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The aim of the present work was to evaluate the anaerobic ammonium oxidation (anammox) activity of simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm with different substrate concentrations and pH values. Kaldnes rings taken from the SNAD biofilm reactor were incubated in batch tests to determine the anammox activity. Haldane model was applied to investigate the ammonium inhibition on anammox process. As for nitrite inhibition, the NH4+-N removal rate of anammox process remained 87.4% of the maximum rate with the NO2--N concentration of 100 mg/L. Based on the results of Haldane model, no obvious difference in kinetic coefficients was observed under high or low free ammonia (FA) conditions, indicating that ammonium rather than FA was the true inhibitor for anammox process of SNAD biofilm. With the pH value of 7.0, the rmax, Ks and KI of ammonium were 0.209 kg NO2--N/kg VSS/day, 9.5 mg/L and 422 mg/L, respectively. The suitable pH ranges for anammox process were 5.0 to 9.0. These results indicate that the SNAD biofilm performs excellent tolerance to adverse conditions. [ABSTRACT FROM AUTHOR]

While the oxidation state Pu(VIII) is shown to be less stable than Pu(V) in the PuO4 molecule, it is not clear if the more electronegative fluorine can help to stabilize Pu(VIII). Our calculations on PuOnF8-2n (n = 0-4) molecules notably confirm that PuO2F4 has both ¹D4h and 5C2v minima with the oxidation states Pu(VIII) and Pu(V), respectively, with the latter having lower energy. The hybrid-DFT, CCSD(T), and CASSCF methods all give the same result. The results conform to a superoxide ligand when n ≥ 2. PuF8 in a ¹Oh state can decompose to PuF6 and F2, and PuOF6 in a ¹C2v state also can break down to PuF6 and 1/2 O2. The Pu(VIII) anion PuO2F5- does have a D5h minimum, which also lies above a 5C2v Pu(V) peroxide structure. However, the energy differences between the different minima are not large, indicating that metastable species with oxidation states higher than Pu(V) cannot be completely excluded. [ABSTRACT FROM AUTHOR]

A multicomposition resistant coating for SiC coated carbon/carbon (C/C) composites was produced by pack cementation technique in an argon atmosphere. This multicomposition coating was characterized by X-ray diffraction and scanning electron microscopy technique, and the oxidation behaviors of C/C with this multicomposition coating were also investigated in air using thermogravimetry. The results indicate that a dense coating with an average thickness of 200 μm can be got using pack cementation technique. The coating is composed of Al2O3, CrAl0.42Si1.58, SiC, and AI4SiC4, This multicomposition costing could effectively protect the composites from exposure to atmosphere at 1873 K for 49 h with the weight loss of the coated C/C composites being only 1.84%. [ABSTRACT FROM AUTHOR]

A new approach to the synthesis of tetrasubstituted furans using aromatic alkynes catalyzed by PdCl2 in DMA (N,N-dimethylacetamide)- H2O with dioxygen as the sole oxidant is described, in which the oxygen atom of the furan was from water. The preliminary mechanistic understanding of this transformation was investigated. [ABSTRACT FROM AUTHOR]

We have developed a simple and practical process for the oxidation of alcohols to the corresponding carbonyl compounds by using a low catalytic amount of DDQ1 NaNO2 as a cocatalyst, and molecular oxygen as terminal oxidant Nitric oxide generated in situ by NaNO2 in the presence of AcOH is essential for the realization of the catalytic cycle at room temperature. The practical utility of this catalytic process has been demonstrated in the gram-scale oxidation of cinnamyl alcohol. [ABSTRACT FROM AUTHOR]

Complex oxides-containing at least two different cations on crystallographically distinct sites-have recently been shown to display redox cycling of platinum group metals (PGMs), such as Pd; for example, Pd-substituted complex oxides can reversibly extrude metallic Pd under reducing conditions and then reincorporate Pd2+ ions into the lattice under oxidizing conditions. The title compounds, YMn0.5Fe0.5-xPdxO3-δ (0 ≤ x ≤ 0.07) crystallizing in the noncentrosymmetric YMnO3 structure, were prepared using a sol-gel process at 800 ¼C, and the structures were refined from high-resolution synchrotron X-ray powder diffraction data. Their redox cycling behavior was monitored using synchrotron X-ray diffraction and EXAFS studies. In contrast to the previously studied complex oxide host compounds, YMn0.5Fe0.5-xPdxO3-δ is only modestly tolerant to cycling: repeated redox cycling leads to the formation of PdO, which, on the time-scale of the oxidation cycles, does not reincorporate in the complex oxide lattice. Both oxidized and reduced samples were tested for the oxidation of CO to CO2 under CO-lean conditions. YMn0.5Fe0.5-xPdxO3-δ performs essentially as well as previously studied YFe1-xPdxO3-δ. The CO oxidation light-off characteristics of the hexagonal hosts are very similar to finely dispersed PdO. Despite evidence that Pd is almost fully dispersed as divalent ions in the host lattice, which is presumably accompanied by the concurrent creation of oxygen vacancies (2 Pd2+:1 VO2-), the as-prepared hexagonal materials do not display any significant improvement in catalytic activity as a function of Pd substitution level. This suggests that the corner-connected trigonal bipyramids that characterize this structural family do not enable the transport of oxygen through the bulk of the lattice. The study casts light on factors in the solid-state chemistry of precious metal-substituted complex oxides that influence the efficacy of redox cycling of the precious metal, and catalytic performance. [ABSTRACT FROM AUTHOR]

