Ce1-xGdxO2-δ固溶体中缺陷物种的拉曼光谱研究

采用溶胶-凝胶法制备一系列Ce1-xGdxO2-δ固溶体。利用紫外(325 nm)和可见(514 nm)Raman光谱,X射线粉末衍射(XRD),透射电子显微镜(TEM)和紫外可见漫反射光谱(UV-Vis DRS),考察了Ce1-xGdxO2-δ固溶体的缺陷物种的分布以及Gd含量对缺陷浓度的影响。结果表明:Ce1-xGdxO2-δ固溶体中存在氧缺位(～560 cm-1)和GdO8型缺陷结构(～600 cm-1)。根据样品对Raman激发光的吸收,紫外Raman光谱反映样品的表层信息,可见Raman光谱反映样品的整体信息。Ce1-xGdxO2-δ固溶体表层氧缺位(να)和GdO8型缺陷物种的浓度(νβ)均高于固溶体体相,这归因于缺陷物种的表面富集。然而,相比于GdO8型缺陷物种,体相中氧缺位浓度增加较表层中的更显著。     

Ce1－xPrxO2－δ (x＝0.05～0.30)固溶体的合成及其性质研究

利用溶胶-凝胶法合成了固溶体Ce1－xPrxO2－δ (x＝0.05～0.30). X射线衍射(XRD)分析表明, 在x≤0.30的范围内形成了单相萤石结构固溶体Ce1－xPrxO2－δ; X射线光电子能谱(XPS)结果表明, 样品中氧缺位浓度随掺杂量增大而增大, 铈离子主要为Ce4＋离子, 镨离子以混合价态Pr3＋和Pr4＋存在; 拉曼光谱(Raman)观察到两个峰, 458 cm－1峰为特征F2g振动谱带, 较宽的570 cm－1峰与样品中氧离子缺位有关; 交流阻抗谱测试表明, 固溶体Ce1－xPrxO2－δ的电导率随掺杂量增加而增大, x＝0.2时, 电导率达到最大, 活化能较低, σ600 ℃＝3.28×10－2 S/cm, σ700 ℃＝6.06×10－2 S/cm, Ea＝0.54 eV (250～650 ℃), Ea＝0.49 eV (650～800 ℃).     

Mn和Fe掺杂SnO2的水热合成与磁结构研究

采用水热法合成了Sn1-x-yMnxFeyO2(0≤x≤0.10, 0≤y≤0.10)稀磁半导体. 通过XRD, Raman, TEM, SQUID和Mössbeaur等技术对化合物进行了结构和性能的表征. 结果表明, XRD中没有出现第二相的沉积, Raman光谱中出现了Mn位于SnO2晶格中的局域模式. 磁性测试结果表明, 当x=0.10, y=0时, 样品在低温下具有较强的磁化强度, 但室温下其磁化强度急剧降低. 而y=0.10, x=0时, 样品的磁化强度和矫顽力都比较小, 但随温度的改变变化不大, Mössbeaur谱测试结果表明, 其中的Fe一部分是铁磁耦合的, 拟合得到超精细场和同质异能移等参数表明, 铁磁性来源于Fe替代SnO2本征性能. Mn和Fe共同掺杂的样品的磁化强度随x的减少和y的增加而减少, 矫顽力却相对于单一元素掺杂的样品大大增加.     

模板沉淀法制备高比表面积MnOx-CeO2催化剂及其CO低温氧化活性

以十六烷基三甲基溴化铵(CTAB)为模板剂, Ce(NO3)3和Mn(NO3)2为前驱体, 通过沉淀法制备了一系列晶粒小于5 nm的高比表面积MnOx-CeO2催化剂, 并考察了催化剂的CO氧化反应性能. 采用XRD、Raman光谱、TPR和N2气吸附脱附等手段对催化剂的比表面积、晶粒大小和物相组成进行了表征. 当Mn摩尔分数≤34%时, 催化剂的比表面积在160~170 m2/g之间; 当锰含量进一步提高后, 催化剂的比表面积呈下降趋势. 当Mn摩尔分数≤34%时, XRD只检测到CeO2物相, 而Raman光谱则检测到α-Mn2O3的存在. 催化剂上表现出较好的CO氧化活性, 这主要归因于高比表面积. 随着锰含量的增加, 催化剂的轻化频率(TOF)下降, 表明高分散、小晶粒的氧化锰物种是催化剂的活性物种. H2-TPR结果表明, 催化剂的CO氧化活性还与催化剂中高价锰物种有关. 焙烧温度升高使催化剂的晶粒增大、比表面积减小, 同时催化剂中锰的平均价态降低, 导致CO氧化活性下降.     

