Pd-Ce0.4Zr0.6O2直接涂覆的整体催化剂的甲苯催化燃烧性能

采用浸渍法制备了Pd-Ce0.4Zr0.6O2/载体整体催化剂,考察了不同温度焙烧的催化剂的甲苯催化燃烧性能,并将SEM,Raman,BET,CO-TPR等表征结果与催化活性进行了有效的关联。结果表明,催化剂的涂层具有良好的抗振荡性能;400℃焙烧的Pd-Ce0.4Zr0.6O2/载体整体催化剂的催化活性最高,甲苯转化率为95%以上的最低反应温度为210℃;与400℃焙烧的催化剂相比,900℃焙烧的催化剂95%以上甲苯转化的所需的最低温度仅提高40℃,说明该催化剂具有良好的热稳定性。     

Metal-support interaction and redox behavior of Pt(1 wt %)/Ce0.6Zr0.4O2

The catalyst Pt(1 wt %)/Ce(0.6)Zr(0.4)O(2) is studied by CO-temperature programmed reduction (CO-TPR), isothermal oxygen storage complete capacity (OSCC), X-ray absorption spectroscopy (XAS) at the Pt L(III) edge, and in situ X-ray diffraction (in situ XRD), with the aim of elucidating the role of supported metal in CO oxidation by ceria-based three-way catalysts (TWC). The redox behavior of Pt(1 wt %)/Ce(0.6)Zr(0.4)O(2) is compared to that of bare ceria-zirconia. OSCC of redox-aged Pt/ceria-zirconia is twice that of bare ceria-zirconia, and the maximum of CO consumption occurs at a temperature about 300 K lower than redox-aged ceria-zirconia. XAS analysis allows one to evidence the formation of a platinum-cerium alloy in redox-aged samples and the stability of the metal particles toward oxidation and sintering during high-temperature treatments. Under CO flux at 773 K, bare ceria-zirconia shows a continuous drift of diffraction peaks toward smaller Bragg angles, due to a progressive increase of Ce(III) content. Under the same treatment, the structural rearrangement of Pt-supported ceria-zirconia starts after an induction time and takes place with an abrupt change of the lattice constant. The experimental evidence points to the role of supported Pt in modifying the redox properties of ceria-zirconia with respect to the bare support. It is proposed that the much faster bulk reduction observed by in situ XRD for redox-aged Pt/ceria-zirconia can be attributed to an easier release of reacted CO(2), producing a more effective turnover of reactants at the catalyst surface.     

新型核壳结构纳米催化剂的三效催化活性及热稳定性

从Pd纳米粒子出发制备了具有核壳结构的新型纳米Pd@SiO₂/Ce_0.4Zr_0.6O₂三效催化剂及作为参比的Pd/Ce_0.4Zr_0.6O₂催化剂, 采用X射线衍射、 透射电子显微镜、 氢气程序升温还原和氮气低温吸附-脱附等技术对催化剂的物化性质进行了表征, 研究了Pd@SiO₂/Ce_0.4Zr_0.6O₂和Pd/Ce_0.4Zr_0.6O₂催化剂的三效反应催化活性和热稳定性. 结果表明, SiO₂壳层可以抑制Pd粒子的团聚, 同时还能抑制Pd物种的再分散, 减少Pd的流失. 具有核壳结构的纳米Pd@SiO₂/Ce_0.4Zr_0.6O₂催化剂具有更好的三效催化活性和更高的热稳定性.     

