介孔分子筛MCM-41的水热稳定性

介孔分子筛MCM-41在催化、吸附分离以及化学组装制备先进材料等方面具有潜在的巨大应用价值,但MCM-41的低水热稳定性使其在催化研究领域中的应用受到了极大的限制。因此,提高介孔分子筛的水热稳定性具有十分重要的科研和实际应用意义。笔者对介孔分子筛MCM-41低水热稳定性的原因作了简要分析,并系统地介绍了近几年来在提高介孔分子筛水热稳定性方面的研究工作。     

Effect of trivalent elements on the thermal and hydrothermal stability of MCM-41 mesoporous molecular materials

Effect of trivalent elements on the thermal and hydrothermal stability of MCM-41 mesoporous molecular sieve materials has been investigated. Al(III) decreases the thermal and hydrothermal stability of MCM-41 materials, whereas La(III) and Fe(III), especially Fe(III), can improve the thermal and hydrothermal stability. Benzene adsorption and IR spectra suggested that thick channel wall and the fewer structural defect sites in MCM-41 would enhance the thermal and hydrothermal stability of MCM-41.     

SXI route to mesostructured materials from Fau and Beta zeolite precursors: A comparative study of their assembly behaviors in extremely acidic media

Mesoporous molecular sieves were synthesized from Beta and Fau zeolite precursors through S⁺X⁻I⁺ route under extremely acidic conditions in parallel (designated as M_Beta and M_Fau, respectively). The textural properties of M_Fau were different from its M_Beta counterpart but resembled normal MCM-41 silica from TEOS. Al content in M_Beta was almost equivalent to that in the initial Beta zeolite precursors, whereas only trace Al species was present in M_Fau from elemental analysis results. The hydrothermal stability of M_Beta after post-synthesis ammonia treatment was considerably improved compared with normal MCM-41 aluminosilicates, whereas the M_Fau after the same procedure was as unstable as normal MCM-41 silica. Thus, the assembly behaviors of Beta and Fau zeolite precursors were comparatively studied based on these results. The microstructure of Fau zeolite precursors were degraded by the extremely acidic condition, and Al species was dissolved into the synthesis mixture. However, Beta zeolite precursors survived the chemical attack of extremely acidic media and were incorporated into mesostructured framework as primary building units.     

Influence of the pore structure of MCM-41 and SBA-15 silica fibers on atomic layer chemical vapor deposition of cobalt carbonyl

Mesoporous high surface area MCM-41 and SBA-15 type silica materials with fibrous morphology were synthesized and used as support materials for the ALCVD (atomic layer chemical vapor deposition) preparation of Co/MCM-41 and Co/SBA-15 catalysts. Co/MCM-41 and Co/SBA-15 catalysts were prepared by deposition of Co2(CO)8 from the gas phase onto the surfaces of preheated support materials in a fluidized bed reactor. For both silica materials, two different kinds of preparation methods, direct deposition and a pulse deposition method, were used. Pure silica supports as well as supported cobalt catalysts were characterized by various spectroscopic (IR) and analytical (X-ray diffraction, Brunauer-Emmett-Teller, elemental analysis) methods. MCM-41 and SBA-15 fibers showed considerable ability to adsorb Co2(CO)8 from the gas phase. For MCM-41 and SBA-15 silicas, cobalt loadings of 13.7 and 12.1 wt % were obtained using the direct deposition method. The cobalt loadings increased to 23.0 and 20.7 wt % for MCM-41 and SBA-15 silicas, respectively, when the pulse deposition method was used. The reduction behavior of silica-supported cobalt catalysts was found to depend on the catalyst preparation method and on the mesoporous structure of the support material. Almost identical reduction properties of SBA-15-supported catalysts prepared by different deposition methods are explained by the structural properties of the mesoporous support and, in particular, by the chemical structure of the inner surfaces and walls of the mesopores. Pulse O2/H2 chemisorption experiments showed catalytically promising redox properties and surface stability of the prepared MCM-41- and SBA-15-supported cobalt catalysts.     

