Ce-Zr-O固溶体的制备和表征

采用硝酸盐直接分解法、共沉淀法、苹果酸溶胶 凝胶法和柠檬酸溶胶 凝胶法制备了Ce Zr O复合氧化物并进行了表征。溶胶 凝胶法制得的Ce Zr O为立方的Ce0 .5Zr0 .5O2 复合氧化物 (其中少量具有立方性质的t″相 ) ,而直接分解和共沉淀法制得的是由立方Ce0 .8Zr0 .2 O2 和四方Ce0 .2 Zr0 .8O2 固溶体组成的复合氧化物。不同制备方法制得的样品由于物相组成不同 ,还原性能也有较大差别。差热分析和X射线衍射分析结果表明 ,凝胶在燃烧的同时生成了Ce0 .5Zr0 .5O2 固溶体。     

高温高压合成的Ce1-xEuxO2-δ固溶体的价态和输运性质研究

Ce O2 具有典型的萤石结构 ,当晶格中产生氧缺位时则形成氧离子固体电解质材料 Ce O2 -δ.Ce O2中的氧缺位浓度可通过掺入不同价态的离子来调整 ,如通过掺杂 Ca,Sr,Y或其它稀土离子所形成的固溶体具有比 Y稳定的 Zr O2 更高的离子电导率 [1] .近年来通过水热法合成了一些 Ce O2 基固体电解质 [2～ 4 ] ,在对 (Ce O2 ) 1- x(Bi O1.5) x 固溶体的研究中发现 ,Bi2 O3在 Ce O2 中的固溶限可达 5 0 % ,而 Sm2 O3在 Ce O2 中的固溶限仅为 3 0 % .高温高压在化合物的合成方面具有可调节离子价态和阴离子缺位数等特点 .本文利用高温高压…     

固溶体Ce0.8Pr0.2O2-δ的合成及性质研究

利用溶胶-凝胶方法合成了Ce0.8Pr0.2O2-δ固溶体, XRD结果表明,经200 ℃焙烧就已经形成立方萤石结构固溶体,晶粒尺寸为8.1 nm, 随焙烧温度的升高,晶粒尺寸增大. X射线光电子能谱(XPS)结果表明,样品中存在氧离子缺位,铈离子主要为Ce4 离子,镨离子以混合价态Pr3 和Pr4 存在. 固溶体Ce0.8Pr0.2O2-δ的拉曼谱(Raman)观察到4个峰,458和1140 cm-1峰为特征F2g振动谱带,较宽的570和187 cm-1峰对应氧离子缺位及引起的不对称振动. 交流阻抗谱表明固溶体Ce0.8Pr0.2O2-δ在600 ℃时的电导率为1.44×10-3 S·cm-1, 活化能为Ea=0.67 eV (650～800 ℃), Ea=0.91 eV (400～600 ℃).     

纳米晶固溶体Ce0.8Nd0.2O2-δ的合成与表征

利用溶胶 -凝胶法合成纳米晶固溶体 Ce0 .8Nd0 .2 O2 -δ.XRD测试表明 ,胶体经 2 0 0℃烧结处理就可以得到晶粒尺寸为 7.2 nm的纳米晶 ,随烧结温度的升高 ,晶粒尺寸增大 .EPR测试给出固溶体 Ce0 .8Nd0 .2 O2 -δ存在少量的 Ce3 +离子 .在纳米晶固溶体 Ce0 .8Nd0 .2 O2 -δ的 Raman光谱上观察到两个峰 ,低频的强峰为特征F2 g振动谱带 ,高频谱带的出现与样品中存在氧缺位有关 .固溶体晶粒尺寸的减小不但使 F2 g振动谱带红移 ,而且谱带明显宽化 .复阻抗谱的测量表明 ,固溶体 Ce0 .8Nd0 .2 O2 -δ具有氧离子导电特性 .4 0 0和 50 0℃时的电导率分别为 4 .55× 1 0 -4 和 2 .65× 1 0 -3 S· cm-1,活化能为 0 .82 e V     

铋杂对Ce-Zr固溶体储氧性能稳定性的影响

以Ce(NO3)3·6H2O,ZrO(NO3)2·2H2O和Bi(NO3)3·5H2O为原料,氨水为沉淀剂,双氧水为氧化剂,在pH值为9.5～10.5条件下,采用氧化共沉淀法制备了不同比例组成的复合氧化物Ce1-x-yZrxBiyOσ.通过XRD,BET和Raman表征可知,该法制备的样品550 ℃焙烧后均可形成固溶体,当x0.15,y0.2时,高温焙烧后易分相.H2-TPR和CO脉冲测试结果显示Ce0.65Zr0.15Bi0.2Oσ较易被还原,且1050℃焙烧4 h后储氧量仍可达625 μmol·(g cat)-1,这是由于Bi3+取代了Ce0.65Zr0.15Bi0.2Oσ中部分Ce4+和Zr4+形成氧空位,增强了体相晶格氧的移动性,从而使Ce0.65Zr0.15Bi0.2Oσ固溶体中的Ce4+和Bi3+同时被还原.     

