Manganese Nitrate Precursor Research Articles

Effects of ferric and manganese precursors on catalytic activity of Fe-Mn/TiO2 catalysts for selective reduction of NO with ammonia at low temperature.

Fe-Mn/TiO2 catalysts were prepared through the wet impregnation process to selective catalytic reduction of NO by NH3 at low temperature, and series of experiments were conducted to investigate the effects of key precursors on their SCR performance. Ferric nitrate, ferrous sulfate, and ferrous chloride were chosen as Fe precursors while manganese nitrate, manganese acetate, and manganese chloride as Mn precursors. These precursors had been commonly used to prepare Fe-Mn/TiO2 catalysts by numerous researchers. The results showed that there were distinct differences in NO conversion efficiencies at low temperature of catalysts prepared with different precursors. Catalysts prepared with ferric nitrate and manganese nitrate precursors exhibited the best catalytic performance at low temperature, while three kinds of catalysts prepared with manganese chloride precursors exhibited significantly low catalytic activity. All catalysts were characterized by XRD, SEM, H2-TPR, NH3-TPD, and XPS. The results indicated that when the catalysts were prepared with manganese nitrate or manganese acetate as precursors, Mn4+ contents and Oβ/(Oβ+ Oα) ratios decreased in an order of ferric nitrate > ferrous sulfate > ferrous chloride, which was consistent with the change of catalytic activities of the corresponding catalysts at low temperature. It can be found that the excellent catalytic performance of Fe(A)-Mn(a)/TiO2 was ascribed to high redox property and enrichment of Mn4+species and surface chemical labile oxygen groups.

Precursor and dispersion effects of active species on the activity of Mn-Ce-Ti catalysts for NO abatement

Mn-Ce-Ti catalysts were prepared by different precursors (including manganese nitrate, manganese acetate, and manganese chloride) and used for selective catalytic reduction (SCR) of NO with ammonia. The relationships among the structure, physicochemical properties, and catalytic activity were explored by N2 adsorption/desorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), scanning electron microprobe (SEM) and energy dispersive spectroscopy (EDS) techniques. The results show that the different Mn precursors play important roles in the catalytic activity. The Mn-Ce-Ti(N) catalyst synthesized by manganese nitrate precursor exhibits the best catalytic activity, while the Mn-Ce-Ti(C) and Mn-Ce-Ti(Cl) catalyst prepared by manganese acetate and manganese chloride, respectively, exhibit relatively low catalytic activity. The manganese nitrate precursor could promote the specific surface area and redox ability, enhance the amounts of Bronsted and Lewis acid sites, and enrich the surface active species such as Mn4+, Ce3+ and surface chemisorbed oxygen of the catalyst, all of which will contribute to the SCR performance. Moreover, the Mn-Ce-Ti(N) catalyst possesses highly dispersed and uniform surface active species, which will result in the optimal physicochemical properties and superior catalytic performance.

Mn/beta and Mn/ZSM-5 for the low-temperature selective catalytic reduction of NO with ammonia: Effect of manganese precursors

Two series of Mn/beta and Mn/ZSM-5 catalysts were prepared to study the influence of how different Mn precursors, introduced to the respective parent zeolites by wet impregnation, affected the selective catalytic reduction (SCR) of NO by NH3 across a low reaction temperature window of 50–350 °C. In this study, the catalysts were characterized using N2 adsorption/desorption, X-ray diffraction, X-ray fluorescence, H2 temperature-programmed reduction, NH3 temperature-programmed desorption and X-ray photoelectron spectroscopy. As the manganese chloride precursor only partially decomposed this primarily resulted in the formation of MnCl2 in addition to the presence of low levels of crystalline Mn3O4, which resulted in poor catalytic performance. However, the manganese nitrate precursor formed crystalline MnO2 as the major phase in addition to a minor presence of unconverted Mn-nitrate. Furthermore, manganese acetate resulted principally in a mixture of amorphous Mn2O3 and MnO2, and crystalline Mn3O4. From all the catalysts screened, the test performance data showed Mn/beta-Ac to exhibit the highest NO conversion (97.5%) at 240 °C, which remained >90% across a temperature window of 220–350 °C. The excellent catalytic performance was ascribed to the enrichment of highly dispersed MnOx (Mn2O3 and MnO2) species that act as the active phase in the NH3-SCR process. Furthermore, together with a suitable amount of weakly acidic centers, higher concentration of surface manganese and a greater presence of surface labile oxygen groups, SCR performance was collectively enhanced at low temperature.

