Oxide Molecular Sieve Research Articles

Semiconducting and magnetic Fe-incorporated cryptomelane powders and foams: Synthesis, characterization and properties

Iron and manganese are both cheap and abundant in resources. Iron-containing octahedral manganese oxide molecular sieves have drawn great interests for their wide range of applications, of which current investigations, however, still remain at the level of macroscopic zero dimensional materials (i.e., powders). In this research, free-standing, macro 3D iron-incorporated cryptomelane foams were prepared through higher temperature hydrothermal crystallization, resuspension and subsequent lyophilization without applying any binder. The combination of XRD, ICP, FT-IR and Raman studies verified successful incorporation of iron into cryptomelane framework. As promising tunable ferromagnetic semiconducting 3D materials, the morphology, electrical properties, mechanical properties as well as magnetic properties (SQUID) of iron-incorporated cryptomelane foams were also investigated.

Ru-modified Octahedral Manganese Oxide Molecular Sieve (Ru-OMS-2) as a Reusable Heterogeneous Catalyst in Selective Oxidation of Olanzapine and Other Polycyclic Compounds

Ru-modified Octahedral Manganese Oxide Molecular Sieve (Ru-OMS-2) as a Reusable Heterogeneous Catalyst in Selective Oxidation of Olanzapine and Other Polycyclic Compounds

Synthesis, characterization and properties of indium-doped manganese oxide molecular sieve sponges

Free-standing In-doped cryptomelane sponges are synthesized by resuspension/freeze-drying process. In-doping generates new FT-IR bands, weaken Raman bands, boost the activity of electrocatalytic oxygen reduction, and enhance electrical conductivity.

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

Metal substitution of molecular sieve systems is a major driving force in developing novel catalytic processes to meet current demands of green chemistry concepts and to achieve sustainability in the chemical industry and in other aspects of our everyday life. The advantages of metal-substituted molecular sieves include high surface areas, molecular sieving effects, confinement effects, and active site and morphology variability and stability. The present review aims to comprehensively and critically assess recent advances in the area of tetra- (Ti, Sn, Zr, Hf) and pentavalent (V, Nb, Ta) metal-substituted molecular sieves, which are mainly characterized for their Lewis acidic active sites. Metal oxide molecular sieve materials with properties similar to those of zeolites and siliceous molecular sieve systems are also discussed, in addition to relevant studies on metal-organic frameworks (MOFs) and some composite MOF systems. In particular, this review focuses on (i) synthesis aspects determining active site accessibility and local environment; (ii) advances in active site characterization and, importantly, quantification; (iii) selective redox and isomerization reaction applications; and (iv) photoelectrocatalytic applications.

Catalytic performance and sulfur resistance of OMS-2 modified by copper for mercury removal at low temperature

Cu-doped manganese oxide molecular sieve catalysts (Cu-OMS-2) are prepared by hydrothermal synthesis method, and their Hg0 removal ability and sulfur resistance are investigated experimentally under simulated flue gas conditions. It indicated that appropriate proportion of Cu doped could increase both the content of Mn4+ active sites on the catalyst surface and the BET specific surface area. The maximum specific surface area of these catalysts is 260.49 m2/g, with the Cu/Mn molar ratio of 0.025. A highest Hg0 removal efficiency of 93.6 % is achieved by the catalyst with Cu/Mn molar ratio of 0.05. SO2 in flue gas significantly inhibits the Hg0 removal ability of OMS-2-H120, but its suppression ability is relatively weak after the addition of Cu to OMS-2-H120. The Hg0 removal efficiency of Cu0.05-OMS-2 can reach 92 % even in the presence of 1000 ppm SO2. The doping of Cu on OMS-2 enhances SO2 adsorbed by CuO, inhibiting the reaction of SO2 with the active center on the catalyst surface. It reduces the generation of sulfate and enhances the sulfur resistance ability of Cu0.05-OMS-2. The process of Hg0 oxidation by O2 over Cu0.05-OMS-2 is found to follow Mars-Maessen mechanism based on the characteristics of fresh and spent catalysts. Elemental mercury is firstly chemisorbed on the Cu0.05-OMS-2 catalyst surface and then oxidized.