三氧化二铝含量对Ni／Zr0.4Ce0.6O2—Al2O3催化剂的CH4—CO2重整反应性能影响

采用水热合成法,制备了不同Al2O3含量的Ni/Zr0.4Ce0.6O2-Al2O3催化剂,采用X－射线衍射（XRD）和扩展X光吸收精细结构（EXAFS）,对催化剂样品进行结构表征;考察了Al2O3的加入对催化剂结构和CH4－CO2重整反应活性的影响。结构表征和活性测试表明,催化剂中存在的主要晶相是Zr0.4Ce0.6O2.Al2O3的加入,使催化剂颗粒度变小,镍的分散度提高,并使反应活性有明显改进;而过量Al2O3的加入,却容易导致积炭。     

具有介孔孔壁的三维有序大孔 Ce0.6Zr0.4O2固溶体的合成与表征

以有序密堆积的聚甲基丙烯酸甲酯(PMMA)单分散微球为大孔模板剂、以三嵌段共聚物EO20PO70EO20(P123)为介孔模板剂、以硝酸亚铈和硝酸氧锆为金属源,采用溶剂挥发自组织法首次合成了具有介孔孔壁的三维有序大孔结构的Ce0.6Zr0.4O2固溶体,并利用XRD,TEM/SAED,N2吸附-脱附等技术表征了所合成的铈锫固溶体的物理性质.结果表明,经500℃灼烧所制得的Ce0.6Zr0.4O2固溶体为多晶单相立方结构,具有三维有序大孔结构,其大孔直径为50～200mm.壁厚为10～40nm,大孔孔壁具有孔径为3～4 nm的蠕虫状介孔结构.     

Ce0.6Zr0.035Y0.05O2 和Pr0.6Zr0.35Y0.05O2 固熔体的氧储存能力及氧化-还原性能的研究

测定了Ce0.6Zr0.35Y0.05O2 和Pr0.6Zr0.35Y0.05O2两种固熔体的晶体结构,氧的储存以及氧化-还原性能. XRD结果表明 Ce0.6Zr0.35Y0.05O2主要以立方的Ce0.75Zr0.25O2结构形式存在,此外还有少量的ZrO1.87. 而Pr0.6Zr0.35Y0.05O2则主要以立方的Pr0.60Zr0.40O2结构形式存在.这两种固熔体粒子都为纳米级,具有多孔和较大表面积的特征.将Y3+掺杂到Ce0.6Zr0.4O2 或Pr0.6Zr0.4O2晶格中,可以提高氧空位, Ce4+或Pr4+浓度. H2(和CO)-O2滴定和TPR-再氧化试验表明在这两种固熔体中分别存在着可逆的Ce4+/Ce3+或Pr4+/Pr3+氧化还原能力.基于试验结果,我们得出以下结论,将Y3+掺杂到Ce0.6Zr0.4O2 或Pr0.6Zr0.4O2晶格中可以(1)提高晶格氧的活动能力,(2)提高Ce4+或Pr4+浓度,(3)提高氧的储存能力和(4)Pr0.6Zr0.35Y0.05O2在Redox性能, 晶格氧的活动能力和氧的储存能力等方面优于Ce0.6Zr0.35Y0.05O2.     

Ce0.6Zr0.35Y0.05O2和Pr0.6Zr0.35Y0.05O2催化剂表面上CO氧化和18O-16O交换反应的研究

测定了在Ce0.6Zr0.4O2,Ce0.6Zr0.35Y0.05O2,Pr0.6Zr0.4O2和Pr0.6Zr0.35Y0.05O2 (分别表示为CZ,CYZ,PZ和PYZ)样品表面上的CO氧化反应和18O-16O 同位素交换反应.结果表明: 在CZ和PZ系列固熔中掺杂Y3 离子可以改善晶格氧的迁移速度;PZ和PZY的晶格氧比CZ 和CZY 的晶格氧具有更高的氧化反应活性.其原因是将Y3 掺杂到Ce0.6Zr0.4O2 或Pr0.6Zr0.4O2晶格中,增加了样品的氧空位浓度,从而提高了晶格氧的迁移性质,而PrOx比CeO2具有更低温度的氧化还原性质,因此PZ和PZY的晶格氧比CZ 和CZY 的晶格氧具有更高的氧化反应活性.     

