Small Amount Of Pr Research Articles

Study on the Catalytic Activity Modification of Pr and Nd Doped Ce0.7Zr0.3O2 Catalysts for Simultaneous Removal of PM and NOX

Cerium-zirconium composite oxides (Ce0.7Zr0.3O2) have a remarkable effect on catalytic removal of carbon particles (PM) and nitrogen oxides (NOX) emitted from diesel engine, in order to further improve the thermal stability, oxygen storage capacity and low temperature catalytic REDOX performance of cerium zirconium composite oxides (Ce0.7Zr0.3O2), a small amount of Pr and Nd rare earth elements are doped to improve the catalytic activity of cerium zirconium composite oxides. In this paper, the composite oxide of Pr6O11–Nd2O3–CeO2–ZrO2 is prepared by unsteady co-precipitation method, and the physicochemical properties of the composite oxide catalyst are analyzed by BET, SEM, XRD and ICP. The gas adsorption capacity and catalytic activity of composite oxide catalysts are measured by temperature programmed reaction technology (TPR). The results show that the composite oxide of Pr0.05Nd0.05Ce0.6Zr0.3O2 prepared by using rare earth elements Pr and Nd inhibits the growth process of grain, refining the grain, and improving the sintering phenomenon at high temperature. The addition of Pr and Nd causes lattice defects, increases the number of oxygen vacancies, and improves the mobility of lattice oxygen, namely promotes oxide oxygen storage property, gas adsorption and catalytic oxidation reduction ability. After modification, Pr0.05Nd0.05Ce0.6Zr0.3O2 has good resistance to high temperature aging performance, prolongs the service life, reduces the PM lowest ignition temperature and minimum catalytic activity temperature of nitrogen oxide, and promotes the NOX reduction rate. For Pr0.05Nd0.05Ce0.6Zr0.3O2, the lowest ignition temperature of PM is about 150 °C, and the lowest catalytic activity temperature of NO is about 130 °C. The maximum CO2 production rate is 68.3%, and the maximum NO reduction rate is 45%.

Coercivity enhancement of hot-deformed Nd–Fe–B magnets with Pr–Cu alloy addition

Effects of low-melting Pr–Cu alloy addition on the microstructure and magnetic properties of the hot-deformation Nd–Fe–B magnets were investigated. A small amount of Pr–Cu addition enhances the coercivity of the hot-deformation Nd–Fe–B magnets obviously. The coercivity of the hot-deformation Nd–Fe–B magnets with 4.0 wt% Pr85Cu15 addition increases to 1271 kA·m−1, 75.69% higher than that of Pr–Cu-free magnet (723 kA·m−1), and then decreases with 5 wt% Pr85Cu15 addition. It is observed that there a uniform RE-rich phase is formed wrapping the Nd2Fe14B main phase in the sample with 4.0% Pr85Cu15 addition by scanning electron microscopy (SEM), which promotes the coercivity. The angular dependence of coercivity for the hot-deformation Nd–Fe–B magnets indicates that the coercivity mechanism is nucleation combined with domain wall pinning. The domain wall pinning is weakened, while the nucleation is enhanced after Pr–Cu addition. The remanence, intrinsic coercivity, and maximum magnetic energy product of the original Nd–Fe–B magnet are 1.45 T, 723 kA·m−1, and 419.8 kJ·m−3, respectively, and those of the sample with 4.0% Pr85Cu15 alloy addition are 1.30 T, 1271 kA·m−1, and 330.0 kJ·m−3, respectively.

Synthesis and photoelectric properties of new Pr-bonded polymers by coordination of isopropyloxide and bipyridine unit

A series of novel praseodymium (Pr)-bonded polymers were successfully synthesized via the coordination reaction and palladium-catalyzed Suzuki coupling reaction of 2,7-dibromo-9,9′-dioctylfluorene and different amounts of 5,5′-dibromo-2,2′-bipyridine. The resulting polymers were characterized by 1H-NMR and GPC. The photoluminescence (PL) and electroluminescence (EL) properties of the resulting polymers were studied to explore the effects of the Pr triisopropyloxide. The results showed that the incorporation of Pr into the polymers caused better coplanarity and effective intermolecular or intramolecular interaction, leading to the higher emission intensity at long-wavelength. Further, it was also found that the emission light color could be tuned from blue to green by introduction of a small amount of Pr into the polymer main chain. A single-layer green emitting EL device based on PF(BipyPr)6 with 6 mol% Pr content was fabricated. The device had a low turn-on voltage of 6 V, a brightness of 705.3 cd·m−2, the maximum luminous efficiency of 1.53 cd·A−1 and the maximum power efficiency of 0.69 lm·W−1.

