NOx storage and reduction over copper-based catalysts. Part 2: Ce0.8M0.2Oδ supports (M = Zr, La, Ce, Pr or Nd)

5% copper catalysts with Ce0.8M0.2Oδ supports (M = Zr, La, Ce, Pr or Nd) have been studied by rapid-scan operando DRIFTS for NOx Storage and Reduction (NSR) with high frequency (30 s) CO, H2 and 50%CO + 50%H2 micropulses. In the absence of reductant pulses, below 200–250 °C NOx was stored on the catalysts as nitrite and nitro groups, and above this temperature nitrates were the main species identified. The thermal stability of the NOx species stored on the catalysts depended on the acid/basic character of the dopant (M more acidic = NOx stored less stable ⇒ Zr4+ < none < Nd3+ < Pr3+ < La3+ ⇐ M more basic = NOx stored more stable). Catalysts regeneration was more efficient with H2 than with CO, and the CO + H2 mixture presented an intermediate behavior, but with smaller differences among the series of catalyst than observed using CO alone. N2 is the main NOx reduction product upon H2 regeneration. The highest NOx removal in NSR experiments performed at 400 °C with CO + H2 pulses was achieved with the catalyst with the most basic dopant (CuO/Ce0.8La0.2Oδ) while the poorest performing catalyst was that with the most acidic dopant (CuO/Ce0.8Zr0.2Oδ). The poor performance of CuO/Ce0.8Zr0.2Oδ in NSR experiments with CO pulses was attributed to its lower oxidation capacity compared to the other catalysts.

An electron spectroscopic study of the surface oxidation of glassy and crystalline Cu-Zr alloys

Surface oxidation of three metglasses in the Cu-Zr system has been investigated by employing X-ray photoelectron spectroscopy and Auger electron spectroscopy with a view to comparing their oxidation behaviour with that of the corresponding crystalline states of the alloys. Surface oxidation of pure Zr metal has also been examined in detail using these techniques. Sub-oxides of Zr are formed during the initial stages of oxidation of Zr (at oxygen exposures <10L), while at higher exposures, ZrO2 is formed together with the highest possible sub-oxide which the authors designate as 'ZrO'. The relative proportion of 'ZrO' goes through a maximum in the range 25-50 L. Both the glassy and the crystalline states of the Cu-Zr alloys exhibit preferential oxidation of Zr. The glassy alloys exhibit a higher rate of oxidation at intermediate exposures compared with the crystalline states of the alloys; the extent of oxidation at higher oxygen exposures is, however, higher for crystalline alloys. Interatomic Auger transitions have been found in the Zr+O2 system as well as in Cu-Zr alloys.

Effects of Zr and Ti doping on the dielectric response of CeO2: A comparative first-principles study

Zr doping in ceria (CeO2) results in enhanced static dielectric response compared to pure ceria. On the other hand, Ti doping in ceria keeps its dielectric constant unchanged. We use first-principles density functional theory calculations based on pseudopotentials and a plane wave basis to determine electronic properties and dielectric response of Zr/Ti-doped and oxygen-vacancy-introduced ceria. Softening of phonon modes is responsible for the enhancement in dielectric response of Zr-doped ceria compared to that of pure ceria. The ceria-zirconia mixed oxides should have potential use as high-k materials in the semiconductor industry. (c) 2010 Elsevier Ltd. All rights reserved.

LiSr1.65 square 0.35B1.3B ' O-1.7(9) (B = Ti, Zr; B ' = Nb, Ta): New lithium ion conductors based on the perovskite structure

We describe the design and synthesis of new lithium ion conductors with the formula, LiSr(1.65)rectangle(0.35)B(1.3)B'O-1.7(9) (rectangle = vacancy; B = Ti, Zr; B' = Nb, Ta), on the basis of a systematic consideration of the composition-structure-property correlations in the well-known lithium-ion conductor, La-(2/3-x)Li(3x)rectangle((1/3)-2x)TiO3 (I), as well as the perovskite oxides in Li-A-B,B'-O (A = Ca, Sr, Ba; B = Ti, Zr; B' = Nb, Ta) systems. A high lithium-ion conductivity of ca. 0.12 S/cm at 360 degrees C is exhibited by LiSr(1.65)rectangle(0.35)Ti(1.3)Ta(1.7)O(9) (III) and LiSr(1.65)rectangle(0.35)Zr(1.3)Ta(1.7)O(9) (IV), of which the latter containing stable Zr(IV) and Ta(V) oxidation states is likely to be a candidate electrolyte material for all-solid-state lithium battery application. More importantly, we believe the approach described here could be extended to synthesize newer, possibly better, lithium ion conductors.

