Sn掺杂MCM-41介孔分子筛的制备、表征及催化性能研究

在低模板剂浓度和弱碱介质中合成催化材料Si-MCM-41、Sn-MCM-41,并用XRD、N2物理吸附-脱附、FT-IR、ICP-AES和TEM等手段对催化材料进行了表征.研究了合成方法对制备Sn掺杂MCM-41介孔分子筛的影响,结果表明:水热晶化法(DHT)合成的Sn-MCM-41,Sn物种主要进入分子筛的骨架中;而模板离子交换法(TIE)合成的Sn-MCM-41,Sn物种主要位于分子筛的表面.Sn-MCM-41介孔分子筛催化环己酮Baeyer-Villiger氧化反应结果表明,n(H2O2):n(酮)=3:1,30g1,4-二氧六环为溶剂,H2O2为氧源,70℃反应6h,环己酮的转化率可达40.02%,ε-己内酯的选择性为45.69%.     

介孔分子筛孔尺寸表征方法比较

MCM-41是由表面活性剂十六烷基三甲基溴化铵为模板剂经水热合成，550℃煅烧5h制备的规则硅质六方介摘要孔材料；Ti-MCM-41是在MCM-41的基础上，将Ti离子涂敷引入到MCM-41的介孔中合成的。该类材料孔尺寸的表征方法有N2吸附、透射电镜TEM、SAXS等，其中N2吸附、透射电镜是传统的介孔尺寸的表征方法，SAXS是近年新的介孔尺寸的表征方法。比较了Ti-MCM-41材料的孔尺寸的表征方法，得出：SAXS得到的Ti-MCM-41孔径与TEM照片的结果符合较好，但与N2吸附的结果偏差较大。SAXS、TEM、N2吸附-脱附等温线给出的Ti-MCM-41的平均孔径分别为2.00nm、2.15nm、3.60nm。     

介孔分子筛MCM-41的合成方法与晶化条件

介孔材料MCM-41具有规则孔道结构,在多相催化、吸附分离、复合材料、纳米组装等领域有着重要的学术研究与应用价值.其可以通过长链季铵盐、伯胺、双子胺或聚氧乙烯类表面活性剂胶束的模板作用,在多种不同的条件下合成.综述了MCM-41介孔分子筛近年来所取得的进展,介绍和讨论了各种合成工艺方法,归纳和分析了影响其合成的主要因素.     

EDTA修饰MCM-41的合成及其对水中Cu2+的吸附研究

采用微波法合成了介孔分子筛氨丙基修饰的MCM-41(MCM-41-(CH2)3NH2),将其与EDTA反应,制得MCM-41-(CH2)3NH2-EDTA,利用XRD、FT-IR、低温N2吸附对其进行了表征,并考察了其对水中Cu2+的吸附性能及材料的化学稳定性.结果表明,产物在弱酸弱碱条件下稳定存在,且有较大的吸附量,在适宜条件下吸附符合Langmuir模型,最大吸附量为33.22mg/g,吸附半衰期为2.04min.最后对其吸附Cu2+的机理进行了分析.     

具有多级孔结构的丝光沸石的合成与性能研究

以表面活性剂十六烷基三甲基溴化铵(CTAB)作为模板剂, 在不添加晶种和有机共溶剂的情况下采用简单的一步水热合成法制备了含有2~4 nm介孔的多级孔纳米丝光沸石。 通过改变 CTAB引入量可以调节所得多级孔丝光沸石样品的外比表面积以及介孔孔容, 最大外比表面积和介孔孔容可分别达到191 m²/g和0.17 cm³/g。均三甲苯在丝光沸石样品上的吸附行为表明, 微孔丝光沸石仅能吸附少量的吸附质, 而多级孔丝光沸石吸附量较大, 并呈现出IV型等温线的特征, 展示出多级孔丝光沸石中介孔的特征。以均三甲苯与苄基氯的苄基化反应来考察多级孔丝光的催化性能。相比于传统微孔丝光沸石, 苄基化反应在多级孔丝光沸石的转化率提高了近7倍, 反应的表观速率常数提高了近19倍。这是由于多级孔丝光沸石较高的外表面积和介孔孔容可以有效地改善大分子反应物的可接近性和产物的传质速率, 从而提高了大分子催化反应的效率。     

