【作者】 许俊强；

【导师】 储伟；

【作者基本信息】 四川大学 ， 工业催化， 2007， 博士

【摘要】 自1992年Mobil公司的研究人员成功合成M41s系列介孔分子筛以来,介孔材料以其高的比表面积、均匀的孔径分布、丰富的表面基团引起了广大科研工作者的兴趣。纯硅M41s分子筛具有中性骨架结构,导致缺陷少,离子交换能力小,酸含量和酸强度低,限制了它们在催化、吸附、分离和环保等方面的应用。研究掺杂的负载型介孔材料成为了近年来研究热点。由于介孔材料较差的水热稳定性和热稳定性,使其工业应用受到限制,合成高热和水热稳定性的介孔材料成为了人们不断努力追求的目标。介孔材料的孔径可控制备是介孔分子筛成为新型材料的有效工具,也是当今分子筛发展前沿的新生长点。本文以廉价的工业级高模数比硅酸钠(Na2O·3.3SiO2)代替传统的有机硅源,以溴化十六烷基三甲基铵(CTAB)为模板剂,水热合成法制备了掺杂的介孔材料。采用X射线粉末衍射(XRD),低温液氮吸附脱附(BET),红外光谱(FT-IR),固体紫外漫反射光谱(UV-Vis),扫描电镜(SEM),透射电镜(TEM),感耦等离子体原子发射光谱(ICP),程序升温还原(TPR)和热重分析(TG/DTG)等技术对介孔材料的结构和织构等方面进行了分析。本文考察了该分子筛的合成条件和水热稳定性和热稳定性,讨论了该分子筛的合成机理,研究了该分子筛的孔径调变方法。本论文主要包括以下几方面的内容:1.首先以水热合成法制备了掺钒的介孔V-MCM-41分子筛。分子筛的制备条件对介孔材料的结构具有很大的影响,其主要影响因素为模板剂用量,晶化温度以及pH值,而活性组分V用量,晶化时间,陈化时间,焙烧气氛以及加料方式等制备条件对分子筛的特征结构影响不显著。合成该介孔V-MCM-41分子筛的最佳制备条件为:原料比为n (Si)∶n (CTAB)∶n (V)=1∶0 .2∶0.04,晶化温度为110℃,pH=9.5,晶化48 h,不陈化,加料方式为先加钒源后加硅源,550℃空气气氛焙烧6 h。2.选择无机硅源和有机硅源,采用水热合成法制备了不同的介孔V-MCM-41分子筛。无机硅源(普通硅酸钠,高模数比的硅酸钠和硅溶胶)制备的分别记为VMC,VMH和VMS;有机硅源(正硅酸乙酯)在酸性和碱性下制备的分别记为VMT-ac和VMT-al。研究了不同硅源对该分子筛制备的影响。不同硅源对介孔V-MCM-41分子筛的制备影响较大,尤其是分子筛合成体系的pH值和晶化温度。无机硅源制备的分子筛的表面积大于有机硅源制备的,主要归因于硅源中的硅物种水解和聚合速度不同,导致其以不同的多聚体硅物种存在,该硅物种与表面活性剂相互作用并自身缩合的作用不一致。无机硅源在碱性条件下制备介孔分子筛,有机硅源既可在酸性条件下也可在碱性条件下制备介孔分子筛,只是碱性条件下制备的分子筛的织构优于酸性条件下的。四种不同分子筛的最优合成条件分别为为:VMT-ac的晶化温度110℃和溶液的pH值为5.5;VMT-al的晶化温度110℃和溶液的pH值为10.5;VMH的晶化温度110℃和溶液的pH值为9.5;VMC的晶化温度125℃和溶液的pH值为10.5;VMS的晶化温度125℃和溶液的pH值为11.5;3.考察了以高模数比硅酸钠制备的介孔V-MCM-41分子筛的水热稳定性和热稳定性。随着水热处理时间的增加该分子筛的织构参数都呈现下降趋势,但其介孔特征保持完好。水热处理8天后,其比表面积,总孔容和平均孔径的保留率分别为84.3%,81.6%和91.9%。XRD谱图观察到(100)晶面,(110)晶面和(200)晶面的特征峰存在,说明介孔特征仍保持完好。但随着水热处理时间的增加,样品的衍射峰出现宽化和峰强度减弱,表明随着水热处理时间的增长,该材料的有序度有一定程度的降低。当样品经10天水热处理后,介孔的特征遭到破坏,其比表面积的保留率可达80.7%,进一步说明该介孔材料高的水热稳定性。当V-MCM-41分子筛样品在空气气氛不同的热处理温度下考察其热稳定性,随着热处理温度的增加,样品的织构参数出现下降趋势。即使在900℃下焙烧12 h,但其介孔的特征仍然保持,其表面积和孔径的保留率分别为83.71%和68.2%。在两种不同焙烧气氛(空气和先氮气后空气)下焙烧该分子筛,其织构参数没有明显的差异,表明该分子筛能抵抗表面活性剂释放的大量的热,进而说明该分子筛是高热稳定性的,XRD谱图进一步的证实了该分子筛是高热稳定的。4.介孔材料的不同的制备体系会有不同的合成机理来解释,对以高模数比的硅酸钠制备的V-MCM-41分子筛的合成机理进行了讨论。实验结果表明该分子筛制备中晶化温度的影响可以归属于协同作用模板机理,而体系的pH值的影响可用层状向六方相的转变机理来解释,模板剂用量的影响主要是液晶模板机理起作用。该分子筛的合成机理不能仅仅只用一种机理来解释,而是多种机理共同作用的结果。5.在介孔材料的合成过程中,研究孔径的调变是介孔材料应用的一个重要内容。在水热过程中通过改变模板剂用量会导致其孔径大小的改变。当改变模板剂CTAB的用量时,该分子筛V-MCM-41的孔径的变化范围为:3.52~5.26 nm;随着模板剂溴化十二烷基三甲基铵(DTAB)用量的改变,导致其孔径的变化范围为:2.21~4.15 nm;采用中性模板剂(P123),其调变的孔径范围为:4.21~10.91 nm。当采用阳离子表面活性剂CTAB和DTAB混合调变孔径时,表面活性剂的链长与分子筛的孔径大小成线性关系。链长越长,孔径越大。孔径变化范围为2.21~3.94 nm。当采用有机胺调节孔径时,以TEA为模板剂制得得孔径可达18.4 nm,且形成的介孔材料的比表面积为189 m2/g;当有机胺与CTAB混合作用调节孔径时,以N,N二甲基十二烷基胺(DMDA)为结构导向剂的扩孔效果最好,孔径变化范围为:3.94~5.49 nm。孔径大小变化并不随着有机胺用量的增加而增加,当有机胺用量增加到一定程度,反而对分子筛孔径扩大有破坏作用。水热后处理也是常用来扩孔的有效方法。采用氨水后处理扩孔,并不能增加分子筛的孔径大小,表明该V-MCM-41分子筛具有较好的结晶度。采用有机胺在后水热处理过程中扩孔,不同的后水热处理温度和不同的有机胺导致的扩孔效果差别显著,其中以TEA和DMDA在高温水热处理下的扩孔效果最优。高温水热后处理,TEA的加入能调变V-MCM-41分子筛的孔径从3.94扩孔到9.30 nm,增加2.36倍。而DMDA的加入能将孔径从3.94扩孔到6.62 nm,增加68%。6.考察了以MCM-41为载体的催化剂的催化性能。①制备了掺杂V的介孔V-MCM-41分子筛,考察了其制备条件对苯乙烯催化氧化反应的影响。在分子筛/H2O2催化氧化苯乙烯反应体系中,副产物为水,具有重要的环保意义和应用价值。先氮气后空气焙烧的样品对双氧水的利用率为55.9%,苯乙酸的选择性为49.44%。②制备了HRh(CO)(PPh3)3络合物负载于MCM-41载体上的负载型催化剂,该负载型催化剂与均相催化剂相比,具有高活性、高选择性和与产物易分离等优点。更多还原

