全硅MCM-41中孔分子筛的合成

在碱性条件下,采用水热晶化法,以水玻璃为硅源,表面活性剂十六烷基三甲基溴化铵为结构模板剂,成功合成出全硅MCM－41中孔分子筛。采用X射线衍射分析研究了合成条件(pH值）、凝胶配比（表面活性剂／SiO2、H2O/SiO2）和凝胶后处理条件（老化时间、晶化温度、晶化时间和焙烧温度）对MCM－41结构的影响。结果表明全硅MCM－41的合成条件为pH10.5-12.5,表面活性剂／SiO20.05-0.7,H2O/SiO2 40－200,老化时间长对合成晶形较的全硅MCM－41有利。晶化温度70℃-100℃,晶化时间24小时,焙烧温度540℃－740℃。     

硼铝骨架改性中孔分子筛的合成与表征

以正硅酸乙酯（TEOS）为硅源,以十六烷基三甲基溴化铵（CTABr)为结构模板剂,在碱必条件下采用水热晶化法成功合成了B－Al骨架改性的中孔分子筛MCM－41。通过XRD、TG－DTG、IR、N2等温物理吸附等多种表征手段对其进行结构、性质分析;发现B有助于Al进入Si-MCM-41中孔分子筛的无机骨架中,B－Al-MCM-41比Al-MCM-41的晶体完整性好;同时掺入B、Al后的中孔结构分子筛与全硅MCM－41中孔分子筛相比,无机墙表面基团的性质不同,比表面积稍小,最可几孔径稍大,孔径分布较宽;Al,B同晶取代Si进入MCM－41无机骨架人会使其中孔结构发生一些变化,因而合成的B－Al-MCM-41必将有不同的催化、吸附性能。     

制备条件对钒硅中孔分子筛的催化氧化性能的影响

通过溶胶-凝胶的方法在室温下制备出结晶度较好的钒硅中孔分子筛V-MCM-4l，并以苯乙烯的液固相催化氧化反应作为指针反应，研究了制备条件影响V-MCM-4l催化氧化性能的本质。在催化剂制备的前处理阶段，降低Si／V比直至Si／V=50(mol比)，并将合成凝胶的pH值控制在11．5左右时能获得较高的催化活性，同时也不会降低催化剂的循环使用寿命。另外，碱源用氢氧化钠比用四甲基氢氧化胺更能提高催化剂活性。在催化剂制备的后处理阶段，晶化时间，晶化温度和焙烧温度对于提高催化剂的活性都有一个最佳值，其最佳值分别为4d，100℃和650℃。研究结果表明，V在分子筛骨架的搀杂量以及分子筛的结晶度是制备条件影响钒硅中孔分子筛催化氧化性能的重要决定因素。     

新型中孔分子筛MCM－41研究新进展

综述了新型中孔分子筛MCM－41的合成、形成机理、分子结构和性能,讨论了MCM－41在催化、吸附及分子筛主体－纳米客体复合材料的制备等领域的应用情况,并对MCM－41的发展前景进行了概述。     

Dy—MCM—41介孔分子筛的合成与表征

以十六烷基三甲基溴化铵为模板剂，以Na2Si3O7为硅源，以DyClO4为稀土镝源，在碱性条件下合成了Dy-MCM-41分子筛，并用XRD，FT－IR、X－射线荧光，TG－DTA等对样品进行表征，实验结果证实了合成的样品为Dy-MCM-41。     

乙二胺体系铝镧MCM-41介孔分子筛的合成、表征及在乙氧基化反应中的催化性能

以十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸乙酯(TEOS)为硅源,乙二胺为碱性介质,当n(TEOS)∶n(NaAlO2)(或LaCl3)∶n(CTAB)∶n(H2NCH2CH2NH2)∶n(H2O)=1∶X∶0 12(或0 14)∶3 5(或8 0)∶130,其中X=0 1,0 05,0 033时,水热法合成了硅铝(硅镧)摩尔比为10、20和30的Al MCM 41和La MCM 41介孔分子筛。通过XRD、IR、NH3 TPD吸附脱附、BET及CCl4吸附等方法对分子筛的晶体结构和表面物性进行了研究,结果表明,合成的分子筛具有典型的六方介孔结构特征。将Al MCM 41和La MCM 41分子筛分别用于催化乙氧基化反应,研究结果表明,Al MCM 41的催化活性高于La MCM 41,当Al MCM 41用量为正辛醇质量的3%,反应温度为120℃,反应压力0 2MPa,n(正辛醇)∶n(环氧乙烷)=1∶2时,正辛醇聚氧乙烯醚产品的收率达85%。     