Thermal stability of Ti–MCM-41

Ti containing mesoporous MCM-41 materials have been synthesized through two methods: heating and non-heating [room temperature (RT)]. The synthesized materials have been characterized using X-ray diffraction, Fourier transform infrared, nitrogen sorption, and X-ray fluorescence methods and their thermal stabilities evaluated using thermogravimetric methods in inert atmosphere. The thermal stabilities have been analyzed based on the synthesis method, as well as on the amount of titanium in the MCM-41 materials. The thermal stability results suggest that uncalcined MCM-41 materials generally show higher mass loss than their calcined counterparts. Also, the RT-synthesized materials showed lower stability than the high-temperature synthesized samples for the uncalcined samples. It is also been found that MCM-41 materials show improved thermal stabilities as the amount of titanium is increased.     

Iron oxide/MCM-41 mesoporous nanocomposites and their magnetorheology

Mesoporous nanocomposite materials of magnetic iron oxide-containing MCM-41 (IO/MCM-41) were prepared by simple thermal oxidation of Fe-containing MCM-41 initially prepared by a direct synthesis route using Fe³⁺ salt. The magnetic saturation of the fabricated nanocomposite materials was measured using a vibrating sample magnetometer, while surface morphology and inner framework of the composite materials were studied using a field emission scanning electron microscope and a transmission electron microscope to confirm their mesoporous nanocomposite formation. The fabricated magnetic materials were then adopted as a magnetorheological (MR) fluid, where the IO/MCM-41 magnetic nanocomposites were dispersed in a nonmagnetic medium oil in addition to as an additive for carbonyl iron-based MR fluid. Their MR properties of flow curve along with yield stress and viscoelastic properties under applied magnetic fields were investigated using a rotational rheometer.     

中微双孔分子筛Beta-MCM-41的微波合成及加氢脱硫性能研究

以四乙基氢氧化铵(TEAOH)为微孔模板剂,十六烷基三甲基溴化铵(CTAB)为介孔模板剂,SiO2、Fumed Silica或TEOS为硅源,通过微波两步自组装合成Beta-MCM-41型中微双孔分子筛。然后以合成的Beta-MCM-41(BM-S-M)、实验室自制的Beta、MCM-41、SBA-15以及γ-Al2O3为载体,通过等体积浸渍15%MoO3,3%NiO和3%CoO,制备得到Co-Mo-Ni-BM-S-M等氧化物催化剂;并在间歇式高温高压反应釜中,在350℃、5.0MPa H2压力下,以二苯并噻吩(DBT)为模拟油品研究所制备催化剂的加氢脱硫性能及反应动力学。结果表明,SiO2为硅源,微波辐射合成的BM-S-M分子筛结构有序性更好,比表面积(1033.923m2/g)和孔容(0.729cm3/g)更大,孔径集中分布在3.08nm(中孔)和1.22nm(微孔),且具有较强的酸性中心。4种不同载体催化剂的DBT加氢脱硫活性顺序为Co-Mo-Ni-BM-S-M>Co-Mo-Ni-MCM-41>商业Co-Mo-Al2O3>Co-Mo-Ni-Beta。此外,4种不同载体催化剂的加氢脱硫过程符合拟一级动力学规律。     

Synthesis, characterization, and catalytic properties of stable mesoporous molecular sieve MCM-41 prepared from zeolite mordenite

Mesoporous molecular sieves (denoted as M-MCM-41) with ordered hexagonal structure have been successfully synthesized from the assembly of precursors from preformed zeolite Mordenite with CTAB surfactant micelle in alkaline media. The samples were characterized by XRD, N₂ adsorption, IR and DTG. The materials exhibit highly hydrothermal stability, as compared with conventional MCM-41. Characterization results indicate that the mesoporous walls of M-MCM-41 contain the secondary building units similar to those in microporous crystal of zeolite Mordenite. In catalytic dealkylation of C10⁺ aromatic hydrocarbon, M-MCM-41 shows higher activities in comparison with Mordenite and MCM-41, which would be ascribed to the combination of advantages of both MCM-41 (large pores) and Mordenite (strong acidity). Furthermore, this synthesis strategy could be used as a new general method for the preparation of hydrothermally stable mesoporous aluminosilicate materials under alkaline conditions.     

