Mn substituted MnxZn1−xCo2O4 oxides synthesized by co-precipitation; effect of doping on the structural,electronic and magnetic properties

Mn substituted Mn_xZn_1−xCo₂O₄ (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by a facile co-precipitation method followed by calcination at 600 °C. The presence of manganese ions causes appreciable changes in the structural and magnetic properties of the Mn-substituted ZnCo₂O₄. The morphologies, structures, and electronic properties of Mn–Zn–Co oxide microspheres were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The X-ray diffraction and Fourier transform infrared spectroscopy results confirmed the formation of spinel Mn_xZn_1−xCo₂O₄. It was shown that the Mn–Zn–Co oxide microspheres increase in size and become regular in shape with increasing Mn concentration with the crystal size lying in the range from 19.1 nm to 51.3 nm. Magnetization measurements were carried out using a vibrating sample magnetometer at room temperature and 10 K. The saturation magnetization is observed to increase with increasing Mn concentration from x = 0 to x = 1.

Mn substituted Mn_xZn_1−xCo₂O₄ (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by a facile co-precipitation method followed by calcination at 600 °C.     

Effect of initial support particle size of MnOx/TiO2 catalysts in the selective catalytic reduction of NO with NH3

A series of manganese-based catalysts supported by 5–10 nm, 10–25 nm, 40 nm and 60 nm anatase TiO₂ particles was synthesized via an impregnation method to investigate the effect of the initial support particle size on the selective catalytic reduction (SCR) of NO with NH₃. All catalysts were characterized by transmission electron microscopy (TEM), N₂ physisorption/desorption, X-ray diffraction (XRD), temperature programmed techniques, X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared transform spectroscopy (DRIFTS). TEM results indicated that the particle sizes of the MnO_x/TiO₂ catalysts were similar after the calcination process, although the initial TiO₂ support particle sizes were different. However, the initial TiO₂ support particle sizes were found to have a significant influence on the SCR catalytic performance. XPS and NH₃-TPD results of the MnO_x/TiO₂ catalysts illustrated that the surface Mn⁴⁺/Mn molar ratio and acid amount could be influenced by the initial TiO₂ support particle sizes. The order of surface Mn⁴⁺/Mn molar ratio and acid amount over the MnO_x/TiO₂ catalysts was as follows: MnO_x/TiO₂(10–25) > MnO_x/TiO₂(40) > MnO_x/TiO₂(60) > MnO_x/TiO₂(5–10), which agreed well with the order of SCR performance. In situ DRIFTS results revealed that the NH₃-SCR reactions over MnO_x/TiO₂ at low temperature occurred via a Langmuir–Hinshelwood mechanism. More importantly, it was found that the bridge and bidentate nitrates were the main active substances for the low-temperature SCR reaction, and bridge nitrate adsorbed on Mn⁴⁺ showed superior SCR activity among all the adsorbed NO_x species. The variation of the initial TiO₂ support particle size over MnO_x/TiO₂ could change the surface Mn⁴⁺/Mn molar ratio, which could influence the adsorption of NO_x species, thus bringing about the diversity of the SCR catalytic performance.

Support particle size could influence the surface Mn⁴⁺/Mn ratio of catalysts, promoting the reactivity of bridge nitrate, therefore enhancing SCR performance.     

Integral structured Co–Mn composite oxides grown on interconnected Ni foam for catalytic toluene oxidation

Considering the three-dimensional ordered network of Ni foam-supported catalysts and the toxicity effects of volatile organic compounds (VOCs), the design of proper active materials for the highly efficient elimination of VOCs is of vital importance in the environmental field. In this study, a series of Co–Mn composite oxides with different Co/Mn molar ratios grown on interconnected Ni foam are prepared as monolithic catalysts for total toluene oxidation, in which Co_1.5Mn_1.5O₄ with a molar ratio of 1 : 1 achieves the highest catalytic activity with complete toluene oxidation at 270 °C. The Co–Mn monolithic catalysts are characterized by XRD, SEM, TEM, H₂-TPR and XPS. It is observed that a moderate ratio of Mn/Co plays significant effects on the textural properties and catalytic activities. From the XPS and H₂-TPR characterization results, the obtained Co_1.5Mn_1.5O₄ (Co/Mn = 1/1) favors the excellent low-temperature reducibility, high concentration of surface Mn³⁺ and Co³⁺ species, and rich surface oxygen vacancies, resulting in superior oxidation performance due to the formation of a solid solution between the Co and Mn species. It is deduced that the existence of the synergistic effect between Co and Mn species results in a redox reaction: Co³⁺–Mn³⁺ ↔ Co²⁺–Mn⁴⁺, and enhances the catalytic activity for total toluene oxidation.

