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211.
The catalytic activity and durability of Rh/ZrO_2 catalyst were investigated compared with Rh/Al_2O_3 catalyst under diverse aging atmospheres, including lean, rich and lean–rich cyclic aging atmospheres, to simulate the real working conditions of three-way catalyst.Oxidation states and microstructures of rhodium species were investigated to correlate with the catalytic performance of the catalysts. The catalytic performance and durability of the Rh catalyst under diverse aging atmospheres were drastically enhanced by ZrO_2 support. ZrO_2 support was confirmed to be able to effectively inhibit rhodium sintering even under diverse aging conditions. It can also successfully keep Rh species in an active low-valence state on the surface of the catalyst. The superiority of ZrO_2 support compared to Al_2O_3 was verified by the Rh-based monolith catalyst. 相似文献
212.
Rapid degradation of carbon tetrachloride by commercial micro-scale zinc powder assisted by citric acid 总被引:1,自引:0,他引:1
Xianchao Gao Feng Yang Yeqing Lan J.-D. Mao Xinyan Duan 《Environmental Chemistry Letters》2011,9(3):431-438
We developed an effective method for degradation of carbon tetrachloride (CT) in contaminated water. Zinc metal as a reducing
agent for CT in aqueous solutions has been previously studied in some detail, but the rapid corrosion of zinc surface usually
reduces its efficiency in removing CT. We assumed that citric acid could enhance the degradation of CT by zinc powder due
to the elimination of a passivation layer of Zn(II) (hydr)oxides on the surface of zinc powder through chelating of organic
ligands with Zn(II) produced from the reaction and keeping the exposure of active sites to targets. Here the influence of
citric acid on the decomposing of CT by commercial micro-scale zinc powder was investigated in a pH range of 3.5–7.5 at 25°C
in batch experiments. Reaction mixtures were analysed by gas chromatography/headspace analysis, and Cl− concentration was determined by turbidimetry. The results demonstrate that the degradation of CT by zinc metal alone is very
weak, but the addition of citric acid can assist zinc powder to decompose CT more completely and rapidly at all pHs. Degradation
of CT took place mainly in the first 10 min of reaction, coupled with 75–95% of CT removal. Maximum dechlorination percentage
(82.4%) of CT was obtained at pH 5.5. In that case, chloroform and dichloromethane, as main intermediates, were found at low
levels during the whole reaction, suggesting that CT may be sequentially and multiply degraded so quickly that methane is
yielded before the intermediates can be desorbed and released to aqueous solution. When compared with the current methods
of nano-scale zinc and bimetallic systems, the application of commercial micro-scale zinc particles assisted by organic ligands
is of environmental significance since it allows decontamination of aqueous chlorinated organic compounds at low cost and
with high efficiency. 相似文献
213.
建设项目景观环境影响评价探讨 总被引:2,自引:0,他引:2
本文在评价实例基础上,尝试性地探讨了建设项目景观环境影响评价的目的、原则、内容、方法和标准体系,以建立一种采用划分级别的定性评价方式。 相似文献
214.
215.
环境中的PAES对蟾蜍蝌蚪红细胞微核的影响研究 总被引:2,自引:0,他引:2
通过对邻苯二甲酸酯对蟾蜍蝌蚪红细胞微核的影响进行了研究。目的探讨邻苯二甲酸酯对蟾蜍蝌蚪的致突变作用。方法以邻苯二甲酸二甲酯为污染物对蟾蜍蝌蚪染毒24小时,并观察其细胞核变化。所用蟾蜍蝌蚪处于变态期,对污染物较为敏感。结果邻苯二甲酸酯使蟾蜍蝌蚪红细胞微核率以及核异常细胞率上升,微核率随着浓度的增大而上升,在浓度为78 ug/ml,对照组相比有极显著差异P〈0.01,浓度在18.5 ug/ml时试验组突变的细胞核的形态发生显著改变,核异常细胞率与对照组核异常细胞率有显著差异P〈0.05。此时显微镜下观察可见微核、双核、核内凹、核碎裂、无丝分裂时核分裂不均等核的形态变化。结论邻苯二甲酸酯对蟾蜍蝌蚪具有明显的致突变作用。 相似文献
216.
217.
Potassium-modified ceria-zirconia catalyst was synthesized by wetness impregnation method.The ageing treatment was performed in static air at 800°C for 20 hr to evaluate the thermal stability of the catalyst.The catalysts were characterized by X-ray diffraction,BET surface area,oxygen storage capacity,NOx-temperature programmed desorption and soot-temperature programmed oxidation measurements.By introduction of potassium,the maximum soot oxidation rate temperature(Tm) of the ceria-zirconia based catalyst de... 相似文献
218.
应用氢化物原子荧光法,测定鲤鱼肝脏中痕量Hg和As,该法具有原子吸收和原子发射光谱两种技术优势,同时它具有分析灵敏度高,干扰少,线性范围宽,可多元素同时测定等优点;在KBH4-酸还原体系中同时测定鱼肝中Hg和As,方法检出限分别为Hg:0.33ng/ml和As0.36ng/ml,线性范围分别为:0.1—2.0ng/ml和1.0—20.0ng/ml。加标回收率分别为Hg:96.0%和As:100.6%。分析结果可靠,方法令人满意,并适合大批量样品的分析. 相似文献
219.
220.
A Pt/WO3/TiO2 catalyst for propane oxidation was prepared by a stepwise wet impregnation method, and was aged at 800℃ for 5 hr. Compared to the sulfate-derived titania supported catalyst, the introduction of tungsten oxide as stable Bronsted acid sites led to the formation of more metallic platinum active sites at the Pt/WO3 interface. The dissociation of surface intermediates for propane oxidation was promoted on the WO3-modified catalyst. This, as well as the inhibition effects of tungsten oxide on the sintering of anatase and the phase transformation to rutile, resulting in a high activity and thermal stability for the Pt/WO3/TiO2 catalyst. 相似文献