Gd~(3+)掺杂锰锌铁氧体的高分子吸附燃烧法制备及电磁性能

采用固态高分子吸附燃烧法合成了Gd3+掺杂锰锌铁氧体Mn0.3Zn0.7Fe2-xGdxO4(x=0,0.01,0.02,0.03,0.04)。借助XRD、SEM和网络分析仪等研究了样品的物相结构和掺杂浓度与电磁特性的关系。结果表明:当x≤0.02时,制得的粉体为单一的锰锌铁氧体,样品的晶格常数随着Gd3+掺杂量的增加先增后减。少量Gd3+掺杂能有效调整锰锌铁氧体的电磁参数,当x=0.02时,微波电磁损耗(RL)最大值达到-18.7dB。     

Ce_(1-x)Ca_xO_(2-x)的溶胶-凝胶法的合成及其性质

用溶胶 -凝胶法合成了 Ce1-x Cax O2 -x(x=0～ 0 .3 5 )系列固体电解质 ,系统地研究了其晶体结构随Ca O含量的变化关系 .XRD测试表明 ,该体系于 1 60℃即形成萤石结构纯相 .高温 XRD表明 ,从室温至80 0℃ ,Ce1-x Cax O2 -x(x=0～ 0 .3 5 )未出现结构相变 .此法合成温度远低于传统的高温固相合成法和水热合成法的温度 .合成物的颗粒小 ,粒度均匀 .在 1 3 0 0℃即可烧结成高致密度样品 .XPS测试表明 ,掺杂 Ca O后吸附氧浓度明显增大 ,氧空位增多 ,电导率和氧离子迁移数增大 ,改善了 Ce O2 基固体电解质的性能 .     

高比表面积纳米结构Ce0.7Zr0.3O2固溶体的模板组装

介绍了模板剂结构诱导下均相沉淀法组装纳米结构Ce0.7Zr0.3O2工艺方法, CTAB为0.02 mol, Ce(NO3)3 6H2O和Zr(NO3)4 5H2O总量为0.01 mol(Ce∶Zr为7∶3), (NH2)2CO为0.44 mol反应108 h可获得肩峰较宽、较纯的铈锆固溶体晶体相, 颗粒粒径在10～20 nm、孔径在2～4 nm、比表面积达178.57 m2*g-1. 高温焙烧及N2吸附分析表明, 样品具有良好热稳定性及吸附催化活性.     

Ce~(4+)掺杂钙钛锆石(CaZr_(1-x)Ce_xTi_2O_7)相变行为的研究

采用高温固相反应法制备了CaZr_(1-x)Ce_xTi_2O_7(0.0≤x≤1.0)系列钙钛锆石样品,借助X射线衍射(XRD)、拉曼光谱(Raman)、背散射电子像(BES)和能谱(EDS)分析,对其相变行为进行了研究。结果表明:随着Ce~(4+)掺杂量的增加,钙钛锆石(CaZrTi_2O_7)表现出有规律的向烧绿石(CaCeTi_2O_7)转变。当x≤0.2时,CaZr_(1-x)Ce_xTi_2O_7样品为单一的钙钛锆石-2M相;0.3≤x≤0.5,部分钙钛锆石-2M结构发生重排(ZrO_7→ZrO_8, TiO_5→TiO_6)向钙钛锆石-4M结构转变,两种晶型共存。Ce~(4+)取代Zr~(4+)量达到60%～70%(0.6≤x≤0.7)时,钙钛锆石-2M相消失;钙钛锆石-4M向烧绿石转变,烧绿石为次晶相;而0.8≤x≤1.0时,样品转变为单一烧绿石相,且烧绿石晶格中阴阳离子的有序化程度随着x取值的增加而增加。这种相变规律也由样品晶粒的BES和EDS分析得到证实。     

低温燃烧法制备纳米Ce1-xNdxO2-x/2(0≤x≤0.6) 粉体的研究

采用低温燃烧合成工艺，在甘氨酸-硝酸盐体系下制备出纳米Ce1-xNdxO2-x/2(0≤x≤0．6)系列粉体(NDC)。X射线衍射(XRD)结果表明。Nd^3 取代Ce^4 进入晶格内部，形成具有单相立方萤石型结构的固溶体，其晶格常数随Nd^3 掺杂浓度的增大而线性增加，晶粒尺寸在17～28nm之间。透射电镜(TEM)结果表明，粉体尺寸在30-40nm之间，具有较高的烧结活性。拉曼光谱(Rman spectrum)表明％宽化峰与掺杂后固溶体中产生的氧空位有关。     

