- Adsorption and reactivity of nitrogen oxides (NO2, NO, N2O) on Fe-zeolites
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Nitrous oxide decomposition and temperature programmed desorption tests on Fe-ZSM-5 and Fe-silicalite show that the catalytic conversion mechanism of N2O into N2 and O2 over Fe-zeolites is more complex than expected. Nitro
- Rivallan, Mickael,Ricchiardi, Gabriele,Bordiga, Silvia,Zecchina, Adriano
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- Tuning the O2 Binding Affinity of Cobalt(II) Centers by Changing the Structural and Electronic Properties of the Distal Substituents on Azole-Based Chelating Ligands
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The effects of the substituents on the chelating ligands located in the secondary coordination sphere on the O2 affinity of cobalt(II) centers have been explored. The combination of facially capping tridentate tris(pyrazolyl)borates (= TpMe2,4R) and bidentate bis(imidazolyl)borates (= [B(ImN-Me)2MeX]- LX) yields square-pyramidal cobalt(II) complexes. The structural properties of the substituent groups X attached to the boron center of LX affect the arrangement of X in the resulting cobalt(II) complexes [CoII(TpMe2,4R)(LX)]. When the boron-attached moiety of X is a relatively bulky sp3-CH2Y group (i.e., X:Y = Me:H and nBu:nPr), the alkyl group X faces the cobalt center, whereas for isopropoxy (OiPr) and phenyl (Ph) groups, of which the boron-attached atoms are a less hindered oxygen atom and a planer sp2-carbon, respectively, the X group is arranged away from the cobalt center. This flexible behavior of LX is reflected in the O2 affinity of the cobalt(II) center, which depends on the extent to which the complex sphere is shielded by the ligands. The dependence of the cobalt(II) oxidation potential on the X substituent of LX is inconsistent with the O2 affinity. On the other hand, the electronic properties of R, which is attached to the fourth position of the pyrazolyl rings in the rigid TpMe2,4R ligand, are reflected in the electrochemical properties and O2 affinity of the cobalt center.
- Nishiura, Toshiki,Chiba, Yosuke,Nakazawa, Jun,Hikichi, Shiro
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- Decomposition of Nitrous Oxide on Palladium Crystal Planes
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The catalysed decomposition of N2O in the range 830 - 1000 K and 0.05 - 1.0 Torr (1 Torr ca. 133 Pa) has been examined on Pd single-crystal surfaces and polycrystalline wires and compared with earlier work.The relative reaction velocities at 1000 deg K an
- Eley, Daniel D.,Klepping, Anthony H.,Moore, Peter B.
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- Oxidatively induced reductive elimination of dioxygen from an η2-peroxopalladium(II) complex promoted by electron-deficient alkenes
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The first example of associative displacement of dioxygen from a peroxopalladium(II) complex is reported. Electron-deficient alkenes, p-X-trans-β-nitrostyrene (X = OCH3, CH3, H, F, Br, CF3, NO2), react quantitatively with (bc)Pd(η2-O2) (bc = bathocuproine) in dichloromethane at room temperature to form the corresponding palladium(0)-alkene complexes. Mechanistic studies indicate that ligand substitution proceeds through an associative mechanism, and the electronic characteristics of the reactions are consistent with an oxidatively induced reductive elimination pathway. Copyright
- Popp, Brian V.,Stahl, Shannon S.
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- Reversible O2 binding to a dinuclear copper(I) complex with linked tris(2-pyridylmethyl)amine units: Kinetic-thermodynamic comparisons with mononuclear analogues
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The kinetics and thermodynamics of reaction of O2 with copper(I) complexes can provide fundamental information relevant to chemical and biological systems. Using diode-array variable-temperature (180-296 K) stopped-flow kinetic methods, we report detailed information on the O2 reactivity (in EtCN) of dicopper(I) complex [(D1)Cu(I)2(RCN)2]2+ (2a) (R = Me or Et) [D1 = dinucleating ligand with a -CH2CH2- group linking two tris(2-pyridylmethyl)amine (TMPA) units at a 5-pyridyl position of each tetradentate moiety]. A comparative study of mononuclear complex [(TMPAE)Cu(RCN)]+ (1a') [TMPAE has a -C(O)OCH3 ester substituent in the 5-position of one pyridyl group of TMPA] has been carried out. The results are compared with data from the previously investigated complex [(TMPA)Cu(RCN)]+ (1a). The syntheses of D1 and 2a-(ClO4)2 are described; an X-ray structure reveals two pentacoordinate Cu(I) ions (Cu···Cu = 11.70 A?), each bound by the N4-tetradentate and an EtCN molecule. Cyclic voltammetric data for 1a' and 2a are reported. At 193 K in EtCN, 2a reacts with O2 (Cd/C2 = 2:1, manometry) to produce an intensely purple colored solution of adduct [(D1)Cu2(O2)]2+ (2c), λ(max) = 540 nm (ε = 11 100 M-1 cm-1). This peroxo-dicopper(II) species reacts with PPh3, liberating O2 and producing the isolatable bis-phosphine adduct [(D1)Cu2(PPh3)2]2+. The kinetic investigation provides spectral characterization of transient Cu/O2 1:1 adducts generated upon oxygenation of cold solutions of 1a' or 2a. [(TMPAE)Cu(O2)]+ (1b') forms reversibly (λ(max) = 415 nm) with k1 = (8.2 ± 0.4) x 103 M-1 s-1 and K1 = k1/k-1 = (284 ± 9) M-1 at 183 K, with ΔH1° = (-32 ± 1) kJ mol-1, ΔS1° = (-127 ± 3) J K-1 mol-1. Two types of Cu(II)-O2- complexes form in the reaction of 2a: a 2:1 open form (i.e., [(D1)Cu2(O2)(EtCN)]2+, 2b) and a bis-O2 2:2 open adduct (i.e., [(D1)Cu2(O2)2]2+, 2b'). For the formation of 2b, k1 = (1.63 ± 0.01) x 104 M-1 s-1 and K1 = (2.03 ± 0.04) x 103 M-1 at 183 K. Complexes 2b and 2b' have identical spectroscopic properties (λ(max) = 416 nm, ? = 4500 M-1 cm-1) per Cu-O2 unit, and their rate constants are statistically related. Intermediates 1b' and 2b further convert into (μ-peroxo)dicopper(II) [(2 Cu):(1O2)] complexes. [{(TMPAE)Cu}2(O2)]2+ (1c') (λ(max) = 532 nm, ? = 9380 M-1 cm-1) forms in a second-order reaction of 1b' with 1a' with K1K2 = (2.1 ± 0.4) x 1011 M-2 at 183 K (ΔH12° = -77 ± 1 kJ mol-1 and AS12° = -203 ± 5 J K-1 mol-1), while [(D1)Cu2(O2)]2+ (2c) (λ(max) = 540 nm, ? = 11 100 M-1 cm-1) is generated from 2b in an intramolecular reaction,with k2 = (3.51 ± 0.05) x 101 s-1 and k(on) = k1k2/k-1 = (7.1 ± 0.2) x 104 M-1 s-1 (183 K). The overall formation of 2c is faster than for 1c' or [{(TMPA)Cu}2(O2)]2+ (1c) because of a more positive entropy of activation (ΔS(on)paragraph = (-139 ± 3) J K-1 mol-1 for 2c vs ΔS(on)paragraph = (-201 ± 5) J K-1 mol-1 for 1c). However, this significantly enhanced kinetic reactivity (for 2a → 2c) is not reflected by an analogous increase in thermodynamic stability. [(D1)Cu2(O2)]2+ (2c) is enthalpically less stable (ΔH12° = (-34.8 ± 0.4) kJ -1) than Cu2O2 species 1c and 1c' (ΔH12° = -81 to -77 kJ mol-1, respectively), which are formed from mononuclear precursors. There is a substantially larger overall formation entropy for 2c [ΔS12° = (-89.3 ± 1.5) J K-1 mol-1 compared to -220 and -203 J K-1 mol-1 for 1c and 1c', respectively] since Cu2O2 formation is an intramolecular, rather than intermolecular, process. Examination of other kinetic parameters and spectral differences provides complementary information that 2c has a strained structure. In fact, 2c is not the ultimate oxidation product: relief of steric constraints occurs at higher temperatures by a slow rearrangement (λ(max) = 540 nm → λ(max) = 529 nm) producing {Cu2O2}(n) oligomers containing intermolecular Cu-O2-Cu bonds. A particularly stable trimer species [{(D1)Cu2(O2)}3]6+ (2d) was characterized, with ΔH3° = (-153 kJ mol-1)/3 = -51 kJ mol-1 per Cu2O2 unit, intermediate between that seen for 2c, 1c, and 1c'.
- Lee, Dong-Heon,Wei, Ning,Murthy, Narasimha N.,Tyeklár, Zoltán,Karlin, Kenneth D.,Kaderli, Susan,Jung, Bernhard,Zuberbühler, Andreas D.
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- N2O decomposition over Fe-zeolites: Structure of the active sites and the origin of the distinct reactivity of Fe-ferrierite, Fe-ZSM-5, and Fe-beta. A combined periodic DFT and multispectral study
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The N2O decomposition over Fe-ferrierite, Fe-beta, and Fe-ZSM-5 has been recently studied [K. Jisa, J. Novakova, M. Schwarze, A. Vondrova, S. Sklenak, Z. Sobalik, J. Catal. 262 (2009) 27] and a superior activity of Fe-ferrierite with respect to Fe-beta and Fe-ZSM-5 has been shown. In this study, we investigated (1) plausible active sites for the N2O decomposition over Fe-ferrierite and (2) the origin of the distinct reactivity of Fe-ferrierite, Fe-ZSM-5 and Fe-beta employing a combined theoretical (periodic DFT) and experimental (UV-vis-NIR spectroscopy, IR spectroscopy, 29Si MAS NMR spectroscopy and catalytic batch experiments) approach. We evidenced that two Fe(II) cations accommodated in two adjacent six-membered rings in the eight-membered ring channel (β sites) of Fe-ferrierite (the calculated Fe-Fe distance is 7.4 ) form the active site responsible for the superior activity of this catalyst in the N2O decomposition in the absence of NO. Similar structures can be formed in Fe-beta. However, the probability of their formation is very low. For Fe-ZSM-5, the geometrical arrangement of the cationic positions is far from that in Fe-ferrierite and it is not suitable for the N2O decomposition. Therefore, the predicted order of the activity of the Fe(II) exchanged zeolites agrees with our experimental findings and it is: Fe-ferrierite ? Fe-beta > Fe-ZSM-5. We further showed that the accommodation of divalent cations in rings forming cationic sites can lead to significant rearrangements of the local structures of the zeolite framework, and therefore, the precise structure of sites binding a divalent cation cannot be derived from results of X-ray diffraction experiments, but can be inferred from theoretical calculations.
