Effect of Dy-substitution on structural and magnetic properties of MnZn ferrite nanoparticles

This paper describes the structural and magnetic properties of Dy-substituted Mn-Zn ferrite nanoparticles. Mn-Zn-Dy ferrite nanoparticles of the composition Mn_(0.5)Zn_(0.5)Dy_xFe_(2-x)O_4(x=0.05, 0.1,0.15 and 0.2) were synthesized by a facile chemical co-precipitation method. The samples were characterized through X-ray diffraction(XRD), transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FTIR), vibrating sample magnetometer(VSM) and Curie temperature. The XRD patterns confirm the synthesis of single crystalline phase of Mn-Zn-Dy ferrite nanoparticles. Lattice parameter increases with increase in Dy-substitution which confirms the replacement of Fe~(3+) ions by Dy~(3+) ions.Crystallite size is of the order of 6-8 nm for all these samples. The particle sizes observed from TEM analysis are in good agreement with the XRD values. The magnetic measurements show superparamagnetic nature of the samples. The saturation magnetization decreases with increase in Dyconcentration and can be correlated to modifications in the A-B exchange interactions as a result of the structural modifications due to Dy-substitution. The Curie temperature for Mn_(0.5)Zn_(0.5)Fe_2 O_4 nanoparticles is 124 ℃ and decreases up to 84 ℃ with the increase in the Dy-concentration. The decrease in Curie temperature can be attributed to the weakening of the superexchange interaction between A-site and B-site as a result of Dy-substitution. The low value of Curie temperature and higher value of thermomagnetic coefficient k_T shown by these samples makes them suitable for the preparation of temperature sensitive ferrofluid for heat transfer applications.     

Effects of cerium doping position on physicochemical properties and catalytic performance in methanol total oxidation

The physicochemical properties of Pd and PdPt catalysts which possess different Ce doping position were investigated by techniques of TEM, XRD, N₂ adsorption-desorption, XPS and FT-IR. The catalytic performance for methanol total oxidation was examined to study the effects of Ce adding position. CeO₂Al₂O₃TiO₂ (CAT) catalysts that Ce is directly introduced into support show higher reactivity and CO₂ selectivity than CeO₂/Al₂O₃TiO₂ (Ce/AT) samples in which Ce is loaded by impregnation method. The characterization results reveal that the Ce doping position does not cause obvious otherness of basic crystalline phase and mesoporous structure of support. However, the Ce doping position affects the pore shapes of support and then influences the pore diameter. CAT catalysts possess more abundant adsorbed oxygen and more Ti³⁺ can transform the more gaseous oxygen into the active oxygen species on the catalyst surface, which is beneficial to the reaction. The AlOTi bridges in CAT facilitate the cooperation of Al and Ti species, which further speeds up the reaction rate.     

Structural properties and catalytic performance of the LaCuZn mixed oxides for CO2 hydrogenation to methanol

A series of La-Cu-Zn-O mixed oxide catalysts were synthesized by a co-precipitation method and calcined under different temperatures. The XRD, BET, TPR, N_2 O-adsorption, XPS, SEM and TPD techniques were carried out to measure the aimed catalysts. The results indicated that the chemical environment of lanthanum element changes with the increase of calcination temperature. The La_2 CuO_4 perovskite structure is obtained at the temperature higher than 823 K and the special copper species appear in the perovskites due to the special structure property. The catalysts with La_2 CuO_4 perovskite structure show higher methanol selectivity compared with the mixed copper catalyst. For the perovskite catalysts, the conversion of CO_2 changes with the same tendency of the copper species ratio((Cu~(α+)+Cu~0)/(Cu_(Total))%), which implied both Cu~(α+) and Cu~0 are important active sites in the perovskite catalyst for the reaction.     

