Mn Ce Research Articles

Structural, magnetic and electric properties of pure, Pr, Ce doped and Ce–Mn co-doped bismuth ferrites

Sol–gel synthesized pure, Pr, Ce doped and Ce–Mn co-doped BiFeO3 samples show that doping and co-doping increases the symmetry with suppressed secondary phases. Microstructural investigation indicated particles and highly dense rectangular grains images with different sizes and shapes. M–H and P–E loop study shows that magnetic and ferroelectric properties are strongly dependent on doping and co-doping. Frequency dependent dielectric properties of samples concluded improvement in various parameters. Leakage current study shows that there is decrease in leakage behavior for Pr, Ce doped samples but increment for Ce–Mn co-doped BiFeO3 for applied field.

Improvement of Low-Temperature Activity of FeBeta Monolith Catalyst in NH3-SCR of NOx

FeBeta||Mn–Ce/FeBeta catalyst was prepared by coating cordierite monolith with FeBeta zeolite followed by an impregnation of its downstream part by Mn–Ce solution. The resulting dual-zone catalyst demonstrates improved catalytic performance in the selective catalytic reduction of NOx by NH3 (NH3-SCR) as compared to the parent Fe-Beta. The catalyst exhibits 80–90% NOx conversion and 100% selectivity to N2 within wide temperature ranges: 180–500 °C (at GHSV = 18,000 h−1) and 260–500 °C (at GHSV = 54,000 h−1). Moreover, the dual-zone catalyst provides favorable NH3-slip removal efficiency even at NH3/NO = 1.60.

Gaseous Elemental Mercury Removal by Magnetic Fe–Mn–Ce Sorbent in Simulated Flue Gas

A magnetic sorbent of Ce-doped Fe–Mn sorbent (Fe–Mn–Ce) was synthesized to capture gaseous elemental mercury from coal-fired flue gas. The physical and chemical properties of Fe–Mn–Ce sorbent were characterized by N2 adsorption, vibrating sample magnetometer, X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectroscopy (XPS). The mercury removal capability of Fe–Mn–Ce sorbent was tested in a fixed-bed system, and the effect of flue gas temperature and O2 was investigated. The valence change of Fe 2p, Mn 2p, Ce 3d, O 1s, and Hg 4f on the sorbent surface during mercury removal process was analyzed. Finally, the mechanism of mercury removal by the Fe–Mn–Ce sorbent was explored. The result shows that the synthesized Fe–Mn–Ce sorbent consists of many extremely small nanoparticles, contains a polycrystalline structure, and shows good mercury removal performance. High temperature is beneficial to mercury removal by the Fe–Mn–Ce sorbent, but the 6% O2 in flue gas plays a negligible ro...

Low‐Temperature De‐NOx Extruded Monolithic Catalysts Based on Highly Dispersive Mn–Ce Oxide Nanoparticles of Low Ce Content

AbstractA facile strategy to produce low‐temperature De‐NOx extruded monolithic catalysts based on the highly dispersive Mn–Ce oxide nanoparticles of low Ce content is described. The design of the materials is based on dual supports composed of reduced graphene oxide and TiO2, which is made by Mn–Ce oxide nanoparticles well separated on the supports without any agglomeration. Compared to the catalysts with only TiO2 support, the specific surface area of the catalysts is significantly increased by 2.8 times. The temperature‐programmed desorption analysis of NH3 shows that the number of Lewis acid sites increases; thus, the binding strength of the NH3 at the surface of the oxides is also increased. Through the temperature‐programmed reduction of the H2, the rate of the reduction reaction also increases. Thus, the efficiency of the overall De‐NOx reaction increases to 90% with a lower Ce content of 40% at 250 °C and shows good stability at a high temperature of 300 °C. By using the above‐mentioned catalysts, a honeycomb‐type extruded monolithic product with De‐NOx efficiency higher than 90% in the temperature range between 200 and 300 °C is made without any additional binders. This indicates a good formability, enough for the fabrication of the commercialized products.

