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Uncovering the dynamics of active sites in the working conditions is crucial to realizing increased activity, enhanced stability and reduced cost of oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane electrolytes. Herein, we identify at the atomic level potential-driven dynamic-coupling oxygen on atomically dispersed hetero-nitrogen-configured Ir sites (AD-HN-Ir) in the OER working conditions to successfully provide the atomically dispersed Ir electrocatalyst with ultrahigh electrochemical acidic OER activity. Using in-situ synchrotron radiation infrared and X-ray absorption spectroscopies, we directly observe that one oxygen atom is formed at the Ir active site with an O-hetero-Ir-N4 structure as a more electrophilic active centre in the experiment, which effectively promotes the generation of key *OOH intermediates under working potentials; this process is favourable for the dissociation of H2O over Ir active sites and resistance to over-oxidation and dissolution of the active sites. The optimal AD-HN-Ir electrocatalyst delivers a large mass activity of 2860 A gmetal−1 and a large turnover frequency of 5110 h−1 at a low overpotential of 216 mV (10 mA cm−2), 480–510 times larger than those of the commercial IrO2. More importantly, the AD-HN-Ir electrocatalyst shows no evident deactivation after continuous 100 h OER operation in an acidic medium., Uncovering the dynamics of active sites in the working conditions is important yet challenging. Here the authors identify dynamic-coupling oxygen on atomically dispersed iridium sites during oxygen evolution reaction using in situ techniques.

On the basis of rigorous dynamical-theory calculations, a complete X-ray polarization-switch effect of silicon crystals at the exact multiple-beam diffraction condition is demonstrated. The underlying physical mechanism of this unique phenomenon can be revealed using a simple multiple-wave propagation and interference model. The constructive and destructive interference of the multiple detoured-diffraction beams along the direction of the primary diffracted beam directly leads to the complete polarization switch. This phenomenon can be realized using both synchrotron and laboratory X-ray sources at many discrete wavelengths, and used to design a novel crystal-based polarizer to achieve a 90° polarization rotation.

Temperature-dependent short-range structural evolution of Au44Ga56 liquid eutectic alloy has been studied by in situ extended X-ray absorption fine structure (EXAFS), in situ high-energy X-ray diffraction (HEXRD) together with first-principles molecular dynamics (FPMD) simulations. It is found that the short-range structure of Au44Ga56 liquid strongly inherits the local atomic packing of the AuGa compound. A short-range structural change in Ga-centered clusters is revealed by in situ EXAFS data at the Ga K-edge at about 970 K, while no such change in Au-centered clusters appears at the Au LIII-edge. The in situ HEXRD and FPMD simulations also confirm the existence of a liquid-to-liquid crossover (LLC) in the Au44Ga56 liquid at a temperature range of about 1000–1100 K, mainly lying in the local structural change around Ga atoms. Indeed, the alloys quenched from the liquid phases below 1000 K and above 1100 K exhibit differences in structure and magnetic properties, which opens a possibility to fabricate ne...

The ternary chalcopyrite AgInSe2 has emerged as a promising n-type thermoelectric material with ultralow lattice thermal conductivity. We report the thermoelectric transport properties of sodium-do...

A dual-bed fixed-bed reactor consisting of a selective catalytic reduction (SCR) catalyst and a lean NOx trap (LNT) catalyst is designed and employed for high-concentration NOx removal under lean-burn condition. The lean NOx could be partially reduced over the upstream SCR catalyst (Cu/Al2O3) by C3H6 in the stream, greatly increasing the efficiencies of both NOx storage and NOx reduction over the downstream LNT catalyst (La0.7Sr0.3CoO3). The activity tests for individual catalyst show that the Cu/Al2O3 containing 5 wt.% Cu is the optimal SCR catalyst, which exhibits similar temperature window of activity (300–350 °C) as the LNT catalyst La0.7Sr0.3CoO3. The relative ratio of CuO nanoparticles to surface CuAl2O4 spinel on Cu/Al2O3 is rather important for NO-SCR due to the requirements of appropriate oxidation ability of SCR catalysts. As compared with the single SCR or LNT catalyst, the dual-bed SCR-LNT coupled system shows much lower NOx leak in both lean- and rich-burn periods, especially under the condition of high NOx concentration and high space velocity. Additionally, the NOx to N2O selectivity over this coupled system is as low as ∼4%, showing obvious advantage over conventional noble metals-based SCR and LNT catalysts.

