CO vibrational frequencies on methanol synthesis catalysts: a DFT study

Periodic, self-consistent density functional theory calculations are used to explain the observed decrease in the vibrational frequency of CO on methanol synthesis catalysts under severe reducing conditions (N.-Y. Topsøe, H. Topsøe, J. Mol. Catal. A Chem. 141 (1999) 95–105). Vibrational frequencies for CO on eight different models of the methanol synthesis catalyst surface have been determined. The calculated vibrational frequency of CO on Cu(111) (1/9 ML CO coverage) with 1/9 ML of Zn adatoms shows a decrease of between 15 and 38 cm⁻¹ from the corresponding calculated CO frequency on clean Cu(111) (2073 cm⁻¹). The calculated vibrational frequency of CO on Cu(111) with 1/9 ML of ZnO species shows a decrease of up to 72 cm⁻¹ from the CO stretch frequency on clean Cu(111). These calculated CO vibrational frequency decreases agree with the experimentally measured decrease (ca. 50 cm⁻¹), suggesting that Zn and/or ZnO species may be present in the vicinity of active Cu sites of methanol synthesis catalysts under highly reducing conditions. In addition, CO vibrational frequencies on partially oxidized Cu(111) surfaces are shown to increase from the corresponding frequencies on clean Cu(111), in agreement with experimental results.     

A Comparative Density Functional Theory Study of Water Gas Shift Over PdZn(111) and NiZn(111)

PdZn catalysts have been proposed as an alternative to Cu low temperature water gas shift (WGS) catalysts due to their similar reactivity but higher thermal stability. Unfortunately, Pd based alloys are likely to be considerably more expensive than Cu catalysts. Therefore, we explore NiZn as a potentially cheaper alternative to PdZn. Both PdZn(111) and NiZn(111) have similar potential energy surfaces for WGS as previous work on Cu(111) suggesting that they may be effective WGS catalysts. However, unlike PdZn (and Cu), the primary mechanism for WGS shifts from the carboxyl mechanism to a redox mechanism over NiZn(111) (although they are similar in magnitude).     

Methanol synthesis by the hydrogenation of CO2 over Zn-deposited Cu(111) and Cu(110) surfaces

The hydrogenation of CO₂ over Zn-deposited Cu(111) and Cu(110) surfaces was performed at 523 K and 18 atm using a high pressure flow reactor combined with XPS apparatus. It was shown that the ZnO _x species formed on Cu(111) during reaction directly promoted the methanol synthesis. However, no such promotional effect of the Zn was observed for methanol formation on Cu(110). Thus, Zn on Cu(111) acts as a promoter, while Zn on Cu(110) acts as a poison. The activation energy and the turnover frequency are in fairly good agreement with those obtained for Cu/ZnO powder catalysts.     

The interaction of sulfur with Cu/Pt(111) and Zn/Pt(111) surfaces: copper-promoted sulfidation of platinum

The interaction of sulfur with Pt(111), Zn/Pt(111) and Cu/Pt(111) has been examined using X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), and thermal desorption mass spectroscopy (TDS). At temperatures between 300 and 600 K, the exposure of Pt(111) to S₂ gas produces a chemisorbed layer of sulfurwithout the formation of bulk sulfides. Exposure of S₂ to a Zn/Pt(111) alloy, at room temperature, results in a breakdown of the alloy and formation of a zinc-sulfide film on Pt(111). Further S₂ exposure at 550 K sulfidizes the remaining metallic zincwithout affecting platinum. For the Cu/Pt(111) surface alloy, on the other hand, exposure to S₂2 at 550 K leads to sulfidation of the platinum. Platinum can effectively compete for sulfur atoms bonded to copper but not for those bonded to zinc. The reaction of S₂ gas with Cu/Pt(111) surfaces produces copper sulfides that promote the sulfidation of Pt by providing surface sites for the dissociation of S₂, and by favoring the diffusion of S into the bulk of the system.     