Decorating CeO2 Nanoparticles on Mn2O3 Nanosheets to Improve Catalytic Soot Combustion

Herein, we synthesized CeO2 nanoparticles-decorated Mn2O3 nanosheets on monolithic Ni foam (Ce/Mn-NF) for catalytic elimination of soot particulates. The macroporous nanostructures created by the Mn2O3 nanosheets improve the soot-catalyst contact efficiency on the external surface of catalysts. The superficial Mn–Ce interaction can produce Mn4+ and oxygen vacancies on the Ce/Mn-NF catalysts through the redox process of Ce4+ + Mn3+ ↔ Mn4+ + Ce3+, simultaneously generating surface active oxygen species. Moreover, our results demonstrate that the surface adsorbed oxygen species induced by the Mn–Ce interaction are more active for catalytic soot oxidation than those on the Mn-NF. Thus, the introduction of the CeO2 nanoparticles to the Mn2O3 nanosheets can significantly improve the catalytic activity for soot combustion. For the Ce/Mn-NF-2, the surface atomic ratio of Ce and Mn is close to 1:1, which will create more Mn–Ce interaction sites to generate active oxygen species compared with other catalysts. Accor...

A Comparative Study of Supported and Bulk Cu–Mn–Ce Composite Oxide Catalysts for Low-Temperature CO Oxidation

A series of supported and bulk Cu–Mn–Ce ternary oxide catalysts was synthesized by wet-impregnation (IM), deposition–precipitation (DP), traditional co-precipitation (CP), co-precipitation with cetyltrimethyl ammonium bromide (CC), and sol–gel (SG) methods. The supported catalysts (CuMn/Ce-IM, CuMn/Ce-DP) exhibited significantly higher activity for CO oxidation than the bulk catalysts (CuMnCe-CP, CuMnCe-CC and CuMnCe-SG). The improved performance could be attributed to the presence of more isolated CuO and MnOx entities on the surface of supported catalysts, which contributed to the efficient utilization of both lattice oxygen from CeO2 and spillover oxygen from surface MnOx. For bulk catalysts, major Cu–Mn species were doped to form $${\text{C}}{{\text{u}}_{\text{x}}}{\text{M}}{{\text{n}}_{\text{y}}}{\text{C}}{{\text{e}}_{1 - {\text{x}} - {\text{y}}}}{{\text{O}}_{2 - {\text{z}}}}$$ solid solutions and a part of them were coated by ceria mechanically. Lowest 50% CO conversion temperature were achieved at 76.9 °C for CuMn/Ce-IM catalyst. Low-temperature CO oxidation activities of all catalysts were in the sequence of CuMn/Ce-IM > CuMn/Ce-DP > CuMnCe-SG > CuMnCe-CC > CuMnCe-CP.

A comparative study on Ce–Pr and Ce–Mn mixed oxide catalysts toward soot catalytic combustion

CePr and CeMn mixed oxide catalysts were synthesized by inserting Pr and Mn atoms into CeO2. Catalytic performance on soot combustion was investigated, and several characterizations were carried out using X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area analysis, H2 temperature-programmed reduction, and X-ray diffraction. Results show that a cubic fluorite structure solid solution can be formed with Pr and Mn doped into CeO2 lattice. Three oxygen species, namely, lattice oxygen OI (O2−), defect oxygen species OII (O2−, O22−, and O−), and hydroxyl-like groups and adsorbed molecular water OIII, exist in the solid solution structure. In general, the defect oxygen species OII is responsible for soot combustion. CePr exhibits fast oxidation rate because of the presence of open oxygen migration channel (OI↔OII↔OIII), and reactive oxygen species OII can continue to be replenished. CeMn possesses a large amount of surface active oxygen, which results in excellent low-temperature catalytic activity.

Evaluation of terrigenous input, diagenetic alteration and depositional conditions of Lower Carboniferous carbonates of Tethys Himalaya, India

Geochemical and isotopic signatures from Lower Carboniferous Limestone of the Lipak Formation of Spiti region, Tethys Himalaya (for the first time) have been studied for palaeo-climatic reconstruction of the region and to evaluate the influence of terrigenous input into the Tethyan Ocean. The principal component analysis (PCA) suggests that CaO exhibits different modes of origin as compared to other elements. The low and relatively constant Al/Si ratio (0.19–0.46) of Lipak limestone suggests that Si has multiple sources besides clay minerals. Higher Al2O3 of the limestone than siliciclastic-contaminated carbonates (1.59%) as well as comparable Y/Ho ratio to terrestrial material suggests terrigenous input into the basin. The Er/Nd ratio ranges from 0.07 to 0.18 which further indicates the influence of detrital input (in normal seawater Er/Nd is 0.27). The Mn/Sr ratio suggests insignificant diagenetic alterations. The lack of correlation between Sr and LREE concentration in the limestone (r = 0.036) lends credence to this conclusion. Geochemical palaeo-redox parameters such as negative Mn and positive Ce anomalies (V/V + Ni) and Th/U ratios indicate that the limestone was deposited in anoxic environmental conditions. δ18O and δ13C isotope composition of whole-rock samples ranges from −10%o to −24%o and +3.34%o to −8.24%o respectively indicating significant climatic change during Carboniferous period. These observations are consistent and match with those of contemporaneous carbonates elsewhere in the world, which can be linked to the alternative occurrences of cold and warm paleoclimates in the Carboniferous. The onset of the Permo-Carboniferous glaciation would have resulted in more positive δ13C and less negative δ18O values for these carbonates. The isotopic values also indicate eustatic sea level changes due to the glacial and interglacial phases during the period. Thus the signatures of Gondwana glaciation events are well preserved in the Lipak limestone of Spiti region.