Luminescence studies of Ce : YAG using vacuum ultraviolet synchrotron radiation

Photoluminescence spectrum of Ce:YAG single crystal was studied employing vacuum ultraviolet (VUV) synchrotron radiation. Intrinsic absorption edge at about 52,000 cm(-1) was observed in the absorption spectrum. From the VUV excitation spectrum, the energy of the highest d-component of 53,191 cm(-1) (188 nm) for the Ce3+ ions in YAG was obtained at 300 K. The disappearance of the third 5d level at 37,735 cm(-1) (265 nm) in absorption and excitation spectra in our samples may be due to the impurity Fe3+ ions absorption. (C) 2006 Elsevier Ltd. All rights reserved.

LnMsbO_6和Ln_2M_2O_7 (M = Zr, Ti)复合氧化物的合成、组成、结构及发光等性质的研究

在综合文献报导的基础上，我们选择了LnMsbO_6和Ln_2M_2O_7 (M = Zr, Ti)做为研究体系，对其合成、组成、结构以及稀土离子在其中的发光性质进行了较为系统的研究。用氢氧化物共沉淀的方法，在等摩尔阳离子原料配比条件下，我们制备了LnMsbO_6和Ln_2M_2O_7(M = Zr, Ti, Ln = La - Yb, Y除Ce和Pm)。根据对组成的分析结果并与文献对比，我们认为得到的化合物组成与给出的分子式是一致的。由热分析并结合x-ray衍射分析对LnZrsbO_6的形成反应进行了研究，其结果表明化合物的形成过程是一个较慢的固相反应过程。通过x-ray粉沫衍射物相分析并结合掺杂Eu~(3+)的发光光谱，我们确定了在不同条件下合成的LnMsbO_6和Ln_2M_2O_7化合物的结构类型，并计算了所有化合物的晶胞参数。在对上述结构特性及其变化规律进行研究后，我们认为Ln_2M_2O_7结构变化规律与ΔZ/(d~2) (Z为阳离子电荷，d为阳离子与阴离距离)有关，随ΔZ/(d~2)值由小到大，Ln_2M_2O_7(M = Zr, Ti)先是形成具有荧石结构的阳离子无序固溶体，然后逐渐过渡到荧石结构的变型——有序的立方烧绿石结构，最后变型到单斜晶系结构。LnMsbO_6(M = Zr, Ti)低温相结构与Ln_2M_2O_7(M = Zr, Ti)是有联系的，即基本保持了其立方晶系结构。然后锑的加入使这种结构变得很不稳定，因此在高温灼烧下上述立方相将不可逆地变为更稳定的高温结构相。利用磁天平对LnMsbO_6和Ln_2M_2O_7进行了室温条件下的磁学性质测量，其玻尔磁子数的实验值与Van Vleck理论值符合较好。由此也可说以说明化合物的组成与给出的分子式是一致的。用荧光光谱仪对Eu~(3+)在不同基质中做发光光谱，其结果表明Eu~(3+)在烧绿石结构的Ln_2M_2O_7中，Ln~(3+)是处于具有反演中心的D_(3d)格位，这时~5D_0 → ~7F_2的电体极跃迁（～610nm）是被禁阻的，因此Eu~(3+)主要的发光为~5D_0 → ~7F_1磁体极跃迁（～590nm），并劈裂为两条谱线。在其它不具有反演中心的格位中Eu~(3+)的~5D_0 → ~7F_2跃迁则是较强的。在La~(3+)有着多个较低对称性格位的La_2Ti_2O_7:Eu中，无论是Eu~(3+)的激发光谱，还是发射光谱，其~5D_0与~7F_0之间的跃迁谱线都不只一条，这与La~(3+)多对称性格位特性是一致的。在立方荧石结构的LnZrsbO_6:Eu中，用Eu~(3+)电荷迁移带激发的发光光谱与用其它激发带激发的很不相同，其~5D_1能级的跃迁谱线非常强，我们认为这可能是由于电荷迁移激发态，将大部分能量传递给3~5D_1能级的结果。另外，我们比较了在Ln_2Zr_2O_7和LnZrsbO_6中Eu~(3+)的发光强度，发现前者要比后者强许多。在研究Bi~(3+)对Eu~(3+)的敏化作用时，我们发现在Y_2M_2O_7:Bi, Bu中Bi~(3+)对Eu~(3+)有较好的敏化作用，而在YMsbO_6:Bi, Eu中则没有。同时我们注意到对于Eu~(3+)取代六配位La~(3+)格位时，其电荷还移带位置和符合Hoefdraad认为是不变的规律，而是随着基质晶格的不同发生变化的。对Dy~(3+)在LnMsbO_6和Ln_2M_2O_7基质中发光性质研究中，我们看到Dy~(3+)的发光主要为兰色的~4F_(9/2) → ~6H_(15/2)跃迁(～480nm)和黄色的~4F_(9/2) → ~6H_(13/2)跃迁(～580nm)。其黄光与兰光的强度比值（R）随基质晶格的不同可以有很大的变化。一般情况下R值总是要大小1，且不随湿度和Dy~(3+)掺杂浓度变化。同时我们比较了在Ln_2Zr_2O_7和LnZrsbO_6 (Ln = Y, Gd, La)基质体系中Dy~(3+)的发光强度，发现同Eu~(3+)类似前者较后者强许多。在论文中我们给出了在Y_2M_2O_7和YMsbO_6 (M = Zr, Ti)中Sm~(3+)的激发光谱与发射光谱，从中可以看到当Sm~(3+)在Y_2Ti_2O_7中取代占据D_(3d)格位的Y~(3+)时，其~4G_(5/2) → ~6H_(9/2) (～650nm)电体极跃迁是被禁阻的。同时还给出了在YZrsbO_6中H_0~(3+)和Er~(3+)的激发光谱与发射光谱。此外，我们研究了Eu~(3+)和Dy~(3+)在一些基质体系中发光强度随温度的变化规律。发现Y_2Zr_2O_7:Eu的临界猝来温度要比La_2Zr_2O_7:Eu的高，Ln_2Zr_2O_7:Dy (Ln = La, Y)的温度猝来曲线则大致相同，且随温度和猝来要比Ln_2Zr_2O_7:Eu缓慢，对于上述现象我们利用位形坐标给出了一定的解释。然而所有的样品发光强度从室温开始，随温度的升高都是单调下降的。