铵盐溶样色谱法测定六种离子的研究

用１６％的醋酸铵溶液溶解样品,用乙醇 醋酸铵 氨 水体系于硅胶Ｈ板上展开,实现Ｐｂ（２价）、Ｎｉ（２价）、Ｃｕ（２价）、Ｃｄ（２价）、Ｃｏ（２价）、Ｚｎ（２价）的有效分离。双硫腙显色后,用双波长薄层扫描仪测定。线性范围：Ｐｂ０．０２～０．６０μｇ,Ｎｉ０．０１～０．３５μｇ,Ｃｕ０．０１～０．３５μｇ,Ｃｄ０．０２～０．４０μｇ,Ｃｏ０．０１～０．３５μｇ和Ｚｎ０．０１～０．４０μｇ。     

一乙醇胺碱水催化氧化合成甘氨酸工艺研究

用共沉淀法制备了一乙醇胺碱水氧化合成甘氨酸用Cu ZnO催化剂 ,考察了催化剂的制备因素对催化剂反应性能的影响 ,得到了合成甘氨酸的适宜反应条件。催化剂的制备过程为 :Cu(NO3) 2 和Zn(Ac) 2 共沉淀顺加法得铜锌氢氧化物 [m(Cu)∶m(Zn) =0 0 8∶1.0 0 ,中和pH值 7.0～7 5 ],再经焙烧和还原得催化剂 (焙烧温度 40 0～ 42 0℃ ,H2 还原温度 2 10～ 2 30℃ )。实验结果表明 :在温度 140～ 170℃ ,H2 压力 0 8～ 1 2MPa,一乙醇胺与碱水催化反应 ,其转化率可达 98%以上 ,甘氨酸的选择性高于 95 %。     

Why Au and Cu Are More Selective Than Pt for Preferential Oxidation of CO at Low Temperature

Self-consistent, periodic density functional theory (DFT) calculations and micro-kinetic modeling are used to compare selectivity for the preferential oxidation of CO (PROX) with respect to H₂ based on studies of elementary reaction steps on the (111) facet of Au, Cu and Pt. The first step of H oxidation (OH formation) has a higher activation barrier than the second step (H₂O formation) on all three metal surfaces, indicating that OH formation competes with CO oxidation for the removal of trace amounts of CO from a typical reformate gas. The activation energy barrier for CO oxidation is found to be 0.18eV on Au(111), 0.82eV on Cu(111) and 0.96eV on Pt(111), whereas the barrier for OH formation is 0.90, 1.28 and 0.83eV respectively. A micro-kinetic model based on the DFT results shows that trends in the selectivity of these metals at different temperatures is due to (i) differences in the rate constants of the competitive CO and H oxidation reactions, and (ii) differences in the CO and H surface coverages. Our results explain why Au and Cu are more selective PROX catalysts compared to Pt at low temperatures. At higher temperatures, Pt and Cu lose some of their selectivity to CO oxidation, whereas the selectivity on Au decreases substantially primarily because of the significantly weaker CO adsorption.     

Photocatalytic Activity of (Copper, Nitrogen)-Codoped Titanium Dioxide Nanoparticles

(Copper, Nitrogen)-codoped titanium dioxide (TiO₂) nanoparticles have been prepared via a sol–gel route, followed by heat treatment at an elevated temperature. Such (Cu, N)-codoped TiO₂ nanoparticles showed a strong absorption in the visible region and a red shift in the band gap transition and exhibited an enhanced photocatalytic activity as compared with the pure, N-doped and Cu-doped TiO₂ for xylenol orange decomposition.     

CHARACTERIZATION AND EVALUATION OF LEVEXTREL EXTRACTION CHROMATOGRAPHIC RESINS FOR TRACE METAL SEPARATION SCHEMES IN AUTOMATIC WATER QUALITY CONTROL SYSTEMS.

