Mn-Fe Catalyst Research Articles

Enhanced Heterogeneous Fenton Degradation of Organic Dyes by Bimetallic Zirconia-Based Catalysts.

The qualitative impact of pollutants on water quality is mainly related to their nature and their concentration, but in any case, they determine a strong impact on the involved ecosystems. In particular, refractory organic compounds represent a critical challenge, and several degradation processes have been studied and developed for their removal. Among them, heterogeneous Fenton treatment is a promising technology for wastewater and liquid waste remediation. Here, we have developed mono- and bimetallic formulations based on Co, Cu, Fe, and Mn, which were investigated for the degradation of three model organic dyes (methylene blue, rhodamine B, and malachite green). The treated samples were then analyzed by means of UV-vis spectrophotometry techniques. Bimetallic iron-based materials achieved almost complete degradation of all three model molecules in very short time. The Mn-Fe catalyst resulted in the best formulation with an almost complete degradation of methylene blue and malachite green at pH 5 in 5 min and of rhodamine B at pH 3 in 30 min. The results suggest that these formulations can be applied for the treatment of a broad range of liquid wastes comprising complex and variable organic pollutants. The investigated catalysts are extremely promising when compared to other systems reported in the literature.

Synergistic promotion effects of surface hydroxyl groups (-OH) and nitrate groups (-NO3) on catalytic ozonation of toluene over MnFe catalyst

A series of MnFe catalysts were prepared by hydrothermal synthesis combined with heat treatment at different temperatures. The characterizations demonstrated that MnFe-120 with both surface -OH and -NO3, MnFe-175 with surface -OH, MnFe-300 containing neither surface -OH nor -NO3, and MnFe-300-NO3 containing surface -NO3 were gained by drying or calcination and impregnation. The activity evaluation showed that the order of catalytic activity was MnFe-120 > MnFe-175 > MnFe-300-NO3 > MnFe-300. Further, characterizations and experiment results revealed that O3 adsorbed on the surface of the catalyst can interact with surface -OH and generated hydroxyl radicals (·OH). The presence of surface -NO3 provided more Lewis acid sites, thereby promoting H2O adsorption and conversion to the surface -OH, which supplemented the surface -OH consumed by the interaction with O3. It was deduced that the coexistence of surface -OH and -NO3 improved the production of·OH, which synergistically promoted the catalytic ozonation of toluene.

Theoretical insights into the performance of single and double transition metal atoms doped on N-graphenes for N2 electroreduction

Single- and double-atom catalysts are normally with high activity and selectivity in N2 electroreduction. However, the properties of impacting their catalytic performances in N2 reduction are still unclear. In order to gain insights into the factors that influence their performances, we have theoretically studied N2 activation and reduction on eight catalysts, including two single-atom catalysts with Mn/Fe supported on nitrogen doped graphenes (N-graphenes), and six double-atom catalysts in which Mn and Fe atoms form three non-bonded centers (Mn⋯Mn, Fe⋯Fe and Mn⋯Fe) and three bonded centers (Mn-Mn, Fe-Fe and Mn-Fe) on N-graphenes. Our calculational results indicate that the two single-atom catalysts and the three non-bonded double-atom catalysts can’t efficiently activate N2 or convert it into NH3, whereas the bonded double-atom catalysts can not only efficiently activate but also convert N2 at low overpotentials. Especially, the bonded Mn-Fe catalyst is found to be the most efficient catalyst due to its very lower overpotential (0.08 V) for N2 reduction reaction among the eight catalysts. Moreover, the charge analysis revealed that the electron-donating capacities and the synergistic effects of the two bonded metal atoms are both responsible for the enhanced catalytic performances.