V-MCM-41介孔分子筛的合成与催化性能

采用三乙醇胺络合物法制备了骨架中含钒量较高的V—MCM-41分子筛催化剂,利用X射线衍射（XRD）和紫外漫反射光谱（UV—vis DRS）等技术对催化剂进行了表征,并考察了硅钒比、反应温度、体积空速、空气与甲苯比对V-MCM-41分子筛在甲苯气相选择性氧化制苯甲醛反应中催化性能的影响。结果表明,骨架中的钒是甲苯选择性氧化生成苯甲醛的活性中心,钒进入骨架中的量与硅钒物质的量比有关,当硅钒比为30时,进入骨架的钒最多,且在甲苯选择性氧化反应中对苯甲醛选择性最高。以硅钒比为30的V-MCM-41分子筛为催化剂,常压下甲苯氧化制苯甲醛较合适的反应工艺为体积空速800h^-1,空气与甲苯物质的量之比5,反应温度450℃。在此条件下,甲苯转化率为20．8％,苯甲醛选择性为41．8％,苯甲醛收率为8．7％。     

苯乙烯环氧化反应分子筛催化剂研究进展

综述了苯乙烯环氧化制取环氧苯乙烷的几种分子筛／H2O2催化体系，介绍了微孔分子筛（TS-1）、Ti-ZSM-5和Ti-ZSM-11分子筛介孔分子筛（MCM-41），β-钛硅分子筛、负载金属配合物的中孔分子筛及其在苯乙烯环氧化反应中的性能。     

苄基磺酸MCM -41催化合成柠檬酸三丁酯

以苄基磺酸化MCM - 41介孔分子筛(SBM)为催化剂,催化合成柠檬酸三丁酯.研究结果表明,SBM在合成柠檬酸三丁酯的反应中具有良好的催化性能,当n(酸):n(醇)=1.0:8.0,w(cat)％=3％,反应时间7h,酯化率为93％,且催化剂重复4次后转化率为76.3％.     

Ti-HMS催化剂的合成及性能研究

分别用十二胺（DDA）和十六烷基三甲基溴化铵（TMAOH）做模板合成了中孔骨轲钛催化剂（HMS为合成的硅氧中孔载体材料类型）FT－IR表征显示催化剂在960cm^-1附近有吸收峰，且强度与硅钛比成正比。研究了催化剂制备条件对苯乙烯环氧化反应的影响，结果表明：焙烧温度为650℃、活化温度为200℃、反应温度45℃-55℃、反应时间6h，苯乙烯转化率接近80％，环氧化苯乙烯收率达70％。     

V-MCM-41催化环己烯环氧化性能

采用水热法合成了V-MCM-41,并用ICP-AES、FTIR、DRS-UV-Vis、XRD、BET等技术对其进行了表征,发现只有部分V进入分子筛,所合成的V-MCM-41具有较高的结晶度,并且其结晶度随晶化液中V/Si摩尔比的增大而升高。V-MCM-41催化环己烯/H₂O₂氧化反应结果表明,当V-MCM-41中V含量大于1.10%（摩尔分数）时,骨架V-O-V物种在催化环己烯氧化反应的同时,也可加速H₂O₂的分解;乙腈是该反应体系的最佳溶剂,最佳反应温度为70℃。最佳反应结果表明,环己烯的单程转化率和H₂O₂有效利用率可分别达到23.91%和95.4%。     

Weak base favoring the synthesis of highly ordered V-MCM-41 with well-dispersed vanadium and the catalytic performances on selective oxidation of benzyl alcohol

