PM-support interfacial effect and oxygen mobility in Pt,Pd or Rh-loaded (Ce,Zr,La)O2 catalysts

• Pt/CZL exhibits the optimum catalytic performance for HC and NO_x elimination. • The strong PM-Ce interaction favors the oxygen mobility and DOSC. • Pd/CZL shows higher catalytic activity for CO conversion due to more O_latt species. • Great oxygen mobility at high temperature broadens the dynamic operation window. • The relationship between DOSC and catalytic performance is revealed. The physicochemical properties of Pt-, Pd- and Rh- loaded (Ce,Zr,La)O₂ (shorted for CZL) catalysts before/after aging treatment were systematically characterized by various techniques to illustrate the relationship of the dynamic oxygen storage/release capacity and redox ability with their catalytic performances for HC, NO_x and CO conversions. Pt/CZL catalyst exhibits the optimum catalytic performance for HC and NO_x elimination, which mainly contribute to its excellent redox ability and dynamic oxygen storage/release capacity (DOSC) at lower temperature due to the stronger PM (precious metals)-support interaction. However, the worse stability of Pt-O-Ce species and volatile Pt oxides easily result in the dramatical decline in catalytic activity after aging. Pd/CZL shows higher catalytic activity for CO conversion by reason of more O_latt species as the active oxygen for CO oxidation reaction. Rh/CZL catalyst displays the widest dynamic operation window for NO_x elimination as a result of greater oxygen mobility at high temperature, and the ability to retain more Rh-O-Ce species after calcined at 1100°C effectively restrains sintering of active RhO_x species, improving the thermal stability of Rh/CZL catalyst.     

Effect of La3+ on the activities of antioxidant enzymes in wheat seedlings under lead stress in solution culture

In order to improve the plant ability to resist lead stress, effect of 0.05 mg/l La(NO₃)₃ on the activities of catalase (CAT), superoxide dismutase (SOD), the level of malondialdehyde (MDA) in wheat seedlings under lead stress was studied. The effect of La³⁺ on plant growth, chlorophyll content in wheat seedlings after adding 0, 50, 100 mg/l Pb(NO₃)₃ to the nutrient solution for 12 days was observed. The plants were grown in nutrient solution in a strictly controlled climate growth room. Effects of La³⁺ (with La treatment) compared with check groups was evidently observed. The activities of SOD and CAT in root were enhanced 0.45–1.69 times and 33.20–77.77% respectively and MDA content was reduced 11.05–27.49% in root after treatments from the second day till the end of the experiment. The activities of SOD and CAT was found to be increased slightly (P<0.05) and MDA content decreased in shoot and root of wheat seedlings by La³⁺ under lead stress within five days after treatments compared with Pb1 and Pb2 groups. It was assumed that antioxidant enzymes was found to be increased by La(NO₃)₃, the antioxidant potential of the wheat seedlings to resist lead stress enhanced. It is suggested that La³⁺ could be used to resist lead stress at the beginning under stress while the stress was not so serious.     

A critical geography approach to land and water use in the tourism economy in Los Cabos,Baja California Sur,Mexico

ABSTRACT

This paper offers a critical assessment of how tourism development in the municipality of Los Cabos, Baja California Sur affects land and water use. Los Cabos is a seaside tourism Mecca located at the southern tip of the Baja California peninsula, in Mexico’s northwest. There, subsidised profits and a process of dispossession in the tourism sector have to do mainly with land and water appropriation in the form of restrictions to beach access by the local population, urban segregation and, in an arid region, privileging water provision for the tourism industry over the needs of the population. In order to sustain these claims, we map water and land use for tourism in Cabo San Lucas. We also analyse the expansion of the Los Cabos type of tourism to the small town of La Ribera, in the East Cape-Cabo Pulmo area, where marinas and high scale housing for residential tourism sprout along the coast. We argue that the seemingly ever-growing presence of tourism in the region carries with it an urgent call for the reappraisal of current approaches to land and water use, if local resources are to deliver quality of life for the population, and not only economic profitability for (mostly) foreign capital. Analytically, we address these issues by unpacking David Harvey’s concept of accumulation by dispossession, which – we argue – is for our purposes a broader tent than the (mostly Latin American) theorisations on extractivism, as we explain later in the relevant section of the paper.     