热处理工艺对Mg-RE-Zn-Zr系合金显微组织及力学性能的影响

通过气体保护制备了Mg-RE-Zn-Zr[RE=Ce-40La(wt%)的富铈稀土]合金,并对合金进行了热处理,测试了不同状态下合金的硬度、抗拉强度及伸长率等力学性能,采用光学显微镜、X射线衍射仪及扫描电镜对合金显微组织、拉伸断口进行了分析。结果发现,采用T6热处理工艺后,合金的晶粒尺寸明显细化,硬度、抗拉强度、屈服强度和伸长率显著提高,分别提高了11%,24%,7.3%和102%

Microstructure and some dynamic performances of Ti0.17Zr0.08V0.34RE0.01Cr0.1Ni0.3 (RE = Ce, Dy) hydrogen storage electrode alloys

Microstructure and some dynamic performances of Ti0.17Zr0.08V0.34RE0.01Cr0.1Ni0.3 (RE=Ce, Dy) hydrogen storage electrode alloys have been investigated using XRD, FESEM-EDS, ICP-MS and EIS measurements. The alloy is composed of V-based solid solution phase with a dendritic shape and a continuous C14 Laves phase with a network shape surrounding the dendrite. Pressure-composition isotherm curves indicate that the alloy with Dy addition has a lower equilibrium hydrogen pressure and a wider plateau region. The alloy electrode with Dy addition has higher discharge capacity, while the alloy electrode with Ce addition has better activation and higher cycle stability. The alloy electrode with Ce addition has better electrochemical activity with higher exchange current density (127.5 mA g(-1)), lower charge transfer resistance (1.37 Omega) and lower apparent activation energy (30.5 kJ mol(-1)). The capacity degradation behavior for the alloy electrode is attributed to two main factors: one is the dissolutions of V and Zr element to KOH solution, and another is the larger charge transfer resistance which increases with increasing cycle number.

Effect of Ce and MgO on NO decomposition over La1-x-Ce-x-Sr-Ni-O/MgO

Ce and MgO were added simultaneously to La-Sr-Ni-O catalyst and a substantial enhancement of activity for NO decomposition was observed, which may be attributed to the formation of a new highly active site caused by the addition of Ce and MgO.

Study on structure and oxide ionic conductivity for new compound Ce(6-x)Ln(x)MoO(15-delta)

A new compound Ce(6-x)Ln(x)MoO(15-delta) has been synthesized by wet-chemistry method. Their crystal structure and oxide ionic conductivity were characterized by powder X-ray diffraction, Raman, IR spectrum and A.C. impedance technique. The XRD results showed that Ce6MO15-delta, Ce(5)LnMoO(15-delta) have cubic symmetry with Fm3m space group. The refined lattice parameters showed that their lattice constants decrease with the decrease of the ionic radius of Ln(3+). The electrochemical measurements showed that the ionic conductivity of resulting oxides Ce(6-x)Ln(x)MoO(15-delta) have an enhance, which may be a kind of promising material for SOFCs.

