In situ formation of an oxygen-evolving catalyst in neutral water containing phosphate and Co2+

The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equivalents. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions. A variety of analytical techniques indicates the presence of phosphate in an approximate 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.     

A synthetic nickel electrocatalyst with a turnover frequency above 100,000 s⁻¹ for H₂ production

Reduction of acids to molecular hydrogen as a means of storing energy is catalyzed by platinum, but its low abundance and high cost are problematic. Precisely controlled delivery of protons is critical in hydrogenase enzymes in nature that catalyze hydrogen (H(2)) production using earth-abundant metals (iron and nickel). Here, we report that a synthetic nickel complex, [Ni(P(Ph)(2)N(Ph))(2)](BF(4))(2), (P(Ph)(2)N(Ph) = 1,3,6-triphenyl-1-aza-3,6-diphosphacycloheptane), catalyzes the production of H(2) using protonated dimethylformamide as the proton source, with turnover frequencies of 33,000 per second (s(-1)) in dry acetonitrile and 106,000 s(-1) in the presence of 1.2 M of water, at a potential of -1.13 volt (versus the ferrocenium/ferrocene couple). The mechanistic implications of these remarkably fast catalysts point to a key role of pendant amines that function as proton relays.     

High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt

The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non-precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).     

Heterogeneous catalysis: some recent developments

In recent years major progress has been made in the area of heterogeneous catalysis by metals. Much has been learned about the nature of metal catalysts and of catalytic phenomena on metals. Characteristic patterns of catalytic behavior among the metallic elements have been established for certain classes of reactions, and these patterns provide a first step toward a more comprehensive understanding of catalytic specificity. Studies on metal alloys and related bimetallic catalysts have revived interest in a geometric factor in surface catalysis to complement the traditional electronic factor. Closely related to this geometric factor is the discovery that selectivity, rather than activity alone, is a major factor in reactions on bimetallic catalysts. Concurrent with progress in understanding how catalysts work, advances are also being made in the development of new catalyst systems, examples of which are the bimetallic (or polymetallic) cluster catalysts. Research in this area provides an example of how advances in catalyst technology can be realized within a framework of fundamental research on catalytic phenomena (38).     

The assimilation of elements ingested by marine copepods

The efficiency with which a variety of ingested elements (Ag, Am, C, Cd, P, S, Se, and Zn) were assimilated in marine calanoid copepods fed uniformly radiolabeled diatoms ranged from 0.9% for Am to 97.1% for Se. Assimilation efficiencies were directly related to the cytoplasmic content of the diatoms. This relation indicates that the animals obtained nearly all their nutrition from this source. The results suggest that these zooplankton, which have short gut residence times, have developed a gut lining and digestive strategy that provides for assimilation of only soluble material. Because the fraction of total cellular protein in the cytoplasm of the diatoms increased markedly with culture age, copepods feeding on senescent cells should obtain more protein than those feeding on rapidly dividing cells. Elements that are appreciably incorporated into algal cytoplasm and assimilated in zooplankton should be recycled in surface waters and have longer oceanic residence times than elements bound to cell surfaces.     

制备邻苯基苯酚的Cu-MgO催化剂失活研究

[目的]探讨引起Cu-MgO催化剂失活的微观因素。[方法]采用共沉淀法制备Cu-MgO催化剂,并采用XRD、BET、NH3-TPD、CO2-TPD、H2-TPD、失重等手段对失活前后的Cu-MgO催化剂进行了表征。[结果]Cu-MgO催化剂对环己烯基环己酮脱氢制备邻苯基苯酚(OPP)有较高的活性,双聚的初始转化率达到99%以上,OPP的选择性达到95%以上,但其催化性能随运转时间的延长呈逐渐下降趋势。表征结果显示,在反应条件下催化剂上Cu原子和MgO随运转时间的延长明显聚集长大,导致Cu与MgO之间作用力减弱,氢吸附能力和碱量降低;催化剂表面积炭,改变了催化剂比表面积和孔结构,从而使催化剂活性和选择性下降。[结论]为抑制催化剂失活的研究奠定了基础。     

Molecular recognition in the selective oxygenation of saturated C-H bonds by a dimanganese catalyst

Although enzymes often incorporate molecular recognition elements to orient substrates selectively, such strategies are rarely achieved by synthetic catalysts. We combined molecular recognition through hydrogen bonding with C-H activation to obtain high-turnover catalytic regioselective functionalization of sp3 C-H bonds remote from the -COOH recognition group. The catalyst contains a Mn(mu-O)2Mn reactive center and a ligand based on Kemp's triacid that directs a -COOH group to anchor the carboxylic acid group of the substrate and thus modify the usual selectivity for oxidation. Control experiments supported the role of hydrogen bonding in orienting the substrate to achieve high selectivity.     