Promoting effect of tantalum and antimony additives on deNOx performance of Ce3Ta3SbOx for NH3-SCR reaction and DRIFT studies

A superior Ce-Ta-Sb composite oxide catalyst prepared using homogeneous precipitation method exhibited excellent deNOx efficiency and nearly 100% N_2 selectivity with broad operation temperature window and better resistance to higher space velocity, meanwhile strong resistance to H_2 O and SO_2. This catalyst was systematically characterized using XRD, N_2 adsorption, SEM, TEM, XPS, ESR, Raman, H_2-TPR,NH3-TPD and in situ DRIFTS. There exists a synergistic effect between Ce, Ta and Sb species. It is further indicated that the prominent deNOx performance of the Ce3 Ta3 SbOx catalyst is attributed to the elevated Ce3+ concentrations, abundant active surface oxygen species, as well as surface acidity and reducibility,which is closely linked with the synergistic effect between Ce, Sb and Ta species. Results from DRIFTS reveal that the reaction mechanism of surface-adsorbed NH3 and NO_x species is linked to temperature,the L-H mechanism mainly occurs at low temperature(300 ℃),while the E-R mechanism occurs at high temperature(300 ℃). Overall,these findings indicate that Ce3 Ta3 SbOx is promising for NO_x practical abatement.     

Catalytic performance of Zr-doped CuO-CeO_2 oxides for CO selective oxidation in H_2-rich stream

Zr-doped CuO-CeO_2 catalysts for CO selective oxidation were designed and prepared by the hydrothermal method and coprecipitation. The experimental samples were characterized by means of N_2 adsorption-desorption isotherms, powder X-ray diffraction, temperature-programmed reduction and Xray photoelectron spectroscopy. It is observed that the catalyst prepared by hydrothermal method exhibits larger specific surface area, smaller crystalline size and higher dispersion of active components compared with those of the catalyst obtained by coprecipitation. Meanwhile, redox properties of copper oxide are improved significantly and highly dispersed copper species providing CO oxidation sites are present on the surface. Furthermore, adsorptive centers of CO and active oxygen species increase on the copper-ceria interfaces. The Zr-doped CuO-CeO_2 catalyst prepared by hydrothermal method possesses superior catalytic activity and selectivity for selective oxidation of CO at low temperature compared with those of the sample prepared by coprecipitation. The temperature corresponding to 50% CO conversion is only 73 ℃ and the temperature span of total CO conversion is expanded from 120 to 160 ℃.     

Tailoring the mechanical anisotropy of sintered NdFeB magnets by PrCu grain boundary reconstruction

Pr_(83)Cu_(17)(wt%) grain boundary reconstruction was applied to prepare sintered NdFeB magnets. The effects of addition amount and annealing on the bending strength were investigated. The results show that Pr_(83)Cu_(17) can not only effectively enhance the bending strength, but also change the mechanical anisotropy in two directions parallel and perpendicular to c-axis. The bending strength perpendicular to c-axis reaches 404 MPa in 10 wt% addition magnet, higher than 348 MPa along parallel direction. This change is attributed to the preferred distribution of boundary phases, i.e., ductile(Nd,Pr)-Fe-Cu phase along perpendicular direction to c-axis and(Nd,Pr)-Fe phase along parallel direction. Moreover, the Cu migration during 480 ℃ annealing is found to be related to this boundary phase distribution.     

Barrier effect of SiO_2 shell over hollow CeO_2/CuO@SiO_2 catalysts for broadening temperature window of total CO conversion