核壳结构Beta/MCM-22双微孔复合分子筛的合成与表征

以Beta分子筛为晶核,通过二步水热晶化法成功制备了形态良好的Beta/MCM-22核壳结构复合分子筛。采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)及N2吸附-脱附技术等对分子筛进行了表征。结果表明,复合分子筛形态规整,Beta与MCM-22分别作为核壳而共生;Beta/MCM-22复合分子筛孔结构性质介于MCM-22、Beta分子筛之间。在酸性分布上,复合分子筛的中强酸及B酸所占比例显著增加(CB/CL=13.8)。通过Ar-H2等离子体对Beta分子筛进行处理,使其表面能提高并使表面正电荷富集、硅羟基增加,这是形成良好Beta/MCM-22核壳结构的内在原因。     

磺酸基功能化MCM-41有机-无机杂化材料的合成与表征

 利用直接合成法和后接枝法将含有磺酸基团的硅烷偶联剂引入MCM-41介孔分子筛中, 合成了酸性介孔有机-无机杂化材料. 利用XRD和TEM等方法对其结构进行了表征. 结果表明,利用直接合成法和后接枝法合成的杂化材料仍保持规整的介孔孔道,该材料作为酸催化剂在苯甲醛与乙二醇的缩醛反应中显示了较好的催化活性.     

Rapid synthesis of highly ordered Si-MCM-41

A very short-time synthesis of highly ordered MCM-41 molecular sieve was formulated by using cetyltrimethylammonium bromide (CTAB) as the template and silica gel from SiliCycle as the silica source. The physical properties of MCM-41 samples were characterized by X-ray diffraction (XRD), nitrogen physisorption, and transmission electron microscopy (TEM). The MCM-41 sample prepared in this study exhibited well defined long-range order and good hydrothermal stability. It was demonstrated that reducing the time of self-assembly step to 2 h during the synthesis had no unfavorable effect on the quality of MCM-41 materials.     

Cerium modified MCM-41 nanocomposite materials via a nonhydrothermal direct method at room temperature

Ce-containing MCM-41 materials were prepared via a direct, nonhydrothermal method at room temperature from tetra-ethoxysilane, n-hexadecyl trimethyl ammonium bromide, ammonia solution, and cerium(IV) ammonium nitrate precursors. Composite materials containing the nominated ratios of 5 and 10% (w/w) CeO2/MCM-41 were targeted. The obtained materials were investigated by TGA, DSC, FTIR, diffuse reflectance UV-vis, XRD, N2 adsorption/desorption isotherms, and SEM. Results indicated the insertion of cerium ions in tetrahedral environment in the framework of MCM-41. BET surface area amounting to 824 and 726 m2/g; total pore volume amounting to 0.427 and 0.515 cm3/g; and narrow pore size distribution maximizing at 22.5 and 23.7 A, respectively were obtained for the 5 and 10% CeO2/MCM-41 calcined composites. SEM showed a spherical type morphology for the composites which is rather similar to their blank MCM-41, and no clear ceria aggregates were observed on the external surfaces of composites spherical particles. Thus, the adopted method allows the persistence of MCM-41 texture with cerium inserts in the framework of MCM-41 and/or forms finely divided ceria nanoparticles on the wall of MCM-41 materials. Moreover, stabilization of any formed ceria nanoparticles was attributed to the short nonintersecting porous nature of MCM-41 matrix, which hinders their aggregation upon calcinations.     

Preparation and Acid Catalytic Activity of TiO2 Grafted Silica MCM-41 with Sulfate Treatment

TiO2 grafted silica MCM-41 catalyst with and without sulfate treatment were prepared. The structural and acid properties of these materials were investigated by XRD, N2 adsorption-desorption, element analysis, thermal analysis, Raman and FTIR measurements. Their acid-catalytic activities were evaluated using the cyclization reaction of pseudoionone. It was found that the obtained materials possess well-ordered mesostructure, and the grafted TiO2 components were in highly dispersed amorphous form. T/MCM41 without sulfation contained only Lewis acid sites, while Br?nsted and Lewis acidities were remarkably improved for the sulfated materials ST/MCM41 and d-ST/MCM41. T/MCM-41 was not active for the cyclization reaction of pseudoionone, but ST/MCM-41 and d-ST/MCM-41 possessed favorable catalytic activities. The catalytic performance of ST/MCM-41 was comparable with that of the commercial solid acid catalyst of Amberlyst-15, and better than that of d-ST/MCM-41, although the latter underwent a second TiO2 grafting process and accordingly had higher Ti and S content. The specific surface structure of Si-O-Ti-O-S=O in ST/MCM-41 and the bilateral induction effect of Si and S=O on Si-O-Ti bonds were speculated to account for its higher acid catalytic activity.     