A series of Co–Mn oxides with different Co/Mn molar ratios grown on interconnected Ni foam were prepared as monolithic catalysts for total toluene oxidation.     

High-yield synthesis of Ce modified Fe–Mn composite oxides benefitting from catalytic destruction of chlorobenzene

Ce–Fe–Mn catalysts were prepared by an oxalic acid assisted co-precipitation method. The influence of Ce doping and calcination temperature on the catalytic oxidation of chlorobenzene (as a model VOC molecule) was investigated in a fixed bed reactor. The Mn₃O₄ phase was formed in Ce–Fe–Mn catalysts at low calcination temperatures (<400 °C), which introduced more chemisorbed oxygen, and enhanced the mobility of O atoms, resulting in an improvement of the reduction active of Mn₃O₄ and Fe₂O₃. Additionally, CeO₂ has strong redox properties, and Ce⁴⁺ would oxidize Mn^x+ and Fe^x+. Therefore, the interaction of Ce, Fe and Mn can improve the content of surface chemisorbed oxygen. As compared with Fe–Mn catalysts, the catalytic conversion of chlorobenzene over Ce(5%)–Fe–Mn-400 was about 99% at 250 °C, owing to high specific surface area, Mn₃O₄ phase, and Ce doping. However, with the increase in roasting temperature, the performance of the catalysts for the catalytic combustion of chlorobenzene was decreased, which probably accounts for the formation of the Mn₂O₃ phase in Ce–Fe–Mn-500 catalysts, leading to a decrease in the specific surface area and concentration of chemically adsorbed oxygen. As a result, it can be expected that the Ce–Fe–Mn catalysts are effective and promising catalysts for chlorobenzene destruction.

Ce–Fe–Mn catalysts were prepared by an oxalic acid assisted co-precipitation method.     

Synthesized akhtenskites remove ammonium and manganese from aqueous solution: removal mechanism and the effect of structural cations

Ammonium and manganese removal by tunnel-structured manganese oxide is still enigmatic. Herein, tunnel-structured akhtenskites with different structural cations (Na–MnO_x, Mg–MnO_x Ca–MnO_x, Fe–MnO_x) were synthesized by the KMnO₄ and Mn²⁺ reaction in the presence of different metal cations, and were used to remove ammonium and manganese from aqueous solution. The results of the batch adsorption experiments indicated that akhtenskites effectively removed NH₄⁺ and Mn²⁺, and the removal process fitted the pseudo-second-order model. By measuring the concentration of nitrate and nitrite, discriminating the adsorbed and oxidized Mn²⁺, and testing the zeta potential of the oxides, it can be concluded that NH₄⁺ was merely removed by electrostatic adsorption via Mn–O⁻; Mn²⁺ could also be adsorbed by ion exchange with Mn–OH, and the adsorbed Mn²⁺ could be partly oxidized. The structural properties of the akhtenskites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific area, and X-ray photoelectron spectroscopy (XPS). The experimental results showed that ions with higher valence can result in a higher percentage of Mn(iii) in akhtenskite. Mg²⁺ can result in a lower proportion of lattice oxygen in the oxide, and Fe³⁺ can increase the pH of the point of zero charge. Both of them were unfavored for the oxidation of Mn²⁺. Moreover, it was found that Ca–MnO_x had optimal removal performance in the catalytic oxidation of Mn²⁺ owing to appropriate percentages of O_latt and Mn(iii) and lower zeta potential. This study provides new insights into the synthesis and application of manganese oxides.