The key to improve the performance of heteroatom catalysts is to ensure the orderliness of catalysts and the good dispersion of heteroatoms. The alkalinity plays the indispensable role in synthetic process of V-MCM-41 catalyst.The excessive alkalinity of synthetic system will make the MCM-41 difficult to crystallize, even to dissolve. It is easy to accumulate for heteroatomic species in the system of low alkalinity. Herein, the highly ordered VMCM-41 with high vanadic content in framework is synthesized in the condition of excessive NH_3·H_2 O in this paper. A series of characterization results prove the good dispersion of vanadium species, and most of vanadium gets into the framework of MCM-41 with the states of tetravalence and pentavalence. Furthermore, the modified MCM-41 by other transition metals is successful synthesized by the method of V-MCM-41 in this paper. The VMCM-41 shows well catalytic activity for the selective oxidation of benzyl alcohol, which up to 74.83% for the conversion of benzyl alcohol and 96.20% for selectivity of benzaldehyde when initial V/Si = 0.10. The paper provides the possibility for industrial application of V-MCM-41 in the oxidation of benzyl alcohol for benzaldehyde.Besides, the work provides a significant idea for the synthesis of modified MCM-41 by well-dispersed transition metals.     

Room temperature synthesized spherical V-MCM-41: a catalyst for vapour phase oxidation of diphenylmethane

Mesoporous spherical Si-MCM-41 and V-MCM-41 materials with a variable Si/V ratio of 25, 50, 75 and 100 were prepared by an economical route at room temperature and characterized by various techniques for qualitative and quantitative understanding of vanadium species. The morphology and mesoporosity of the spherical particles were confirmed by SEM and TEM micrographs. The catalytic activity of the synthesized catalysts was tested for vapour phase oxidation of diphenylmethane to benzophenone using CO₂ free air as oxidant at atmospheric pressure. The conversion of diphenylmethane and selectivity for benzophenone were measured in the temperature range of 593?C713?K over V-MCM-41 catalysts synthesized by adopting room temperature method as well as by direct hydrothermal method. The catalytic performance was related to vanadium content on the surface of the catalysts.     

Vanadium incorporated high surface area MCM-41 catalysts

High surface area MCM-41 (1452 m²/g) and V-MCM-41 materials were synthesized by a direct hydrothermal synthesis method. Characteristic XRD patterns, SEM and AFM photographs indicated no significant change in the morphology of MCM-41 by incorporation of vanadium. XPS and EDS results proved that incorporation of vanadium into the MCM-41 structure was successfully achieved when vanadyl sulfate hydrate was used as the vanadium source. However, use of ammonium vanadate as the vanadium source was not equally successful.     

Microwave Synthesized Mesoporous Vanadium-MFI Catalysts for Epoxidation of Styrene Using Molecular Oxygen

Carbon templated mesoporous vanadium MFI catalysts with different Si/V ratios were successfully synthesized using microwave irradiation. X-ray diffraction studies revealed the formation of more crystalline MFI structures. SEM and TEM imaging also showed well ordered zeolite single crystals having mesoporosity. The N₂ sorption isotherm showed the formation of bimodal mesoporous zeolites. FT-IR studies showed absorbance around 970 cm^?1 corresponding to Si–O–V stretching vibration and the UV–Vis studies revealed strong peaks in the range of 230–340 nm which is related to the presence of tetrahedral V⁵⁺ state. The catalytic activity of the microwave synthesized catalysts was evaluated for epoxidation of styrene using molecular oxygen. The catalysts exhibited 20–40% styrene conversion with 60–75% epoxide selectivity. With increasing Vanadium content, the conversion as well as the selectivity was observed to increase. The catalyst could be recycled for three cycles without a loss in activity.     

The C-radioisotopic study of methanol conversion on V-MCM-41: The influence of methyl iodide on the transformation

The methanol conversion and a feasible methanol co-reaction with methyl iodide were studied on a vanadium incorporated MCM-41 type (V-MCM-41) mesoporous catalyst, which was prepared by a direct hydrothermal synthesis method. Adsorption/desorption as well as conversion derivates of radioactive methanol were easily followed by radioactivity detectors on V-MCM-41. The transformation and co-reaction products were analyzed by a gas chromatograph equipped with Radio/FID detectors. The radiodetector was applied to distinguish ¹¹C-derivates from the non-radioactive methyl iodide and its derivates. The radio-labeling method proved methanol transformation to methylal and, in the presence of methyl iodide, decided the roles of methyl group and iodide of methyl iodide in newly synthesized methyl iodide formation in the absence of oxygen gas.     

