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1.
刘利  崔文权  邱发礼 《化学学报》2010,68(3):211-216
采用高温固相法合成了铈掺杂的K2La2Ti3O10催化剂, 利用X射线衍射(XRD)、紫外-可见漫反射(UV-vis DRS)、透射电镜(TEM)和X射线光电子能谱(XPS)对催化剂进行了表征. 考察了催化剂的可见光催化分解甲醇水溶液制氢的活性, 并对可见光催化机理进行了分析. 研究表明, 铈的掺杂没有改变K2La2Ti3O10的微晶结构, 并使催化剂粒径有所减小. 紫外可见漫反射分析表明禁带宽度为2.3 eV左右, 对可见光具有较高吸收. XPS表明La和Ti为+3和+4价, 而Ce则是+3和+4的混合价态. 担载2 wt% Pt后, 在可见光下光催化活性大大提高, 当铈的掺杂量为0.5 mol%(即Ce取代La的摩尔百分量)时, 光催化活性达到最大, 产氢速率为0.05 mmol/h; 光照5 h后产氢量为0.22 mmol, 而纯K2La2Ti3O10的产氢量只有0.037 mmol.  相似文献   

2.
利用高温固相反应、离子交换、层间插入反应和硫化处理制备了PbS插层的K2Ti4O9催化剂。利用XRD、TEM、SEM、XRF、PL和紫外-可见漫反射光谱对催化剂进行了表征,考察了催化剂紫外光和可见光光催化制氢活性。结果表明,制备的PbS插层K2Ti4O9催化剂对可见光的吸收范围较宽,其吸收边界约为710 nm,在紫外光和可见光下3 h累积产氢量可达到115.46 mmol.gcat-1和0.92 mmol.gcat-1,与CdS插层K2Ti4O9催化剂相比具有更高的催化活性。  相似文献   

3.
Thin crystals of La2O3, LaAlO3, La2/3TiO3, La2TiO5, and La2Ti2O7 have been irradiated in situ using 1 MeV Kr2+ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La2O3 remained crystalline to a fluence greater than 3.1×1016 ions cm−2 at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (Tc) of 647 K for LaAlO3, 840 K for La2Ti2O7, 865 K for La2/3TiO3, and 1027 K for La2TiO5. The Tc values observed in this study, together with previous data for Al2O3 and TiO2, are discussed with reference to the melting points for the La2O3-Al2O3 and La2O3-TiO2 systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between Tc and melting temperature (Tm) in the two systems. More complex relationships exist between Tc and crystal structure, with the stoichiometric perovskite LaAlO3 being the most resistant to amorphisation.  相似文献   

4.
The gaseous penetration of La-Ce into PbTiO3 ceramics is reported. The compounds of La2Ti6O15 and CeTi21O38 are formed and the new La2Ti6O15-CeTi21O38-PbTiO3 ceramics are prepared by the penetration of La and Ce in the gaseous state. The new ceramic materials have a significant change in electric properties. The room temperature resistivity decreases from 2.0×1010 to 0.248 Ω. m, and the grain resistance exhibits an obvious PTCR effect with the change of temperature. However, the grain boundary resistance decreases rapidly with increase in temperature. The change rule of the total resistance is similar to that of the grain boundary, and the PTCR effect disappears and the tendency of transition to a conductive body is manifest. The XPS analysis suggests that the particles that are Pb, Ti, La and Ce in La2Ti6O15-CeTi21O38-PbTiO3 ceramics all change their valence and lead to decreasing resistivity, and the bound energy peak values of elements in La2Ti6O15-CeTi21O38-PbTiO3 ceramics are also reported. The La2Ti6O15-CeTi21O38-PbTiO3 ceramics have a better thermal stability in high temperatures through TG-DTA analysis.  相似文献   