Ce1-xM′xCa0.2O1.8-0.4x (M=Y,La和Gd)

采用水热法合成了系列双掺杂的萤石结构Ce1-xLnxCa0.2O1.8-0.4x固溶体, 并研究了3种稀土离子对固溶体导电性的影响, 发现掺杂离子半径接近Ce4+时, 体系电导率增大而活化能降低. 同时发现水热合成的Ce1-xLnxCa0.2O1.8-0.4x样品的平均粒度按着掺入离子Y3+, Gd3+, La3+的顺序逐渐减小, 分别为32, 20和15 nm. 这种变化是由于Y3+半径比La3+和Gd3+更接近Ce4+, 因而在水热合成过程中, 掺Y3+的体系更有利于晶粒的生长, 得到的晶体粒度较大.     

Zr(WMo)1-x/2VxO8-x/2：多元素同/低价取代立方ZrW2O8结构类型热收缩固溶体的合成、结构与性质

利用酸蒸气水热法合成了Zr(WMo)1-x/2VxO7-x/2(OH)2·2H2O(x=0.04,0.08,0.10,0.14,0.20,0.22,0.26,0.32)四方晶相固溶体。以此为前驱体,通过高温脱水和相转变法合成了立方相Zr(WMo)1-x/2VxO8-x/2(x=0.04,0.08,0.10,0.14,0.20,0.22)固溶体。立方Zr(WMo)1-x/2VxO8-x/2固溶体具有Pa3空间群。Zr(WMo)1-x/2VxO8-x/2的平均晶体结构描述为按照化学计量的ZrV2O7结构与β-ZrWMoO8结构的叠加。ZrV2O7在立方ZrWMoO8中的固溶度为11mol%;立方Zr(WMo)1-x/2VxO8-x/2固溶体的相变温度低于200 K;在200 K～573 K温度范围内具有负热膨胀系数;线热膨胀系数近似为常数。     

Ce0.5Zr0.5O2固溶体的制备、晶粒增长及应用研究

采用柠檬酸溶胶-凝胶法,以乙醇为溶剂,制备得到形貌良好的铈锆固溶体Ce0.5Zr0.5O2,通过XRD,SEM,BET等手段进行了表征,XRD结果表明该法合成的Ce0.5Zr0.5O2具有四方晶相,无富铈或富锆相峰的出现。1000℃退火3 h后,表面积仍达25.1 m2.g-1。比表面积(SBET)和理论比表面积(SXRD)、晶粒尺寸(DXRD)和理论晶粒尺寸(SXRD)的计算比较,证明发生了颗粒团聚。根据XRD数据计算,Ce0.5Zr0.5O2的颗粒增长活化能为3.99 kJ.mol-1,较低的活化能归结为氧空位的产生。将制备的Ce0.5Zr0.5O2应用于催化碳酸二甲酯(DMC)的合成,催化效果良好。     

铋掺杂对Ce-Zr固溶体储氧性能稳定性的影响

以Ce(NO3)3.6H2O,ZrO(NO3)2.2H2O和Bi(NO3)3.5H2O为原料,氨水为沉淀剂,双氧水为氧化剂,在pH值为9.5~10.5条件下,采用氧化共沉淀法制备了不同比例组成的复合氧化物Ce1-x-yZrxBiyOσ。通过XRD,BET和Raman表征可知,该法制备的样品550℃焙烧后均可形成固溶体,当x0.15,y0.2时,高温焙烧后易分相。H2-TPR和CO脉冲测试结果显示Ce0.65Zr0.15Bi0.2Oσ较易被还原,且1050℃焙烧4 h后储氧量仍可达625μmo.l(g cat)-1,这是由于Bi3+取代了Ce0.65Zr0.15Bi0.2Oσ中部分Ce4+和Zr4+形成氧空位,增强了体相晶格氧的移动性,从而使Ce0.65Zr0.15Bi0.2Oσ固溶体中的Ce4+和Bi3+同时被还原。     

