| 11. |
- Hu, Guangzhi, et al.
(författare)
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Small palladium islands embedded in palladium-tungsten bimetallic nanoparticles form catalytic hotspots for oxygen reduction
- 2014
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Ingår i: Nature Communications. - : Macmillan Publishers Ltd.. - 2041-1723. ; 5, s. Article number: 5253-
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Tidskriftsartikel (refereegranskat)abstract
- The sluggish kinetics of the oxygen reduction reaction at the cathode side of proton exchange membrane fuel cells is one major technical challenge for realizing sustainable solutions for the transportation sector. Finding efficient yet cheap electrocatalysts to speed up this reaction therefore motivates researchers all over the world. Here we demonstrate an efficient synthesis of palladium-tungsten bimetallic nanoparticles supported on ordered mesoporous carbon. Despite a very low percentage of noble metal (palladium: tungsten = 1:8), the hybrid catalyst material exhibits a performance equal to commercial 60% platinum/Vulcan for the oxygen reduction process. The high catalytic efficiency is explained by the formation of small palladium islands embedded at the surface of the palladium-tungsten bimetallic nanoparticles, generating catalytic hotspots. The palladium islands are similar to 1 nm in diameter, and contain 10-20 palladium atoms that are segregated at the surface. Our results may provide insight into the formation, stabilization and performance of bimetallic nanoparticles for catalytic reactions.
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| 12. |
- Ivanova, T M, et al.
(författare)
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X-ray photoelectron spectra of heterometallic 3d-metal carboxylate complexes
- 2011
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Ingår i: Russian Journal of Inorganic Chemistry. - : Maik Nauka/Interperiodica. - 0036-0236 .- 1531-8613. ; 56:1, s. 104-109
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and magnetic states in the heterometallic hexanuclear complex Mn4II Fe2III (μ4-O)2(Piv)10 · MeCN4 have been studied by X-ray photoelectron spectroscopy (XPS). The substitution of two Mn atoms for two Fe atoms in the hexanuclear complex was found to have an effect on the patterns of iron and manganese X-ray photoelectron spectra. XPS data are evidence of the high-spin paramagnetic state of MnII and FeIII atoms, as well as of the ligand-metal charge transfer upon complex formation. In the heteroatomic complex, the degree of bond covalence increased for both the manganese and iron atoms. The results obtained are in good agreement with X-ray diffraction data.
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| 13. |
- Ivanova, TM, et al.
(författare)
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XPS study of the electronic structure of binuclear 3d transition metal pivalate complexes
- 2012
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Ingår i: Russian Journal of Inorganic Chemistry. - 0036-0236 .- 1531-8613. ; 57:11, s. 1484-1489
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Tidskriftsartikel (refereegranskat)abstract
- Binuclear pivalate complexes of 3d transition metals (manganese, iron, cobalt, and nickel) with the same ligand environment and a lantern structure have been studied by X-ray photoelectron spectroscopy. The M2p, M3s, C1s, O1s, and N1s X-ray photoelectron spectra have been examined. A redistribution of electron density in the OCO group has been revealed. It has been shown that the theory fits the experimental data on the energy separation between the high- and low-spin components in the M3s spectra and between the spin doublet components in the M2p spectra. It has been demonstrated that the iron, cobalt, and nickel complexes are paramagnetic at room temperature, whereas the manganese complex exhibits antiferromagnetic properties. There is a correlation between the size of the 3d subshell of the transition metal atom and the M-O and M-N bond lengths.
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| 14. |
- Jonsson, Sofi, 1984-, et al.
(författare)
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Mercury methylation rates for geochemically relevant HgII species in sediments
- 2012
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 46:21, s. 11653-11659
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Tidskriftsartikel (refereegranskat)abstract
- Monomethylmercury (MeHg) in fish from freshwater, estuarine and marine environments are a major global environmental issue. Mercury levels in biota are mainly controlled by the methylation of inorganic mercuric mercury (HgII) to MeHg in water, sediments and soils. There is, however, a knowledge gap concerning the mechanisms and rates of methylation of specific geochemical HgII species. Such information is crucial for a better understanding of variations in MeHg concentrations among ecosystems and, in particular, for predicting the outcome of currently proposed measures to mitigate mercury emissions and reduce MeHg concentrations in fish. To fill this knowledge gap we propose an experimental approach using HgII isotope tracers, with defined and geochemically important adsorbed and solid HgII forms in sediments, to study MeHg formation. We report HgII methylation rate constants, km, in estuarine sediments which span over two orders of magnitude depending on chemical form of added tracer: metacinnabar (β-201HgS(s)) < cinnabar (α-199HgS(s)) < HgII reacted with mackinawite (≡FeS-202HgII) < HgII bonded to natural organic matter (NOM-196HgII) < a typical aqueous tracer (198Hg(NO3)2(aq)). We conclude that a combination of thermodynamic and kinetic effects of HgII solid-phase dissolution and surface desorption control the HgII methylation rate in sediments and causes the large observed differences in km-values. The selection of relevant solid-phase and surface adsorbed HgII tracers will therefore be crucial to achieving biogeochemically accurate estimates of ambient HgII methylation rates.