- Sklenak, Stepan,Andrikopoulos, Prokopis C.,Boekfa, Bundet,Jansang, Bavornpon,Novakova, Jana,Benco, Lubomir,Bucko, Tomas,Hafner, Juergen,Ddeek, Jii,Sobalik, Zdenk
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- Adsorbed Oxygen Species Formed by the Decomposition of N2O on Li/MgO Catalysts
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A considerable amount of adsorbed oxygen species were produced by the decomposition of N2O on Li/MgO.The amount of the oxygen species greatly increases by Li(I)-doping on MgO.Over 0.7 wtpercent Li/MgO, the amount of the oxygen species formed was 10.67 μmol m-2.The temperature-programmed desorption of the oxygen species revealed that two types of adsorbed oxygen species were present on Li/MgO; one (α-oxygen species) desorbed in proportion to the second order in the amount of the adsorbed species with an activation energy of 141 kJ mol-1, giving a peak (α-oxygen peak) at 673-693 K; the other (β-oxygen species) desorbed in proportion to the first order in the amount of the adsorbed species with an activation energy of 219 kJ mol-1, giving a peak (β-oxygen peak) at 753-768 K.A weak α-oxygen peak occurred on MgO and no β-oxygen peak was discerned.On Li/MgO, a β-oxygen peak appeared along with an α-oxygen peak.At higher Li-loadings the β-oxygen peak was more intense than the α-oxygen peak.The sites for these oxygen species were suggested to be derived by the addition of Li(I) on MgO.It was suggested that the α-oxygen species were present at the surface sites on higher index faces of MgO, whereas the β-oxygen species were present at oxygen vacancies in the vicinity of Li(I) substituting for Mg(II).The hydrolysis of these adsorbed oxygen species yielded an appreciable amount of H2O2, suggesting that these species were primarilly present as surface peroxide on MgO and Li/MgO.
- Nakamura, Masato,Yanagibashi, Hiroshi,Mitsuhashi, Hiroyuki,Takezawa, Nobutsune
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- A comparative XAS and X-ray diffraction study of new binuclear Mn(III) complexes with catalase activity. Indirect effect of the counteranion on magnetic properties
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Four new binuclear Mn(III) complexes with carboxylate bridges have been synthesized: [{Mn(nn)(H2O)}2(μ-ClCH2-COO) 2(μ-O)](ClO4)2 with nn = bpy (1) or phen (2) and [{Mn(bpy)(H2O)}2(μ-RCOO)2(μ-O)] (NO3)2 with RCOO = ClCH2COO (3) or CH 3COO (4). The characterization by X-ray diffraction (1 and 3) and X-ray absorption spectroscopy (XAS) (1-4) displays the relevance of this spectroscopy to the elucidation of the structural environment of the manganese ions in this kind of compound. Magnetic susceptibility data show an antiferromagnetic coupling for all the compounds: J = -2.89 cm-1 (for 1), -8.16 cm-1 (for 2), -0.68 cm-1 (for 3), and -2.34 cm-1 (for 4). Compounds 1 and 3 have the same cation complex [{Mn(bpy)(H2O)}2(μ-ClCH2COO) 2(μ-O)]2+, but, while 1 shows an antiferromagnetic coupling, for 3 the magnetic interaction between Mn(III) ions is very weak. The four compounds show catalase activity, and when the reaction stopped, Mn(II) compounds with different nuclearity could be obtained: binuclear [{Mn(phen) 2}(μ-ClCH2COO)2](ClO4) 2, trinuclear [Mn3(bpy)2(μ-ClCH 2COO)6], or mononuclear complexes without carboxylate. Two Mn(II) compounds without carboxylate have been characterized by X-ray diffraction: [Mn(NO3)2(bpy)2][Mn(NO 3)(bpy)2(H2O)]NO3 (5) and [Mn(bpy)3](ClO4)2·0.5 C 6H4-1,2-(COOEt)2·O.5H2O (8).
- Fernandez, Gema,Corbella, Montserrat,Alfonso, Montserrat,Stoeckli-Evans, Helen,Castro, Isabel
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- Kinetics of N2O Decomposition on the Surface of γ-Al2O3 doped with Sodium Ions
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The kinetics of N2O decomposition on a series of specimens prepared by doping γ-Al2O3 with various amounts of Na+ ions has been studied at various temperatures using a flow-bed reactor working under atmospheric pressure.This doping promotes the adsorption of oxygen anions produced from surface decomposition, presumably via the formation of surface species +...O-...Na+>, bringing about a transformation of the rate equation from R=k into R=kbN2OPN2O/bO2P1/2O2 (where bN2O and bO2 are adsorption coefficients and PN2O and PO2 are partial pressures).Moreover, a decrease in catalytic activity, expressed either as fractional conversion or rate of reaction, was observed on increasing the surface coverage C, of γ-Al2O3 with Na+ ions determined by X-ray photoelectron spectroscopy.Specifically, the dependence of the catalytic activity on the surface coverage of γ-Al2O3 is described by the relationship 1n(1/R) = 15.4+(281/K)C (where K is a proportionality constant) and it was concluded that the deactivation observed is due to the promotion of the O2 adsorption caused by the Na+ ions.Finally, the linear dependence of the surface coverage of γ-Al2O3 on the sodium content strongly suggests that the dispersion of the sodium supported species is constant irrespective of the surface concentration of sodium.
- Kordulis, Christos,Vordonis, Leonidas,Lycourghiotis, Alexis,Pomonis, Phillipos
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- Formation of the surface NO during N2O interaction at low temperature with iron-containing ZSM-5
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Interaction of N2O at low temperatures (473-603 K) with Fe - ZSM-5 zeolites (Fe, 0.01-2.1 wt %) activated by steaming and/or thermal treatment in He at 1323 K was studied by the transient response method and temperature-programmed desorption (TPD). Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) of NO adsorbed at room temperature as a probe molecule indicated heterogeneity of surface Fe(II) sites. The most intensive bands were found at 1878 and 1891 cm-1, characteristic of two types mononitrosyl species assigned to Fe2+(NO) involved in bi- and oligonuclear species. Fast loading of atomic oxygen from N2O on the surface and slower formation of adsorbed NO species were observed. The initial rate of adsorbed NO formation was linearly dependent on the concentration of active Fe sites assigned to bi- and oligonuclear species, evolving oxygen in the TPD at around 630-670 K. The maximal coverage of a zeolite surface by NO was estimated from the TPD of .NO at ~700 K. This allowed the simulation of the dynamics of the adsorbed NO formation at 523 K, which was consistent with the experiments. The adsorbed NO facilitated the atomic oxygen recombination/desorption, the rate determining step during N2O decomposition to O2 and N2, taking place at temperatures ≥563 K.
- Bulushev, Dmitri A.,Renken, Albert,Kiwi-Minsker, Lioubov
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- The RuII(OH2)-RuIV(O) Couple in a Ruthenium Complex of 2-(Phenylazo)pyridine: Homogeneous Catalysis of the Oxidation of Water to Dioxygen
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In acidic solution II(OH2)(py)L2>2+ can be oxidised to IV(O)(py)L2>2+ in a single reversible step (E0298 = 1.20 V) and the oxidised complex catalyses the dehydrogenation of water to dioxygen in the presence of Ce4+ .
- Goswami, Sreebrata,Chakravarty, Akhil R.,Chakravorty, Animesh
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- Photodecaging of a Mitochondria-Localized Iridium(III) Endoperoxide Complex for Two-Photon Photoactivated Therapy under Hypoxia
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Despite the clinical success of photodynamic therapy (PDT), the application of this medical technique is intrinsically limited by the low oxygen concentrations found in cancer tumors, hampering the production of therapeutically necessary singlet oxygen (1O2). To overcome this limitation, we report on a novel mitochondria-localized iridium(III) endoperoxide prodrug (2-O-IrAn), which, upon two-photon irradiation in NIR, synergistically releases a highly cytotoxic iridium(III) complex (2-IrAn), singlet oxygen, and an alkoxy radical. 2-O-IrAn was found to be highly (photo-)toxic in hypoxic tumor cells and multicellular tumor spheroids (MCTS) in the nanomolar range. To provide cancer selectivity and improve the pharmacological properties of 2-O-IrAn, it was encapsulated into a biotin-functionalized polymer. The generated nanoparticles were found to nearly fully eradicate the tumor inside a mouse model within a single treatment. This study presents, to the best of our knowledge, the first example of an iridium(III)-based endoperoxide prodrug for synergistic photodynamic therapy/photoactivated chemotherapy, opening up new avenues for the treatment of hypoxic tumors.