ABSTRACT

This paper presents the results of the selective removal of Zn(II) from Cu(II), Cd(II), Ni(II) and Pb(II) using ‘Extraction Chromatographic Resins’ Lewatit TP80T84, which contains dK2,4,4-trimethylpentyl)pbosphinic acid as active component. The extraction and selectivity patterns of the resin were obtained from the metal distribution coefficients as a fiinction of pH. Experimental data of Pb(II), Ni(II) and other natural water occurring metal ions, such as Ca(II), were analyzed graphically and numerically in order to describe the metal extraction reactions. Analysis of the results showed that the extraction of these metal ions can be explained assuming the formation of metal complexes in the resin phase with a general composition ML2(_{q 3}HL)q, where q takes different values depending on the metal studied. Finally the efficiency of the resin in the selective removal of Zn(II) from the toxic heavy metal group Cu(T±), Cd(II), Ni(II) and Pb(II) were evaluated.of divalent metal ions (Zn(II), Cu(II), Cd(n), Ni(II), Pb(n)). Concerning the extraction selectivity of Lewatit TP80784 resins versus Zn(II), Cu(II)( Cd(n), Ca(n), Pb(n) and Ni(II), no differences have been found in comparison with the selectivity of this extractant in organic solvents (36). The results of the numerical treatment indicate that the extraction of Pb(n) and Ni(II) can be explained by assuming the formation of PbL₂(HL₂ and NiL₂(HL)₂. However, the extraction of Ca(II) can be explained assuming the formation of two species CaL₂ and Ca(NO₃)L|The analysis of the separation factors indicates that Lewatit TP80784 allows a quantitative separation of Zn(II) from Cd(II), Ni(II) and Pb(II) with ApHso greater that 2 and quasi-quantitative separations (90-95%) from Cu(II)|The results obtained in the extraction of Zn(IT), Cu(H), Cd(II), Ni(II), and Pb(n) from water samples in column experiments are very satisfactory, and the sytem will be used on-line in a multicomponent spectrophotometric method for the monitoring of low levels of toxic metal ions in surface waters.     

微波固相法合成邻苯二甲酸锌、铜配合物

以邻苯二甲酸(H2phth)、乙酸锌或乙酸铜为原料,通过微波固相法合成了邻苯二甲酸锌、铜配合物Zn(phth).2H2O和Cu(phth).H2O,用化学分析、元素分析、傅里叶变换红外光谱、X射线粉末衍射、热分析对配合物的组成和结构进行了表征。结果表明,邻苯二甲酸配体中的羧基以双齿桥式与Zn(Ⅱ)或Cu(Ⅱ)结合形成配合物,其热分解包括失水、配体的氧化分解过程,最后完全分解为金属氧化物。     

克霉唑金属配合物的合成与表征

以无水甲醇为溶剂,以克霉唑为配体分别与二水合氯化铜、无水氯化锌反应,合成了2种新的药物金属配合物。化合物经元素分析、摩尔电导率、IR、TG及UV等分析表征,表明2种配合物的可能结构式为:[Cu(C22H17ClN2)C l2]n,[Zn(C22H17ClN2)2Cl2]。     

垃圾水分对垃圾焚烧过程重金属迁移转化影响的实验研究(英文)

The effect of moisture in municipal solid waste (MSW) on partitioning of lead (Pb), zinc (Zn), copper (Cu) and cadmium (Cd) was studied in a laboratory tubular furnace by using simulated MSW. The moisture in MSW influences heavy metals in following ways, to increase the moisture in flue gas and decrease the combustion temperature, to prolong the combustion time, and to prolong the releasing time of volatiles with the furnace temperature decreased by increasing the moisture. The volatilization of Pb, Zn and Cd was enhanced by increasing the moisture in MSW because of the prolonged combustion time. For Pb and Zn, the combustion time was important at higher temperature, while for Cd, it was important at low temperature. The moisture content showed slight effect on Cu partitioning. When extra chlorine was added to MSW, such as 1%PVC + 0.5%NaCl, the volatilization of Pb, Zn and Cu was enhanced by increasing the moisture because water evaporation reduced the temperature and increased devolatilization time. At higher temperature, NaCl tends to decompose and generates more free chlorine, producing more metal chlorides. Since Cd is a strong volatile heavy metal in MSW, the effect of moisture content on its volatilization is less than that of Pb, Zn or Cu during the MSW incineration.     

Reaction behaviors and specific exposed crystal planes manipulation mechanism of TiC nanoparticles

Titanium carbide (TiC) nanoparticles with well-designed exposed crystal planes perform intriguing prospects for functional and engineering applications. In this study, a simple and controllable in situ synthesis strategy was proposed for the synthesis of TiC nanoparticles with specific morphology. Reaction behaviors suggested that most of TiC nanoparticles were formed by an instantaneous reaction between Al₃Ti and Al₄C₃ in the Al-rich melt and the resultant morphology was controlled by the discrepant growing rates of (100) and (111) crystal planes. In addition, a growth morphology control model was presented for the prediction and manipulation of the morphology of TiC nanoparticles by the doping of different alloying elements Me (Me = Cu, Mg, Mn, Zn, and Si). According to the morphological observations and density functional theory analyses including the interface energy, charge density differences, and orbital hybridization: Cu, Mg, and Zn atoms could stabilize the Al/TiC(111) interface, whereas Mn and Si atoms promoted the rapid growing and disappearance of the TiC(111) planes in the Al melt. This work provides a feasible way to intelligently design and manipulate TiC nanoparticles with desirable exposed crystal planes, and exhibits a promising prospect for personalized applications.     