The hollow inverse CeO_2/CuO@SiO_2 catalysts with different Ce/Cu mass ratios were synthesized by the two-step hydrothermal and incipient wetness impregnation methods,and characterized by multitechnique characterizations,such as SEM,TEM,XRD,H_2-TPR,XPS and N_2 adsorption-desorption techniques.It is found that the hollow shell is composed of CuO and SiO_2,and CeO_2 nanoparticles are coated on the surface of CuO@SiO_2 support.And the CeO_2/CuO@SiO_2 catalyst with the Ce/Cu mass ratios of 1:1 denoted as 1 CeO_2/CuO@SiO_2,which possesses a maximum amount of highly dispersed copper species and medium-sized CuO as well as the highest concentration of oxygen vacancies,exhibits the highest catalytic activity and widest full CO conversion window.The barrier effect of the SiO_2 shell effectively prevents the reduction of CuO species,which broadens temperature window of CO total conversion and enhances CO_2 selectivity above 155℃over the 1 CeO_2/CuO@SiO_2 catalyst in comparison with the CuO-CeO_2 and CeO_2-CuO catalysts.     

The influence of temperature on rare earth flotation with naphthyl hydroxamic acid

The influence of temperature on the complex process of Bayan Obo rare earth (RE) ore flotation with a collector of naphthyl hydroxamic acid (LF8#) was investigated. Industrial test data shows that the grade and recovery of RE increase with the temperature. However, the proportion of bastnaesite in the bulk concentrate increases as the RE grade improves. Adsorption mechanism of LF8# on the surfaces of bastnaesite and monazite were confirmed via zeta potential, UV/Vis Spectrophotometer (UV/Vis), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy analyses (XPS). Although the results indicate that the total amount of the LF8# adsorption on the surface of bastnaesite and monazite decreases with increasing the temperature, the amount of stable adsorbed predominance of characteristic bonds (C(O)N) from LF8# uptake on bastnaesite surfaces increases significantly at high temperatures. This conclusion indicates that the adsorption stability increases with increasing the temperature. For monazite, the amount of characteristic elements C and N in LF8# does not increase as the temperature increases on the mineral surface, but the proportion of characteristic bonds increases, which shows that the adsorption stability of LF8# on the surface of monazite also increases, but it is not as significant as bastnaesite, which may be one of the reasons that the floatability of bastnaesite is better than those of monazite. Pulp dispersion results show that the temperature improve the dispersions of both the gangue and RE minerals. This improved the flotation selectivity so that it favored RE minerals. The calculated bubble size distribution confirms that higher temperatures generate smaller bubbles, thereby increasing the bubble-particle collision probability and the recovery of RE minerals.     

Al_2O_3 supported hybrid Pd-CeO_2 colloidal spheres and its enhanced catalytic performances for methane combustion

Fabrication of novel nano-catalyst with improved activity and stability has been a hot topic in heterogeneous catalysis. Herein a novel approach was designed to synthesize Pd-CeO_2 colloidal assembled spheres(CASs) in one-pot fashion. The Pd clusters were encompassed by the CeO_2 nanocrystals with a high dispersity. Based on this hybrid structure, the Pd/ceria interface area can be greatly improved. After Pd-CeO_2 CASs was supported on γ-Al_2O_3, its catalytic activity for CH_4 combustion was evaluated. The result shows that Al_2O_3 supported Pd-CeO_2 CASs exhibits an improved catalytic activity and stability,compared to the Pd/CeO_2 catalyst prepared by impregnation method. The results of several characterization techniques indicate that the enhanced catalytic activity of Al_2O_3 supported Pd-CeO_2 CASs can be attributed to the more interfacial Pd-O-Ce species and the more surface active oxygen species.     

Preparation and properties of temperature sensitive paint based on Eu(DBM)3phen as probe molecule