MCM-41介孔分子筛和纳米TiO2/MCM-41的合成与结构表征

以工业水玻璃为硅源,表面活性剂十六烷基三甲基溴化铵为结构模板剂,利用室温晶化法合成出MCM-41介孔分子筛,并以钛酸丁酯为前驱体,通过溶胶凝胶法及液相沉积法对介孔分子筛MCM-41进行纳米TiO2的组装。运用XRD、FT-IR、N2吸附-脱附等表征手段对其结构特征和氧化钛分散状态进行了研究,结果表明：TiO2与MCM-41端基硅氧键反应形成Ti-O-Si键;纳米TiO2不仅进入孔道,较均匀地修饰了介孔分子筛MCM-41的孔壁,而且使介孔分子筛MCM-41仍保持有序的孔道结构。     

中空ZSM-5分子筛微球及其吸附与催化性能

首先利用聚乙二醇作为软模板合成出具有一定介孔结构的ZSM-5分子筛微球, 再通过快速可控碱刻蚀的方法, 成功制备出尺寸均一的中空分子筛微球。利用X射线衍射(XRD)、氮气吸附等温线分析(N₂ isotherm)、扫描和透射电子显微镜(SEM, TEM)对所制备的中空分子筛微球进行了表征, 并研究了中空分子筛微球对有机物废水的吸附性能和对大分子的催化裂解性能。结果表明, 刻蚀后分子筛结晶度略有下降, 但是介孔度和孔体积明显提升。中空分子筛微球外径在600 nm, 壳层厚度在100 nm左右。此外, 该中空结构不仅对苯等有机分子具有吸附富集作用, 其饱和吸附量几乎达到了常规分子筛微球的3倍, 并且六次循环使用后的吸附容量依然保持基本不变, 显示出较高的吸附容量和循环使用稳定性。在异丙苯和三异丙苯裂解反应中中空分子筛微球也显示出较高的催化活性。     

超临界CO_2中MCM-41-g-PHEMA介孔复合物的制备及性能

以甲基丙烯酸羟乙酯(HEMA)为单体,用乙烯基三乙氧基硅烷改性的介孔分子筛MCM-41为载体,偶氮二异丁腈为引发剂,在超临界二氧化碳中通过沉淀聚合,成功合成了聚甲基丙烯酸羟乙酯-二氧化硅介孔复合材料(MCM-41-gPHEMA)。考察了反应物配比、反应时间和反应压力对所制复合物形貌与产率的影响。对所合成的复合物进行红外光谱分析、比表面积、小角X射线衍射、扫描电镜、透射电镜、热重分析等表征。研究了复合物的溶胀性及在不同pH下对牛血清白蛋白(BSA)水溶液的吸附性能与吸附动力学。结果表明,MCM-41-g-PHEMA的孔径约为6.3nm,热稳定性明显提高,复合物对BSA的吸附动力学符合伪二级速率方程,最大吸附量为35mg/g。     

不同孔径MCM-41介孔分子筛的合成及吸附性能研究

以十六烷基三甲基溴化铵(CTAB)为表面活性剂,以1,3,5-三甲基苯(TMB)为辅助剂,合成出了不同孔径的MCM-41介孔分子筛.通过吸水率、XRD、N2吸附-脱附测试手段表征了合成样品的结构与性质.结果表明,当TMB与CTAB的摩尔比小于3时,随着TMB∶CTAB摩尔比(0.5∶1～3∶1)的增大,分子筛的晶胞参数(4.411～4.861 nm)、平均孔径(3.5～4.1 nm)、比表面积(899～1021 m2/g)都相应增加;当TMB与CTAB的摩尔比大于3时,随着TMB:CTAB摩尔比(3∶1～4∶1)的增大,分子筛的晶胞参数(4.861～4.584 nm)相应减小.此外,还研究了不同孔径MCM-41在处理含汞废水方面的应用.结果显示,MCM-41介孔分子筛对废水中的二价汞具有良好的吸附性,且随着孔径的增大,吸附率(78%～92.6%)逐渐增大.     

