【作者】 谢鲜梅；

【导师】 王志忠；

【作者基本信息】 太原理工大学 ， 应用化学， 2007， 博士

【摘要】 水滑石是一种具有层状结构的天然矿物，其理想结构式为Mg₆Al₂（OH）₁₆CO₃·4H₂O（Hydrotalcite简称HT），板层上Mg（OH）₆八面体通过共用棱边形成土板层结构，其中的Mg²⁺在一定程度上被Al³⁺同晶取代而导致层上带有正电荷，CO₃^2-处于层间作为平衡离子，使整个结构呈电中性。一定条件下，水滑石结构中的Mg²⁺、Al³⁺可被其它电荷相同、半径相近的二价或三价金属离子同晶取代，层间阴离子CO₃^2-可被NO₃^-、Ac^-、Cl^-、SO₄^2-等无机阴离子取代，从而形成结构相同、组成各异的类水滑石化合物（Hydrotalcite-Like Compounds简称HTLcs），其结构通式为：[M_1-x²⁺ M_x³⁺（OH）₂]^x+(A_x／n^n-)·mH₂O，其中M²⁺、M³⁺分别代表+2、+3价金属阳离子，A代表阴离子，n代表阴离子的价数，m代表结晶水的数目，x为+3价阳离子在阳离子总数中所占的分数。由于该物质的结构特点，使其具有层间阴离子的可交换性、板层元素组成多变性和孔径可调变性。依据类水滑石中M²⁺和M³⁺的种类及比例不同，HTLcs具有不同的酸碱性和氧化还原性，它们在加氢、裂解、催化氢化、酯化、费—托合成等反应中表现出高的催化活性。另外，类水滑石化合物作为新型功能材料和催化剂载体的应用也有着广泛的前景。类水滑石应用于催化领域，其一是直接作为催化剂，应用于一些较低温度的碱催化反应；其二是以类水滑石为前驱体经焙烧制备的复合金属氧化物，具有晶粒小、比表面积大、孔容和表面性质可控的特性，应用于氧化还原反应具有很好的反应活性和选择性；其三是以类水滑石为催化剂载体，使其担载的催化材料具有更高的催化活性和选择性；其四是以HTLcs为前驱体，将同多或杂多阴离子嵌入到其层间，可望获得大层间距的多功能柱撑催化材料。但是，由于天然类水滑石品种少、结晶度低，杂质含量高，组成不稳定等缺陷，其广泛应用就受到一定的限制。所以，利用不同方法人工控制合成板层组成元素不同、M³⁺对M²⁺同晶取代程度不同即板层电荷密度不同、粒径大小不同的一系列精细结构差异的类水滑石就很有必要。本论文研究中，采用共沉淀法，从测定不同比例的混和盐溶液的NaOH滴定曲线着手，详细而深入地探讨了合成体系中pH值、反应原料配比、合成方式、晶化处理温度和时间对合成过程的影响，利用XRD对合成过程中不同pH值阶段合成物物相进行鉴定，借助现代分析仪器手段FT-IR、ICP、BET、TG—DTA表征合成物的物化性能，筛选出合成HTLcs的适宜条件，推断合成机理，总结合成类水滑石的一般规律，为该领域的进一步研究提供理论基础。实验结果表明：合成过程中采用新煮沸过的蒸馏水配制溶液制备ZnAl-HTLcs、MgAl-HT、NiAl-HTLcs，无需N₂保护，产物中检验不出CO₃^2-的存在，层间离子为单一的NO₃^-离子；首次提出短时间水热处理，完全可以代替传统的回流处理，使HTLcs合成过程操作简化，合成时间大大缩短；pH值是共沉淀法合成类水滑石的关键因素，合成二元类水滑石的适宜pH值介于Al（OH）₃和M（OH）₂形成时的pH值之间；共沉淀合成类水滑石的机理是，随着NaOH碱液加入二价和三价金属离子混合盐溶液中，体系的pH值不断提高，首先生成Al（OH）₃，随后M²⁺部分取代Al³⁺，形成具有层状结构的类水滑石。以类水滑石为前驱体经焙烧制备的复合金属氧化物具有比表面积大、活性元素分布均匀、金属离子还原条件温和的优点，可应用于许多酸碱催化和氧化还原催化过程。研究HTLcs的热解过程、揭示热分解机理、关联热解产物性能与前驱体的联系是获取性能优异的复合金属氧化物的重要保证。研究中利用TG-DTA技术考察了NiAl、ZnAl、MgAl类水滑石的热分解行为，通过Ozawa法和Kissinger法计算热分解动力学参数。实验结果表明：MgAl-HT、NiAl-HTLcs、ZnAl-HTLcs三种二元类水滑石由于构成元素不同，热稳定性不同，稳定性由高到低顺序为：MgAl-HT＞NiAl-HTLcs＞ZnAl-HTLcs，热稳定性分别达400℃、300℃、200℃。MgAl-HT在热解过程中，当Mg／Al=1-2时，热解过程分三个阶段完成，即脱吸附水和层间结晶水、脱铝羟基、脱镁羟基和层间硝酸根离子；当Mg／Al=3-6时，热解过程分两个阶段完成，即脱吸附水和层间结晶水、脱结构羟基及层间硝酸根离子。不论Ni／Al比如何，NiAl-HTLcs的热解过程均分两个阶段完成，即脱吸附水和层间结晶水、脱结构羟基及层间硝酸根离子。不论Zn／Al比例如何，ZnAl-HTLcs的热解过程一步完成，即吸附水和层间结晶水、结构羟基及层间硝酸根离子一步脱去。利用Ozawa法和Kissinger法计算HTLcs的表观活化能，相应值存在E_Ozawa＞E_Kissinger规律；相同热解过程，存在E_MgAl-HT＞E_NiAl-HTLcs＞E_ZnAl-HTLcs规律；此外，Ozawa法计算结果表明，在二元类水滑石热解过程中，表观活化能是动态变化的。类水滑石的组成、结构、粒度大小等性质很大程度上决定其应用领域。特别是在许多应用中，要求类水滑石化合物具有规定的粒径尺寸，以便最大限度地发挥其功能性。本论文采用平衡晶化法、改变过饱和度法和超声波晶化三种方法进行NiAl类水滑石粒径控制的研究，详细考察了各种因素对合成类水滑石粒径的影响。研究结果表明：平衡晶化法中随水热处理温度的提高和水热处理时间的延长，合成物粒径逐渐增大，是制备大粒径类水滑石的有效办法，在其他条件相同时，通过水热处理可使合成物中值粒径由1.01μm增加到4.39μm；采用超声晶化法是合成粒径尺寸较小，粒径分布范围窄的超细类水滑石化合物的有效办法，一定条件下，合成物中值粒径为0.38μm，而（0.26-0.51）μm之间的粒子占到总数的83.04％。在质子型溶剂乙酸存在下，应用NiAl-HTLcs作催化剂，完成液相空气氧化苯甲醛至苯甲酸。考察反应影响因素，确定反应机理，并对反应动力学参数进行计算。研究结果表明：NiAl-HTLcs催化剂能有效地活化分子氧，质子型溶剂乙酸可以借助氢键与氧气缔合，有利于氧气在反应液中溶解与扩散，在最佳反应条件下，苯甲醛的转化率达100％，苯甲酸的选择性近100％。此反应属扩散控制反应，为动力学上零级反应，反应活化能为15.277kJ／mol，按自由基历程进行。研究结果开创了有质子型溶剂存在下，液相空气氧化苯甲醛制苯甲酸的新途径。论文中用NiAl-HTLcs作催化剂，催化苯甲醛与乙醇反应生成安息香乙醚。在最佳实验条件下，苯甲醛转化率为54.83％，安息香乙醚的选择性近100％。此反应属一级反应，反应活化能为42.189kJ／mol。以类水滑石为催化剂一步合成安息香乙醚的方法大大改进了传统的以苯甲醛为原料，经过缩合和醚化两步完成，并在第一步中使用氰盐作催化剂的安息香乙醚生产工艺，具有很大的创新性。Cu²⁺在羟基配位的八面体结构中姜—太勒效应严重，单独Cu²⁺与三价金属离子进行共沉淀时，优先生成变形八面体复合盐而不能形成层状结构的HTLcs，即使能形成，合成条件也较苛刻，且稳定性也较差。但负载型铜系催化剂在一些碱催化、氧化还原催化方面应用广泛。而以含铜类水滑石为前驱体经焙烧所得氧化物具有比表面大、铜分散度高、颗粒大小均匀的特点，在催化应用上有很大潜力。本研究以共沉淀法制备了铜锌铝、铜镁铝类水滑石，对其主要影响因素进行详细考察，筛选出合成该化合物的适宜条件，利用苯酚羟化作为探针反应对CuZnAl-HTLcs的催化性能进行评价。