Abstract: To protect carbon/carbon (C/C) composites from oxidation at elevated temperature, an effective WSi2–CrSi2–Si ceramic coating was deposited on the surface of SiC coated C/C composites by a simple and low-cost slurry method. The microstructures of the double-layer coatings were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy analyses. The coating exhibited excellent oxidation resistance and thermal shock resistance. It could protect C/C composites from oxidation in air at 1773K for 300h with only 0.1wt.% mass gain and endure the thermal shock for 30 cycles between 1773K and room temperature. The excellent anti-oxidation ability of the double-layer WSi2–CrSi2–Si/SiC coating is mainly attributed to the dense structure of the coating and the formation of stable vitreous composition including SiO2 and Cr2O3 produced during oxidation. [ABSTRACT FROM AUTHOR]

Ln-containing AlPO-5 (Ln = La, Ce, Sm, Dy, Y, Gd) were synthesized hydrothermally in the presence of HF, and characterized by XRD, UV-vis, SEM, N2 adsorption/desorption, FT-IR, solid state 27Al MAS NMR and ICP-AES techniques. The results showed that all the samples had good crystallinity and high specific area. Isomorphous substitution of Ln ions for Al+3 occurred. The lanthanide ions were incorporated into the frameworks or were highly dispersed on extra frameworks of the samples. The newly synthesized catalysts all were efficient for the oxidation of cyclohexane in a solvent-free system, especially Gd–AlPO-5. Near 13% conversion of cyclohexane were achieved on the catalyst Gd(60)–AlPO-5 with Al/Gd of 60 under the conditions of 0.5 MPa O2, 413 K and 4 h reaction. The total selectivity to cyclohexanol and cyclohexanone was up to 92%. In addition, the catalyst Gd(60)–AlPO-5 was recyclable for the titled reaction system. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: To prevent carbon/carbon (C/C) composites from oxidation, a multilayer oxidation resistant coating was prepared. The inner SiC coating was prepared by pack cementation, and the outer SiC–MoSi2 three-layer coating was obtained by slurry coating using silicon–sol as the caking agent. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to analyze the phase, microstructure and element distribution of the as-prepared coating. The results show that, the as-received multilayer coating has a crack-free structure with the thickness of about 300μm. It is provided with excellent oxidation resistance from room temperature to 1500°C in air and can protect C/C composites from oxidation for more than 120h at 900°C and more than 110h at 1500°C in air. The weight loss of the coated samples during oxidation tests mainly resulted from the oxidation of Mo5Si3 and the volatilization of SiO2 in the coating. [Copyright &y& Elsevier]

The article presents a study on the functions and characteristics of the sub-fractions of soluble soybean polysaccharides (SSPS), the high-molecular-weight fraction (HMF) and low-molecular-weight fraction (LMF). It reveals that HMF, comprised of a large polysaccharide molecule with covalently-attached peptides, stabilizes α-casein dispersions and emulsifies oil droplets. Meanwhile, LMF which has free peptides and small sizes saccharides prevents the oxidation of emulsified lipids.

In order to protect carbon/carbon (C/C) composites against oxidation, a Si–Mo–W coating was prepared on the surface of SiC-coated C/C composites by a simple reaction method. The microstructures of the as-received coating were characterized by scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy analyses. The results show that the SiC/Si–Mo–W coating can protect C/C composites from oxidation in air at 1673 K for 220 h with a mass loss of 0.003%, and at 1773 K for 252 h with a mass gain of 1.56%. The excellent oxidation-resistant property of the SiC/Si–Mo–W coating at 1673–1773 K is attributed to the formation of SiO2 film on the coating surface. The mass loss of the coated C/C composites during the oxidation test at 1873 K in air primarily resulted from the reaction of C/C substrate and oxygen diffusing through the penetration cracks in the coating. [ABSTRACT FROM AUTHOR]