Comprehensive evaluation of cobalt incorporated cryptomelane-type manganese oxide molecular sieve as an efficient adsorbent for enhanced removal of europium from wastewater systems

Extraction of radionuclide contaminants from wastewater systems has recently drawn widespread attention, and then developing a novel and green extracting technology has also become an enormous challenge. Herein, a facile hydrothermal method was employed to fabricate cobalt-incorporated cryptomelane-type manganese oxide molecular sieve (Co-OMS-2) for extraction Eu(III) from wastewater under diverse experimental conditions. All kinds of characterized techniques, such as SEM, TEM, XRD, FTIR, BET, EDS and XPS had verified the qualified synthesis process and splendid structural features of the Co-OMS-2. The maximum adsorption capacity of Co-OMS-2 was 7.62 × 10−4 mol/g for Eu(III) at 298 K, which was superior than primarily traditional materials reported previous literatures. The high adsorption capacity of Eu(III) onto Co-OMS-2 was primarily attributed to high specific surface area and abundant surface functional groups, and the interactions were mainly contributed to strong surface complexation and electrostatic attraction. Under the condition of low pH, the outer-sphere surface complexation and cation exchange were primary mechanisms to Eu(III) adsorption onto Co-OMS-2 composites, while inner-sphere surface complexation was mainly assigned to Eu(III) adsorption onto Co-OMS-2 under the high pH sections. The Co-OMS-2 composite achieved equilibrium in a relatively short time, and this excellent performance was conducive to the treatment of Eu(III) under the extreme emergency conditions. In view of the extraordinary adsorption capacity and recycled reusability, the Co-OMS-2 composites can be as prospective adsorbents adopted for the extraction of Eu(III) in real wastewater management.

Novel synthesis of highly dispersed molybdenum oxide over nanorods cryptomelane octahedral manganese oxide molecular sieve (MoOx/nanorod-OMS-2) as a high performance catalyst for oxidative desulfurization process

Oxidative desulfurization(ODS) is an effective method for obtaining fuels that contain ultra-low sulfur. The purpose of this paper is to prepare a novel and effective bifunctional heterogeneous catalytic system for the desulfurization process by using nanorods cryptomelane octahedral manganese oxide molecular sieve(nanorod-OMS-2) and molybdenum oxide as active components. The MoOX/nanorod-OMS-2 catalysts were synthesized with different molybdenum loadings. The catalytic activities were evaluated for oxidative desulfurization of dibenzothiophene (DBT) in the presence of H2O2 and acetonitrile. Results of characterization analyzes showed that the synthesized catalysts contain the conventional surface area, pore-volume, mixed micro-mesoporous structures, and the molybdenum oxides species highly dispersed on the nanorod-OMS-2 surface. A synergistic effect was observed between Mn and Mo species which created strong acidic sites. In addition, the activity of catalysts is dependent on the composition of meso-microporous structures and the presence of strong acidic sites due to the interactions between the Manganese‑molybdenum oxide species. In optimum condition over the Mo(7.5 wt%)/nanorod-OMS-2 catalyst, the percentage of sulfur removal was achieved to 99%. The kinetic of ODS reaction was studied, and the pseudo-first-order rate law was obtained with respect to DBT. The reusability of Mo(7.5 wt%)/nanorod-OMS-2 was studied and the efficiency of catalyst has decreased from 99% to 98% during three cycles. The effects of oxidant/sulfur molar ratio, reaction time, reaction temperature were studied, and the optimum values were 8:1, 2 h and 65 °C, respectively.

One‐Pot Hydrothermal Synthesis for a Manganese Oxide Molecular Sieve for Application in Mercury Removal in Chloride‐Free Flue Gas

AbstractOMS‐2 (manganese oxide octahedral molecular sieve) were prepared by one pot hydrothermal method under different temperatures in this work, and their performances of oxidizing elemental mercury (Hg0) in the flue gas derived from coal combustion were evaluated. Moreover, the effects of the reaction temperature and flue gas component on Hg0 oxidation ability of these catalysts were also investigated. It is found that OMS‐2 catalysts have an excellent mercury oxidizing ability under 100–200 °C, and 94 % Hg0 oxidation efficiency could be achieved by catalyst prepared under 120 °C (OMS‐2‐H120) in the chlorine free flue gas. The process of elemental mercury oxidation over OMS‐2‐H120 by O2 is found to follow Mars‐Maessen mechanism based on the XPS and FTIR analysis of the fresh and spent catalysts. NO is the precursors of the active species such as NO−, NO2, which is benefit to improve Hg0 oxidation ability of OMS‐2‐H120. SO2 have a negative effect on Hg0 oxidation over OMS‐2‐H120 while water vapor exhibits nearly no influence.