Akhtenskites merely remove NH₄⁺ by adsorption, but remove Mn²⁺ by adsorption and catalytic oxidation simultaneously. The removal efficiency and crystal structure are obviously affected by the structure cations.     

Mn-doped nickeltitanate (Ni1−xMnxTiO3) as a promising support material for PdSn electrocatalysts for methanol oxidation in alkaline media

Nickeltitanate (Ilmenite) has been prepared with stoichiometric variation by substituting Mn in the ‘A’ site, using the sol–gel method in a highly active form. The PdSn electrocatalyst was then impregnated with nickeltitanate by a microwave-assisted polyol method. The physiochemical characterisation of the synthesized electrocatalyst PdSn–Ni_1−xMn_xTiO₃ was done by X-ray diffractometry, UV-visible spectrophotometry, Raman spectroscopy and transmission electron microscopy. The elemental composition was obtained using energy dispersive spectra which confirmed the presence of Ni, Mn, Ti, O, Pd and Sn. Electrochemical characterization using cyclic voltammetry and polarization experiments showed that the synthesized PdSn–Ni_1−xMn_xTiO₃ exhibited an enhanced catalytic activity and better stability in the alkaline medium, compared to conventional PdSn/C catalysts. It was observed that the charge transfers from the support material (Ni_1−xMn_xTiO₃) to the PdSn electrocatalyst boosted the oxidation reaction. By varying the methanol concentration from 0.5 M to 2.0 M, the resulting current density also varied from 129 to 151 mA cm⁻². This result demonstrated that the prepared material PdSn–Ni_1−xMn_xTiO₃/C electrocatalyst is an excellent candidate for the methanol oxidation reaction.

Nickeltitanate (Ilmenite) has been prepared with stoichiometric variation by substituting Mn in the ‘A’ site, using the sol–gel method in a highly active form.     

Copper-doped lanthanum manganite La0.65Ce0.05Sr0.3Mn1−xCuxO3 influence on structural,magnetic and magnetocaloric effects

Bulk nanocrystalline samples of La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method. The effect of the substitution for Mn with Cu upon the structural and magnetic properties has been investigated by means of X-ray diffraction (XRD), Raman spectroscopy and dc magnetization measurements. The structural parameters obtained using Rietveld refinement of XRD data showed perovskite structures with rhombohedral (R$\bar{3}$c) symmetry without any detectable impurity phase. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing copper concentration. The analysis of the crystallographic data suggested a strong correlation between structure and magnetism, for instance a relationship between a distortion of the MnO₆ octahedron and the reduction in the Curie temperature, T_c. A paramagnetic to ferromagnetic phase transition at T_C is observed. The experimental results confirm that Mn-site substitution with Cu destroys the Mn³⁺–O²⁻–Mn⁴⁺ bridges and weakens the double exchange (DE) interaction between Mn³⁺ and Mn⁴⁺ ions, which shows an obvious suppression of the FM interaction in the La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ matrix. The maximum magnetic entropy change −ΔS^max_M is found to decrease with increasing Cu content from 4.43 J kg⁻¹ K⁻¹ for x = 0 to 3.03 J kg⁻¹ K⁻¹ for x = 0.15 upon a 5 T applied field change.

Bulk nanocrystalline samples of La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method.     

Investigation on structure,thermodynamic and multifunctional properties of Ni–Zn–Co ferrite for Gd3+ substitution

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni–Zn–Co ferrite tailored by Gd³⁺ substitution at the B-site replacing Fe³⁺ ions. The synthesized composition of Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) crystallized with a single-phase cubic spinel structure that belongs to the Fd$\bar{3}$m space group. The average particle size decreases due to Gd³⁺ substitution at Fe³⁺. Raman and IR spectroscopy studies illustrate phase purity, lattice dynamics with cation disorders and thermodynamic conditions inside the studied samples at room temperature (RT = 300 K). Ferromagnetic to paramagnetic phase transition was observed in all samples where Curie temperature (T_C) decreases from 731 to 711 K for Gd³⁺ substitution in Ni–Zn–Co ferrite. In addition, Gd³⁺ substitution reinforces to decrease the A-B exchange interaction. Temperature-dependent DC electrical resistivity (ρ_DC) and temperature coefficient of resistance (TCR) have been surveyed with the variation of the grain size. The frequency-dependent dielectric properties and electric modulus at RT for all samples were observed from 20 Hz to 100 MHz and the conduction relaxation processes were found to spread over an extensive range of frequencies with the increase in the amount of Gd³⁺ in the Ni–Zn–Co ferrite. The RLC behavior separates the zone of frequencies ranging from resistive to capacitive regions in all the studied samples. Finally, the matching impedance (Z/η₀) for all samples was evaluated over an extensive range of frequencies for the possible miniaturizing application.