Probe molecule Eu(DBM)3 phen is made up of europium oxide(Eu_2 O_3),dibenzoylmethane(DBM) and1,10-phenanthroline(phen). The temperature sensitive paint(TSP) was compounded by the polymerization of the probe molecule, methyl methacrylate(MMA) and the initiator of benzoyl peroxide(BPO).The structure, morphology, luminescence property of probe molecule and the temperature quenching property of the temperature sensitive paint(TSP) were characterized by infrared spectrometer, UV-vis spectrometer, scanning electron microscopy and fluorescence spectrometer respectively. The infrared spectrum and UV-vis spectra show that Eu and DBM form six membered rings, and Eu-O coordinate bonds form. The nanocrystals are in sphere-like morphology with an average size of approximately100 nm. Fluorescence spectra present that the performance of temperature quenching is excellent,what's more, TSP sample has different temperature sensitivity in various temperature scope. Particularly,under excitation of 286 nm, TSP has a highest temperature sensitivity between 50 and 60 ℃, and the strongest fluorescence emission reaches a peak(615 nm). It indicated that probe molecule(Eu(DBM)_3 phen) has strong luminescent intensity and the temperature quenching properties of Eu(DBM)_3 phen/PMMA is good.     

Development of a microfluidic-chip system based on parallel flow for intensified Gd(III) extraction from nitrate media using cationic extractant

Microfluidic solvent extraction (micro SX) of gadolinium was conducted using a mono- and di-ester mixture (MDEHPA) as the cationic extractant. A microfluidic YY channel was fabricated using CO₂-laser technique in a glass microchip used as the extraction system. Compared with batch extraction, extraction kinetic is found fast, and extraction equilibrium is attained within 15 s. Stoichiometry of the extracted complex is found to be Gd(NO₃)₃·3MDEHPA using log–log plot method. Additionally, the operating parameters and overall volumetric mass transfer coefficient $\left(k_{\mathrm{L}}\alpha \right)$ were investigated to determine the mass transfer performance. Optimal condition of microextraction for gadolinium using response surface methodology was determined (feed solutions 31 mg/L adjusted to pH value 2.5, extractant concentration 2.9 vol% and extraction time 13.5 s). In optimal condition, gadolinium extraction yield is obtained 95.5%. Findings of this study approve simplicity, portability, effectiveness, swiftness, and environmental friendliness microfluidic solvent extraction process and reveal that micro SX is useful in the field of extraction strategic metals present at low concentrations, which are otherwise not technically amenable or economically feasible to extract using current traditional methods.     

Surface exsolution and local atomic structure of amorphous CeTiOx

We made precipitated nano-ceria (～5 nm) on the surface of the catalyst by heat treatment of Ce-supersaturated amorphous CeTiO_x to improve the oxygen storage properties of CeO₂. The catalysts were prepared by sol-gel methods and TiO₂ nanoparticles were preferentially generated as a core material to form selective Ce-supersaturated structure on the catalyst surface. Reaction temperature and amount of doping element are optimized to induce selective crystallization of CeO₂. CeCe (2nd shell) bond around 0.38 nm of Ce L₃-edge extended X-ray absorption fine structure is reduced and nanostructure of precipitated ceria on the surface is observed by HREM. The catalyst is present as amorphous with precipitated nano-CeO₂ on the surface. The de-NO_x efficiency of the catalyst, which has precipitated CeO₂, improves by ～50% owing to the simultaneous reactions of the nano CeO₂ and the amorphous CeTiO_x.     

Effect of OH~- on fluorescence properties in 1.5-1.6 μm for Er:Yb:YCOB crystal

FTIR absorption spectra indicate that H+ can easily enter the crystal structure and form OH-centers in Er:Yb:YCOB and O—H bonds prefer to lie in the a-c plane. Within our current studied concentration level,crystal samples with higher OH-abso rption coefficie nts demonstrate stro nger fluo rescence intensity and longer fluorescence lifetime at 1535 nm. As the stretching vibration energy of OH-group approximately corresponds to the energy gap between the ~4 I_(11/2) and ~4 I_(13/2) levels of Er~(3+), and thus, OH-ions can shorten the fluorescence lifetime of Er~(3+)-~4I_(11/2) level by the phonon-assisted cross-relaxation process between the Er~(3+) and OH-ions. Our curre nt results confirm that a certain conte nt of OH ions can enhance the ene rgy transfer process from Yb~(3+) to Er~(3+) and subsequently promote fluorescence output in 1.5-1.6 μm.     

