MnO2 Catalyst Research Articles

B-Site modification of LaMn0.9Co0.1O3 perovskite using a selective dissolution method in C3H6 oxidation

LaMnCoO3 is treated with HNO3 to generate a Co-doped MnO2 phase, which shows better catalytic performance than LaMnO3 and pure MnO2 catalysts for C3H6 oxidation.

Highly selective electrocatalytic oxidation of benzyl C–H using water as safe and sustainable oxygen source

H2O serves as a safe oxygen source in the electrocatalytic oxidation of benzyl C–H, with significantly improved overpotential and faradaic efficiency on layered MnO2 catalysts.

Microwave-assisted synthesis of gold nanoparticles supported on Mn3O4 catalyst for low temperature CO oxidation

ABSTRACT In the present work, Mn3O4 was prepared by various methods and successfully loaded with metallic Au nanoparticles reduced by hydrazine hydrate using microwave irradiation (MWI) method. The surface morphology and composition of the prepared samples were characterized with X-ray diffraction (XRD), N2 adsorption–desorption, temperature programmed reduction (H2-TPR), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The experimental results showed that no significant changes in some textural and structural properties of the samples due to preparation method or Au nanoparticles deposition. While the surface composition and reducibility of the samples were greatly affected by preparation method and Au deposition. The CO oxidation reaction over the samples was selected as a model reaction to study the relation between surface properties of the samples and their catalytic performance. The results showed that a direct proportionality exists between the reducibility and the CO oxidation activity of catalysts. The kinetic study of the reaction showed that the reaction is first order. Moreover, the samples exhibited good stability in CO oxidation at 100% conversion for around 30 h under the reaction conditions.

Highly efficient mesoporous MnO2 catalysts for the total toluene oxidation: Oxygen-Vacancy defect engineering and involved intermediates using in situ DRIFTS

To elucidate the role of oxygen vacancy defects, various Mn-based oxides with oxygen vacancy defects are employed to the toluene oxidation, which are synthesized by adjusting solvent and double-complexation routes. The MnOx-ET catalyst shows the highest catalytic activity (T90 = 225 °C) for toluene oxidation. Compared with other Mn-based oxides, the as-prepared MnOx-ET catalyst has more surficial oxygen vacancies and good oxygen storage capacity (OSC), which is the reason on its remarkable activity for toluene oxidation. In addition, in situ DRIFTS study reveals that both lattice oxygen and adsorbed oxygen species can participate in the activation-oxidation process of toluene, which results in two reaction routes for the toluene oxidation. The rich oxygen-vacancy concentration of catalysts accelerates the key steps for the activation and generation of oxidized products. Quasi-in situ XPS results further confirm that enrich adsorbed-oxygen species as active oxygen and increasing Mn4+ concentration enhance the superior activity for toluene oxidation.

Catalytic oxidation of toluene over MnO2 catalysts with different Mn (II) precursors and the study of reaction pathway

MnO2-Ac, MnO2-N, MnO2-Cl and MnO2-S samples were prepared by the redox reaction between potassium permanganate and manganese acetate, manganese nitrate, manganese chloride and manganese sulfate and the effect of Mn (II) precursor on the toluene oxidation was studied. The physicochemical properties of these samples were characterized by XRD, TEM, N2 asdorption-desorption isotherms, H2-TPR and XPS. Results showed that the catalytic activity of the four samples decreased in the order of MnO2-Ac > MnO2-N > MnO2-Cl > MnO2-S, which was highly related to the specific surface areas, oxygen vacancy concentration and the content of adsorbed oxygen. MnO2-Ac owned potential for practical applications. It showed superior toluene oxidation activity with T90 of 200 °C, as well as excellent water-resistance and stability during 50 h at 300 °C. The good catalytic activities under high WHSV and high toluene concentration were also observed over MnO2-Ac. Moreover, the reaction pathway of toluene oxidation was presented with the aid of In-situ DRIFTS.