Abstract: To prevent carbon/carbon (C/C) composites from oxidation, a Si–SiC coating has been prepared by a two-step pack cementation technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis show that the coating obtained by the first step pack cementation is a porous β-SiC structure, and a dense structure consisting α-SiC, β-SiC and Si is obtained after heat-treatment by the second step pack cementation. By energy dispersive spectroscopy (EDS) analysis, a gradient C–SiC transition layer can be formed at the C/C-coating interface. The as-received coating has excellent oxidation protection ability and can protect C/C composites from oxidation for 166h at 1773K in air. The weigh loss of the coated C/C is due to the formation of bubble holes on the coating surface and through-coating cracks in the coating. [Copyright &y& Elsevier]

Large-molecule polyhydroxy organic acids such as tartaric acid and citric acid were found to significantly promote the cooperative formation of mesoporous silica SBA-15 with homogeneous well-defined hexagonal mesostructure under much weaker acidities without addition of volatile inorganic acids; therefore a novel environmental benign route for SBA-15 synthesis was developed. It is suggested that the polar groups of polyhydroxy acid molecules can greatly strengthen the assembly interactions between the silica species and the triblock copolymer by providing hydrogen bonding. More interestingly, by controlling the strength of hydrogen-bonding interaction that is dependent on the concentration of carboxylic acids, the particle size of the product can be tailored. The silica with small particle size synthesized with a small amount of polyhydroxy acids was favorable support of palladium catalyst for the complete oxidation of volatile organic compounds in atmosphere, probably due to the facilitated diffusion of reactant molecules. [ABSTRACT FROM AUTHOR]

In order to protect carbon/carbon (C/C) composites from oxidation at 1700°C, a MoSi2–SiC–Si/MoSi2 coating was prepared on the surface of these composites by a simple and effective method. The MoSi2–SiC–Si inner layer was obtained by pack cementation, and the MoSi2 outer layer was prepared by slurry coating using silicon-sol as the caking agent. The microstructures of the as-prepared coating were examined by X-ray diffraction and scanning electron microscope. Oxidation test shows that, the as-received coating can protect C/C composites from oxidation for more than 107 h at 1700°C in air. The excellent anti-oxidation ability of this coating is attributed to its dense structure and the formation of the SiO2 film on the coating surface during oxidation. [ABSTRACT FROM AUTHOR]

Platinum electrocatalysts supported on multi-walled carbon nanotubes (MWCNTs) with various diameters and lengths were studied by using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) and Chronoamperometry. The results indicated that the MWCNTs with smaller diameter generated more amorphous carbon after a sonochemical oxidation treatment. Compared with the long MWCNTs, the short MWCNTs had more open ends, resulting in high-Pt dispersion and electrocatalytic activity towards methanol oxidation. Pt nanoparticles supported on short MWCNTs with a diameter of 30–50 nm exhibited the best Pt dispersion and highest methanol oxidation activity among the catalysts studied. The high activities of the catalysts based on short MWCNTs were due to both the intrinsic high activity of the ends of MWCNTs and a good Pt distribution. [ABSTRACT FROM AUTHOR]

Abstract: A SiC whisker-toughened SiC–CrSi2 oxidation protective coating was prepared on the surface of C/C composites by a two-step technique of slurry and pack cementation. The oxidation protective ability and thermal stress resistance of the coating exhibit the trend of increase first and decrease afterwards as the SiCw content increases from 0 to 20wt.%. The compound effect of SiCw and CrSi2 on the oxidation protective ability of SiC coating is better than their individual ones. [Copyright &y& Elsevier]

Abstract: To prevent carbon/carbon (C/C) composites from oxidation at 1873 K, a dense SiC–Si–MoSi2 coating toughened with SiC whiskers (SiCw) was prepared by a two-step technique. The first step technique is to prepare a porous SiC coating toughened with SiCw by slurry, and the second one is to fill Si and MoSi2 in the holes of SiC coating by pack cementation. Oxidation test shows that the oxidation protective ability of SiC–Si–MoSi2 coating can be improved largely by adding 5–15 wt.% SiCw. After 38 h oxidation in air at 1873 K, the weight loss of the coated C/C sample without SiCw was up to 3.52%, while the weight loss of the coated sample with 10 wt.% SiCw was only 1.43%. [Copyright &y& Elsevier]

