One-pot cascade reactions catalyzed by acid–base mesoporous MCM-41 materials

Acid–base bifunctional mesoporous materials (AB-MCM-41) with aminopropyl and propanesulfonic acid in the same mesoporous material have been synthesized by two different methods: postsynthetic grafting and direct synthesis. AB-MCM-41-g was gained by the modification of SO₃H-MCM-41 surfaces with organic amine functional groups, while AB-MCM-41-co was prepared through co-condensation of trialkoxyorganosilanes with tetraethyl orthosilicate. The bifunctional samples possess hexagonal arrays of uniform pores, large surface area, high pore volume and excellent acid–basic properties. One-pot acid–base cascade reactions were wonderfully achieved in the presence of the efficient acid–base catalysts, which demonstrate the coexistence of acid and base sites in the same material. In addition, the AB-MCM-41-g possesses higher activity for one-pot deacetalization–Knoevenagel and deacetalization–nitroaldol (Henry) reactions in contrast to AB-MCM41-co and this outcome is achieved under simpler synthetic conditions utilizing less time and less material.     

杂多酸固载催化剂的合成及窄分子量纤维素制备的研究

通过水热合成法制备MCM-41型介孔分子筛,采用浸渍法负载磷钨酸于MCM-41介孔分子筛中,煅烧得到新型HPW/MCM-41固载催化剂。利用傅里叶红外光谱(FT-IR)、X射线衍射(XRD)、热重分析(TG)和扫描电镜(SEM)对固载催化剂进行表征;考察催化剂对棉纤维催化降解反应的性能。结果表明,新型HPW/MCM-41固载催化剂即持有了磷钨酸的Keggin结构,同时又保持了分子筛的完整介孔结构,具有催化、筛分双重性能。棉纤维催化降解反应数据显示,磷钨酸负载量、反应温度、催化剂用量、液固比及停留时间均影响HPW/MCM-41降解纤维素的性能。在单因素实验最佳反应条件下,棉纤维素降解产物的分子量分布较为均匀,降解产物的产率较优。     

Preparation of highly dispersed tungsten oxide on MCM-41 via atomic layer deposition and its application to butanol dehydration

Highly dispersed tungsten oxide on MCM-41 was synthesized using a novel atomic layer deposition (ALD) method. BET, XRD, XPS, NH3-TPD, and pyridine-IR were used to study the physicochemical properties of the supported tungsten oxides. In this study, the maximum loading of tungsten oxide on MCM-41 that could be prepared using the modified ALD method was 27.0 wt%. It was confirmed that the textural properties of the mesoporous silica were maintained after tungsten oxide loading. The NH3-TPD and Py-IR results indicated that weak acid sites, mainly Lewis acid sites, were produced over the WO3/MCM-41 samples. Moreover, 2-butanol dehydration was performed to demonstrate the potential advantages of the WO3/MCM-41 catalysts. The WO3/MCM-41 catalyst with 27.0 wt% tungsten oxide loading showed the highest activity in the dehydration of 2-butanol, which was attributed to the highest overall number of acid sites among the WO3/MCM-41 catalysts. The highly dispersed tungsten oxide on MCM-41 prepared via ALD can be an effective catalyst for producing butenes through 2-butanol dehydration.     

Preparation of TiO2/Al-MCM-41 mesoporous materials from coal-series kaolin and photodegradation of methyl orange

TiO₂/Al-MCM-41 mesoporous materials were prepared via sol-gel method by loading titania onto Al-MCM-41 mesoporous molecular sieve by hydrothermal treatment from coal-series kaolin as raw material. The TiO₂/Al-MCM-41 mesoporous materials were characterized by XRD, FT-IR, HRTEM, N₂ adsorption-desorption and the photocatalytic degradation of methyl orange solution under visible light irradiation. The results showed that the TiO₂/Al-MCM-41 mesoporous materials possessed a high surface area of 369.9–751.3 m²/g and a homogeneous pore diameters of 2.3–2.8 nm. The titania crystalline phase was anatase, and the particles size of TiO₂ increased with TiO₂ content. The Al-MCM-41 mesoporous materials exhibited excellent photodegradation activity under visible-light irradiation for methyl orange.     