- Chao, Hui,Gasser, Gilles,Ji, Liangnian,Karges, Johannes,Ke, Libing,Kuang, Shi,Liao, Xinxing,Wei, Fangmian,Xiong, Kai
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supporting information
p. 4091 - 4101
(2022/03/03)
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- Electrocatalytic Water Oxidation with α-[Fe(mcp)(OTf)2] and Analogues
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The complex α-[Fe(mcp)(OTf)2] (mcp = N,N′-dimethyl-N,N′-bis(pyridin-2-ylmethyl)-cyclohexane-1,2-diamine and OTf = trifluoromethanesulfonate anion) was reported in 2011 by some of us as an active water oxidation (WO) catalyst in the presence of sacrificial oxidants. However, because chemical oxidants are likely to take part in the reaction mechanism, mechanistic electrochemical studies are critical in establishing to what extent previous studies with sacrificial reagents have actually been meaningful. In this study, the complex α-[Fe(mcp)(OTf)2] and its analogues were investigated electrochemically under both acidic and neutral conditions. All the systems under investigation proved to be electrochemically active toward the WO reaction, with no major differences in activity despite the structural changes. Our findings show that WO-catalyzed by mcp-iron complexes proceeds via homogeneous species, whereas the analogous manganese complex forms a heterogeneous deposit on the electrode surface. Mechanistic studies show that the reaction proceeds with a different rate-determining step (rds) than what was previously proposed in the presence of chemical oxidants. Moreover, the different kinetic isotope effect (KIE) values obtained electrochemically at pH 7 (KIE ~10) and at pH 1 (KIE = 1) show that the reaction conditions have a remarkable effect on the rds and on the mechanism. We suggest a proton-coupled electron transfer (PCET) as the rds under neutral conditions, whereas at pH 1 the rds is most likely an electron transfer (ET).
- D'Agostini, Silvia,Kottrup, Konstantin G.,Casadevall, Carla,Gamba, Ilaria,Dantignana, Valeria,Bucci, Alberto,Costas, Miquel,Lloret-Fillol, Julio,Hetterscheid, Dennis G.H.
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p. 2583 - 2595
(2021/03/03)
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- Pt-core silica shell nanostructure: a robust catalyst for the highly corrosive sulfuric acid decomposition reaction in sulfur iodine cycle to produce hydrogen
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The platinum core silica shell catalyst has facilitated stable sulfuric acid decomposition at higherature which was not possible over bare Pt nanoparticles due to sintering and agglomeration. Helium (He) gas supplies the heat (550-900 °C) in a high temperature gas cooled reactor (VHTR). The major challenge is designing a stable catalyst for the variable heat efficiency of He. Pt catalysts loaded on different supports, such as SiC, Al2O3, SiC-Al2O3, BaSO4, TiO2, SBA-15, and SiO2, have been extensively studied but they have not provided a simple method to form robust catalysts for sulfuric acid decomposition. The core-shell scheme, whereby nanoparticles are enclosed by protecting agents (CTAB) and are covered by a silica shell, delivered mesopores and exhibited higher activity and stability over testing for more than 100 h. TEM images confirmed that the Pt particles on the Pt@mSiO2 catalyst are more stable during sulfuric acid decomposition, and no significant evidence of agglomeration or sintering of the Pt core particles was found, despite some broken shells and dislocated Pt nanoparticles from the silica core. ICP-OES analysis of the spent catalysts after 100 h showed minimal Pt loss (9.0%). These types of catalysts are highly desirable for practical applications. This journal is
- Khan, Hassnain Abbas,Jung, Kwang-Deog,Ahamad, Tansir,Ubaidullah, Mohd,Imran, Muhammad,Alshehri, Saad M.
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p. 1247 - 1252
(2021/02/03)
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- Syntheses, characterizationsna and water-electrolysis properties of 2D α- and β-PdSeO3 bulk and nanosheet semiconductors
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In contrast to alkaline water electrolysis, water electrolysis in an acidic environment has higher energy efficiency, more compact cell design, higher gas purity, and less sensitivity to environmental impurity. Herein, the syntheses of the known 2D α- and β-PdSeO3 were improved. The bulk materials were exfoliated into nanosheets using an ultrasonic-assisted liquid-phase exfoliation similar to that of preparing graphene nanosheets. Their band-gaps, valence band maximums (VBMs) and conduction band minimums (CBMs) were determined using Mott-Schottky plots and the linear potential scan method in acidic aqueous solution, 0.2 ?M Na2SO4 aqueous solution and non-aqueous solution. Their transient photocurrent properties were also examined, along with their Electrochemical Impedance Spectra (EIS). The bulk materials are stable in pH ?= ?0–14 value water solution for at least 48 ?h. α- and β-PdSeO3 nanosheets exhibit moderate catalytic activities for hydrogen evolution reactions in 0.5 ?M ?H2SO4 (η10 (overpotential at 10 ?mA ?cm-2: 185 and 209 ?mV, respectively; catalyst loading: 0.28 ?mg ?cm-2), much better than the performances of the bulk materials. In addition, β-PdSeO3 bulk and nanosheets materials show good and similar OER catalytic activities in 0.5 ?M ?H2SO4 (η10: 381 and 405 ?mV, respectively; catalyst loading: 0.28 ?mg ?cm-2). Thus, β-PdSeO3 nanosheets were found to be a good overall water splitting catalyst in acidic solution. The above catalysts all show long-term stability. In contrast, α-PdSeO3 does not have OER catalytic property. To our knowledge, Pd-based acidic overall water splitting catalysts are very rare.
- Wu, Yusheng,Wang, Lin,Zhang, Hongyan,Ding, Jie,Han, Min,Fang, Min,Bao, Jianchun,Wu, Yong
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- Dual Ag/Co cocatalyst synergism for the highly effective photocatalytic conversion of CO2by H2O over Al-SrTiO3
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Loading Ag and Co dual cocatalysts on Al-doped SrTiO3(AgCo/Al-SrTiO3) led to a significantly improved CO-formation rate and extremely high selectivity toward CO evolution (99.8%) using H2O as an electron donor when irradiated with light at wavelengths above 300 nm. Furthermore, the CO-formation rate over AgCo/Al-SrTiO3(52.7 μmol h?1) was a dozen times higher than that over Ag/Al-SrTiO3(4.7 μmol h?1). The apparent quantum efficiency for CO evolution over AgCo/Al-SrTiO3was about 0.03% when photoirradiated at a wavelength at 365 nm, with a CO-evolution selectivity of 98.6% (7.4 μmol h?1). The Ag and Co cocatalysts were found to function as reduction and oxidation sites for promoting the generation of CO and O2, respectively, on the Al-SrTiO3surface.
- Wang, Shuying,Teramura, Kentaro,Hisatomi, Takashi,Domen, Kazunari,Asakura, Hiroyuki,Hosokawa, Saburo,Tanaka, Tsunehiro
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p. 4940 - 4948
(2021/04/14)
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- Effects of SiO2-based scaffolds in TiO2 photocatalyzed CO2 reduction
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CO2 photoreduction has claimed as appealing process to upgrade a waste gas into valuable fuels or chemicals. Titanium dioxide (TiO2) is one of the most popular material used as catalyst for this reaction, having however a poor activity. The utilization of transparent, insulating and highly porous scaffolds to support a photoactive phase has been reported as one of the possible strategies to improve the performances of this material. In this work, two silica-based materials with different porosity type and level, were involved as support for the TiO2 and assessed in the gas-phase CO2 photoreduction with H2O. The morphological, structural and surface properties were then evaluated by means of different characterization techniques, aiming to correlate them with the catalytic activity and selectivity. The TiO2-SiO2 composites revealed a comparable activity compared to pure TiO2, despite the low fraction of photoactive phase due to improved light harvesting and reagents adsorption on the composites. The CO2 capture/photoconverting ability was evaluated, to explore the potentiality as multifunctional material.
- Cruciani, Giuseppe,Di Michele, Alessandro,Forghieri, Giulia,Ghedini, Elena,Menegazzo, Federica,Signoretto, Michela,Tieuli, Sebastiano,Zanardo, Danny
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- The tin sulfates Sn(SO4)2and Sn2(SO4)3: Crystal structures, optical and thermal properties
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We report the crystal structures of two tin(iv) sulfate polymorphs Sn(SO4)2-I (P21/c (no. 14), a = 504.34(3), b = 1065.43(6), c = 1065.47(6) pm, β = 91.991(2)°, 4617 independent reflections, 104 refined parameters, wR2 = 0.096) and Sn(SO4)2-II (P21/n (no. 14), a = 753.90(3), b = 802.39(3), c = 914.47(3) pm, β = 92.496(2)°, 3970 independent reflections, 101 refined parameters, wR2 = 0.033). Moreover, the first heterovalent tin sulfate Sn2(SO4)3 is reported which adopts space group P1 (no. 2) (a = 483.78(9), b = 809.9(2), c = 1210.7(2) pm, α = 89.007(7)°, β = 86.381(7)°, γ = 73.344(7)°, 1602 independent reflections, 152 refined parameters, wR2 = 0.059). Finally, SnSO4-the only tin sulfate with known crystal structure-was revised and information complemented. The optical and thermal properties of all tin sulfates are investigated by FTIR, UV-vis, luminescence and 119Sn M?ssbauer spectroscopy as well as thermogravimetry and compared.
- Daub, Michael,H?mmer, Matthias,H?ppe, Henning A.,Hillebrecht, Harald,Klenner, Steffen,Netzsch, Philip,Neuschulz, Kai,P?ttgen, Rainer,Struckmann, Mona,Wickleder, Mathias S.
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p. 12913 - 12922
(2021/10/12)
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- Photocatalytic activity of metal oxide supported gallium oxide for CO2 reduction with water
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The photocatalytic activities of Ga2O3 supported by various metal oxides for H2O splitting and CO2 reduction with water under UV light irradiation were investigated. The Ga2O3 photocatalyst supported by metal oxides was prepared via an impregnation method. Some oxides used as a supporting oxide of Ga2O3 photocatalyst enhanced activities of H2O splitting and CO2 reduction. Specifically, the CO production rates were well correlated to various properties of the supporting oxide. These oxides satisfied the three criteria greatly improving the CO production rate. First, their band gap was wider than that of Ga2O3 and the position of its conduction band was at a negative potential with respect to that of Ga2O3. Second, they were not miscible with Ga2O3 and third, mixed phases of α and γ or defective γ phase of Ga2O3 were well dispersed on them exhibiting columnar shape.
