沉淀方法对CeO2-ZrO2系储氧材料性能的影响

利用不同沉淀方法制备了一系列CeO2-ZrO2系储氧材料,并应用BET、XRD、TPR及其储氧性能测定等方法对储氧材料进行了研究.结果表明,不同的沉淀方法对样品的结构和性能有重要的影响.并流法可得到耐高温,储氧性能好,比表面积高的储氧材料;正滴法所得样品储氧量低但稳定,其比表面积抗老化性能差;反滴法所制备的样品储氧性能好,老化后比表面积较低.三种沉淀方法均可形成CeO2-ZrO2固溶体,材料的还原性能取决于比表面积,但与储氧性能无直接关系.     

硼掺杂对稀土贮氢合金相结构和电化学性能的影响

研究了用B掺杂替代Al对AB5型稀土贮氢合金相结构和电化学性能的影响。对M1Ni3．55Co0．75Mn0.4Al0．3-xBx（x=0，0．1，0．2，0．3）合金的研究结果表明：掺B后贮氢合金出现了CeCo4B第二相，导致贮氢合金的电化学容量下降；随B含量的增加和Al含量的减少，氢的扩散系数明显上升，合金的极化电阻减小，合金的高倍率放电性能和低温性能得到明显改善。     

均相沉淀法制备AACHH阻燃晶须及其生长机理研究

采用均相沉淀法制备了一种新型铝系阻燃晶须AACHH，通过FTIR、TG/DTA、化学分析、XRD、SEM、AFM等手段对AACHH的结构、成分、形貌、结晶过程进行了分析与表征。结果表明：AACHH中阻燃气体释放量为63.8%，其结构分子式为NH₄Al(OH)_3.24(CO₃)_0.38·H₂O，六方晶系，晶胞参数为a₀=1.333 5 nm、c相似文献   

Mn含量对CeO2-ZrO2-MnOx催化剂甲苯氧化净化性能的影响

采用氧化还原沉淀法制备了一系列CeO_2-ZrO_2-MnO_x催化剂(CZM_X,X为Mn在催化剂总金属中的摩尔含量),探讨了Mn含量对CZM_X催化甲苯燃烧性能的影响。结果表明,CZM_(0.6)催化剂具有最好的活性,在230℃下即可实现甲苯的完全转化。XRD表征结果发现,随着锰掺杂量的增加,CZM_X催化剂结晶度先降低后增加。H_2-TPR表征结果表明,随着Mn含量的增加,Ce-Zr-Mn之间的相互作用力先增强后减弱。CZM_(0.6)结晶度最差,金属之间相互作用力最强,表面氧物种更易溢出;同时,Raman和O_2-TPD表征结果也证明CZM_(0.6)催化剂上具有较高的表面氧空位浓度,有利于催化剂表面活性氧物种的迁移,促进了甲苯的氧化。此外,通过in-situ DRIFTS对中间产物进行观测,发现苯甲酸盐是CZM_(0.6)催化剂上甲苯氧化反应的重要中间体;在O_2参与下,苯甲酸盐可迅速转化为CO_2和H_2O。     

固相反应制备纳米CeO2粉体

氧化铈用途广泛,用量大。目前用氧化铈作为汽车尾气净化器助催化剂,细度和纯度直接影响的净化效率,因此需要加强高纯度纳米氧化铈的研究开发。     

硼掺杂对稀土贮氢合金相结构和电化学性能的影响

研究了用B掺杂替代A1对AB5型稀土贮氢合金相结构和电化学性能的影响.对M1Ni3.55Co0.75Mn0.4Al0.3-xBx(x=0,0.1,0.2,0.3)合金的研究结果表明:掺B后贮氢合金出现了CeCo4B第二相,导致贮氢合金的电化学容量下降;随B含量的增加和A1含量的减少,氢的扩散系数明显上升,合金的极化电阻减小,合金的高倍率放电性能和低温性能得到明显改善.     

表面活性剂对均相沉淀法制备单晶Ce2O(CO3)2·H2O微粉形貌及形成机理的影响

Three kinds of ultra-fine Ce2O(CO3)2.H2O powders with different morphologies were prepared by adding CTAB, PEG19000 and OP-10 to a solution of Ce2O (NO3)3.6H2O and urea according to the principle and the characteristics of the homogeneous precipitation method. The products were characterized by TEM and XRD. The results showed that the precursor was a single crystal, and that different surfactants had different influences on the morphology of the products. The cationic surfactant CTAB had little effect on crystal morphology merely reducing its size. Nonionic surfactants PEG19000 and OP-10 are both able to change the crystal morphology to a much greater extent. Adding PEG19000 produces an array of rod-like particles with ordered formation and uniform dimension. Meanwhile, in the system of OP-10, a sort of flower-like with different morphologies occured because of the mechanism of formation and grain growth.     

