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Schematic illustrations on crystal structure of various manganese oxide catalysts The structures and property relationship of manganese oxides is showed in the Fig.7. The 1D structure differs in arrangement and size of the tunnels. Among them, α-MnO 2 possesses both (2X2) and (1X1) tunnels surrounded by double binding octahedral chains. The β-MnO 2 consists of merely (1X1) tunnels separated by single chains and λ-MnO 2 displays (1X1) and (1X2) tunnels enveloped in double chains.
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Ambient temperature catalytic oxidation of carbon monoxide (CO) has been widely applied in catalytic converters for cleaning of air and lowering the automotive emissions. Carbon monoxide is a very dangerous gas present in automobile exhausts. Manganese oxide catalysts have generated much interest over the last two to three decades due to their diff...
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... which is one of the major reason for catalyst deactivation. In the initial phase decrease in catalytic activity can be attributed to the production of carbonate species on the catalyst surface and occupy the active sites on catalyst by CO 2 [111][112]. The deposition of chemical poisoning on the Mn-oxide catalysts surfaces is showed in the Fig. ...
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DFT theoretical calculations for the Ag2O-induced isomerization process of diaminocarbenes to formamidines, coordinated to Mn(I), have been carried out. The reaction mechanism found involves metalation of an N-H residue of the carbene ligand by the catalyst Ag2O and the formation of a key transition state showing a μ-η2:η2 coordination of the forma...
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... Considering the characterization results, BMC-Ce presented Mn(IV) as the main oxidation state in the bulk (as well as the highest reducibility and the highest oxygen mobility of BMC-A series); meanwhile, BM-Ce presented Mn(III) as the main oxidation state in the bulk. Considering that it is well established that Mn(IV) is more active than Mn(III) for CO oxidation [56,57], the increase in the amount of bulk Mn(IV) in BMC-A with respect to BM-A (caused by the presence of Cu(II)), and only found for BMC-Ce, seems being the main reason for the highest improvement in the catalytic performance featured by BMC-Ce catalyst with respect to BM-Ce. ...
The sol–gel method, adapted to aqueous media, was used for the synthesis of BaMn0.7Cu0.3O3 (BMC) and Ba0.9A0.1Mn0.7Cu0.3O3 (BMC-A, A = Ce, La or Mg) perovskite-type mixed oxides. These samples were fully characterized by ICP-OES, XRD, XPS, H2-TPR, BET, and O2–TPD and, subsequently, they were evaluated as catalysts for CO oxidation under different conditions simulating that found in cars exhaust. The characterization results show that after the partial replacement of Ba by A metal in BMC perovskite: (i) a fraction of the polytype structure was converted to the hexagonal BaMnO3 perovskite structure, (ii) A metal used as dopant was incorporated into the lattice of the perovskite, (iii) oxygen vacancies existed on the surface of samples, and iv) Mn(IV) and Mn(III) coexisted on the surface and in the bulk, with Mn(IV) being the main oxidation state on the surface. In the three reactant atmospheres used, all samples catalysed the CO to CO2 oxidation reaction, showing better performances after the addition of A metal and for reactant mixtures with low CO/O2 ratios. BMC-Ce was the most active catalyst because it combined the highest reducibility and oxygen mobility, the presence of copper and of oxygen vacancies on the surface, the contribution of the Ce(IV)/Ce(III) redox pair, and a high proportion of surface and bulk Mn(IV). At 200 °C and in the 0.1% CO + 10% O2 reactant gas mixture, the CO conversion using BMC-Ce was very similar to the achieved with a 1% Pt/Al2O3 (Pt-Al) reference catalyst.
... Another layered structure of MnO 2 is vernadite MnO 2 ·nH 2 O, a fine grained, poorly crystalline natural Mn oxide phase. Vernadite is a variety of birnessite that is disordered in the layer-stacking direction [ [49], Elsevier, 2020). ...