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni–Zn–Co ferrite tailored by Gd³⁺ substitution at the B-site replacing Fe³⁺ ions.     

Nonstoichiometric oxygen in Mn–Ga–O spinels: reduction features of the oxides and their catalytic activity

The subject of this study was the content of oxygen in mixed oxides with the spinel structure Mn_1.7Ga_1.3O₄ that were synthesized by coprecipitation and thermal treatment in argon at 600–1200 °C. The study revealed the presence of excess oxygen in “low-temperature” oxides synthesized at 600–800 °C. The occurrence of superstoichiometric oxygen in the structure of Mn_1.7Ga_1.3O_4+δ oxide indicates the formation of cationic vacancies, which shows up as a decreased lattice parameter in comparison with “high-temperature” oxides synthesized at 1000–1200 °C; the additional negative charge is compensated by an increased content of Mn³⁺ cations according to XPS. The low-temperature oxides containing excess oxygen show a higher catalytic activity in CO oxidation as compared to the high-temperature oxides, the reaction temperature was 275 °C. For oxides prepared at 600 and 800 °C, catalytic activity was 0.0278 and 0.0048 cm³ (CO) per g per s, and further increase in synthesis temperature leads to a drop in activity to zero. The process of oxygen loss by Mn_1.7Ga_1.3O_4+δ was studied in detail by TPR, in situ XRD and XPS. It was found that the hydrogen reduction of Mn_1.7Ga_1.3O_4+δ proceeds in two steps. In the first step, excess oxygen is removed, Mn_1.7Ga_1.3O_4+δ → Mn_1.7Ga_1.3O₄. In the second step, Mn³⁺ cations are reduced to Mn²⁺ in the spinel structure with a release of manganese oxide as a single crystal phase, Mn_1.7Ga_1.3O₄ → Mn₂Ga₁O₄ + MnO.

The hydrogen reduction of Mn_1.7Ga_1.3O_4+δ proceeds in two steps. In the first step, excess oxygen is removed, Mn_1.7Ga_1.3O_4+δ → Mn_1.7Ga_1.3O₄. In the second step, Mn³⁺ cations are reduced to Mn²⁺ in the spinel structure and formation of MnO, Mn_1.7Ga_1.3O₄ → Mn₂Ga₁O₄ + MnO.     

3D printed interdigitated supercapacitor using reduced graphene oxide-MnOx/Mn3O4 based electrodes

In this study hybrid nanocomposites (HNCs) based on manganese oxides (MnO_x/Mn₃O₄) and reduced graphene oxide (rGO) are synthesized as active electrodes for energy storage devices. Comprehensive structural characterizations demonstrate that the active material is composed of MnO_x/Mn₃O₄ nanorods and nanoparticles embedded in rGO nanosheets. The development of such novel structures is facilitated by the extreme synthesis conditions (high temperatures and pressures) of the liquid-confined plasma plume present in the Laser Ablation Synthesis in Solution (LASiS) technique. Specifically, functional characterizations demonstrate that the performance of the active layer is highly correlated with the MnO_x/Mn₃O₄ to rGO ratio and the morphology of MnO_x/Mn₃O₄ nanostructures in HNCs. To that end, active layer inks comprising HNC samples prepared under optimal laser ablation time windows, when interfaced with a percolated conductive network of electronic grade graphene and carbon nanofibers (CNFs) mixture, indicate superior supercapacitance for functional electrodes fabricated via sequential inkjet printing of the substrate, current collector layer, active material layer, and gel polymer electrolyte layer. Electrochemical characterizations unequivocally reveal that the electrode with the LASiS synthesized MnO_x/Mn₃O₄–rGO composite exhibits significantly higher specific capacitance compared to the ones produced with commercially available Mn₃O₄–graphene NCs. Moreover, the galvanostatic charge–discharge (GCD) experiments with the LASiS synthesized HNCs show a significantly larger charge storage capacity (325 F g⁻¹) in comparison to NCs synthesized with commercially available Mn₃O₄–graphene (189 F g⁻¹). Overall, this study has paved the way for use of LASiS-based synthesized functional material in combination with additive manufacturing techniques for all-printed electronics with superior performance.