【Abstract】 The M41s mesoporous molecular sieves successfully synthesized by Mobil researchers in 1992 have attracted great interest due to their large specific surface area, uniform pore size distribution and rich surface functional groups. However, the nature of the neutral framework with few lacuna, weak acid intensity, poor ion-exchange ability and hydrothermal stability of M41s materials, limits their potential in catalysis, adsorption and separation, environmental protection and so on. Molecular sieves with transition metals incorporated into the framework have become the hot topic. It has been demonstrated that V-MCM-41 materials has poor hydrothermal stability and thermal stability, which is considered to be a serious problem in any practical application of this material that requires structural integrity. The materials with high hydrothermal and thermal stability become the aim of several scientists. The preparation of mesoporous materials with tunable pore size is the efficient method for its application as novel catalytic materials.In this work, the industrial inorganic silicate Na2O·3.3SiO2 was selected as a cheaper source of silica instead of expensive organic precursors, using CH3(CH2)15·(CH3)3NBr (CTAB) as surfactant, and the supported mesoporous materials was prepared by direct hydrothermal synthesis. The framework structure , texture, thermal stability and hydrothermal stability of V-MCM-41 materials had been investigated; the X-ray diffraction (XRD), N2 adsorption/desorption, Fourier-transformed infrared spectroscopy(FT-IR), diffuse reflectance UV-Vis spectra, inductively coupled plasma technique (ICP), scanning electron microscopy (SEM),Transmission electron microscopy (TEM) and differential thermogravimetric analysis(TG/DTG) were utilized for the characterizations of the supported mesoporous materials. The aim of the current work was to synthesize and characterize the mesoporous molecular sieves, investigate the thermal and hydrothermal stabilities of the samples, discuss the synthesis mechanism of the materials and probe the method of the tunable pore size of the materials. This dissertation mainly was consisted by the following several aspects.1. V-MCM-41 mesoporous materials were synthesized by hydrothermal method. The results indicated that several factors affected the synthesis. The crystallizing temperature, pH value and ratio of Si and CTAB were the most important factors. The texture parameters of the materials were affected by the following factors, active component V amounts, crystallizing time, aging time, calcination atmosphere, the order of materials adding and so on. The proper parameters were selected: n (Si): n (CTAB): n (V)=1: 0.2: 0.08, pH=9.5, crystallizing at 110℃for 48 h, no aging, adding vanadium source first and then silica source, calcination at 550℃for 6 h in air.2. V-MCM-41 mesoporous materials with different silica source were synthesized by hydrothermal method with Na2SiO3·9H2O, colloidal silica, and Na2O·3.3SiO2 as silica source, which was noted as VMC, VMS and VMH, respectively. V-MCM-41 mesoporous materials prepared by tetraethylorthosilicate.