- Akatsuka, Masato,Ito, Ryota,Ozawa, Akiyo,Tanabe, Tetsuo,Yamamoto, Muneaki,Yoshida, Tomoko
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supporting information
p. 694 - 700
(2020/09/15)
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- Pressure-induced dehydrogenative coupling of methane to ethane by platinum-loaded gallium oxide photocatalyst
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Pt/Ga2O3exhibited high activity for dehydrogenative coupling of methane into ethane (2CH4→ C2H6+ H2) in a fixed-bed flow reactor at 25 °C under 254 nm UV irradiation. The C2H6formation was negligible at CH4pressure of 10 kPa, but it was linearly increased with an increase in the pressure to 300 kPa.
- Akamoto, Chiho,Amano, Fumiaki,Inagaki, Satoshi,Ishimaru, Mizuki,Yoshida, Hisao
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supporting information
p. 6348 - 6351
(2020/06/21)
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- Three-dimensional nickel foam templated MgCo2O4 nanowires as an efficient catalyst for the thermal decomposition of ammonium perchlorate
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Spinel–type oxides MgCo2O4 and Co3O4 nanowires (NWs) were successfully prepared using nickel foam (NF) as a template. The catalytic performance of MgCo2O4 NWs on the thermal decomposition of ammonium perchlorate (AP) was investigated by differential scanning calorimetry (DSC) and simultaneous thermogravimetry–mass spectrometry (TG/MS) techniques. In the presence of MgCo2O4 NWs, the process of the high temperature decomposition (HTD) and the low temperature decomposition (LTD) of AP was combined to one with a peak temperature of 277.35 ?°C. Meanwhile, the apparent activation energy decreased from 139.05 to 123.61 ?kJ·mol?1 on the basis of thermal analysis kinetics. This was attributed to the synergistic effect between the metals of this ternary metal oxide and the larger specific surface area of MgCo2O4 NWs. Therefore, MgCo2O4 with nanowires morphology holds a promise to catalyze energetic components.
- Guo, Zhaoqi,Li, Cuicui,Li, Jiachen,Li, Yaoyao,Ma, Haixia,Zhang, Ting
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- Decomposition of ammonium perchlorate: Exploring catalytic activity of nanocomposites based on nano Cu/Cu2O dispersed on graphitic carbon nitride
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Copper (Cu) and its oxides are well-known catalysts for thermal decomposition of ammonium perchlorate (AP). Nano Cu/Cu2O dispersed on graphitic carbon nitride (g-C3N4) based nanocomposites were synthesised by single displa
- Chandrababu, Parvathy,Raghavan, Rajeev,Sukumaran Nair, Vishnu,Thankarajan, Jayalatha
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- Crystal and Electronic Structures of A2NaIO6Periodate Double Perovskites (A = Sr, Ca, Ba): Candidate Wasteforms for I-129 Immobilization
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The synthesis, structure, and thermal stability of the periodate double perovskites A2NaIO6 (A= Ba, Sr, Ca) were investigated in the context of potential application for the immobilization of radioiodine. A combination of X-ray diffraction and neutron diffraction, Raman spectroscopy, and DFT simulations were applied to determine accurate crystal structures of these compounds and understand their relative stability. The compounds were found to exhibit rock-salt ordering of Na and I on the perovskite B-site; Ba2NaIO6 was found to adopt the Fm-3m aristotype structure, whereas Sr2NaIO6 and Ca2NaIO6 adopt the P21/n hettotype structure, characterized by cooperative octahedral tilting. DFT simulations determined the Fm-3m and P21/n structures of Ba2NaIO6 to be energetically degenerate at room temperature, whereas diffraction and spectroscopy data evidence only the presence of the Fm-3m phase at room temperature, which may imply an incipient phase transition for this compound. The periodate double perovskites were found to exhibit remarkable thermal stability, with Ba2NaIO6 only decomposing above 1050 °C in air, which is apparently the highest recorded decomposition temperature so far recorded for any iodine bearing compound. As such, these compounds offer some potential for application in the immobilization of iodine-129, from nuclear fuel reprocessing, with an iodine incorporation rate of 25-40 wt%. The synthesis of these compounds, elaborated here, is also compatible with both current conventional and future advanced processes for iodine recovery from the dissolver off-gas.
- Dixon Wilkins, Malin C.,George, Jonathan,Hyatt, Neil C.,Kim, Eunja,Kirk, Cameron,Knight, Kevin S.,Montoya, Eduardo,O'Sullivan, Sarah E.,Sun, Shi-Kuan,Weck, Philippe F.
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p. 18407 - 18419
(2020/12/23)
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- A molten calcium carbonate mediator for the electrochemical conversion and absorption of carbon dioxide
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High-temperature molten salts are an excellent electrolyte to bring about redox reactions at a rapid rate without using rationally designed nano-structured catalysts. However, the large-scale electrolyzer is constrained by the use of expensive and resource-deficient lithium salts. Using Earth-abundant CaCO3 releases the pressure of using strategic lithium resources, but the low solubility of CaO in molten carbonates disables the capability of capturing CO2. In addition, the separation of carbon from water-insoluble CaO and CaCO3 consumes a large amount of acids. To tackle these challenges, we report a CaCO3-containing molten carbonate electrolyzer to prevent the use of lithium salts, and a molten CaCl2 dissolver to separate carbon from CaO that is soluble in molten CaCl2 and can capture CO2 by carbonization. More importantly, we develop a salt-soluble-to-water-insoluble approach for producing ultrafine CaCO3 using molten salt as a soft template. Overall, this study opens a pathway to use cheap and Earth-abundant molten CaCO3 as a mediator to convert CO2 to oxygen at a cost-effective inert anode, with value-added carbon at the cathode, and ultrafine CaCO3 through a salt-to-solution process.
- Chen, Xiang,Qu, Jiakang,Tang, Diyong,Wang, Dihua,Xie, Hongwei,Yin, Huayi,Zhao, Haijia,Zhao, Zhuqing
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p. 7946 - 7954
(2020/12/01)
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- Low overpotential water oxidation at neutral pH catalyzed by a copper(ii) porphyrin
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Low overpotential water oxidation under mild conditions is required for new energy conversion technologies with potential application prospects. Extensive studies on molecular catalysis have been performed to gain fundamental knowledge for the rational designing of cheap, efficient and robust catalysts. We herein report a water-soluble CuII complex of tetrakis(4-N-methylpyridyl)porphyrin (1), which catalyzes the oxygen evolution reaction (OER) in neutral aqueous solutions with small overpotentials: the onset potential of the catalytic water oxidation wave measured at current density j = 0.10 mA cm?2 is 1.13 V versus a normal hydrogen electrode (NHE), which corresponds to an onset overpotential of 310 mV. Constant potential electrolysis of 1 at neutral pH and at 1.30 V versus NHE displayed a substantial and stable current for O2 evolution with a faradaic efficiency of >93%. More importantly, in addition to the 4e water oxidation to O2 at neutral pH, 1 can catalyze the 2e water oxidation to H2O2 in acidic solutions. The produced H2O2 is detected by rotating ring-disk electrode measurements and by the sodium iodide method after bulk electrolysis at pH 3.0. This work presents an efficient and robust Cu-based catalyst for water oxidation in both neutral and acidic solutions. The observation of H2O2 during water oxidation catalysis is rare and will provide new insights into the water oxidation mechanism.
- Liu, Yanju,Han, Yongzhen,Zhang, Zongyao,Zhang, Wei,Lai, Wenzhen,Wang, Yong,Cao, Rui
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p. 2613 - 2622
(2019/03/05)
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- Assembly of Ultra-Thin NiO Layer Over Zn1?xCdxS for Stable Visible-Light Photocatalytic Overall Water Splitting
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Photocatalytic splitting of water into hydrogen and oxygen by using visible light is considered to be a clean, green, and renewable route for solar energy conversion and storage. Although the Zn1?xCdxS catalysts show comparatively higher activity for photocatalytic hydrogen generation under visible-light irradiation, they suffer from serious photocorrosion during the photocatalytic reaction. The deposition of a protective layer over the Zn1?xCdxS catalysts is believed to be an effective way to inhibit photocorrosion. However, only a few materials exhibit satisfactory catalytic properties for hydrogen evolution as well as a good protection ability. In this work, a new Zn1?xCdxS photocatalyst was developed for water splitting under visible-light illumination by assembling an ultrathin NiO layer over Zn0.8Cd0.2S through an in situ photodeposition method. The as-prepared NiO/Zn0.8Cd0.2S showed significantly higher activity for overall water splitting compared with Pt/Zn0.8Cd0.2S under the same conditions without photocorrosion. An apparent quantum efficiency of 0.66 % was achieved for hydrogen evolution at 430 nm with an accomplished multicycle stability for up to 12 h without any significant decay. The strong electronic coupling between the NiO layer and Zn1?xCdxS also promoted efficient charge separation and migration.
- Ning, Xiaofeng,Zhen, Wenlong,Zhang, Xuqiang,Lu, Gongxuan
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p. 1410 - 1420
(2019/03/21)
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- Solar-driven CO2 to CO reduction utilizing H2O as an electron donor by earth-abundant Mn-bipyridine complex and Ni-modified Fe-oxyhydroxide catalysts activated in a single-compartment reactor
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Photoelectrochemical CO2 to CO reduction was demonstrated with 3.4% solar-to-chemical conversion efficiency using polycrystalline silicon photovoltaic cells connected with earth-abundant catalysts: a manganese complex polymer for CO2 reduction and iron oxyhydroxide modified with a nickel compound for water oxidation. The system operated around neutral pH in a single-compartment reactor.