LASiS-based HNCs of nanostructured MnO_x/Mn₃O₄.     

Improved NO reduction by using metal–organic framework derived MnOx–ZnO

Derivatives based on metal frameworks (MOFs) are attracting more and more attention in various research fields. MOF-based derivatives x% MnO_x–ZnO are easily synthesized by the thermal decomposition of Mn/MOF-5 precursors. Multiple technological characterizations have been conducted to ascertain the strengthening interaction between Mn species (Mn²⁺ or Mn³⁺) and Zn²⁺ (e.g., XRD, FTIR, TG, XPS, SEM, H₂-TPR and Py-FTIR). The 5% MnO_x–ZnO exhibits the highest NO conversion of 75.5% under C₃H₆-SCR. In situ FTIR and NO-TPD analysis showed that monodentate nitrates, bidentate nitrates, bridged bidentate nitrates, nitrosyl groups and C_xH_yO_z species were formed on the surface, and further hydrocarbonates or carbonates were formed as intermediates, directly generating N₂, CO₂ and H₂O.

Derivatives based on metal frameworks (MOFs) are attracting more and more attention in various research fields.     

Cerium and tin oxides anchored onto reduced graphene oxide for selective catalytic reduction of NO with NH3 at low temperatures

A series of cerium and tin oxides anchored on reduced graphene oxide (CeO₂–SnO_x/rGO) catalysts are synthesized using a hydrothermal method and their catalytic activities are investigated by selective catalytic reduction (SCR) of NO with NH₃ in the temperature range of 120–280 °C. The results indicate that the CeO₂–SnO_x/rGO catalyst shows high SCR activity and high selectivity to N₂ in the temperature range of 120–280 °C. The catalyst with a mass ratio of (Ce + Sn)/GO = 3.9 exhibits NO conversion of about 86% at 160 °C, above 97% NO conversion at temperatures of 200–280 °C and higher than 95% N₂ selectivity at 120–280 °C. In addition, the catalyst presents a certain SO₂ resistance. It is found that the highly dispersed CeO₂ nanoparticles are deposited on the surface of rGO nanosheets, because of the incorporation of Sn⁴⁺ into the lattice of CeO₂. The mesoporous structures of the CeO₂–SnO_x/rGO catalyst provides a large specific surface area and more active sites for facilitating the adsorption of reactant species, leading to high SCR activity. More importantly, the synergistic interaction between cerium and tin oxides is responsible for the excellent SCR activity, which results in a higher ratio of Ce³⁺/(Ce³⁺ + Ce⁴⁺), higher concentrations of surface chemisorbed oxygen and oxygen vacancies, more strong acid sites and stronger acid strength on the surface of the CeSn(3.9)/rGO catalyst.

A series of cerium and tin oxides anchored on graphene oxide (CeO₂–SnO_x/rGO) catalysts are synthesized for selective catalytic reduction of NO with NH₃ in the temperature range of 120–280 °C.     

The preparation of a novel iron/manganese binary oxide for the efficient removal of hexavalent chromium [Cr(vi)] from aqueous solutions