Re/Pt/Ce0.8Zr0.2O2/蜂窝整体催化剂上低温水煤气变换反应动力学研究

采用微分反应器,研究了新型Re/Pt/Ce0.8Zr0.2O2/蜂窝催化剂上低温水煤气变换反应的动力学行为。利用非线性最小二乘法处理正交设计的实验数据,获得了动力学方程的模型参数。所得的结果符合幂函数型动力学方程,经F检验和相关指数检验,实验值和模拟计算值符合较好。在该催化剂上水煤气变换反应的活化能为70kJ/mol,与文献中报道的数值相吻合。该催化剂上反应速率对CO、H2O、H2和CO2的反应级数分别为0.09、0.88、-0.54和-0.11,与传统的Cu基低变催化剂上的反应级数相差较大。这表明,低温水煤气变换反应在两种催化剂上遵循不同的反应机理。     

Structural and Morphological Investigation of Ce0.6Zr0.4O2 Oxides Synthesized by Sol-Gel Method: Influence of Calcination and Redox Treatments

Ceria-zirconia mixed oxides of nominal composition Ce_0.6Zr_0.4O₂ were prepared by sol-gel method. The structural and morphological modifications of these materials due to calcination and redox treatments up to 1000°C were studied by X-ray diffraction (XRD) and Rietveld refinements, specific surface area measurements (BET), oxygen storage capacity (OSC), TEM and SEM analyses. The materials maintain high OSC after several hours of treatments at 1000°C in oxidizing and reducing atmosphere, showing good resistance to the thermal ageing. An improvement of the OSC is manifested after repetitive redox cycles, even though textural characterization shows that reduction/oxidation processes induce sintering of the crystallites.     

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。     

Dry reforming of methane over Ni/Ce0.62Zr0.38O2 catalysts: Effect of Ni loading on the catalytic activity and on H2/CO production

The activity of ceria–zirconia-supported nickel catalysts (Ni/CZ) with various loadings of nickel (2, 4 and 10 wt. %) was studied in the case of low-temperature dry reforming of methane (DRM). XRD, S_BET, SEM, TPD-CO₂ and thermogravimetry were used to determine the physicochemical properties of the catalysts and of the carbon deposits formed on the surface. It was found that the agglomerates of the Ni-active phase are formed on the surface of the support for high loadings of nickel. The best conversions of CO₂ and CH₄ and an optimum ratio H₂/CO = 1 were obtained for the catalysts with the highest Ni content. It was also found that loading has an influence on the amount of carbon deposits formed in the DRM process.     

微波加热分解法制备CuO-Ce0.6Zr0.4O2及其催化CO氧化性能

采用微波加热分解法制备了一系列CuO含量(0-25%, w)不同的CuO-Ce_0.6Zr_0.4O₂催化剂, 并用X射线衍射(XRD)、透射电镜(TEM)、N₂吸附-脱附(BET)和H₂程序升温还原(H₂-TPR)技术对催化剂进行了表征, 利用色谱流动法考察了其催化CO低温氧化性能. 结果表明: 当CuO含量为15%时, 所制备催化剂的催化活性最佳. 在催化剂中存在三种不同类型的铜物种, 即高分散、小颗粒和大颗粒的CuO. 催化剂表面高分散和小颗粒的CuO有利于催化活性的提高, 而大颗粒的CuO对催化活性具有抑制作用.     

Catalytic methanol decomposition to carbon monoxide and hydrogen over Pd/CeO2-ZrO2-La2O3 with different Ce/Zr molar ratios

The catalytic behaviors of Pd (1.4 wt%) catalysts supported on CeO₂-ZrO₂-La₂O₃ mixed oxides with different Ce/Zr molar ratios were investigated for methanol decomposition. Nitrogen adsorption-desorption (BET), X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (H₂-TPR), X-ray diffraction (XRD) and Pd dispersion analysis were used for their characterization. Pd/Ce_0.76Zr_0.18 La_0.06O_1.97 catalyst showed the highest BET surface area, best Pd dispersion capability and strongest metal-support interaction. Moreover, XPS showed that there was lattice defect oxygen or mobile oxygen. According to the result of O 1s measurements the lattice defect oxygen or mobile oxygen helped to maintain Pd in a partly oxidized state and increased the activity for methanol decomposition. The Pd/Ce_0.76Zr_0.18La_0.06O_1.97 catalyst exhibited the best activity. A 100% conversion of methanol was achieved at around 260 °C, which was about 20-40 °C lower than other catalysts     