5.
Subsolidus phase equilibria and crystal chemistry were studied for the La2O3-MgO-TiO2 system and for the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3 in the quaternary La2O3-CaO-MgO-TiO2 system. Dielectric properties (relative permittivity and temperature coefficient of resonant frequency, τf) were measured at 5-10 GHz and mapped onto the phase equilibria relations to reveal the compositions of temperature-stable (τf=0) compounds and mixtures. Phase equilibria relations were obtained by X-ray powder diffraction analysis of approximately 80 specimens prepared by solid-state reactions in air at ∼1450°C. Six ternary phases were found to form in the La2O3-MgO-TiO2 system, including the three previously reported compounds LaMg1/2Ti1/2O3, La5Mg0.5Ti3.5O15, and “La6MgTi4O18”; and the new phases La10MgTi9O34, La9Mg0.5Ti8.5O31, and a perovskite-type solid solution (1−x)LaMg1/2Ti1/2O3-xLa2/3TiO3 (0?x?0.5). The phase previously reported as “La6MgTi4O18” was found to form off-composition, apparently as a point compound, at La6Mg0.913Ti4.04O18. Indexed experimental X-ray powder diffraction patterns are given for LaMg1/2Ti1/2O3, La5Mg0.5Ti3.5O15, La6Mg0.913Ti4.04O18, La10MgTi9O34, and La9Mg0.5Ti8.5O31. LaMg1/2Ti1/2O3 exhibits a slightly distorted perovskite structure with ordered B-cations (P21/n; a=5.5608(2) Å, b=5.5749(3) Å, c=7.8610(5) Å, β=90.034(4)°). La5Mg0.5Ti3.5O15 (Pm1; a=5.5639(1), c=10.9928(5) Å) and La6Mg0.913Ti4.04O18 (R3m; a=5.5665(1), c=39.7354(9) Å) are n=5 and n=6 members, respectively, of the (111) perovskite-slab series AnBn−1O3n. The new phases La10MgTi9O34 (a=5.5411(2), b=31.3039(9), c=3.9167(1) Å) and La9Mg0.5Ti8.5O31 (a=5.5431(2), b=57.055(1), c=3.9123(1) Å) are n=5 and n=4.5 members, respectively, of the (110) perovskite-slab series AnBnO3n+2, which exhibit orthorhombic subcells; electron diffraction revealed monoclinic superlattices with doubled c-parameters for both compounds. Extensive perovskite-type solid solutions form in the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3. The La2O3-MgO-TiO2 system contains two regions of temperature-stable (τf=0) compositions. The quaternary La2O3-CaO-MgO-TiO2 system contains an extensive single-phase perovskite-type volume through which passes a surface of temperature-stable compositions with permittivities projected to be in the 40-50 range. Traces of this surface occur as lines of τf=0 perovskite-type phases in the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3.  相似文献   

6.
随着稀薄燃烧(lean-burn)发动机的推广使用和环保法规的日趋严格,消除稀燃尾气中的氮氧化物(N O x)已刻不容缓。N O x储存还原技术被认为是最具应用前景的方法之一[1,2]。目前,对Pt/BaA l2O4-A l2O3体系中N O x储存与还原机制的研究较多[1 ̄4],但对该体系中微量铂物种微观结构及其与性能的关系研究较少,这主要是由于Pt含量(0.1w t% ̄0.5wt%)太低,分散度较高,使表征方法受到很大限制。本文采用共沉淀-浸渍法制得具有较高比表面积和热稳定性的N O x储存还原催化剂Pt/BaA l2O4-A l2O3,应用荧光X-射线吸收精细结构方法(Fluores-cence-…  相似文献   

7.
Garnet-structure related metal oxides with the nominal chemical composition of Li5La3Nb2O12, In-substituted Li5.5La3Nb1.75In0.25O12 and K-substituted Li5.5La2.75K0.25Nb2O12 were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li5La3Nb2O12. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In3+(rCN6: 0.79 Å) for smaller Nb5+ (rCN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K+ for La3+ and In3+ for Nb5+ in Li5La3Nb2O12 exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li5.5La3Nb1.75In0.25O12 exhibits the highest bulk lithium ion conductivity of 1.8×10−4 S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10−10-10−7 cm2/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li5La3Nb2O12 was found to be unsuccessful under the investigated conditions.  相似文献   