Abstract: To protect carbon/carbon (C/C) composites from oxidation, a new type of oxidation protective coating has been produced by a two-step pack cementation technique. XRD and SEM analysis show, the coating obtained by the first step pack cementation was a porous β-SiC structure, and a new phase of CrSi2 was generated in the porous SiC coating after heat-treatment according to the second step pack cementation process. Oxidation test shows that, the weight loss of the SiC coated C/C is up to 11.26% after 5h oxidation in air at 1773K, and the weight loss of the CrSi2–SiC coated C/C composites is only 4.15% after oxidation in air at 1773K for 34h. The oxidation of C/C composites was primarily due to the reaction of C/C matrix and oxygen diffusing through the penetrable cracks in the coating. [Copyright &y& Elsevier]

Abstract: A double-layer oxidation protective coating was prepared on carbon/carbon composites using a simple and low cost method. The coating consists of an inner buffer layer of β-SiC and an outer layer of molybdenum disilicide particles dispersed in a magnesium boron aluminosilicate glass (SABM). Oxidation test shows that, after oxidation in air at 1573 K for 150 h and thermal cycling between 1573 K and room temperature for 20 times, the weight loss of the coated material is only 1.07%. The decreasing of the sample weight is primarily due to the debonding of some glass on the coating surface. [Copyright &y& Elsevier]

Abstract: To prevent carbon/carbon composites from oxidation at 1773 K, an efficient oxidation protective glass coating has been prepared on the surface of SiC coated C/C composites by a simple and low-cost method. The microstructures and phase composition of the as-prepared coating were examined by SEM and XRD. Oxidation testing shows, after oxidation in air at 1773 K for 140 h and thermal cycling between 1773 K and room temperature for 8 times, the weight loss of the coated sample is only 0.98%. The oxidation of the coated C/C composites is attributed to the formation of bubble holes on the coating surface and microcracks in the coating. [Copyright &y& Elsevier]

For the first time, kinetics of aniline oxidation with chlorine dioxide( ClO2) were investigated systematically by detecting concentration of aniline with HPLC at regular intervals. Results showed that the reaction was first-order both in ClO2 and in aniline, and the oxidation reaction could be described as second-order reaction. Stoichiometric factor η was experimentally determined to be 2.44. The second-order-reaction rate constant k was 0.11 L/(mol·s) under condition of pH 6.86 and water temperature ( Tw) 287K. Reaction activation energy was 72.31 kJ/mol, indicating that the reaction could take place under usual water treatment conditions. The reaction rate constants in acidic and alkali media were greater than that in neutral medium. Chlorite ion could slightly increase reaction rate in acidic medium. p-aminophenol and azobenzene were detected by Gd-MS as intermediates. [ABSTRACT FROM AUTHOR]

Morphology modification of nanostructures is of great interest, because it can be used to fabricate nanostructures which are hard to be done using other methods. Different from traditional lithographic technique which is slow and expensive, morphology modification is easy, cheap, and reproducible. In this paper, modification of the optical and morphological properties of a hollow gold nanoshell (HGNS) is achieved by using H2O2 as an oxidizer. The reshaping of these nanostructures has been demonstrated as a consequence of an oxidation process in which HGNSs are dissolved by H2O2 under the acidic conditions provided by HCl. We investigate the oxidation process by a transmission electron microscope and propose a reshaping model involving four different shapes (HGNS, HGNS with hole, gold nanoring, and C-shaped gold nanoparticle) which are corresponding to the oxidation products of HGNSs at different pH values. Besides, the surface enhanced Raman scattering (SERS) activity of each oxidation product has been evaluated by using rhodamine 6G as the Raman active probe. It has been observed that the C-shaped gold nanoparticles which are corresponding to the oxidation products at the minimum pH value have the highest SERS activity and this result can also be interpreted by discrete-dipole approximation simulations. We demonstrate that the morphology modification of HGNSs becomes possible in a controlled manner using wet chemistry and can be used in preparation of gold nanoparticles such as HGNS with hole, gold nanoring, and C-shaped gold nanoparticle with large SERS activity. These nanostructures must have potential use in many plasmonic areas, including sensing, catalysis, and biomedicine. [ABSTRACT FROM AUTHOR]

A novel, direct para-selective oxidative cross-coupling of benzene derivatives with cycloalkanes catalyzed by ruthenium was developed. A wide range of arenes bearing electron-withdrawing substituents was functionalized directly with simple cycloalkanes with high para-selectivity; arenes with electron-donating groups were mainly para-functionalized. Benzoic acid can be used directly. [ABSTRACT FROM AUTHOR]