MCM-41的微波合成与比较

采用微波法合成出MCM-41介孔材料,并与水热法、室温法进行比较.结果表明:在120W微波功率下加热40min就可得到结构较理想的MCM-41介孔材料,且微波加热时间的变化会影响到样品的有序性,但对孔径影响不大.通过与水热法和室温法进行比较发现,微波法合成的MCM-41煅烧后的收缩率与水热法相近,比室温合成的MCM-41要小,因而其热稳定性比室温法好,与水热法差不多.     

ZSM-5分子筛介孔的构筑

在微孔结构的ZSM-5沸石分子筛中构筑介孔,可以有效地解决ZSM-5分子筛在催化反应过程中的扩散传质和催化剂失活问题.重点阐述了在初始的合成体系中加入炭黑、介孔碳、表面活性剂等作为模板剂来构筑含介孔结构的ZSM-5和利用碱液或酸液对已合成的微孔的ZSM-5进行后处理来构筑介孔,并对含有介孔结构的ZSM-5的性质和相关的应用做了评价和展望.     

Hollow mesoporous aluminosilicate spheres with acidic shell

Hollow mesoporous aluminosilicate spheres (HMAS) with middle strong acidity have been successfully synthesized by simply hydrothermally treating mesoporous silica spheres (MSS) in zeolite precursor solution. Based on a set of time-dependent experiments, it was found that the hollowing process was associated with a progressive mass redistribution and changes of pores structures. The surfactant cetyltrimethylammonium bromide (CTAB) located in the pores of MSS protected the mesoporous silica spheres from dissolving into strongly basic zeolite precursor solution and acted as the template for mesoporous shell. Under the templating function of CTAB, primary zeolite units were introduced into the mesopore walls of HMAS. The acidity of the resultant samples HMAS was measured by NH₃-TPD techniques. Catalytic tests showed that the HMAS catalysts exhibited high catalytic activity compared with the MSS and Hβ zeolite for catalytic cracking of 1,3,5-triisopropylbenzene.     

一步合成核壳结构ZSM-5/EU-1复合分子筛及其表征

在添加适量柠檬酸的条件下采用双模板剂一步法, 一次晶化合成ZSM-5/EU-1核壳共生复合分子筛, 对其物理化学性质进行表征, 结果显示: 核壳分子筛中存在ZSM-5和EU-1两种分子筛晶相, 且EU-1分子筛在ZSM-5分子筛表面缺陷处外延生长; 复合以后核壳分子筛为微孔-介孔多级孔道结构, 且其微孔孔径达到0.94 nm; 相比于单一分子筛, 核壳分子筛的强酸量相对提高, 酸性质有所改善。通过对柠檬酸加入量、晶化时间影响因素的分析, 得到合成核壳共生结构的最佳条件为: n(citrate)/n(Al₂O₃)=0.8~1.2, 晶化时间为72~96 h, 并推测核壳分子筛可能的生长过程。     

Amphiphilic organosilane-directed synthesis of crystalline zeolite with tunable mesoporosity

Zeolites are a family of crystalline aluminosilicate materials widely used as shape-selective catalysts, ion exchange materials, and adsorbents for organic compounds. In the present work, zeolites were synthesized by adding a rationally designed amphiphilic organosilane surfactant to conventional alkaline zeolite synthesis mixtures. The zeolite products were characterized by a complementary combination of X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The analyses show that the present method is suitable as a direct synthesis route to highly mesoporous zeolites. The mesopore diameters could be uniformly tailored, similar to ordered mesoporous silica with amorphous frameworks. The mesoporous zeolite exhibited a narrow, small-angle XRD peak, which is characteristic of the short-range correlation between mesopores, similar to disordered wormhole-like mesoporous materials. The XRD patterns and electron micrographs of the samples taken during crystallization clearly showed the evolution of the mesoporous structure concomitantly to the crystallization of zeolite frameworks. The synthesis of the crystalline aluminosilicate materials with tunable mesoporosity and strong acidity has potentially important technological implications for catalytic reactions of large molecules, whereas conventional mesoporous materials lack hydrothermal stability and acidity.     