CeO2-ZrO2-Y2O3对Pt-Rh型三效催化剂性能的影响

采用共沉淀法技术制备了Ce0.35Zr0.55Y0.10固溶体,并对其进行了比表面积、储氧量的测试和XRD的表征.将其用于低贵金属Pt-Rh型三效催化剂的制备,考察了CeO2-ZrO2-Y2O3对三效催化剂性能的影响.结果表明,Ce0.35Zr0.55Y0.10具有与Ce0.50Zr0.50O2相似的立方结构和相近的储氧量,经高温(1000 ℃)后仍能保持较大的比表面积(38.66 m2·g-1).和含Ce0.50Zr0.50O2的三效催化剂相比,含CeO2-ZrO2-Y2O3的三效催化剂经高温老化后,C3H8,CO,NO仍具有较高的转化率和较低的起燃温度.     

Structural characterization of CeO(2)-ZrO(2)/TiO(2) and V(2)O(5)/CeO(2)-ZrO(2)/TiO(2) mixed oxide catalysts by XRD, Raman spectroscopy, HREM, and other techniques

Structural characteristics of CeO(2)-ZrO(2)/TiO(2) (CZ/T) and V(2)O(5)/CeO(2)-ZrO(2)/TiO(2) (V/CZ/T) mixed oxide catalysts have been investigated using X-ray diffraction (XRD), BET surface area, Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HREM) techniques. The CeO(2)-ZrO(2) (1:1 mole ratio) solid solution was deposited over a finely powdered TiO(2) support by a deposition precipitation method. A nominal 5 wt % V(2)O(5) was impregnated over the calcined (773 K) CZ/T mixed oxide carrier by a wet impregnation technique. The obtained CZ/T and V/CZ/T samples were further subjected to thermal treatments from 773 to 1073 K to understand the dispersion and temperature stability of these materials. In the case of CZ/T samples, the XRD results suggest the formation of different cubic and tetragonal Ce-Zr-oxide phases, Ce(0.75)Zr(0.25)O(2), Ce(0.6)Zr(0.4)O(2), Ce(0.5)Zr(0.5)O(2), and Ce(0.16)Zr(0.84)O(2) in varying proportions depending on the treatment temperature. With increasing calcination temperature from 773 to 1073 K, the intensity of the lines pertaining to cubic Ce(0.6)Zr(0.4)O(2) and Ce(0.5)Zr(0.5)O(2) phases increased at the expense of cubic Ce(0.75)Zr(0.25)O(2), indicating more incorporation of zirconia into the ceria lattice. The TiO(2) was mainly in the anatase form whose crystallite size also increased with increasing treatment temperature. A better crystallization and more incorporation of zirconia into the ceria lattice was noted when CZ/T was impregnated with V(2)O(5). However, no crystalline V(2)O(5) could be seen from both XRD and RS measurements. In particular, a preferential formation of CeVO(4) compound and an intense tetragonal Ce(0.16)Zr(0.84)O(2) phase were noted beyond 873 K. The HREM results indicate, in the case of CZ/T samples, a well-dispersed Ce-Zr-oxide of the size approximately 5 nm over the bigger crystals ( approximately 40 nm) of TiO(2) when treated at 873 K. The exact structural features of these crystals as determined by digital diffraction analysis of experimental images reveal that the Ce-Zr-oxides are mainly in the cubic fluorite geometry and the TiO(2) is in anatase form. A better crystallization of Ce-Zr-oxides ( approximately 8 nm) over the surface of bigger crystals of TiO(2) was noted at 1073 K. A further enhancement in the crystallite size and zirconia-rich tetragonal phase was noted in the case of V/CZ/T samples. Further, the structure of CeVO(4) formed was also clearly identified in conformity with XRD and RS results.     

Pt/Ce0.6Zr0.4O2催化剂在水煤气变换反应中的电导研究

采用浸渍法制备了不同载体(Ce0.6Zr0.4O2,CeO2和ZrO2)负载的Pt基水煤气变换反应(WGSR)催化剂, 并对其进行了活性评价. 利用X射线衍射(XRD), 程序升温还原(TPR)和原位电导等技术对样品进行了表征. 结果表明, Ce0.6Zr0.4O2固溶体具有比CeO2更高的氧转移能力, 因此促进了Pt/Ce0.6Zr0.4O2催化剂的WGSR活性.     