Apart from our imagination, the nanotechnology industry is rapidly growing and promises that the substantial changes that will have significant economic and scientific impacts be applicable to a wide range of areas, such as aerospace engineering, nanoelectronics, environmental remediation, and medical healthcare. In the medical field, magnetic materials play vital roles such as magnetic resonance imaging (MRI), hyperthermia, and magnetic drug delivery. Among them, manganese oxide garnered great interest in biomedical applications due to its different oxidation states (Mn2+, Mn3+, and Mn4+). Manganese oxide nanostructures are widely explored for medical applications due to their availability, diverse morphologies, and tunable magnetic properties. In this review, cogent contributions of manganese oxides in medical applications are summarized. The crystalline structure and oxidation states of Mn oxides are highlighted. The synthesis approaches of Mn-based nanoparticles are outlined. The important medical applications of manganese-based nanoparticles like magnetic hyperthermia, MRI, and drug delivery are summarized. This review is conducted to cover the future impact of MnOx in diagnostic and therapeutic applications.
... Within soil minerals, manganese primarily exists in the quadrivalent state; however, there is also a substitution of Mn 2þ and Mn 3þ for Mn 4þ , which is balanced by the replacement of O 2À ions with OH À ions. Birnessite ((Na,Ca)Mn 7 O 14 .2.8H 2 O), lithiophorite (LiAl 2 (Mn 2 4þ Mn 3þ )O 6 (OH) 6 ), hollandite (Ba x (Mn 4þ ,Mn 3þ ) 8 O 16 ), todorokite ((Ca,Na,K) x (Mn 4þ ,Mn 3þ ) 6 O 12 .3.5H 2 O), and pyrolusite (β-MnO 2 ) are the manganese-based mineral compositions found in soils [2]. Relating to phase formation, manganese oxides are considered to be the most complex of all other metallic elements [3][4][5][6]. ...
... Birnessite ((Na,Ca)Mn 7 O 14 .2.8H 2 O), lithiophorite (LiAl 2 (Mn 2 4þ Mn 3þ )O 6 (OH) 6 ), hollandite (Ba x (Mn 4þ ,Mn 3þ ) 8 O 16 ), todorokite ((Ca,Na,K) x (Mn 4þ ,Mn 3þ ) 6 O 12 .3.5H 2 O), and pyrolusite (β-MnO 2 ) are the manganese-based mineral compositions found in soils [2]. Relating to phase formation, manganese oxides are considered to be the most complex of all other metallic elements [3][4][5][6]. Manganese oxide is renowned for its remarkable versatility among transition metal oxides due to its capacity to achieve oxidation states ranging from þ4 to þ2. Depending on the temperature and oxygen partial pressure, manganese can give rise to various oxides of MnO, MnO [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. ...
... Manganese oxide is renowned for its remarkable versatility among transition metal oxides due to its capacity to achieve oxidation states ranging from þ4 to þ2. Depending on the temperature and oxygen partial pressure, manganese can give rise to various oxides of MnO, MnO [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Mn 2 O 3 possesses a broad spectrum of uses [6,7,10,11,13,15,16], particularly in the realm of fabric printing and dyeing processes. ...
In this work, few precursors (MnCl2.4H2O, MnCO3, MnO2, and KMnO4) were simply heated at 650ºC for 10 hours and examined their phase formation and thermal features of Mn-based oxides. Cubic Mn2O3 phase materials with space group, Ia-3 (206) formed for the heat treated products of MnCl2.4H2O and MnO2 precursors. However, the purity is differed for the heat treated product of MnCl2.4H2O, for this three weak impurities are noted along with the major Mn2O3 phase. Mixed phases of Mn2O3 and Mn5O8 were observed for the heating of MnCO3 precursor. The resemblance of δ-MnO2 phase was observed for the heat treated product of KMnO4 precursors. While the heat treated products of MnCl2.4H2O, MnCO3, and MnO2 precursors show the low weight loss of 1.5 – 3.3 %, the heat treated KMnO4 precursor shows relatively high weight loss of 22.6 % with weak exothermic and endothermic peaks at 100 and 797°C, respectively. The Mn2O3 nanomaterials exhibit a morphology resembling nanorods.
... Different manganese oxides exhibit variations in chemical properties and oxidation capabilities, which are determined by many factors such as solution, ionic strength, pH, and co-existing ligands. MnO x are stable, economical, efficient, and easy to synthesize in an environment-friendly way (Dey and Kumar, 2020;Frey et al., 2017). They are considered as promising catalysts for water purification (Hocking et al., 2011). ...