研究结果表明：合成CuMAl-HTLcs(M为Ni²⁺或Zn²⁺)适宜的pH范围介于Al（OH）₃、M（OH）₂和Cu（OH）₂形成的pH值之间，且适宜pH范围较合成相应二元类水滑石的pH范围窄。随着CuZnAl-HTLcs中Cu含量的增加，催化剂对苯酚羟化反应的催化活性逐渐增大，苯酚最高转化率可达56.1％。稀土金属结构特殊，在许多反应中催化效果较好，控制条件，将离子半径较大的稀土离子引入类水滑石结构中，制备含稀土金属类水滑石化合物，以它为前驱体，经焙烧后可望得到具有比表面积大、稀土元素分布均匀、各种金属离子之间协同良好的复合金属氧化物催化剂，应用于环境友好催化领域，具有一定的经济效益和社会效益。本研究从Ce³⁺、Al³⁺、Zn²⁺、Ni²⁺几种金属离子混合盐溶液的氢氧化钠滴定曲线入手，深入研究将离子半径较大的稀土离子Ce³⁺引入类水滑石结构中的方法和制备NiAlCe-HTLc和ZnAlCe-HTLcs的适宜条件，初步探索含稀土类水滑石衍生复合氧化物在催化消除NO反应中的应用。研究结果表明：合成MAlCe-HTLcs(M为Ni²⁺或Zn²⁺)适宜的pH值介于Al（OH）₃、M（OH）₂、Ce（OH）₃形成时相应的pH值之间。以ZnAlCe-HTLcs为前驱体经过750℃焙烧后所得复合氧化物应用于催化消除NO，680℃进行反应，可使NO转化率近100％。NiAlCe-HTLcs在催化消除NO反应中表现出高的低温活性，400℃进行反应，NO转化率达95％。更多还原

【Abstract】 Hydrotalcite, a kind of natural mineral, has an ideal formula Mg₆Al₂（OH）₁₆CO₃·4H₂O with a sheet structure, in which Mg²⁺ ions are arranged in sheets and each of them is octahedrally surrounded by six hydroxide groups while each hydroxide spans three magnesium ions. The sheet structure shows a positive charge of the layer when the divalent cations(Mg²⁺ ) are partially substituted with some comparable size trivalent ones such as Al³⁺, balanced by the anions CO₃^2- between the hydroxylated layers. Under certain condition, Mg²⁺ and Al³⁺ can be substituted by other divalent and trivalent cations with similar radius, respectively; and CO₃^2- can also be replaced with NO₃^-, Ac^-, SO₄^2- and etc.. Thus a large number of hydrotalcite-like compounds （HTLcs） can be synthesized in the same structure but with different compositions, whose general formula can be therefore shown like [M （II）_1-xM （III）_x （OH）₂]^x+(A^n-)_x/2·mH₂O, where M （II） and M （III） represent the divalent and trivalent cations, respectively; A^n- represents anions in the octahedral positions; ’m’ is the number of the water molecules and ’x’ is the ratio of trivalent to all the cations.With the characteristics of exchangeable anions in the interlayer, adjustable cations on the sheets and variable pore sizes, HTLcs have different acidic-basic capacity and oxidation-reduction property if given different cation species and ratio of n(M²⁺) to n(M³⁺) and thereout have been widely used to catalyze the reactions of hydrogenation , degradation , catalytic hydrogenation , esterification and Fischer-Tropsch low-carbon alcohol. Moreover, HTLcs have also potential to be utilized as new type materials and carriers of catalysts.However, the application of the natural HTLcs have been limited because of fewer species, lower crystallization, higher impurity, and unstable constituent. Therefore, it is urgent to build a system of producing a series of structurally refined HTLcs with different compositions on the sheets, different isomorphous replacement degree or different charge density on the plates and different particle sizes under certain conditions.In this current project, we started with measuring the NaOH titration curves of nitrate salt by co-precipitation method to study the effect of pH, raw material, procedure, temperature and time of crystallization on the synthesis of HTLcs; then identifying the phases of complex with different pH values by XRD; eventually selecting an optimal condition of preparing HTLcs through characterization of physicochemical performances of the complex by using the modern instrumentals of FT-IR, ICP, BET and TG-DTA. More importantly, we