Effect of hierarchical element doping on the low-temperature activity of manganese-based catalysts for NH3-SCR

A series of metals doped Mn-Me-Mx (Me = Fe, Cu, Ce; Mx = Ce, Mg, Co, Ni, W) catalyst were synthesized by a co-precipitation method for low-temperature selective catalytic reduction of NOx with NH3. The results showed that among the binary oxides catalysts, the Mn-Fe catalyst exhibited the best low-temperature activity, and more than 80 % NOx conversion in a reaction temperature range of 150−200 °C. and the ternary oxide catalysts Mn-Fe-Ce (0.1) prepared on this basis can reach about 95 % NOx conversion and excellent the tolerance of SO2 and H2O at the same condition. The activity test results indicate that Ce-modification has a clear promoting effects on low temperature activity and resistance to SO2 and/or H2O of the Mn-Fe catalyst. The effect of element doping on physiochemical properties of catalyst were investigated by XRD, BET, XPS, NH3-TPD and H2-TPR. The results show that there is a strong interaction between Ce, Co or Ni and Mn, Fe oxides, resulting in high dispersibility and reduced crystallinity of these oxides. In addition, the results always prove doping Ce could not only prominently modify and optimize the structure of mixed metal oxides, but also increase the relative content of Mn4+, Mn3+, Fe3+ and surface oxygen (Oα) of Mn-Fe catalyst. Moreover, The specific surface area of the catalyst was increased and its surface acidity was strengthened after Ce doping, which is beneficial to increase the adsorption of NH3. Finally, The typical Eley-Rideal mechanism over Mn-Fe-Ce (0.1) were proposed via the in situ DRIFTs experiments.

The Influence of the Support on the Activity of Mn–Fe Catalysts Used for the Selective Catalytic Reduction of NOx with Ammonia

Mono and bimetallic Mn–Fe catalysts supported on different materials were prepared and their catalytic performance in the NH3–SCR of NOx was investigated. It was shown that Mn and Fe have a synergic effect that enhances the activity at low temperature. Nevertheless, the activity of the bimetallic catalysts depends very much on the support selected. The influence of the support on the catalyst activity has been studied using materials with different textural and acid–base properties. Microporous (BEA-zeolite), mesoporous (SBA15 and MCM41) and bulk (metallic oxides) materials with different acidity have been used as supports for the Mn–Fe catalysts. It has been shown that the activity depends on the acidity of the support and on the surface area. Acid sites are necessary for ammonia adsorption and high surface area produces a better dispersion of the active sites resulting in improved redox properties. The best results have been obtained with the catalysts supported on alumina and on beta zeolite. The first one is the most active at low temperatures but it presents some reversible deactivation in the presence of water. The Mn–Fe catalyst supported on beta zeolite is the most active at temperatures higher than 350 °C, without any deactivation in the presence of water and with a 100% selectivity towards nitrogen.

Performance of an innovative VUV-PCO purifier with nanoporous TiO2 film for simultaneous elimination of VOCs and by-product ozone in indoor air

An innovative vacuum ultraviolet photocatalytic oxidation (VUV-PCO) air purifier, consisting of a photocatalytic unit bearing nanoporous TiO2 film, an ozone removal unit bearing Mn-Fe catalyst and a radial fan, was designed and constructed. The performance of the VUV-PCO air purifier in simultaneous elimination of VOCs and O3 by-product was, for the first time, evaluated in a sealed actual room. The evaluation was conducted in both intermittent on/off and continuous operations. The results illustrated that the air purifier had high efficiency in removing formaldehyde and moderate efficiency in removing benzene, toluene, ofm-xylene, ortho-xylene, pentanal, octanal and nonanal, which were released from particleboard into the sealed room. During the removal of formaldehyde decomposition and TVOC in intermittent three-time on/off operation, the air purifier exhibited good stability. During the operation without heating, the air purifier had high formaldehyde and TVOC removal efficiencies, reaching values of about 48.00% and 78.71%, respectively after 90 min. During the continuous operation, the air purifier was able to continuously and effectively remove formaldehyde, benzene homologues, aldehyde and ketone compounds, while the ozone removal unit was able to effectively eliminate ozone generated during VUV photocatalysis. The removal of TVOC by 38.25% was reached after 240 min. In addition, heating the ozone removal unit was found to not only accelerate the release of VOCs from particleboard, but also promote the decomposition of ozone. The ozone removal unit operated with heating was able to reduce ozone content from 250 to 75 ppb.