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| 15. |
- Kang, Mingliang, et al.
(författare)
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Redox reaction of aqueous selenite with As-rich pyrite from Jiguanshanore mine (China) : reaction products and pathway
- 2014
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Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 47, s. 130-140
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of an As-rich natural pyrite (FeS2.08As0.043) with aqueous Se(IV) was investigated as a function of pH, ferrous iron concentration, and reaction time. Arsenic is often the most abundant minor constituent of natural pyrite, and is believed to substitute for S in the pyrite structure. EXAFS measurements confirmed the presence of AsS dianion group, with arsenic in the same local configuration as in the arsenopyrite. Speciation studies indicated that Se(0) was the unique reduction product in the pH range 5.05–8.65 over a reaction period of >1 month, while trace amounts of FeSeO3 might be formed at pH ⩟ 6.10. At pH > 6.07, the formation of Fe(III)-(oxyhydr)oxide is kinetically favored, and it consumed nearly all the aqueous iron, including the extra added Fe2+, thereby inhibiting the formation of the thermodynamically most stable product: FeSe2. After oxidation by Se(IV), the occurrence of surface S0, significant aqueous sulfur deficit, and excessive leaching of arsenic in solution, indicate the preferential release of As impurity via arsenopyrite oxidation. The data suggest that the polysulfide-elemental sulfur pathway, which prevails in acid-soluble metal sulfides, is an important pathway in the oxidation of As-rich pyrite, in addition to the thiosulfate pathway for acid-insoluble pyrite. Control experiments on As-free natural pyrite further support this mechanism. This study confirms the potential of reductive precipitation to attenuate the mobility of Se in the environment and demonstrates that minor elements commonly present in natural pyrite can play a significant role on its dissolution pathway.
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| 16. |
- Khoshkhoo, Mohammed, et al.
(författare)
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Chalcopyrite leaching and bioleaching : An XPS study to characterize the nature of hindered dissolution
- 2014
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Ingår i: Hydrometallurgy. - : Elsevier BV. - 0304-386X .- 1879-1158. ; 149, s. 220-227
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Tidskriftsartikel (refereegranskat)abstract
- Chalcopyrite (CuFeS2) is both the most economically important and the most difficult copper mineral to (bio)leach. The main reason for the slow rate of chalcopyrite dissolution is the formation of a layer on the surface of the mineral that hinders dissolution, termed “passivation”. The nature of this layer is still under debate. In this work, the role of bacterial activity was examined on the leaching efficiency of chalcopyrite by mimicking the redox potential conditions during moderately thermophilic bioleaching of a pure chalcopyrite concentrate in an abiotic experiment using chemical/electrochemical methods. The results showed that the copper recoveries were equal in the presence and absence of the mixed culture. It was found that the presence of bulk jarosite and elemental sulphur in the abiotic experiment did not hamper the copper dissolution compared to the bioleaching experiment. The leaching curves had no sign of passivation, rather that they indicated a hindered dissolution. XPS measurements carried out on massive chalcopyrite samples leached in the bioleaching and abiotic experiments revealed that common phases on the surface of the samples leached for different durations of time were elemental sulphur and iron-oxyhydroxides. The elemental sulphur on the surface of the samples was rigidly bound in a way that it did not sublimate in the ultra-high vacuum environment of the XPS spectrometer at room temperature. Jarosite was observed in only one sample from the abiotic experiment but no correlation between its presence and the hindered leaching behaviour could be made. In conclusion, a multi-component surface layer consisting of mainly elemental sulphur and iron-oxyhydroxides was considered to be responsible for the hindered dissolution.
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| 17. |
- Khoshkhoo, Mohammad, et al.
(författare)
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Chalcopyrite leaching and bioleaching : An X-ray photoelectron spectroscopic (XPS) investigation on the nature of hindered dissolution
- 2014
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Ingår i: Hydrometallurgy. - : Elsevier. - 0304-386X .- 1879-1158. ; 149, s. 220-227
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Chalcopyrite (CuFeS2) is both the most economically important and the most difficult copper mineral to (bio)leach. The main reason for the slow rate of chalcopyrite dissolution is the formation of a layer on the surface of the mineral that hinders dissolution, termed “passivation”. The nature of this layer is still under debate. In this work, the role of bacterial activity was examined on the leaching efficiency of chalcopyrite by mimicking the redox potential conditions during moderately thermophilic bioleaching of a pure chalcopyrite concentrate in an abiotic experiment using chemical/electrochemical methods. The results showed that the copper recoveries were equal in the presence and absence of the mixed culture. It was found that the presence of bulk jarosite and elemental sulphur in the abiotic experiment did not hamper the copper dissolution compared to the bioleaching experiment. The leaching curves had no sign of passivation, rather that they indicated a hindered dissolution. XPS measurements carried out on massive chalcopyrite samples leached in the bioleaching and abiotic experiments revealed that common phases on the surface of the samples leached for different durations of time were elemental sulphur and iron-oxyhydroxides. The elemental sulphur on the surface of the samples was rigidly bound in a way that it did not sublimate in the ultra-high vacuum environment of the XPS spectrometer at room temperature. Jarosite was observed in only one sample from the abiotic experiment but no correlation between its presence and the hindered leaching behaviour could be made. In conclusion, a multi-component surface layer consisting of mainly elemental sulphur and iron-oxyhydroxides was considered to be responsible for the hindered dissolution.
