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Steven L. Suib - One of the best experts on this subject based on the ideXlab platform.

  • ion induced promotion of activity enhancement of mesoporous Manganese Oxides for aerobic oxidation reactions
    Applied Catalysis B-environmental, 2015
    Co-Authors: Sourav Biswas, Altug S Poyraz, Yongtao Meng, Curtis Guild, Hannah Tripp, Steven L. Suib
    Abstract:

    Abstract Inverse micelle templated mesoporous Manganese oxide (University of Connecticut mesoporous material, UCT-1) and ion promoted mesoporous Manganese Oxides (UCT-18-X, X = Mg2+, Ca2+, K+, Na+ and Cs+) having trace amount of alkali metal ions as promoters with tunable porosity and crystallinity were synthesized. The synthesis was based on the use of inverse micelles as soft templates and unique NOx chemistry as established for recently discovered UCT materials. The materials were tested for selective aerobic alcohol oxidation and the catalytic activity followed the order of UCT-1  90% conversion and 90% selectivity for the acid and 9% selectivity for the ester.

  • understanding the role of gold nanoparticles in enhancing the catalytic activity of Manganese Oxides in water oxidation reactions
    Angewandte Chemie, 2015
    Co-Authors: Weikun Li, Steven L. Suib, Thorsten Ressler, Abdelhamid M Elsawy, Curtis Guild, Lakshitha Pahalagedara, David A Kriz, Nina Sharmen Genz, Jie He
    Abstract:

    The Earth-abundant and inexpensive Manganese Oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn3+ species, a small amount of AuNPs (<5 %) in α-MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α-MnO2.

  • water oxidation catalysis using amorphous Manganese Oxides octahedral molecular sieves oms 2 and octahedral layered ol 1 Manganese oxide structures
    Journal of Physical Chemistry C, 2012
    Co-Authors: Aparna Iyer, Joselyn Delpilar, Cecil K Kingondu, Edward Kissel, Hector F Garces, Hui Huang, Abdelhamid M Elsawy, Prabir K Dutta, Steven L. Suib
    Abstract:

    Water oxidation is the bottleneck in artificial photosynthetic systems that aim to split water into hydrogen and oxygen. However, water oxidation occurs readily in plants, catalyzed by the Mn4O4Ca Manganese cluster. In addition to this, Manganese minerals are ubiquitous in nature displaying layered and tunnel structures. In this study, mixed valent porous amorphous Manganese Oxides (AMO), along with cryptomelane type tunnel Manganese Oxides (OMS-2) and layered birnessite (OL-1) have been used as water oxidation catalysts. Significantly higher turnovers were obtained with AMO (290 mmol O2/mol Mn) compared to tunnel structure OMS-2 (110 mmol O2/mol Mn) and layered structure OL-1 (27 mmol O2/mol Mn) in water oxidation tests with Ce4+. Oxygen evolution was also confirmed under photochemical conditions using Ru(bpy)3 2+ as a photosensitizer and persulfate as a sacrificial agent. The differences in catalytic activity among these catalysts have been probed using X-ray diffraction, transmission electron microscop...

  • adsorptive and acidic properties reversible lattice oxygen evolution and catalytic mechanism of cryptomelane type Manganese Oxides as oxidation catalysts
    Journal of the American Chemical Society, 2008
    Co-Authors: Qiuhua Zhang, Javier Garciamartinez, Steven L. Suib
    Abstract:

    Cryptomelane-type Manganese Oxides have been synthesized, characterized, and tested in the total oxidation of volatile organic compounds and CO oxidation. The structural, compositional, morphological, acid−base, physisorptive−chemisorptive, and thermal stability properties (especially the reversible evolution of lattice oxygen) have been studied in detail using ICP-AES (inductively coupled plasma-atomic emission spectroscopy), HRSEM (high-resolution scanning electronic microscope), XRD (X-ray diffraction), IR (infrared) and adsorbate-IR, N2 and CO2 physisorption at 77 and 273 K, respectively, TPD-MS (temperature-programmed decomposition−mass spectroscopy), and TGA-DSC (thermogravimetric analysis−differential scanning calorimetry) techniques. Kinetic and mechanistic studies for the catalytic function have been conducted and related to the characterization results. Cryptomelane has shown to be highly microporous, by using CO2 physisorption, and highly hydrophobic, possessing both Bronsted and Lewis acid sit...