Role of cerium in improving NO reduction with NH3 over Mn–Ce/ASC catalyst in low-temperature flue gas

Mn–Ce mixed oxide was loaded onto activated semi-coke (ASC) via impregnation method and the low temperature selective catalytic reduction (SCR) of NO with NH3 was investigated. The NO conversion and NO oxidation rates were both influenced by the ratios of Ce/(Mn+Ce), and Mn–Ce(0.3)/ASC with loading 5% (mass ratio) Mn–Ce oxides performed the highest catalytic conversion rate of 96.6% and NO oxidation rate of 18.4% at 250°C and GHSV=6000h−1. The changes of physical properties, microstructure, functional groups, crystal structure, surface atomic state, redox property and acid strength for the catalysts were characterized by BET, SEM, FT-IR, XRD, XPS, H2-TPR and NH3-TPD. The results showed that surface functional groups were increased after nitric acid treatment and abundant oxygen groups were observed on semi-coke surface, which were considered to be beneficial for the gas adsorption. Ce doping could raise the Mn4+/Mnx+ rate which played a vital role in catalytic reaction, enhancing the amount of weak and strong acid sites, increasing oxygen vacancies and accelerating the molecular oxygen turning into reactive oxygen species, which could enhance the NO oxidation activity thus contributed to the denitration efficiency.

NO Adsorption and Oxidation on Mn Doped CeO2 (111) Surfaces: A DFT+U Study

The adsorption of NO molecules on Mn-doped CeO2 (111) surfaces for NO oxidation has been studied by employing the periodic density functional theory plus U (DFT+U) method. Through our calculations, it is demonstrated how Mn-doped CeO2 with superior NO oxidation activity benefits from the high mobility of the oxygen near the Mn cations. On unreduced Mn-doped CeO2 (111) surfaces, the NO molecule preferentially interacted with the first neighboring O of the Mn cation, with the N also bonding to an Mn cation (Eads = –3.30 eV) or Ce cation (Eads = –2.90 eV). When NO adsorbs on the surface of defective Mn-doped CeO2 with O2 adsorbed in advance, an ONOO* four atoms species is formed on the surface (Eads = –2.51 eV and –2.02 eV), which is an intermediate and can decompose into NO2, NO2* and O*. The adsorption structure with higher adsorption energy has a closer geometry to NO2, indicating a deeper oxidation of NO. The calculation results indicate that the presence of Mn only has a strong effect on the nearby oxygen atoms and that the Mn-doped CeO2 surface has similar properties to a noble metal in NO oxidation catalysis. In DOS plots, the spin of the electron state of the adsorption structures involving the oxidation of NO is symmetric, indicating that electron transfer occurs from the slab to NO and strong covalent bonds are formed between N and O on the slab, which can also be confirmed by the charge density difference plots.

Promotional effect of Ce on the SCR of NO with NH3 at low temperature over MnO x supported by nitric acid-modified activated carbon

Different amounts of Mn and Ce oxides were loaded onto nitric acid-modified activated carbon (ACN) by wet impregnation. The series of catalysts were employed for the selective catalytic reduction of NO x by NH3 at temperatures between 100 and 250 °C. Cerium-modified catalysts exhibited higher de-NO x performance than those modified with Mn/ACN, even with the same total loadings. The precursor solution with a molar ratio for Ce/(Mn + Ce) of 0.4 exhibited the highest catalytic activity. Enhanced resistance to SO2 and H2O and better stability were observed for 10%Mn–Ce(0.4)/ACN relative to 10%Mn/ACN. The catalysts were further characterized by N2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), and temperature-programmed desorption of ammonia (NH3-TPD). The N2 physisorption and XRD results suggested that co-doping Ce with Mn increased the surface area and promoted the dispersion of Mn–Ce binary metal oxides. H2-TPR the NH3-TPD results demonstrated that the interaction between manganese oxide and cerium oxide species enhanced the redox and surface acidity of 10%Mn–Ce(0.4)/ACN.