Prearation of Highly Ordered Mesoporous Silica Materials and Application as Enzeme Supports

An enzyme, horseradish peroxidase (HRP), was adsorbed in the manner of single immersion method on the silica mesoporous materials, FSM-16, MCM-41 and SBA-15 with various pore diameters from 27 to 92 and their enzymatic activity in an organic solvent and the thermal stability were studied. FSM-16 and MCM-41 showed larger amount of adsorption of HRP than SBA-15 or silica gel,when the pore sizes were larger than the spherical molecular diameter of HRP (ca 64×37). The increased enzyme adsorption capacity may be due to the surface characteristics of FSM-16 and MCM-41, which would be consistent with the observed larger adsorption capacity of cationic pigment compared with anionic pigment for these materials. The immobilized HRP on FSM-16 and MCM-41 with pore diameter above 50 showed the highest enzymatic activity in an organic toluene and thermal stability in aqueous solution at the temperature of 70℃. The immobilized enzymes on the other mesoporous materials including large or small pore sized FSM-16 showed lower enzymatic activity in an organic solvent and the thermal stability. Both surface character and size matching between pore sizes and the molecular diameters of HRP were important in achieving high enzymatic activity in organic solvent and high thermal stability.     

PtSn/Al2O3/MCM-41催化剂的丙烷脱氢催化性能

用微型催化反应装置评价, 并结合X射线粉末衍射(XRD)、表面积和孔结构测试、程序升温还原(TPR)、氢化学吸附和热重分析等方法研究了负载型PtSn/γ-Al2O3, PtSn/MCM-41和PtSn/Al2O3/MCM-41催化剂的丙烷脱氢反应催化性能. 发现PtSn/Al2O3/MCM-41催化剂具有较PtSn/MCM-41催化剂高的丙烷脱氢反应活性和较PtSn/γ-Al2O3催化剂高的反应稳定性. 实验结果表明, 纯硅MCM-41载体表面的锡物种因与载体相互作用较弱故易被还原, 导致铂金属分散度和催化剂的丙烷脱氢活性较低. 用Al2O3修饰MCM-41可以增强Sn物种与Al2O3/MCM-41载体之间的相互作用, 提高PtSn/Al2O3/MCM-41催化剂铂金属分散度和丙烷脱氢催化活性. 并且, 积炭后的PtSn/Al2O3/MCM-41催化剂具有较高的铂金属表面裸露度, 故具有较高的丙烷脱氢反应稳定性. PtSn/Al2O3/MCM-41催化剂优良的丙烷脱氢催化性能可能不仅与Sn-载体Al2O3/MCM-41较强的相互作用有关, 而且与Al2O3/MCM-41载体的介孔结构有关.     

Structure, hydrophobicity, and hydrothermostability of MCM-41 organo-inorganic mesoporous silicates silylated with dimethoxydimethylsilane and dichloromethylphenylsilane

Changes in the structure, hydrophobicity, and hydrothermal stability of organo-inorganic composite materials based on MCM-41 as a result of silylation with dimethoxydimethylsilane (DMODMS) and dichloromethylphenylsilane (DCMPS) were considered. Based on the data on the competitive adsorption of water and toluene it was shown, using the Weitkamp procedure, that the grafting of organosilyl groups affects the sorption properties of mesoporous materials. Hydrothermal treatment led to considerable changes in the structure and properties of the materials. The thermal stability of MCM-41 composites and changes in their hydrophilicity due to the grafting of DMODMS and DCMPS and hydrothermal treatment were studied by thermogravimetry.     

WP／MCM-41催化剂的制备及其加氢脱硫性能

以磷钨酸铵、磷酸氢二铵和自制的MCM-41为原料,采用超声波振荡、程序升温和高纯氢气还原的方法制备了高比表面积的WP和WP/MCM-41,用XRD、BET、BJH、SEM和EDX表征了所制备的催化剂,并考察了催化剂对噻吩的加氢脱硫性能.结果表明,采用超声波振荡法制得的WP催化剂其比表面积、孔容和对噻吩加氢脱硫活性明显高于常规搅拌制得的WP催化剂,WP的比表面积达到56.357 m2/g,孔容达到0.058 cm3/g,35%WP/MCM-41催化剂的比表面积分别为287.522 m2/g,孔容为0.362 cm3/g,在613 K时WP催化剂的噻吩转化率达到81.22%,负载量为35%的WP/MCM-41催化剂的噻吩转化率达到92.78%;35%WP/MCM-41的噻吩HDS活性较好.     

