000 ppm NOx at elevated pressure; however, at atmospheric pressure, the effect was within experimental uncertainty. The promoting effect is explained by a catalyzed redox reaction between SO2 and NO2, and since more NO2 is formed at elevated pressure, a higher degree of promotion by NOx is observed at elevated pressures.

Increased use of natural gas as a fuel in efficient, lean-burning engines could offer environmental advantages, but this necessitates a catalytic oxidation of methane escaping from the engine. The challenge for the catalytic oxidation of CH4 is that the catalyst must operate in the exhaust, which contains H2O (5–15 vol %) and SO2 (∼1 ppm), and both components cause a severe inhibition of the catalyst. Here, we report that a 2 wt % Rh/ZSM-5 catalyst offers great promise by showing that high methane conversion can be reached at practically achievable conditions and high space velocities also in the presence of H2O and SO2. Rh-based catalysts, which are in the form of Rh2O3 under reaction conditions, become superior to the state-of-the-art Pd-based catalysts in an atmosphere with both H2O and SO2. Although both H2O and SO2 inhibit Pd and Rh catalysts, water is found to have a destabilizing effect on rhodium sulfate that enables a partial decomposition of the sulfate below 400 °C. We propose that this partly alleviates the sulfur poisoning of Rh catalysts; wherefore, the combined inhibition from H2O + SO2 is weaker for Rh than that for Pd.

The activity of Rh/ZSM-5 catalysts for methane oxidation was investigated under conditions simulating the exhaust from lean burning, natural gas fueled engines to evaluate the influence of reaction atmosphere on catalytic activity. The Rh-catalysts yield high methane conversion at conditions achievable in real exhaust systems, despite the inhibiting effects of H2O and SO2. The influence of temperature and SO2 concentration (1−20 ppm) on the activity were studied. The deactivation caused by SO2 was intensified with decreasing temperature and increasing SO2 concentration, and the SO2-poisoning could be modeled as the occupation of active sites following a Temkin adsorption isotherm. At 400 °C essentially full coverage of S-species was reached with 1−2 ppm of SO2, but at 500 °C the coverage had decreased significantly, and considerable catalytic activity was preserved in the presence of SO2. Significant activity was regenerated in SO2-free gas, but the nature of the SO2-free regeneration atmosphere was unimportant.

The emission of particulate matter (PM) and NO x from diesel engines has proven to have a negative influence on health, and future regulations will require more than 90% PM and NO x removal. For land-based trucks using low-sulfur fuels, a sequential catalyst system is foreseen consisting of an upstream diesel oxidation catalyst (DOC), a catalyzed diesel particulate filter (cDPF), and a downstream SCR NO x removal catalyst together with an ammonia slip catalyst (ASC). Urea is injected as a precursor for ammonia: engine → DOC → cDPF → Urea inj → SCR → ASC → out. The SCR function can with process advantage be integrated into the filter and reduce volume. The trapped soot in the cDPF must currently be combusted away. Three different soot combustion mechanisms are used: (1) passive soot regeneration by NO 2 , (2) combustion by direct catalyst soot contact, and (3) active soot regeneration with O 2 at around 600 °C. Full soot combustion by direct catalyst soot contact is not needed in a system as soot combustion by NO 2 and O 2 gases plays major roles. For marine vessels, no PM emission regulation exists today. The emission problem is especially severe for vessels using heavy-fuel oil (HFO) with up to 3.5% sulfur and high (heavy) metal content, fuel properties that until now have prevented a reliable PM removal process. Recently, however, a catalyst-assisted passive soot regeneration process above 350 °C was developed including an “in situ” ash removal. This new process was validated on a ship using a sulfur-resistant Pd,V 2 O 5 filter catalyst that combusts soot, CO, and HC including PAHs, and it is well suited as front end for an SO x scrubber.

Lithium-O2 (Li-O2) batteries are currently limited by a large charge overpotential at practically relevant current densities, and the origin of this overpotential has been heavily debated in the literature. This paper presents a series of electrochemical impedance measurements suggesting that the increase in charge potential is not caused by an increase in the internal resistance. It is proposed that the potential shift is instead dictated by a mixed potential of parasitic reactions and Li2O2 oxidation. The measurements also confirm that the rapid potential loss near the end of discharge ("sudden death") is explained by an increase in the charge transport resistance. The findings confirm that our theory and conclusions in ref 1, based on experiments on smooth small-area glassy carbon cathodes, are equally valid in real Li-O2 batteries with porous cathodes. The parameter variations performed in this paper are used to develop the understanding of the electrochemical impedance, which will be important for further improvement of the Li-air battery.