Pr- and La-doping effects on the magnetic anisotropy in the antiferromagnetic phase of Kondo semiconductorCeRu2Al10

We have studied the Pr- and La-doping effects on the magnetic anisotropy in the antiferro-magnetic (AFM) phase of ${\mathrm{CeRu}}_{2}{\mathrm{Al}}_{10}$. The crystalline electric field (CEF) splitting in ${\mathrm{PrRu}}_{2}{\mathrm{Al}}_{10}$ was found to be as large as $\ensuremath{\sim}800$ K with a singlet ground state. In ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ru}}_{2}{\mathrm{Al}}_{10}$, the CEF level scheme of the Pr ion is not changed with $x$. The AFM moment (${m}_{\mathrm{AF}}$) is rotated from $c$ to $b$ axis in both systems at ${x}_{c}^{\mathrm{sr}}\ensuremath{\sim}0.03$ and $\ensuremath{\sim}0.07$ for Ln=Pr and La, respectively. As the ionic radius of La and Pr is larger and smaller than that of Ce, respectively, these results indicate that the chemical pressure effect is not associated with the rotation of ${m}_{\mathrm{AF}}$, but is caused by the suppression of the $c\ensuremath{-}f$ hybridization originating from the decrease of $4f$ electrons of Ce ions by Ce-site substitution. Since a small amount of Pr or La doping changes easily the magnetization easy axis of all the moments on Ce sites, the origin of the magnetic anisotropy is not the local single ion effect but the bandlike effect through the anisotropic $c\ensuremath{-}f$ hybridization. The magnetic phase diagrams of ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{Ln}}_{x}{\mathrm{Ru}}_{2}{\mathrm{Al}}_{10}$ indicate that above ${x}_{c}^{\mathrm{sr}}$, the AFM order with ${m}_{\mathrm{AF}}\ensuremath{\parallel}b$ continues to exist up to ${x}_{c}$, which is $\ensuremath{\sim}0.4$ and $\ensuremath{\sim}0.6$ in Ln=Pr and Ln=La, respectively. This indicates that even in the sample with an AFM transition temperature (${T}_{0}$) near ${x}_{c}$, the anisotropic $c\ensuremath{-}f$ hybridization dominates the AFM order. A large positive transverse magnetoresistance is seen below ${T}_{0}$, but a very small one above ${T}_{0}$. Together with the results of Hall resistivity and the observation of Shubnikov--de Haas oscillation, we propose that there exist large Fermi surfaces above ${T}_{0}$ and small ones below ${T}_{0}$. A gap is opened by the AFM order on almost the area of the large Fermi surface, and small Fermi surfaces are constructed below ${T}_{0}$, although we do not know the mechanism, which might be specific to the AFM order in Kondo semiconductors. The largest suppression of the magnetic scattering below ${T}_{0}$ is observed for the current $I\ensuremath{\parallel}a$ and the smallest one for $I\ensuremath{\parallel}b$. This anisotropy may be associated with the anisotropic $c\ensuremath{-}f$ hybridization, which may contribute to the anisotropic magnetic scattering of the conduction electron below ${T}_{0}$.

Synthesis and characterization of praseodymium-containing ZrSiO 4 solid solutions from gels

The preparation and characterization of a series of praseodymium–zircon solid solution (Pr x –ZrSiO 4) materials with increasing nominal amounts of Pr is reported. Pr-doped zircon gels were prepared by gelling mixtures of zirconium n-propoxide, praseodymium acetylacetonate and tetraethylorthosilicate, and annealed over the range of temperature up to the formation of Pr–zircon solid solutions. The reaction sequence was followed by X-ray powder diffraction (XRD), ultraviolet–visible diffuse reflectance (DR) and infrared spectroscopy (IR). The first crystalline phase detected on annealing gels was a tetragonal praseodymium-containing ZrO 2 phase (t-Pr–ZrO 2). On further annealing, the subsequent transformation to the monoclinic form (m-Pr–ZrO 2) took place. The formation of final Pr–ZrSiO 4 solid solutions occurred by the reaction between m-Pr–ZrO 2 and amorphous silica phase. The mechanism of solid solution formation inferred from energy dispersive X-ray microanalysis (SEM/EDX) data, variation of lattice parameters and DR of final Pr–ZrSiO 4 solid solutions involved the replacement of Zr 4+ by Pr 4+ in dodecahedral sites of the zircon structure. DR revealed that a relatively small amount of Pr 3+ was still present in final Pr-containing ZrSiO 4 products. The estimated solubility of praseodymium in the zircon was around 0.067 mol of praseodymium per mol of zircon (∼11.5 wt% as Pr 2O 3). This study opens new perspectives to the development of more ecological zircon-based ceramic pigmenting systems by using mineralizer-free sol–gel synthetic techniques.