Effect of Mn loading onto MnFeO nanocomposites for the CO2 hydrogenation reaction

This work describes the preparation of mesoporous xMnFe oxide (x=0, 0.05, 0.1, 0.2, 0.3 and 0.5 molar ratios) nanocomposites through a one-step sol–gel process in the presence of a triblock copolymer as a structure-directing agent. The prepared oxides were used as catalysts in the CO2 hydrogenation via Fischer–Tropsch reactions for the production of valuable hydrocarbons. Among the catalysts, the 0.05MnFe catalyst performed best under the selected reaction conditions: a reaction temperature of 340°C, overall pressure of 20bar, reactant mixture of 23% CO2/69% H2/8% N2 and flow rate of 20mLmin−1. This catalyst provided a much higher conversion of CO2 to hydrocarbons (63.2%C2–C5, 3.9% to C6+ and 3.6% to oxygenates) and the lowest levels of CO and methane formation among the xMnFe series. Moreover, 0.05MnFe was the only catalyst with a mesoporous structure, and it had a substantially lower reduction temperature than did the other members of the series. The enhanced catalytic activity of the 0.05MnFe catalyst, which contains only a small amount of Mn, appears to result primarily from its high specific area and relatively easy reduction.

Decomposition of high-level ozone under high humidity over Mn–Fe catalyst: The influence of iron precursors

Manganese–iron mixed oxide, an efficient and stable catalyst, has been successfully used in the decomposition of ozone. The influence of different iron precursors on the catalytic decomposition activity of high-level ozone under high-humidity over manganese–iron catalysts prepared using a hydrothermal approach was studied. The catalytic performance over MnFe0.5Ox–Fe(NO3)3 was much better than that of MnFe0.5Ox–FeSO4 and MnFe0.5Ox–FeCl3. From the results of characterization by N2 physical adsorption, XRD, XPS and SEM, it was concluded that the largest specific surface area, the lowest crystallinity, the most evenly distributed particle size and the most surface-active Mn2+ and Mn3+ led to the best catalytic activity for the MnFe0.5Ox–Fe(NO3)3 catalyst.

Modeling and kinetic analysis of CO2 hydrogenation using a Mn and K-promoted Fe catalyst in a fixed-bed reactor

Hydrogenation of CO2 to hydrocarbons is investigated over γ-alumina-supported modified iron-based catalysts under fixed-bed reactor conditions to produce unsaturated hydrocarbons as feedstock chemicals for jet-fuel synthesis. The results are compared to those obtained in a continuously stirred tank/thermal reactor (CSTR) environment. It is shown that the maximum C2–C5+ yield obtained in the fixed-bed experiments is 49% higher than those obtained by CSTR at lower gas hourly space velocity (GHSV) of 0.000093liters per second gram (L/s-g). However, at much higher GHSV (0.0015L/s-g), C2–C5+ yield is reduced by 47% in the fixed-bed environment. Modeling and kinetic analysis of the data obtained under fixed-bed reactor conditions is expanded upon by including the formation of methane as a by-product and providing kinetic constants. The results show that our Fischer–Tropsch (FT) reaction rate is much slower than the reverse water gas shift (RWGS) reaction rate. Therefore the FT reaction becomes the rate-controlling step in overall conversion of CO2 to olefins. The model was further expanded to show the potential beneficial effects of water removal from the reactor on CO2 conversion and product yield.

Catalytic conversion of syngas to olefins over Mn–Fe catalysts

Abstract A series of MnO 2 –Fe 2 O 3 with various contents of Mn (0–40% atomic ratio) was synthesized by the co-precipitation method. XRD patterns indicate that the sharp and intense peaks are related to the excellent crystal quality of α-Fe 2 O 3 nanostructures. HR-TEM images showed that α-Fe 2 O 3 and MnO 2 , were partly in close contact and the lattice fringes exhibit the typical distances, i.e., α-Fe 2 O 3 (104) (2.7 A) and MnO 2 (310) (3.1 A). X-ray photoelectron spectroscopy (XPS) results of the Fe 2p core-level binding energy spectrum of the α-Fe 2 O 3 and Mn 2p, indicated the presence of Fe 3+ and Mn 4+ . The direct synthesis of olefins from syngas was carried out over the MnO 2 –Fe 2 O 3 catalysts under pressurized fixed-bed continuous flow conditions. The results showed that Mn–Fe catalyst had high catalytic activity and high olefins selectivity without the addition of any promoters at low pressure. It was found that the catalyst containing 20 at% Mn–Fe was an optimal catalyst for the conversion of synthesis gas to hydrocarbons especially light olefins. The maximum CO conversion rate was 15%, and the yield of olefins (totally about 23.77%) with a predominance of CH 4 (12.24%), and C 2 H 6 (2.80%) components. Mn–Fe catalyst can be regarded as a potential candidate for catalytic conversion of biomass-derived syngas to olefins.