- Arai, Takeo,Sato, Shunsuke,Sekizawa, Keita,Suzuki, Tomiko M.,Morikawa, Takeshi
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supporting information
p. 237 - 240
(2019/01/04)
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- Role of Lattice Oxygen in the Oxygen Evolution Reaction on Co3O4: Isotope Exchange Determined Using a Small-Volume Differential Electrochemical Mass Spectrometry Cell Design
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This work demonstrates the role of lattice oxygen of metal oxide catalysts in the oxygen evolution reaction (OER) as evidenced by isotope labeling together with the differential electrochemical mass spectrometry (DEMS) method. Our recent report assessed this role for Co3O4 using a flow-through DEMS cell, which requires a large volume of electrolyte. Herein, we extend this procedure to different Co3O4 catalyst loadings and particle sizes as well as the mixed Ag + Co3O4 catalyst. We introduce, for the first time, a novel small-volume DEMS cell design capable of using disc electrodes and only 3O4 catalyst is higher than that on the single Co3O4 catalyst, which illustrates the improved electrocatalytic activity previously reported on this mixed catalyst. Furthermore, the real surface area of the catalysts is estimated using different methods (namely, the ball model, double layer capacitance, isotope exchange, and redox peak methods). The surface areas estimated from the Brunauer-Emmett-Teller (BET) and ball models are comparable but roughly three times higher than that of the redox peak method. Our method represents an alternative approach for probing the mechanism and real surface area of catalysts.
- Amin, Hatem M. A.,K?nigshoven, Peter,Hegemann, Martina,Baltruschat, Helmut
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p. 12653 - 12660
(2019/10/11)
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- Role of water oxidation in the photoreduction of graphene oxide
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By means of a H218O labeling experiment in combination with mass spectrometry tracking, we studied GO photoreduction. Observation of 18O labeled O2 provides direct evidence to confirm that water oxidation occurs during GO photoreduction. In combination with DFT calculations, we propose a mechanism for O2 and CO2 evolution in the photoreduction of GO.
- Li, Hongjiang,Song, Xuedan,Shi, Yantao,Gao, Yan,Si, Duanhui,Hao, Ce
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p. 1837 - 1840
(2019/02/12)
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- Chlorination of Pr2O3 and Pr6O11. Crystal structure, magnetic and spectroscopic properties of praseodymium oxychloride
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The reactions of Pr2O3 and Pr6O11 with Cl2(g) were studied thermodynamically and experimentally, and proposed in the systems Pr2O3/Cl2(g) and Pr6O11/Cl2(g). A kinetic analysis was performed on Pr6O11 chlorination, which differs from with other light rare earth oxide chlorinations. The praseodymium oxychlorides obtained by full chlorination of Pr6O11 at 425 °C and 800 °C are different, being well characterized by X-ray diffraction, scanning electron microscopy, magnetic susceptibility measurements and X-ray photoelectron spectroscopy. The crystal structures of the oxychlorides were refined with the Rietveld method. The comparison between the theoretical magnetic moment of Pr3+ and the estimated magnetic moment in the praseodymium oxychloride obtained at 425 °C revealed the presence of Pr3+ and Pr4+, whereas no significant difference was observed between the theoretical and the experimental values of Pr3+ obtained for the praseodymium oxychloride prepared at 800 °C. These observations are consistent with the analyses in the X-ray photoelectron spectra for both oxychlorides. Finally, a general formula of PrO1+xCl is proposed for the oxychlorides synthesized at T 800 °C.
- Pomiro, Federico J.,Gaviría, Juan P.,Fouga, Gastón G.,Vega, Leonardo D.,Bohé, Ana E.
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p. 919 - 926
(2018/11/06)
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- A study on decomposition of environmentally noxious gas with simultaneous synthesis of metal oxide powder in transferred DC thermal plasma
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Carbon dioxide was directly decomposed by a transferred DC thermal plasma and the effects of plasma induced current on the decomposition efficiency were investigated. The thermal plasma system was operated in a way that the metal oxide particles could be simultaneously produced from an anodic bulk metal (Zn) placed on a carbon crucible, so as to continuously consume atomic and molecular oxygens (O and O2) generated from the CO2 decomposition. As the induced current increased from 120 to 160 A by 20 A, the decomposition efficiency increased almost linearly from 53 to 68 %. The amount of ZnO particles produced from the bulk also increased and the particle crystallinity was improved. Although the concentration of carbon monoxide in the effluent was sharply increased at 160 A, further destruction can be done by re-circulating the effluent to plasma chamber.
- Choi, In-Chang,Kim, Heon Chang
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p. 449 - 452
(2019/01/10)
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- Fabrication of an Fe-Doped SrTiO3 Photocatalyst with Enhanced Dinitrogen Photofixation Performance
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SrTiO3 as semiconducting photocatalyst has been extensively investigated due to its band edges meeting the thermodynamic requirements for water splitting, but a few attention has been concentrated on its application in the NH3 synthesis via N2 photofixation process. Herein, Fe-doped SrTiO3 (FexSr1–xTiO3) products (0 ≤ x ≤ 0.20) were synthesized via a hydrothermal process followed by calcination at 700 °C. All FexSr1–xTiO3 products (0.03 ≤ x ≤ 0.20) deliver an enhanced N2 fixation ability, and FexSr1–xTiO3 (x = 0.10) achieves the best NH3 production activity of 30.1 μmol g–1 h–1, which is 3.2-hold higher than that of SrTiO3 alone. Once the x value is higher than 0.10, FexSr1–xTiO3 will transform into composites containing Fe-doped SrTiO3 and α-Fe2O3, which acts as charge recombination sites, thus causes a decreased N2 fixation activity. Further investigations demonstrate that the surface Fe3+-doped sites can not only chemisorb and activate N2 molecules, but also promote the interfacial electron transfer from Fe-doped SrTiO3 to N2 molecules, and thus significantly improve the N2 fixation ability. The present Fe-doped SrTiO3 products exhibit characteristic features such as stable and efficient N2 fixation ability as well as simultaneous realization of N2 reduction and H2O oxidation without co-catalyst, which are of significance in artificial photosynthesis with H2O as electron and proton sources.
- Ying, Zihao,Chen, Shengtao,Peng, Tianyou,Li, Renjie,Zhang, Jing
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p. 2182 - 2192
(2019/04/13)
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- "off-on" switching of intracellular singlet oxygen release under biocompatible conditions
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Precise spatiotemporal control of singlet oxygen generation is of immense importance considering its involvement in photodynamic therapy. In this work, we present a rational design for an endoperoxide which is highly stable at ambient temperatures yet, can rapidly be converted into a highly labile endoperoxide, thus releasing the "stored" singlet oxygen on demand. The "off-on" chemical switching from the stable to the labile form is accomplished by the reaction with fluoride ions. The potential utility of controlled singlet oxygen release was demonstrated in cell cultures.
- Ucar, Esma,Xi, Dongmei,Seven, Ozlem,Kaya, Cansu,Peng, Xiaojun,Sun, Wen,Akkaya, Engin U.
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supporting information
p. 13808 - 13811
(2019/11/21)
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- Synthesis and characterization of Zn2GeO4/Mg-MOF-74 composites with enhanced photocatalytic activity for CO2 reduction
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Strategies for effectively enhancing the photoreduction of CO2 have been studied for several decades. In this work, Zn2GeO4/Mg-MOF-74 composites were prepared via a hydrothermal method. The X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) images and transmission electron microscopy (TEM) images demonstrate the successful synthesis of Zn2GeO4/Mg-MOF-74 composites. The infrared spectra and TEM images indicate a close interaction between Zn2GeO4 and Mg-MOF-74, which is attributed to tetramethylammonium hydroxide (TMAOH) adsorbed on Zn2GeO4 and interacts with 2,5-dioxide-1,4-benzenedicarboxylate (H4DOBDC) from Mg-MOF-74. The CO2 adsorption isotherms illustrate that the incorporation of Mg-MOF-74 into Zn2GeO4 nanorods improved the adsorption of CO2. Only with water as the sacrificial agent, the hydrothermally prepared Zn2GeO4/Mg-MOF-74 catalyst exhibited a superior performance for the conversion of CO2 into carbon monoxide compared to that of single Zn2GeO4 or a physical mixture of Zn2GeO4/Mg-MOF-74, which is attributed to its higher adsorption capacity for CO2 and reduced recombination of photogenerated electron-hole pairs. In situ photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) further demonstrated that the Zn2GeO4/Mg-MOF-74 catalyst exhibits superior charge-transfer properties. This work may provide a useful strategy to design novel and efficient photocatalysts to reduce the atmospheric concentration of CO2.
- Zhao, Hui,Wang, Xusheng,Feng, Jifei,Chen, Yanning,Yang, Xue,Gao, Shuiying,Cao, Rong
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p. 1288 - 1295
(2018/03/13)
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- Z-Scheme MoS2/g-C3N4 heterojunction for efficient visible light photocatalytic CO2 reduction
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Z-Scheme MoS2/g-C3N4 heterojunction photocatalysts were fabricated using a hydrothermal deposition procedure together with a calcination route, and then applied for CO2 photoreduction. Experimental results indicated that the 10% MoS2/g-C3N4 heterojunction displayed the best photocatalytic performance. Furthermore, the maximum CO yields of 58.59 μmol (g-cat)?1 under 7 h-visible light irradiation was up to 2.94 times that of the unadulterated g-C3N4. The enhanced photocatalytic performance of 10% MoS2/g-C3N4 catalyst was due to the favored visible light response, the efficient separation of photogenerated electron-hole pairs as well as its larger specific surface area.
- Qin, Hao,Guo, Rui-Tang,Liu, Xing-Yu,Pan, Wei-Guo,Wang, Zhong-Yi,Shi, Xu,Tang, Jun-Ying,Huang, Chun-Ying
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supporting information
p. 15155 - 15163
(2018/11/10)
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- Reactions of antimony compounds with fluorine gas by thermogravimetric and differential thermal analyses and X-ray diffraction analysis
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Antimony is one of the key fission products in the reprocessing of spent nuclear fuel by the fluoride volatility method because of the high volatility of antimony fluorides. Since the fluorination reaction of antimony compounds is not well understood, the reaction behavior of antimony compounds with F2 was investigated by thermogravimetric and differential thermal analyses and X-ray diffraction analysis in this study. The target antimony compounds were antimony metal, SbF3, Sb2O3, Sb2O4, and Sb2O5. The fluorination reaction of antimony metal started at 150 °C, and the fluorination product was SbF3. SbF3 volatilized completely by the reaction with F2 above 190 °C; it was considered that volatile SbF5 was formed by the reaction with F2. In the series of fluorination of the antimony oxides, Sb2O3, Sb2O4, and Sb2O5, they started to react with F2 and volatilize at 330 °C as SbF5. During the fluorination of Sb2O3, Sb2O4 was formed temporarily in the course of the reaction. Oxygen released from the fluorination reaction of a part of Sb2O3 would oxidize remained Sb2O3 to Sb2O4. The reaction mechanism for the fluorination of antimony compounds obtained in this study is applicable to evaluate the transfer of antimony in the reprocessing process of the fluoride volatility method.