  • Structural studies on colloidal tetraalkylammonium Manganese Oxides.
    Journal of Synchrotron Radiation, 1999
    Co-Authors: Thorsten Ressler, Stephanie L. Brock, Joe Wong, Steven L. Suib
    Abstract:

    t. Introduction Mixed valent Manganese Oxides are of interest due to their diverse range of electrical, magnetic, and catalytic properties. Recently, novel colloids of Manganese oxide have been prepared using tetraalkylammonium cations (allcyl = methyl, ethyl, propyl, and butyl) to prevent agglomerization (Brock et al., 1998). These materials are of interest due to unique optical properties associated with quantum confinement and their potential as starting materials for novel Manganese oxide materials. In this work Mn K-edge XAFS studies were performed on colloidal MnOx samples prior and upon sol to gel transition and after different heat treatment procedures to reveal structural and electronic changes in the colloidal particles. Theoretical XAFS calculations known to yield reliable backscattering phases and amplitudes are applied in combination with suitable fitting routines to the analysis of colloidal Manganese oxide systems. 2. Experimental section 2.1 Preparation of colloidal Manganese Oxides A detailed description of the synthesis of tetraalkylammonium (TAA) Manganese oxide colloids appears elsewhere (Brock et al., 1999). The materials are prepared via reduction of tetraalkylanunonium permanganate salts (alkyl = ethyl, prowl) with 2-butanol in aqueous solutions. XAFS measurements have been obtained on the colloids as-prepared (TAA-A), with the residual 2-butanol removed (TAA-H), and on the gels (TAA-G). Measurements have been made on both tetraethylammonium (TEA) and tetrapropylammonium (TPA) Manganese oxide colloids and gels with Manganese concentrations from 0.1-0.4 M.

Youngjoon Shin - One of the best experts on this subject based on the ideXlab platform.

  • factors influencing the capacity fade of spinel lithium Manganese Oxides
    Journal of The Electrochemical Society, 2004
    Co-Authors: Youngjoon Shin, Arumugam Manthiram
    Abstract:

    With the aim of developing a better understanding of the capacity fading mechanisms of spinel Manganese Oxides, the percent capacity fade of a number of singly substituted LiMn 2-y M y O 4 (M = Li, Al, Ti, Co. Ni, and Cu and 0 ≤ y ≤ 0.2) and doubly substituted LiMn 2-y-z M y Li z O 4 (M = Al. Ti, Fe, Co, Ni, Cu, and Ga, 0 ≤ y ≤ 0. 1, and 0 ≤ z ≤ 0.1) Oxides is correlated to the initial lattice parameter, initial Manganese valence, degree of Manganese dissolution, electrode resistance, irreversible capacity (IRC) loss in the first cycle, and lattice parameter difference Δa between the two cubic phases formed in the two-phase region during the charge-discharge process. The doubly substituted LiMn 2-y-z Ni y Li z O 4 samples exhibit a combination of superior capacity retention and rate capability with lower IRC compared to LiMn 2 O 4 despite a similar amount of Manganese dissolution due to a low Aa and the consequent low microstrain. The samples with a low Δa are also characterized by a lower initial lattice parameter and a higher initial Mn valence of >3.58+ for the as-prepared samples. The percent capacity fade, IRC, and Δa all exhibit a sharp decrease as the initial Mn valence in the as-prepared sample exceeds 3.58+.

  • Factors Influencing the Capacity Fade of Spinel Lithium Manganese Oxides
    Journal of The Electrochemical Society, 2004
    Co-Authors: Youngjoon Shin, Arumugan Manthiram
    Abstract:

    With the aim of developing a better understanding of the capacity fading mechanisms of spinel Manganese Oxides, the percent capacity fade of a number of singly substituted LiMn2-yMyO4 (M = Li, Al, Ti, Co, Ni, and Cu and 0 less than or equal to y less than or equal to 0.2) and doubly substituted LiMn2-y-zMyLizO4 (M = Al, Ti, Fe, Co, Ni, Cu, and Ga, 0 less than or equal to y less than or equal to 0.1, and 0 less than or equal to z less than or equal to 0.1) Oxides is correlated to the initial lattice parameter, initial Manganese valence, degree of Manganese dissolution, electrode resistance, irreversible capacity (IRC) loss in the first cycle, and lattice parameter difference Deltaa between the two cubic phases formed in the two-phase region during the charge-discharge process. The doubly substituted LiMn2-y-zNiyLizO4 samples exhibit a combination of superior capacity retention and rate capability with lower IRC compared to LiMn2O4 despite a similar amount of Manganese dissolution due to a low Deltaa and the consequent low microstrain. The samples with a low Deltaa are also characterized by a lower initial lattice parameter and a higher initial Mn valence of >3.58+ for the as-prepared samples. The percent capacity fade, IRC, and Deltaa all exhibit a sharp decrease as the initial Mn valence in the as-prepared sample exceeds 3.58+. (C) 2004 The Electrochemical Society.