La2O3/ZnO/TiO2光催化降解活性艳红K-2BP的研究

采用溶胶-凝胶法制备了La2O3/ZnO/TiO2复合光催化剂,以紫外灯为光源,活性艳红K-2BP为模型降解物,研究了La2O3/ZnO/TiO2的光催化性能.结果表明:当锌和镧的掺杂量w(zno)=20%,w(La2O3)=0.5%,煅烧温度为500℃时,La2O3/ZnO/TiO2复合光催化剂的光催化活件最高;当催化荆投加量4 g/L,通气量800 mL/min,初始pH值3.12时,La2O3/ZnO/TiO2对活性艳红K-2BP的降解效果最好.实验证明.La2O3/ZnO/TiO2对活性艳红K-2BP的降解遵从Lang-muir-Hinshelwood动力学模型,测得其反应速率常数k=11.5 mg/(L·min);吸附常数K=2.88×10-2L/mg.     

各类VOCs在蜂窝陶瓷型La0.8Sr0.2MnO3催化剂上的催化燃烧性能

以涂有CeO2-ZrO2固溶体的堇青石蜂窝状陶瓷为载体,用浸渍法制备堇青石蜂窝陶瓷型整体La0.8Sr0.2MnO3催化剂,测试了该催化剂催化燃烧各类VOCs的特性。研究表明,VOCs催化燃烧的难易程度为：含氯烃〉烷烃〉酸〉芳烃〉酮〉酯〉醇〉醛。La0.8Sr0.2MnO3催化剂对含氧有机化合物具有较好的催化活性,完全燃烧温度均在280℃之内。通过关联VOCs的理化性质,发现VOCs在La0.8Sr0.2MnO3催化剂上的反应活性与VOCs分子中最弱C—H键键能和VOCs分子极性密切联系。     

镧(Ⅲ)离子诱导的菲律宾蛤仔金属硫蛋白性质研究

稀土离子能否诱导海洋生物的金属硫蛋白(MT)合成,将影响到MT对海水重金属的指示作用.以菲律宾蛤仔(Ruditapes philippinarum)为试验动物,采用含镧(Ⅲ)离子(La3+)的人工海水对其进行暴露培养,测定蛤仔鳃部和内脏中MT含量.结果表明,La3+暴露能够增加蛤仔体内MT含量,其中,10～1×100μg·L-1的La3+对鳃部诱导作用较大;10～1×10000μg·L-1的La3+对内脏MT均有较好诱导;同时,过柱层析洗脱液的光谱扫描及十二烷基的硫酸盐钠-聚丙烯酰胺凝胶电泳法(SDS-PAGE)分析表明,La3+诱导的蛤仔内脏中的MT在258nm处有特征吸收峰,主要以二聚体和三聚体的形式存在,分子量为13.1kD和18.3kD.     

Changes in the quality of river water before, during and after a major flood event associated with a La Niña cycle and treatment for drinking purposes

The treatment of organics present in the lower reaches of a major river system（the Murray–Darling Basin, Australia） before（March–July 2010）, during（December 2010–May 2011） and after（April–December 2012） a major flood period was investigated. The flood period（over 6 months）occurred during an intense La Nia cycle, leading to rapid and high increases in river flows and organic loads in the river water. Dissolved organic carbon（DOC） increased（2–3 times） to high concentrations（up to 16 mg/L） and was found to correlate with river flow rates. The treatability of organics was studied using conventional jar tests with alum and an enhanced coagulation model（mEnCo）. Predicted mean alum dose rates（per mg DOC） were higher before（9.1 mg alum/mg DOC） and after（8.5 mg alum/mg DOC） than during the flood event（8.0 mg alum/mg DOC）,indicating differences in the character of the organics in raw waters. To assess the character of natural organic matter present in raw and treated waters, high performance size exclusion chromatography with UV and fluorescence detectors were used. During the flood period, high molecular weight UV absorbing compounds（〉2 kDa） were mostly detected in waters collected,but were not evident in waters collected before and afterwards. The relative abundances of humic-like and protein-like compounds during and following the flood period were also investigated and found to be of a higher molecular weight during the flood period. The treatability of the organics was found to vary over the three climate conditions investigated.     

