【作者】 吴跃辉；

【导师】 罗来涛；

【作者基本信息】 南昌大学 ， 工业催化， 2008， 博士

【摘要】 钙钛矿复合氧化物具独特的物理化学性质和催化活性，但因本身的比表面积和孔容较小而限制了其应用，因此，许多研究工作者试图寻找一种大比表面、活性高的钙钛矿复合氧化物制备方法。本文采用固相法、氨基乙酸法、柠檬酸法、氨基乙酸燃烧法、柠檬酸燃烧法等制备一系列La_0.95Ce_0.05CoO₃钙钛矿催化剂，研究了制备方法对钙钛矿催化剂的比表面积和催化活性的影响。为进一步提高催化剂的比表面积和活性，本文考察了氨基乙酸与金属组分的配比、前驱体溶液pH值、焙烧温度和焙烧时间等制备条件对La_0.95Ce_0.05CoO₃钙钛矿催化剂比表面、甲烷催化燃烧活性的影响。本文采用柠檬酸燃烧法合成了La_0.95Sr_0.05Ni_0.05Co_0.95O₃钙钛矿型复合氧化物，考察了复合掺杂对LaCoO₃催化剂的晶体结构、颗粒度、表面形态、结构、比表面积、平均孔径和孔体积等性能的影响。以大比表面La_0.95Ce_0.05CoO₃钙钛矿氧化物为载体，制备M／La_0.95Ce_0.05CoO₃钙钛矿催化剂（M=Pd、Pt、Ni），研究了不同金属组分负载对催化剂结构与性能的影响，同时采用M（M=Pd、Pt、Ni）对La_0.95Ce_0.05CoO₃钙钛矿氧化物进行掺杂，研究了不同金属掺杂对催化剂结构与性能的影响，比较了负载型与掺杂型催化剂的异同。最后还研究了不同稀土和有机燃料与氧化剂的化学计量比（（?））对Ln_0.8Sr_0.2CoO₃复合氧化物催化剂结构、表面性能和甲烷催化燃烧活性影响。以甲烷催化燃烧为探针反应对所合成的催化材料进行了活性评价，研究了制备方法、制备条件、负载和掺杂M、不同稀土和有机燃料与氧化剂的化学计量比（（?））等对甲烷催化燃烧活性影响。并分别采用X射线粉末衍射（XRD）、电子显微镜扫描（SEM）、红外光谱（FT-IR）、比表面积和孔径测定（BET）、TG-DTA等技术对催化剂结构、晶相和比表面积进行了表征分析，探讨了各种制备方法和条件、负载和掺杂M对催化材料性能的影响。制备方法的研究结果表明，各种方法制备的La_0.95Ce_0.05CoO₃样品均为单一钙钛矿结构。相对于LaCoO₃化合物，A位掺杂的Ce离子进入了晶格，部分取代了晶格内相应位置上的La离子。按氨基乙酸燃烧法、柠檬酸燃烧法、氨基乙酸法、柠檬酸法及固相法的次序，所制La_0.95Ce_0.05CoO₃催化剂的孔结构和比表面积依次递减，氧空穴和可移动晶格氧依次减少，甲烷燃烧反应的催化活性依次下降。其中氨基乙酸燃烧法制备的La_0.95Ce_0.05CoO₃比表面积最大（32．4m²／g）、粒径最小（10～20nm）、化学吸附氧和晶格氧最多、甲烷催化燃烧活性最好。氨基乙酸燃烧法制备条件的研究表明，氨基乙酸与金属组分的不同配比、焙烧温度、焙烧时间和前驱体溶液pH值等制备条件对La_0.95Ce_0.05CoO₃催化材料的结构和性能有较大影响。氨基乙酸与金属组分配比量太小不利于形成钙钛矿结构，不利于保持样品的大比表面积和提高催化剂的活性；随着焙烧温度的升高、焙烧时间的延长，La_0.95Ce_0.05CoO₃催化材料的平均孔径、比表面积和孔容逐渐减小，催化剂的吸附氧和晶格氧活动性逐渐减弱，催化活性下降；前驱体溶液pH=7时金属组分的分散程度较好，有利于形成钙钛矿结构，催化材料的催化活性也较高。M（M=Pd、Pt、Ni）负载和掺杂的研究表明，La_0.95Ce_0.05Co_0.95Pd（Pt）_0.05O₃和Pd（Pt）／La_0.95Ce_0.05CoO₃催化剂甲烷催化燃烧反应活性明显高于La_0.95Ce_0.05CoO₃催化剂；Ni／La_0.95Ce_0.05CoO₃和La_0.95Ce_0.05Co_0.6O₃催化活性变化不大，可能是因为Ni的负载量和掺杂量较大，样品比表面积有所减小；La_1-xSr_xNi_xCo_1-xO₃掺杂量较小时，复合掺杂有利于样品孔结构和大比表面积的形成，有利于改善催化活性，但过量掺杂使较多杂相氧化物微晶析出，从而影响了催化剂的活性。稀土和有机燃料与氧化剂的化学计量比（（?））的研究表明，不同稀土对Ln_0.8Sr_0.2CoO₃复合氧化物甲烷催化燃烧的催化活性影响不同，其活性顺序为La_0.8Sr_0.2CoO₃>Ce_0.8Sr_0.2CoO₃>Nd_0.8Sr_0.2CoO₃。A位中的不同稀土导致活性单元BO₆八面体的畸变率不同，其畸变率大小顺序与活性顺序相同。不同有机燃料与氧化剂的化学计量比（（?））对La₀₈Sr₀₂CoO₃催化剂性能有一定的影响，在（?）=0．76～1．52内，催化剂的甲烷催化燃烧活性随（?）值的增大而提高，其中（?）=1．52时所制备催化剂的比表面积和晶格畸变率最大、平均晶粒度最小、表面吸附氧和氧空穴处的化学吸附氧更容易移动、表观活化能最低，因此活性最高。本文制备的一系列催化材料的甲烷催化燃烧反应符合一级反应的动力学特征，基本遵循Eley-Rideal型的反应机理，不同催化材料的甲烷催化燃烧反应活化能各不相同。更多还原

【Abstract】 Perovskite mixed oxides have been extensively studied due to its particular physical and chemical properties, but the perovskite mixed oxides prepared via conventional synthesis routes have relatively low specific surface areas, pore volume and show low catalytic activity in the reactions, and its applications were limited. So it is urgent affairs to develop a new method to prepare the kind of perovskites with large specific surface areas（SSA） and high catalytic activity. In this dissertation, the perovskite La_0.95Ce_0.05CoO₃ mixed oxides were synthesized by solide state reaction method, citric-acid method, glycine method, citric-acid combustion method and glycine combustion method in order to study the effects of preparation methods