Synthesis-dependent luminescence properties of Y3Al5O12 : Re3+ (Re=Ce, Sm, Tb) phosphors

By using metal nitrates and oxides as the starting materials, Y2Al5O12 (YAG) and YAG:Re3+ (Re = Ce, Sm, Th) powder phosphors were prepared by solid-state (SS), coprecipitation (CP) and citrate gel (CG) methods. The resulting YAG and YAG-based phosphors were characterized by XRD, FT-IR, SEM and photoluminescent excitation and emission spectra. The purified crystalline phases of YAG were obtained at 800 degreesC (CG) and 900 degreesC (CP, SS). At an identical annealing temperature and doping concentration, the doped rare-earth ions showed the stronger emission intensity in the CP- and SS-derived phosphors than the CG-derived YAG phosphors. The poor emission intensity for the CG-derived phosphors is mainly caused by the contamination of carbon impurities from citric acid in the starting materials.

Energy transfer from Ce3+ to Eu2+ and electron transfer from Ce3+ to Eu3+ in BaY2F8 : Ce, Eu systems

Phorsphors of BaY2F8 : Ce3+, BaY2F8: EU2+ and BaY2F8 : Ce, Eu were prepared by higher temperature solid reaction and their excitation, emission and diffuse reflection spectra were made. We firstly found that the competition of energy transfer from Ce3+ to Eu2+ and electron transfer from Ce3+ to EU3+ existed in CeF3 and EuF3-co-doped BaY2F8 systems. The f-f transition emission of EU2+ was increased with increasing x in systems BaY2F8 : 0. 03Ce, xEU. Ce4+ ions coexist,with Ce3+ ions and substitute Y3+ for Ce4+ in the systems BaY2F8 : Eu, Cc.

PREPARATION STRUCTURE AND PHYSICAL-PROPERTIES OF NEW SILVER LANTHANIDE MOLYBDENUM OXIDES [AGLNMO(2)O(8)(LN=LA-ND AND SM)]

We present the synthesis of AgLnMo(2)O(8) compounds with Ln = La-Nd and Sm. These compounds represent a scheelite-type structure characterized by MoO4- tetrahedrons. IR spectra show five absorption peaks in the region of 1000-400cm(-1), around 800cm(-1) and 400cm(-1), which correspond to the modes of the tetrahedral MoO42- groups. All of AgLnMo(2)O(8) (Ln = La-Nd and Sm) oxides are dielectric materials at room temperature. The temperature dependence of the magnetic susceptibility ofAgLnMo(2)O(8) (Ln = Ce-Nd and Sm) shows Curie-Weiss law behavior from 100K to 300K. This indicates that both Ce and Pr exist in +3 oxidation state in AgLnMo(2)O(8). For AgLaMo2O8, diamagnetic properties are found as expected.

Preparation and properties of rare earth hydroxides and oxides ultrafine powders in alcohol

A series of rare earth hydroxides and oxides ultrafine powders have been prepared by precipitation method using alcohol as dispersive and protective reagent. It was first to find that the crystallite size of cubic rare earth oxides had Lanthanide shrinking effect,but average crystal lattice distortion rate possessed lanthanide swelling effect;the change of diffraction intensity with atomic number presented an inverted W type, and double peaks structure was formed.

THE CATALYTIC BEHAVIOR AND REACTION-MECHANISM OF THE BI-CE-O SYSTEM CATALYSTS IN THE OXIDATIVE DEHYDROAROMATIZATION OF PROPYLENE

Oxidative dehydroaromatization of propylene was investigated by the pulse technique over two kinds of single oxide catalysts. With the Bi2O3 catalyst, the main dimer product was 1,5-hexadiene, and the dimerization activity was stable to pulse number even if the catalyst was partly reduced to the bulk. With the CeO2 catalyst, benzene was mainly formed instead of 1,5-hexadiene, but the activity decreased rapidly with increasing pulse number, indicating that only the lattice oxygen near the catalyst surface could be used for oxidative dimerization and the further aromatization. The Bi-Ce-O system catalyst was found in this study to give higher aromatization activity and showed better stability, compared to the Bi-Sn-O catalyst. Although the Bi-Ce-O catalyst was only a mixture of the two component oxides from X-ray diffraction analysis, there was a significant combination effect on the selectivity to benzene. The highest and the most stable selectivity of benzene was obtained at Bi/Ce = 1. In the TPD spectrum of Bi-Ce-O catalyst, there are not only the lattice oxygen (beta-oxygen) over 620-degrees-C due to the reduction of Bi2O3, but also a great deal of the alpha-oxygen desorbed about 400-degrees-C, which is considered the absorbed oxygen in the bulk. This absorbed oxygen could probably be a compensation of the lattice oxygen through the route of gaseous --> absorbed --> lattice oxygen in the binary catalyst system. By the kinetic study on the Bi-Ce-O catalyst, the dimer formation rate was the first-order with respect to the partial pressure of propylene and zero-order of oxygen. Although detail investigation would be made further, it was considered that the complete oxidation of propylene would mainly take place parallelly on some different sites, and the rate-determining step of propylene dimerization occurred probably between an adosrbed propylene and a gaseous one by an Eley-Rideal type mechanism.