[Angewandte Chemie International Edition, 2015, 54(8), 2345-2350]

……………………………………………………………………………………………………………………………………………………………………

[ACS Catalysis, 2015, 5 (7), 4394–4403]

……………………………………………………………………………………………………………………………………………………………………

Synthesis of crystalline mesoporous K2–xMn8O16 (Meso-OMS-2), and ε-MnO2 (Meso-ε-MnO2) is reported. The synthesis is based on the transformation of amorphous mesoporous manganese oxide (Meso-Mn-A) under mild conditions: aqueous acidic solutions (0.5 M H+and 0.5 M K+), at low temperatures (70 °C), and short times (2 h). Meso-OMS-2 and Meso-ε-MnO2 maintain regular mesoporosity (4.8–5.6 nm) and high surface areas (as high as 277 m2/g). The synthesized mesoporous manganese oxides demonstrated enhanced redox (H2-TPR) and catalytic performances (CO oxidation) compared to nonporous analogues. The order of reducibility and enhanced catalytic performance of the samples is Commercial-Mn2O3 < nonporous-OMS-2 < Meso-Mn2O3 < Meso-OMS-2 < Meso-ε-MnO2 < Meso-Mn-A.

[Appl. Mater. Interfaces, 2014, 6, 10986-10991.]

……………………………………………………………………………………………………………………………………………………………………

Manganese oxides of various structures (α-, β-, and δ-MnO2 and amorphous) were synthesized by facile methods. The electrocatalytic properties of these materials were systematically investigated for catalyzing both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline media. Extensive characterization was correlated with the activity study by investigating the crystal structures (XRD, HRTEM), morphologies (SEM), porosities (BET), surfaces (XPS, O2-TPD/MS), and electrochemical properties (Tafel analysis, Koutechy–Levich plots, and constant-current electrolysis). These combined results show that the electrocatalytic activities are strongly dependent on the crystallographic structures, and follow an order of α-MnO2 > AMO > β-MnO2 > δ-MnO2. Both OER studies and ORR studies reveal similar structure-determined activity trends in alkaline media. In the OER studies, α-MnO2 displays an overpotential of 490 mV compared to 380 mV shown by an Ir/C catalyst in reaching 10 mA cm–2. Meanwhile, α-MnO2 also exhibits stability for 3 h when supplying a constant current density of 5 mA cm–2. This was further improved by adding Ni2+ dopants (ca. 8 h). The superior OER activity was attributed to several factors, including abundant di-μ-oxo bridges existing in α-MnO2 as the protonation sites, analogous to the OEC in PS-II of the natural water oxidation system; the mixed valencies (AOS = 3.7); and the lowest charge transfer resistances (91.8 Ω, η = 430 mV) as revealed from in situ electrochemical impedance spectroscopy (EIS). In the ORR studies, when reaching 3 mA cm–2, α-MnO2 shows 760 mV close to 860 mV for the best ORR catalyst (20% Pt/C). The outstanding ORR activity was due to the strongest O2 adsorption capability of α-MnO2 suggested by temperature-programmed desorption. As a result, this discovery of the structure-related electrocatalytic activities could provide guidance in the further development of easily prepared, scalable, and low-cost catalysts based on metal oxides and their derivatives.

[Journal of the American Chemical Society 2014, 136 (32), 11452-11464]