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.     

BST和BZT系列固溶体的均相沉淀法合成及表征

采用均相沉淀法, 在低温(90 ℃)、低pH值(8～9)、短时间(3～3.5 h)条件下成功地合成了系列Ba_1－xSr_xTiO₃ (BST)和BaZr_xTi_1－xO₃ (BZT)固溶体. 通过XRD、化学分析法、SEM和AFM等手段表征了固溶体的结构、组成和形貌. 结果表明: BST, BZT的晶胞常数随组成呈线性关系, 符合Vegard定律, 该系列固溶体为完全互溶固溶体, 且目标产物组成精确, 颗粒为球形, 分布均匀. 初步讨论了复合矿化剂的均相化作用及羟基释放作用、分散剂对BST, BZT晶粒的聚集生长及分散机理.     

CeO2基氧化物储氧材料研究(Ⅱ)添加贵金属改进储氧能力

在高温老化的复合氧化物CZO和CZYO体系中,添加微量贵金属(Pt,Pd,Rh)明显提高还原速度并增加OSC.含贵金属的CZO或CZYO的OSC与其组成和贵金属的种类有关.较长时间(10 h)老化后含Pd的CZO3样品的OSC明显下降,CZYO2样品的OSC略有下降.含Pt/Rh,10 h老化后CZO3和CZY02样品的OSC均高于相应同条件老化的含Pd样品的OSC.     

Pd/γ-Al2O3三效催化剂中CeO2-ZrO2-La2O3的作用

用浸渍法制备了CeO2-ZrO2-La2O3复合氧化物,用XRD,TG-DTA,拉曼光谱、H2-TPR和BET表面积测定等方法对合成的样品进行了表征,研究了在单钯Pd/γ-Al2O3催化剂中添加CeO2-ZrO2-La2O3对催化剂活性和热稳定性的影响.结果表明,在Pd/γ-Al2O3中加入三元复合氧化物有利于提高三效催化剂的热稳定性,有利于阻止γ-Al2O3在高温时的相变以稳定Al2O3结构,防止在高温条件下催化剂表面积的损失.在Pd的负载量为1 g*L-1条件下,测定了Pd/CeO2-ZrO2-La2O3/γ-Al2O3/蜂窝陶瓷催化剂对CO,C3H6和NO净化的三效活性,研究了催化剂的结构和三效催化活性之间的关系.结果表明,CeO2-ZrO2-La2O3的存在能明显提高Pd基催化剂对CO,C3H6和NO的三效净化活性,扩大催化剂的操作窗口,提高在富氧条件下对NOx的还原性能.     

Co-modified Pd/CeO2-ZrO2 catalysts for methanol decomposition

Pd/Ce0.8Zr0.2O2 catalysts modified by cobalt were prepared by a sequential impregnation method and characterized by X-ray powder diffraction(XRD), N2adsorption/desorption(Brunauer-Emmet-Teller), oxygen storage capacity(OSC), CO-chemisorption, H2-temperature-programmed reduction(H2-TPR) and X-ray photoelectron spectroscopy(XPS). The effect of Co on the performance of methanol decomposition was evaluated at a fixed-bed microreactor. The results showed that the addition of Co can improve the oxygen storage capacity of the catalyst and the dispersion of Pd. XPS results indicated that Pd was in a partly oxidized(Pdδ+, 1δ2) state and Co2+was present in Pd catalysts modified by Co. A 90% conversion of methanol was achieved at around 280°C over Pd-Co/Ce0.8Zr0.2O2 catalyst which was 20°C lower than that over Pd/Ce0.8Zr0.2O2, indicating that both Pdδ+and Co2+play an important role in improving the catalytic activity of methanol decomposition.     

La对柴油车尾气中可溶性有机物氧化催化剂CeO2-ZrO2的影响

采用共沉淀法分别制备CeO₂-ZrO₂(质量比60:40)和CeO₂-ZrO₂-La₂O₃(质量比60:30:10)催化剂.利用热重-差热分析(TG-DTA)对柴油车尾气中可溶性有机物(SOF)的催化活性进行测试.结果表明La改性的CeO₂-ZrO₂催化剂相较于CeO₂-ZrO₂催化剂表现出更好的活性, SOF的起燃温度为164 ℃,最大失重点温度为212 ℃;对CeO₂-ZrO₂来说, SOF在168 ℃开始转化, 221 ℃转化最快. X射线衍射(XRD)结果表明, La的添加有效降低老化催化剂的晶粒尺寸增大速率. N₂吸附-脱附的结果说明La的添加有利于增大CeO₂-ZrO₂催化剂的比表面积; O₂-程序升温脱附(O₂-TPD)和X射线光电子能谱(XPS)结果表明La的改性有效增加化学吸附氧含量.因此, CeO₂-ZrO₂-La₂O₃催化剂表现出较好的催化活性和抗老化性.     