(TEOS)in acid condition and alkaline condition were noted as VMT-ac and VMT-al, respectively. The results indicated that .the synthesis processes were different with different silica sources, especially in the crystallizing temperature and pH value. The specific surface area of materials prepared by inorganic silica is lager than that of organic silica. It was due to the different speed of hydrolyzation and polymerization of different silica sources, which resulted in different polymer form. The different polymer would make difference with the reciprocity between the surfactants and silica source. The materials were prepared by inorganic silica in alkali condition, but the materials obtained by organic silica were synthesized in acid conditions. The optimal parameters of synthesis for the four silica were listed in following: crystallizing temperature at 110℃and pH value≈5.5 for VMT-ac materials; crystallizing temperature at 110℃and pH value≈10.5 for VMT-al materials; crystallizing temperature at 110℃and pH value≈9.5 for VMH materials; crystallizing temperature at 125℃and pH value≈10.5 for VMC materials; crystallizing temperature at 125℃and pH value≈11.5 for VMS materials.3. The hydrothermal and thermal stability of V-MCM-41 materials using Na2O·3.3SiO2 as silica source were investigated. The surface area, pore volume and pore size of the V-MCM-41 materials decreased with augmentation of hydrothermal treatment time. The mesoporous structure of V-MCM-41 materials was retained, the remaining ratio of surface area, pore volume and pore diameter were 84.3%, 81.6% and 91.9%, respectively, for the sample under hydrothermal treatment for 8 d. Clearly, well-resolved (100), (110) and (200) diffraction peaks of V-MCM-41 were observed from the XRD picture, which indicated that the mesopore-structure was kept almost totally even after 8 d aging in boiling water. The diffraction peaks became slightly broad and peak intensities decreased slightly with the augmentation of aging time in the boiling water, which indicated that the order of the materials was weaken with the increasing of aging in the boiling water. Furthermore, after 10d hydrothermal treatment, the mesoporous structure of this material was destroyed. However, the remaining ratio of specific surface area was 80.7%. The hydrothermal treatment indicated the mesoporous materials V-MCM-41 was of good hydrothermal stability. The sample was thermal treated at 900℃for 12 h, the mesopore-structure of this materials was retained. The remaining ratio of specific surface area and pore diameter of the sample were 83.71 % and 68.2 %. No remarkable changes were observed for the isotherms of the V-MCM-41 sample calcined at air and nitrogen/air atmosphere, which indicated that the samples could resist the released heat of template combustion and desorption when the samples were calcined in the air, which farther indicated that the samples were of high thermal stability.4. The different formation mechanism in the different system would explain the synthesis of the mesoporous materials. The formation mechanism of the materials prepared by the Na2O·3.3SiO2 was