8.
利用微波法合成纳米尺寸Ag@AgBr表面敏化K2Ti4O9的复合光催化剂(Ag@AgBr/K2Ti4O9),并通过SEM、X-射线能量色散谱(EDX)、TEM、选定区域电子衍射(SAED)、XRD、紫外-可见漫反射(UV-VisDiffuseReflectance)、XPS等对其进行了表征,同时在可见光下测定催化剂对有机物降解的光催化活性。结果表明,粒径为0.2~0.5μm的Ag@AgBr均匀分散在K2Ti4O9表面,Ag@AgBr/K2Ti4O9对可见光有很好的吸收且Ag@AgBr的担载量影响可见光的吸收。当Ag@AgBr的担载量为25wt%时,复合光催化剂具有最高的光催化活性,光照1h对罗丹明B(RhB)的降解率可达97%。另外,催化剂的担载量和稳定性也做了考察。催化剂较高的光催化活性主要归因于Ag纳米粒子的表面等离子体效应和有效的光生电子-空穴的分离。  相似文献   

9.
采用优化的高温固相方法制备了稀土离子Eu~(3+)和Tb~(3+)掺杂的La_7O_6(BO_3)(PO_4)_2系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La_7O_6(BO_3)(PO_4)_2∶Eu~(3+)材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为5D0→7F2特征能级跃迁,Eu~(3+)的最优掺杂浓度为0.08,对应的CIE坐标为(0.610 2,0.382 3);La_7O_6(BO_3)(PO_4)_2∶Tb~(3+)材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb~(3+)的5D4→7F5能级跃迁,Tb~(3+)离子的最优掺杂浓度为0.15,对应的CIE坐标为(0.317 7,0.535 2)。此外,对2种材料的变温光谱分析发现Eu~(3+)和Tb~(3+)掺杂的La_7O_6(BO_3)(PO_4)_2荧光材料均具有良好的热稳定性。  相似文献   

10.
王非  塔娜  李勇  申文杰 《催化学报》2014,35(3):437-443
通过调节溶液的pH值,在水热条件下合成出长径比为2-45的La(OH)3纳米棒. 对水热合成过程中间体的结构演变分析,发现高碱度有利于小尺寸晶核的形成,La(OH)3晶体结构的各向异性导致这些晶种沿着C轴方向生长,进而形成纳米棒结构. 将La(OH)3纳米棒前驱体于773 K焙烧可以得到长径比为2-20的La2O2CO3纳米棒. 随着长径比的增加,La2O2CO3纳米棒暴露的(110)晶面逐渐增加,La3+-O2-碱性位的数目也从0.08增加到0.24 mmol/g. 因此,在Claisen-Schmidt缩合反应中,La2O2CO3纳米棒催化剂上的反应速率随着长径比的增加而逐渐增大.  相似文献   

11.
The compound previously reported as Ba2Ti2B2O9 has been reformulated as Ba3Ti3B2O12, or Ba3Ti3O6(BO3)2, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO3:BaTiB2O6 (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F2)=0.039 for 504 unique reflections. Ba3Ti3O6(BO3)2 is isostructural with K3Ta3O6(BO3)2. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba3Ti3O6(BO3)2 is equal to 95% of that of LiNbO3.  相似文献   

12.
Potassium peroxotitanate was synthesized by the peroxo method. During the thermal decomposition K2Ti2O5 can be obtained. The isothermal conditions for decomposition of K2[Ti2(O2)2(OH)6]·3H2O were determined on the base of DTA, TG and DSC results. DTA and TG curves were recorded in the temperature range 20 and 900°C at a heating rate of 10°C min–1. The obtained intermediate compounds were characterized by means of quantitative analysis and IR spectroscopy. The mechanism of thermal decomposition of K2[Ti2(O2)2(OH)6]·3H2O to K2Ti2O5 was studied. The optimal conditions for obtaining K2Ti2O5 were determined (770°C for 10 h).  相似文献   