Biomimetic superhydrophobic films drop-coated with zinc oxide modified molecular sieves

Superhydrophobic films have a wide range of applications in industry due to their hydrophobic and self-cleaning properties. A simple and economical method is proposed in this paper to prepare a superhydrophobic surface by creatively using microstructures consisting of zinc oxide particles on molecular sieves. The combination of zinc oxide particles and molecular sieves are embedded into polydimethylsiloxane films to form stable biomimetic superhydrophobic surfaces. In this way, a superhydrophobic surface with a water contact angle of up to 162.3° and a water rolling angle of about 3.2° have been prepared. The surface has excellent self-cleaning ability, thermal stability, water impact resistance, UV stability and environmental friendliness. The film could be prepared using a drop-coating method, which greatly broaden the range of applications for the superhydrophobic film.

Water-in-salt electrolyte enabled active carbon||Mg-OMS-1 capacitor-batteries with high voltage and wide operating temperature

Aqueous lithium-ion batteries possess great potential due to their low cost and high safety. However, the narrow voltage window of the electrolyte significantly hinders their energy density and electrode materials selection. Herein, sheet-like todorokite-type magnesium manganese oxide molecular sieve (Mg-OMS-1) is synthesized and applied as cathode materials for aqueous lithium-ion batteries with water-in-salt electrolyte. The water-in-salt lithium difluorosulfonimide (LiTFSI) electrolyte enlarges the working window of the device and enhance the capacity of the Mg-OMS-1. Mg-OMS-1 displays a high capacity, remarkable rate ability, and stable cycling performance. Moreover, the water-in-salt electrolyte promises the device to work in the temperature range of 0–70 ℃. In addition, an active carbon (AC)|15 mol kg−1 LiTFSI|Mg-OMS-1 capacitor battery is designed and assembled. The device presents a capable electrochemical performance, demonstrating the potential application of the water-in-salt electrolyte and Mg-OMS-1 for the aqueous batteries with high energy density and wide operating temperature.

Effect of Ce metal modification on the hydrothermal stability of Cu-SAPO-34 catalyst

A series of copper-cerium composite oxide molecular sieve catalysts (Cu-Ce/SAPO-34) were prepared by impregnation method, and the effects of Ce loading on the hydrothermal stability of Cu/SAPO-34 catalyst were discussed. The reasons for the difference in activity and stability of different catalysts were analyzed by XRD, SEM, H2-TPR, XPS, and NH3-TPD. The present studyshowed that hydrothermal aging at 750°C did not cause the chabazite (CHA) framework of Cu-Ce/SAPO-34 catalyst to collapse, but destroyed part of the pore structure and acid sites, and reduced the crystallinity of the catalyst surface. Hydrothermal aging promoted tensile distortion of the catalyst lattice, causing Cu2+ to migrate to the catalyst surface, and Cu2+ and Ce4+ clustered to form CuO and CeO2, which resulted in the reduction of the Cu active species and the decrease of the oxygen hole concentration of the catalyst. Therefore, the performance of Cu-Ce/SAPO-34 for the selective catalytic reduction of NOx by NH3 (NH3-SCR) decreased. Ce doping could increase the amount of Cu2+ and Cu+ active species on the surface of Cu/SAPO-34 catalyst, reduce Cu species clusters to form CuO, and improve the distribution of active Cu species on the catalyst surface. Increasing the loading of Ce could stabilize the structure of Cu-Ce/SAPO-34 catalyst and maintain themedium and weak acid sites, thereby improving its hydrothermal stability. The results indicated that the Cu/Ce mass ratio of 4:5 had the best hydrothermal stability among the series of Cu-Ce/SAPO-34 catalysts in this study.