In the context of growing arsenic (As) contamination in the world, there is an urgent need for an effective treat-
ment approach to remove As from the environment. Industrial wastewater is one of the primary sources of As
contamination, which poses significant risks to both microorganisms and human health, as the presence of As can
disrupt the vital processes and synthesis of crucial macromolecules in living organisms. The global apprehension
regarding As presence in aquatic environments persists as a key environmental issue. This review summarizes the
recent advances and progress in the design, strategy, and synthesis method of various manganese-based adsor-
bent materials for As removal. Occurrence, removal, oxidation mechanism of As(III), As adsorption on man-
ganese oxide (MnOx)-based materials, and influence of co-existing solutes are also discussed. Furthermore, the
existing knowledge gaps of MnOx-based adsorbent materials and future research directions are proposed. This re-
view provides a reference for the application of MnOx-based adsorbent materials to As removal.
... In the case of manganese oxides [7,8], the oxidation states typically oscillate between Mn 3+ and Mn 4+ rather than Mn 2+ , as suggested by Post et al. [9]. This makes them excellent catalysts in redox catalytic processes [10], such as the oxidation of toluene [11], benzene [12], ethyl acetate [13,14], nitrogen monoxide [15], carbon monoxide [16], alcohols [17], and trichloroethylene [18]. In the work [19], MnO x (1.61 < x < 1.67) was considered to have more remarkable activity than Mn 2 O 3 and Mn 3 O 4 . ...
With the goal of finding low-cost materials that can completely substitute the precious- and noble-containing catalysts and be active toward the oxidation of CO at low temperatures (around 100 °C), transition metal oxide-doped cryptomelane (e.g., K-OMS-2, MeOx/K-OMS-2, and CuOx-MeOx/K-OMS-2; Me = Ni, Fe, Cd, Sn, Mn, Cr, Co, Zn, and Al) were obtained by the impregnation method with different synthesis conditions. The synthesized samples were then tested for CO conversion and characterized by means of powder X-ray diffraction, elemental mapping and composition, as well as scanning electron microscopy. It was demonstrated that the K-OMS-2 support doped by a composite of CuOx-NiOx (promoter) and calcined at 400 °C gave higher catalytic activity than the other samples, with a 90% CO conversion at around 120 °C. Other factors that could be controlled for increasing CuOx-NiOx/K-OMS-2_400 activity were to set the mass percentage of dopants and the atomic ratio of Cu:Ni to about 15 mass% and 1:1, respectively. Under different catalytic reaction conditions such as various inlet CO concentrations (CCO, 750–4000 ppm), amounts of catalyst (mcat, 0.25–1.25 g), and gas-air flow rates (Fgas, 0.5–1.25 L/min), the catalyst activity was found to be enhanced when the CCO and Fgas were reduced and the mcat raised. Moreover, the CuOx-NiOx/K-OMS-2_400 catalyst exhibited high stability and durability. The calculated average size of K-OMS-2 crystallites was approximately 12 nm, while the composite phase was in its amorphous state. This sample showed a morphology of nanofiber-like shapes with different lengths.
Graphical Abstract
... These trends continue for ex situ hydrogen, methane, and ethane, with manganese impregnated alumina generating gases far above the baseline. Various forms of manganese have been used in a wide array of catalytic reactions due to the numerous oxidation states, ranging from the targeting of C-H hydroxylation to assist with the 'magic methyl effect' [62], to promoting oxidation of CO waste streams [63]. The concentrations of available oxygen and operating temperature affect the form manganese oxides commonly take as either MnO 2 , Mn 2 O 3 , or Mn 3 O 4 [64,65] though more states exist. ...
... Excess oxygen present from the Al 2 O 3 may interact with the manganese to form more productive species than its in situ counterpart. Higher oxygen contents and lower temperatures have shown to favor the formation of MnO 2 [63] which may account for the difference in activity. ...