Stability and Electric Conductivity of Barium Cerate Perovskites Co- Doped with Praseodymium

Co-doping of yttrium doped mixed barium cerate/zirconate perovskite (BCZY) with small amounts of Pr (BCZYP) substantially increases electrical conductivity while retaining structural and chemical stability. BCZYP is pre- dominantly a proton conductor at temperatures up to 600-650˚C, whereas it is a mixed proton/oxide ion/electron conduc- tor at higher temperatures. The co-doped BCZYP perovskite can be useful for applications requiring proton conduction at intermediate temperatures.

Microstructure and Electrical Conductivity of Ce0.85Y0.15-xRExO2-/ (RE=Pr,Tb)

Ce0.85Y0.15-xRExO2-δ (RE=Pr,Tb) with x = 0.02 and 0.06 solid solutions were synthesized by the coprecipitation technique to study the effect of Pr and Tb additions in the microstructure and electrical conductivity of yttria-doped ceria solid electrolyte. For comparison purposes, the solid solution Ce0.85Y0.13Pr0.02O2-δ was prepared by mixing Pr6O11 to the precipitated gel of ceria-yttria. Reductions in the average grain size and in the full width at half maximum height of the grain size distribution curve were obtained with increasing praseodymium additions to ceria-yttria. In contrast, Tb additions to yttria-doped ceria do not result in any significant microstructural change. Although an increase in grain conductivity with small amounts of Pr was observed at 300 ºC, both co-dopants exert a deleterious effect on the electrical conductivity of yttria-doped ceria at temperatures of typical solid oxide fuel cells operation.

Synthesis and magnetic characterization of the La0.6Ln0.1Pb0.3MnO3(Ln=Pr, Nd, and Y) manganites

La 0.6 Ln 0.1 Pb 0.3 MnO 3 ( Ln=Pr, Nd, and Y) oxides have been synthesized by a standard ceramic fabrication method. The partial replacement of La ions by small amounts of Pr, Nd, or Y ions results in a considerable decrease in the ferromagnetic transition temperature and clearly irreversible behavior in the field-cooling–zero-field-cooling curve at low field, showing a short-range spin order phase. These facts are in agreement with the smaller ionic radii of Pr, Nd, and Y ions in contrast to La ions, and the corresponding larger distortion of perovskite structures. The hysteresis loops of these samples illustrate that the magnetization still remains unsaturated in high field and the saturation moments are larger for Pr-doped and Nd-doped manganites. This can be interpreted in terms of canted spins between Mn ions and magnetic Pr or Nd ions with f-shell electrons.

Search for the Kondo effect of Pr ions doped in non-magnetic matrices

The results of electrical resistivity rho measurements in the temperature interval 1.5-300 K on the intermetallic compounds YCu2Si2, YNi2Si2, YCu2Ge2, YNi2Sn2, YPd2Si2, YPt2Si2, YRu2, YPt2, YPd3 and ScAl2 containing small amounts of Pr as well as on Sc0.95Pr0.05 are reported in order to look for the Kondo behaviour of Pr ions. The logarithmic variation in rho , however, is not apparent in the temperature range of investigation in any of the alloys, although these alloys are potential candidates for exhibiting Kondo behaviour.

Significant improvement of magnetic properties and corrosion resistance in evaporated Co-Ni recording media

An addition of a very small amount of Pr in Co-Ni films of a recording medium improves both corrosion resistance and frequency response. The columnar grains, which are induced by oblique incidence of evaporation, becomes remarkably finer by the addition of rare-earth elements. The TEM image of the cross section of the films shows a dense packed structure. High magnetization and a better corrosion resistance are considered to be due to the dense packed structure. The fine grain improves the frequency response. Among several rare-earth elements, especially Pr doping yields a best recording performance.