Preparation and characterization of Cu–Mn composite oxides in N2O decomposition

A series of CuxMn composite oxide catalysts with different Cu/Mn molar ratios (x = 1, 1.5 and 2) was synthesized by the co-precipitation method. The catalytic performance of CuxMn in N2O decomposition has been studied with a continuous flowing microreactor system. The obtained catalysts were characterized by XRD, BET, Raman, FT-IR, ICP-AES and H2-TPR. The catalytic tests show that the CuxMn catalysts exhibit more excellent N2O catalytic decomposition activity compared with the pure CuO and Mn2O3 catalysts, and the Cu1.5Mn shows the highest catalytic activity under the reaction conditions of N2O 0.1%, GHSV 10000 h−1. The characterizations results suggest that bulk CuO and Mn2O3 existed in pure CuO and Mn2O3 catalysts, respectively. In the CuxMn catalysts, with the decreasing of x, the amount of bulk CuO gradually decreases until it disappears, while the amount of newly formed CuMn2O4 gradually increases. However, the amount of small crystal CuO increases first and then decreases, which might be considered as an important active phase that contributes to the excellent catalytic performance of CuxMn in N2O decomposition.

Highly efficient Mn2O3 catalysts derived from Mn-MOFs for toluene oxidation: The influence of MOFs precursors

The effect of Mn-MOFs precursors (Mn-MIL-100, Mn-MOF-74 and Mn-BTC) on the performance of Mn2O3 catalysts pretreated with different atmosphere (Ar, O2 and O2 after Ar treatment) for toluene oxidation is investigated in this work, respectively. The characteristics of the catalysts are investigated by using scanning electron microscope (SEM), the X-ray diffraction (XRD), Brunauer Emmett Teller (BET), X-ray photoelectron spectroscopy (XPS) and H2 temperature programmed reduction (H2-TPR). It is observed that Mn-MIL-100 pretreated with Ar and then with O2 (Mn-100-Ar-O) shows better catalytic activity for toluene oxidation than Mn-MIL-100 pretreated with single Ar or O2. Furthermore, MOFs precursors have strongly influence on the structure and performance of Mn2O3 catalysts. The order of catalytic activity is as follows: Mn-100-Ar-O > Mn-BTC-Ar-O > Mn-74-Ar-O. In addition, Mn-100-Ar-O exhibits high stability, circulation performance and water resistance. The catalytic performance of Mn-100-Ar-O is obviously improved with the better reduction at low-temperature and the increase of surface molar ratio of Mn3+/Mn4+ and Oads/Olatt.

Investigation of promotion effect of Cu doped MnO2 catalysts on ketone-type VOCs degradation in a one-stage plasma-catalysis system

Acetone and methyl ethyl ketone are two typical ketone-type VOCs which are commonly used as solvent in manufacturing factories. Their removal under plasma-catalysis over Cu-doped MnO2 catalysts were carried out in a coaxial dielectric barrier discharge (DBD) reactor in this study. The effects of Cu doping on the removal efficiency and CO2 selectivity of two ketone-type VOCs in this system are deeply investigated and compared as a function of specific energy density (SED). Experimental results show that the introduction of the Cu-doped MnO2 catalysts significantly enhances the VOCs removal performance and CO2 selectivity. Among them, Cu0.133Mn presents the highest removal efficiency (97% for methyl ethyl ketone and 82.1% for acetone) and the best CO2 selectivity (91.7% for methyl ethyl ketone and 89.4% for acetone) at the SED of ~600 J L−1 and a high GHSV of 300,000 mL·(g·h)−1. Based on the structure-function analysis of catalysts, it is believed that the synergistic effect between Cu and Mn in Cu-Mn solid solution can promote the amount of surface active oxygen and reducibility to improve catalytic performance. Furthermore, with the help of in situ FTIR and GC–MS, it is found that Cu-doped MnO2 catalysts can not only accelerate the VOCs degradation rate but also improve the oxygen and ozone utilization for VOCs complete oxidation. Besides, the possible degradation pathways of two ketone-type VOCs under the plasma and plasma-catalysis process have also been suggested and discussed at last.