proposed a reasonable mechanism and a general principle of synthesizing HTLcs that will provide a theoretical basis for further study in this field.The result showed that 1) through the optimal procedure, CO₃² was not detectable in the product and NO₃^- was the unique ion in the interlayer of complex when MgAl-HT, NiAl-HTLc and ZnAl-HTLc solution were prepared by the freshly boiled distilled water without protection of N₂. 2) We found that the hydrothermal treatment with shorter time could replace the conventional reflux of over 20h at 80℃completely , and such procedure would simplify the synthesis process and shorten the preparation time significantly. 3 ) The pH value is a crucial factor in the preparation of HTLcs. The pH value in the synthesis of bi-HTLcs should be higher than in the preparation pH of Al（OH）₃ and lower than in that of M（OH）₂. 4) The preparation mechanism of HTLcs by co-precipitation was describe as: by adding NaOH aqueous into the mixed salt solutions, the pH value in the system increased generally, Al（OH）₃ was got and then subsequently, with the M replacing Al³⁺ partially, HTLcs with layered structure formed.HTLcs are facile to be decomposed when heated and the obtained complex oxides will have fine application prospects in some acid-base catalysis or redox catalysis reactions. Because of their typical characteristics such as big specific surface area, even distribution of catalytic active sites and mild reduction condition of metallic cations. However, the thermal decomposition procedure is complicated and the properties of complex oxides are mainly determined by the composition of the precursor and calcination temperatures of thermal decomposition process. In this paper, the thermal decomposition process of HTLcs was investigated and the decomposition mechanism was also proposed in order to obtain such complex oxides possessing perfect performances. TG-DTA technology was adopted to study the thermal decomposition processes of MgAl-HT, NiAl-HTLcs and ZnAl-HTLcs. Kinetic parameters of the process were calculated and analyzed by Ozawa method and Kissinger method, and then the reaction mechanism was deduced afterwards. The results showed that the thermal stability of the three kinds of HTLcs was different and the stability order was: MgAl-HT>NiAl-HTLcs>ZnAl-HTLcs. The temperatures of stability were 400℃, 300℃and 200℃, respectively. In the thermal decomposition process of MgAl-HT, when Mg/Al=1～2, the TG curves showed three mass loss stages: the weight loss of the deformation of the interlayer water molecules under the first stage, the removal of the Al-OH on the sheets of the second and the loss of Mg-OH on the sheets and nitrate ions of the third; while when the Mg/Al=3～6, the curves showed two stages: the loss of interlayer water molecules and dehydroxylation of the sheets as well as the loss of nitrate ions. For the thermal behavior of NiAl-HTLcs, all the samples showed two weight loss stages: one stage to the loss of interlayer water molecules and the other to dehydroxylation of the sheets as well as the loss of nitrate ions in the interlayer. As to the ZnAl-HTLcs, the thermal decomposition was completed under one stage; i.e. the loss of interlayer water molecules and dehydroxylation