International audience

A novel base metal-palladium catalytic coating was applied on commercial silicon carbide wall flow diesel filters and tested in an engine test bench. This catalytic coating limits the NO2 formation and even removes NO2 within a wide temperature range. Soot combustion, HC conversion and CO conversion properties are comparable to current platinum-based coatings, but at a lower cost. This paper compares the results from engine bench tests of present commercial solutions as regards NO2-, HC-, CO-removal and soot combustion with the novel coating. Furthermore, emission test results from base metal-palladium coated diesel particulate filters installed on operating taxis and related test cycle data are presented. A significant reduction in NO2 emission compared to present technology is measured.

In order to meet the Euro V heavy-duty diesel emission standard legislation limits, a diesel engine can be optimized by internal means to give low particulate emissions and lower fuel consumption. These modifications of the engine lead inevitably to higher NOx emissions due to the NOx/PM trade off. An efficient Urea SCR after-treatment system is then able to reduce the higher NOx emission to below the Euro V 2.0g/kWh legislation limit. This paper presents tests made on a PM optimized 12 liter heavy-duty diesel engine together with a urea SCR after-treatment system. The optimized engine had engine out particulate emissions of about 0.04 g/kWh and NOx emissions of 9 g/kWh for the ESC and 8,5 g/kWh for the ETC. The fuel consumption of the optimized engine was 194 g/kWh for the ESC and 198 g/kWh for the ETC as compared to state of the art Euro III engines of typically 210 g/kWh for the ESC, giving significant fuel savings of 7.5 %. Combining the engine with a 20 liter 300-cpsi SCR catalyst, catalyst volume to cylinder ratio of 1.7, the particulate emissions dropped to 0.017 g/kWh for the ESC and 0.020 for the ETC. Particle size measurements also showed a decrease in the number of fine particles. With a urea injection corresponding to about 8-9% of the fuel flow the NOx emissions were reduced to 1.4 g/kWh for the ESC and 1.5g/kWh for the ETC with low ammonia slip. These reductions correspond to a NOx conversion of 84 % and 82% for the ESC and ETC respectively. Thus the optimized engine combined with the urea SCR after-treatment system was compliant with the Euro V emission limits. INTRODUCTION In order to comply with the Euro V regulations for heavyduty diesel engines due in 2008, both the NOx and particulate emissions must be greatly reduced for today’s state of the art diesel engines. The regulations of 2008, namely 2.0 g/kWh NOx and 0.02 g/kWh particulates for the ESC and 0.03 g/kWh for the ETC driving cycles, cannot be achieved solely by engine management or improved engines, rather some sort of aftertreatment must be used. A preferred solution to comply with the Euro V emission limits is to optimize a diesel engine by internal means to give very low particulate emissions and considerably lower fuel consumption [1]. Due to the NOx/PM trade-off for diesel engines this will lead to higher NOx emissions, from Euro III levels of 5-6 g/kWh to 8-10 g/kWh, that have to be reduced with an efficient NOx aftertreatment system below the 2.0 g/kWh limit, preferably Urea-SCR. The Urea SCR systems have been shown to be both very efficient and durable in vehicle applications [2,3,4,5,6]. The higher NOx emission of the optimized engine therefore requires the Urea SCR system to have a high NOx conversion efficiency of about 80-85%. The combination of the optimized engine and Urea SCR system eliminates the need for a particulate filter to comply with Euro V emissions leading to a lower pressure drop of the exhaust system and also less complexity of the total system. Furthermore the significant fuel savings of the optimized engine compared to a standard Euro III engine could give a payback time for the optimized engine and the SCR system depending on the urea price and the application as to make the concept commercially interesting even prior to the legislation limits. This concept could also be a serious candidate for the Euro IV legislation (NOx limit of 3.5 g/kWh and particulates the same as Euro V). The optimized engine and SCR concept has an even greater fuel saving compared to a concept of a standard Euro III engine with EGR and particulate filter. EGR increases the fuel consumption of the engine and the addition of the particulate trap increases the fuel consumption further by increasing the pressure drop giving the combination of the optimized engine and Urea SCR system an even greater fuel consumption advantage. The purpose of this work was to demonstrate a PM and fuel optimized heavy-duty diesel engine and Urea SCR concept able to comply with the Euro V legislation emission limits. The total work consisted of 3 parts: • SCR catalyst optimization and selection [7] • Engine optimization • Combination of the optimized engine with the chosen SCR system. In previous work the catalyst selection to achieve a high NOx conversion above 80% with ammonia slip less than 10 ppm and development of a novel Urea SCR injection system were discussed [7]. This present paper deals with the optimization work on the engine, performance of the optimized engine, final selection of catalyst and the performance of the combination of the PM and fuel optimized engine with the efficient Urea-SCR system. The optimization targets of the engine optimization were to achieve low soot emissions (i.e. carbon particulates less than 0.010/0.015 g/kWh in ESC/ETC test) by internal means while maintaining very low fuel consumption at engine-out NOx emissions of 8 to 10 g/kWh in the ESC test.