酸处理对FeN/ZIF-8催化剂氧还原反应催化性能的影响

研发高性能、低成本的非贵金属阴极氧还原反应催化剂是目前质子交换膜燃料电池的主要研究方向之一。以1, 10-菲啰啉为氮源, FeSO₄·7H₂O为铁源, 考察以ZIF-8为载体制备的FeN/ZIF-8催化剂的氧还原反应催化性能, 并探究酸处理对FeN/ZIF-8催化剂结构及性能的影响。通过X射线衍射、比表面积和孔径分布测试、透射电子显微镜等物理表征手段对催化材料进行结构表征, 使用旋转圆盘电极对催化剂氧还原反应催化活性和稳定性进行测试。结果表明: 以ZIF-8为载体制备的催化剂含有Fe₃C, 以及具有较大的比表面积, 这可能是催化剂具有较高氧还原反应初始催化活性的原因。酸处理可去除催化剂中部分不稳定的含铁碳化物和无序碳结构, 使催化剂具有更大的比表面积、更丰富的介孔结构和更高的孔体积; 同时, 酸处理可提高碳基体的耐腐蚀性, 在老化测试中维持催化剂所具有的较高比表面积和丰富的介孔结构, 从而使FeN/ZIF-8-A催化剂表现出更好的氧还原反应活性和稳定性。     

简易合成不同孔径尺寸的半石墨化有序介孔炭

以SBA-15介孔硅为模板,硼酸为扩孔剂,调控合成出不同孔径尺寸的半石墨化有序介孔炭.采用X射线衍射仪(XRD)、氮气吸附、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、热重(TG),以及拉曼(Raman)光谱等手段对样品的成分、结构和形貌进行了分析.结果表明:通过合成过程添加硼酸的方法可以实现对介孔炭材料的孔径在3nm～7nm范围内精确调控,而且合成的介孔炭材料具有半石墨化的墙壁结构.该方法简单易行,对介孔炭材料的孔结构调控合成具有很好的应用价值.     

硅烷修饰对环氧树脂/纳米介孔MCM-41复合材料性能的影响

用偶联剂将纳米介孔MCM-41粉体修饰后与环氧树脂溶液共混,制备出环氧树脂/MCM-41纳米复合材料.研究了偶联剂的含量和不同溶剂的修饰对纳米介孔MCM-41粉体分散性和复合材料力学性能的影响.结果表明,加入适量的偶联剂和在极性较小的介质中修饰,可制备出单分散的纳米介孔MCM-41颗粒增强的新型网络复合材料.偶联剂中的有机基团-(CH2)3-NH2不仅进入孔道、修饰了MCM-41的孔壁,而且使介孔分子筛保持了有序的孔道结构.环氧树脂高分子链与偶联修饰后的MCM-41颗粒的内、外表面以强烈的化学键结合,使MCM-41颗粒均匀分散在聚合物基体中,提高了材料的力学性能,其拉伸强度比基体树脂提高了69%,杨氏模量提高了90%.     

Synthesis of mesoporous Co/Ce-SBA-15 materials and their catalytic performance in the catalytic oxidation of benzene

Cerium-containing SBA-15 mesoporous materials, with different Ce/Si molar ratios, were synthesized by a direct hydrothermal synthesis method and further modified by impregnation with 10, 15 and 20 wt.% Co. Characterizations by powder X-ray diffraction (XRD), N₂ sorption, inductively coupled plasma (ICP) and UV-vis spectroscopy were carried out. The small-angle XRD and N₂ sorption characterizations showed that these Co supported materials have less-ordered mesoporous structures with partial blockage of pores, and their specific surface area, pore volume and pore size were relatively lower than those of unsupported cerium-containing SBA-15. Spinel Co₃O₄ constituted the predominant cobalt phase in the prepared catalysts, and CeO₂ was also detected. All the Co supported catalysts exhibited high catalytic activity in the oxidation of benzene.     