To remove hexavalent chromium Cr(vi) efficiently, a novel Fe–Mn binary oxide adsorbent was prepared via a “two-step method” combined with a co-precipitation method and hydrothermal method. The as-prepared Fe–Mn binary oxide absorbent was characterized via transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectra (FTIR), thermogravimetric analysis (TGA), zeta potential, BET and X-ray photoelectron spectroscopy (XPS). The results indicated that the morphology of the adsorbent was rod-like with length of about 100 nm and width of about 50–60 nm, specific surface area was 63.297 m² g⁻¹, has the composition of α-Fe₂O₃, β-MnO₂ and MnFe₂O₄ and isoelectric point was observed at pH value of 4.81. The removal of Cr(vi) was chosen as a model reaction to evaluate the adsorption capacity of the Fe–Mn binary oxide adsorbent, indicating that the Fe–Mn binary oxide adsorbent showed high adsorption performance (removal rate = 99%) and excellent adsorption stability (removal rate > 90% after six rounds of adsorption). The adsorption behavior of the Fe–Mn binary oxide was better represented by the Freundlich model (adsorption isotherm) and the pseudo-second-order model (adsorption kinetic), suggesting that the adsorption process was multi-molecular layer chemical adsorption. The possible adsorption mechanism of the Fe–Mn binary oxide for the removal of Cr(vi) included the protonation process and the electrostatic attraction interactions.

A novel Fe–Mn binary oxide adsorbent prepared via “co-precipitation and hydrothermal” method, for the efficient and fast removal of Cr(vi).     

The promotion effect of manganese on Cu/SAPO for selective catalytic reduction of NOx with NH3

The activity and hydrothermal stability of Cu/SAPO and xMn–2Cu/SAPO for low-temperature selective catalytic reduction of NO_x with ammonia were investigated. An ion-exchanged method was employed to synthesize xMn–2Cu/SAPO, which was characterized by N₂ adsorption, ICP-AES, X-ray diffraction (XRD), NH₃-temperature programmed desorption (NH₃-TPD), NO oxidation, X-ray photoelectron spectrum (XPS), UV-vis, H₂-temperature programmed reduction (H₂-TPR) and diffuse reflectance infrared Fourier transform spectra (DRIFTS). 2Mn–2Cu/SAPO and 4Mn–2Cu/SAPO showed the best SCR activity, in that at 150 °C NO conversion reached 76% and N₂ selectivity was above 95% for the samples. NO oxidation results showed that the 2Mn–2Cu/SAPO had the best NO oxidation activity and the BET surface area decreased as manganese loading increased. XRD results showed that the metal species was well dispersed. NH₃-TPD showed that the acid sites have no significant influence on the SCR activity of xMn–2Cu/SAPO. H₂-TPR patterns showed good redox capacity for xMn–2Cu/SAPO. UV-vis and H₂-TPR showed that the ratio of Mn⁴⁺ to Mn³⁺ increased as manganese loading increased. XPS spectra showed a significant amount of Mn³⁺ and Mn⁴⁺ species on the surface and addition of manganese increased the ratio of Cu²⁺. The promotion effect of manganese to 2Cu/SAPO comes from the generation of Mn³⁺ and Mn⁴⁺ species. Deduced from the DRIFTS spectra, the Elay–Rideal mechanism was effective on 4Mn–2Cu/SAPO.

The activity and N₂ selectivity of Cu/SAPO and xMn–2Cu/SAPO for low-temperature selective catalytic reduction of NO_x with NH₃ were investigated.     

Comparative study of mesoporous NixMn6−xCe4 composite oxides for NO catalytic oxidation

In this work, a series of mesoporous Ni_xMn_6−xCe ternary oxides were prepared to investigate their NO catalytic oxidation ability. The sample Ni₂Mn₄Ce₄ showed a 95% NO conversion at 210 °C (GHSV, ∼80 000 h⁻¹). Characterization results showed the good catalytic performance of Ni₂Mn₄Ce₄ was due to its high specific surface area, more surface oxygen and high valance manganese species, which can be ascribed to the incorporation of three elements. Based on the results of XRD, H₂-TPR, O₂-TPD and XPS, we confirmed the existence of Ni³⁺ + Mn³⁺ → Ni²⁺ + Mn⁴⁺, Ce⁴⁺ + Ni²⁺ → Ce³⁺ + Ni³⁺ in Ni₂Mn₄Ce₄, and the oxidation–reduction cycles were proved to be helpful for NO oxidation. The results from an in situ DRIFTS study indicated the presence of bidentate nitrate and monodentate nitrate species on the catalyst''s surface. The nitrate species were proved to be intermediates for NO oxidation to NO₂. A nitrogen circle mechanism was proposed to explain the possible route for NO oxidation. Nickel introduction was also helpful to improve the SO₂ resistance of the NO oxidation reaction. The activity drop of Ni₂Mn₄Ce₄ was 13.15% in the presence of SO₂, better than Mn₆Ce₄ (25.29%).