四甲基锡在MCM-41分子筛表面的接枝反应及产物性能

研究了真空条件下SnMe4在MCM-41分子筛表面的接枝反应，并用元素分析、ICP、GC-MS、XRD、FTIR、DRS、13C及119Sn MAS NMR、XPS、BET、TPD、TPR等方法对产物的组成、结构和性质进行了表征.结果表明, 两者可以定量地进行化学反应，将确定数目的甲基锡基团接枝在分子筛表面, 形成SnMe3/MCM-41物种；接枝反应发生在分子筛表面上, 不破坏MCM-41分子筛骨架结构；改性分子筛的BET比表面积有所降低，孔体积变小, 表面性质发生变化.四甲基锡在MCM-41上接枝反应的温度为343 K,比它与HY沸石的反应温度(193 K)高得多，并且产物SnMe3/MCM-41的热稳定性也高于SnMe3/HY.     

Preparation, characterization and optical properties of lanthanum-(nanometer MCM-41) composite material

Nanometer MCM-41 molecular sieve was prepared under a base condition by using cetyltrimethylammonium bromide as template and tetraethyl orthosilicate as silica source by means of hydrothermal method. Lanthanum(III) was incorporated into the nanometer MCM-41 by a liquid phase grafting method. The prepared nanocomposite materials were characterized by means of powder X-ray diffraction, spectrophotometric anaylsis, Fourier transform infrared spectroscopy, low temperature nitrogen adsorption-desorption technique, solid diffuse reflectance absorption spectra and luminescence. The powder X-ray diffraction studies show that the nanometer MCM-41 molecular sieve is successfully prepared. The highly ordered mesoporous two-dimensional hexagonal channel structure and framework of the support MCM-41 is retained intact in the prepared composite material La-(nanometer MCM-41). The spectrophotometric anaylsis indicates that lanthanum exists in the prepared nanocomposite materials. The Fourier transform infrared spectra indicate that the framework of the MCM-41 molecular sieve still remains in the prepared nanocomposite materials and some framework vibration peaks show blue shifts relative to those of the MCM-41 molecular sieve. The low temperature nitrogen adsorption-desorption indicates that the guest locates in the channel of the molecular sieve. Compared with bulk lanthanum oxide, the guest in the channel of the molecular sieve has smaller particle size and shows a significant blue shift of optical absorption band in solid diffuse reflectance absorption spectra. The observed blue shift in the solid state diffuse reflectance absorption spectra of the lanthanum-(nanometer MCM-41) sample show the obvious stereoscopic confinement effect of the channel of the host on the guest, which further indicates the successful encapsulation of the guest in the host. The La-(nanometer MCM-41) sample shows luminescence.     

Heteropolyacid (H3PW12O40) supported MCM-41: An efficient solid acid catalyst for the green synthesis of xanthenedione derivatives

HPWA/MCM-41 mesoporous molecular sieves of appropriate ratios were prepared by loading HPWA on siliceous MCM-41 by the wet impregnation method. The prepared HPWA/MCM-41 materials were characterized by X-ray diffraction analysis (XRD) and BET surface area and FT-IR measurements. The morphology of mesoporous materials was studied by TEM observation. The catalytic activity of the above materials was tested for the condensation of dimedone (active methylene carbonyl compound) and various aromatic aldehyes under liquid phase conditions at 90 °C. The products were confirmed by FT-IR, ¹H NMR and ¹³C NMR studies. HPWA supported MCM-41 catalysts catalyses efficiently the condensation of dimedone and aromatic aldehydes in ethanol and other solvents under liquid phase conditions to afford the corresponding xanthenedione derivatives. Activities of the catalysts follow the order: HPWA/MCM-41(20 wt.%) > HPWA/MCM-41(30 wt.%) > H₃PW₁₂O₄₀·nH₂O > HPWA/MCM-41(10 wt.%) > HPWA/SiO₂ (20 wt.%) > HM (12) > Hβ (8) > Al-MCM-41 (50). Various advantages associated with these protocols include simple workup procedure, short reaction times, high product yields and easy recovery and reusability of the catalyst.