Coking- and sintering-resistant palladium catalysts achieved through atomic layer deposition

We showed that alumina (Al(2)O(3)) overcoating of supported metal nanoparticles (NPs) effectively reduced deactivation by coking and sintering in high-temperature applications of heterogeneous catalysts. We overcoated palladium NPs with 45 layers of alumina through an atomic layer deposition (ALD) process that alternated exposures of the catalysts to trimethylaluminum and water at 200°C. When these catalysts were used for 1 hour in oxidative dehydrogenation of ethane to ethylene at 650°C, they were found by thermogravimetric analysis to contain less than 6% of the coke formed on the uncoated catalysts. Scanning transmission electron microscopy showed no visible morphology changes after reaction at 675°C for 28 hours. The yield of ethylene was improved on all ALD Al(2)O(3) overcoated Pd catalysts.     

Renewable hydrogen from ethanol by autothermal reforming

Ethanol and ethanol-water mixtures were converted directly into H2 with approximately 100% selectivity and >95% conversion by catalytic partial oxidation, with a residence time on rhodium-ceria catalysts of <10 milliseconds. Rapid vaporization and mixing with air with an automotive fuel injector were performed at temperatures sufficiently low and times sufficiently fast that homogeneous reactions producing carbon, acetaldehyde, ethylene, and total combustion products can be minimized. This process has great potential for low-cost H2 generation in fuel cells for small portable applications where liquid fuel storage is essential and where systems must be small, simple, and robust.     

Perovskite oxides: materials science in catalysis

In a time of growing need for catalysts, perovskites have been rediscovered as a family of catalysts of such great diversity that a broad spectrum of scientific disciplines have been brought to bear in their study and application. Because of the wide range of ions and valences which this simple structure can accommodate, the perovskites lend themselves to chemical tailoring. It is relatively simple to synthesize perovskites because of the flexibility of the structure to diverse chemistry. Many of the techniques of ceramic powder preparation are applicable to perovskite catalysts. In their own right, they are therefore of interest as a model system for the correlation of solid-state parameters and catalytic mechanisms. Such correlations [See figure in the PDF file] have recently been found between the rate and selectivity of oxidation-reduction reactions and the thermodynamic and electronic parameters of the solid. For commercial processes such as those mentioned in the introduction, perovskite catalysts have not yet proven to be practical. Much of the initial interest in these catalysts related to their use in automobile exhaust control. Current interest in this field centers on noble metalsubstituted perovskites resistant to S poisoning for single-bed, dual-bed, and three-way catalyst configurations. The formulations commercially tested to date have shown considerable promise, but long-term stability has not yet been achieved. A very large fraction of the elements that make up presently used commercial catalysts can be incorporated in the structure of perovskite oxides. Conversely, it is anticipated that perovskite oxides, appropriately formulated, will show catalytic activity for a large variety of chemical conversions. Even though this expectation is by no means a prediction of commercial success in the face of competition by existing catalyst systems, it makes these oxides attractive models in the study of catalytic chemical conversion. By appropriate formulation many desirable properties can be tailored, including the valence state of transition metal ions, the binding energy and diffusion of O in the lattice, the distance between active sites, and the magnetic and conductive properties of the solid. Only a very small fraction of possible perovskite formulations have been explored as catalysts. It is expected that further investigation will greatly expand the scope of perovskite catalysis, extend the understanding of solid-state parameters in catalysis, and contribute to the development of practical catalytic processes.     

功能化二氧化硅固载七钼酸盐催化葡萄糖差向异构反应

采用硅烷偶联剂改性硅载体锚链Mo7O2-4的方法制备了8种固载型催化剂,以D-葡萄糖水相差向异构化制备D-甘露糖反应,评价了催化剂的催化性能,并通过ICP和UV-vis对催化剂的稳定性进行了表征。结果表明,正辛基及十二烷基硅烷修饰的SiO2催化剂（C4、C8）具有较高的催化活性和稳定性,在反应温度80℃、初始pH 4~5的条件下反应6 h,D-甘露糖质量收率分别为28.0%和27.2%。     

The manganese site of the photosynthetic water-splitting enzyme

As the originator of the oxygen in our atmosphere, the photosynthetic water-splitting enzyme of chloroplasts is vital for aerobic life on the earth. It has a manganese cluster at its active site, but it is poorly understood at the molecular level. Polarized synchrotron radiation was used to examine the x-ray absorption of manganese in oriented chloroplasts. The manganese site, in the "resting" (S1) state, is an asymmetric cluster, which probably contains four manganese atoms, with interatomic separations of 2.7 and 3.3 angstroms; the vector formed by the 3.3-angstrom manganese pair is oriented perpendicular to the membrane plane. Comparisons with model compounds suggest that the cluster contains bridging oxide or hydroxide ligands connecting the manganese atoms, perhaps with carboxylate bridges connecting the 3.3-angstrom manganese pair.     

基于MATLAB平台的可视化图像处理系统设计方法

以MATLAB为工作语言和开发环境,开发了一个在MATLAB平台下的可视化图像处理系统,可实现包括对测井图像在内的一般图像的精细处理,并能和用户开发的程序接口.为MATLAB的再开发和可视化系统的设计作了有益的探索.     