  • influence of the lattice parameter difference between the two cubic phases formed in the 4 v region on the capacity fading of spinel Manganese Oxides
    Chemistry of Materials, 2003
    Co-Authors: Youngjoon Shin, Arumugam Manthiram
    Abstract:

    To develop a better understanding of the capacity-fading mechanisms of spinel lithium Manganese Oxides, the electrochemical properties, degree of Manganese dissolution, and crystal chemistry of a number of singly substituted LiMn2-yMyO4 (M = Li, Al, Ti, Co, and Ni and 0 ≤ y ≤ 0.2) and doubly substituted LiMn2-y-zMyLizO4 (M = Ti, Co, and Ni, 0 ≤ y ≤ 0.1, and 0 ≤ z ≤ 0.1) Oxides have been compared with those of LiMn2O4. The cation-substituted spinel Manganese Oxides show better electrochemical performances than LiMn2O4. Especially, the doubly substituted LiMn1.85Ni0.075Li0.075O4 exhibits excellent cyclability at both ambient and elevated temperatures with a capacity of around 100 mAh/g. It also exhibits remarkable rate capability and excellent capacity retention (>95%) after storage at 60 °C at various depths of discharge (DOD). Although the degree of Manganese dissolution does not vary significantly, the spinel Manganese Oxides show a clear relationship between the percent capacity fade and the lattice par...

  • Origin of the high voltage (>4.5 V) capacity of spinel lithium Manganese Oxides
    Electrochimica Acta, 2003
    Co-Authors: Youngjoon Shin, Arumugan Manthiram
    Abstract:

    With an objective to develop a better understanding of the origin of high voltage (>4.5 V) capacities, the electrochemical behaviors of a number of spinel lithium Manganese Oxides with and without other transition metal ions have been studied and compared. The Oxides investigated are LiMn2-yMyO4(M=Co, Ni, and Cu), LiMn2-y-zMyLizO4, LiMn2-yLiyO4, Li2Mn4O9-δ, and Li4Mn5O12. The LiMn2-yLiyO4(0.05≤y≤0.12) Oxides are found to exhibit capacity above 4.5 V although they do not contain other transition metal ions. In the case of Li2Mn4O9-δand Li4Mn5O12, charging above 4.5 V is found to increase the discharge capacity below 4.5 V. While both LiMn2-yCoyO4and LiMn2-y-zCoyLizO4show a similar behavior at >4.5 V, LiMn2-yNiyO4and LiMn2-y-zNiyLizO4differ significantly. Also, while LiMn1.9Li0.1O4and LiMn1.8Co0.2O4show a rapid decrease in their discharge capacity above 4.5 V with rest time allowed in the fully charged state (self-discharge), LiMn2-yNiyO4does not suffer from such a difficulty. Additionally, long-range periodicity with good crystallinity is found to be essential to observe discharge capacity above 4.5 V. The results are explained on the basis of the participation of the O2-:2p band in the redox process and the relative positions of the other transition metal ion redox energies with respect to the top of the O2-:2p band. © 2003 Elsevier Ltd. All rights reserved.

Arumugam Manthiram - One of the best experts on this subject based on the ideXlab platform.

  • factors influencing the capacity fade of spinel lithium Manganese Oxides
    Journal of The Electrochemical Society, 2004
    Co-Authors: Youngjoon Shin, Arumugam Manthiram
    Abstract:

    With the aim of developing a better understanding of the capacity fading mechanisms of spinel Manganese Oxides, the percent capacity fade of a number of singly substituted LiMn 2-y M y O 4 (M = Li, Al, Ti, Co. Ni, and Cu and 0 ≤ y ≤ 0.2) and doubly substituted LiMn 2-y-z M y Li z O 4 (M = Al. Ti, Fe, Co, Ni, Cu, and Ga, 0 ≤ y ≤ 0. 1, and 0 ≤ z ≤ 0.1) Oxides is correlated to the initial lattice parameter, initial Manganese valence, degree of Manganese dissolution, electrode resistance, irreversible capacity (IRC) loss in the first cycle, and lattice parameter difference Δa between the two cubic phases formed in the two-phase region during the charge-discharge process. The doubly substituted LiMn 2-y-z Ni y Li z O 4 samples exhibit a combination of superior capacity retention and rate capability with lower IRC compared to LiMn 2 O 4 despite a similar amount of Manganese dissolution due to a low Aa and the consequent low microstrain. The samples with a low Δa are also characterized by a lower initial lattice parameter and a higher initial Mn valence of >3.58+ for the as-prepared samples. The percent capacity fade, IRC, and Δa all exhibit a sharp decrease as the initial Mn valence in the as-prepared sample exceeds 3.58+.