Denitrification performance of non-pitch coal-based activated coke by the introduction of MnOx–CeOx–M (FeOx, CoOx) at low temperature

Modified activated coke was prepared by the introduction of MnOx, CeOx, and M (FeOx, CoOx) into non-pitch coal-based activated coke (NPAC) using a novel non-pitch binder. The modified non-pitch coal-based activated coke was characterized in detail by N2 physical adsorption, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, temperature-programmed reduction of H2, temperature-programmed desorption of NH3, and its catalytic activity was examined by the selective catalytic reduction of NO with NH3 at low temperature. In addition, the SO2 and H2O tolerance was investigated. The results indicated that compared to MnOx–CeOx–4.39, Mn–Ce–Co/NPAC-7 and Mn–Ce–Fe/NPAC-7 exhibit considerably higher catalytic activities while simultaneously maintaining NOx removal rates of 78.98% and 77.85%, respectively, at 150°C. The high catalytic performance of Mn–Ce–Co/NPAC-a and Mn–Ce–Fe/NPAC-a is related to several better properties compared to MnOx–CeOx–4.39, namely, considerably higher specific surface areas and percentages of Oα/(Oα+Oβ+Oγ) and Ce3+/(Ce3++Ce4+), more easily reduced of Mn species, high reducibility, and more acidic sites. Furthermore, Mn–Ce–Co/NPAC-7 and Mn–Ce–Fe/NPAC-7 exhibited specific resistance to SO2 and H2O poisoning, and the SO2 deactivation mechanism was proposed.

CO Oxidation over Nanostructured Ceria Supported Bimetallic Cu–Mn Oxides Catalysts: Effect of Cu/Mn Ratio and Calcination Temperature

Nanostructured CeO2 supported CuO–MnO2 (CuMn/Ce) catalysts were synthesized by wet co-impregnation method and compared with CuO/CeO2 and MnO2/CeO2 catalysts on CO oxidation. The former shows significantly higher catalytic activity toward CO oxidation than the bimetallic oxides catalysts with minimum T50. Dual synergistic effects in the interfaces of CuO–MnO2 and CuO–CeO2 shall be responsible for the higher oxidation performance of CuMn/Ce catalyst. As Cu/Mn mass ratio varies from 1/0.2 to 1/9, CO oxidation activities of the catalysts present unimodal distribution, and the catalyst with Cu/Mn = 1/1 shows the highest performance (T50 = 45.8 °C; Ea = 24.11 kJ mol−1). Cu acts as CO dissociative adsorption sites, and Mn–Ce supplies activated O species from gas molecule and lattice oxygen, which are both indispensable for improving utilization efficiency of the reactants in the dual redox processes. The catalytic performance of catalyst is also vitally correlated with calcination temperature (160–320 °C). The optimum calcination temperature of CuMn/Ce catalyst is 320 °C. Catalyst characterization results indicate that the pretreatment at 320 °C is decent to obtain desired metal oxides along with fine texture properties.

Fabrication of silica supported Mn–Ce benzene oxidation catalyst by a simple and environment-friendly oxalate approach

A series of silica supported Mn–Ce composite oxides with different Mn/Ce molar ratios were obtained by a simple and environment-friendly oxalate route. The physical and chemical properties were characterized by TG, BET, SEM, TEM, XPS and TPR analysis. All catalysts showed excellent activity towards deep oxidation of benzene. The effects of Mn/Ce ratio, calcination temperature on the structure and catalytic activity of catalysts were investigated. Catalyst from nitrate precursor was also characterized to compare the influence of different precursors. The 6Mn4Ce sample from oxalate route sintered at 400 °C showed the maximum reaction rate of 0.50 mmol gcat−1h−1; T90 of the catalyst is 216 °C. The catalytic activity is related to surface area, pore size distribution, surface elemental species, particle size distribution and low temperature reducibility which may derived from synergistic effect between manganese and cerium oxide. Compared with nitrate precursors, catalyst from oxalate route can be more finely dispersed on the pores of silica without damaging the pore structure of support. The role of silica is not only a support, but also an in situ reaction site for precursor’s decomposition, which ensure the finely distribution of active components. In addition, the best catalyst showed good stability with prolonged time on stream.