Ce1 - x Tbx O2 - δ复合氧化物氧缺位的拉曼光谱研究

采用溶胶-凝胶法制备了Ce1-xTbxO2-δ复合氧化物,利用不同Raman激发波长(514和785 nm),结合X射线衍射(XRD)、氢气-程序升温还原(H2-TPR)和氧气-程序升温脱附(O2-TPD)表征,考察了Ce1-xTbxO2-δ复合氧化物在O2,He和H2气氛下氧缺位的原位变化情况和CeO2的F2g特征Raman峰位的偏移. 实验结果表明,随着Tb掺杂量的提高,由于晶胞收缩使得CeO2的F2g特征Raman振动峰发生蓝移. 514 nm Raman激发波长反映了催化剂的表面信息,而785 nm激发波长反映了整体信息. 正是由于表面和整体变化的不一致,造成原位Raman实验过程中氧缺位浓度变化趋势的不同. 在He和H2气氛下,由于温度升高时伴随着Ce1-xTbxO2-δ中O2气的脱出,使复合氧化物的微观结构发生改变,以致Ce0.9Tb0.1O2-δ中的氧缺位浓度(A587/A465)在785 nm激发波长下出现先升高后下降的现象.     

Low-temperature CO oxidation over CuO-CeO2/SiO2 catalysts：Effect of CeO2 content and carrier porosity

The effects of CeO2 contents and silica carder porosity with their pore diameters ranging from 5.2 nm to 12.5 nm of CuO-CeO2/SiO2 catalysts in CO oxidation were investigated. The catalysts were characterized by N2 adsorption/desorption at low temperature, X-ray diffraction (XRD), temperature-programmed reduction by H2 (H2-TPR), oxygen temperature programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). The results suggested that, the ceria content and the porosity of SiO2 carder possessed great impacts on the structures and catalytic performances of CuO-CeO2/SiO2 catalysts. When appropriate content of CeO2(Ce content ≤8 wt%) was added, the catalytic activity was greatly enhanced. In the catalyst supported on silica carrier with larger pore diameter, higher dispersion of CuO was observed, better agglomeration-resistant capacity was displayed and more lattice oxygen could be found, thus the CuO-CeO2 supported on Si-1 showed higher catalytic activity for low-temperature CO oxidation.     

Ce0.5+xZr0.4-xLa0.1O2-Al2O3催化剂催化燃烧柴油车碳烟

采用共沉淀法制备了系列Ce_0.5+xZr_0.4-xLa_0.1O₂-Al₂O₃催化剂, 其中0≤x≤0.4且Ce_0.5+xZr_0.4-xLa_0.1O₂与Al₂O₃的质量比为1:1. 考察了该系列催化剂对柴油车排放碳烟的催化燃烧性能, 并用低温N2吸附-脱附、X射线衍射(XRD)、X射线光电子能谱(XPS)、氢气程序升温还原(H₂-TPR)和氧气程序升温脱附(O₂-TPD)等手段对催化剂进行了表征. 研究结果表明该系列催化剂均形成了具有立方萤石结构的固溶体. 当x=0.2时, Ce³⁺离子在催化剂表面有一定的富集, 此时催化剂具有最大的β氧脱附峰和最好的表面还原性能, 同时具有良好的催化碳烟氧化活性, 碳烟在该催化剂的起燃温度为360 °C, 具有较好的应用前景.     