Separation/Preconcentration of Zn(II), Cu(II), and Cd(II) by Saccharomyces carlsbergensis Immobilized on Silica Gel 60 in Various Samples

Abstract

This study presents a solid phase extraction procedure based on column biosorption of Zn(II), Cu(II), and Cd(II) ions on Saccharomyces carlsbergensis immobilized on silica gel 60. The analytes were determined by flame atomic absorption spectrometry (FAAS). The optimum conditions for the quantitative recovery of the analytes, including pH, amount of solid‐phase, eluent type and flow rate of sample solution were examined. The effect of interfering ions on the recovery of the analytes was also investigated. Under the optimum conditions, recoveries of Zn(II), Cu(II), and Cd(II) were 99±2%, 98±2%, and 100±2% at 95% confidence level, respectively for spiked water samples. The analytical detection limits for Zn(II), Cu(II), and Cd(II) were 1.14, 1.66, and 1.48 ng mL^?1, respectively. The validation of the method was checked by the analysis of standard reference material (Tea leaves GBW‐07605) and spiked water, samples. The proposed method was applied for the determination of analytes in green onion, parsley, dam water, lake water, and tap water samples. The analytes has been determined in real samples with relative error lower than 8% and relative standard deviation lower than 10%.     

Investigation of Heavy Metal Ion Adsorption Characteristics of Poly(N,N Dimethylamino Ethylmethacrylate) Hydrogels

Abstract

In this study, Poly(N,N dimethyl‐amino ethylmethacrylate) (Poly(DMAEMA)) hydrogels with varying compositions were prepared in the form of rods by irradiating ternary mixtures of N,N‐dimethylamino ethylmethacrylate/ethyleneglycoldimethacrylate/water with gamma rays at ambient temperature. Swelling studies of poly (DMAEMA) hydrogels were performed at different pH values and maximum swelling values reached at pH 2. The adsorption characteristics of Pb(II), Cd(II), Ni(II), Zn(II), Cu(II), and Co(II) ions to poly(N,N dimethylamino ethylmethacrylate) hydrogels were investigated by a batch process. The order of affinity based on amount of metal ion uptake was found as follows: Cu(II)>Zn(II)?Co(II)>Pb(II) >> Ni(II)>Cd(II). In the adsorption studies of Cu(II), Zn(II), Co(II), Pb(II), Ni(II), and Cd(II) ions the Langmuir type adsorption isotherms were observed for all gel systems.     

Mextral V10–Mextral 973H体系脱除酸性矿山废水中重金属的研究

矿山选、冶废水成分复杂、水量大,目前所用方法对重金属的脱除效果不理想、成本高,为解决矿山废水重金属污染问题,开发适用于酸度较高、重金属浓度较低、对钙、镁离子有抑萃作用的协同萃取法脱除并回收废水中的重金属。通过绘制萃取等温线、FT-IR及紫外吸收光谱对Mextral V10–Mextral 973H协同萃取体系进行分析,研究了萃取剂浓度、有机相和水相体积比(简称相比,O/A)和Mextral V10皂化率对废水中重金属分离影响。结果表明,Mextral V10–Mextral 973H协同萃取体系能有效脱除酸性废水中Cu2+, Pb2+, Cd2+和Zn2+。在10vol% (Mextral V10+Mextral 973H)+90vol% Mextral DT100,Mextral V10:Mextral 973H=1:1的最佳实验条件下连续萃取六次,萃后废水中Cu2+, Cd2+, Zn2+, Pb2+, Mg2+和Ca2+的萃取率分别为99.1%±0.1%, 99.9%±0.02% 99.5%±0.05%, 97.6%±0.03%, 10.11%±0.1%和18.3%±0.05%,废水中残留Cu2+, Zn2+, Cd2+和Pb2+浓度分别为1.720±0.10, 0.256±0.03, 0.054±0.01和0.929±0.01 mg/L,低于GB8978-1996中第一类污染物最高允许排放标准值。     