镧、锰掺杂改性CeO2-ZrO2-Al2O3固溶体的性能

采用共沉淀法制备了一系列La, Mn共掺杂的CeO2-ZrO2-A12O3(CZA)复合氧化物, 采用BET, XRD, H2-TPR, XPS和XRF等方法对样品进行表征. 结果表明, 全部样品均形成了稳定的CZA固溶体, 经600 ℃焙烧后表现出良好的织构性能, 1000 ℃老化后, La, Mn共掺杂样品具有最佳的高温稳定性; H2-TPR测试表明, La, Mn之间存在正协同效应, 共掺杂的样品具有最佳的低温还原性能和高温稳定性; XPS结果表明, 掺杂La可有效抑制在焙烧过程中Mn向表面的迁移, 从而保持较高的表面吸附氧浓度.     

还原热处理对铈锆铝复合氧化物性能的影响

采用共沉淀法制备铈锆铝复合氧化物(CeO2-ZrO2-Al2O3,CZA)和铈锆复合氧化物(CeO2-ZrO2,CZ),将样品分别在空气和10%H2/Ar气氛下进行热处理,利用X射线粉末衍射(XRD)、O2脉冲吸附、H2程序升温还原(H2-TPR)等手段研究了复合氧化物的结构及性能.结果表明:CZA样品经950℃还原热处理后出现CeAlO3晶相,热处理温度越高,越有利于CeAlO3物相生成.CZA储氧量(OSC)随着还原热处理温度升高逐渐增大,至900℃达到1270.3μmo·lg-1;温度继续升高,OSC减小,1100℃还原热处理后CZA的OSC仅为23.2μmo·lg-1.研究发现还原热处理中形成CeAlO3,其显著影响CZA样品的储氧性能和还原性能.     

复合沉淀剂制备的CeO2-ZrO2-Al2O3材料及其负载的单Pd三效催化剂

采用了一种由氨水和碳酸铵组成的复合沉淀剂来制备CeO₂-ZrO₂-Al₂O₃ （CZA）复合氧化物。作为对比,分别采用氨水和碳酸铵为沉淀剂制备了另外两个CZA复合氧化物。系统地研究了各CZA材料在织构、结构、氧化还原性能、热老化行为之间的区别,以及其负载的单Pd三效催化剂的催化性能。结果表明,不同的沉淀剂制得的材料中其CeO₂-ZrO₂ （CZ）和Al₂O₃之间的相互作用不同。用氨水做沉淀剂时,得到的材料中CZ和Al₂O₃之间的相互作用很小,导致其热稳定性较差。在碳酸铵做沉淀剂的情况下,CZ和Al₂O₃之间具有很强的相互作用,可以提高材料的热稳定性,但同时,CZ固溶体的均一性被严重破坏,使得材料的氧化还原性能不理想。而复合沉淀剂的使用可以有效地平衡CZ和Al₂O₃之间的相互作用,导致得到的CZA材料具有优异的织构、结构性能及良好的热稳定性。因此,其负载的单Pd催化剂表现出最为优异的氧化还原性能和三效催化活性。     

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     

水蒸汽对Ni/CeO2-ZrO2-Al2O3催化剂上CO2+CH4重整反应的影响

The Ni/CeO2 -ZrO2 -Al2O3 catalyst was prepared with the hydrothermal method. The catalytic performance for the CO2 reforming of CH4 reaction with or without small amount of steam was tested and the amount of coke deposition was measured. The XAFS of Ni K-edge was attained. The results show that the formation of CeAlO3 occurs in reaction,but the coke deposition is responsible for the deactivation of the catalyst. The addition of steam into feed gas can decrease the amount of coke deposition,and promote the stability. Due to the carbon atom penetration into the Ni lattice,for the catalyst sample after reaction without the addition of steam into feed gas,the coordination number of the first Ni-Ni shell decreases sharply. For the catalyst sample after reaction with the addition of steam in feed gas,the coordination numbers of the first Ni-Ni shell decrease slightly. It is due to the addition of steam into feed gas,which can suppress the coke formation and maintain the metallic structure of active Ni metal.     

CeO2-ZrO2-La2O3-Al2O3 composite oxide and its supported palladium catalyst for the treatment of exhaust of natural gas engined vehicles

Composite supports CeO2-ZrO2-Al2O3 (CZA) and CeO2-ZrO2-Al2O3-La2O3 (CZALa) were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles (NGVs) operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction (XRD) and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperature-programmed reduction (H2-TPR) and oxygen storage capacity (OSC) measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.