Mono (V, Nb) or bimetallic (V–Ti, Nb–Ti) ions modified MCM-41 catalysts: synthesis, characterization and catalysis in oxidation of hydrocarbons (aromatics and alcohols)

Mesoporous MCM-41 molecular sieves modified by single (V and Nb) or bimetal (Nb–Ti and V–Ti) ions with highly ordered hexagonal arrangement of their cylindrical channels were prepared by direct synthesis with two different silica sources (sodium silicate and TEOS) and characterized (as-synthesized samples and those used after reaction) by XRD, N₂ adsorption–desorption, TEM, SEM and FTIR techniques. Niobium and titanium were stabilized in the autoclavized gel by complexation with a ligand (acetylacetone and oxalic acid, respectively). V modified MCM-41 catalysts gave a very high activity in hydroxylation reaction of benzene and toluene and a low conversion in oxidation of styrene while Nb-modified MCM-41 samples showed very high conversion in oxidation of styrene but low oxidation conversion of benzene and toluene. Further introduction of titanium in V- and Nb-modified MCM-41 materials conducted to the less well-ordered hexagonal arrangement and gave very different effect on activity in oxidation of aromatics. Introduction of Ti into V-MCM-41 solids led to an increase in activity in oxidation of styrene and benzene but a decrease in conversion in oxidation of toluene. While the addition of Ti in Nb-MCM-41 resulted in a slight increase in conversion of styrene oxidation but a significant decrease in activity of benzene and toluene oxidation. It reveals that the introduction mode of oxidant in the reactors can also influence the activity and selectivity of reaction. An increase in reaction rate of oxidation, in the first 20 h, was obtained by introduction of H₂O₂ step by step during the reaction. The present paper evidenced that the side chain oxidation is main reaction of styrene oxidation while the hydroxylation is main reaction of benzene and toluene. That is why these two reactions need different catalytic centers as revealed by this paper. The oxidation of alcohols using V-modified MCM-41 as catalysts has also been explored and these catalysts showed a very low catalytic activity which increases in the order: hexanol相似文献   

Vanadium-containing ordered mesoporous silicas: Synthesis, characterization and catalytic activity in the hydroxylation of biphenyl

A series of vanadium-containing ordered mesoporous MCM-41 materials (V-OMS) have been synthesized by direct hydrothermal (V-MCM-41) and grafting (V/MCM-41) methods using hexadecyl trimethyl ammonium bromide (HDTMABr) as the structure-directing agent. The physico-chemical properties of the vanadium-containing materials were characterized in detail by ICP-OES, XRD, FT-IR, N₂ adsorption–desorption, DRUV-VIS, TPR, XPS and SEM techniques. The redox performances of the vanadium-modified mesoporous materials were tested in the hydroxylation of biphenyl using aqueous H₂O₂ (30 wt.%) as oxidant. For a better exploitation of the catalytic activity, the reaction parameters are optimized in terms of temperature, solvent, oxidant, etc. A comparison between the catalytic activity values of the vanadium-containing mesoporous materials prepared by the two routes shows that vanadium-substituted (V-MCM-41) materials had increased activity and improved selectivity for mono hydroxyl products in the hydroxylation reaction of biphenyl compared to the V/MCM-41 catalysts. The heterogenity of the catalysts was verified by a series of leaching studies. Both the catalysts enhance the leaching of active vanadia species during the reaction; among them, V/MCM-41 shows the least heterogenity.     

A Study on VPO Specimen Supported on Aluminum-Containing MCM-41 for Partial Oxidation of n-Butane to MA

Dispersed vanadium–phosphorus oxide species supported on Al-MCM-41 with different vanadium loadings have been synthesized for the first time for partial oxidation of butane to MA. It was found that the VPO species was dispersed over the Al-MCM-41 support material, both in the internal channel and on the external surface. With increasing vanadium loading, n-butane conversion increased but MA selectivity decreased considerably under the same reaction conditions. At lower conversions (<30%), rather high MA selectivity (ca. 70%) can be achieved on the low loading sample. Compared with the amorphous structure of large pore SiO₂ support, the unique structure of the MCM-41 and the incorporated Al³⁺ in the framework do have an impact on the reaction behavior of the supported VPO specimen. The chemical nature of the supported VPO species and the interaction between the applied VPO species and the support was found to vary notably with the content of vanadium in the sample and likewise affected the related physico-chemical characteristics and their reaction behaviors.