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| 18. |
- Khoshkhoo, Mohammad, et al.
(författare)
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Electrochemical simulation of redox potential development in bioleaching of a pyritic chalcopyrite concentrate
- 2014
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Ingår i: Hydrometallurgy. - : Elsevier BV. - 0304-386X .- 1879-1158. ; 144, s. 7-14
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Tidskriftsartikel (refereegranskat)abstract
- The majority of the world's copper reserves are bound in the sulphide mineral chalcopyrite (CuFeS2), but supply of the copper is hindered by the recalcitrance of chalcopyrite to (bio)leaching. The main reason for the slow rate of chalcopyrite dissolution is the formation of a layer on the surface of the mineral that hinders dissolution, termed "passivation". The nature of this layer and the role of microorganisms in chalcopyrite leaching behaviour are still under debate. Moderately thermophilic bioleaching of a pyritic chalcopyrite concentrate was mimicked in an electrochemical vessel to investigate the effect of the absence and presence of microorganisms in copper dissolution efficiency. Data from the redox potential development during bioleaching was used to program a redox potential controller in an electrochemical vessel to accurately reproduce the same leaching conditions in the absence of microorganisms. Two electrochemical experiments were carried out with slightly different methods of redox potential control. Despite massive precipitation of iron as jarosite in one of the electrochemically controlled experiments and formation of elemental sulphur in both electrochemical experiments, the efficiencies of copper dissolution were similar in the electrochemical tests as well as in the bioleaching experiment. No passivation was observed and copper recoveries exhibited a linear behaviour versus the leaching time possibly due to the galvanic effect between chalcopyrite and pyrite. The data suggest that the main role of microorganisms in bioleaching of a pyritic chalcopyrite concentrate was regeneration of ferric iron. It was also shown that the X-ray photoelectron spectroscopy measurements on the residues containing bulk precipitates cannot be employed for a successful surface characterisation.
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| 19. |
- Kirilin, A, et al.
(författare)
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Chemo-Bio Catalyzed Synthesis of R-1-Phenylethyl Acetate over Bimetallic PdZn Catalysts, Lipase, and Ru/Al2O3 : part II
- 2011
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Ingår i: Kinetics and catalysis. - : Maik Nauka/Interperiodica. - 0023-1584 .- 1608-3210. ; 52:1, s. 77-81
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Tidskriftsartikel (refereegranskat)abstract
- One-pot synthesis of R-1-phenyethylacetate at 70 degrees C was investigated using three different catalysts simultaneously, namely a bimetallic PdZn/Al2O3 as a hydrogenation catalyst, an immobilized lipase as an acylation catalyst and Ru/Al2O3 as a racemization catalyst. The most active bimetallic catalyst was PdZn/Al2O3 calcined at 300 degrees C and reduced at 400 degrees C, whereas the most selective although less active catalyst was the one being calcined and reduced at 500 degrees C. The highest selectivity to R-1-phenylethyl acetate over this catalyst was 32 at 48% conversion. Ru/Al2O3 was confirmed to have a positive effect on the formation of the desired product, although it was not very active in the racemization during one-pot synthesis.
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| 20. |
- Kirilin, A, et al.
(författare)
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Chemo-bio catalyzed synthesis of R-1-phenylethyl acetateover bimetallic PdZn catalysts, lipase and Ru/Al2o3. Part I
- 2011
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Ingår i: Kinetics and catalysis. - Moskva : Nauka. - 0023-1584 .- 1608-3210. ; 52:1, s. 78-82
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Tidskriftsartikel (refereegranskat)abstract
- The effect of calcination and reduction temperature on the physical properties of PdZn/Al2O3 catalysts, prepared by coprecipitation deposition technique and characterized by XPS, XRD and TEM methods are reported. The temperatures were varied in a range of 300–500°C. The catalyst calcined at 300°C and reducedat 400°C exhibited the metal particle size of 2–6 nm and contained the highest surface concentrations of Pd and Zn according to XPS measurements. The size and the fraction of large particles (above 10 nm) increased with increasing the calcinations and reduction temperatures.
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