This paper discusses the choice of catalyst types to reduce the NOx emissions down to the Euro V level. A novel Urea injection system is also presented, which is based on a mass produced digital dosing pump that is combined with an electronic control unit specially developed for controlling the Urea-SCR process onboard vehicles. It is shown that it is possible to have a NOx conversion above 80% with ammonia slip below 10 ppm using 30 liters of 130 cpsi catalysts for a 12 diesel engine. By increasing the cell density to 300 cpsi it is possible to reduce the catalyst volume by 2/3 down to 20 liters for the same engine.

Test samples of two different “advanced” diesel fuels were prepared from the raw diesel of North Sea Light Gas Oil. A commercial “Ultralight” diesel fuel was used as a reference. The three fuels were tested on two engines with and without an oxidation catalyst: 1) a VOLVO 10.0 1 DI was mounted in an engine test bench and a full ECE R49 13 mode test was performed and 2) a VW GOLF 1.6 l engine was mounted in a car and a full transient FTP-75 test was performed. Regulated emissions and unregulated emissions as SOF, sulphur, nitrate, PAH in PM plus vapour phase were measured. Genotoxic activity of the organic solvent extraction fraction from PM and PUF (vapour phase) was determined in a bacterial mutagenesis assay using Salmonella Thyphi-murium TA 98 with and without metabolic activation S9 and TA 98NR.

Two techniques of Doppler ultrasound examination, continuous-wave and range-gated, applied to the anterior cerebral artery and to the internal carotid artery, were compared with 133 xenon clearance after intravenous injection. Thirty-two sets of measurements were obtained in 16 newborn infants. The pulsatility index, the mean flow velocity, and the end-diastolic flow velocity were read from the Doppler recordings. Mean cerebral blood flow was estimated from the 133 Xe clearance curves. The correlation coefficients between the Doppler and the 133 Xe measurements ranged from 0.41 to 0.82. In the subset of 16 first measurements in each infant, there were no statistically significant differences between the correlation coefficients of the various Doppler ultrasound variables, but the correlation coefficients were consistenly lower for the pulsatility index than for mean flow velocity or end-diastolic flow velocity, and they were consistently higher for the range-gated than for the continuous-wave Doppler technique.

Natural gas can be an alternative fuel for ships in coastal zones to minimize the emissions of CO2, NOX, and particulates from diesel engines. However, unburnt methane can slip from the engine, causing another emission problem. CH4 is a green-house gas with an atmospheric potential of 26-28 times that of CO2 [1] and it need to be mitigated from the exhaust gas. Converting CH4 to CO2 and H2O catalytically in the after treatment system can be promising. However, an efficient catalyst that remains sufficiently active under real exhaust gas conditions (350-550 °C, 5-10 vol.% H2O and 1-2 ppm SO2) is still being sought. Pd based catalysts are the most active in the absence of H2O and SO2[2], but they deactivate severely by SO2 even at low ppm levels. In this contribution, it is investigated if Rh catalysts on a suitable carrier material can be developed to tolerate the exhaust gas conditions above. Here Rh/ZSM-5 was prepared and tested under simulated engine exhaust gas conditions with both H2O and SO2 present. The influence of operating temperature and SO2 concentration were studied.

Central blood flow (CBF) was estimated by an intravenous 133-xenon technique in six preterm infants before and after administration of indomethacin for closure of patent ductus arteriosus. CBF fell in all infants (range 12%-40%), the mean fall was 24% (P less than 0.005). Though none of the infants showed signs of impaired cerebral function during or following the injections, the results do not indicate whether or not the use of indomethacin is a potential hazard.

We have previously reported correlations between 133-Xenon cerebral blood flow measures and two forms of Doppler ultrasound measure — continuous wave and range-gated — in studies of neonatal cerebral blood flow (Greisen, Johansen, Ellison et al). In the present study, the contributions of pCO2, heart rate (HR), gestational age (GA) and blood pressure (BP) to these correlations were analyzed. Using jackknife techniques (Mosteller and Tukey), we also examined the stability of prediction of 133-Xenon flow from the ultrasound measures.