Electrocatalysis plays an essential role in diverse electrochemical energy conversion processes that are vital for improving energy utilization efficiency and mitigating the aggravating global warming challenge. The noble metals such as platinum are generally the most frequently used electrocatalysts to drive these reactions and facilitate the relevant energy conversion processes. The high cost and scarcity of these materials pose a serious challenge for the wide-spread adoption and the sustainability of these technologies in the long run, which have motivated considerable efforts in searching for alternative electrocatalysts with reduced loading of precious metals or based entirely on earth-abundant metals. Of particular interest are graphene-supported single atom catalysts (G-SACs) that integrate the merits of heterogeneous catalysts and homogeneous catalysts, such as high activity, selectivity, stability, maximized atom utilization efficiency and easy separation from reactants/products. The graphene support features a large surface area, high conductivity and excellent (electro)-chemical stability, making it a highly attractive substrate for supporting single atom electrocatalysts for various electrochemical energy conversion processes. In this review, we highlight the recent advancements in G-SACs for electrochemical energy conversion, from the synthetic strategies and identification of the atomistic structure to electrocatalytic applications in a variety of reactions, and finally conclude with a brief prospect on future challenges and opportunities.

Uncovering the dynamics of active sites under working state is crucial to realizing increased activity, enhanced stability and reduced cost of oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane electrolytes. Herein, we identify at atomic level a potential-driven dynamic-coupling oxygen on the hetero-nitrogen configured single-atomic Ir sites (HN-Ir NC) during OER working conditions to successfully endow the single-atomic Ir catalyst with an ultrahigh electrochemical acidic-OER activity. Using operando synchrotron radiation infrared and X-ray absorption spectroscopies, we directly observe in the experiment that a dynamic oxygen atom is formed at the Ir site with the O-hetero-Ir-N4 structure as more electrophilic active center and then effectively promote the generation of the key *OOH intermediates under working potentials, which is exceptionally favourable for the dissociation of H2O over Ir sites and resistance to over-oxidation and dissolution of the active sites.The optimal single-atomic HN-Ir NC catalyst delivers a large mass activity of 2860 A gmetal−1 and a huge turnover frequency of 5110 h− 1 at a low overpotential of 216 mV (10 mA cm− 2), 480˗510 times than that of commercial IrO2 catalyst. More importantly, the HN-Ir NC catalyst shows no evident deactivation after continuous 100 h OER operation in acidic medium.

The quaternary compound Cu2ZnSnSe4 (CZTSe), as a typical candidate for both solar cells and thermoelectrics, is of great interest for energy harvesting applications. Materials with a high thermoelectric efficiency have a relatively low thermal conductivity, which is closely related to their chemical bonding and lattice dynamics. Therefore, it is essential to investigate the lattice dynamics of materials to further improve their thermoelectric efficiency. Here we report a lattice dynamic study in a cobalt-substituted CZTSe system using temperature-dependent X-ray absorption fine structure spectroscopy (TXAFS). The lattice contribution to the thermal conductivity is dominant, and its reduction is mainly ascribed to the increment of point defects after cobalt substitution. Furthermore, a lattice dynamic study shows that the Einstein temperature of atomic pairs is reduced after cobalt substitution, revealing that increasing local structure disorder and weakened bonding for each of the atomic pairs are achieved, which gives us a new perspective for understanding the behavior of lattice thermal conductivity.

Herein, we report the high catalytic activity of the potassium-promoted Co 3 O 4 nanowires supported on the monolithic three-dimensional macroporous (3-DM) nickel foam substrate (xKCo-NW) for soot combustion. The 3-DM structure of Ni foam and the space among these nanowires can extremely improve the contact efficiency between soot and catalysts. Loading of potassium provides the new active sites for soot oxidation, improves catalyst-soot contact as a molten salt and increases the number of the surface adsorbed oxygen species. The 5KCo-NW catalyst loaded with 5% potassium shows the highest catalytic performance, as well as a high water resistance. There are two types of potassium species in the catalysts, most potassium species is in the form of separate phases, and few interacts with cobalt oxide. The interaction between potassium species and cobalt oxide stabilizes a part of potassium species, and the stabilized potassium species can promote the catalytic activity for the consecutive soot combustion cycle. Moreover, our results show that the chemisorbed NO x species on the 5KCo-NW catalyst are more active than the gaseous NO 2 for soot oxidation. In the presence of O 2 , soot combustion is accelerated to react with the chemisorbed NO x species; whereas the formed nitrate/nitrite species are catalytically inert.