Review of Researches on SCR Catalyst with Low Temperature and high Sulfur Tolerance and Theoretical Design

Selective catalytic reduction (SCR) of nitrogen oxides (NOx) using ammonia (NH3) is currently the main technology for flue gas denitration. However, the currently widely used commercial catalysts (such as V2O5-WO3 / TiO2, V2O5-MoO3 / TiO2, etc.) have the disadvantages of high operating temperature, narrow active temperature window, and high catalytic cost. Therefore, in recent years, researchers have devoted themselves to the development of low-cost and efficient low-temperature SCR catalytic materials. This paper summarizes the research progress of low-temperature (less than 250 °C) selective catalytic reduction of NOx by unsupported metal oxide catalysts, supported metal oxide catalysts, precious metals, and molecular sieve catalysts. Among them, manganese-based catalysts show good low-temperature selectivity and stability, and have good application prospects. Finally, the research directions of manganese low temperature SCR catalysts are prospected and theoretically designed based on the existing problems.

Octahedral magnesium manganese oxide molecular sieves as the cathode material of aqueous rechargeable magnesium-ion battery

Aqueous magnesium-ion batteries have shown the desired properties of high safety characteristics, similar electrochemical properties to lithium and low cost for energy storage applications. The micro-sheet morphology of todorokite-type magnesium manganese oxide molecular sieve (Mg-OMS-1) material, which applies as a novel cathode material for magnesium-ion battery, is obtained by the simple hydrothermal method. The structure and morphology of the particles are confirmed by X-ray power diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma, scanning and transmission electron microscopy. The electrochemical performance of Mg-OMS-1 is researched by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and constant current charge-discharge measurement. Mg-OMS-1 shows a good battery behavior for Mg2+ insertion and deinsertion in the aqueous electrolyte. When discharging at 10mAg−1 in 0.2moldm−3 MgCl2 aqueous electrolyte, the initial discharge capacity reaches 300mAhg−1. The specific capacity retention rate is 83.7% after cycling 300 times at 100mAg−1 in 0.5moldm−3 MgCl2 electrolyte with a columbic efficiency of nearly 100%.

Heterogeneous selective synthesis of 1,2-dihydro-1,3,5-triazines from alcohols and amidines via Cu/OMS-2-catalyzed multistep oxidation

Copper supported on octahedral manganese oxide molecular sieve (OMS-2) which was obtained via reducing KMnO4 by TBHP was prepared and found to be an efficient catalyst for the synthesis of 1,2-dihydro-1,3,5-triazines directly from alcohols and amidines in one-pot via multistep oxidation. The recyclable heterogeneous catalyst was characterized by BET, XRD, FTIR, TEM and SEM, and the catalytic system can tolerate a wide range of substrates under air with low catalyst loading of supported copper (0.25mol%), employing OMS-2 as the electron-transfer mediator (ETM) and support.

Heterogeneous synthesis of 1,4-enediones and 1,4-diketones with manganese oxide molecular sieves OMS-2 as a recyclable catalyst

An efficient manganese oxide octahedral molecular sieves OMS-2-catalyzed chemoselective synthesis of 1,4-enediones and 1,4-diketones from 1,3-dicarbonyls and α-iodoacetophenones is described. The present catalytic system can be applied in one-pot, three-component reactions of methyl ketones, 1,3-dicarbonyls and iodine. Moreover, OMS-2 can be reused at least 5 times without loss of activity.

High performance of manganese oxide octahedral molecular sieve adsorbents for removing sulfur compounds from fuel gas

Properties of porous manganese oxide adsorbents for adsorptive removal of tert-butylmercaptan (TBM) from CH4 fuel gas were investigated at ambient temperature and atmospheric pressure. The adsorbents were prepared by oxidation reactions of Mn2+ with KMnO4 and via the sol-gel method by reduction of KMnO4 using fumaric acid as the reducing agent. The effects of preparation method, precursor, temperature, and time for the structure and desulfurization properties of the resulting adsorbents were studied. Cryptomelane octahedral manganese oxide molecular sieve (OMS-2) adsorbents exhibited high breakthrough TBM adsorption (1.3–2.5mmol g-1) with the properties varied by the synthesis condition. The OMS-2-Ac prepared by the oxidation reactions of manganese acetate resulted in smaller OMS-2 crystallites with higher surface area compared to those prepared from manganese sulfate and chloride precursors, and it exhibited an enhanced TBM adsorption uptake. TBM adsorption capacity of OMS-2 could be further enhanced by introducing Cu into the structure. This gave rise to a markedly high TBM breakthrough adsorption (7.4mmol g-1) for Cu-OMS-2 (7.8 wt% Cu doping), which is significantly greater than the values reported for activated carbon, zeolite, and other porous oxide based solid adsorbents at similar conditions in the literature.