While energy dense liquid biofuels can be produced from sustainable waste feedstocks via thermochemical conversion techniques, these biofuels are plagued by high acidity and low stability, largely due to the presence of oxygenated functional groups. By utilizing transition metal catalysts during pyrolysis either in situ within the biomass, or ex situ (directly downstream supported on an alumina substrate) acting on the pyrolysis vapors, the quality of the bio-oil can be improved via deoxygenation. Four transition metals (Cu, Mn, Ni, Zn) were either wet impregnated on cherry pit biomass, or were impregnated on alumina wool fibers placed downstream of the biomass to act on the devolatilized gases. The in situ catalysts Cu, Mn and Zn increase the pyrolysis bio-oil yield. The Mn, Ni and Zn used as ex situ catalysts increase the total non-condensable gas produced, suggesting that these downstream catalysts crack the pyrolyzed molecules into smaller organics and water. The ex situ catalysts result in larger quantities of especially oxygen-containing gases like CO 2 , which in turn lowered the bio-oil's O/C ratio. However, such reactions also increase the water content of the resulting bio-oil. Both Mn and Zn used in either location enhance the concentration of alcohols relative to aromatic carbons, and when used ex situ, Mn shows a decrease in the ratio of aromatic to aliphatic carbon content.
... As a result, MnO x has been extensively used as heterogeneous oxidative catalyst of organic pollutants (Li et al. 2015). Many methods such as sol-gel, wet chemical precipitation, hydrothermal, reflux, and microwave have been employed to synthesize various shapes of MnO x , such as tubes, wires, tubes, rods, urchin-like, flowers, and plates (Rao et al. 2020, Dey et al. 2020, in different particle sizes, crystallites, and porosity. The synthesis of multidimensional MnO x is particularly preferred for the progress of the catalysis reaction owing to its higher surface area other than complicated structures (Perez-Larios et al. 2016). ...
The present study proposed the synthesis of low-toxicity and eco-friendly spherically shaped manganese oxides (α-MnO2, Mn2O3, and Mn3O4) by using the chemical precipitation method. The unique variable oxidation states and different structural diversity of manganese-based materials have a strong effect on fast electron transfer reactions. XRD, SEM, and BET analyses were used to confirm the structure morphology, higher surface area, and excellent porosity. The catalytic activity of as-prepared manganese oxides (MnOx) was investigated for the rhodamine B (RhB) organic pollutant with peroxymonosulfate (PMS) activation under the condition of control pH. In acidic conditions (pH = 3), complete RhB degradation and 90% total organic carbon (TOC) reduction were attained in 60 min. The effects of operating parameters such as solution pH, PMS loading, catalyst dosage, and dye concentration on RhB removal reduction were also tested. The different oxidation states of MnOx promote the oxidative–reductive reaction under acidic conditions and enhance the SO4•−/•OH radical formation during the treatment, whereas the higher surface area offers sufficient absorption sites for interaction of the catalyst with pollutants. A scavenger experiment was used to investigate the generation of more reactive species that participate in dye degradation. The effect of inorganic anions on divalent metal ions that genuinely occur in water bodies was also studied. Additionally, separation and mass analysis were used to investigate the RhB dye degradation mechanism at optimum conditions based on the intermediate’s identification. Repeatability tests confirmed that MnOx showed superb catalytic performance on its removal trend.
... However, increasing applied voltage might not guarantee an optimal energy efficiency. A high applied voltage caused a high conversion that is negatively correlated with the energy efficiency [21,41]. Therefore, it's essential to find appropriate applied voltage in order to maintain a high energy efficiency. ...
... Ogata et al. (2007) demonstrated that electrons captured on the TiO 2 catalyst's surface excite active lattice oxygen, which is very useful for oxidizing CCl 2 F 2 [16]. According to Dey and Kumar (2020), Mn tends to produce oxides with varying oxidation states, which may affect the characteristics and activity of the catalyst [41]. Through interaction with reducing or oxidant agents, Mn could quickly undergo a reduction-oxidation cycle. ...
... Ogata et al. (2007) demonstrated that electrons captured on the TiO 2 catalyst's surface excite active lattice oxygen, which is very useful for oxidizing CCl 2 F 2 [16]. According to Dey and Kumar (2020), Mn tends to produce oxides with varying oxidation states, which may affect the characteristics and activity of the catalyst [41]. Through interaction with reducing or oxidant agents, Mn could quickly undergo a reduction-oxidation cycle. ...