Crossed nanosheets of transition metal oxide (TMO-NS: Co-NS, Mn-NS and Fe-NS) were synthesized by a facile hydrothermal method and employed for soot combustion in the NO/O2/N2 and O2/N2 atmosphere under gravitational contact mode (GCM). They show high catalytic activities for soot combustion due to the macroporous structure of the as-prepare catalysts increasing the soot-catalyst contact efficiency. The XRD and XPS results reveal that the active phases in the corresponding catalysts exist as Co3O4, Mn2O3 and Fe2O3, respectively. Among these catalysts, the Co-NS shows the best activity for soot combustion, especially in the presence of NO, whose catalytic activity of T50 (391 °C) and SCO2 (100%) is as good as that of the Pt/Al2O3 catalyst. The excellent performance of the Co-NS catalyst results from several factors: the highest intrinsic activity (TOF = 1.77 × 10−5 s−1); the highest redox property as revealed by H2-TPR and soot-TPR; the largest amount of active oxygen species as clarified by XPS; the highest ability of NO oxidation to NO2 supported by NO-TPO. In addition, the multiporous structure of Co3O4 nanosheets is facilitated for the mass transfer. In the O2 atmosphere, soot particulates are directly oxidized by the surface adsorbed oxygen. After introducing of NO, the soot particulates are readily oxidized by NO2 at the low temperature (

Pt/TiO2 and WO3 modified Pt/TiO2 catalysts have been investigated for the selective catalytic reduction of NOx by H2 (H2-SCR) in the presence of oxygen. It was found that the addition of WO3 leads to a significant promoting effect on the low-temperature activity of Pt/TiO2 catalyst and the optimal loading is 2%. X-ray absorption near-edge structure (XANES) revealed the electron transfer from WO3 to Pt active sites, leading to the formation of metallic Pt, which is responsible for the low-temperature H2-SCR of NOx. In-situ DRIFTS demonstrated that the introduction of WO3 to Pt catalyst not only contributes to the formation of reactive adsorbed NOx species on the catalyst, but also promotes the formation of NH4+ species. All of these factors, collectively, account for the improved low-temperature activity of Pt-WO3/TiO2 catalyst.

The distribution and speciation of mercury (Hg) were investigated in contaminated soils collected from two adjacent land use systems (arid land and rice paddy) near the Wanshan Mercury mine, SW China. In both sites, fine soil aggregate size fractions (

Single-atom catalysts (SACs) have recently attracted broad research interest as they combine the merits of both homogeneous and heterogeneous catalysts. Rational design and synthesis of SACs are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report a general approach to a series of monodispersed atomic transition metals (for example, Fe, Co, Ni) embedded in nitrogen-doped graphene with a common MN4C4 moiety, identified by systematic X-ray absorption fine structure analyses and direct transmission electron microscopy imaging. The unambiguous structure determination allows density functional theoretical prediction of MN4C4 moieties as efficient oxygen evolution catalysts with activities following the trend Ni > Co > Fe, which is confirmed by electrochemical measurements. Determination of atomistic structure and its correlation with catalytic properties represents a critical step towards the rational design and synthesis of precious or nonprecious SACs with exceptional atom utilization efficiency and catalytic activities.

Simulations of the periods, split regularities and mirror symmetries of the glitch pattern of a Si(111) crystal along with the azimuthal angles are presented. The glitch patterns of Si(111) double-crystal monochromators (DCMs) are found to be the superposition of the two sets of glitch patterns from the two crystals. The optimal azimuthal orientation φ1,2= [(2n+1)π]/6 (n= 0, ±1, ±2…) for Si(111) DCMs to achieve the least amount of glitches in the hard X-ray region has been suggested.

Vanadium(V)-doped hexagonal turbostratic birnessites were synthesized and characterized by multiple techniques and were used to remove Pb 2+ from aqueous solutions. With increasing V content, the V(V)-doped birnessites have significantly decreased crystallinity, i.e., the thickness of crystals in the c axis decreases from 9.8 nm to ∼0.7 nm, and the amount of vacancies slightly increases from 0.063 to 0.089. The specific surface areas of these samples increase after doping while the Mn average oxidation sates are almost constant. V has a valence of +5 and tetrahedral symmetry, and exists as oxyanions, including V 6 O 16 2− , and VO 4 3− on birnessite edge sites by forming monodentate corning-sharing complexes. Pb L III -edge extended X-ray absorption fine structure (EXAFS) spectra analysis shows that, at low V contents (V/Mn ≤ 0.07) Pb 2+ mainly binds with birnessite on octahedral vacancy and especially edge sites whereas at higher V contents (V/Mn > 0.07) more Pb 2+ associates with V oxyanions and form vanadinite [Pb 5 (VO 4 ) 3 Cl]-like precipitates. With increasing V(V) content, the Pb 2+ binding affinity on the V-doped birnessites significantly increases, ascribing to both the formation of the vanadinite precipitates and decreased particle sizes of birnessite. These results are useful to design environmentally benign materials for treatment of metal-polluted water.