A novel synthesis of MnO[formula omitted], nanoflowers as an efficient heterogeneous catalyst for oxidative desulfurization of thiophenes

[Mn2(bit)4 (H2O)2] complex was used in this study as a novel precursor for the synthesis of MnO2 nanoflowers. The inorganic precursor was synthesized from the reaction between chloride salt of Mn(II) and benzisothiazolinate. The chemical composition and the nanostructure of the prepared MnO2 catalyst was characterized using several identification techniques (XRD, Thermal gravimetry, FTIR, N2-physisorption, and SEM-EDX). The results showed that the new precursor is a suitable Mn source for the synthesis of highly crystalline MnO2 nanoflowers of a small particle size with a large surface area. Manganese dioxide nanoflowers were examined for its catalytic ability in the oxidative desulfurization process of a model and real diesel fuels. Oxidative desulfurization conditions have been found to influence the removal efficiency of thiophene, 4,6-dimethyldibenzothiophene and dibenzothiophene. The optimum desulfurization parameters were examined, and the results show that the amount of catalyst is 0.5 g, extraction solvent/ oil ratio is 6, reaction time is 35 min, reaction temperature is 65°C and oxidant: sulfur (O/S) mole ratio is 4. Under these optimum conditions, the MnO2 catalyst is capable of removing more than 95% of thiophenes from commercial and crude diesel, in the presence of tert-butyl hydroperoxide (TBHP) as an oxidant. The newly prepared catalyst is recyclable for seven sequential oxidative desulfurization runs without the requirement for reactivation steps. This catalytic reaction including TBHP as an effective oxidant was presented through a suggested mechanistic pathway.

Incorporating Pb2+ Templates into the Crystalline Structure of MnO2 Catalyst Supported on Monolith: Applications in H2O2 Decomposition.

Several MnO2 catalysts, promoted with Pb2+ ions and supported on a wash-coated monolith (WMon), briefly, xPbyMn-WMon (x = 0, 0.5, 1.0, 1.5, 2, and 2.5 and y = 8 wt %), were prepared. The presence of Pb2+ affects the manganese oxidation state, crystalline phase, thermal resistance, metal dispersion, and catalytic performance. According to XPS spectra, XRD patterns and HRTEM images, manganese was dispersed on the monolith surface as Mn3+ and Mn4+ species in both α and β crystalline phases. The ratios of Mn4+/Mn3+ states and α/β phases were highly enhanced, and the desired PbxMn8O16 phase (coronadite) was formed. Concentrations of the defect oxygen (Mn–O–H) and oxygen vacancies, which improve the catalyst reducibility and the MnO2 reduction temperature, were also increased. Further, based on the H2 chemisorption analysis, the Pb2+ template would increase the manganese dispersion and the reaction sites. Meanwhile, the average MnO2 crystallite size was decreased from 13.26 to 8.15 nm. The optimum catalyst 1.5Pb8Mn-WMon exhibited an activity 149% more than the manganese-only catalyst in decomposition of H2O2. Evaluation of catalyst stability in the presence of Pb2+ after 10 recycles showed only a 6.8% decrease. The catalytic reaction was evaluated based on different criteria.

Plasma-induced redox reactions synthesis of nanosized α-, γ- and δ-MnO2 catalysts for dye degradation

Mesoporous α- and δ-MnO2 with specific surface areas of 98 and 186 m2/g, were obtained via plasmachemical-reduction of KMnO4 solutions induced by flashing them with a gliding arc plasma operated at respectively high and low voltages. Correspondingly, γ- and δ-MnO2 with 48 and 289 m2/g, were obtained via plasmachemical-oxidation of Mn(CH3COO)3 solutions. At lower humid airflow, the plasma also led during the reduction of KMnO4 to changes of structure and morphology, and to increased specific surface areas. These changes are hypothesized to be due to a variation of the amount of radicals generated by the plasma along its creation parameters. Performances of the prepared catalysts were evaluated in the oxidation of Tartrazin Yellow (TY) chosen as a model dye polluting wastewaters. TY bleaching was significantly different from one plasma-synthesized material to another. α-MnO2, being the best of the plasma synthesized material appears to be recyclable and resistant to dissolution. This contribution confirms the importance of mastering the structure and texture of MnO2 catalysts during their synthesis. Gliding arc plasma is revealed as an easy and efficient method to achieve so.