13.
The ferroelectric ceramics of Bi4Ti3O12, SrBi4Ti4O15, and lanthanum-doped Bi4Ti3O12-SrBi4Ti4O15 were synthesized, and their Raman spectra were investigated. La-doping resulted in the enlargement of remnant polarization of Bi4Ti3O12-SrBi4Ti4O15. The structure of the Bi2O2 layers and TiO6 octahedra of the intergrowth was found to be different from those of Bi4Ti3O12 and SrBi4Ti4O15. La3+ ions exhibit pronounced selectivity for the occupation of A site as La content is lower than 0.50, and tend to be incorporated into Bi2O2 layers when the La content is higher than 0.50. Lanthanum substitution brings about the structural phase transition in Bi4Ti3O12-SrBi4Ti4O15. The variation of ferroelectric property may be attributed to combined contribution from the decreasing of the oxygen vacancies, the relaxation of the lattice distortion, the destroying of the insulation and the space charge compensation effects of the Bi2O2 slabs.  相似文献   

14.
利用硝基甲烷还原法在室温条件下得到了纳米Pt粒径可控的担载Pt/γ-Al2O3催化剂, 并利用甲醇重整反应为反应探针考察了Pt粒径与催化反应性能之间的关系, 发现催化反应的性能与担载贵金属颗粒粒径之间存在明显的相关性. 通过透射电镜(TEM)、X射线衍射(XRD)、程序升温还原(TPR)等测试手段对催化剂进行表征, 发现钠米Pt的粒径大小不但影响甲醇重整反应的活性, 同时也影响反应的选择性, 即催化剂的催化性能与担载贵金属粒径之间存在明显的尺度效应.  相似文献   

15.
二氧化锰(MnO2)材料具有比容量大、电极电位高、储量丰富以及价格低廉等优势,成为水系锌电池正极最受关注的一类材料,然而其仍然存在着结构稳定性差和电化学储存机理复杂的问题。因此,我们通过两步合成法制备了一种花苞状结构的MnO2负载在Ti3C2Tx表面形成Ti3C2Tx/MnO2复合材料,通过X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)对复合样品的结构、成分和形貌进行表征。通过将Ti3C2Tx/MnO2复合材料作为正极,与锌负极匹配组装成水系锌电池,研究了其分别在2 mol·L-1 ZnSO4、2 mol·L-1 ZnSO4+0.1 mol·L-1 MnSO4、30 mol·L-1三氟甲基磺酸四乙基铵(TEAOTf)+1 mol·L-1三氟甲烷磺酸锌(ZnOTf)和3 mol·L-1 ZnOTf四种电解液中的电化学性能。结果表明,Ti3C2Tx/MnO2在2 mol·L-1 ZnSO4中的比容量较高,但循环稳定性很差。将TEAOTf盐和ZnOTf盐共溶于水中,设计了一种新型的含惰性阳离子的超高浓度盐包水电解液(30 mol·L-1 TEAOTf+1 mol·L-1 ZnOTf),不仅提高了Ti3C2Tx/MnO2材料的可逆性,而且有效抑制了电极材料在循环过程中的溶解。  相似文献   

16.
为探索一种高性能的锂离子电池负极材料,采用酸刻蚀法制备了高导电性、高稳定性的二维层状Ti3C2Tx,通过溶剂热法制备了具有高理论比容量的花瓣状VS2纳米片,再经过简单的液相混合得到了二维层状Ti3C2Tx-MXene@VS2复合物。通过扫描电子显微镜、透射电子显微镜、X射线光电子能谱、X射线衍射和能谱分析对复合材料的形貌和结构进行了表征,采用循环伏安、恒流充放电、长循环和交流阻抗谱对复合材料的电化学性能进行了研究。结果表明:VS2纳米片均匀地分布在Ti3C2Tx的层间及表面,该复合物具有高的可逆容量(电流密度为0.1A·g-1时,比容量为610.5mAh·g-1)、良好的倍率性能(电流密度为2A·g-1时,比容量为197.1mAh·g-1)和良好的循环稳定性(电流密度为0.2 A·g-1时,循环600圈后比容量为874.9 mAh·g-1;电流密度为2 A·g-1时,循环1 500圈后比容量为115.9mAh·g-1)。  相似文献   

