The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Kevin W Waddell - One of the best experts on this subject based on the ideXlab platform.
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irreversible Catalyst Activation enables hyperpolarization and water solubility for nmr signal amplification by reversible exchange
Journal of Physical Chemistry B, 2014Co-Authors: Milton L Truong, Ping He, Bingxin Yuan, Kyle N Plunkett, Aaron M Coffey, Roman V Shchepin, Danila A Barskiy, Kirill V Kovtunov, Igor V Koptyug, Kevin W WaddellAbstract:Activation of a Catalyst [IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD = cyclooctadiene)] for signal amplification by reversible exchange (SABRE) was monitored by in situ hyperpolarized proton NMR at 9.4 T. During the Catalyst-Activation process, the COD moiety undergoes hydrogenation that leads to its complete removal from the Ir complex. A transient hydride intermediate of the Catalyst is observed via its hyperpolarized signatures, which could not be detected using conventional nonhyperpolarized solution NMR. SABRE enhancement of the pyridine substrate can be fully rendered only after removal of the COD moiety; failure to properly activate the Catalyst in the presence of sufficient substrate can lead to irreversible deActivation consistent with oligomerization of the Catalyst molecules. Following Catalyst Activation, results from selective RF-saturation studies support the hypothesis that substrate polarization at high field arises from nuclear cross-relaxation with hyp...
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irreversible Catalyst Activation enables hyperpolarization and water solubility for nmr signal amplification by reversible exchange
The Journal of Physical Chemistry, 2014Co-Authors: Milton L Truong, Bingxin Yuan, Kyle N Plunkett, Aaron M Coffey, Roman V Shchepin, Danila A Barskiy, Kirill V Kovtunov, Igor V Koptyug, Fan Shi, Kevin W WaddellAbstract:Activation of a Catalyst [IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD = cyclooctadiene)] for signal amplification by reversible exchange (SABRE) was monitored by in situ hyperpolarized proton NMR at 9.4 T. During the Catalyst-Activation process, the COD moiety undergoes hydrogenation that leads to its complete removal from the Ir complex. A transient hydride intermediate of the Catalyst is observed via its hyperpolarized signatures, which could not be detected using conventional nonhyperpolarized solution NMR. SABRE enhancement of the pyridine substrate can be fully rendered only after removal of the COD moiety; failure to properly activate the Catalyst in the presence of sufficient substrate can lead to irreversible deActivation consistent with oligomerization of the Catalyst molecules. Following Catalyst Activation, results from selective RF-saturation studies support the hypothesis that substrate polarization at high field arises from nuclear cross-relaxation with hyperpolarized ¹H spins of the hydride/orthohydrogen spin bath. Importantly, the chemical changes that accompanied the Catalyst’s full Activation were also found to endow the Catalyst with water solubility, here used to demonstrate SABRE hyperpolarization of nicotinamide in water without the need for any organic cosolventpaving the way to various biomedical applications of SABRE hyperpolarization methods.
Philippe Miele - One of the best experts on this subject based on the ideXlab platform.
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more reactive cobalt chloride in the hydrolysis of sodium borohydride
International Journal of Hydrogen Energy, 2009Co-Authors: Ouardia Akdim, Umit B Demirci, Philippe MieleAbstract:Cobalt chloride (CoCl2) is one of the most reactive Catalysts in the hydrolysis of sodium borohydride (NaBH4). The present study reports hydrogen release results for NaBH4CoCl2 systems, both solids having been mixed together via a ‘solvent’ route. Actually, the ‘solvent’ route using tetrahydrofuran (THF), compared to the mechanical mixing (‘mortar’ route), improves the CoCl2 reactivity in terms of Catalyst Activation time, hydrogen generation rate (HGR) and total conversion. SEM and XRD observations suggest that the ‘THF’ route favors the ex-situ reduction of Co2+ to an active cobalt phase. Other metal (cobalt or ruthenium) salts are also reported.
J L G Fierro - One of the best experts on this subject based on the ideXlab platform.
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enhanced methylcyclohexane dehydrogenation to toluene over ir usy Catalyst
Catalysis Today, 2016Co-Authors: D K Cromwell, P T Vasudevan, B Pawelec, J L G FierroAbstract:Abstract Selective dehydrogenation of methylcyclohexane (MCH) to toluene over Ir, Pt, Pd and Ni supported on ultrastable USY zeolite was studied in the context of the hydrogen storage using MCH-toluene-hydrogen cycle. The MCH dehydrogenation was carried out in a fixed-bed flow reactor at 250 °C, total hydrogen pressure of 30 bar and WHSV of 92.4 h −1 . The fresh and spent Catalysts were characterized by variety of techniques such as X-ray fluorescence spectrometry, N 2 physisorption, TPD-NH 3 , TPR, TEM, X-ray photoelectron and Raman spectroscopic techniques. Under steady-state conditions, the initial activity of the Catalysts followed the order: Ir/USY >> Pt/USY > Pd/USY > Ni/USY. The reduced Ir/USY Catalyst exhibited higher activity and selectivity toward toluene (≈90%) than its Pt, Pd and Ni-based counterparts. From the combined TPR and TEM analysis, the enhancement of activity and selectivity of the Ir/USY sample with respect to the Pt/USY Catalyst was ascribed to moderate metal-support interaction leading to formation of larger Ir particles having lower amount of hydrogenolysis sites (kink sites). MCH hydroconversion over the Ir/USY Catalyst decayed strongly during the time course of the reaction whereas simultaneously an increase in the toluene selectivity occurred. The Catalyst Activation by sulfidation was found to be less effective than the Catalyst Activation by reduction.