  • influence of the lattice parameter difference between the two cubic phases formed in the 4 v region on the capacity fading of spinel Manganese Oxides
    Chemistry of Materials, 2003
    Co-Authors: Youngjoon Shin, Arumugam Manthiram
    Abstract:

    To develop a better understanding of the capacity-fading mechanisms of spinel lithium Manganese Oxides, the electrochemical properties, degree of Manganese dissolution, and crystal chemistry of a number of singly substituted LiMn2-yMyO4 (M = Li, Al, Ti, Co, and Ni and 0 ≤ y ≤ 0.2) and doubly substituted LiMn2-y-zMyLizO4 (M = Ti, Co, and Ni, 0 ≤ y ≤ 0.1, and 0 ≤ z ≤ 0.1) Oxides have been compared with those of LiMn2O4. The cation-substituted spinel Manganese Oxides show better electrochemical performances than LiMn2O4. Especially, the doubly substituted LiMn1.85Ni0.075Li0.075O4 exhibits excellent cyclability at both ambient and elevated temperatures with a capacity of around 100 mAh/g. It also exhibits remarkable rate capability and excellent capacity retention (>95%) after storage at 60 °C at various depths of discharge (DOD). Although the degree of Manganese dissolution does not vary significantly, the spinel Manganese Oxides show a clear relationship between the percent capacity fade and the lattice par...

  • nanocrystalline Manganese Oxides for electrochemical capacitors with neutral electrolytes
    Journal of The Electrochemical Society, 2002
    Co-Authors: Y U Jeong, Arumugam Manthiram
    Abstract:

    With an objective to develop inexpensive electrode materials for electrochemical redox capacitors, nanocrystalline Manganese Oxides have been synthesized by reducing aqueous KMnO 4 solution with various reducing agents such as potassium borohydride, sodium dithionite, sodium hypophosphite, and hydrochloric acid under various controlled pH conditions. The products have been characterized by X-ray diffraction, thermogravimetric analysis, surface area measurements, and cyclic voltametry in various neutral electrolytes such as aqueous NaCI, KCl, LiCI, and Na 2 SO 4 . Optimized samples exhibit specific capacitance values of around 250 F/g in the range of 0-1 V vs. SCE with excellent cyclability in 2 M NaCI electrolyte.

W. F. Maier - One of the best experts on this subject based on the ideXlab platform.

  • structural and catalytic aspects of sol gel derived copper Manganese Oxides as low temperature co oxidation catalyst
    Applied Catalysis A-general, 2006
    Co-Authors: M. Krämer, Katie Stowe, T. Schmidt, W. F. Maier
    Abstract:

    Abstract The influence of the preparation method on structural properties and on the catalytic activity of sol–gel derived binary copper Manganese Oxides for CO oxidation in dry air at room temperature has been investigated. The catalysts were characterised by means of BET and X-ray diffraction. All results were compared with a commercial Hopcalite sample. Subsequent conventional optimisation of the most active sample – prepared by the so-called ethylene–glycol method (EG I) – including compositional and calcination temperature variation revealed Cu20Mn80Ox (EG I) calcined at 400 °C as very active catalyst. Sintering processes induced by the crystallisation of the amorphous material above 400 °C cause a dramatic decrease of the catalysts’ surface area accompanied by deactivation. XPS data recordings were used to investigate the oxidation states of the metals in this catalyst and in the reference material. In conclusion a combination of high surface area, amorphous state and the presence of Cu2+ and Mn3+ was found to be essential for the high catalytic activity of the binary copper Manganese Oxides. The reactivity of the best catalyst was tested under application-relevant conditions, i.e. in moist air and at low-temperature fuel cell conditions.