investigated. The effect of the crystallizing temperature could be explained by the Cooperative Formation Mechanism. The effect of the mol ratio of surfactants and silica source could be attributed to the Liquid Crystal Template Mechanism. The effect of the pH value was ascribed as Lamellar Transformation Hexangular Mechanism. The formation mechanism of this material could be explained by the cooperative results of several formation mechanisms, not only by one formation mechanism.5. The different surfactant amounts in the mesoporous materials synthesis can result in the different pore size of the materials. The pore size of the materials changed from 3.52 nm to 5.26 nm with the CTAB amounts shift; the amounts of CH3(CH2)11·(CH3)3NBr (DTAB) could change the pore size of the materials: from 2.21 to 4.15 nm; the pore size of the materials changed from 4.21 nm to 10.91 nm using P123 surfactant. The pore size of the materials was linear with length of long-chain alkyl of surfactants. The longer alkyl of surfactants, the larger pore size of the materials was. The pore size shifted from 2.21 to 3.94 nm with less DTAB and more CTAB. The organic amine was selected to expand the pore size of these materials. the (C2H5)3N (TEA) was used as surfactants, the pore size can be enlarged to 18.4 nm and specific surface area was 189 m2/g. the pore size could be changed with the different ratio of CTAB and CH3(CH2)11N(CH3)2 (DMDA), the range of pore size was 3.94~5.49 nm. The pore size didn’t increase with the increasing of amounts of organic amine. The organic amine could destroy the expansion of pore size with the condition of adding excess amounts of amine. Ammonia hydrothermal treatment couldn’t expand the pore size which indicated the V-MCM-41 materials remained good crystal structure. The application of excessive amounts of DMDA was somewhat less effective for expansion of mesopore pore size. It was shown that the use of DMDA and TEA to restructure MCM-41 with 3.94 nm pores prepared under conventional hydrothermal synthesis afforded mesoporous silica with up to 6.62 and 9.30 nm pores, respectively. 2.36 times expansion of pore size for TEA and 68% improvement for DMDA was achieved successfully.6. The catalytic performance of catalysts using MCM-41 supports was investigated.①the selective oxidation of styrene using hydrogen peroxide as oxidant over V-MCM-41 samples was investigated; the phenylacetic acid was the principal most important product. The selectivity of phenylacetic acid was 49.44% and the conversion of H2O2 was 55.9% for the sample of V-MCM-41, which was calcined at 550 ?C in flowing nitrogen at first, then in air. The sample of V-MCM-41, which was calcined only in air at 550℃gave 63% H2O2 conversion and 38.74% selectivity in phenylacetic acid.②Mesoporous MCM-41 zeolite supported HRh(CO)(PPh3)3 complex for isobutene hydroformylation was prepared. Compared with homogeneous catalysts, the catalysts were of high catalytic performance and high selectivity of isovaleraldehyde besides the advantage of easy separation of catalyst from the product mixture.更多还原