Synthesis and mechanism study of mesoporous SnO2/SiO2 composites

Mesoporous SnO2/SiO2 composite particles (Si/Sn < or = 0.25) sustainable to calcination up to 600 degrees C have been fabricated using a stepwise sol-gel technique on nonionic surfactant template (tetradecylamine, TDA). The newly designed preparation method involved the pre-formation of SnO2 sol solution from SnCl4. Subsequently, SnO2 nanocrystals were covered by the silicate species (from the hydrolysis of tetraethylorthosilicate, TEOS) in a pH controlled colloidal solution. Upon mixing with the surfactant solution, mesophase composite was obtained. After the removal of templates at various temperatures (400 to 600 degrees C), worm-like mesoporous SnO2/SiO2 with large specific surface area and pore volume as high as 362 m2/g and 0.33 cc/g were obtained, respectively. High thermal stability is mainly due to the effective inhibition of SnO2 crystal growth (mean crystallite size <30 A) by the amorphous SiO2 species at the grain boundaries. Formation of mesoporous silicate skeleton such as M41S family material was prevented. The obtained materials maintain the relatively narrow pore size distribution typically in the range of 30 to 70 A. Relations between material properties and key synthesis parameters (i.e. TDA/Si/Sn molar ratio and calcination temperature) were investigated by TGA, wide/small-angle X-ray scattering, (HR)TEM, BET, and FTIR techniques. Mechanisms on the mesostructure formation and crystal growth inhibition were also proposed with detailed discussion.     

Transition-metal (Ti,V,Cr,Mn,Fe,Co,Cu) containing ordered nanoporous materials: novel heterogeneous catalysts for selective oxidation reactions

Transition-metal (Ti,V,Cr,Mn,Fe,Co,Cu) containing periodic nanoporous catalysts, were synthesized hydrothermally and characterized using various analytical and spectroscopic techniques. The catalytic performance of the different catalysts was systematically evaluated with a detailed study on TiMCM-41. All the catalysts showed promise for the selective oxidation of cycloalkanes, viz., cyclohexane, cyclooctane, and cyclododecane, under mild reaction conditions. Furthermore, these mesoporous molecular sieves were also active for all the chosen reactions even after several recycling and/or washing treatments. Among the various materials under investigation, the catalysts TiMCM-41 and VMCM-41 showed much higher substrate conversion and excellent product selectivity in conjunction with a minimal leaching of the active species. More importantly, the influence of pore size on the catalytic activity of the bulkier substrates such as cyclooctane and cyclododecane is demonstrated.     

单分散纳米介孔二氧化硅的制备

在温和碱性条件下,以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯为硅源,三嵌段共聚物F127为助剂,制备出粒径为60～80 nm的单分散纳米介孔二氧化硅MCM-41.研究了F127的用量对介孔结构和纳米粒子分散性的影响.结果表明,适量的非离子表面活性剂F127具有助模板剂的作用,可以有效地提高纳米介孔粉体的有序性;过量的F127阻碍六方介孔相的形成,降低样品的有序性.F127与十六烷基三甲基溴化铵的摩尔比在0.04～0.08范围内,可以得到有序性好、孔径均一和孔隙率大的单分散纳米介孔二氧化硅MCM-41.     

NaY/MCM-48复合分子筛的合成与表征

以微孔分子筛NaY为内核, 合成一种中微孔复合分子筛NaY/MCM-48. 通过XRD、SEM、TEM、IR、N_2吸附脱附和TPD等手段对复合材料进行了表征, 此外对复合材料的水热稳定性进行了考察. 研究结果表明, 复合材料同时具有中孔分子筛MCM-48和微孔NaY型沸石的特点, 并且和纯MCM-48分子筛相比孔壁增厚, 孔径变大; 与纯中孔分子筛MCM-48相比, 复合分子筛的酸性明显增强, 并且水热稳定性提高. DFT计算其孔径分布主要集中于1.2和3.2nm.     