Huijun Zhao - One of the best experts on this subject based on the ideXlab platform.
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iron vacancies induced bifunctionality in ultrathin feroxyhyte nanosheets for overall water splitting
Advanced Materials, 2018Co-Authors: Bin Liu, Yun Wang, Huiqing Peng, Ruoou Yang, Zheng Jiang, Xingtai Zhou, Chunsing Lee, Huijun Zhao, Wenjun ZhangAbstract:Exploring of new Catalyst Activation principle holds a key to unlock catalytic powers of cheap and earth-abundant materials for large-scale applications. In this regard, the vacancy defects have been proven to be effective to initiate catalytic active sites and endow high electrocatalytic activities. However, such electrocatalytically active defects reported to date have been mostly formed by anion vacancies. Herein, it is demonstrated for the first time that iron cation vacancies induce superb water splitting bifunctionality in alkaline media. A simple wet-chemistry method is developed to grow ultrathin feroxyhyte (δ-FeOOH) nanosheets with rich Fe vacancies on Ni foam substrate. The theoretical and experimental results confirm that, in contrast to anion vacan-cies, the formation of rich second neighboring Fe to Fe vacancies in δ-FeOOH nanosheets can create catalytic active centers for both hydrogen and oxygen evolution reactions. The atomic level insight into the new Catalyst Activation principle based on metal vacancies is adaptable for developing other transi-tion metal electroCatalysts, including Fe-based ones.
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cobalt covalent doping in mos2 to induce bifunctionality of overall water splitting
Advanced Materials, 2018Co-Authors: Yun Wang, Qizhong Xiong, Peng Fei Liu, Lirong Zheng, Guozhong Wang, Hua Gui Yang, Po Keung Wong, Haimin Zhang, Huijun ZhaoAbstract:The layer-structured MoS2 is a typical hydrogen evolution reaction (HER) electroCatalyst but it possesses poor activity for the oxygen evolution reaction (OER). In this work, a cobalt covalent doping approach capable of inducing HER and OER bifunctionality into MoS2 for efficient overall water splitting is reported. The results demonstrate that covalently doping cobalt into MoS2 can lead to dramatically enhanced HER activity while simultaneously inducing remarkable OER activity. The Catalyst with optimal cobalt doping density can readily achieve HER and OER onset potentials of -0.02 and 1.45 V (vs reversible hydrogen electrode (RHE)) in 1.0 m KOH. Importantly, it can deliver high current densities of 10, 100, and 200 mA cm-2 at low HER and OER overpotentials of 48, 132, 165 mV and 260, 350, 390 mV, respectively. The reported Catalyst Activation approach can be adapted for bifunctionalization of other transition metal dichalcogenides.
Milton L Truong - One of the best experts on this subject based on the ideXlab platform.
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irreversible Catalyst Activation enables hyperpolarization and water solubility for nmr signal amplification by reversible exchange
Journal of Physical Chemistry B, 2014Co-Authors: Milton L Truong, Ping He, Bingxin Yuan, Kyle N Plunkett, Aaron M Coffey, Roman V Shchepin, Danila A Barskiy, Kirill V Kovtunov, Igor V Koptyug, Kevin W WaddellAbstract:Activation of a Catalyst [IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD = cyclooctadiene)] for signal amplification by reversible exchange (SABRE) was monitored by in situ hyperpolarized proton NMR at 9.4 T. During the Catalyst-Activation process, the COD moiety undergoes hydrogenation that leads to its complete removal from the Ir complex. A transient hydride intermediate of the Catalyst is observed via its hyperpolarized signatures, which could not be detected using conventional nonhyperpolarized solution NMR. SABRE enhancement of the pyridine substrate can be fully rendered only after removal of the COD moiety; failure to properly activate the Catalyst in the presence of sufficient substrate can lead to irreversible deActivation consistent with oligomerization of the Catalyst molecules. Following Catalyst Activation, results from selective RF-saturation studies support the hypothesis that substrate polarization at high field arises from nuclear cross-relaxation with hyp...
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irreversible Catalyst Activation enables hyperpolarization and water solubility for nmr signal amplification by reversible exchange
The Journal of Physical Chemistry, 2014Co-Authors: Milton L Truong, Bingxin Yuan, Kyle N Plunkett, Aaron M Coffey, Roman V Shchepin, Danila A Barskiy, Kirill V Kovtunov, Igor V Koptyug, Fan Shi, Kevin W WaddellAbstract:Activation of a Catalyst [IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD = cyclooctadiene)] for signal amplification by reversible exchange (SABRE) was monitored by in situ hyperpolarized proton NMR at 9.4 T. During the Catalyst-Activation process, the COD moiety undergoes hydrogenation that leads to its complete removal from the Ir complex. A transient hydride intermediate of the Catalyst is observed via its hyperpolarized signatures, which could not be detected using conventional nonhyperpolarized solution NMR. SABRE enhancement of the pyridine substrate can be fully rendered only after removal of the COD moiety; failure to properly activate the Catalyst in the presence of sufficient substrate can lead to irreversible deActivation consistent with oligomerization of the Catalyst molecules. Following Catalyst Activation, results from selective RF-saturation studies support the hypothesis that substrate polarization at high field arises from nuclear cross-relaxation with hyperpolarized ¹H spins of the hydride/orthohydrogen spin bath. Importantly, the chemical changes that accompanied the Catalyst’s full Activation were also found to endow the Catalyst with water solubility, here used to demonstrate SABRE hyperpolarization of nicotinamide in water without the need for any organic cosolventpaving the way to various biomedical applications of SABRE hyperpolarization methods.