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1.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
2.
We discuss how the standard Cost-Benefit Analysis should be modified in order to take risk (and uncertainty) into account. We propose different approaches used in finance (Value at Risk, Conditional Value at Risk, Downside Risk Measures, and Efficiency Ratio) as useful tools to model the impact of risk in project evaluation. After introducing the concepts, we show how they could be used in CBA and provide some simple examples to illustrate how such concepts can be applied to evaluate the desirability of a new project infrastructure. 相似文献
3.
Angela S. Rocha Arnaldo C. Faro Jr. Laetitia Oliviero Jacob Van Gestel Franoise Maug 《Journal of Catalysis》2007,252(2):321-334
The activity of NiMoS catalysts supported on niobia, alumina, and niobia/alumina was compared for the thiophene hydrodesulfurization (HDS) and 2,6-dimethylaniline (2,6-DMA) hydrodenitrogenation (HDN) reactions. To evaluate the acidity of the supports and identify the nature of the sulfide sites, adsorption of 2,6-dimethylpyridine, pyridine, and CO was performed and followed by IR spectroscopy. This study has shown that with niobia as a support, the activity of NiMoS catalysts in thiophene HDS and in HDN of 2,6-DMA was no longer promoted by the synergy between Ni and Mo. The absence of synergy between molybdenum and nickel on niobia can be explained by the strong interaction of each metal with niobia at the expense of interaction with each other. Moreover, it has been shown that on a niobia/alumina support, the formation of the NiMoS phase can be directly linked to the presence of alumina not covered by niobia. However, niobia is an interesting support for the HDN of 2,6-DMA, because it favors the formation of xylene through direct ammonia elimination involving low H2 consumption. The activity for xylene formation on niobia is linked to the electron-deficient nature of the Mo sulfide site, as demonstrated by CO adsorption followed by IR. 相似文献
4.
The catalytic activity of Pt catalysts supported on high surface area tin(IV) oxide in the complete oxidation of CH4 traces under lean conditions at low temperature was studied in the absence and in the presence of water (10 vol.%) or H2S (100 vol.ppm). Their catalytic properties were compared to those of Pd/Al2O3 and Pt/Al2O3. In the absence of H2S in the feed, Pt/SnO2appears as a very promising catalyst for CH4 oxidation, being even significantly more active under wet conditions than the best reference catalyst, Pd/Al2O3. Catalysts steamed-aged at 873 K were also studied in order to simulate long term ageing in real lean-burn NGV exhaust conditions. To this respect, Pt/SnO2 is slightly less resistant than Pd/Al2O3. In the presence of H2S, Pt/SnO2catalysts are rapidly and almost completely poisoned, comparably to Pd/Al2O3and the catalytic activity is hardly restored upon oxidising treatment below 773 K. A synergetic effect between Pt and specific surface SnO2sites active in CH4oxidation is proposed to explain the superior catalytic behaviour of Pt/SnO2. 相似文献
5.
Jérôme Andrieux Dariusz Swierczynski Laetitia Laversenne Anthony Garron Simona Bennici Christelle Goutaudier Philippe Miele Aline Auroux Bernard Bonnetot 《International Journal of Hydrogen Energy》2009
In the present work, hydrogen generation through hydrolysis of a NaBH4(s)/catalyst(s) solid mixture was realized for the first time as a solid/liquid compact hydrogen storage system using Co nanoparticles as a model catalyst. The performance of the system was analysed from both the thermodynamic and kinetic points of view and compared with the classical catalyzed hydrolysis of a NaBH4 solution. The kinetic analysis of the NaBH4(s)/catalyst(s)/H2O(l) system shows that the reaction is first order with respect to the catalyst concentration, and the activation energy equal to 35 kJ molNaBH4−1. Additionally, calorimetric measurements of the heat evolved during the hydrolysis of NaBH4 solutions evidence the global process energy (−217 kJ molNaBH4−1). Characterization of the cobalt nanoparticles before and after the hydrolysis associated with the calorimetric measurements suggests the “in situ” formation of a catalytically active CoxB phase through “reduction” of an outer protective oxide layer that is regenerated at the end of reaction. 相似文献
6.