on specific surface area and catalysts performances. It was discussed the effects of the preparation condition, such as glycine-to-metal ratio, pH value of the precurors solution, calcination temperature and calcination time, on the specific surface area and catalytic activity for methane combustion. La_0.95Sr_0.05Ni_0.05Co_0.95O₃ was prepared by citric acid combustion method, and the effects of composite doping on structure, surface patterns, pore size, surface area and pore volume of the catalysts were investigated. Catalytic materials M/La_0.95Ce_0.05CoO₃ were prepared by metal M（M=Pt, Pd, Ni） supported on the perovskite mixed oxides with large SSA , the effects of loaded M on the structure and properties of the catalysts were discussed. La_0.95Ce_0.05Co_0.95M_0.05O₃ were prepared and the effects of doped M on the structure and performances of the catalysts were also discussed, its internal causes were discussed. The effects of rare earths and stoichiometric ratio of organic fuel to oxidizer （（?）） on structure, surface properties and catalytic activities of Ln_0.8Sr_0.2CoO₃ catalysts were studied.All catalysts were used successfully for CH4 combustion. The properties of these catalysts, such as crystal structures, particle sizes, surface patterns, pore sizes, surface areas and pore volumes, were characterized by X-ray diffraction （XRD）, electron microscopy （TEM/SEM）, thermal analysis （TG-DTA）, nitrogen adsorption experiments （BET）, （FT-IR Spectrometer） IR, temperature-programmed desorption （TPD） and temperature-programmed reduction （TPR）, respectively.The experiment results show that all catalysts synthesized by different methods were perovskite-type mixed oxides. Doping Ce³⁺ ions on A sites entered the crystal lattices of LaCoO₃ in the place of La³⁺. At the order of La_0.95Ce_0.05CoO₃ prepared by solidc state reaction method, citric-acid method, glycine method, citric-acid combustion method and glycine combustion method, oxygen vacancies, mobile lattice oxygen, the porous structures and SSA of the La_0.95Ce_0.05CoO₃catalysts increase gradually, which enhance the catalytic activity of the catalysts. La_0.95Ce_0.05CoO₃ prepared by glycine combustion method has higher catalytic activity for methane combustion, whose BET specific surface area and crystallite size were 32.4 m²/g and10～20 nm, respectively. It can be explained in terms of its more mobile chemical-adsorped oxygen and lattice oxygen.Preparation conditions of La_0.95Ce_0.05CoO₃ catalyst were investigated, the results indicate that the structure and properties of catalyst can remarkably affect by glycine/metal molar ratio, calcined temperature, calcined time and pH value of the precurors solution. The increase of glycine/metal molar ratio is propitious to form perovskite structure, increases the BET specific surface area and improves the the catalytic activity of La_0.95Ce_0.05CoO₃. The BET specific surface area, pore