MnO2/Al foil decorated air cleaner with self-driven property for the abatement of indoor formaldehyde

In this work, a self-driven indoor formaldehyde cleaner is designed by integrating α-MnO2 with exposed (3 1 0) crystal facet onto an electrothermal carbon membrane. The integrated device features bi-functions (air cleaning, and heating) and consists of four parts: painted board, the carbon membrane, the aluminum (Al) board, and the MnO2 decorated Al (Mn/Al) foil. The electrothermal carbon membrane can convert electrical energy into heat energy. At the maximum power of 846 W, the saturated temperature can be up to 97.1 °C and the heated MnO2 catalysts inhibit the accumulation of intermediates (formate and bicarbonate species) during formaldehyde abatement process. Furthermore, due to the temperature difference, the generated gradient force drives the movement of the gas and leads to the formation of four large recirculation zones in a simulated room, which facilitates the air disturbance. As a result, the concentration of formaldehyde in a chamber reduced from 1.24 to 0.13 mg/m3 in 90 min at operating temperature of 97.1 °C. More importantly, the contribution of temperature to mass transfer was comparable (only 11.9% less) to that of the fan disturbance reinforcement, which makes it possible to operate without additional fan assistance. This type of air cleaner by integrating MnO2 catalysts with heating equipment not only utilizes the residual heat to prolong the life span of active components but also provides a novel idea for the design of indoor formaldehyde cleaner.

Applications of Electron Beam to Environmental Conservation

The treatment of electron beam was tested for gaseous pollutants of volatile organiccompounds (VOCs), dioxin, and inorganic oxides (NOX and SOX). The representative VOCs of xylene and toluene were oxidized completely with electron beams using prototype hybrid system equipped with electron accelerator and MnO2 catalysts. More than 90% of dioxin in municipal solid waste incinerator gases was decomposed at a dose of 14 kGy. Nitrogen oxides and sulfur oxides in coal-fired flue gases were recovered as a fertilizer by the addition of NH3 under electron-beam irradiation.Electron beam is expected to be a promising method for treating gaseous pollutants.

Highly selective oxidation of amines to imines by Mn2O3 catalyst under eco-friendly conditions

Enhancing the selectivity of imines for the oxidative self-coupling of primary amines was found to be challenging in the heterogeneous catalysis. Three different manganese oxides (M-3, M-4, M-5) were synthesized by controlling the calcination temperature using a simple template-free oxalate route. The prepared manganese oxides were systematically characterized using XRD, N2 sorption, SEM, TEM, XPS, H2-TPR techniques. M-4 gave 96.2% selectivity of imine at 100% conversion of benzylamine, which was far more superior than other existing protocols. Mn3+/Mn4+ ratio was found to affect the selectivity of the imines. The probable reaction pathway for amines oxidation catalyzed by manganese oxides was proposed for the first time.

A Gas Diffusion Layer Impregnated with Mn3O4‐Decorated N‐Doped Carbon Nanotubes for the Oxygen Reduction Reaction in Zinc‐Air Batteries

AbstractMn3O4‐decorated N‐CNTs are synthesized and impregnated into porous carbon paper (gas diffusion layer or GDL) to form a composite catalyst‐GDL material in a simple and novel one‐pot process. The impregnated electrode features high active surface area, improved discharge performance, and reduced vulnerability to flooding when compared with other electrode preparation techniques for similar catalysts. Electrochemical and battery testing show catalytic activity and a maximum discharge potential superior to other CNT supported Mn3O4 catalysts, and comparable to commercially used Pt−Ru (1.21 V at 20 mA cm−2). The composite is cycled at 10 mA cm−2 and 20 mA cm−2 as a bifunctional catalyst and as an oxygen reduction reaction (ORR) exclusive catalyst, respectively. Discharge performance is stable over 200 cycles at 20 mA cm−2 when used exclusively for ORR with a discharge‐charge efficiency superior to Pt−Ru when coupled with electrodeposited Co−Fe as the OER catalyst (efficiency of 59 % after cycling).