Oxazolination of C70 has been achieved via the aerobic oxidation of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. in the presence of PhCN. Only one C70 oxazoline regioisomer (1) is obtained, indicating that the oxazolination of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. occurs with an unusual regioselectivity. Further benzylation of 12- with benzyl bromide leads to the formation of the first cis-1 C70 derivative with respect to the apical pentagon (2), as shown by the X-ray single-crystal structure and various spectral characterizations. The structure of the obtained C70 oxazoline (1) is resolved with H/D labeling benzylation and HMBC (heteronuclear multiple bond coherence) NMR on the basis of the structure of 2. The result shows that for compound 1, the O atom is selectively bonded to the C1, while the N atom is bonded to the C2 of C70. The exhibited regioselectivity for the orientation of oxazolino group on C70 is further rationalized with computational calculations, and a reaction mechanism for the oxazolination of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. is proposed. [ABSTRACT FROM AUTHOR]

Uranium chlorides are important in actinide chemistry and nuclear industries, but their chemical bonding and many physical and chemical properties are not well understood yet. Here, we report the first experimental observation of two gaseous uranium hexachloride anions, UCl6- and UCl62-, which are probed by photoelectron spectroscopy in conjunction with quantum chemistry calculations. The electron affinity of UCl6 is measured for the first time as +5.3 eV; its second electron affinity is measured to be +0.60 eV from the photoelectron spectra of UCl62-. We observe that the detachment cross sections of the 5f electrons are extremely weak in the visible and UV energy ranges. It is found that the one-electron one-determinental molecular orbital picture and Koopmans' theorem break down for the strongly internally correlated U-5f2 valence shell of tetravalent U+4 in UCl62-. The calculated adiabatic and vertical electron detachment energies from ab initio calculations agree well with the experimental observations. Electronic structure and chemical bonding in the uranium hexachloride species UCl62- to UCl6 are discussed as a function of the oxidation state of U. [ABSTRACT FROM AUTHOR]

Low-temperature catalysts of mesoporous Co3O4 and Au/Co3O4 with high catalytic activities for the trace ethylene oxidation at 0 °C are reported in this paper. The catalysts were prepared by using the nanocasting method, and the mesostructure was replicated from three-dimensional (3D) cubic KIT-6 silicas. High resolution transmission electron microscopy (HRTEM) studies revealed that (110) facets were the - exposed active surfaces in the mesoporous Co3O4, whereas the Co3O4 nanosheets prepared by the precipitation method exhibited the most exposed (112) facets. We found that the mesoporous Co3O4 was significantly more active for ethylene oxidation than the Co3O4 nanosheets. The results indicated that the crystal facet (1 10) of Co3O4 played an essential role in determining its catalytic oxidation performance. The synthesized Au/Co3O4 materials, in which the gold nanoparticles were assembled into the pore walls of the Co3O4 mesoporous support, exhibited stable, highly dispersed, and exposed gold sites. Gold nanoparticles present on Co3O4 readily produced surface-active oxygen species and promoted ethylene oxidation to achieve a 76% conversion at 0 °C, which is the highest conversion reported yet. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve the oxidation resistance of carbon/carbon composites at intermediate temperatures, a novel double-layer SiC/indialite coating was prepared by a simple and low-cost method. The internal SiC transition layer was prepared by pack cementation and the external indialite glass–ceramic coating was produced by in situ crystallization of ternary MgO–Al2O3–SiO2 glass. The microstructures and morphologies of coating were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Oxidation resistance of the as-coated C/C composites was evaluated in ambient air at temperature from 800°C to 1200°C. Nearly neglectable mass loss was measured after 100h isothermal oxidation test, indicating that SiC/indialite coating possesses excellent oxidation protection ability. The as-coated samples have a good thermal shock resistance and no obvious damage was found in the coating even after suffered more than 11 thermal cycles between test temperature and room temperature. The oxidation protection mechanism of this coating was also discussed. [Copyright &y& Elsevier]

A new type of oxidation-protective multi-composition coating for carbon/carbon (C/C) composites has been produced by a pack cementation technique in an argon atmosphere. XRD analyses shows that the phases of the composite coating are composed of Al2O3, mullite, SiC and Al4SiC4, and the bonding layer between the coating and C/C composites are composed of Al4C3, SiC and Al4SiC4. It is found by SEM surface observation and EDS area scanning analyses that the coating has two kinds of surfaces that are distinctly different in element content of Si and C. In the meantime, cross-section SEM observation of the coating also displays a dense microstructure. Oxidation test shows that the as-prepared coating characterized by excellent thermal shock resistance on the surface of C/C composites during exposure to an oxidizing atmosphere at 1773 K could effectively protect the C/C composites from oxidation for 41 h. [Copyright &y& Elsevier]