……………………………………………………………………………………………………………………………………………………………………

Tungsten (0–30%)-promoted University of Connecticut mesoporous materials (UCT-X, X = 55 (Ti), 50 (Zr), and 56 (Hf)) were synthesized in one step using a recently discovered approach. The approach relies on inverse micelle formation and unique NOx chemistry to control the sol–gel chemistry of inorganic components. The tungsten-promoted mesoporous transition-metal (TM) oxides consist of monodispersed nanocrystalline particle aggregates with a particle size of ∼12 nm. The mesopores are formed by connected intraparticle voids of these aggregates, and the pore sizes vary between 3.8 and 6.1 nm, depending on the tungsten loading and TM oxide support. The materials were closely examined using PXRD, HRTEM, XPS, FTIR, Raman, and N2 sorption. The tungsten exist as very small (<1 nm) nano-WOxclusters that are well-dispersed on the TM support. Nano-WOx clusters were found to promote the formation of Brønsted acid sites. Catalytic activity was tested for solvent-free room-temperature acetalization and ketalization reactions. A 20% tungsten loading was found to be the optimum loading for the reactions. The catalyst can convert benzaldehyde with a conversion of 99% and yield of 93% to the corresponding acetal and can convert cyclohexanone with a conversion of 96% and yield of 94% to the corresponding ketal. The strong adsorption of products and intermediates on the mesopores was found to be the reason for the moderate performance in the conversion of other substrates.

[Chemistry of Materials 2014 26 (9), 2803-2813]

……………………………………………………………………………………………………………………………………………………………………

Manganese-containing MFI-type Mn–ZSM-5 zeolite was synthesized by a facile one-step hydrothermal method using tetrapropylammonium hydroxide (TPAOH) and manganese(III)-acetylacetonate as organic template and manganese salts, respectively. A highly crystalline MFI zeolite structure was formed under pH = 11 in 2 days, without the need for additional alkali metal cations. Direct evidence of the incorporation of Mn in the zeolite framework sites was observed by performing structure parameter refinements, supported by data collected from other characterization techniques such as IR, Raman, UV–vis, TGA, N2-adsorption, SEM, TEM, EDAX, and XPS. UV–vis spectra from the unique optical properties of Mn–ZSM-5 show two absorption peaks at 250 and 500 nm. The absorption varies in different atmospheres accompanied by a color change of the materials due to oxygen evolution. Raman spectra show a significant and gradual red shift from 383 cm–1 to 372 cm–1 when the doping amount of Mn is increased from 0 to 2 wt %. This suggests a weakened zeolite structural unit induced by the Mn substitution. The catalytic activity was studied in both gas-phase benzyl alcohol oxidation and toluene oxidation reactions with remarkable oxidative activity presented for the first time. These reactions result in a 55% yield of benzaldehyde, and 65% total conversion of toluene to carbon dioxide for the 2% Mn–ZSM-5. Temperature programmed reduction (TPR) using CO in He demonstrates two reduction peaks: one between 300 and 500 °C and the other between 500 and 800 °C. The first reduction peak, due to manganese-activated oxidation sites shifted from higher temperature to lower temperature, and the peak intensity of CO2 rises when the dopant amount increases. For the first time, calculated photophysical properties of a model Mn(O-SiH3)4– compound, an Mn-embedded zeolite cluster, and model Mn oxides help to explain and interpret the diffuse reflectance spectroscopy of Mn–ZSM-5 zeolites.

[Journal of the American Chemical Society 2013, 135 (23),8594-8605]

……………………………………………………………………………………………………………………………………………………………………

The development of sorbents for next-generation CO2 mitigation technologies will require better understanding of CO2/sorbent interactions. Among the sorbents under consideration are shape-selective microporous molecular sieves with hierarchical pore morphologies of reduced dimensionality. We have characterized the non-equilibrium CO2 sorption of OMS-2, a well-known one-dimensional microporous octahedral molecular sieve with manganese oxide framework. Remarkably, we find that the degree of CO2 sorption hysteresis increases when the gas/sorbent system is allowed to equilibrate for longer times at each pressure step. Density functional theory calculations indicate a “gate-keeping” role of the cation in the tunnel, only allowing CO2 molecules to enter fully into the tunnel via a highly unstable transient state when CO2 loadings exceed 0.75 mmol/g. The energy barrier associated with the gate-keeping effect suggests an adsorption mechanism in which kinetic trapping of CO2 is responsible for the observed hysteretic behavior.