添加稀土氧化物助剂的CeO2-ZrO2固溶体的储氧性及热稳定性研究

大多数工业催化剂都是在稳定的操作条件下进行的,然而汽车尾气净化催化剂却被暴露在大气中,使用条件经常变化,尤其是空燃比(A/F)的变化,直接影响了对氧敏感的三效催化剂的氧化和还原性能[1].CeO2则是一种具有储氧/释氧能力的催化材料,它作为助剂加入三效催化剂中,可在贫况下储存氧(以Ce4+存在)利于NOx的还原,在富况下释放氧(以Ce3+存在),利于HC、CO的氧化,从而提高了催化剂的活性.然而,CeO2 的储氧性通常局限在表面上,当温度超过400℃以上时,其比表面积降低从而引起储氧性能急剧下降,直接影响催化剂的性能和寿命.     

Pt/γ-Al2O3/CexZr1-xO2催化剂低温催化燃烧去除饮食油烟

以CexZr1-xO2固溶体做载体, 制备了系列Pt/γ-Al2O3/CexZr1-xO2催化剂(x=1, 0.75, 0.5, 0.25, 0). 应用Brunauer-Emmet-Teller (BET)比表面积分析、X射线衍射(XRD)和H2程序升温还原(H2-TPR)等手段对催化剂进行相关表征, 并系统研究了催化剂在饮食油烟催化燃烧中的催化活性. BET结果表明催化剂的比表面积随Ce/Zr摩尔比的减小而减小. XRD结果表明贵金属Pt很好地分散在氧化铝和CexZr1-xO2固溶体上. H2-TPR结果发现催化剂Pt/γ-Al2O3/Ce0.5Zr0.5O2的还原峰面积最大且氧离子的流动性最好. 催化活性研究结果表明Pt负载在CexZr1-xO2固溶体上有利于油烟的催化燃烧, 降低了反应温度. 随着CexZr1-xO2固溶体中Ce/Zr摩尔比的变化, 催化剂的活性顺序为Pt/γ-Al2O3/Ce0.5Zr0.5O2>Pt/γ-Al2O3/Ce0.25Zr0.75O2>Pt/γ-Al2O3/Ce0.75Zr0.25O2>Pt/γ-Al2O3/CeO2>Pt/γ-Al2O3/ZrO2.     

Au/Ce1-xZrxO2催化剂的制备、表征及其在CO氧化和水煤气变换反应中的催化性能

采用共沉淀法制备了不同锆铈摩尔比的Ce1-xZrxO2(x=0,0.1,0.3,0.5,0.7,0.9和1.0)氧化物,并以改性的浸渍法制备了金担载量为1%(质量分数)的Au/Ce1-xZrxO2催化剂.考察了催化剂在低温CO氧化和水煤气变换反应中的催化性能.应用氮物理吸附、X射线衍射、透射电镜和H2程序升温还原等技术对氧化物载体及其负载金催化剂进行了表征,并与其催化性能进行了关联.结果表明,与纯CeO2和ZrO2相比,Ce1-xZrxO2的比表面积增大而孔径减小,孔分布更加集中.Zr的加入使表面Ce4 的还原更加困难,使体相Ce4 的还原更加容易.活性组分金的加入有利于铈锆氧化物的还原.ZrO2载体较大的孔径使金在载体表面分散均匀而粒子较小,因此与Au/CeO2和Au/Ce1-xZrxO2相比,Au/ZrO2具有更好的低温CO氧化活性和水煤气变换活性,而Au/CeZrO在高温下的水煤气变换反应中表现出更好的催化性能.     

铈铁锆三元复合氧化物上碳烟的催化燃烧

采用水热法制备了纯CeO₂、Fe₂O₃和系列Ce₀.5Fe₀.5-xZr_{xO2复合氧化物催化剂,采用XRD、Raman、H2-TPR和BET等方法对其进行了表征,并利用程序升温氧化反应(TPO)技术研究了其碳烟燃烧催化性能。结果表明,Zr⁴+完全进入CeO2晶格中形成了固溶体,而Fe³+较难进入CeO2晶格中,部分Fe2O3分散在固溶体表面。固溶体形成产生的氧空位和表面高度分散的氧化铁协同作用是铈铁锆三元复合氧化物具有较高碳烟燃烧催化性能的关键。同时,与单纯的铈铁二元复合氧化物相比,Zr⁴+的掺杂明显提高了催化剂的抗老化能力,使Ce0.5Fe0.5-xZrxO2复合氧化物显示出更好的应用前景。在系列样品中,Ce0.5Fe0.30Zr0.20O2样品由于形成了最多的固溶体并具有良好分散性的表面Fe2O3,显示出最好的催化活性和稳定性。其催化碳烟的起燃温度(ti)和峰顶温度(tp)分别为251℃和310℃,长时间高温老化后其ti和tp仍较低,分别为273℃和361℃。}     