- Watanabe, Daisuke,Akiyama, Daisuke,Sato, Nobuaki
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- Catalytic Alkyl Hydroperoxide and Acyl Hydroperoxide Disproportionation by a Nonheme Iron Complex
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Alkyl hydroperoxides are commonly used as terminal oxidants because they are generally acknowledged to be stable toward disproportionation compared with H2O2. We show that alkylperoxide disproportionation is effectively catalyzed by the [Fe(tpena)]2+ (tpena = N,N,N′-tris(2-pyridylmethyl)ethylendiamine-N′-acetate). A peroxidase-type mechanism, in other words, involvement of iron(IV)oxo species, is consistent with the rates and product distribution. Accordingly, O2, tert-butanol, and cumyl alcohol are concurrently produced for substrates tert-butyl hydroperoxide and cumene hydroperoxide, respectively, in the presence of [Fe(tpena)]2+ with O2 yields of 88% and 44%, respectively. Rate constants for initial O2 production ([Fe] 0.005 mol %) were measured to 3.66(6) and 0.29(3) mM s-1, respectively. Participating in the mechanism are spectroscopically detectable (UV-vis, EPR, resonance Raman) transient alkyl- and acyl-peroxide adducts, [FeIIIOOR(tpenaH)]2+ [R = C(CH3)3, C(CH3)2Ph, C(O)PhCl; T1/2 = 30 s (5 °C), 20 s (5 °C), 1 s (-30 °C)] with their common decay product [FeIVO(tpenaH)]2+. Concurrently organic radicals proposed to be ROO? were detected by EPR spectroscopy. A lower yield of O2 at 23% with an initial rate of 0.10(3) mM s-1 for the disproportionation of m-chloroperoxybenzoic acid is readily explained by catalyst inhibition by coordination of the product m-chlorobenzoic acid. Oxidative decomposition of the alkyl groups by a unimolecular β-scission pathway, favored for cumene hydroperoxide, competes with ROOH disproportionation. Despite the fact that the catalytic disproportionation is effective, external C-H substrates - when they are present in excess of ROOH - can be targeted and catalytically and selectively oxidized by ROOH using [Fe(tpena)]2+ as the catalyst.
- Wegeberg, Christina,Browne, Wesley R.,McKenzie, Christine J.
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p. 9980 - 9991
(2018/10/15)
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- Oxygen-Oxygen Bond Cleavage and Formation in Co(II)-Mediated Stoichiometric O2 Reduction via the Potential Intermediacy of a Co(IV) Oxyl Radical
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In reactions of significance to alternative energy schemes, metal catalysts are needed to overcome kinetically and thermodynamically difficult processes. Often, high-oxidation-state, high-energy metal oxo intermediates are proposed as mediators in elementary steps involving O-O bond cleavage and formation, but the mechanisms of these steps are difficult to study because of the fleeting nature of these species. Here we utilized a novel dianionic pentadentate ligand system that enabled a detailed mechanistic investigation of the protonation of a cobalt(III)-cobalt(III) peroxo dimer, a known intermediate in oxygen reduction catalysis to hydrogen peroxide. It was shown that double protonation occurs rapidly and leads to a low-energy O-O bond cleavage step that generates a Co(III) aquo complex and a highly reactive Co(IV) oxyl cation. The latter was probed computationally and experimentally implicated through chemical interception and isotope labeling experiments. In the absence of competing chemical reagents, it dimerizes and eliminates dioxygen in a step highly relevant to O-O bond formation in the oxygen evolution step in water oxidation. Thus, the study demonstrates both facile O-O bond cleavage and formation in the stoichiometric reduction of O2 to H2O with 2 equiv of Co(II) and suggests a new pathway for selective reduction of O2 to water via Co(III)-O-O-Co(III) peroxo intermediates.
- Nurdin, Lucie,Spasyuk, Denis M.,Fairburn, Laura,Piers, Warren E.,Maron, Laurent
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supporting information
p. 16094 - 16105
(2018/11/27)
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- CO2 capture, storage, and conversion using a praseodymium-modified Ga2O3 photocatalyst
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Praseodymium-modified gallium oxide (Pr/Ga2O3) was found to show enhanced activity and selectivity toward CO evolution in the photocatalytic conversion of CO2 using H2O as an electron donor in an aqueous solution of NaHCO3 as compared to those of bare Ga2O3. The as-prepared Pr species, including Pr(OH)3 and Pr2O2CO3, on the surface of Ga2O3 were transformed into Pr hydroxycarbonates (Pr2(OH)2(3-x)(CO3)x) and Pr carbonate hydrates (Pr2(CO3)3·8H2O) in an aqueous solution of NaHCO3, and then the Pr2(OH)2(3-x)(CO3)x was further transformed into Pr2(CO3)3·8H2O by CO2 bubbling under photoirradiation. This indicates that CO2 molecules dissolved in water can be captured and stored using Pr species in an aqueous solution of NaHCO3 under CO2 bubbling. More importantly, Pr2(OH)2(3-x)(CO3)x and Pr2(CO3)3·8H2O accumulated on the surface were decomposed to CO over the Ga2O3 photocatalyst with a Ag cocatalyst. Consequently, Ag/Pr/Ga2O3 exhibits much higher activity (249 μmol h-1 of CO) than the pristine Ag-loaded Ga2O3 (136 μmol h-1 of CO).
- Huang, Zeai,Teramura, Kentaro,Asakura, Hiroyuki,Hosokawa, Saburo,Tanaka, Tsunehiro
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supporting information
p. 19351 - 19357
(2017/09/25)
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- Synthesis of Pyridylanthracenes and Their Reversible Reaction with Singlet Oxygen to Endoperoxides
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The ortho, meta, and para isomers of 9,10-dipyridylanthracene 1 have been synthesized and converted into their endoperoxides 1-O2 upon oxidation with singlet oxygen. The kinetics of this reaction can be controlled by the substitution pattern an
- Fudickar, Werner,Linker, Torsten
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p. 9258 - 9262
(2017/09/11)
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- On the incompatibility of lithium-O2 battery technology with CO2
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When solubilized in a hexacarboxamide cryptand anion receptor, the peroxide dianion reacts rapidly with CO2 in polar aprotic organic media to produce hydroperoxycarbonate (HOOCO2-) and peroxydicarbonate (-O2COOCO2-). Peroxydicarbonate is subject to thermal fragmentation into two equivalents of the highly reactive carbonate radical anion, which promotes hydrogen atom abstraction reactions responsible for the oxidative degradation of organic solvents. The activation and conversion of the peroxide dianion by CO2 is general. Exposure of solid lithium peroxide (Li2O2) to CO2 in polar aprotic organic media results in aggressive oxidation. These findings indicate that CO2 must not be introduced in conditions relevant to typical lithium-O2 cell configurations, as production of HOOCO2- and -O2COOCO2- during lithium-O2 cell cycling will lead to cell degradation via oxidation of organic electrolytes and other vulnerable cell components.
- Zhang, Shiyu,Nava, Matthew J.,Chow, Gary K.,Lopez, Nazario,Wu, Gang,Britt, David R.,Nocera, Daniel G.,Cummins, Christopher C.
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p. 6117 - 6122
(2017/08/29)
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- Syngas production: Diverse H2/CO range by regulating carbonates electrolyte composition from CO2/H2O: Via co-electrolysis in eutectic molten salts
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We present a novel sustainable method for the direct production of syngas (H2 + CO) from CO2/H2O co-electrolysis using a hermetic device, to address the continuously increasing level of environmental carbon dioxide (CO2). All experiments were conducted using a two-electrode system with a coiled Fe cathode and coiled Ni anode in eutectic mixtures of binary and ternary carbonates with hydroxide in a 0.1:1 hydroxide/carbonate ratio. With an applied voltage of 1.6-2.6 V and an operating temperature of 500-600 °C, the H2/CO product ratio was easily tuned from 0.53 to 8.08 through renewable cycling of CO2 and H2O. The Li0.85Na0.61K0.54CO3-0.1LiOH composite had the highest current efficiency among those tested, with an optimum value approaching ~93%. This study provides a promising technique for the electrochemical conversion of CO2/H2O to a controllable syngas feedstock that can be used in a broad range of industrial applications.
- Liu, Yue,Yuan, Dandan,Ji, Deqiang,Li, Zhida,Zhang, Zhonghai,Wang, Baohui,Wu, Hongjun
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p. 52414 - 52422
(2017/11/24)
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- Insights into decomposition pathways and fate of Ru(bpy)32+ during photocatalytic water oxidation with s2O82? as sacrificial electron acceptor
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The most widely accepted system for homogeneous photocatalytic water oxidation process consists of a water oxidation catalyst, RuII(bpy)32+ as a photopump, and S2O82? as the sacrificial electron acceptor. However, this system is far less than ideal because RuII(bpy)32+ undergoes very rapid decomposition and as a result the process stops before all of the S2O82? is consumed. In this regard its decomposition pathways and the fate of RuII(bpy)32+ should be elucidated to design more efficient photocatalytic water oxidation systems. We found that two pathways exist for decomposition of RuII(bpy)32+ in the light?RuII(bpy)32+? S2O82? system. The first is the formation of OH? radicals at pH >6 through oxidation of OH? by RuIII(bpy)33+ in the dark, which attack the bpy ligand of RuII(bpy)32+. This is a minor, dark decomposition pathway. During irradiation not only RuII(bpy)32+ but also RuIII(bpy)33+ becomes photoexcited and the photoexcited RuIII(bpy)33+ reacts with S2O82? to produce an intermediate which decomposes into catalytically active Ru μ-oxo dimers when the intermediate concentration is low or into catalytically inactive oligomeric Ru μ-oxo species when the intermediate concentration is high. This is the major, light-induced decomposition pathway. When the RuII(bpy)32+ concentration is low, the light?RuII(bpy)32+?S2O82? system produces O2 even in the absence of any added catalysts through the O2-producing dark pathway. When the RuII(bpy)32+ concentration is high, the system does not produce O2 because the overall rate for the light-induced decomposition pathway is much faster than that of the O2-producing dark pathway.
