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51.
Catalytic Reduction of Nitrogen Oxides in Automotive Exhaust Containing Excess Oxygen by NOx Storage-Reduction Catalyst 总被引:2,自引:0,他引:2
Shin'ichi Matsumoto 《CATTECH》2000,4(2):102-109
Automotive catalyst technology is now faced with very difficult problems. As a result of automakers' efforts to produce more efficient and lower-emission vehicles, lean-burn gasoline engines have been introduced into the market. While these are much more efficient than the conventional engines, the NOx removal has become significantly more difficult. After enormous efforts, we succeeded to solve the problem by inventing a new class of catalyst. Here, our challenge to develop the new catalyst that stores and then reduces NOx is described. The catalyst made it possible for emissions of lean-burn engines to meet the strict NOx regulations. 相似文献
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Kitiya Hongsirikarn James G. Goodwin Jr. Scott Greenway Stephen Creager 《Journal of power sources》2010,195(1):30-38
The effect of NH3 and NH4+ poisoning on the conductivity of Nafion membranes was investigated via electrochemical impedance spectroscopy. The conductivities of membranes prepared with different NH4+ compositions were measured in deionized water at room temperature and compared to those at 80 °C in a gas phase for various relative humidities. The liquid-phase conductivity decreased linearly with an increase in the NH4+ composition in the membrane (yNH4+), with that of the NH4+-form having a conductivity 25% that of the H+-form. The gas-phase conductivity of the NH4+-form, on the other hand, declined by 66–98% relative to the H+-form depending on humidity. The conductivities of fresh membranes in the presence of gas-phase NH3 at different humidities were also studied. The conductivity decreased with time-on-stream and reached the same conductivity at a given humidity regardless of the NH3 concentration, but the time to reach steady-state varied with NH3 concentration. The yNH4+ at steady-state conductivity was equivalent for all the NH3 concentrations studied. The kinetics of conductivity decrease was slower at higher humidities. The humidity and yNH4+ appear to have a concerted effect on the conductivity. The quantitative conductivity data under practical fuel cell conditions should be useful for future fuel cell modeling. 相似文献
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This paper reports the results of investigations of shellfish toxin contamination of products obtained from Shanghai seafood markets. From May to October 2003, 66 samples were collected from several major seafood markets. Paralytic shellfish poisoning (PSP) and diarrhetic shellfish poisoning (DSP) toxins in shellfish samples were monitored primarily by a mouse bioassay, then analysed by HPLC for the chemical contents of the toxins. According to the mouse bioassay, eight samples were detected to be contaminated by PSP toxins and seven samples were contaminated by DSP toxins. Subsequent HPLC analysis indicated that the concentrations of the PSP toxins ranged from 0.2 to 1.9 µg/100 g tissues and the main components were gonyautoxins 2/3 (GTX2/3). As for DSP, okadaic acid was detected in three samples, and its concentration ranged from 3.2 to 17.5 µg/100 g tissues. Beside okadaic acid, its analogues, dinophysistoxins (DTX1), were found in one sample. According to the results, gastropod (Neverita didyma) and scallop (Argopecten irradians) were more likely contaminated with PSP and DSP toxins, and most of the contaminated samples were collected from Tongchuan and Fuxi markets. In addition, the contaminated samples were always found in May, June and July. Therefore, consumers should be cautious about eating the potential toxic shellfish during this specific period. 相似文献