In this work, a series of mesoporous Ni_xMn_6−xCe ternary oxides were prepared to investigate their NO catalytic oxidation ability.     

The investigation of structural and vibrational properties and optical behavior of Ti-doped La0.67Ba0.25Ca0.08Mn(1−x)TixO3 (x = 0.00, 0.05 and 0.10) manganites

The influence of Ti⁴⁺ ions incorporated into the B site on the structural, vibrational and optical properties of La_0.67Ba_0.25Ca_0.08Mn_(1−x)Ti_xO₃ (LBCM_(1−x)T_x), a polycrystalline compound prepared by a molten salt method, was discussed. The X-ray diffraction (XRD) studies confirmed that at room temperature these compounds crystallize in the rhombohedral phases of R$\bar{3}$c. Rietveld refinement indicated that the octahedron (Mn/Ti)O₆ underwent a slight deformation and the θ_{(Mn/Ti)–O–(Mn/Ti)} bond angles decreased with the increase in the Ti content. Furthermore, Raman spectra were recorded at room temperature for the LBCM_(1−x)T_x ceramics to investigate the influence of incorporated Ti⁴⁺ ions in LBCM_(1−x)T_x. Moreover, we controlled the frequency and damping of the optic modes based on Ti incorporation. The infrared (IR) absorption spectrum (FTIR) analysis in the span of 420–750 cm⁻¹ supports the XRD results. The diffuse reflectance data at room temperature verified that both transition levels (⁵E_g → ⁵T_5g) and (⁴A_2g → ⁴T_2g) correspond to the Mn³⁺ and Mn⁴⁺ ions. The optical band gap (E_g) values decreased from 2.90 eV to 2.70 eV with the increase in the Ti⁴⁺ content, implying that our samples could be good candidates for some applications in luminescent devices, such as ultrafast optoelectronic devices. Moreover, the photoluminescence spectra (PL) features at room temperature decreased for all samples. CIE were estimated for all the concentrations of Ti⁴⁺ ions. The results indicated that are a shifts in the CIE values of the compounds.

The influence of Ti⁴⁺ ions incorporated into the B site on the structural, vibrational and optical properties of La_0.67Ba_0.25Ca_0.08Mn_(1−x)Ti_xO₃ (LBCM_(1−x)T_x), a polycrystalline compound prepared by a molten salt method, was discussed.     

Sm-doped manganese-based Zr–Fe polymeric pillared interlayered montmorillonite for low temperature selective catalytic reduction of NOx by NH3 in metallurgical sintering flue gas

In this work, Sm-doped manganese supported Zr–Fe polymeric pillared interlayered montmorillonites (Mn/ZrFe-PILMs) were prepared for the low-temperature selective catalytic reduction (SCR) of NO_x with NH₃ in metallurgical sintering flue gas. These pillared interlayered montmorillonite catalysts were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, nitrogen adsorption–desorption isotherm, ammonia temperature-programmed desorption, and hydrogen temperature-programmed reduction to study the influence of Sm doping on the SCR performance. The ZrFe-PILMs with a Mn/Sm molar ratio of 18 : 2 showed the excellent SCR activity among these catalysts, where a 95.5% NO_x conversion ratio at 200 °C at a space velocity of 20 000 h⁻¹ was obtained. Samarium oxide and manganese oxides were highly dispersed on the ZrFe-PILMs with different Mn/Sm molar ratios by the XRD results and SEM-EDS results. Meanwhile, the Mn–Sm/ZrFe-PILM (18 : 2) had the lowest temperature hydrogen reduction peak by H₂-TPR results, which indicated that it had the lowest active bond energy on its surface. And the NH₃-TPD results expressed that the Mn–Sm/ZrFe-PILM (18 : 2) had the most acidic sites, especially the weakly acidic sites. Therefore, it was found that the introduction of a small amount of Sm (Mn : Sm = 18 : 2) to Mn/ZrFe-PILM can significantly improve catalytic activity by the increased active oxygen component and the surface acidity.