- Akhtar, Umme Sarmeen,Tae, Eunju Lee,Chun, Yu Sung,Hwang, In Chul,Yoon, Kyung Byung
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p. 8361 - 8369
(2018/05/22)
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- Synergistic Cocatalytic Effect of Carbon Nanodots and Co3O4 Nanoclusters for the Photoelectrochemical Water Oxidation on Hematite
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Cocatalysis plays an important role in enhancing the activity of semiconductor photocatalysts for solar water splitting. Compared to a single cocatalyst configuration, a cocatalytic system consisting of multiple components with different functions may realize outstanding enhancement through their interactions, yet limited research has been reported. Herein we describe the synergistic cocatalytic effect between carbon nanodots (CDots) and Co3O4, which promotes the photoelectrochemical water oxidation activity of the Fe2O3 photoanode with a 60 mV cathodically shifted onset potential. The C/Co3O4-Fe2O3 photoanode exhibits a photocurrent density of 1.48 mA cm-2 at 1.23 V (vs. reversible hydrogen electrode), 78 % higher than that of the bare Fe2O3 photoanode. The slow reaction process on the single CoIII-OH site of the Co3O4 cocatalyst, oxidizing H2O to H2O2 with two photogenerated holes, could be accelerated by the timely H2O2 oxidation to O2 catalyzed on CDots.
- Zhang, Peng,Wang, Tuo,Chang, Xiaoxia,Zhang, Lei,Gong, Jinlong
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p. 5851 - 5855
(2016/05/09)
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- Low-temperature nitric oxide reduction over silver-substituted cobalt oxide spinels
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Catalytic reduction of NO by CO is performed over novel silver-substituted cobalt oxide nano-sized spinels, prepared via a citric acid-assisted sol-gel method. The catalysts are characterized by XRD, TEM, BET surface area measurements and CO chemisorption studies. Ag substitution in the cobalt oxide spinel lattice enhances CO chemisorption, hence the catalytic activity significantly. The prepared catalysts show excellent stability under the reaction conditions. The effect of moisture and oxygen dosage is studied for the reaction. The catalysts are found to be highly selective for N2 over N2O.
- Salker,Fal Desai
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p. 430 - 433
(2016/02/03)
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- Tuning the selectivity toward CO evolution in the photocatalytic conversion of CO2 with H2O through the modification of Ag-loaded Ga2O3 with a ZnGa2O4 layer
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Stoichiometric evolutions of CO, H2, and O2 were achieved for the photocatalytic conversion of CO2 with H2O as an electron donor using Ag-loaded Zn-modified Ga2O3. The selectivity toward the evolution of CO over H2 can be controlled by varying the amount of Zn species added in the Ag-loaded Zn-modified Ga2O3 photocatalyst. The production of H2 gradually decreased with increasing amounts of Zn species from 0.1 to 10.0 mol%, whereas the evolution of CO was almost unchanged. The XRD, XAFS, and XPS measurements revealed that a ZnGa2O4 layer was generated on the surface of Ga2O3 by modification with Zn species. The formation of the ZnGa2O4 layer eliminated the proton reduction sites on Ga2O3, although the crystallinity, surface area, and morphology of Ga2O3 as well as the particle size and chemical state of Ag did not change. In conclusion, we designed a highly selective photocatalyst for the conversion of CO2 with H2O as an electron donor using Ag (the cocatalyst for the CO evolution), ZnGa2O4 (the inhibitor of the H2 production), and Ga2O3 (the photocatalyst).
- Wang, Zheng,Teramura, Kentaro,Huang, Zeai,Hosokawa, Saburo,Sakata, Yoshihisa,Tanaka, Tsunehiro
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p. 1025 - 1032
(2016/02/27)
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- A ZnTa2O6 photocatalyst synthesized: Via solid state reaction for conversion of CO2 into CO in water
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Because of the environmental problems and the resulting exigent demand for CO2 recycling processes, great attention is being paid to the photocatalytic conversion of CO2 into useful chemicals such as CO, HCOOH, HCHO, CH3OH, and CH4. We have previously reported that the Ag-loaded, Zn-modified Ga2O3 photocatalyst exhibits excellent photocatalytic activity required for the conversion of CO2 into CO by using H2O as a reductant and that the Ag particles that exist together with the Zn species act as good cocatalysts for the selective formation of CO. In this study, we demonstrated the photocatalytic activity of ZnTa2O6 under UV light irradiation, which was prepared via solid-state reaction, for the conversion of CO2 in an aqueous NaHCO3 solution. A Ag cocatalyst-loaded ZnTa2O6 photocatalyst evolved CO as a reduction product of CO2 with 46% selectivity toward CO evolution among the reduction products. In contrast, when Pt and Au were introduced as cocatalysts, the ZnTa2O6 photocatalyst evolved H2 with high selectivity (>99.9%).
- Iguchi, Shoji,Teramura, Kentaro,Hosokawa, Saburo,Tanaka, Tsunehiro
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p. 4978 - 4985
(2016/07/11)
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- Kinetics and Mechanism of Oxidation of S2O32? by a Co-Bound μ-Amido-μ-Superoxo Complex
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In acetate buffer media (pH 4.5–5.4) thiosulfate ion (S2O32?) reduces the bridged superoxo complex, [(NH3)4CoIII(μ-NH2,μ-O2)CoIII(NH3)4]4+ (1) to its corresponding μ-peroxo product, [(NH3)4CoIII(μ-NH2,μ-O2)CoIII(NH3)4]3+ (2) and along a parallel reaction path, simultaneously S2O32? reacts with 1 to produce the substituted μ-thiosulfato-μ-superoxo complex, [(NH3)4CoIII(μ-S2O3,μ-O2)CoIII(NH3)4]3+ (3). The formation of μ-thiosulfato-μ-superoxo complex (3) appears as a precipitate which on being subjected to FTIR shows absorption peaks that support the presence of Co(III)-bound S-coordinated S2O32? group. In reaction media, 3 readily dissolves to further react with S2O32? to produce μ-thiosulfato-μ-peroxo product, [(NH3)4CoIII(μ-S2O3,μ-O2)CoIII(NH3)4]2+ (4). The observed rate (k0) increases with an increase in [TThio] ([TThio] is the analytical concentration of S2O32?) and temperature (T), but it decreases with an increase in [H+] and the ionic strength (I). Analysis of the log At versus time data (A is the absorbance of 1 at time t) reveals that overall the reaction follows a biphasic consecutive reaction path with rate constants k1 and k2 and the change of absorbance is equal to {a1 exp(–k1t) + a2 exp(–k2t)), where k1 > k2.
- Singh, Bula,Das, Ranendu Sekhar,Banerjee, Rupendranath,Mukhopadhyay, Subrata
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- TG–MS study on the kinetics and mechanism of thermal decomposition of copper ethylamine chromate, a new precursor for copper chromite catalyst
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Copper chromite is a well-known burn rate modifier for the combustion of composite solid propellants. In this study, basic copper ethylamine chromate (CEC), a new precursor for copper chromite catalyst, was synthesized by precipitation method. The thermal decomposition of the precursor was followed by thermogravimetry–mass spectroscopy (TG–MS) and X-ray diffraction techniques and compared with that of copper ammonium chromate, a conventional precursor for copper chromite catalyst. TG–MS analysis for the decomposition of CEC revealed that the decomposition starts with the liberation of ethylamine. The change in enthalpy for the decomposition reaction of copper ethylamine chromate was higher than that of copper ammonium chromate due to the oxidation of ethyl group. The reducing atmosphere created by the presence of carbon during the decomposition of CEC produced a mixture of Cu, CuCr2O4, CuCrO2 and CuO, while the oxidizing atmosphere of copper ammonium chromate produced a mixture of CuCr2O4 and CuO. Mechanistic study based on Criado and Coats–Redfern methods showed that CEC follows random nucleation (F1) mechanism as the rate-determining step for the thermal decomposition process.
- Paulose, Sanoop,Thomas, Deepthi,Jayalatha,Rajeev,George, Benny K.
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p. 1099 - 1108
(2016/07/06)
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- Multi-emitter chemiluminescence in the solid-phase interaction of xenon difluoride with uranyl hydrogen phosphate
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Chemiluminescence (CL) was found in the solid-phase interaction of xenon difluoride with uranyl hydrogen phosphate; the CL emitters are *Xe, UO22+ and the singlet oxygen dimole (1O2)2.
- Ostakhov, Sergey S.,Masyagutova, Gul'shat A.,Mamykin, Alexander V.,Khursan, Sergey L.
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p. 405 - 406
(2016/10/05)
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- Electron transfer mechanism of catalytic superoxide dismutation: Via Cu(II/i) complexes: Evidence of cupric-superoxo/-hydroperoxo species
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To understand the electron transfer mechanisms (outer versus inner sphere) of catalytic superoxide dismutation via a Cu(ii/i) redox couple such as occur in the enzyme copper-zinc superoxide dismutase, the Cu(ii/i) complexes [(L1)2Cu](ClO4
- Maji, Ram Chandra,Das, Partha Pratim,Mishra, Saikat,Bhandari, Anirban,Maji, Milan,Patra, Apurba K.