volue and average pore diameter of La_0.95Ce_0.05CoO₃ perovskite-type catalyst decrease with the increase of calcined temperature and calcined time, which decrease adsorption oxygen, mobile lattic oxygen and the catalytic activity for methane combustion. When pH value of precurors solution is about 7, the performance of the catalysts is improved.The results indicate that M/La_0.95Ce_0.05CoO₃,La_0.95Ce_0.05Co_0.95M_0.05O₃ （M=Pt, Pd） synthesized by the modified glycine combustion method are porous catalysts. BET surface areas are large, which are favorable for their catalytic activities. The activity of M/La_0.95Ce_0.05CoO₃ is better than that of La_0.95Ce_0.05Co_0.95M_0.05O₃（M=Pt, Pd）, because Pt, Pd disperse in La_0.95Ce_0.05CoO₃ surface, which increases the catalytic activities of the catalysts. The activitie of Ni/La_0.95Ce_0.05CoO₃ and La_0.95Ce_0.05Co_0.6Ni_0.4O₃ do not change much compared with La_0.95Ce_0.05CoO₃. The effects of composite doped Sr ions and Ni ions on the properties of La_1-xSr_xNi_xCo_1-xO₃ were investigated. The BET specific surface area can be increase and the catalytic performance of La_1-xSr_xNi_xCo_1-xO₃ can be improved when part La ions of A-sites and Co ions of B-sites were replaced by Sr ions and Ni ions, respectivly. When x=0.3 perovskite and other phases coexite, which lead to lower catalytic activity of the catalysts.The effects of different rare earths （La, Nd, Ce） on structure and catalytic activities of the catalysts are different , the sequences of catalysts activities are La_0.8Sr_0.2CoO₃>Ce_0.8Sr_0.2CoO₃>Nd_0.8Sr_0.2CoO₃. Rare earths on site A lead to lattice distortion of the CoO₆ octahedral, The activities of the catalysts are relative to the distortion of BO₆ octahedra. With the enlarging of distortion of BO₆, catalytic activity of the catalyst increases. All La_0.8Sr_0.2CoO₃ mixed oxides with the different coefficient of （?） have perovskite structure, whose structure and catalytic activities alter regularly with the change coefficient of （?）. The catalytic activities of La_0.8Sr_0.2CoO₃ （（?）=0.76-1.52） for CH₄ combustion improve gradually with the increase of （?） When （?） is equal to 1.52, the catalytic activity of La_0.8Sr_0.2CoO₃ is the best, which can be explained in terms of the smaller of average crystal size, the higher of specific surface area, the bigger of lattice distortion, the lower of activation energy and more mobile chemical-adsorped oxygen and lattice oxygen.The reaction mechanism of the catalytic combustion of methane over the prepared catalysts was studied, the results indicate that the reaction of the catalytic combustion of methane accords approximately with features of first order kinetics equation. A probable Eley-Rideal mechanism is considered to interprete the observed kinetic results. The activation energy for the catalytic combustion of methane varies with the catalysts prepared by varied methods.更多还原