Junlin Xie

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.

Influence of nucleating agent on the formation of C4A3S

The reference test methods are carried out parallelly, by means of chemical analysis, X-ray diffraction, differential scanning calorimetry-thermogravimetry, scanning electron microscopy and polarized optical microscope to study the formation of C4A3S in the presence and absence of nucleating agent. The results show that nucleating agent with high calcium and low heat consumption as tricalcium silicate (C3S) promotes the formation of C4A3S and increases desulfurization degree obviously. During calcining raw meals doped with C3S, the grain sizes of C4A3S are larger compared with that without C3S. And at the same calcining level, the mass loss and the heat consumption belonged to CaCO3 decomposition is reduced.

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.

Effect of aluminum addition on microstructure and properties of SiO2-B2O3-Al2O3-CaO vitrified bond

Influence of aluminum addition on the structures and properties of SiO2-B2O3-Al2O3-CaO vitrified bond at low sintering temperature and high strength was discussed. FTIR and XRD analyses were used to characterize the structures of the basic vitrified bond with different contents of aluminum. The bending strength and the thermal expansion coefficients were also tested. Meanwhile, the microstructures of composite specimens at sintering temperature of 660 °C were observed by scanning electron microscope (SEM). The experimental results showed that the properties of vitrified bond with 1wt% aluminum were improved significantly, where the bending strength, Rockwell hardness, and thermal expansion coefficient of the vitrified bond reached 132 MPa, 63 HRB, and 6.73×10-6 °C-1, respectively.

Structure and luminescent properties of Sm3+ doped SrO-MgO-SiO2 glass ceramics

A new type of samarium ion activated luminescent glass ceramics with main crystal phase of melilite was prepared. The effect of heat-treatment temperature on the structure of glass ceramics was investigated by X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and fluorescence spectrometer. In the Sm3+ doped SrO-MgO-SiO2 glass ceramic, its excitation spectra are in the wavelength range of 350–500 nm, and its excitation peaks are at 360 nm, 374 nm, 404 nm, 417 nm, and 475 nm with the host excitation peak of 404 nm, showing a strong orange-red luminescence when using 404 nm violet to excite it, and its emission peaks are at 564 nm, 600 nm and 648 nm with the host emission peak at 600 nm. The increase in the heat-treatment temperature has no influence on the position of the fluorescent spectra. However, with the increase of heat-treatment temperature, the intensity of fluorescence spectrum shows an increasing tendency. The increase in the concentration of Sm3+ also improves the intensity of the fluorescent spectra. In the experimental concentration range (0.05mol%–0.30mol%), a special concentration quenching phenomenon happens.

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.

Performance regulation of Mn/TiO2 catalysts by surfactants for the selective catalytic reduction of NO with NH3 at low temperatures

A series of Mn/TiO2 catalysts were prepared using different dosage of cetyl trimethyl ammonium bromide (CTAB) and polyethylene glycol (PEG) 600 as surfactants by sol–gel method. When CTAB/Ti and PEG/Ti were 0.075 and 0.13, the morphology of the catalysts exhibited nano rod and regular sphere structure, respectively, and the activity was also the highest. The superior SCR activity of NC(0.075)-Mn/TiO2 and NP(0.13)-Mn/TiO2 catalysts was mainly due to the larger surface area and stronger reduction ability. In addition, it was found that the SCR activity of the catalysts with PEG600 as surfactants was generally higher than that of CTAB as surfactants, which may be due to its advantages in specific surface area, crystallinity, acidity, surface ion and chemisorbed oxygen concentration, and reducibility.

NH 3 -SCR Activity of MnOx/CeO 2 Catalyst at Low Temperature

In this paper, CeO2 was synthesized and used as carrier, meanwhile, MnOx was supported by different methods. The NH3-SCR activity of MnOx/CeO2 at low temperature has also been studied. The results show that the performance of the MnOX/CeO2 catalyst prepared by hydrothermal deposition method (MC-h) can reach up to 80% at 180 ℃, while the impregnation method (MC-i) is only 70% at 180 ℃. Testing results indicate that the catalysts synthesized by the hydrothermal deposition method have larger specific surface area and higher reducibility, and manganese oxide existed in the form of nanorods is more favorable for the contact between the active component and the reactive gas. All of these are beneficial to the SCR reaction.