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supporting information
p. 11898 - 11910
(2016/07/29)
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- Novel hierarchical NiO nanoflowers exhibiting intrinsic superoxide dismutase-like activity
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Novel hierarchical NiO nanoflowers assembled by ultrathin nanoflakes were found to exhibit intrinsic superoxide dismutase-like activity for the first time. Arising from the unique flower-like structure and the appropriate redox potential of NiII/sup
- Mu, Jianshuai,Zhao, Xin,Li, Jie,Yang, En-Cui,Zhao, Xiao-Jun
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supporting information
p. 5217 - 5221
(2016/08/17)
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- Facile structure design based on C3N4 for mediator-free Z-scheme water splitting under visible light
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In this work, two photocatalysts (i.e., C3N4 and WO3) were successfully combined into a heterojunction structure by a facile hydrothermal method for mediator-free overall water splitting, analogous to the natural photosynthesis over a two-step photoexcitation Z-scheme system. Hydrogen and oxygen are evolved with a 2:1 ratio by irradiating the C3N4-WO3 composites loaded with Pt under visible light (λ > 420 nm) without any redox mediator. Introducing reduced graphene oxide (rGO) into the C3N4-WO3 composites enhances the water splitting efficiency. Through optimizing the mass ratio in the C3N4-WO3 composites, rGO content, amount of loaded Pt and pH value of the reacting system, the highest H2/O2 evolution rates of 2.84 and 1.46 μmol h-1 can be obtained, with a quantum yield of 0.9%. Our findings demonstrate that the hydrothermal method is a promising strategy for constructing intimate heterostructures for Z-scheme water-splitting systems without using any redox mediator, and that rGO can be used to further enhance the performance in optimized conditions.
- Zhao, Guixia,Huang, Xiubing,Fina, Federica,Zhang, Guan,Irvine, John T. S.
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p. 3416 - 3422
(2015/06/08)
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- Photocatalytic water splitting and CO2 reduction over KCaSrTa5O15 nanorod prepared by a polymerized complex method
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Single-crystal KCaSrTa5O15 nanorods were successfully synthesized by a polymerized complex method. SEM and TEM observations revealed that the nanorods growing along the c axis of a tungsten bronze structure measured 40100 nm in diameter and 100300 nm in length. Tb(0.03 atom%)-doped KCaSrTa5O15 nanorods gave a green luminescence due to the 5D4 → 7F6 and 5D4 → 7F5 transition of Tb3+, when the KCaSrTa5O15 host was excited. The intensity of the luminescence was much higher than that by polycrystalline KCaSrTa5O15 prepared by a solid-state reaction. This indicates that nonradiative deactivation at grain boundaries was suppressed in the KCaSrTa5O15 nanorods compared to the polycrystalline KCaSrTa5O15. NiO cocatalyst-loaded KCaSrTa5O15 nanorods split water into H2 and O2 with an apparent quantum yield of 6.6% at 254 nm. The efficiency was three times as high as that of the polycrystalline KCaSrTa5O15. The KCaSrTa5O15 nanorods also showed photocatalytic activity for CO2 reduction, when a Ag-cocatalyst was loaded. Stoichiometric amounts of CO and H2 as reduction products and O2 as an oxidation product were obtained. The activity for CO2 reduction was improved by adding NaHCO3 into the reactant solution, giving about 90% CO selectivity (CO/ (CO + H2)).
- Takayama, Tomoaki,Iwase, Akihide,Kudo, Akihiko
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p. 538 - 543
(2015/09/08)
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- Photoelectrochemical reaction for the efficient production of hydrogen and high-value-added oxidation reagents
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A porous and thick photoelectrode of WO3 in the monoclinic phase was prepared to realize the recovery of H2 and high-value-added oxidation reagents with efficient solar energy conversion. The WO3 photoelectrode enabled the efficient production and accumulation of O2, S2O82-, Ce4+, and IO4- as oxidation products. Most notably, S2O82-, which possesses the highest oxidizability among all the peroxides, was generated with high applied bias photon-to-current efficiency (2.2 %) and faraday efficiency (≈100 %) upon irradiation from the back side of the photoelectrode. The design of a tandem photoelectrode system combining a dye-sensitized solar cell (DSSC) was also challenged for the realization of this photoelectrode system without external bias. A high solar energy conversion efficiency (5.2 %) was achieved in the tandem system comprising the WO3 photoelectrode connected to two DSSCs with a near-IR-utilizing dye in series for the production of H2 and S2O82-.
- Fuku, Kojiro,Wang, Nini,Miseki, Yugo,Funaki, Takashi,Sayama, Kazuhiro
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p. 1593 - 1600
(2015/05/20)
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- Promoting effect of CeO2 on the catalytic activity of Ba-Y2O3for direct decomposition of NO
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The effect of CeO2 additive on the catalytic performance of Ba-Y2O3 prepared by coprecipitaion for the direct decomposition of NO was investigated. Although Ba-Y2O3 effectively catalyzed NO decomposition, its activity was clearly increased by addition of CeO2. The optimum CeO2 content was 10 mol%. CO2-TPD measurement revealed that the addition of CeO2 into Ba-Y2O3 caused an increase in the CO2 desorption peak in the temperature range of 473 and 723K derived from highly dispersed Ba species. The predominant role of CeO2 additive was suspected to effectively create the highly dispersed Ba species as catalytically active sites. Kinetic studies of NO decomposition on Ba-CeO2(10)-Y2O3 suggested that coexisting O2 suppresses the NO decomposition reaction by competitive adsorption. Isotopic transient kinetic analysis suggested a reaction pathway in which the surface NOx adspecies act as reaction intermediates for the formation of N2 in NO decomposition over Ba-CeO2-Y2O3. We concluded that CeO2 additive does not directly participate in the NO decomposition reaction as catalytically active species.
- Doi, Yasuyuki,Haneda, Masaaki,Ozawa, Masakuni
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p. 117 - 123
(2015/01/30)
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- Activity on Leishmania tropica of metal complexes with NNOO tetradentate Schiff base ligand: Kinetic and thermodynamic studies from TG-DTA analysis
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In the search for antileishmanial drug, tetradentate Schiff base ligand 2-{(E)-[(2-{[(Z)-(2-hydroxyphenyl)methylidene]amino}phenyl)imino]methyl}phenol (H2L) was reacted with transition metal ions to yield the complexes of the composition ML [where M = Co (II), Ni (II), Cu (II), & Zn (II)]. The copper based compound 3 (IC50 = 5.857 μM) showed activities even higher than the standard drug. TG and DTA analyses under static air in the temperature range 30-1000 °C were also observed for all the compounds. The TG-DTA analyses and the subsequent themodynamic and kinetic parameters calculated using the TG-DTA curves, have potential relevance for the biological activities. Horowitz-Metzger method was applied for calculating the activation energies and order of pyrolysis. Thermodynamic parameters like ΔS?, ΔH? and ΔG? were subsequently calculated using the corresponding expressions. The order of decreasing thermal stability and decreasing activation energy follow the orders Ni(II) >Co(II) >Zn(II) >Cu(II) and E?Cu>E?Co>E?Ni>E?Zn, respectively.
- Ikram, Muhammad,Rehman, Sadia,Jamal, Qaisar,Shah, Akram
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p. 869 - 878
(2016/01/12)
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- Molten copper hexaoxodivanadate: An efficient catalyst for SO3 decomposition in solar thermochemical water splitting cycles
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Molten copper hexaoxodivanadate (CuV2O6) was identified as an active catalyst for SO3 decomposition, which is an oxygen generation step in solar thermochemical water splitting cycles, at moderate temperatures (ca. 600 °C). The SO3 decomposition over CuV2O6 was significantly accelerated when the reaction temperature approached the melting point (ca. 630 °C) compared with solid phases of Cu2V2O7 as well as other compounds in the CuO-V2O5 system with higher melting points (≥780 °C). A possible intermediate CuSO4 species formed by SO 3 adsorption onto the Cu oxide site may decompose promptly to evolve SO2 and O2 on contact with the molten catalyst phase. Furthermore, the molten catalyst contained a large fraction of monovalent Cu formed by spontaneous desorption of oxygen. A possible reaction mechanism consisting of the fast dissolution of CuSO4 and Cu 2+/Cu+ redox cycles in the melt is proposed.
- Kawada, Takahiro,Tajiri, Tonami,Yamashita, Hiroaki,Machida, Masato
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p. 780 - 785
(2014/03/21)
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- Enhanced Au-Pd activity in the direct synthesis of hydrogen peroxide using Nanostructured titanate nanotube supports
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Nanostructured supports with tubular morphologies can impose one dimensional external constraints to supported metal nanoparticles affording small sizes (a key role in determining the morphology and stability of the supported Au-Pd nanoparticles. This strategy is presented as an alternative nanoparticle stabilisation approach rather than encapsulation within porous structures or the use of organic capping agents with associated diffusional limitations. Here, we report the enhancement achieved in the Au-Pd alloy reactivity for the direct synthesis of hydrogen peroxide when supported on titanate nanotubes (Ti-NT) with a productivity above 11600 molH2O2kgmetal-1h-1 afforded by the high metal-support interaction.
- Torrente-Murciano, Laura,He, Qian,Hutchings, Graham J.,Kiely, Christopher J.,Chadwick, David
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p. 2531 - 2534
(2015/04/14)
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- A doping technique that suppresses undesirable H2 evolution derived from overall water splitting in the highly selective photocatalytic conversion of CO2 in and by water
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Photocatalytic conversion of CO2 to reduction products, such as CO, HCOOH, HCHO, CH3OH, and CH4, is one of the most attractive propositions for producing green energy by artificial photosynthesis. Herein, we found that Ga2O3 photocatalysts exhibit high conversion of CO2. Doping of Zn species into Ga2O 3 suppresses the H2 evolution derived from overall water splitting and, consequently, Zn-doped, Ag-modified Ga2O3 exhibits higher selectivity toward CO evolution than bare, Ag-modified Ga 2O3. We observed stoichiometric amounts of evolved O 2 together with CO. Mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species on the photocatalyst surface, but the CO2 introduced in the gas phase. Doping of the photocatalyst with Zn is expected to ease the adsorption of CO2 on the catalyst surface.
- Teramura, Kentaro,Wang, Zheng,Hosokawa, Saburo,Sakata, Yoshihisa,Tanaka, Tsunehiro
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supporting information
p. 9906 - 9909
(2014/08/18)
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