[J. Am. Chem. Soc. 2012, 134, 7944-7951]

……………………………………………………………………………………………………………………………………………………………………

Self-assembled multidoped cryptomelane hollow microspheres with ultrafi ne particles in the size range of 4–6 nm, and with a very high surface area of 380 m 2 g − 1 have been synthesized. The particle size, morphology, and the surface area of these materials are readily controlled via multiple framework substitutions. The X-ray diffraction and transmission electron microscopy (TEM) results indicate that the as-synthesized multidoped OMS-2 materials are pristine and crystalline, with no segregated metal oxide impurities. These results are corroborated by infrared (IR) and Raman spectroscopy data, which show no segregated amorphous and/or crystalline metal impurities. The fi eld-emission scanning electron microscopy (FESEM) studies confi rm the homogeneous morphology consisting of microspheres that are hollow and constructed by the self-assembly of pseudo-fl akes, whereas energy-dispersive X-ray (EDX) analyses imply that all four metal cations are incorporated into the OMS-2 structure. On the other hand, thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC) demonstrate that the as-synthesized multidoped OMS-2 hollow microspheres are more thermally unstable than their single-doped and undoped counterparts. However, the in-situ XRD studies show that the cryptomelane phase of the multidoped OMS-2 hollow microspheres is stable up to about 450 ° C in air. The catalytic activity of these microspheres towards the oxidation of diphenylmethanol is excellent compared to that of undoped OMS-2 materials.

[Advanced Functional Materials (2011), 21, 312-323]

……………………………………………………………………………………………………………………………………………………………………

Molecular adsorption and oxidation at manganese oxide/liquid interfaces has attracted increased interest due to its importance in the development of heterogeneous catalysts, microbial fuel cells, and selective adsorption materials. Here we report the adsorption and oxidation of phenolic compounds on Cu2+, Co3+, and Ce4+ doped K-OMS-2 nanofibers. Different metal ion doped K-OMS-2 catalysts show distinct adsorption and oxidation ability. The structure and compositions of doped K-OMS-2 catalysts were characterized by X-ray diffraction and atomic absorption analyses. The relationships of catalyst structure-catalytic properties were discussed. The adsorbed polymeric nanospheres on doped K-OMS-2 nanofibers were investigated by field emission scanning electron microscopy, Fourier transform infared spectroscopy, transmission electron microscopy, and energy dispersive X-ray analyses. These nanospheres were totally oxidized to CO2 in oxygen or air at 553-603 K catalyzed by doped and undoped K-OMS-2 itself. OMS-2 was regenerated with air or oxygen. The chemisorption and oxidation of phenol in an anaerobic environment (N2) demonstrate that lattice oxygen of cryptomelane is involved in these processes. Free-radical mechanisms are proposed for the oxidation of phenol in O2 and for the formation of phenolic nanospheres. Compared with undoped K-OMS-2, metal ion doped K-OMS-2 shows higher adsorption capacity of phenolic compounds and higher phenol removal rate.

[ J. Phys. Chem. C (2010),  XXX, 000, early view]

……………………………………………………………………………………………………………………………………………………………………

Using OMS-2 as the catalyst in C2H6 dehydrogenation in the presence of CO2, is an example where extreme conditions are used to drive high conversions of ethane (>70 %) and CO2 (up to 56 %) with high selectivity towards ethylene (87 %) with a short contact time (0.6 s) .  The reaction pathway involved two steps: ethane catalytic dehydrogenation and a reverse water- gas shift reaction.  High ethylene yields (66 %) were obtained and could be improved by using OMS- 2 as an active support.  This inexpensive material also showed high stability during the process, and the presence of CO2 removed coke depositions throughout the catalyst.  Such impressive activity, selectivity, and stability open up new possibilities for olefin dehydrogenations in the presence of CO2, a perfect feedstock for any process involving ethylene carbonylation with the recycling of the greenhouse gas.