Eu3+ ions grafted polyacrylonitrile nanofibers possessing enhanced fluorescence performance by introducing benzoic acid as assistant ligand

Eu³⁺ ions were grafted onto the surface of electrospun polyacrylonitrile (PAN) nanofibers through coordination effect between CN groups on PAN nanofibers and Eu³⁺ ions, and benzoic acid (BA) was introduced as an assistant ligand. The impacts of concentrations of Eu³⁺ ions and BA, and reaction time on the properties of final products were investigated. The results reveal that Eu³⁺ ions can be successfully grafted onto PAN nanofibers, but the fluorescence intensity of the obtained PAN@Eu³⁺ nanofibers is very weak. After BA is introduced as the assistant ligand, the fluorescence intensity of the obtained PAN@(Eu³⁺/BA) nanofibers is greatly stronger than that of PAN@Eu³⁺ nanofibers, and meanwhile, concentration quenching effect of Eu³⁺ ions can be effectively restrained. Furthermore, the superior structure of PAN@(Eu³⁺/BA) nanofibers not only brings the effective utilization of precious elemental europium, but also guarantees high mechanical strength.     

Preparation and reaction mechanism of novel CexCoyCuz oxide composite catalysts towards oxidation of o-xylene

Ce_xCo_yCu_z oxide composite catalysts were prepared by using polyethylene glycol, citrate sol–gel method combined with PMMA template for the oxidation of o-xylene. The catalysts were characterized by the X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR), etc. The catalytic activity for o-xylene was investigated. The catalytic degradation pathway and mechanism of o-xylene were inferred. The results show that CeO₂ is mainly present on the surface of all catalysts. The surface area of Ce₂Co₁Cu₁ is up to 77.2 m²/g, and the average pore size is 10.62 nm. It exhibits redox and sufficient Ce⁴⁺ and Ce³⁺, and reactive oxygen species, and has maximum O–H and CO in the five catalyst samples. The catalytic activity of Ce₂Co₁Cu₁ is the best at low temperature, with the T₅₀ and T₉₀ values of 235 and 258 °C at a space velocity of 32000 h^?1, respectively. The o-xylene is oxidized to o-methyl benzaldehyde, and then further oxidized to o-methylbenzoic acid, and finally CO₂ and H₂O are formed.     

Effect of rare earth elements(La,Y,Pr)in multi-element composite perovskite oxide supports for ammonia synthesis

A series of BaCe0₃modified with different rare earth elements(La,Y,Pr)were synthesized by coprecipitation and calcination and the effect of rare earth elements for catalytic ammonia synthesis under mild conditions was studied.The ammonia synthesis performance tests show that 2.5%Ru/BaCe_0.9La_0.1O_3-δcatalyst(All the percentages of Ru in this article are in mass fraction)exhibits the highest ammonia synthesis rate(34 mmol/(g·h))at 3 MPa,450℃,and no sign of deactivation after 100 h of reaction.H₂-TPR and XPS analyses indicate that the introduction of La increases the amount of oxygen vacancies of the catalyst,which is beneficial to increasing the electron density of Ru surface.HRTEM analysis shows that the Ru particle size is reduced greatly after La is introduced,which facilitates the catalyst generating more Bs-type sites(active sites of Ru species for N=N dissociation).CO₂-TPD analysis indicates that BaCe_0.9La_0.1O_3-δhas stronger basicity,which promotes electrons transfer from support to Ru.This work provides an effective method for design and synthesis of Ru-based multi-element composite perovskite oxide catalysts.     

Synergistic effects of PtFe/CeO2 catalysts afford high catalytic performance in selective hydrogenation of cinnamaldehyde

Selective hydrogenation of unsaturated aldehydes remains a grand challenge in controlling chemoselectivity up to now.We synthesized a series of PtFe_x/CeO₂ catalysts,which were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS) as well as temperature-programmed-reduction by hydrogen(H₂-TPR).The catalytic performance of PtFe_x/CeO₂,including cinnamaldehyde(CAL) conversion and sele...     