Structural analysis of manganese oxides supported on SiO2 for benzene oxidation with ozone

Catalytic oxidation of benzene with ozone was carried out over SiO2-supported manganese oxides (Mn/SiO2) prepared by impregnation methods using two kinds of manganese precursors, manganese nitrate and acetate. The structure of manganese oxides were characterized by X-ray diffraction and X-ray absorption measurements and effects of the manganese oxide structures on their catalytic properties were investigated. EXAFS studies revealed that by using manganese nitrate precursor in catalyst preparation, aggregated manganese oxides Mn2O3 were formed, whereas highly dispersed manganese oxides were formed when manganese acetate precursor was used. In both cases, the structures were not strongly affected by the manganese loading levels. The average oxidation state estimated form the absorption edge in the XANES region was also almost unchanged by changing the manganese loading for both catalysts. The catalytic activities of Mn/SiO2 for benzene oxidation with ozone at 343K were much higher for the catalysts prepared from manganese acetate precursors than those prepared from manganese nitrate precursor at any given manganese loading levels, indicating that highly dispersed manganese oxides on SiO2 exhibited much higher activities for the reaction than the aggregated manganese oxides on SiO2. The product distribution and the efficiency for ozone utilization were not so much affected by the manganese oxide structures.

Effect of Sulfur on Mn/Ti Catalysts Prepared Using Chemical Vapor Condensation (CVC) for Low-Temperature NO Reduction

Mn/Ti catalysts prepared through impregnation of manganese acetate and a manganese nitrate precursor via the chemical vapor condensation (CVC) method were investigated in this study to assess NH3-selective catalytic reduction (SCR) activity. Manganese (Mn) loaded on a synthesized TiO2 catalyst showed good low-temperature NO reduction activity and better resistance to sulfur poisoning in presence of SO2. Mn loaded on synthesized TiO2 prepared from manganese acetate precursor especially exhibited a high NO conversion of 98.4% at 150 °C. Moreover, it presented high NO conversions within the entire operating temperature window in comparison with other catalysts, which may be attributed to smaller particle size, scattered amorphous Mn over the catalyst surface, higher dispersion, and an abundant Mn2O3 phase. X-ray photoelectron spectroscopy (XPS) analysis of the spent catalyst following the SCR reaction in presence of SO2 verified that the formation of sulfated titanium and manganese sulfate was significantly ...

Alumina-supported manganese oxide sorbent prepared by sub-critical water impregnation for hot coal gas desulfurization

Manganese oxide was loaded on the surface of γ-Al2O3 by sub-critical water impregnation using manganese acetate and manganese nitrate precursors to synthesize Mn(A) and Mn(N) sorbents for removing H2S from hot coal gas. Active component precursors present very obvious effect on the desulfurization capacity of sorbent. Mn(A, 11) sorbent with 11% Mn content in γ-Al2O3 maintains a desulfurization efficiency of close to 100% over 480min. However, it reduces to below 90% for Mn(N, 11) sorbent when the reaction lasts over 75min. The characterizing results of fresh and used sorbents from different precursors using AAS, SEM, BET, Raman, XAS and XPS techniques show that the acidity and alkalinity of active component precursor solution greatly influences the loading rate, valence state and dispersion of manganese on γ-Al2O3, which are the main properties for improving desulfurization performance of sorbents. The manganese loading rate of Mn(A) sorbent is much higher than Mn(N) sorbent. The better dispersion of manganese on γ-Al2O3 and the higher Mn2+ and Mn3+ contents on the surface of sorbent afford the high desulfurization activity of Mn(A). Moreover, Mn(A, 11) performs well in removing H2S from hot gas at 400°C after three desulfurization -regeneration cycles.

Preparation and Characterization of MnO<sub>X</sub>-CeO<sub>2</sub>/TiO<sub>2</sub> Catalytic Material for SCR of NO<sub>X</sub> with NH<sub>3</sub> at Low Temperature

The MnOX-CeO2/TiO2 catalytic material for low temperature SCR of NOX with NH3 was prepared using aqueous solutions of three manganese salt as well as cerous nitrate and TiO2(anatase) powder by impregnation method. The properties of the catalytic materials were investigated by TG-DSC, XRF, XRD, XPS, BET and SEM. And the low temperature catalytic activity of the catalytic materials was measured. The results showed that, when manganese nitrate and manganese chloride and manganese acetate were used as precursors, respectively, the primary phases of catalytic materials were MnOx/MnO2, MnO2/Mn8O10Cl3 and Mn3O4/MnO2, the surface Mn/Ti molar ratio were 0.68, 0.19 and 0.88, the surface area were 45.1m2/g, 25.1 m2/g and 48.6 m2/g ,respectively. The optimum NOX conversion rate of catalytic material from manganese nitrate precursor and manganese chloride precursor and manganese acetate precursor were 97.9% at 483K, 86.6% at 513K, 97.2% at 423K, respectively. Consequently, the higher low-temperature activity of MnOX-CeO2/TiO2 from manganese acetate precursor may be attributed to higher surface and higher surface concentration of activity component.