[ ChemCatChem 2009, 1, (4), 441-444 ]

……………………………………………………………………………………………………………………………………………………………………

The invention relates to a method for producing a mixt. of ethylene and carbon monoxide by contacting ethane and carbon dioxide with a catalyst comprising synthetic cryptomelane or octahedral mol. sieve. The invention also provides reactions of ethylene and carbon monoxide with an alc. to produce an alkyl propionate, which can further react with formaldehyde to produce an alkyl methacrylate.

[Eur. Pat. Appl. ( 2010 ), EP 2165997 A1 20100324]

……………………………………………………………………………………………………………………………………………………………………

Cryst. tunnel structure cryptomelane type manganese oxides (OMS- 2) have been studied as photocatalysts for the selective oxidn. of 2- propanol to acetone.  The reaction is carried out with visible light irradn. at room temp.  The activities of various K- OMS- 2 and metal doped OMS- 2 (M- OMS- 2) catalysts prepd. by different synthesis procedures have been evaluated.  K- OMS- 2 and M- OMS- 2 (M = Fe, Ni) with nanorod morphol. were the most active photocatalysts.  Conversions obtained for these catalysts ranged from 50 to 15 %.  K- OMS- 2 fibers gave only 5- 6 % conversion.  All reactions gave 100 % selectivity to acetone.  The reusability of the K- OMS- 2 catalyst was also tested.  Characterization of K- OMS- 2 catalysts was done using several techniques like temp. programmed desorption, UV- vis spectroscopy, av. oxidn. state anal., XRD, BET and FE- SEM.  As suggested by the photochem. and characterization data, synthesis methodol., morphol., mixed valency and the release of oxygen from the OMS- 2 structure are important factors for the design of active OMS- 2 photocatalysts.  XRD and FTIR were also used to study structural changes in the catalyst after photolysis.

[ Applied Catalysis, A: General 2010, 375, (2), 295-302 ]

……………………………………………………………………………………………………………………………………………………………………

Tungsten was successfully doped at 1 and 2 mol % tungsten into the K-OMS-2 framework. Sodium tungstate and tungsten pentabromide were used in a reflux synthesis preparation. The data collected from the characterization methods collectively affirm the substitution of tungsten into the K-OMS-2 framework. Conductivity measurements showed an increase in the resistivity. Conversion of benzyl alcohol to benzaldehyde had a conversion of 25 and 15% for the sodium tungstate and tungsten pentabromide, respectively, while retaining 100% selectivity. Properties such as the resistivity, thermal stability, and crystallinity of the material were altered depending on the amount and type of starting reactants used.

[ Chemistry of Materials ( 2008 ), 20(20), 6382-6388 ]

……………………………………………………………………………………………………………………………………………………………………

The control of synthesis methods allows the preparation of unique materials such as octahedral layer (OL) and octahedral molecular sieve (OMS) systems. These mixed valent porous materials are excellent semiconductors. Conductivity in porous molecular sieve materials is unusual and leads to more favorable characterization such as less charging in relation to insulating materials like clays and zeolites. Semiconductivity of OL and OMS materials allows potential applications as sensors, redox catalysis, and in fuel cells. This review will focus on the use of composition and redox to control the structure, morphology, porosity, catalytic activity, and conductivity of such materials. A major emphasis in this field has been on the generation of new materials and the mechanism of formation of such systems.

[J. Mater. Chem., 2008, 18, 1623–1631]

……………………………………………………………………………………………………………………………………………………………………

Indium-doped manganese oxide materials have been hydrothermally synthesized. Doped indium was found to be in framework sites in synthetic cryptomelane, based on the results of XRD, average oxidation state (AOS) of manganese, Raman, and IR. TEM images show that indium-free OMS-2 and K-In-OMS-2(R=1/5) have a morphology of nanorods. Cyclic voltammetry (CV) was used to test the electrocatalytic activity in the oxygen reduction. CV results show that manganese oxide doped with indium generates electrocatalytic activity for the O 2 reduction reaction.