In order to exploit the unique high temperature mechanical properties of carbon/carbon (C/C) composites, a new type of oxidation protective coating has been produced by a two-step pack cementation technique in an argon atmosphere. XRD analysis showed that the internal coating obtained from the first step was a gradient SiC layer that acts as a buffer layer, and the multi-layer coating formed in the second step was an Al2O3-mullite layer. It was found that the as-received coating characterized by excellent thermal shock resistance on the surface of C/C composites during exposure to an oxidizing atmosphere at 1873 K, could effectively protect the C/C composites from oxidation for 45 h. The failure of the coating is due to the formation of bubble holes on the coating surface. [Copyright &y& Elsevier]

The article reports that Carbon/carbon (C/C) composites are important engineering materials for high-temperature structural applications due to their low thermal expansion coefficient, low weight, high specific strength and modulus, high creep resistance and excellent thermal shock resistance. Yttrium silicates are good oxidation resistant materials for high temperature applications because of their excellent properties such as high melting point and low oxygen infiltration. High temperature silicates such as mullite and zircon are promising candidate materials for oxidation protective coatings for C/C composites.

Gold (Au) catalysts exhibit a significant size effect, but its origin has been puzzling for a long time. It is generally believed that supported Au clusters are more or less rigid in working condition, which inevitably leads to the general speculation that the active sites are immobile. Here, by using atomic resolution in situ environmental transmission electron microscopy, we report size-dependent structure dynamics of single Au nanoparticles on ceria (CeO2) in CO oxidation reaction condition at room temperature. While large Au nanoparticles remain rigid in the catalytic working condition, ultrasmall Au clusters lose their intrinsic structures and become disordered, featuring vigorous structural rearrangements and formation of dynamic low-coordinated atoms on surface. Ab initio molecular-dynamics simulations reveal that the interaction between ultrasmall Au cluster and CO molecules leads to the dynamic structural responses, demonstrating that the shape of the catalytic particle under the working condition may totally differ from the shape under the static condition. The present observation provides insight on the origin of superior catalytic properties of ultrasmall gold clusters. [ABSTRACT FROM AUTHOR]

We demonstrate a rationally designed fluorescent and colorimetric dual-readout strategy for the highly sensitive, quantitative determination of inorganic pyrophosphatase (PPase) activity, a key hydrolytic enzyme involved in a variety of metabolic processes. Inspired by the selective oxidative and chromogenic reaction of o-phenylenediamine (OPD) with Cu2+, the special inhibitory effects of pyrophosphate (PPi) on the oxidative ability of Cu2+, and the specific hydrolysis of PPi into orthophosphate by PPase, a convenient small molecule OPD-based analytical system was developed for Cu2+/PPi recognition and PPase activity assay. We have confirmed that Cu2+ acts as the oxidant in the reaction and the main chromogenic product of OPD is 2,3-diaminophenazine (usually called OPDox) in the assay by combining the ESI-MS, 1H NMR, and XPS spectra analysis. Direct electrochemical insights into the Cu2+-triggered and PPi-inhibited mechanism were performed by cyclic voltammetry characterizations of the Cu2+ in the absence and presence of PPi for the first time. Furthermore, the proposed analytical system with clear response mechanism exhibits a promising outlook for the PPase activity assay in real biological samples and inhibitor screening. [ABSTRACT FROM AUTHOR]

BiVO4 was found to be an efficient photocatalyst under visible light irradiation for selective oxidation of amines to imines with high activity (99% conversion) and selectivity (up to 99%) using oxygen as an oxidant. [ABSTRACT FROM AUTHOR]

The article offers information on the use of peroxides for palladium-catalyzed methylation of aryl C-H bond. A study was conducted to determine the Pd-catalyzed direct functionalizations of aryl C-H to form C-C bonds. The result of the study confirms the method for direct methylation of aryl C-H bonds by using peroxide compounds as both methylating reagents and hydrogen acceptor.

In neutral chemical compounds, the highest known oxidation state of all elements in the Periodic Table is +VIII. While PuO4 is viewed as an exotic Pu(+VIII) complex, we have shown here that no stable electronic homologue of octavalent RuO4 and OsO4 exists for PuO4, even though Pu has the same number of eight valence electrons as Ru and Os. Using quantum chemical approaches at the levels of quasi-relativistic DFT, MP2, CCSD(T), and CASPT2, we find the ground state of PuO4 as a quintet 5C2v-(PuO2)+(O2)- complex with the leading valence configuration of an (f³)plutonyl(V) unit, loosely coupled to a superoxido (π*³)O2- ligand. This stable isomer is likely detectable as a transient species, while the previously suggested planar ¹D4h-Pu(VIII)O4 isomer is only metastable. Through electronic structure analyses, the bonding and the oxidation states are explained and rationalized. We have predicted the characteristics of the electronic and vibrational spectra to assist future experimental identification of (PuO2)+(O2)- by IR, UV-vis, and ionization spectroscopy. [ABSTRACT FROM AUTHOR]