Trace amount of Sm-doped Mn-based Zr–Fe polymeric pillared interlayered montmorillonite promotes low temperature catalytic activity in excess oxygen.     

Selective oxidation of n-buthanol to butyraldehyde over MnCo2O4 spinel oxides

Partial oxidation of n-butanol to butyraldehyde, propionaldehyde and acetaldehyde over MnCo₂O₄ spinel oxides has been investigated. Physicochemical characteristics of samples, prepared by co-precipitation with different amounts of precipitating agent, were studied by XRD, N₂ adsorption–desorption isotherms, FT-IR, SEM and XPS. The ratio between the precipitating agent and the precursors has a considerable influence both on the structure, which is evidenced by XRD, due to switching from a crystalline structure to an amorphous one and on the surface (XPS) by an obvious change in the ratio Co³⁺/Co²⁺ and Mn⁴⁺/Mn³⁺ and in the content of oxygen vacancies. The reaction rate is not influenced by the oxygen pressure, emphasizing that n-butanol oxidation occurs through the Mars van Krevelen mechanism. The conversion of n-butanol and yield of butyraldehyde are directly proportional to the cobalt content on the surface, while the propionaldehyde yield is proportional to the Mn⁴⁺/Mn³⁺ ratio.

Partial oxidation of n-butanol to butyraldehyde, propionaldehyde and acetaldehyde over MnCo₂O₄ spinel oxides has been investigated.     

Thermochemistry of cation disordered Li ion battery cathode materials, (M′ = Nb and Ta,M′′ = Mn and Fe)

High temperature oxide melt solution calorimetry studies on (M′ = Nb⁵⁺, M′′ = Mn³⁺ and Fe³⁺ and x = 0.20, 0.30 and 0.40) oxides and a new family of Ta containing Li excess disordered cathode materials, (M′ = Ta⁵⁺, M′′ = Fe³⁺ and x = 0.20, 0.30 and 0.40), synthesized by a rapid quenching method, are reported in this study. The enthalpies of formation determined from high temperature calorimetry studies reveal that the stability of compounds increases with the increasing Li content per formula unit. The reaction between more basic Li₂O and acidic transition metal oxides results in the more negative enthalpies of formation for these compounds. The work reveals that the formation enthalpy term plays a more important role in the stabilization of such disordered Li ion materials at room temperature whereas configurational entropy along with lattice entropy (vibrational and magnetic) contributes to the stabilization at high temperature from which the samples are quenched.

Enthalpies of formation from oxides (ΔH_f,ox) of novel disordered Li_1+xTa_xFe_1−2xO₂ and reported (M′′ = Mn³⁺ and Fe³⁺).     

Influence of neodymium substitution on structural,magnetic and spectroscopic properties of Ni–Zn–Al nano-ferrites

Ni_0.6Zn_0.4Al_0.5Fe_1.5−xNd_xO₄ ferrite samples, with x = 0.00, 0.05, 0.075 and 0.1, were synthesized using the sol–gel method. The effects of Nd³⁺ doping on the structural, magnetic and spectroscopic properties were investigated. XRD Rietveld refinement carried out using the FULLPROF program shows that the Ni–Zn ferrite retains its pure single phase cubic structure with Fd$\bar{3}$m space group. An increase in lattice constant and porosity happens with increasing Nd³⁺ concentration. FTIR spectra present the two prominent absorption bands in the range of 400 to 600 cm⁻¹ which are the fingerprint region of all ferrites. The change in Raman modes in the synthesized ferrite system were observed with Nd³⁺ substitution. The magnetization curves show a typical transition, at the Curie temperature T_C, from a low temperature ferrimagnetic state to a high temperature paramagnetic state. The saturation magnetization, coercivity and remanence magnetization are found to be decreasing with increasing the Nd³⁺ concentration.

The incorporation of Nd³⁺ in the Ni–Zn–Al ferrite spinel causes an improvement in magnetic parameters. Spectroscopic properties were discussed based on FTIR and Raman measurements and proved the purity and good crystallization of the samples.