可控合成La（OH）3纳米球光催化去除NO及其催化性能机制研究

以KOH和La(NO3)3·6H2O为前驱体,柠檬酸为保护剂,采用一步水热法合成三维La(OH)3纳米球光催化剂.通过XRD、SEM、PL和UV-vis DRS等对样品进行结构表征.结果表明,柠檬酸的加入量对La(OH)3的形貌均匀性和催化活性均有较大影响.柠檬酸和La(NO3)3·6H2O的物质的量的比为2∶1时,得到的样品为形貌均匀的纳米球,光催化活性最佳且稳定性好.这是因为三维的纳米球结构更容易促进光生载流子的分离;此外,形貌均匀无团聚,增加了催化剂表面的活性位点,使反应过程中反应物和中间产物迅速扩散,从而光催化活性最高.在光催化过程中,羟基自由基(·OH)和超氧自由基(·O-2)是最主要的氧化物种.NO可以和产生的·OH和·O-2反应生成HNO2和HNO3,从而去除NO.本文研究结果充实了La(OH)3光催化材料的合成基础理论,探讨了La(OH)3光催化活性机理,为La(OH)3应用打开了新的视野.     

ZrO2掺杂对La2Ce2O7力学和热物理性能 影响的研究

目的提高La_2Ce_2O_7(LC)陶瓷材料的断裂韧性。方法采用固相反应方法合成Y_2O_3稳定ZrO_2(YSZ)掺杂的La_2Ce_2O_7(LC)陶瓷材料(LCZ),研究LCZ块材的弹性模量、断裂韧性等力学性能,以及热膨胀系数、热传导率等热物理性能。结果 10%YSZ摩尔分数掺杂的LCZ块材的断裂韧性约为1.4 MPa·m1/2,比LC提高了近10%。YSZ掺杂有效地抑制了LC在200～400℃温度区间热膨胀系数下降的现象。在200～1200℃温度范围内,LCZ块材的热膨胀系数为10×10-6～12×10-6K-1,在1200℃的热导率约为0.75W/(m·K),比YSZ降低了50%以上,显示了优异的隔热性能。结论 YSZ的掺杂使LC中部分Zr4+取代了La3+,降低了晶格中的O空位浓度,原子的横向剪切运动被削弱,有效地抑制了LC在200～400℃温度区间热膨胀系数下降的现象。由于t-ZrO_2→m-ZrO_2的相变对微裂纹的愈合作用,10%YSZ掺杂使LC块材的断裂韧性得到有效提高。     

不同浓度镧处理对铅胁迫下玉米生长和铅吸收的影响

采用温室盆栽试验的方法,研究不同浓度的镧处理(0、50、200和800 mg·kg~(-1))对中度铅胁迫下(200 mg·kg~(-1))玉米生长、矿质营养元素吸收、C∶N∶P生态化学计量比及Pb和La吸收的影响,探讨土壤-植物系统中稀土重金属的相互作用,旨在为稀土矿区稀土重金属复合污染土壤的治理提供基础数据和理论依据.结果表明,随着外源La浓度的增加土壤中乙酸铵-EDTA提取态La的浓度显著增加,而乙酸铵-EDTA提取态Pb的浓度显著降低;玉米地上部干重显著降低了17.90%~81.17%,根冠比显著增加了21.74%~86.96%;随着土壤中La浓度的增加根部P含量显著降低了19.16%~89.68%,La浓度为200 mg·kg~(-1)和800 mg·kg~(-1)时,地上部P和N含量分别显著降低了65.51%~91.98%和48.27%~76.58%;随着土壤中La浓度的增加,植株C∶P、N∶P和植株La浓度显著增加,地上部和根部Pb浓度分别显著增加了52.61%~99.01%和15.99%~44.34%;随着La浓度的升高显著降低了玉米植株K、Ca和Mg的含量.结果初步证明,在稀土-重金属复合污染土壤中,稀土元素的存在加剧了重金属对植物生长的毒害效应及其所引发的生态风险问题,应进一步深入研究稀土对植物吸收重金属的影响及作用机制.