A series of CuMnCeO catalysts with 10% CuO (weight loading) and variable atomic ratios of Mn/Mn + Ce (0, 0.02, 0.05 or 0.10) were synthesized by co-precipitation and employed for CO preferential oxidation (CO PROX). After doping a small amount of manganese into ceria, the catalysts show improved catalytic performance as compared with the undoped one, especially the catalyst with the Mn/Mn + Ce atomic ratio of 0.05 (CMC-0.05) which displays the lowest temperatures for half CO conversion (T50 = 73 °C) and full CO conversion (T100 = 108 °C). In addition, it also exhibits the widest temperature window of full CO conversion (108–149 °C) and 100% selectivity of oxygen to CO2 below 117 °C. As revealed by XRD and UV-Raman, the presence of appropriate amount of Mn cannot only enhance the formation of Ce–Cu–Mn–O ternary oxide solid solution with fluorite structure, inhibiting the growth of CeO2 crystallite size, but also increase the oxygen vacancies. The results of H2-TPR and XPS indicate that the reducibility and amount of surface oxygen species of CMC-0.05 are also improved, both of which are beneficial to catalytic performance. In situ XANES results suggest that the bulk copper species still remain as Cu2+ ions below 200 °C even in H2-rich CO PROX atmosphere; however, the in-situ DRIFTS spectra indicate that during CO PROX below 120 °C the surface copper species are Cu+ ions which are regarded as the main active sites for CO PROX; above 120 °C Cu0 species appear, which enhance H2 oxidation, decreasing the oxygen to CO2 selectivity.

Samarium hydroxide (Sm(OH)3) is an important samarium compound with many potential applications in electronics, optics and catalysis. Based on a facile hydrothermal method assisted by oleic acid surface modifications we synthesized Sm(OH)3 nanocrystals with various morphologies. In this system, by adding the oleic acid surfactant both crystallization and grain size of nanocrystals can be tuned. Furthermore, the paramagnetic resonance and magnetic measurements point out that rod-like Sm(OH)3 samples are non-magnetic, while Sm(OH)3 disc-like samples exhibit weak ferromagnetism. The correlation between magnetism and morphology in Sm(OH)3 nanocrystals is associated with the surfactant-induced surface modification as well as with the changes in the localization of electrons in Sm 5d orbitals, in agreement with X-ray absorption spectroscopy data.

Ce-substituted ternary oxide catalysts ZnAlCex were prepared and employed in dimethyl ether steam reforming (DME SR) to produce hydrogen. XRD, XAFS (XANES & EXAFS), H2O-TPD, CH3OH-TPD and TPSR techniques were used for catalyst characterization. It is found that the catalytic performance of these catalysts is dependent on Ce content. The catalyst containing 20 wt% CeO2 exhibits the best catalytic performance. Its calculated TOF (0.034 s−1) is nearly three times to that of ZnAlO. The kinetic results reveal that the addition of 20 wt% CeO2 to ZnAlCex greatly decreases the apparent activation energy (Ea) of DME SR, due to the formation of new reaction sites such as Ce4+–O–Zn2+ linkages. XRD and EXAFS analyses indicate that Ce addition can not only decrease the crystallite size of ZnO and ZnAl2O4, but also tune the relative contents of them. The results of H2O-TPD and CH3OH-TPD show that Ce addition can lower H2 desorption temperature, which accounts well for the better catalytic performance of ZnAlCex. It is worth noting that the Zn-based catalysts display much lower CO selectivity than the Cu-based one, especially the Ce-substituted ZnAlCex. Start-off durability tests demonstrate that this series of catalysts also possess high catalytic stability.

A series of hydrotalcite-derived multicomponent oxide catalysts Co2.5Mg0.5Al1-x%La-x%O (denoted as CMALa(x), x=0, 5, 8, 10 or 15) with different La contents were synthesized by co-precipitation, and employed for catalytic soot combustion and NOx storage at lean condition. It is found that the La-substituted catalysts are more active than the one without La for soot combustion and NOx storage. Among all the catalysts CMALa(x), CMALa(10) (x=10) exhibits the highest catalytic performance, showing the largest NOx storage capacity (300 mu mol/g) and the lowest temperature for the maximal soot oxidation rate (T-m = 388 degrees C). The results of H-2-TPR and O-2-TPD indicate that the La-substitution can enhance the redox properties and increase the amount of surface lattice oxygen species of the catalysts. The results of soot combustion kinetics show that the apparent activation energy of CMALa(10) is the lowest (92.75 kJ/mol). Based upon the catalytic performance and in situ DRIFTS characterization, a nitrate and/or NO2 enhanced soot combustion mechanism over CMALa(10) was proposed. It is revealed that at low temperature the stored nitrate can directly promote soot ignition, while at high temperature the NO2 species arising from NO oxidation or nitrate decomposition act as the main active species for soot combustion. (C) 2014 Elsevier B.V. All rights reserved.