Platinum-based heterogeneous catalysts are critical to many important commercial chemical processes, but their efficiency is extremely low on a per metal atom basis, because only the surface active-site atoms are used. Catalysts with single-atom dispersions are thus highly desirable to maximize atom efficiency, but making them is challenging. Here we report the synthesis of a single-atom catalyst that consists of only isolated single Pt atoms anchored to the surfaces of iron oxide nanocrystallites. This single-atom catalyst has extremely high atom efficiency and shows excellent stability and high activity for both CO oxidation and preferential oxidation of CO in H2. Density functional theory calculations show that the high catalytic activity correlates with the partially vacant 5d orbitals of the positively charged, high-valent Pt atoms, which help to reduce both the CO adsorption energy and the activation barriers for CO oxidation. [ABSTRACT FROM AUTHOR]

Abstract: To prevent carbon/carbon (C/C) composites from oxidation, a dense SiC nanowire-toughened SiC–MoSi2–CrSi2 multiphase coating was prepared by the two-step technique composed of chemical vapor deposition (CVD) and pack cementation. The coatings were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). SiC nanowires could decrease the dimension of cracks and improve the oxidation and thermal shock resistance of SiC–MoSi2–CrSi2 multiphase coating. Oxidation test shows that, after introducing SiC nanowires, the weight loss of the coated sample can be reduced from 1.06% to 0.64% after oxidation at 1773K for 155h and decreased from 6.92% to 3.42% after thermal cycling between 1773K and room temperature for 30 times. [Copyright &y& Elsevier]

The existence of a novel octahedral UO6complex had been suggested by Pyykkö et al. [Pyykkö, P.; Runeberg, N.; Straka, M.; Dyall, K. G. Chem. Phys. Lett.2000, 328, 415]. We have now investigated the stability, the geometric and electronic structures, and the vibrations of various UO6molecules, using spin−orbit density functional and scalar-relativistic coupled-cluster approaches. We find four different (meta-)stable species, namely 3D2h-UO2(η2-O2•)2at lowest energy, 3C2v-UO4•(η2-O2•) and 1D3-U(η2-O2)3at medium energies, and 1Oh-UO6at highest energy. The decay of Oh-UO6occurs via an activated spin-flip mechanism. The UO6species correspond to local minima on singlet and triplet energy surfaces and might be trapped in noble gas matrices. Experimentally, the four species might be identified through their vibrational spectra. Uranium is best described as coordinated by oxygen atoms in various oxidation states as oxo O2−, oxido(1) O•−, peroxido O22−, and superoxido O2•−ligands. The occurrence of monovalent oxygen is remarkable. The resulting characterization of the central ion as UVIin all four cases does not fully reflect the electronic differences, nor the “valence-activity” of the U-6p6semicore shell. [ABSTRACT FROM AUTHOR]

La4LiAuO8 and La2BaPdO5, two previously known oxides, are presented as model compounds for examining the role of isolated and immobilized Au3+ and Pd2+ ions in heterogeneous catalysis. Structural characterization, stability, surface composition, and electronic structure of these compounds are presented. These are examined in studies ranging from synchrotron X-ray scattering, including pair distribution function (PDF) and maximum entropy method (MEM) analysis, to density functional calculations of the electronic structures. The exceptional stability displayed by these compounds as verified by thermogravimetric analysis can be attributed to the presence of covalent Au—O and Pd—O interactions revealed in MEM studies, which suggests a criterion for stabilizing these highly oxophobic transition metals in oxide environments. Catalytic testing of the two compounds as heterogeneous catalysts in the oxidation of CO to CO2 are presented. La2BaPdO5 appears to be an effective catalyst for CO oxidation, despite the low surface area of the oxide being used. This is the first time that a fully ordered (rather than doped) Pd2+ oxide had been used to catalyze CO oxidation. La4LiAuO8 on the other hand, is much less effective at catalyzing CO oxidation. Differences in the reactivities of the two compounds are discussed with respect to differences in their density functional electronic structures. [ABSTRACT FROM AUTHOR]