of the sheets as well as the loss of nitrate ions in the interlayer. The active energy values calculated by Ozawa method were higher than that by Kissinger method under the same decomposition stage of the same samples. Active energy values of the corresponded stages presented the order of E_MgAl-HT> E _NiAl-HTLcs >E_ZnAl-HTLcs. The calculated results by Ozawa method showed that the active energy values of thermal decompositions kept changing dynamically.HTLcs are new type functional materials and their application fields are mainly dependent on their compositions, structures and particle sizes. Particularly in many applications, the particle sizes were specified to make full use of their advantages. In this paper, NiAl-HTLcs with different particle size distribution were prepared by methods of equilibrium crystallization, variation of the degree of super-saturation and ultrosonic crystallization. And also the effect of many factors on particle size was systematically studied. The results showed that the big particle sizes of HTLcs could be obtained when increasing temperature and extending time of the hydrothermal treatment during equilibrium crystallization, in which the average particle size of samples would increase from 1.01μm to 4.39μm. However, an effective means to acquire HTLcs with small particle sizes and narrow particle sizes distribution was by the method of ultrosonic crystallization, from which the average particle size of samples was 0.38μm and took 83.04% of （0.26-0.51）μm.In order to study the catalytic activity of HTLcs, NiAl-HTLcs was introduced to the oxidation reaction of phenyl aldehyde into benzoic acid where acetic acid was solvent and oxygen in the air as the oxidant. Effects of different factors on the reaction were investigated in detail, and then the reaction mechanism was deduced by the calculation of kinetics parameters including the reaction activity energy and reaction grades. The result showed that the NiAl-HTLcs could be used as an excellent catalyst in the synthesis of benzoic acid with acetic acid and phenyl aldehyde. In this reaction, oxygen could be dissolved and diffused much more easily because NiAl-HTLcs activated the oxygen molecules in the air and at the same time acetic acid as solvent was associated with oxygen in the presence of hydrogen bond. Under optimal condition, both the conversional rate of phenyl aldehyde and the selectivity of benzoic acid were up to 100%. The kinetic study showed this reaction was a typical controlled diffuse reaction or could be also called zero progression reaction, in which the active energy was got to be 15.277kJ·mol^-1 following the free radical reaction. This experiment pioneered a completely new path of reaction where phenyl aldehyde was oxidized into benzoic acid using protonic solvent as medium .NiAl-HTLcs was also introduced into another synthetic reaction of benzoin ethyl ether with ethanol and phenyl aldehyde, in which the conversion of phenyl aldehyde was up to 54.86% and the selectivity of benzoin ethyl ether was nearly 100% at the optimal condition. This reaction was kind of one progression reaction and the reaction activity energy was 42.189kJ·mol^-1 where NiAl-HTLcs and ethanol were as the catalyst and the solvent, respectively. This