Dichlorodifluoromethane (CCl2F2/CFC-12) is widely used as refrigerant, foaming agent and aerosol propellant in industry. Due to its chemical stability, CCl2F2 gradually diffuses from the troposphere to the stratosphere once released and catalyzes the destruction of ozone through photodegradation. In addition, CCl2F2 is listed as a potent greenhouse gas with a high global warming potential (GWP = 10.2). Current technologies for treating CCl2F2 include combustion, catalysis, and plasma destruction. This study aims to develop a catalyst with good activity and integrate it with plasma to form a hybrid system for the removal of CCl2F2 from gas streams. The results obtained show that combined plasma with catalyst (plasma catalysis system) is effective in removing CCl2F2 and the highest removal efficiency of 99.0% is achieved for the operating conditions of applied voltage 17 kV, gas flow rate 500 sccm, [CCl2F2] = 800 ppm and [O2] =1%. Nitrogen atoms, excited N2 molecules such as N2(A3Σu+) N*(4S, 2D, 2P) and high-energy electrons generated by plasma are beneficial for the removal mechanism of CFC-12. In the presence of oxygen, the main byproducts of CCl2F2 conversion include CO2, CClF3, N2O and NOx. This study confirms that addition of Mn into TiO2 greatly improves the removal efficiency of CCl2F2 and this system has good potential for industrial application.
... The synthetic routes of getting the nanomaterial from metal oxides are well-known due to their wide application in sensing [14], catalysis [15], as the contrasting agents for fluorescent microscopy or MR imaging [16] and therapy [17]. Similar with the Gd-based nanoparticulate CAs great number of Mn 2+ -CAs are based on manganese oxides (MnO or MnO 2 ), although the production of heterometallic oxides mostly exemplified by manganese-ferrite nanoparticles is also represented by the great number of works [18]. ...
... Over the last couple of decades, transition metal oxides have been manifested as heterogeneous catalysts and possess potential for low temperature catalytic activity for harmful CO oxidation (Jansson, 2000;Jansson et al., 2002;Lin et al., 2003;Wang et al., 2005). Cobalt oxide (Co 3 O 4 ) (Jansson et al., 2002;Yu et al., 2009;Molavi et al., 2021) and manganese oxides (MnO, Mn 3 O 4 , Mn 2 O 3 and MnO 2 ) (Dey and Kumar, 2020;Frey et al., 2012) are the most brilliant candidates owing to the reducible mobile oxygen on the surface to weaken the Co-O and/or Mn-O bond, which easily releases the species of active oxygen or mobile lattice oxygen simultaneously with formation of oxygen vacancies. And next for the CuO and NiO (Royer and Duprez, 2011;Yu et al., 2009) on the CO catalytic oxidation among these transition metal oxides. ...
This work aimed at evaluating the effect of nickle (Ni) dopant on the catalytic performance of Co3 O4 catalyst for abatement of harmful carbon monoxide (CO), a resistance toward sintering and durability of catalytic activity were also pursued. Choose the Co(NO3 )2 ×6H2 O(aq) as precursor and NaOH as precipitant to prepare cobalt oxide (Co3 O4 ) with precipitation method, then calcined at 300 and 500 °C, separately (named as C3 and C5). The Ni dopant (0.1 ~ 5 wt%) was added by deposited precipitation through Ni(NO3)2 ×6H2 O(aq) with drop wisely added NaOH(aq) into suspended Co3 O4 solution, then put the NaOCl for oxidation to obtain series 0.1%Ni-Co3 O4 , 0.2%Ni-Co3 O4 , 1%Ni-Co3 O4 and 5%Ni-Co3 O4 catalysts. All catalysts were characterized through BET, XRD, TEM/SEM, Raman, ICP and TPR instruments, and evaluated the catalytic performance of CO oxidation with a self-devised fluidized micro-reactor. It was observed that the calcination temperature and loading of dopant remarkably influenced the physicochemical characteristics and catalytic performance of the catalysts. Preferential catalyst was obtained for calcination at 300 °C and loading of Ni dopant below 1%. The doping of Ni on the surface of Co3 O4 enhanced the performance due to the inducing of synergistic effect between Co3 O4 and NiO, while the excessive NiO incorporated to the surface constrained the activity due to the abundant NiO on the surface, overlaying the active sites caused the decreasing of surface area and reducible capacity. Among these series Ni-Co3 O4 catalysts, the 0.2%Ni-Co3 O4 (C3) catalyst behaved an eminent activity with T50 of 98 °C and durability without apparent deactivation for 50 hr reaction at 125 °C. The excellent performance is primarily attributed to the synergistic effect and formation of NiCo2 O4 composite oxide.