Abstract: A hot-pressing reactive sintering (HPRS) technique was explored to prepare SiC coating for protecting carbon/carbon (C/C) composites against oxidation. The microstructures of the coatings were analyzed by X-ray diffraction and scanning electron microscopy. The results show that, SiC coating obtained by HPRS has a dense and crack-free structure, and the coated C/C lost mass by only 1.84wt.% after thermal cycles between 1773K and room temperature for 15 times. The flexural strength of the HPRS-SiC coated C/C is up to 140MPa, higher than those of the bare C/C and the C/C with a SiC coating by pressure-less reactive sintering. The fracture mode of the C/C composites changes from a pseudo-plastic behavior to a brittle one after being coated with a HPRS-SiC coating. [Copyright &y& Elsevier]

A highly efficient alkynylation-cyclization of terminal alkynes with salicylaldehydes leading to substituted 2,3-dihydrobenzofuran-3-ol derivatives was developed by using Cy3P-silver complex as catalyst in water. Counter anions in the silver complex proved to be the key factor to Z/E stereoselectivity control. Aurones can also be obtained effectively from the cascade reaction followed by oxidation without further purification. [ABSTRACT FROM AUTHOR]

A general two-step approach has been developed for the synthesis of very small and sintering-resistant bimetallic gold−silver nanoparticles on inert supports including commercial silica and alumina. In this approach, gold particles were formed in the first step on amino-functionalized silica or alumina support. Our density functional theory (DFT) calculations on selected model clusters show that the surface atoms of the gold particles formed in the first step carry slightly negative charges, which facilitates the subsequent Ag+adsorption on the gold particle surface. Upon Ag+adsorption and reduction by NaBH4in the second step, specific nanoparticles with gold−silver alloy core and a silver nanoshell have been formed, as confirmed by our ultraviolet−visible spectroscopy (UV−vis), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS) characterizations. Such particles have been found to be highly thermally stable, and their sizes remain substantially unchanged (∼3 nm) even upon calcination in air at 500 °C. After the final reduction treatment in H2, a randomly distributed alloy composed of gold and silver is formed, and the resultant Au−Ag alloy particles are highly catalytically active for CO oxidation, even superior to Au/TiO2. The role of Ag in stabilizing the particles has been discussed. [ABSTRACT FROM AUTHOR]

Abstract: The catalyst of CuOx/Al2O3 was prepared by the dipping-sedimentation method using γ-Al2O3 as a supporter. CuO and Cu2O were loaded on the surface of Al2O3, characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). In the presence of CuOx/Al2O3, the microwave-induced chlorine dioxide (ClO2) catalytic oxidation process was conducted for the treatment of synthetic wastewater containing 100 mg/L phenol. The factors influencing phenol removal were investigated and the results showed that microwave-induced ClO2-CuOx/Al2O3 process could effectively degrade contaminants in a short reaction time with a low oxidant dosage, extensive pH range. Under a given condition (ClO2 concentration 80 mg/L, microwave power 50 W, contact time 5 min, catalyst dosage 50 g/L, pH 9), phenol removal percentage approached 92.24%, corresponding to 79.13% of CODCr removal. The removal of phenol by microwave-induced ClO2-CuOx/Al2O3 catalytic oxidation process was a complicated non-homogeneous solid/water reaction, which fitted pseudo-first-order by kinetics. Compared with traditional ClO2 oxidation, ClO2 catalytic oxidation and microwave-induced ClO2 oxidation, microwave-induced ClO2 catalytic oxidation system could significantly enhance the degradation efficiency. It provides an effective technology for the removal of phenol wastewater. [Copyright &y& Elsevier]

The article discusses that C-H bonds of organic molecules can transform into the desired structures directly without other factors and if chemical reactions can be developed with the use of water. It contains examples of direct transformations of C-H bonds into other bonds with the use of aqueous media.

• Highly selective synthesis of ethyl pyruvate was realized in liquid-phase. • Na-doped OMS-2 enhanced the selectivity of the reaction under mild conditions. • O 2 was activated by OMS-2 catalyst and used as an efficient green oxidant. The direct oxidation of lactate to pyruvate is an important process for catalytic conversion of biomass, although low selectivity and harsh reaction conditions limit its potential for industrial application. In this study, catalytic oxidation of ethyl lactate (EL) to ethyl pyruvate (EP) over OMS-2-based materials was conducted using O 2 as the green oxidant. A 78 % EL conversion and 95 % EP selectivity were obtained in CH 3 NO 2 at 50 °C over a Na-doped OMS-2 catalyst. The conversion and selectivity of the reaction were affected by the dopant loading of catalyst and reaction temperature. Kinetic study found that original OMS-2 showed slightly higher initial reaction rate than modified OMS-2, and the latter gave higher EP yield due to its more labile lattice oxygen. Characterization of the catalyst indicates that the enhancement of surface oxygen vacancies and reducibility from the Na-doping might contribute to the superior catalytic activity. [ABSTRACT FROM AUTHOR]