Low-temperature NO oxidation over Mn/TiO2 nanocomposite synthesized by chemical vapor condensation: Effects of Mn precursor on the surface Mn species

Mn/TiO2 nanocomposite materials for low-temperature selective NO oxidation was prepared through the impregnation of manganese acetate or manganese nitrate precursors on TiO2 particles fabricated by chemical vapor condensation. Improved low-temperature NO conversion resulted when manganese acetate precursor was used: NO oxidation activity was maximized at 88% at 225°C. The materials were characterized by BET, XRD, HR-TEM, XPS and H2-TPR. The increased activity was attributed to the manganese acetate precursor providing well-dispersed Mn species on the material’s surface and increasing its surface area. Abundant Mn3+ species, hydroxyl groups, increased oxygen linking to Mn, and high concentrations of amorphous Mn on the surface resulted in the material’s improved activity towards NO oxidation at lower temperatures.

A Highly Active and Selective Manganese Oxide Promoted Cobalt-on-Silica Fischer–Tropsch Catalyst

A highly active and selective manganese oxide-promoted silica-supported cobalt catalyst for the Fischer–Tropsch reaction is reported. Co/MnO/SiO2 catalysts were prepared via impregnation of a cobalt nitrate and manganese nitrate precursor, followed by drying and calcination in an NO/He flow. The catalysts were studied with STEM–EELS, infrared spectroscopy measurements of adsorbed CO and Steady-State Isotopic Transient Kinetic Analysis experiments. Based on those experiments, a relation between C5+-selectivity and surface-coverages of CH x -intermediates on cobalt was found.

Stabilization of ZnMnO3 phase from sol–gel synthesized nitrate precursors

The stabilization and analysis of pure ZnMnO3 phase may help to understand the solubility limits of Mn in ZnO in wurtzite and cubic structures. In this report, synthesis and characterization of stable ZnMnO3 phase is discussed which is extracted from sol–gel synthesis of zinc and manganese nitrate precursors. The reflections at higher diffraction angles for this known cubic system with space group Fd3 m were calculated with the help of JADE 8.0 program. The reliability factor for ZnMnO3 calculated from Rietveld refinement was 2%. A narrow phase pure ZnMnO3 stabilization region was identified with the help of energy dispersive spectroscopy mapping. High resolution X-ray photoelectron spectroscopy measurements of Mn3p position of ZnMnO3 compared with ZnMn2O4 showed a higher binding energy shift ~0.85 eV indicating Mn4+ valence state in ZnMnO3.

Effects of Processing Parameters on the Morphology of Precipitated Manganese Oxide Powders

It is desirable that the surface area of catalytic materials can be controlled by adjusting the processing parameters. In this paper we report that the morphology of precipitated manganese oxide powders after 500 °C calcination is affected by the volume ratio between the manganese nitrate precursor and ammonium hydroxide and also by the concentration of the precursor solution. When a large amount of ammonium hydroxide (nominal concentration of NH4OH in the final suspension greater than 4 N) was used, the synthesized powder had plate-like particles with higher specific surface area compared to spherical particles made by a small amount of ammonium hydroxide (nominal concentration of NH4OH less than 1 N). Thinner plates were synthesized from the system with lower nominal concentration of Mn(NO3)2, resulting in even higher specific surface area. The surface area differences between these powders synthesized by different conditions decreased as the calcination temperatures increased from 500 to 900 °C because the high calcination temperatures eliminated the morphology difference among them.

Effects of precursors on the surface Mn species and the activities for NO reduction over MnO /TiO2 catalysts

Abstract TiO2-supported manganese oxide catalysts were prepared from two different precursors, manganese nitrate (MN) and manganese acetate (MA), and these samples were characterized by BET, XRD, TG/DTA, XPS and FT–IR. The characterization results showed that the MN precursor resulted primarily in MnO2, accompanied with some Mn-nitrate, while the MA precursor caused mainly Mn2O3 species. These two different precursors also led to different surface Mn atom concentrations indicated by XPS and NH3 adsorption. Consequently, the higher low-temperature activity of MnOx/TiO2 from MA precursor was attributed to higher surface Mn concentration and the surface Mn2O3 species.

Oxygen reduction reaction on nanosized manganese oxide particles dispersed on carbon in alkaline solutions

In this work a manganese oxide dispersed on a high surface area carbon powder at two ratios (Mn y O x /C) was evaluated as catalyst for the oxygen reduction reaction (ORR) in alkaline solutions. An impregnation method was used to prepare the catalysts, starting from a manganese nitrate precursor solution containing the carbon powder (Vulcan XC-72). A thin porous coating rotating disk electrode was employed to collect the experimental ORR polarization data and the results obtained were analyzed with the application of the flooded-agglomerate/thin film model for the catalyst layer. Results indicated that the reaction is sensitive to the manganese oxide to carbon ratio on the catalyst. The catalyst containing lower Mn y O x /C ratio tended to follow the peroxide pathway (2e − mechanism) forming peroxide ions. When the Mn y O x content is increased the complete reduction of oxygen to hydroxide ions pathway (the 4e − mechanism) takes place into some extent at low potentials due to the occurrence of a catalytic disproportionation of HO 2 −.