Construction and O2 sensing performance of a core–shell structured magnetic-mesoporous composite functionalized with a ruthenium complex

In the present work, a core–shell structured magnetic-mesoporous composite was functionalized with a ruthenium complex and applied for site-specific oxygen sensing purpose. Superparamagnetic ferroferric oxide and silica molecular sieve MCM-41 were used as the inner core and the outer shell, respectively. A 5H-cyclopenta[1,2-b:5,4-b′]dipyridin-5-one (Dafo) derived ligand and its corresponding Ru(II) complex were covalently grafted into MCM-41 tunnels, serving as sensing probe. Electron microscopy photos, XRD patterns, IR spectra, thermogravimetry and N2 adsorption/desorption measurement were performed to confirm and characterize this core–shell structure. It was found that emission of this composite decreased with increasing O2 concentrations, making it a potential oxygen sensing system. Sensitivity of 5.62 and short response time of 10 s were observed.

A magnetic mesoporous nanocomposite modified with a ruthenium complex for site-specific molecular oxygen sensing: Construction and characterization

In this paper, we constructed a core–shell structured organic–inorganic hybrid composite, where superparamagnetic ferroferric oxide and silica molecular sieve MCM-41 were used as the inner core and the outer shell, respectively. A Ru(II) complex was covalently grafted into these MCM-41 tunnels. Electron microscopy images, XRD analysis, IR spectra, thermogravimetry and N2 adsorption/desorption analysis were applied to confirm this Ru(II)-functionalized hybrid composite. Emission of this composite decreased with increasing O2 concentrations, which made itself an O2 sensing system. High selectivity (12.2), linear working curve (linearity=0.99) and short response time (12s) were obtained from this composite.

A luminescent-magnetic nanocomposite for Hg(II) recognition and extraction: Preparation, characterization, sensing and removal performance

The present paper constructed an organic–inorganic hybrid composite with core–shell structure for Hg(II) sensing, where superparamagnetic ferroferric oxide and silica molecular sieve MCM-41 were used as the inner core and the outer shell, respectively. A rhodamine derivative was firstly modified by sulfur substitution and then covalently connected to MCM-41 tunnels. This composite was supposed to recognize and extract Hg(II) ions. Electron microscopy images, X-ray diffraction analysis, IR spectra, thermogravimetry and N2 adsorption/desorption analysis were performed on this composite, which confirmed its structure. It was found that emission of this composite increased with increasing Hg(II) concentrations, showing emission “off–on” effect. High selectivity, linear working curve and good recycling performance were obtained from this composite.

The Role of Ti and Lewis Acidity in Manganese Oxide Octahedral Molecular Sieves Impregnated with Titanium in Oxidation Reactions

Octahedral manganese oxide molecular sieves (OMS-2) was prepared by precipitation method and modified by impregnation of titanium with different titanium/manganese (Ti/Mn) ratio. It was also discovered that Ti/Mn ratio of less than 0.5 still retains the original pure cryptomelane structure of OMS-2. However, for sample with Ti/Mn ratio of more than 0.5, some rutile phases of titania (TiO2) can be detected together with the cryptomelane phase. Lewis acid sites were also observed in the titanium modified OMS-2 (Ti-OMS-2). Ti-OMS-2 was then used as catalysts for the oxidation of cyclohexane, cyclohexene and styrene, where Ti-OMS-2 with Ti/Mn ratio of 0.67 was most active in all three of the oxidation reactions as compared to TiO2 and OMS-2. The results suggest that both titanium sites in framework and non-framework and the Lewis acidity created by the impregnation of Ti, increased the activity of OMS-2 in oxidation reactions. © 2014 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)