Thermodynamic investigation of the redox properties for ceria-hafnia, ceria-terbia, and ceria-praseodymia solid solutions

Ceria-hafnia, ceria-terbia, and ceria-praseodymia solid solutions were prepared by the citric-acid (Pechini) method and characterized using X-ray diffraction (XRD) for structure and coulometric titration for redox thermodynamics. Following calcination at 973 K, XRD showed that both Ce(0.5)Hf(0.5)O2 and Ce(0.8)Hf(0.2)O2 exist as single-phase solid solutions and that the lattice parameters of the cubic fluorite structures shifted linearly with Hf content. Following calcination at 1323 K, Ce(0.8)Hf(0.2)O2 remained single phase but Ce(0.5)Hf(0.5)O2 separated into two phases with compositions of Ce(0.81)Hf(0.19)O2 and Ce(0.15)Hf(0.85)O2. At 973 K, oxidation isotherms for Ce(0.8)Hf(0.2)O2 and Ce(0.5)Hf(0.5)O2 were almost identical to oxidation isotherms for Ce(0.8)Zr(0.2)O2 and Ce(0.5)Zr(0.5)O2. Mixed oxides of ceria with terbia and praseodymia also formed single-phase fluorite structures, but each of the solid solutions was phase stable to calcination at 1323 K. The oxidation isotherms for the solid ceria-terbia and ceria-praseodymia solutions were similar to what would be expected for physical mixtures of these oxides.     

铈锆氧化物固溶体对全钯三效催化剂性能的影响

铈锆氧化物固溶体对全钯三效催化剂性能的影响     

水热法制备Ni/ Zr0.4Ce0.6O2-Al2O3催化剂上CH4-CO2重整反应研究: NiO含量的影响

采用水热合成法制备不同NiO含量的Ni/Zr0.4Ce0.6O2-Al2O3催化剂，使用X射线衍射（XPD）和H2的程序升温还原（H2-TPR）对样品进行表征，研究了NiO的含量对催化剂结构和CH4-CO2重整性能的影响。结果表征表明，少量Ni组分能在催化剂表面分散并进入CeO2-ZrO2固熔体晶格间隙而被固熔体包裹，并使固熔体晶粒变小，促进了固熔体的低温还原，而过量的NiO暴露在外生成NiO颗粒。活性测试结果表明，NiO含量少的样品活性随反应进行有较高的增长。选择适当空速，能使CH4-CO2以1：1反应。     

Surface stabilized nanosized Ce(x)Zr(1-x)O(2) solid solutions over SiO(2): characterization by XRD, Raman, and HREM techniques

Ce(x)Zr(1)(-)(x)O(2) solid solutions deposited over silica surface were investigated by X-ray diffraction (XRD), Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HREM) techniques in order to understand the role of silica support and the temperature stability of these composite oxides. For the purpose of comparison, an unsupported Ce(x)Zr(1)(-)(x)O(2) was also synthesized and subjected to characterization by various techniques. The Ce(x)Zr(1)(-)(x)O(2)/SiO(2) (CZ/S) (1:1:2 mole ratio based on oxides) was synthesized by depositing Ce(x)Zr(1)(-)(x)O(2) solid solution over a colloidal SiO(2) support by a deposition precipitation method and unsupported Ce(x)Zr(1)(-)(x)O(2) (CZ) (1:1 mole ratio based on oxides) was prepared by a coprecipitation procedure, and the obtained catalysts were subjected to thermal treatments from 773 to 1073 K. The XRD measurements disclose the presence of cubic phases with the composition Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) in CZ samples, while CZ/S samples possess Ce(0.75)Zr(0.25)O(2), Ce(0.6)Zr(0.4)O(2), and Ce(0.5)Zr(0.5)O(2) in different proportions. The crystallinity of these phases increased with increasing calcination temperature. The cell a parameter estimations indicate contraction of ceria lattice due to the incorporation of zirconium cations into the CeO(2) unit cell. Raman measurements indicate the presence of oxygen vacancies, lattice defects, and displacement of oxygen ions from their normal lattice positions in both the series of samples. The HREM results reveal, in the case of CZ/S samples, a well-dispersed nanosized Ce-Zr-oxides over the surface of amorphous SiO(2). The structural features of these crystals as determined by digital diffraction analysis of experimental images reveal that the Ce-Zr-oxides are mainly in the cubic geometry and exhibit high thermal stability. Oxygen storage capacity measurements by a thermogravimetric method reveal a substantial enhancement in the oxygen vacancy concentration of CZ/S sample over the unsupported CZ sample.