Influence of the addition of transition metals (Cr, Zr, Mo) on the properties of MnOx–FeOx catalysts for low-temperature selective catalytic reduction of NOx by Ammonia

The co-precipitation and citric acid methods were employed to prepare MnOx–FeOx catalysts for the low-temperature selective catalytic reduction (SCR) of NOx by ammonia. It was found that the Mn–Fe (CP) sample obtained from the co-precipitation method, which exhibited low crystalline of manganese oxides on the surface, high specific surface area and abundant acid sites at the surface, had better catalytic activity. The effects of doping different transition metals (Mo, Zr, Cr) in the Mn–Fe (CP) catalysts were further investigated. The study suggested that the addition of Cr can obviously reduce the take-off temperature of Mn–Fe catalyst to 90°C, while the impregnation of Zr and Mo raised that remarkably. The texture and micro-structure analysis revealed that for the Cr-doped Mn–Fe catalysts, the active components had better dispersion with less agglomeration and sintering and the largest BET surface specific area. In situ FTIR study indicated that the addition of Cr can increase significantly the surface acidity, especially, the Lewis acid sites, and promote the formation of the intermediate –NH3+. H2-TPR results confirmed the better low-temperature redox properties of Mn–Fe–Cr.

Preparation, Characterization and Decolorization Performance of Magnetic Fe-Mn Binary Oxide with High Surface Area

Magnetic mesoporous Mn-Fe oxide catalyst with high surface area was prepared by calcining the corresponding oxalate precursor. The calcined sample was characterized by XRD, FTIR, N2 adsorption, TEM, and SEM. The catalytic property of the porous Mn-Fe oxide catalyst was evaluated by catalytic decolorization of methyl orange (MO). XRD, SEM, and TEM analysis and N2 adsorption–desorption isotherm revealed mesoporous Mn-Fe oxide strucutre with high-surface area and uniform pore-size distribution. The results of catalytic performance measurements showed that the Mn-Fe binary oxide was an effective catalyst. The as-prepared catalyst could be recycled as a magnetically separatable catalyst to treat dye-containing wastewater.

Carbon-supported, [alkali metal] [Fe 2Mn(CO) 12]-derived catalysts : Adsorption properties and catalytic behavior in carbon monoxide hydrogenation

The properties of carbon-supported Fe, Fe Mn, and alkali metal (AM) Fe Mn catalysts derived from stoichiometric carbonyl clusters have been characterized by hydrogen and carbon monoxide adsorption, integral heat of adsorption measurements on both fresh and used catalysts, and kinetic studies of the carbon monoxide hydrogenation reaction. The precursors employed were Fe 3(CO) 12, N(C 2H 5) 4[Fe 2Mn(CO) 12] and AM[Fe 2Mn(CO) 12], with AM representing Li, Na, K, Rb or Cs so that the entire family of AM promoters was studied under identical conditions. The support was a microporous carbon prepared from olive pits activated in carbon dioxide which had a BET surface area of 876 m 2/g. Nitrogen adsorption at 77 K and carbon dioxide adsorption at 273 K gave quite similar adsorbed amounts for all the iron-containing samples. High iron dispersion was attained with the Fe 3(CO) 12 cluster but addition of manganese reduced carbon monoxide chemisorption, and further addition of an AM to a sample cluster resulted in a smaller additional decrease except for the Na[Fe 2Mn(CO) 12] precursor, which gave the highest uptake among the AM-promoted catalysts. Importantly, it is shown that active catalysts can be obtained without a prereduction step when these carbon-supported clusters are handled under anaerobic conditions, and high selectivities to light alkenes were attained with the promoted samples. The integral carbon monoxide heat of adsorption at 300 K on the supported, manganese-promoted iron crystallites was consistent with recent values for bulk Mn Fe catalysts, and the highest Q ad value was obtained by the further addition of potassium to the Mn Fe catalyst.