Catalytic methanol decomposition to carbon monoxide and hydrogen over Pd/CeO2-ZrO2-La2O3 with different Ce/Zr molar ratios

The catalytic behaviors of Pd (1.4 wt%) catalysts supported on CeO2-ZrO2-La2O3 mixed oxides with different Ce/Zr molar ratios were investigated for methanol decomposition. Nitrogen adsorption-desorption (BET), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD) and Pd dispersion analysis were used for their characterization. Pd/Ce0.76Zr0.18 La0.06 O1.97 catalyst showed the highest BET surface area, best Pd dispersion capability and strongest metal-support interaction. Moreover, XPS showed that there was lattice defect oxygen or mobile oxygen. According to the result of O 1s measurements the lattice defect oxygen or mobile oxygen helped to maintain Pd in a partly oxidized state and increased the activity for methanol decomposition. The Pd/Ce0.76Zr0.18La0.06O1.97 catalyst exhibited the best activity. A 100% conversion of methanol was achieved at around 260℃, which was about 20-40 ℃ lower than other catalysts     

Hydrogen adsorption kinetics on Pd/Ce0.8Zr0.2O2

Hydrogen adsorption on Pd/Ce(0.8)Zr(0.2)O(2) was studied by temperature-programmed reduction, volumetric measurements and IR spectroscopy. Hydrogen uptake and reduction rate at 353 K are strongly dependent on the hydrogen pressure. At relatively high hydrogen partial pressure, reduction involves PdO, the surface and a significant fraction of the bulk of the ceria based oxide. Formation of oxygen vacancies even at low temperature (<373 K) is observed. The hydrogen adsorption process is mainly irreversible, as is shown by an increase in the (2)F(5/2)-->(2)F(7/2) electronic transition of Ce(3+) with hydrogen pressure and surface dehydroxylation. This "severe" reduction has a negative effect on the subsequent hydrogen adsorption capability. The decrease of hydrogen uptake capacity and rate during adsorption can be associated with the partial loss of superficial OH and the presence of Ce(3+), which deactivates Pd electronically.     

三维虫孔状介孔纳米粒子Ag2O/Ce0.6Zr0.35Y0.05O2的制备、表征及其对甲烷氧化反应的催化性能

以十六烷基三甲基溴化铵(CTAB)为模板剂, 采用改进的共沉淀法合成了高比表面积的虫孔状介孔Ce0.6Zr0.35Y0.05O2(CZY)立方晶相结构的纳米粒子, 用浸渍法制备了Ag2O质量分数为0.2%—4.0%的Ag2O/CZY催化剂, 以XRD, HRSEM, HRTEM/SAED, H2-TPR和XPS等表征手段测定了CZY 和Ag2O/CZY催化剂的物化性质, 考察了其对甲烷氧化反应的催化性能. 结果表明, 质量分数为2.0%的Ag2O/CZY催化剂在空速为50000 h-1、甲烷/氧气摩尔比为1:4和反应温度为600 ℃的条件下, 可使甲烷完全氧化成CO2和H2O, 且基本上消除了在升温、降温过程中甲烷转化率随温度变化的“滞后回线”现象. 可见, Ag2O/CZY的优良催化性能与CZY具有发达的三维虫孔状介孔结构、较大的比表面积、较强的储释氧能力及其稳定活性相Ag2O等因素有关.     