[Chemistry of Materials (2008), 20(6), 2069-2071]

……………………………………………………………………………………………………………………………………………………………………

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, HRSEM, XRD, IR and adsorbate-IR, N2 and CO2physisorption at 77 and 273 K, respectively, TPD-MS, and TGA-DSC 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 Bro¨nsted and Lewis acid sites. A part of the lattice oxygen atoms can be reversibly removed from the framework and recovered at elevated temperature without changing the framework structure. These lattice oxygen atoms can react with CO even at room temperature and are active sites for the oxidation of benzene. The consumed lattice oxygen atoms are replenished by gaseous oxygen to complete a catalytic cycle. The ease of reversible evolution of lattice oxygen, together with the high porosity, hydrophobicity, and acidity, leads to the excellent oxidation
properties of OMS-2.

[Journal of the American Chemical Society (2008), 130(10), 3198-3207]

……………………………………………………………………………………………………………………………………………………………………

This Account first gives a historical overview of the development of octahedral molecular sieve (OMS) and octahedral layer (OL) materials based on porous mixed-valent manganese oxides. Unique properties of such systems include excellent semiconductivity and porosity. Materials that are conducting and porous are rare and can offer novel properties not normally available with most molecular sieve materials. The good semiconductivity of OMS and OL systems not only permits potential applications of the conductivity of these materials but also allows characterization of these systems where charging effects are often a problem. Porous manganese oxide natural materials are found as manganese nodules, and these materials when dredged from the ocean floors have been used as excellent adsorbents of metals such as from electroplating wastes and have been shown to be excellent catalysts. Rational for synthesis of novel OMS and OL materials is related to the superb conductivity, microporosity, and catalytic activity of these natural materials.

[Accounts of Chemical Research (2008), 41(4), 479-487]

……………………………………………………………………………………………………………………………………………………………………

A new and facile route was developed to manipulate the growth of hierarchically ordered Mn2O3 architectures via a solvothermal approach. Various solvents are employed to control the product morphologies and structures. Mn2O3 with unique cuboctahedral, truncated-octahedral, and octahedral shapes are obtained, and a possible formation mechanism is proposed.

[J. Phys. Chem. C, 2007, 111, 14694-14697]

……………………………………………………………………………………………………………………………………………………………………

[Journal of Inorganic and Organometallic Polymers and Materials, 2007, 17(2), 459-467]

……………………………………………………………………………………………………………………………………………………………………

[Chem. Mater. 2007, 19, 229-234]

……………………………………………………………………………………………………………………………………………………………………

A method for forming an imine comprises reacting a first reactant comprising a hydroxyl functionality, a carbonyl functionality, or both a hydroxyl functionality and a carbonyl functionality with a second reactant having an amine functionality in the presence of ordered porous manganese-based octahedral molecular sieves and an oxygen containing gas at a temperature and for a time sufficient for the imine to be produced.

[U.S. Pat. Appl. Publ., 2007, US 2007027344 , 10pp.]

……………………………………………………………………………………………………………………………………………………………………

[Advanced Functional Materials, 2006, 16(9), 1247-1253]

……………………………………………………………………………………………………………………………………………………………………

[J. Am. Chem. Soc., 2006, 128 (14), 4570 -4571]

……………………………………………………………………………………………………………………………………………………………………

[Journal of Physical Chemistry B, 2006, 110(7), 3066-3070]

……………………………………………………………………………………………………………………………………………………………………

[Journal of the American Chemical Society, 2005, 127(17), 6166-6167]

……………………………………………………………………………………………………………………………………………………………………

[Advanced Materials ( Weinheim , Germany ), 2004, 16(19), 1729-1732]

……………………………………………………………………………………………………………………………………………………………………

[Chemistry of Materials, 2004, 16(25), 5327-5335]