Pollutant trends and hazard ranking in Elefsis Bay, Greece

This study investigates the trends in pollutant distributions in Elefsis Bay and establishes an approach to rank contaminants according to their potential hazard. Sampling locations include points along the coast and within the bay. The investigation focuses on four metals, lead (Pb), zinc (Zn), chromium (Cr) and copper (Cu). Temporal trends are investigated by comparing average yearly concentrations for an 18-year long record. Only Cr in seawater exhibits a clear decreasing trend, both at the coast and within the bay. Spatial trends are studied by plotting average yearly concentrations along the coast for every year in the record. Only Cr exhibits systematically peak concentrations in water samples close to a stream outfall and periodic peaks in the sediment at the same location. Periodic peaks of Cu, Zn and Pb are also detected in both water and sediment samples obtained close to the two shipyards of Elefsis Bay. A comparative study of spatial trends confirms that the areas by the two shipyards are the most heavily impacted. Finally, the four metals are ranked by defining a hazard index as the ratio of the 95 percentile for the pollutant concentration and an allowable concentration for each pollutant. According to this ranking, the order of the four metals in seawater is: Pb, Cu, Cr, Zn. The respective ranking in sediments gives: Cu, Zn, Pb, Cr. These results indicate that if the priority is on improving water quality, the focus should be on lead. If, on the other hand, the two hazard indices are considered jointly, then copper becomes the highest-ranking metal, while lead is second.     

Concentration of trace elements in arable soil after long-term application of organic and inorganic fertilizers

The Ruzyně Fertilizer Experiment (RFE, the Czech Republic) was established on a permanent arable field (illimerized Luvisol) in 1955. The effects of long-term application of several organic fertilizers (dung water, farmyard manure, poultry litter) and mineral N, P and K fertilizers on plant-available (extracted by CaCl₂), easily mobilizable (extracted by EDTA), potentially mobilizable (extracted by HNO₃) and total concentrations of trace elements were investigated in 2008. Concentrations of all analyzed trace elements in the applied fertilizers did not exceed the limits permitted by Czech national legislation. Concentrations of As, Cd and Cr were highest in single superphosphate, those of Cu, Mn and Ni were highest in poultry litter and those of Pb and Zn were highest in dung water. Poultry litter had the second highest concentration of As and Zn. Poultry litter supplied the soils with considerable amounts of Cu, Mn and Zn and increased their concentrations in the soil. There was also a significant increase in plant availability of Mn, Ni and Zn and a decrease in soil pH. Although all fertilizers were applied for five decades, total concentrations of As, Cr, Cu, Ni, Pb and Zn in soil remained far below Czech legislation limits. For Cu and Zn this was probably due to the relatively low mean annual application rates of poultry litter. Total Cd concentrations in soil exceeded the legislative limit even in the control (without any fertilizer inputs) and the effect of treatment was not significant. This indicates that fertilizers were not the main source of Cd in the experimental area. Therefore, common cropping practices do not induce soil contamination by trace elements even if they have been applied for more than 50 years.     

In Situ Hydrogenation of CO2 by Al/Fe and Zn/Cu Alloy Catalysts under Mild Conditions

The development of efficient metal catalysts for in situ hydrogenation of CO₂ in water under mild conditions has gained considerable attention. Three Al alloys (Al/Fe, Al/Fe/Cu, Al/Cu) and three Zn/Cu alloys for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions were investigated. Hydrogen was generated by reaction of Al, Fe, and Zn in the alloys with water. In situ hydrogenation of CO₂ was likely to be catalyzed by intermetallic compounds and generated metal oxides. Al alloys catalyzed the hydrogenation to methane while Zn/Cu alloys produced CO and formic acid. Zn/Cu5 possessed the highest catalytic activity, which was attributed to the CuZn5 crystal planes in the alloys. Insights are provided into the importance of compositions and structures of alloys for the selectivity for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions.     

Water adsorption—quantum chemical approach

The chemisorption of a single water molecule on the Cu, Ag, Au and Zn, Cd, Hg low index faces and of the (H₂O)_n associates (n = 2−5) on Ag(111) and on a close-packed mercury surface has been investigated by CNDO method together with geometrical optimization of the atom positions. For substrate, a cluster consisting of a few atoms, as a model, has been used. A new “microscopic” sequence of the metal hydrophilicity is proposed. Calculations are critically discussed in the light of experimental and other quantum chemical data. Water structuring near a mercury surface has been also studied by using Metropolis Monte Carlo procedure.