A series of nonplatinic ceria-based oxides supported catalysts LaCoO3/K2CO3/S (S=CeO2, Ce0.75Zr0.25O2 or 5%Y/Ce0.75Zr0.25O2) were prepared by successive impregnation and employed for lean-burn NOx trapping. It is found that the doping of Zr or YZr into CeO2 facilitates the formation of CeZrO binary or YCeZrO ternary solid solutions, increasing the specific surface area and improving the redox property of ceria. The results of EXAFS and H2-TPR reveal that the LaCoO3 in the solid solution supported catalysts possesses higher dispersion and better reducibility than that in CeO2 supported one. The result of O2-TPD shows that the surface active oxygen species are remarkably increased after loading LaCoO3 on the supports. The YCeZrO ternary solid solution supported catalyst containing 5 wt % K2CO3 exhibits the best performance for NO oxidation and reduction at 350 °C, showing a high NO-to-NO2 conversion (66.5%) at lean condition, and a very high NOx reduction percentage (98.2%) and an extremely high NOx-to-N2 s...

Obtaining sub-10 pm spatial resolution by extended X-ray absorption fine structure (EXAFS) spectroscopy is required in many important fields of research, such as lattice distortion studies in colossal magnetic resistance materials, high-temperature superconductivity materialsetc.However, based on the existing EXAFS data analysis methods, EXAFS has a spatial resolution limit of π/2Δkwhich is larger than 0.1 Å. In this paper a new data analysis method which can easily achieve sub-10 pm resolution is introduced. Theoretically, the resolution limit of the method is three times better than that normally available. The method is examined by numerical simulation and experimental data. As a demonstration, the LaFe1–xCrxO3system (x= 0, 1/3, 2/3) is studied and the structural information of FeO6octahedral distortion as a function of Cr doping is resolved directly from EXAFS, where a resolution better than 0.074 Å is achieved.

Metal species in rhizosphere soil profoundly influence their mobility and phytoavailability. Clarifying the speciation transformation of heavy metals helps understand their translocation and accumulation in plants. Single extraction, selective sequential extraction (SSE) and X-ray absorption near-edge structure (XANES) spectroscopy were employed to investigate the speciation transformation of lead (Pb) and its influence on metal accumulation in tea plants after the addition of tea polyphenols (TPs). Pb content was decreased in young leaves and stems, whereas increased in roots, after TPs were amended to soil. Both SSE and XANES analysis suggested bioavailable Pb was transformed to organically bound Pb after the addition of TPs. The increased percentage of organically bound Pb might be fixed in the cell wall of plant root through a ternary complex formed between the Pb-organic matter complex and cell wall components. Therefore, Pb translocation from roots to young tissues was decreased. Pb phytoavailability change was driven by its speciation transformation after the addition of TPs. Combined SSE and XANES spectroscopy represent powerful tools to study metal speciation transformation in plant and soil systems.

The catalyst obtained through the co-precipitation of Mn(Ac)(2) and (NH4)(2)CO3 (denoted as Mn-Ac-NH4) displays the highest performance for soot oxidation. Compared with other MnOx catalysts, the catalyst Mn-Ac-NH4 exhibits much better reducibility and more uniform sponge-like nanostructure. The characterization results indicate that the oxygen species on the surface of Mn-Ac-NH4 are more active for soot combustion. The NO species can also be captured and oxidized by these oxygen species, generating more reactive NO2 which can enhance soot oxidation.

CeO2-TiO2 composite nanorods and nanoparticles were synthesized by hydrothermal and co-precipitation methods, respectively; with the CeO2-TiO2 composite of different morphologies as supports, Au/CeO2-TiO2 catalysts were prepared by the colloidal deposition method and used in CO oxidation at ambient temperature. N-2 sorption, XRD, HRTEM, H-2-TPR, XPS and XAS characterizations were used to clarify the relationship between the morphologic properties of CeO2-TiO2 and the catalytic performance of Au/CeO2-TiO2. HRTEM results show that Au/CeO2-TiO2 nanorods are dominated by CeO2 nanocrystals with (1 1 0) and (1 0 0) facets, while the Au/CeO2-TiO2 nanoparticles mainly expose (1 1 1) planes. XPS and XAS results reveal that both Au/CeO2-TiO2 nanorods and Au/CeO2-TiO2 nanoparticles are similar in the state of gold species. H-2-TPR results indicate that the presence of Au strongly promotes the reduction of CeO2 in the Au/CeO2-TiO2 nanorods. The catalytic activity of Au/CeO2-TiO2 in CO oxidation is strongly related to the morphology of CeO2-TiO2; the CeO2-TiO2 nanorods as support endow the Au/CeO2-TiO2 catalyst with much higher activity than the CeO2-TiO2 nanoparticles. The (1 1 0) and (1 0 0) facets of CeO2 dominated in the Au/CeO2-TiO2 nanorods are able to promote the oxygen migration and gold dispersion, which may then evidently enhance the redox capacity and catalytic activity of the Au/CeO2-TiO2 nanorods in CO oxidation at low temperature. (C) 2013 Elsevier B.V. All rights reserved.