  • Structural and catalytic aspects of sol-gel derived copper Manganese Oxides as low-temperature CO oxidation catalyst
    Applied Catalysis A: General, 2006
    Co-Authors: M. Krämer, Katie Stowe, T. Schmidt, W. F. Maier
    Abstract:

    The influence of the preparation method on structural properties and on the catalytic activity of sol-gel derived binary copper Manganese Oxides for CO oxidation in dry air at room temperature has been investigated. The catalysts were characterised by means of BET and X-ray diffraction. All results were compared with a commercial Hopcalite sample. Subsequent conventional optimisation of the most active sample - prepared by the so-called ethylene-glycol method (EG I) - including compositional and calcination temperature variation revealed Cu20Mn80Ox(EG I) calcined at 400 °C as very active catalyst. Sintering processes induced by the crystallisation of the amorphous material above 400 °C cause a dramatic decrease of the catalysts' surface area accompanied by deactivation. XPS data recordings were used to investigate the oxidation states of the metals in this catalyst and in the reference material. In conclusion a combination of high surface area, amorphous state and the presence of Cu2+and Mn3+was found to be essential for the high catalytic activity of the binary copper Manganese Oxides. The reactivity of the best catalyst was tested under application-relevant conditions, i.e. in moist air and at low-temperature fuel cell conditions. © 2006 Elsevier B.V. All rights reserved.

Yasuhiro Tokura - One of the best experts on this subject based on the ideXlab platform.

  • origins of colossal magnetoresistance in perovskite type Manganese Oxides invited
    Journal of Applied Physics, 1996
    Co-Authors: Yasuhiro Tokura, Hirokazu Kuwahara, Atsushi Asamitsu, Yutaka Moritomo, Y Tomioka, M Kasai
    Abstract:

    Phenomena of colossal magnetoresistance (MR) or magnetic field induced insulator–metal (I–M) transitions have been investigated for single crystals of perovskite‐type Manganese Oxides with controlled carrier density and one‐electron bandwidth. In addition to the canonical MR behavior near the Curie temperature, the first‐order phase transition accompanying several orders of magnitude change in resistivity has been observed under an external magnetic field for many of the composition‐controlled crystals as an intrinsic bulk phenomenon. It was proved by the systematic experimental investigations that the field‐induced destruction of the charge‐ordered state accompanying the lattice structural as well as metamagnetic transition is a major origin of such a colossal MR. Versatile MR phenomena and I–M phase diagrams in the T–H plane are presented with their interpretation.

  • giant magnetoresistance of Manganese Oxides with a layered perovskite structure
    Nature, 1996
    Co-Authors: Yutaka Moritomo, Hirokazu Kuwahara, Atsushi Asamitsu, Yasuhiro Tokura
    Abstract:

    Manganese Oxides with the cubic perovskite structure (typified by LaMnO3) have stimulated considerable interest because of their magnetoresistive properties1–9; they exhibit extremely large changes in electrical resistance in response to applied magnetic fields, a property that is of technological relevance for the development of magnetic memory and switching devices. But for such applications to be viable, great improvements will be needed in both the sensitivity and temperature dependence of the magnetoresistive response. One approach under consideration for optimizing these properties is chemical substitution10. Here we demonstrate an alternative strategy, in which we synthesize layered variants of the cubic perovskite parent compounds that have a controlled number of MnO2 sheets per unit cell. This strategy is structurally analogous to that employed for the systematic exploration of the high-transition-temperature copper oxide superconductors11. We find that the magneto-resistive properties of these materials depend sensitively on the dimensionality of the Manganese oxide lattice. Although the properties of our materials are still far from optimal, further exploration of this series of layered perovskites may prove fruitful.

  • Giant magnetoresistance of Manganese Oxides with a layered perovskite structure
    Nature, 1996
    Co-Authors: Yutaka Moritomo, Hirokazu Kuwahara, Atsushi Asamitsu, Yasuhiro Tokura
    Abstract:

    Manganese Oxides with the cubic perovskite structure (typified by LaMnO3) have stimulated considerable interest because of their magnetoresistive properties(1-9); they exhibit extremely large changes in electrical resistance in response to applied magnetic fields, a property that is of technological relevance for the development of magnetic memory and switching devices. But for such applications to be viable, great improvements will be needed in both the sensitivity and temperature dependence of the magnetoresistive response. One approach under consideration for optimizing these properties is chemical substitution(10). Here we demonstrate an alternative strategy, in which we synthesize layered variants of the cubic perovskite parent compounds that have a controlled number of MnO2 sheets per unit cell. This strategy is structurally analogous to that employed for the systematic exploration of the high-transition-temperature copper oxide superconductors(11). We find that the magnetoresistive properties of these materials depend sensitively on the dimensionality of the Manganese oxide lattice. Although the properties of our materials are still far from optimal, further exploration of this series of layered perovskites may prove fruitful.