Ce0.67Zr0.33O2对CH4燃烧催化剂Fe2O3/Al2O3的改性作用

固定n（Ce）／n（Zr）比为0．67／0．33,用共沉淀法制得一系列CeO2-ZrO2-Al2O3固溶体,采用这些固溶体作载体,以Fe2O3为活性组分,用浸渍法制备了一系列催化剂,BET结果显示,将适量Ce0.67Zr0．33O2引入到Al2O3载体中有助于催化剂保持较高的比表面积,TPR结果显示,载体中引入适量的Ce0．67Zr0.33O2可以改善催化剂的氧化还原性能,XRD结果表明,Fe2O3在CeO2-ZrO2-Al2O3载体上呈现出良好的分散状况,老化前后催化剂的晶相结构基本无明显变化,特别是当载体中m（Ce0.67Zr0.33O2）：m（Al2O3）的值为1：2时,Fe2O3／CeO2-ZrO2-Al2O3催化剂在甲烷催化燃烧中显示出最佳的催化性能和抗高温老化性能。     

掺杂助剂Ce和Zr的Ni/Al2O3催化剂的X光电子能谱分析

以Na2CO3为沉淀剂,在pH 9.0的沉淀条件下,采用并流沉淀法制备了Ni/Al2O3、Ni/CeO2-Al2O3、Ni/ZrO2-Al2O3和Ni/ZrO2-CeO2-Al2O34种催化剂,催化剂中Ni负载量(质量分数)为10%。采用XPS表征手段及常压固定床反应器对催化剂进行活性评价,考察了助剂Ce和Zr及二者的协同作用对Ni基催化剂表面物种结合能的影响以及对甲烷自热重整制氢反应性能的影响。结果表明,助剂Ce和Zr的添加及二者的协同作用对Ni基催化剂表面各物种的结合能均有一定的影响,结合评价结果可知,Ce和Zr二者的协同作用对Ni基催化剂的催化性能提高最大。     

Electrochemical characteristics of La0.6Sr0.4CoO3-δ, Pr0.6Sr0.4CoO3-δ and Gd0.6Sr0.4CoO3-δ on Ce0.85Sm0.15O1.925 electrolyte

Cyclic voltammetry, chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium temperature half-cells: Ce_0.85Sm_0.15O_1.925| La_0.6Sr_0.4CoO_3-δ, Ce_0.85Sm_0.15O_1.925| Pr_0.6Sr_0.4CoO_3-δ and Ce_0.85Sm_0.15O_1.925| Gd_0.6Sr_0.4CoO_3-δ. The influence of the atomic mass of the A–site cation in the perovskite cathode on the oxygen reduction kinetics has been discussed. The total polarisation resistance, obtained from the Z′′, Z′-plots, increases with the rise of atomic mass of the cation in the A-site position. Two different time constants have been obtained for the oxygen electroreduction process, and the replacement of La³⁺ by Gd³⁺ in the cathode material decreases somewhat the surface catalytic activity, but the noticeably higher low-frequency series resistance, i.e. mainly diffusion-like mass transfer resistance, values have been obtained. However, the mainly diffusion-limited process at T≤773 K for Gd_0.6Sr_0.4CoO_3-δ and the kinetically mixed process (diffusion + charge transfer) for Pr_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ have been established. At higher temperature (T≥993 K) and more negative potentials, the O₂ reduction process is limited mainly by the heterogeneous charge transfer step. Presented at the fourth Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

Effect of H_2S on the transformation of 1-hexene over NiMoS/γ-Al_2O_3 with hydrogen

The effect of H2S contents on the transformation of 1-hexene with hydrogen over NiMoS/γ-Al2O3 catalyst was investigated.Inhibition of H2S on both hydrogenation and isomerization reactions of olefin has been demonstrated.And the promotion effect of H2S on the formation of C6 thiols and C12 thioethers has also been observed.It was found out that there was only one type of active site on the NiMoS/γ-Al2O3 for reactions which include hydrogenation reaction,isomerization reaction and sulfides formation reaction,...