Rare-earth free sensitizer in NaLuCrF4:Er upconversion material

Upconversion phosphors are known as a material system that can convert near-infrared light into visible/ultraviolet emissions by sequentially absorbing multiple photons. The studies on upconversion materials often use two rare earth (RE) ions as a sensitizer-activator pair. We investigated the influences on luminescence intensity depending on Cr-doping content (x) of hexagonal NaLu_0.98–xCr_xF₄Er_0.02 (x = 0–0.9) upconversion material by substituting Lu³⁺ ions with Cr³⁺in the absence of Gd³⁺. The change in upconversion luminescence intensity appears with saddle-like shape. We suggest that Cr³⁺ ions play the dual role as a constituent in host lattice and a sensitizer in the upconversion process. Optimal conditions for gaining the strongest upconversion emission correspond to x = 0.3–0.5, where there are effective energy transfers between Cr³⁺ and Er³⁺ ions and CrEr dimers. Apart from these values, the emission intensity decreases rapidly which can be ascribed to the absence of multiple-photon absorption for the case of low Cr³⁺ contents, and to the coupling between Cr³⁺ and/or Er³⁺ ions for the case of high Cr³⁺ contents. Magnetization and electron-spin-resonant measurements were performed to understand the correlation between the optical and magnetic properties.     

Lanthanum-doped Cu-Mn composite oxide catalysts for catalytic oxidation of toluene

CuMn mixed oxides catalysts doped with La were prepared following a co-precipitation method and used for the catalytic oxidation of toluene. Catalysts properties of the catalysts were investigated by X-ray diffraction, N_2 adsorption/desorption,scanning electron microscopy, H_2-temperature-programmed reduction(H_2-TPR), O_2-temperature-programmed desorption(O_2-TPD) and X-ray photoelectron spectroscopy techniques. Characterization data reveal that the phase change and decrease in crystallinity of the La-doped catalysts increase the number of oxygen vacancies. Improvements in reducibility and an increase in the amount of chemisorbed oxygen of the La-doped catalysts were also verified by H_2-TPR and O_2-TPD. The activity of the CuMn mixed oxides catalysts is significantly improved by the addition of a nominal amount of La. The CuMn/La-4 mol% catalyst exhibits the best catalytic activity, with a 90%conversion temperature of 255 ℃,attributed to a high Mn~(3+)ratio, superficial chemisorbed oxygen,and high surface area. This study indicates La to be a promising dopant for Cu-Mn catalysts toward toluene oxidation.     

Electrochemical properties of gadolinium on liquid gallium electrode in LiClKCl eutectic

This work presents the electrochemical properties of gadolinium(Gd), a significant rare earth element in spent nuclear fuel(SNF), in the LiCl-KCl eutectic. To explore thermodynamic properties of Gd at the liquid gallium(Ga) electrode, experiments were performed both on the inert tungsten(W) and liquid gallium(Ga) electrode at different temperatures in a range from 723 to 823 K, which show that the Gd metal can be oxidized to Gd(Ⅲ) by exchanging of 3 electrons. Electrochemical techniques including cyclic voltammetry(CV), open circuit potential(OCP), potentiostatic electrolysis and galvanostatic electrolysis were utilized to detect the electrochemical behavior and evaluate standard apparent potential of the Gd(Ⅲ)/Gd couple,and E_(Gd(Ⅲ)/Gd)~*=-3.456 + 6.2×10~(-4)T(±0.046)( vs Cl_2/Cl~-) is obtained.In addition, electromotive force(EMF) and coulometric titration were employed to calculate the activity and activity coefficient of Gd in metal Ga. After calculation, the activity is 1.791×10~(-15) at 723 K and function of activity coefficient and temperature is lgγ = 3.485-10927/T(±0.0875).