十八烷基三甲基溴化铵为模板合成有序介孔氧化硅及其表征

利用表面活性剂十八烷基三甲基溴化铵(STAB)为模板、正硅酸乙酯(TEOS)为硅源、盐酸为催化剂,在较低的表面活性剂浓度下(小于4%)合成了介孔氧化硅,并研究了不同的反应条件对介孔结构及有序度的影响。在热乙醇萃取或者高温煅烧除去模板剂之后,利用红外(IR)、X射线电子衍射(XRD)、高分辨透射电子显微镜(HRTEM)以及N2的吸附-脱附曲线对合成的介孔材料进行了表征。结果表明,合成的介孔氧化硅具有MCM-41型有序的孔道结构、大的孔体积(不小于1cm3/g)和BET比表面积(不小于1400m2/g),孔径均一且分布较窄。     

Preparation of mesoporous alumina particles by spray pyrolysis and application to double bond migration of 2-butene

The objective of the present study is to investigate the catalytic performance of mesoporous alumina that were prepared via spray pyrolysis for double bond migration from 2-butene to 1-butene. The mesoporous alumina particles were prepared via spray pyrolysis by changing the types of organic surfactants and Al precursors. The texture and acidic properties of mesoporous alumina were analyzed through N2 adsorption, SEM, ammonia-temperature programmed desorption, and FT-IR of adsorbed pyridine. The morphologies and texture properties of the mesoporous alumina were found to have been strongly influenced by the combination of the Al precursor and the structure-directing agents. The mesoporous alumina samples had two kinds of acidic sites: a Lewis acid site and a H-bonded weak acid site. 1-Butene was produced selectively through double bond migration of 2-butene over all of the mesoporous alumina catalysts. The catalyst prepared by using a chloride compound as an aluminium precursor and CTAC as a structure-directing agent showed the highest activity in the double bond migration of 2-butene, which was attributed to its large surface area and an overall high amount of acid sites.     

SO24-／ZrMCM-48和H-ZrMCM-48的制备与催化性能

以正硅酸乙酯为硅源、硫酸锆为锆源、十六烷基三甲基溴化铵为模板剂,在氟化物存在的条件下,120℃下水热法合成ZrMCM-48介孔分子筛．分别用H2S04和NH4NO3对ZrMCM48进行修饰,得到酸性的SO24-／ZrMCM-48和H-zrMCM48介孔分子筛．通过x射线衍射仪（XRD）、NH3-TPD、N2吸附-脱附、透射电子显微镜（TEM）等方法对所得样品进行表征,并通过苯酚与叔丁醇的烷基化反应考察其催化性能．结果表明：ZrMCM-48、SO24-／ZrMCM-48和H-ZrMCM48都具有MCM48典型的立方介孔结构．经H2SO4和NH4NO3修饰后得到的样品的介孔有序性下降,ZrMCM48的弱酸中心较多,强酸中心相对缺乏;样品H-ZrMCM-48和SO24-／ZrMCM-48,除具有弱酸中心外,还有一定量的强酸中心,并且SO24-／ZrMCM-48比H-ZrMCM-48的强酸中心多．在相同的实验条件下,SO24-／ZrMCM-48催化剂的催化活性明显高于H-zrMCM48和zrMCM48,反应温度为140℃时,苯酚转化率高达91．6％．对于SO24-／ZrMCM-48催化剂,在低温时有利于选择性制备2,4-DTBP,高温时有利于选择性制备4-TBP．     

Mesoporous niobium oxides with tailored pore structures

Novel thermally stable and 2D mesoporous niobia phases were prepared by the evaporation induced self-assembly (EISA) with high surface areas (up to 211 m²/g). The pore size of these novel mesoporous niobium oxides was tuned in a wide range from 4.6 to 21 nm by increasing the aging temperature, aging time, and humidity of aging atmosphere. Mixtures of two nonionic surfactants, Pluronic P123 and Brij 35, were for the first time used to tune the pore structure of resultant mesoporous niobia phases which showed that the mesopore shape may be switched from cylindrical to ink-bottle. The niobia mesostructures obtained in this study were thermally stable up to 500 °C. These novel mesoporous niobium oxides with tunable pore sizes are highly promising as catalytic supports and a major component in the synthesis of porous Nb-containing mixed metal oxides, such as MoVTeNbO _x catalysts for selective (amm)oxidation of propane.     