Preparation of highly dispersed Mn–Ce mixed metal oxides supported on the nitric vapour functionalised CNTs for low‐temperature NO reduction with NH 3

Highly dispersed Mn–Ce mixed metal oxide catalysts supported on the nitric vapour functionalised carbon nanotubes (CNTs) were synthesised by a polyol process for the low-temperature NO reduction with NH3. The obtained samples possessed high Mn4+/Mn and Oα/Oα + Oβ ratios and exhibited 90–100% NO conversion at 180–240°C.

Facile preparation of high-performance Fe-doped Ce–Mn/TiO2 catalysts for the low-temperature selective catalytic reduction of NOx with NH3

A Ce–Mn–Fe/TiO2 catalyst has been successfully prepared using a single impregnation method with excellent low-temperature NH3-SCR activity.

Influence of transition metal (Fe, Co, and Ag) doping on the MnOx–CeO2/Ti-bearing blast furnace slag catalyst for selective catalytic reduction of NOx with NH3 at low temperature

Mn–Ce based catalysts supported on Ti-bearing blast furnace slag (industrial solid waste) and the doping of transition metals were studied.

Highly active MnOx–CeO2catalyst for diesel soot combustion

Optimized Ce–Mn composite oxide, possessing abundant active Ce3+–Mn4+ions, exhibits excellent activity for catalytic soot combustion in NOx/O2.

Catalytic Degradation of Benzene over Nanocatalysts containing Cerium and Manganese.

A Ce–Mn composite oxide possessing a rod‐like morphology (with a fixed molar ratio of Ce/Mn=3:7) was synthesized through a hydrothermal method. Mn ions were doped into a CeO2 framework to replace Ce ions, thereby increasing the concentration of oxygen vacancies. The formation energies of O vacancies for the Ce–Mn composite oxide were calculated by applying density functional theory (DFT). The data showed that it was easier to form an O vacancy in the composite. The catalytic behavior of the Ce–Mn composite oxide for benzene degradation was researched in detail, which exhibited a higher activity than the pure phases. Based on this, the Ce–Mn composite oxide was chosen as a supporter to load PdO nanoparticles. The activity was enhanced further compared with that of the supporter alone (for the supporter, the reaction rate R 214 °C=0.68×10−4 mol gcat −1 s−1 and apparent activation energy E a=12.75 kJ mol−1; for the supporting catalyst, R 214 °C=1.46×10−4 mol gcat −1 s−1, E a=10.91 kJ mol−1). The corresponding catalytic mechanism was studied through in situ Raman and FTIR spectroscopy, which indicated that the process of benzene oxidation was related to different types of oxygen species existing at the surface of the catalysts.

Synergistic removal of NO and N2O in low-temperature SCR process with MnOx/Ti based catalyst doped with Ce and V

Aiming at understanding N2O formation in a low-temperature SCR process, mechanistic studies regarding the synergistic removal of NO and inhibition of N2O formation by the addition of Ce and V into MnOx/Ti based catalysts prepared by the sol-gel method were conducted and analyzed by various techniques, including BET, XRD, XPS, NH3-TPD, and FTIR. The results show that the addition of Ce raises the NO conversion efficiency and shifts the high performance region toward the low temperature range, while the addition of V generates less N2O. As an optimal formula, Mn(0.4)Ce(0.1)V(0.01)/Ti ensures a high NO conversion efficiency and low N2O formation. N2O mainly originates from (1) the direct oxidation of NH3 with O2 and (2) the reaction of NO and adsorbed NH3 in the low-temperature SCR process. The latter plays a dominant role at temperatures below 240°C. The strong redox properties on the MnOx/Ti catalyst surface result in a high NO conversion efficiency and generates numerous NH(ads) species that cause N2O formation. The slight addition of V promotes the formation of acid by bringing Lewis acid sites to the catalyst surface and effectively restricts N2O formation. Lewis acid sites have a positive function in maintaining a high NO conversion and inhibiting N2O formation compared to Brønsted acid sites. In addition, the well-dispersed V on the surface of Mn(0.4)Ce(0.1)V(0.01)/Ti results in improved textural properties, more lattice oxygen and less labile oxygen, as well as comparable Mn4+/Mn3+, which also improves the catalyst performance at low temperature.