De Fang

Effect of CuMn2O4 spinel in Cu–Mn oxide catalysts on selective catalytic reduction of NOx with NH3 at low temperature

Using the impregnation method, a series of Cu–Mn oxide catalysts were prepared and investigated for the selective catalytic reduction (SCR) of NOx with NH3 at temperatures ranging from 353 K to 453 K. The 0.05Cu–MnOx/TiO2 catalyst shows the highest activity and yields nearly 100% NOx conversion at 453 K using GHSV = 40 000 h−1, while the 0.20Cu–MnOx/TiO2 catalyst exhibits a certain level of potassium tolerance. In addition, the catalysts show favorable stability and water resistance. According to the XRD, EDS and SCR performance results, the existence of a new crystallized CuMn2O4 spinel phase is the dominant parameter for outstanding SCR activity between 413 K and 453 K. TPR, XPS and in situ DRIFT experiments indicate that CuMn2O4 is responsible for low reduction temperature, strong interaction between manganese oxides and copper oxides, high Mn3+ content and numerous acid sites on the surface. Compared with MnOx/TiO2 catalysts, Cu–Mn oxide catalysts could reduce the poisoning effect of potassium, illustrating that the CuMn2O4 phase may play a significant role in K-tolerance. Meanwhile, based on a certain level of potassium tolerance in CuMn2O4, an oxidation mechanism for NO is proposed due to the increase in Mn3+ and the special structure of a spinel oxide.

Effects of atmospheres and precursors on MnOx/TiO2 catalysts for NH3-SCR at low temperature

The effects of atmospheres and precursors on MnOx/TiO2 catalysts were studied, which were prepared by the impregnation method and tested for their NOx conversion activity in ammonia selective catalytic reduction (NH3-SCR) reactions. Results showed that the manganese carbonate (MC) precursor caused mainly Mn2O3, while the manganese nitrate (MN) precursor resulted primarily in MnO2 and the manganese sulfate (MS) precursor was unchanged. The manganese acetate (MA) precursor leaded obtaining a mixture of Mn2O3 and Mn3O4. NOx conversion decreased in the following order: MA/TiO2 > MC/TiO2 > MN/TiO2 > MS/TiO2 > P25, with a calcination temperature of 773 K in air. Catalysts that were prepared by MA and calcined in oxygen performed strong interaction between Ti and Mn, while MnTiO3 was observed. Compared to the catalysts calcined in nitrogen, those calcined in oxygen had larger diameter and smaller surface area and pore. Catalysts that were prepared by MA and calcined in nitrogen tended to gain higher denitration rates than those in air, since they could be prepared with significant specific surface areas. NOx conversion decreased with calcination atmospheres: Nitrogen> Air> Oxygen. Meanwhile, amorphous Mn2O3 turned into crystalline Mn2O3, when the temperatures increased from 673 to 873 K.

N 2 气氛下焙烧制备的Mn基催化剂催化NO x 脱除性能的提升机理:低MnO x 结晶度与氧化度

Abstract Among multitudinous metal-oxide catalysts for the selective catalytic reduction of NOx with NH3 (NH3-SCR), Mn-based catalysts have become very popular and developed rapidly in recent years because of its superior low-temperature denitrification activity, mainly originating from multi-valence of Mn. Most studies suggest that the catalytic activity of multi-component oxides is superior to that of single-component catalysts owing to the synergistic effect among the metallic elements in such materials, of which more attentions have been given to Ce as an additive owing to its powerful oxygen storage capacity, redox ability and its ready availability. As the core of SCR technology, the research points in catalyst development at the present stage of all researchers in countries mainly centralize on the optimization of active components, carriers, calcination temperature, calcination time and temperature-raising procedure, giving little thought to the effects of the calcination atmosphere. In the present work, Ce-modified Mn-based catalysts were prepared by a simple impregnation method. The effects of the calcination atmosphere (N2, air or O2) on the performance of the resulting materials during NH3-SCR and its causes of the differences were subsequently investigated and characterized using various analytical methods. Data obtained from X-ray diffraction, thermogravimetry and temperature-programmed reduction with hydrogen show that calcination under N2 reduces both the degree of oxidation and crystallization of the MnOx. Scanning electron microscopy also demonstrates that the use of N2 inhibits the growth of grains and increases the dispersion of the catalysts. In addition, the results of temperature-programmed desorption with ammonia indicate that catalysts calcined under N2 exhibit a greater quantity of acid sites. Finally, X-ray photoelectron spectrometry and activity results demonstrate that MnOx in the lower valence states is more favorable for NH3-SCR reactions. In conclusion, catalysts calcined under N2 show superior performance during NH3-SCR for NOx removal, allowing NO conversions up to 94% at 473 K.

Distributions and Species of MnOx Included in MnOx/TiO2 Catalysts for Denitration at Low Temperature

MnOx/TiO2 catalysts are active and stable at low temperature, and it is appropriate for cement production to enforce NOx emissions. In this study, the denitration process was promoted by the transformation of a variety of MnOx forms in the SCR reaction. The efficiency and selectivity of catalysts depended on the form and dispersion degree of MnOx. By changing the precursors, calcination temperatures, synthesis methods and calcination atmospheres, a series of MnOx/TiO2 catalysts were prepared. The contents and distributions of Mn2+, Mn3+ and Mn4+ in catalysts were tested through the titration method. The titration results showed that the content of Mn4+ was the highest during the precursor was Mn (NO3)2, while the content of Mn2+ in the catalysts calcinated in nitrogen atmosphere was the highest. The mechanisms of different MnOx states in the catalytic process were discussed. It was found that a mixture of more MnOx with low valence state and less MnOx with high valence state were beneficial to the catalytic process.