Farrell RA Kinahan NT Hansel S Stuen KO Petkov N Shaw MT West LE Djara V Dunne RJ Varona OG Gleeson PG Jung SJ Kim HY Koleśnik MM Lutz T Murray CP Holmes JD Nealey PF Duesberg GS Krstić V Morris MA 《Nanoscale》2012,4(10):3228-3236
Extending the resolution and spatial proximity of lithographic patterning below critical dimensions of 20 nm remains a key challenge with very-large-scale integration, especially if the persistent scaling of silicon electronic devices is sustained. One approach, which relies upon the directed self-assembly of block copolymers by chemical-epitaxy, is capable of achieving high density 1?:?1 patterning with critical dimensions approaching 5 nm. Herein, we outline an integration-favourable strategy for fabricating high areal density arrays of aligned silicon nanowires by directed self-assembly of a PS-b-PMMA block copolymer nanopatterns with a L(0) (pitch) of 42 nm, on chemically pre-patterned surfaces. Parallel arrays (5 × 10(6) wires per cm) of uni-directional and isolated silicon nanowires on insulator substrates with critical dimension ranging from 15 to 19 nm were fabricated by using precision plasma etch processes; with each stage monitored by electron microscopy. This step-by-step approach provides detailed information on interfacial oxide formation at the device silicon layer, the polystyrene profile during plasma etching, final critical dimension uniformity and line edge roughness variation nanowire during processing. The resulting silicon-nanowire array devices exhibit Schottky-type behaviour and a clear field-effect. The measured values for resistivity and specific contact resistance were ((2.6 ± 1.2) × 10(5)Ωcm) and ((240 ± 80) Ωcm(2)) respectively. These values are typical for intrinsic (un-doped) silicon when contacted by high work function metal albeit counterintuitive as the resistivity of the starting wafer (~10 Ωcm) is 4 orders of magnitude lower. In essence, the nanowires are so small and consist of so few atoms, that statistically, at the original doping level each nanowire contains less than a single dopant atom and consequently exhibits the electrical behaviour of the un-doped host material. Moreover this indicates that the processing successfully avoided unintentional doping. Therefore our approach permits tuning of the device steps to contact the nanowires functionality through careful selection of the initial bulk starting material and/or by means of post processing steps e.g. thermal annealing of metal contacts to produce high performance devices. We envision that such a controllable process, combined with the precision patterning of the aligned block copolymer nanopatterns, could prolong the scaling of nanoelectronics and potentially enable the fabrication of dense, parallel arrays of multi-gate field effect transistors. 相似文献
7.
Laetitia Philippe Chris Sammon Stuart B. Lyon Jack Yarwood 《Progress in Organic Coatings》2004,49(4):C29-323
A detailed temperature variation (18–50 °C) FTIR/ATR study of sorption and desorption of water into a series of cured epoxy resins has been reported. For higher temperatures (35–50 °C) the data were modelled with a single Fickian diffusion equation, giving an increased D as the temperature increased and an activation energy (EA) in the 55–60 kJ mol−1 region. At lower temperatures (18–35 °C)—well-below the Tg—a two-stage sorption equation was needed and the apparent EA was negative. This is probably associated with changes in water clustering among the distributed ‘voids’ in the glassy polymer associated with chain relaxation at extended times. The use of D2O as a penetrant allowed diffusion coefficient measurements for highly dense epoxy matrices, where FTIR/ATR cannot detect the ν(OH) band of water over and above the residual polymer–OH groups (in the dry state). The data for the D2O studies were notably influenced by isotopic exchange; which was found to be a diffusion controlled process, even in a polymer matrix. 相似文献
8.
9.
We consider discrete mechanical systems subject to perfect unilateral constraints. Moreau's impact law uses the decomposition of the velocity on the normaland tangent cones to the set of admissible positions at the impact point, and it iswell-known that this gives the only possible rule in the case of a singleperfect unilateral constraint. In the multi-constraint case, there areother possible energetically and geometrically consistant impact laws. Weshow here that in a number of cases, the limiting behavior of impact asits rigidity tends to infinity is given by Moreau's rule, i.e., in a more mathematical language, we justify this impact law by a penalty approach.First we describe the penalty method, then we apply it to amulti-constraint model problem. We choose an overdamped approximationand we obtain Moreau's rule for inelastic shocks in the limit. Finally,we present the computational drawbacks of the penalty method. 相似文献
10.
Laetitia?Petit Fabienne?Baraige Anne-Marie?Balois Yves?Bertheau Patrick?FachEmail author 《European Food Research and Technology》2003,217(1):83-89
Polymerase chain reaction (PCR)-enzyme linked immunosorbent assays (ELISAs) targeting either the 35S promoter or the Bt176 specific junction sequence were developed to screen for the presence of genetically modified organisms (GMOs) and specifically detect Bt176 maize in flours and starches. Two additional PCR-ELISA assays were developed to validate the results: one, based on the detection of the maize alcohol dehydrogenase 1 promoter specifically detected the presence of maize, and the other, based on the detection of a conserved sequence of plants ( 26S ribosomal RNA gene), validated the extracted DNA amplification. The PCR-ELISA assays developed here were highly specific and found to be as sensitive as the reference Southern hybridisation assay. The PCR-ELISA tests were at least 6 times more sensitive than gel electrophoresis and allowed 0.1% GMOs to be detected in Bt176, Bt11, Mon810 maize and Roundup Ready soybean. The PCR-ELISA tests are a method of choice for GMO screening and identifying Bt176 maize in flours and native starches. They may offer a cheaper alternative to the expensive real-time PCR assays and may be useful in laboratory GMO monitoring. 相似文献