technology completely innovated the traditional design of the synthesis of benzoin ethyl ether, i.e. NiAl-HTLcs replaced cyanide as the catalyst in the reaction. By this new method, not only the cyanide poisoning was avoided but also the synthesis of benzoin ethyl ether could be completed in one step instead of the traditional two steps with both condensation and etherification.As the John-Tellor effect of Cu²⁺, when Cu²⁺ was used to prepare HTLcs with trivalent cations by coprecipitation method, Cu would form deforming octahedral complex rather than HTLcs. Even if it could be introduced into the preparation of HTLcs, the preparation conditions would be harsh and the stability of the resultant would be poor. However, catalysts loading copper have wide applications in alkali and redox catalysis. Moreover, the complex oxides of HTLcs with copper as the precursor possess potential application capacity because of whose typical characteristics such as big specific surface area, high dispersion degree of Cu and even particle sizes. Here, CuMAl-HTLcs (M=Mg²⁺ or Zn²⁺) were prepared by coprecipitation method. Effects of different factors on the preparation were studied elaborately. Based on the above research, the most optimal preparation conditions were acquired and the obtained HTLcs was also used in the reaction of phenol hydroxylation to study its catalytic performances. The results showed that the feasible pH value range for preparation of CuMAl-HTLcs (M=Mg²⁺ or Zn²⁺) fell in the range of that of Al（OH）₃, M（OH）₂ and Zn（OH）₂. By increasing Cu content in CuZnAl-HTLcs, it catalytic activity in the reaction of phenol hydroxylation would be elevated gradually and the highest conversion of phenol could reach to 56.1%.Rare metals with special structures have shown champion effectiveness in many reactions. Here, by introducing rare metals with larger ionic radius into the structure of HTLcs by controlling the synthesis factors. The complex oxides obtained from calcinating the above HTLcs were expected to have advantages to be an environment benign catalyst such as big specific surface area, even distribution of rare metal elements and fine coordinating action among the metal cations. Starting by the titration curve of mixed salt solution of several metal ions (Ce³⁺, Al³⁺, Zn²⁺ and Ni²⁺) with NaOH solution as the precipitator, a feasible way was modified to introduce Ce³⁺ with larger ionic radius into the structure of HTLcs and the optimal conditions were nvestigated elaborately for preparing NiAlCe-HTLcs and ZnAlCe-HTLcs. Subsequently, the posibility of the complex oxides with HTLcs containing rare metal as the precursor in elimination reaction of NO was preliminarily researched. The experiments results showed that the feasible pH value range for preparation of MAlCe-HTLcs (M=Ni²⁺ or Zn²⁺) was among the ranges of that of Al（OH）₃, Zn（OH）₂ and Ce（OH）₃. The complex oxides obtained from calcination of ZnAlCe-HTLcs at 750℃was used in catalytic reduction reaction of NO; when the reaction temperature was 680℃, the conversion of NO was up to 100%. NiAlCe-HTLcs showed high activity at lower temperatures in the catalytic reduction reaction of NO; when the reaction temperature was 400℃, the conversion of NO could reach 95%.更多还原