Low-cost computer interfaced rain gauge

A conventional tipping bucket rain gauge was directly interfaced with a battery-powered portable lap top computer for digital data acquisition, storage, processing, and uploading to a mainframe computer system. A simple software program was written in BASIC to allow rainfall data recordings of each 0.254 mm of rain with a time resolution of 1 s. The method provides an inexpensive means to improve the time resolution of tipping bucket rain gauges, reduces the costs associated with data processing, and decreases data analysis time.     

催化湿式二氧化氯氧化法处理高浓度有机农药废水的研究

通过浸渍法制备了4类主活性组分的负载型催化剂,用于二氧化氯催化湿式氧化(CWCDO)法处理有机农药废水的研究,并确定了催化湿式氧化的条件。结果表明:4元组合MnO2-CuO-CeO2-V2O(5 24∶1∶1∶)催化剂性能较好;当反应在常温常压下,维持pH值为3～5,反应时间为30 min时,COD的去除率大于85%,色度去除率大于90%。     

Computers in production agriculture

Modern production agriculture in the United States is becoming so complex and sophisticated that computers may soon be an essential tool of successful farm operation and management. Farmers are vigorously seeking information on relevant computer technology and using it as rapidly as economics and availability permit. Their demand for this technology is, however, price-sensitive under current economic conditions. The agricultural research and development system has a long way to go to provide the large integrated software and hardware packages-including simulators and expert systems interfaced with monitoring and control devices-needed to help American farmers retain their competitive edge.     

Cu-Zn/ZSM-5催化剂催化湿式氧化H-酸

以萘系染料中间体中具有代表性的H-酸(1-氨基-8-萘酚-3,6-二磺酸,分子式为C10H9O7S2N)的水溶液为研究对象,分别采用以等体积浸渍法制备的不同负载量的Cu-Zn/ZSM-5催化剂、以共沉淀法制得的Cu-Zn-Al催化剂对H-酸水溶液进行湿空气催化氧化降解。研究结果表明:对于处理H-酸水溶液,Cu-Zn/ZSM-5系列催化剂的COD去除率更高,这主要是由于催化活性中心在分子筛上获得了更优的分散性;最佳的CuO负载量为3.41%,ZnO负载量为1.16%,此时H-酸COD去除率为88.18%。     

酸性催化剂对木材苯酚液化能力的影响

为了探讨酸性催化剂对木材 (杉木和三倍体毛白杨 )苯酚液化的影响 ,该研究采用磷酸 (85 % )、低浓硫酸(36 % )、盐酸 (37% )、草酸 (99 5 % ) 4种弱酸性无机酸 ,在不同温度下进行了木材的液化试验 .结果表明 ,磷酸和低浓硫酸是木材苯酚液化效果较好的催化剂 .在温度为 15 0℃、液化时间为 2h、液体比 (苯酚 木材 )为 4、催化剂含量为10 %的条件下 ,采用磷酸或低浓硫酸 ,可以分别使木材液化后的残渣率降至 3 2 %和 4 0 % .     

小麦颖果发育中筛分子和导管结构变化及酸性磷酸酶作用

导管经历了完整的细胞程序性死亡过程(programmed cell death,PCD),形成运送水分的管状通道;而筛分子分化则经历了细胞程序性半死亡过程,形成运输有机养分的通道。为了进一步弄清二者在小麦(Triticumaestivum L.)颖果发育过程中超微结构上的变化,本研究利用生物电镜和酶的超微细胞化学定位技术比较了筛分子和导管分化过程中超微结构的变化,以及酸性磷酸酶(ACPase,acid phosphatase)活性的分布动态。结果表明:筛分子呈对称性半圆形分布于导管的两侧,且筛分子内细胞核的降解晚于导管,筛分子细胞质主要通过液泡膜内陷包裹细胞器,形成自噬体进行降解,最终仍保留了部分细胞器碎片,筛分子仍然存活;而在导管分化中,主要是液泡破裂后,胞内细胞质被完全降解,导管最终死亡,形成管状分子。ACPase作为液泡的标志性酶,在导管液泡膜破裂后,多定位于线粒体等发生降解的细胞器上。而在筛分子中,不仅在发生降解的线粒体等细胞器上检测到了ACPase活性,在成熟筛分子胞间连丝上也检测到了ACPase活性,表明ACPase不仅参与了小麦颖果筛分子和导管发育中PCD进程,可能还与细胞间物质运输有关。     

植物细胞X射线能谱分析方法的研究

X射线微区分析在我国的植物学研究中应用较少.快速冷冻、冷冻干燥、真空渗透、塑料包埋的薄切片生物制备新技术被证明很适用于对植物细胞中可溶性离子进行X射线微区分析.这对于植物学,诸如矿质营养、生理及抗性等理论问题的研究有着很重要的意义.本文通过实验证明此法除了在冷冻干燥过程中可能会造成某些植物细胞中的液泡结构固缩或破坏以外,与其它生物制备技术相比,大大降低了植物细胞中可溶性离子在制备过程中的流失和移位,从而保证了对植物细胞特别是成熟组织细胞中可溶性离子进行X射线能谱亚细胞定位、定量分析的可靠性.