A series of ternary composite oxide catalysts CuO/CO3O4-CeO2 with variable Ce/(Co + Ce) atomic ratios were prepared and employed for the preferential oxidation of CO (CO PROX). Many techniques such as N-2-sorption, XRD, H-2-TPR, O-2-TPO, CO-TPD, O-2-TPD, Cu K-edge XAFS (including EXAFS and XANES) and in situ DRIFTS were used for catalyst characterization. The catalyst CuO/CO3O4-CeO2 with Ce/(Ce + Co) ratio of 0.1 exhibits the best performance, showing not only the lowest temperature for the complete oxidation of CO (98 degrees C), but also the broadest operating temperature window for full CO conversion (98-173 degrees C). The results of N-2-sorption and temperature-programmed characterizations including H2-TPR, O-2-TPO, CO-TPD and O-2-TPD show that the CuCoCe10 catalyst possesses the highest BET surface area, the best reducibility/oxidizability and the best performance for CO and O-2 adsorption. Linear combination fitting of Cu K-edge XANES spectra reveals that multiple Cu species including Cu-0, Cu+ and Cu2+ species co-exist in the spent catalyst CuCoCe10. Stable Cu+ carbonyl species are identified as the main active reaction intermediates as revealed by in situ DRIFTS. High temperature (>120 C) can lead to the reduction of Cu+ to Cu-0, enhancing H-2 oxidation; as a result, the selectivity of O-2 towards CO2 is decreased. Based upon in situ DRIFTS results, a potential CO PROX mechanism over CuO/CO3O4-CeO2 catalysts is proposed. (C) 2013 Elsevier B.V. All rights reserved.

The release of nanoparticles (NPs) to the environment poses an increasing potential threat to biological systems. This study investigated the phytotoxicity and accumulation of copper oxide (CuO) NPs to Elsholtzia splendens (a Cu-tolerant plant) under hydroponic conditions. The 50% effective concentration (EC50) of CuO NPs to E. splendens was about 480 mg/L, implying the tolerance of E. splendens to CuO NPs. The Cu content in the shoots treated with 1000 mg/L CuO NPs was much higher than those exposed to the comparable 0.5 mg/L soluble Cu and CuO bulk particles. CuO NPs-like deposits were found in the root cells and leaf cells. Cu K-edge X-ray absorption near-edge structure analysis further revealed that the accumulated Cu species existed predominantly as CuO NPs in the plant tissues. All these results suggested that CuO NPs can be absorbed by the roots and translocated to the shoots in E. splendens.

In combination with a single-crystal diamond anvil cell (DAC), a polycapillary half-lens (PHL) re-focusing optics has been used to perform high-pressure extended X-ray absorption fine-structure measurements. It is found that a large divergent X-ray beam induced by the PHL leads the Bragg glitches from single-crystal diamond to be broadened significantly and the intensity of the glitches to be reduced strongly so that most of the DAC glitches are efficiently suppressed. The remaining glitches can be easily removed by rotating the DAC by a few degrees with respect to the X-ray beam. Accurate X-ray absorption fine-structure (XAFS) spectra of polycrystalline Ge powder with a glitch-free energy range from -200 to 800 eV relative to the Ge absorption edge are obtained using this method at high pressures up to 23.7 GPa, demonstrating the capability of PHL optics in eliminating the DAC glitches for high-pressure XAFS experiments. This approach brings new possibilities to perform XAFS measurements using a DAC up to ultrahigh pressures.

The environment of Guizhou province of SW China is in part significantly impacted by mercury (Hg) mining activities. The exploitation and processing of Hg-bearing ore in the past have led to multiple sources of Hg contamination, including unprocessed ores and Hg waste calcines and liquid elemental Hg, making source control strategies difficult and expensive to implement. In this study, initially extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the Hg species and to estimate the relative proportions of these species present in Hg-bearing wastes from the Wanshan Hg mine (WSMM) of the eastern Guizhou province. The results showed that cinnabar is the dominant Hg species in the unroasted ore samples, while the most prevalent Hg compounds in mine waste calcine is in the following order: meta-cinnabar, cinnabar and mercuric chloride. Our study demonstrated that mass dependent fractionation of Hg isotopes may occur during transformation of cinnabar to by-products (such as meta-cinnabar and mercuric chloride) by the roasting process. Hg stable isotope analysis of unroasted Hg ores and Hg waste calcines showed that Hg waste calcines (0.08 +/- 0.20 parts per thousand, 26, n=11) were enriched by similar to 0.80 parts per thousand in delta Hg-202 values compared to the unroasted Hg ores (-0.74 +/- 0.11 parts per thousand, 26, n=14). Finally, using a combined triple mixing model, the source attribution of the downstream sediment in WSMM was estimated. Our study suggested that the Hg isotope could be a useful tool to trace and quantify the source of Hg in the environment. (C) 2012 Elsevier B.V. All rights reserved.