高效 CeO2-MnOx-Al2O3催化剂的制备、表征及催化消除 NO性能

机动车在给人类生活带来便利的同时,也造成了严重的大气污染.其尾气净化成为人们关注的焦点.一氧化氮(NO)、一氧化碳(CO)和碳氢化合物(HCs)是机动车尾气中的三大典型污染物,主要通过三效催化(TWC)技术进行脱除. TWC技术涉及几个重要的催化反应,其中 CO催化还原 NO由于能够同时消除 CO和 NO两种污染物而引起研究者的极大关注.研究表明,负载型贵金属催化剂在该反应中显示出优异的催化性能,但存在资源匮乏、价格昂贵以及热稳定性欠佳等不足.因此,低价、高效的过渡金属氧化物催化剂成为近年研究重点.稀土金属氧化物 CeO2由于具有良好的氧化还原性能、较高的储释氧容量以及丰富的表面氧空位而被广泛用于 CO催化还原 NO反应.研究表明,对 CeO2进行离子掺杂可进一步增大其比表面积,改善其氧化还原性能和储释氧容量.并且,我们在先前的研究中还发现,将具有多种可变价态的钛离子或锡离子掺入 CeO2晶格由于掺杂离子能与 Ce4+/Ce3+发生电子转移而更有利于改善 CeO2的理化性质.此外,锰氧化物(MnOx)在氧化还原气氛中容易实现不同价态之间的切换,从而在一些重要的氧化还原反应中表现出优异的催化性能.近年来,有研究者将 CeO2与 MnOx相结合制备了 CeO2-MnOx催化剂用于 NO消除、碳烟燃烧和挥发性有机物(VOCs)氧化等反应,并取得一些有意义的结果.然而,对于实际应用来说, CeO2-MnOx催化剂存在比表面积偏小等不足.众所周知,γ-Al2O3是一种常用的具有高比表面积和高热稳定性的催化剂载体材料,可有效增大催化剂比表面积.我们前期研究结果表明,通过共沉淀法将 Al3+掺入铈基复合氧化物的晶格相比于以γ-Al2O3为载体更有利于改善铈基复合氧化物的理化性质和催化性能.因此,我们通过简单的氨水反滴加共沉淀法制备了一系列 CeO2-MnOx-Al2O3(Ce：Mn：Al摩尔比=6：4：x,x =0.25,0.5,1,2)复合氧化物催化剂用于 CO催化还原 NO反应.并运用 X射线衍射、拉曼光谱、氮气物理吸附、氢气程序升温还原、X射线光电子能谱以及原位漫反射红外光谱等表征技术对上述催化剂进行了系统分析.重点考察了 Al3+掺杂量对 CeO2-MnOx-Al2O3复合氧化物催化剂理化性质和催化性能的影响.结果表明,在 CeO2-MnOx复合氧化物中掺入少量 Al3+会导致其晶粒尺寸减小,从而增大其比表面积和孔体积,并增加 Ce3+和 Mn4+的含量.比表面积和孔体积增大有助于催化剂与反应物分子之间充分接触; Ce3+和 Mn4+含量增加能分别促进 CO物种吸附以及吸附态 NO物种脱附、转化和解离.这些变化有利于提高 CeO2-MnOx复合氧化物在 CO催化还原 NO反应中的催化性能.最后,基于催化剂的理化性质表征及其催化性能评价,我们尝试提出了一个可能的催化反应机理,以进一步理解 CeO2-MnOx-Al2O3复合氧化物催化剂在 CO催化还原 NO反应中的优异性能.     

Ce0.1+xTi0.5-xAl0.2Y0.1La0.1O1.8材料的制备及在三效催化剂中的应用

采用共沉淀法制备了Ce0.1+xTi0.5-xAl0.2Y0.1La0.1O1.8(0≤x≤0.4)材料, 并对所制备的材料进行了X射线衍射(XRD)和X射线光电子能谱(XPS)的表征, 测定了材料的比表面积(BET法)和储氧量(OSC), 同时采用氢气程序升温还原(H2-TPR)和氨气程序升温脱附(NH3-TPD)研究了材料的还原性能和表面酸性. 研究结果表明, Ce/Ti摩尔比大于1∶2的材料能形成立方萤石结构的固溶体, Ce/Ti摩尔比为1时, 材料表面Ce4+/Ce3+摩尔比达到最大; 随着Ce/Ti摩尔比的增大, 材料的储氧能力先增大后减小, 而TPR还原峰温则是先减小后增大, 当Ce/Ti摩尔比为1时, 材料的储氧量达到最大, 为660 μmol/g; 还原峰峰温最低, 为616 ℃. 以制备的材料为载体制备了一系列Pt/Ce0.1+xTi0.5-xAl0.2Y0.1La0.1O1.8三效催化剂, 并对催化剂进行了活性评价. 活性测试结果表明, 以Ce/Ti比为1的载体材料制成的催化剂对C3H8, CO和NO的起燃温度分别为236, 147和228 ℃, 表现出了优异的温度特性.     

Controlled synthesis, characterization, and catalytic properties of Mn(2)O(3) and Mn(3)O(4) nanoparticles supported on mesoporous silica SBA-15