Modelling of emerging contaminant removal during heterogeneous catalytic ozonation using chemical kinetic approaches

This study evaluated the prediction of emerging contaminant (EC) removal during heterogeneous catalytic ozonation by chemical kinetic models. Six ECs with differing ozone reactivity were spiked in a synthetic water and a groundwater, then treated by conventional ozonation and heterogeneous catalytic ozonation with α- or β-MnO2 catalysts. Results show that catalysts did not considerably influence the removal of ECs with high and intermediate ozone reactivity (diclofenac, gemfibrozil, and bezafibrate), but enhanced the removal efficiencies of ECs with low ozone reactivity (2,4-dichlorophenoxyacetic acid, clofibric acid, and ibuprofen) to varied extent (˜10–30%). The removal efficiencies of ECs could be reasonably predicted using chemical kinetic models based on the ozone (O3) and hydroxyl radical (OH) rate constants of ECs, pseudo-first-order rate constants observed for EC adsorption on the MnO2 catalysts, and O3 and OH exposures observed for catalytic ozonation. Furthermore, the model reveals that ECs are removed mainly by O3 and/or •OH oxidation during heterogeneous catalytic ozonation, while adsorption of ECs on catalysts contributes negligibly. Therefore, the removal efficiencies of ECs could be satisfactorily predicted using a simplified model based only on the O3 and OH rate constant and the O3 and OH exposures.

Mesoporous Mn2O3 rods as a highly efficient catalyst for Li-O2 battery

Li-O2 batteries are considered as one of the future candidates for electrochemical power sources due to their high theoretical energy density. As the dominating component affects the performance of Li-O2 batteries, O2-cathode catalyst with high efficiency, low price, facile preparation is important. Herein, polyhedral and porous Mn2O3 rods are fabricated for cathode catalysts in Li-O2 batteries via electrospinning method followed by calcination. The Mn2O3 catalyst possesses a three-dimensional porous structure, which can offer good catalytic activity, expose plenty of active sites and improve the diffusion of electrolyte and O2. When employed as the cathode catalyst, the Li-O2 batteries show enhanced initial discharge capacity of 9701 mA h g−1 at a current density of 200 mA g−1, superior rate capacity and good cycling stability within 160 cycles at the capacity of 500 mA h g−1. These enhanced performances demonstrate a facile method to fabricate Mn2O3 with unique structure as a promising catalytic material for Li-O2 batteries.

A New Understanding of Mn3O4 Catalysts Different Fuels for Highly Selective Oxidation of Cyclohexene

A New Understanding of Mn₃O₄ Catalysts Different Fuels for Highly Selective Oxidation of Cyclohexene

Electro-assisted catalytic wet air oxidation of organic pollutants on a MnO@C/GF anode under room condition

Catalytic oxygen (O2) activation for oxidative removal of pollutants under ambient condition is important for pollution control. Herein, we report a hybrid of MnO catalyst confined in a porous carbon matrix on a graphite felt support (MnO@C/GF) for electro-activation of O2 toward degradation of various pollutants at ambient condition. The electro-assisted catalytic wet air oxidation (ECWAO) process on anodic MnO@C/GF is able to completely mineralize dyes and typical pharmaceuticals and personal care products. Mechanistic studies indicate the oxidation of the organic pollutants in the ECWAO process involves chemisorption of O2 on MnO, activation of the chemisorbed oxygen species via electro-oxidation reaction, and oxidation of organic pollutants by the activated chemisorbed oxygen species. The carbon matrix prevents MnO leaching during the ECWAO process, thus endowing the composite with excellent stability and reusability. The process demonstrates high efficiency, low energy input and environmental friendliness, exhibiting a great potential for practical wastewater treatment.

Ceramic-monolith-supported La0.8Ce0.2MnO3 catalysts for toluene oxidation

A series of ceramic monolith (cordierite, corundum and mullite-cordierite) supported La0.8Ce0.2MnO3 catalysts for toluene oxidation were prepared and characterized to study the structure-activity relationship. The effects of loading and support were investigated by discussing the specific surface area, reduction ability, oxygen vacancies, and toluene oxidation efficiency. Finally, the optimum catalyst was obtained; when loading of La0.8Ce0.2MnO3 was 15 wt% and the carrier was cordierite, the catalyst exhibited the largest specific surface area (21.4 m2·g−1) and best toluene conversion (T50 = 167 °C, T90 = 273 °C).