A series of MnOx-NiO composite oxide catalysts were prepared by co-precipitation method and used in the catalytic combustion of lean methane at low temperature. Compared with the corresponding single NiO and MnOx oxides, the MnOx-NiO composite oxide with proper composition exhibits much higher catalytic performance in the lean methane oxidation. XRD and HRTEM results demonstrate that MnOx-NiO is in the form of a Ni-Mn-O solid solution. XAFS and XPS results indicate that the content of manganese in MnOx-NiO has a significant influence on the oxidation state of manganese and the crystal defect of nickel oxide. MnOx-NiO catalyst with an atomic Mn/(Mn + Ni) ratio of 0.13 is provided with abundant highly dispersed manganese species of higher valence (Mn4+) and higher coordination number as well as certain nickel vacancies, due to the strong interaction between Ni and Mn species. H-2-TPR and O-2-TPD results show that the MnOx-NiO composite oxide exhibits better reducibility and oxygen mobility than NiO. All these characterizations suggest a prominent synergism between NiO and MnOx in the MnOx-NiO composite oxide, which contributes to its high performance in the lean methane combustion. (C) 2012 Elsevier B.V. All rights reserved.

A new quick-scanning X-ray absorption fine-structure (QXAFS) system has been established on beamline 1W1B at the Beijing Synchrotron Radiation Facility. As an independent device, the QXAFS system can be employed by other beamlines equipped with a double-crystal monochromator to carry out quick energy scans and data acquisition. Both continuous-scan and trapezoidal-scan modes are available in this system to satisfy the time scale from subsecond (in the X-ray absorption near-edge structure region) to 1 min. Here, the trapezoidal-scan method is presented as being complementary to the continuous-scan method, in order to maintain high energy resolution and good signal-to-noise ratio. The system is demonstrated to be very reliable and has been combined with in situ cells to carry out time-resolved XAFS studies.

In this report, AI-BL1.0, an open-source Labview-based program for automatic on-line beamline optimization, is presented. The optimization algorithms used in the program are Genetic Algorithm and Differential Evolution. Efficiency was improved by use of a strategy known as Observer Mode for Evolutionary Algorithm. The program was constructed and validated at the XAFCA beamline of the Singapore Synchrotron Light Source and 1W1B beamline of the Beijing Synchrotron Radiation Facility.

The Co2.5Mg0.5Al1-x%Cex%O hydrotalcite-derived catalysts (CMACex) with different Ce/AI atomic ratios were synthesized by co-precipitation, which simultaneously possess multiple properties for soot combustion, lean-burn NOx storage and simultaneous NOx-soot removal. The techniques including XRD, EXAFS, BET, H-2-TPR, O-2-TPD and in-situ DRIFTS were used for catalyst characterization. It is found that Ce-substituted catalysts are much more active than Ce-free one for soot combustion. NOx storage and simultaneous NOx-soot removal. Among the catalysts containing Ce. CMACe8 exhibits the highest performance, showing the lowest temperature of 384 degrees C for the maximal soot oxidation rate (T-m), the largest NOx storage capacity (336 mu mol g(-1)), and the largest NOx reduction percentage of 15.4%. Compared with Ce-free sample. Ce-substitution increases the specific surface area, the redox properties and the amount of surface lattice oxygen species of the catalyst. The optimal Ce-substitution amount in Co2.5Mg0.5Al1-x%Cex%O is x=8. In-situ DRIFTS results reveal that NO is readily oxidized to NO2 and stored as nitrates over Ce-substituted catalysts, which are very reactive intermediates for simultaneous NOx-soot removal. (C) 2012 Elsevier B.V. All rights reserved.

Whether and how nanoclusters possessing a rich diversity of possible geometric configurations can transform from one structural type to another are critical issues in cluster science. Here we demonstrate an icosahedral-to-cuboctahedral structural transformation of Au nanoclusters driven by changing the chemical environment. For icosahedral Au(13) clusters protected by a mixture of dodecanethiol and triphenylphosphine ligands, solvent exchange of ethanol by hexane leads to quick selective desorption of the thiolate layers from the cluster surface. The surviving Au cores then undergo a much slower energy-minimization process via structural rearrangement, stabilized in the cuboctahedral structure and protected by triphenylphosphine in the hexane environment. In response to the dramatically changed atomic structure, the character of the electronic structure of the Au clusters is converted from semiconducting to metallic. This work addresses the structure-property correlation and its strong dependence on the chemical environment for metal nanoclusters.