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The extent of irreversible deactivation of Pt towards hydrogen oxidation reaction (HOR) due to sulfur adsorption and subsequent electrochemical oxidation is quantified in a functional polymer electrolyte membrane (PEM) fuel cell. At 70 °C, sequential hydrogen sulfide (H2S) exposure and electrochemical oxidation experiments indicate that as much as 6% of total Pt sites are deactivated per monolayer sulfur adsorption at open-circuit potential of a PEM fuel cell followed by its removal. The extent of such deactivation is much higher when the electrode is exposed to H2S while the fuel cell is operating at a finite load, and is dependent on the local overpotential as well as the duration of exposure. Regardless of this deactivation, the H2/O2 polarization curves obtained on post-recovery electrodes do not show performance losses suggesting that such performance curves alone cannot be used to assess the extent of recovery due to sulfur poisoning. A concise mechanism for the adsorption and electro-oxidation of H2S on Pt anode is presented. H2S dissociatively adsorbs onto Pt as two different sulfur species and at intermediate oxidation potentials, undergoes electro-oxidation to sulfur and then to sulfur dioxide. This mechanism is validated by charge balances between hydrogen desorption and sulfur electro-oxidation on Pt. The ignition potential for sulfur oxidation decreases with increase in temperature, which coupled with faster electro-oxidation kinetics result in the easier removal of adsorbed sulfur at higher temperatures. Furthermore, the adsorption potential is found to influence sulfur coverage of an electrode exposed to H2S. As an implication, the local potential of a PEM fuel cell anode exposed to H2S contaminated fuel should be kept below the equilibrium potential for sulfur oxidation to prevent irreversible loss of Pt sites. 相似文献
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目的 了解济南市售生鸡肉中金黄色葡萄球菌污染状况和分离株肠毒素基因携带情况,评估生鸡肉产品对消费者的健康风险。方法 2021年3~11月对济南市主要人口密集区域的部分大型超市、农贸市场、肉制品零售店等流通环节及电商平台进行样品采集,依据GB 4789.10—2016《食品微生物学检验 金黄色葡萄球菌检验》要求对样品进行金黄色葡萄球菌检验;通过聚合酶链式反应(PCR)对分离株进行复核鉴定和5种肠毒素基因(sea、seb、sec、sed、see)的检测;使用Risk ranger风险评估软件评估济南市售生鸡肉中金黄色葡萄球菌对消费者健康的影响。结果 在采集的180份样品中,共55份样品检出金黄色葡萄球菌,其中大型超市、电商平台来源的冷冻鸡制品16份(16/61);农贸市场,肉制品零售店来源的冷冻鸡制品30份(30/60),鲜整鸡9份(9/59)。55株分离株中有9株携带至少一种经典肠毒素基因。半定量风险评估结果提示,济南市售生鸡肉中金黄色葡萄球菌导致消费者罹患食物中毒的风险等级为高风险水平,其中农贸市场、肉制品零售店来源的冷冻鸡制品风险值为53;鲜整鸡风险值为52;大型超市、电商平台来源的冷冻鸡制品风险值为49。结论 济南市市售生鸡肉中金黄色葡萄球菌污染水平较为严重。结合风险评估结果,建议有关部门加强监管力度,规范市售冷冻肉制品的运输和存放条件,降低冷冻鸡制品细菌污染的风险,保障消费者健康。 相似文献
59.
M. Ziolek I. Sobczak I. Nowak M. Daturi J. C. Lavalley 《Applied catalysis. B, Environmental》2000,28(3-4):197-207
NO adsorption and decomposition were studied on sulphided and sulphated copper-exchanged ZSM-5, AlMCM-41 and NbMCM-41 molecular sieves. FTIR, temperature-programmed reduction (H2-TPR) techniques, adsorption, and catalytic measurements were applied. H2S adsorption drastically decreases the activity of copper-containing micro- and mesoporous materials studied in NO decomposition due to their sulphidation. This decrease is higher than that observed after SO2 treatment and is assigned to the formation of sulphide species. H2S is strongly chemisorbed on all copper active sites. Oxidation of sulphide species leading to the formation of sulphates does not increase the activity in the decomposition of NO, suggesting that some sulphided species are not oxidised. 相似文献
60.
Proton exchange membrane fuel cell (PEMFC) performance degrades when carbon monoxide (CO) is present in the fuel gas; this is referred to as CO poisoning. This paper investigates CO poisoning of PEMFCs by reviewing work on the electrochemistry of CO and hydrogen, the experimental performance of PEMFCs exhibiting CO poisoning, methods to mitigate CO poisoning and theoretical models of CO poisoning. It is found that CO poisons the anode reaction through preferentially adsorbing to the platinum surface and blocking active sites, and that the CO poisoning effect is slow and reversible. There exist three methods to mitigate the effect of CO poisoning: (i) the use of a platinum alloy catalyst, (ii) higher cell operating temperature and (iii) introduction of oxygen into the fuel gas flow. Of these three methods, the third is the most practical. There are several models available in the literature for the effect of CO poisoning on a PEMFC and from the modeling efforts, it is clear that small CO oxidation rates can result in much increased performance of the anode. However, none of the existing models have considered the effect of transport phenomena in a cell, nor the effect of oxygen crossover from the cathode, which may be a significant contributor to CO tolerance in a PEMFC. In addition, there is a lack of data for CO oxidation and adsorption at low temperatures, which is needed for detailed modeling of CO poisoning in PEMFCs. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献