Direct synthesis of nanosized-ZSM-5/SBA-15 analog composites from preformed ZSM-5 precursors for improved catalytic performance as cracking catalyst

Nanosized-ZSM-5/SBA-15 analog composites (ZSC) were successfully synthesized in a two-step process from zeolite seed solutions containing intact ZSM-5 nanocrystals (nano-ZSM-5) by high-temperature synthesis in mild acidic media (200 °C, pH 3.5). The ZSC solids exhibit domains of nano-ZSM-5 blended homogeneously with highly condensed, well-ordered mesoporous SBA-15 analogs containing zeolite building units. The content of nano-ZSM-5 phase and SBA-15 analog phase can be controlled by a single synthesis parameter, i.e., the precrystallization time of the initially formed zeolite seed solution. Compared to conventional Al-SBA-15, the acidic properties, particularly the surface density of strong Brønsted acid sites, of the ZSC are significantly improved while its micro-/mesostructures are well maintained even upon steaming at 800 °C for 24 h. The catalytic activity of the ZSC solids compared to that of commercial ZSM-5 and Al-SBA-15 samples was evaluated in the gas phase cracking of cumene and 1,3,5-tri-isopropylbenzene (TIPB) as probe reactions. The results show that the ZSC materials are effective for the conversion of both cumene and TIPB due to the increased density of the Brønsted acid sites with high accessibility provided by well-dispersed nano-ZSM-5 in the mesoporous SBA-15 analog matrix.     

A high acid mesoporous USY zeolite prepared by alumination

A high-acidity HUSY zeolite with mesoporous structure was prepared by alumination with a dilute aqueous NaAlO₂ solution and characterized by XRD, N₂ adsorption, IR framework vibration and ²⁹Si MAS NMR methods. The results indicated the extra-framework aluminum was reinserted into the tetrahedral framework through isomorphic substitution of framework Si (0Al) sites by Al ions, whereas the crystal and micropore structure were unaltered. FTIR spectra of hydroxyl vibrations and pyridine adsorbed on realuminated zeolites showed that the number of Brønsted acid sites and strong Lewis acid sites increased whereas weak Lewis acid sites decreased twice. The mesoporous structure composed of inter-and intra-crystalline pores in the aluminated HUSY increased the external surface area of the zeolite, improving accessibility of molecules to the active sites and enhancing its catalytic ability. The realuminated HUSY zeolite supported with Ru catalyst exhibited a higher catalytic activity for benzene hydrogenation than the parent HUSY zeolite; the reaction rate in comparison to the mesozeolite increased by 5.5 times.     

Steam-assisted crystallization of TPA+-exchanged MCM-41 type mesoporous materials with thick pore walls

Hierarchical MCM-41/MFI composites were synthesized through ion-exchange of as-made MCM-41 type mesoporous materials with tetrapropylammonium bromide and subsequent steam-assisted recrystallization. The obtained samples were characterized by powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis, FT-IR, ¹H–¹³C CP/MAS and nitrogen adsorption–desorption. The XRD patterns show that the MCM-41/MFI composite possesses both ordered MCM-41 phase and zeolite MFI phase. SEM and TEM images indicate that the recrystallized materials retained the mesoporous characteristics and the morphology of as-made mesoporous materials without the formation of bulky zeolite, quite different from the mechanical mixture of MCM-41 and MFI structured zeolite. Among others, lower recrystallization temperature and the introduction of the titanium to the parent materials are beneficial to preserve the mesoporous structure during the recrystallization process.     

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.     

Preparation of nanosized micro/mesoporous composites

Micro/mesoporous composite material is prepared via reaction of zeolite Beta seeds solution and mesoporous precursor solution under hydrothermal conditions. The resulted micro/mesoporous composite contains nanoparticles with a mean radius of about 90 nm, while pure zeolite Beta and MCM-41 have particles with size of about 50 and 230 nm, respectively. The presence of highly cross-linked silicon framework walls and tetrahedrally coordinated aluminum in the framework structure are confirmed with solid-state ²⁹Si and ²⁷Al NMR investigations. Adsorption measurements show the presence of micropores, mesopores and high interparticle porosity due to the nanometer-sized particles in the micro/mesoporous composite. Various techniques such as dynamic light scattering, scanning electron microscopy, X-ray diffraction, FT-IR, NMR spectroscopy and nitrogen sorption measurements were carried out in order to investigate the properties of the prepared material.