A series K/Cu simultaneously substituted nanometric perovskite catalysts La1-xKxCo1-yCuyO3-delta (x = 0, 0.1; y = 0, 0.05, 0.1, 0.2, 0.3) were synthesized by citric acid complexation, which were employed for soot combustion, NOx storage and simultaneous NOx-soot removal. The physico-chemical properties of the catalysts were characterized by XRD, FT-IR, EXAFS, SEM, H-2-TPR, Soot-TPR, TG/DTA, XPS and in situ DRIFTS techniques. When K and Cu are simultaneously introduced into LaCoO3, soot combustion is largely accelerated, decreasing the characteristic temperature (T-m) corresponding to the maximal soot combustion rate at least 80 degrees C; moreover, NOx reduction by soot is also remarkably facilitated. Among all the catalysts La0.9K0.1Co0.9Cu0.1O3-delta shows the lowest T-m of 360 degrees C, the highest NOx storage capacity (NSC) of 284 mu mol g(-1) and the largest NOx reduction percentage of 32%; for soot combustion, it also exhibits the lowest activation energy (80.04 kJ mol(-1)). The XPS and Soot-TPR results reveal that the catalyst La0.9K0.1Co0.9Cu0.1O3-delta possesses more active and larger amount of surface oxygen species (O-2(-) and O-), more tetravalent cobalt ions and better reducibility than others, which determines its better catalytic performance. Based on in situ DRIFTS and other characterization results, the potential mechanisms for soot combustion, NOx storage and simultaneous NOx-soot removal are proposed. (c) 2012 Elsevier B.V. All rights reserved.

In this research, Mn-doped ZnO nanorods were synthesized by a solvothermal method and their magnetic behavior was tuned from paramagnetism to ferromagnetism via a change in their surface environment. The structure and electronic configuration of Mn ions were investigated by means of X-ray diffraction and X-ray absorption fine structure to understand the surface-controlled magnetic properties. The surface electronic configuration was studied by Mn L-3,L-2-edge XANES, which were simulated using the ligand field multiplet theory and the ligand-to-metal charge transfer effects. The results pointed out that Mn3+ ions occupy distorted tetrahedronal sites near the surface region and different surface modifications produce changes in the Mn 3d-anion p hybridization strength. A midgap state with strong O-2p character has been also recognized at the O K-edge XANES, and the density of such a state is strongly related to the observed ferromagnetism. This research represents a novel promising route for tuning the magnetic behavior of nano-dilute magnetic semiconductor systems via surface atomic changes.

The nanometric substituted perovskite catalysts La1-xKxCo1-yNiyO3-delta (x = 0, 0.1; y = 0, 0.05, 0.1) were synthesized by citric acid complexation method, and employed for soot combustion, NOx storage and simultaneous NOx-soot removal. Their structures and physico-chemical properties were characterized by XRD, EXAFS, BET, SEM, H-2-TPR, and XPS techniques. When K and Ni are simultaneously introduced into LaCoO3 catalyst, soot combustion is largely accelerated, with the temperature (T-m) for maximal soot conversion lowered by at least 50 degrees C; moreover, NOx reduction by soot is also facilitated. The La0.9K0.1Co0.95Ni0.05O3-delta catalyst exhibits not only the lowest T-m (367 degrees C) temperature but also the highest soot combustion rate (67.3 mu g/s g catalyst). Meanwhile, the NOx reduction percentage over this catalyst can reach 21%. The kinetic results show that the activation energy for soot combustion over La0.9K0.1Co0.95Ni0.05O3-delta (81.34 kJ mol(-1)) is much lower than that over LaCoO3 (107.7 kJ mol(-1)). The H-2-TPR and XPS results show that the La0.9K0.1Co0.95Ni0.05O3-delta catalyst possesses better redox properties, more tetravalent cobalt ions and larger amount of surface adsorbed oxygen species, which determines its novel performance for soot combustion, NOx storage and soot-NOx removal. (C) 2011 Elsevier Ltd. All rights reserved.

A series of hydrotalcite-derived K/MnMgAlO catalysts were synthesized by co-precipitation and impregnation methods. Their catalytic performances for soot combustion, NOx storage and simultaneous soot-NOx removal were evaluated, respectively. Techniques of TG/DTA, BET, XRD, EXAFS, and in situ DRIFTS were employed for catalyst characterization. The catalyst K/Mn1.5Mg1.5AlO containing 7.5 wt% K shows not only the highest soot oxidation rate of 58.0 mu gs(-1) per gram catalyst, but also the maximal NOx reduction percentage of 26.9%. Over the catalysts containing K less than 10 wt%, the soot combustion follows oxygen spillover mechanism, while over those containing more than 10 wt% K it follows a different mechanism involving the participation of potassium nitrate species. In situ DRIFTS results indicate that introduction of proper amount of K can facilitate the formation of monodentate nitrate, which shows higher reactivity with soot than nitrite, chelating bidentate nitrate and ionic nitrate species. In the catalysts promoted by K, a new phase namely K2Mn4O8 was identified, which is highly active for soot combustion and NOx reduction by soot. (C) 2012 Elsevier B.V. All rights reserved.