17.
A series of Pt/Al2O3 catalysts were prepared using a sol-gel method. The influence of several parameters used in the synthesis including: metal content, identity of the metal precursor, and the water/alkoxide ratio on the structural properties of the fresh (dried) and calcined samples were studied. It was found that the BET surface area decreased with an increase in the platinum content. A surface area of 500 m2/g was obtained following calcination at 773 K. The structure of fresh samples as determined by FTIR corresponded to that of a pseudoboehmite structure. Samples prepared using a water/alkoxide ratio (H2O/ATB) of 9 showed a well-defined, uniform pore size distribution following calcination at 773 K. Metal dispersions comparable to those obtained using impregnation methods were obtained. Aging studies (calcination at 873 K for 24 h) performed on these catalysts, exhibited sintering behavior which were similar to Pt/Al2O3 catalysts prepared by other methods. The sample prepared using a H2O/ATB ratio of 9 had the highest surface area and was more thermally resistant towards metal sintering. A bimodal metal particle size distribution was observed: some particles exhibited sintering while others of similar size showed a greater thermal stability to sintering. The sample having the largest surface area and the highest thermal stability following thermal treatment was a consequence of a more condensed structure and a higher pore roughness obtained after drying the gel. This enabled the formation of an alumina structure which was more amorphous and limited aggregation of platinum particles due to surface diffusion within the pore structure.  相似文献   

18.
Recucibility of Mo species in Pt/MoO3 and PtMo/Al2O3 has been investigated by temperature-programmed reduction (TPR), temperature-programmed desorption of hydrogen (H2-TPD) and temperature programmed electronic conductivity (TPEC) techniques. In Pt/MoO3 at H2 atmosphere, it was found by TPEC and TPR that, a slight amount of Pt could activate the transfer of the species and H atoms between H2 and MoO3, and thus accelerate the reduction of MoO3. In PtMo/Al2O3, TPR and H2-TPD revealed that the reduction of surface Mo species could also be facilitated by Pt. Two kinds of hydrogen molybdenum species were proposed on the surface of the catalyst after prereduction.  相似文献   

19.
The effects of H2 and H2 + O2 gas mixtures of varying composition on the state of the surface of the Pt/MoO3 model catalyst prepared by vacuum deposition of platinum on oxidized molybdenum foil were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature and a pressure of 5–150 Torr. For samples with a large Pt/Mo ratio, the XP spectrum of large platinum particles showed that the effect of hydrogen-containing mixtures on the catalyst was accompanied by the reduction of molybdenum oxide. This effect results from the activation of molecular hydrogen due to the dissociation on platinum particles and subsequent spill-over of hydrogen atoms on the support. The effect was not observed at low platinum contents in the model catalyst (i.e., for small Pt particles). It is assumed for the catalyst that the loss of its hydrogen-activating ability is a consequence of the formation of platinum hydride. Possible participation of platinum hydride as intermediate in hydrogen oxidation to H2O2 is discussed.  相似文献   

20.
采用优化的高温固相方法制备了稀土离子Eu3+和Tb3+掺杂的La7O6(BO3)(PO42系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La7O6(BO3)(PO42:Eu3+材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为5D07F2特征能级跃迁,Eu3+的最优掺杂浓度为0.08,对应的CIE坐标为(0.610 2,0.382 3);La7O6(BO3)(PO42:Tb3+材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb3+5D47F5能级跃迁,Tb3+离子的最优掺杂浓度为0.15,对应的CIE坐标为(0.317 7,0.535 2)。此外,对2种材料的变温光谱分析发现Eu3+和Tb3+掺杂的La7O6(BO3)(PO42荧光材料均具有良好的热稳定性。  相似文献   

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