Synthesis of carbon nanotubes using mesoporous Fe-MCM-41 catalysts

MWNTs (multi-walled carbon nanotubes) were made by catalytic CVD process using iron-containing mesoporous silica, Fe-MCM-41, with 4 mol% Fe loading prepared by direct synthesis route. Uniform 5 nm size Fe2O3 nano-particles impregnated onto a mesoporous silica support, SBA-15 were also prepared for CNTs synthesis. The catalysts were characterized using XRD, SEM/TEM, N2 physisorption, UV-vis diffuse reflectance and FT-IR spectroscopies. Acetylene gas was introduced as a carbon source, and the gas mixture of Ar:H2:C2H2 = 14:5:1 pyrolyzed at 750 degrees C for 60 min was found to be the optimum synthesis condition. Fe-MCM-41 due to higher dispersion of nano-sized Fe-species was efficient as catalyst for MWNTs with more uniform size distribution. Cobalt-impregnated Fe-MCM-41 (Co/Fe = 1) produced a small fraction of SWNTs of ca. 2 nm diameter mixed with MWNTs.     

固体酸对介孔氧化铝导电性能影响

在介孔氧化铝(Al2O3)中掺杂固体酸硫酸氢铯(CsHSO4)制备具有高质子导电性能的材料.通过SEM、XRD表征其孔道形貌和晶型特点,采用氮吸脱附测试孔径大小和比表面积等性能参数,运用TG-DSC研究材料的热稳定性及水含量,并应用交流阻抗法测试材料导电率.结果表明,以仲丁醇铝为铝源,通过溶胶-凝胶法合成孔径约为25nm的介孔γ-Al2O3材料,材料具有介孔大小均匀、比表面积大、热稳定性高等特点;掺杂固体酸后,介孔Al2O3的导电率在低温范围提高一个数量级,热分析结果进一步证实固体酸的添加使介孔Al2O3的吸水率提高,从而使质子传导的速率增加,最终提高固体酸掺杂介孔Al2O3的导电率.     

Adsorption performance of VOCs in ordered mesoporous silicas with different pore structures and surface chemistry

Ordered mesoporous silicas with different pore structures, including SBA-15, MCM-41, MCM-48 and KIT-6, were functionalized with phenyltriethoxysilane by a post-synthesis grafting approach. It was found that phenyl groups were covalently anchored onto the surface of mesoporous silicas, and the long-range ordering of the mesoporous channels was well retained after the surface functionalization. The static adsorption of benzene and the dynamic adsorption of single component (benzene) and bicomponent (benzene and cyclohexane) on the original and functionalized materials were investigated. As indicated by the adsorption study, the functionalized silicas exhibit improvement in the surface hydrophobicity and affinity for aromatic compounds as compared with the original silicas. Furthermore, the pore structure and the surface chemistry of materials can significantly influence adsorption performance. A larger pore diameter and cubic pore structure are favorable to surface functionalization and adsorption performance. In particular, the best adsorption performance observed with phenyl-grafted KIT-6 is probably related to the highest degree of surface functionalization, arising from the relatively large mesopores and bi-continuous cubic pore structure which allow great accessibility for the functional groups. In contrast, functionalized MCM-41 exhibits the lowest adsorption efficiency, probably owing to the small size of mesopores and 1D mesoporous channels.     

酸对合成二氧化钛介孔材料的影响

以硫酸和乙酸为酸度调节试剂,采用Sol-Gel过程和水热处理结合,在没有添加任何表面活性剂作模板剂的条件下,通过钛酸丁酯（TBOT）在酸性体系中的控制水解和自组装制备TiO₂介孔材料.产物采用XRD、N₂吸附-脱附等温线、TG-DSC进行分析表征.通过选择酸的种类和控制酸的浓度,添加配位抑制剂TEA减缓Ti的水解速率,可合成介孔纯TiO₂材料.使用硫酸（H₂SO₄∶TBOT＝1∶1,摩尔比）和TEA制备出比表面积为176m²/g,孔容为0.222cm³/g,平均孔径约5nm,孔径分布窄,热稳定性较好的TiO₂介孔材料.