A method established in the present study has proven to be effective in the synthesis of Mn(2)O(3) nanocrystals by the thermolysis of manganese(III) acetyl acetonate ([CH(3)COCH=C(O)CH(3)](3)-Mn) and Mn(3)O(4) nanocrystals by the thermolysis of manganese(II) acetyl acetonate ([CH(3)COCH=C(O)-CH(3)](2)Mn) on a mesoporous silica, SBA-15. In particular, Mn(2)O(3) nanocrystals are the first to be reported to be synthesized on SBA-15. The structure, texture, and electronic properties of nanocomposites were studied using various characterization techniques such as N2 physisorption, X-ray diffraction (XRD), laser Raman spectroscopy (LRS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results of powder XRD at low angles show that the framework of SBA-15 remains unaffected after generation of the manganese oxide (MnO(x)) nanoparticles, whereas the pore volume and the surface area of SBA-15 dramatically decreased as indicated by N2 adsorption-desorption. TEM images reveal that the pores of SBA-15 are progressively blocked with MnO(x) nanoparticles. The formation of the hausmannite Mn(3)O(4) and bixbyite Mn(2)O(3) structures was clearly confirmed by XRD. The surface structures of MnO(x) were also determined by LRS, XPS, and TPR. The crystalline phases of MnO(x) were identified by LRS with corresponding out-of-plane bending and symmetric stretching vibrations of bridging oxygen species (M-O-M) of both MnO(x) nanoparticles and bulk MnO(x). We also observed the terminal Mn=O bonds corresponding to vibrations at 940 and 974 cm-1 for Mn(3)O(4)/SBA-15 and Mn(2)O(3)/SBA-15, respectively. These results show that the MnO(x) species to be highly dispersed inside the channels of SBA-15. The nanostructure of the particles was further identified by the TPR profiles. Furthermore, the chemical states of the surface manganese (Mn) determined by XPS agreed well with the findings of LRS and XRD. These results suggest that the method developed in the present study resulted in the production of MnO(x) nanoparticles on mesoporous silica SBA-15 by controlling the crystalline phases precisely. The thus-prepared nanocomposites of MnO(x) showed significant catalytic activity toward CO oxidation below 523 K. In particular, the MnO(x) prepared from manganese acetyl acetonate showed a higher catalytic reactivity than that prepared from Mn(NO(3))2.     

The behavior of mixed-metal oxides: physical and chemical properties of bulk Ce1-xTbxO2 and nanoparticles of Ce1-xTbxOy

The physical and chemical properties of bulk Ce(1-x)Tb(x)O(2) and Ce(1-x)Tb(x)O(y) nanoparticles (xTb exchange nor the introduction of oxygen vacancies in Ce(1-x)Tb(x)O(y) significantly affect the charge on the Ce cations. In contrast, the O K-edge and Tb L(III)-edge XANES spectra for Ce(1-x)Tb(x)O(y) nanoparticles show substantial changes with respect to the corresponding spectra of Ce and Tb single oxide references. The Ce(0.5)Tb(0.5)O(y) compounds exhibit a much larger Tb(3+)/Tb(4+) ratio than TbO(1.7). A comparison with the properties of Ce(1-x)Zr(x)O(y) and Ce(1-x)Ca(x)O(y) shows important differences in the charge distribution, the magnitude of the dopant induced strain in the oxide lattice, and a superior behavior in the case of the Ce(1-x)Tb(x)O(y) systems. The Tb-containing oxides combine stability at high temperature against phase segregation and a reasonable concentration of O vacancies, making them attractive for chemical and catalytic applications.     

Mn掺杂Ce0.7Zr0.3O2催化剂同时去除碳烟和氮氧化物的性能

采用柠檬酸络合燃烧法制备了一系列x%Mn/Ce0.7Zr0.3O2(x=0,5,10,15,30,50)复合金属氧化物催化剂,对其同时去除柴油机尾气中碳烟颗粒物(PM)和氮氧化物(NOx)反应的催化活性进行了评价,并采用XRD、低温氮吸附-脱附、H2-TPR、O2-TPD和原位漫反射红外光谱(in situ DRIFTS)等技术对催化剂的性能进行了表征。结果表明,不同含量Mn掺杂入铈锆固溶体中均形成了三元固溶体催化剂,在同时去除PM和NOx的催化反应中,固溶体催化剂的催化活性与其氧化能力直接相关。其中30%Mn/Ce0.7Zr0.3O2催化剂具有较好的同时去除PM和NOx的催化活性,催化去除PM的Ti和Tm分别为298和504℃,NO的转化率达到30.6%。结合O2-TPD和原位红外结果可知,30%Mn/Ce0.7Zr0.3O2表面吸附的超氧物种(O2-)及其与NO反应生成的硝酸盐物种(NO3-)是同时去除PM和NO反应的主要活性物种,进而指出PM和NO在30%Mn/Ce0.7Zr0.3O2表面反应过程中形成了异氰酸盐(-NCO)中间物种,在原位红外实验的基础上提出了30%Mn/Ce0.7Zr0.3O2复合氧化物催化剂同时去除PM和NOx的反应机理。     

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.