Effects of surface physicochemical properties on NH 3 -SCR activity of MnO 2 catalysts with different crystal structures

Abstract α-, β-, δ-, and γ-MnO2 nanocrystals are successfully prepared. We then evaluated the NH3 selective catalytic reduction (SCR) performance of the MnO2 catalysts with different phases. The NOx conversion efficiency decreased in the order: γ-MnO2 > α-MnO2 > δ-MnO2 > β-MnO2. The NOx conversion with the use of γ-MnO2 and α-MnO2 catalysts reached 90% in the temperature range of 140–200 °C, while that based on β-MnO2 reached only 40% at 200 °C. The γ-MnO2 and α-MnO2 nanowire crystal morphologies enabled good dispersion of the catalysts and resulted in a relatively high specific surface area. We found that γ-MnO2 and α-MnO2 possessed stronger reducing abilities and more and stronger acidic sites than the other catalysts. In addition, more chemisorbed oxygen existed on the surface of the γ-MnO2 and α-MnO2 catalysts. The γ-MnO2 and α-MnO2 catalysts showed excellent performance in the low-temperature SCR of NO to N2 with NH3.

Synthesis of porous cordierite and application for MnOx/TiO2 catalyst support

In this study the porous cordierite supports were synthesized from kaolin, magnesium oxide, silicon dioxide, and starch as pore-forming agent. A firing temperature, a optimum added amount of the starch, an acid treating time, and impregnation times for the cordierite support were all discussed. The results showed that when the firing temperature was 1300°C and the amount of the pore-forming agent was 8%, the bending strength and thermal expansion coefficient of the cordierite sample were 19.48 MPa and 1.94 × 10−6 °C−1, respectively, which fitted for MnOx/TiO2 SCR catalyst’s support. The FTIR indicated that it was necessary for the cordierite to be treated by 2mol L−1 nitric acid, this process could introduce a larger number of oxygen-containing functional groups and create a more hydrophilic surface structure. The SEM images illustrated that the acid treatment resulted in developing the amount of pores, which contributed to the gas-solid phase reaction. When the cordierite supports were impregnated 5 times in the MnOx/TiO2 solution, a loading amount of MnOx/TiO2 was 20.05%. With this MnOx/TiO2/cordierite samples, the maximum NO conversion could reach 85.4% at 200°C, which met the requirement of cement industry for selective catalytic reduction (SCR) with NH3.

Low Temperature Selective Catalytic Reduction of NOx with NH3 over MnOx /TiO2 Catalyst

Amorphous phase MnOx/TiO2 catalysts were prepared by two different methods, their catalytic activities for low temperature selective catalytic reduction (SCR) of NOx with NH3 in the presence of excess oxygen were investigated. The catalysts were characterized by XRD, XPS and HRTEM. The results showed that the catalyst prepared by soft template method had better catalytic active than those prepared by sol-gel method, its catalytic property could reach 98.2% at 200°C. From the microstructure characterization, it could be known that the catalyst prepared by soft template had the shape of nanorod, this shape was contributed to the dispersion of the manganese oxides and possessed higher surface lattice oxygen concentration. Furthermore, narrow slit-shaped pores associated with rod-like particles could provide efficient transport pathways to reactant molecules and products. Due to these, the catalyst performed catalytic active very well.

NH3-SCR Performance and Applicability of Mn-Based Spinels over TiO2 Catalyst

A series of Mn-based spinels over TiO2 catalysts have been prepared with the impregnation method. Catalysts were comprehensively characterized using XRD, FESEM, H2-TPR, and the activity evaluation of NH3-SCR, while long-time stability tests and the effect of H2O on NH3-SCR were also investigated. Meanwhile, K poisoning effect was studied by preparing K-doped catalysts (K-Mn/TiO2, K-Cu-Mn/TiO2, K-Mg-Mn/TiO2 and K-Co-Mn/TiO2). According to the characterizations, Cu-Mn/TiO2, Mg-Mn/TiO2 and Co-Mn/TiO2 catalysts exhibited superior low-temperature SCR activity, stability, K resistance and H2O resistance due to the formation of spinels (MgMn2O4, CoMn2O4, CuMn2O4).

Effect of Calcination Temperature on the SCR Activity of Fe–S/TiO 2 Catalysts

A series of Fe–S/TiO2 catalysts were prepared at different calcination temperatures by impregnation method and its performance of selective catalytic reduction (SCR) of NO with NH3 was investigated at temperatures ranging from 200 to 400 °C. Fe–S/TiO2-300 °C catalyst showed the highest activity, the NO conversion reaching over 80% in the range of 280–400 °C. With the help of XRD, H2-TPR and NH3-TPD, the structures and properties of catalysts were characterized. With the increase of calcination temperature, the Fe(OH)SO4 content in the catalyst decreased gradually. In addition, When the calcination temperature was below 400 °C, the main crystal phase in the catalyst is Fe(OH)SO4 and FeSO4. However, when it was 500 °C, the crystal phase of the active material became Fe2(SO4)3 and FeSO4. What’s more, the reduction ability of several catalysts showed no much difference, but the surface acidity was quite different, as the acidity of the Fe–S/TiO2-300 °C catalyst was the strongest.

Study on Interaction between Cerium and Phosphor in High-Carbon Steel

This paper did the research on Interaction mechanism between Ce and P added in high-carbon steel.with the use of QUANTA-400 SEM and EDS, the morphology of Ce-P-O inclusions were observed.By the Ce，O，P，S surface scanning observation of the inclusion, the inclusions were sured to be Ce-P or Ce-P-O compounds.furthermore,Ce-P compounds were irregular spherical , mainly in the grain. Ce-P-O compounds were long strip, mainly along the grain boundaries.