MCM-22分子筛的合成研究进展

MCM-22分子筛是一种高硅铝比分子筛,具有独特的晶体结构、高孔容及微孔率、优良的水热稳定性能和酸性性能,在烃类催化裂化、甲苯岐化、芳烃芳构化和烷基化等反应表现出了优异的催化性能,因此引起了科研工作者的极大研究热情。本文综述了MCM-22分子筛的结构特征、合成的影响因素以及在催化反应上的应用。提出了目前MCM-22分子筛合成所存在的问题,并对其今后的主要研究工作进行了展望。     

MCM-22、MCM-49和MCM-56三种分子筛的合成

MWW结构分子筛是一类新型的催化材料,具有独特的10元环孔道和12元环孔穴结构,在多种反应中表现出良好的催化活性。以六亚甲基亚胺作为模板剂,合成了MCM-22、MCM-49和MCM-56三种分子筛,并详细考察了不同硅源、凝胶配比、晶化温度和晶化时间对合成过程的影响。结果表明,凝胶配比和晶化温度对分子筛物相的影响较大。以硅胶粉为硅源,无论在何种晶化时间下都不能得到MCM-56,只能合成出MCM-49。而以碱性硅溶胶为硅源,在较短的晶化时间内就可以得到MCM-56。     

MCM-22、MCM-49和MCM-56分子筛的表征

MWW结构分子筛是一类新型的催化材料,具有独特的10元环孔道和12元环孔穴结构、优良的水热稳定性和特殊的酸中心分布,在多种反应中表现出良好的催化活性。以六亚甲基亚胺为模板剂,合成了具有MWW结构的MCM-22、MCM-49和MCM-56三种分子筛,并采用XRD、BET、TG/DTG和SEM手段对合成分子筛进行了表征,表明它们具有相同的单层结构,彼此之间的区别只有层间排列的结合层度和结合方式不同。MCM-56是薄层结构,晶体的层数少,MCM-22和MCM-49是多层结构,层数多。MCM-22的层间结合比较疏松,MCM-49的层间结合比较紧密。     

高硅MCM-22型分子筛的合成及催化性能

考察了晶化温度、模板剂用量、硅铝比和搅拌等条件对MCM-22分子筛结晶性的影响,并采用X射线衍射（XRD）、电感耦合等离子体发射光谱（ICP-AES）、氮吸附和氨气-程序升温脱附（NH3-TPD）等对分子筛样品进行表征。结果表明,在135℃,模板剂六亚甲基亚胺与SiO2的物质的量之比为0．75和硅铝比（SiO2与Al2O3的物质的量之比）为120的条件下,合成出纯相的MCM-22分子筛。将合成的分子筛样品作为甲醇脱水催化剂与甲醇合成催化剂混合用于合成气一步法制二甲醚,发现高硅MCM-22分子筛是良好的一步法制二甲醚脱水催化剂,二甲醚选择性达到67％以上,副产物二氧化碳和烃类选择性仅为29％和0．07％。     

分子筛催化法合成仲丁醇

简要介绍正丁烯合成仲丁醇的传统方法。本文主要研究利用分子筛催化正丁烯合成仲丁醇，重点考察了压力、温度、空速和水烯摩尔比对正丁烯水合反应的影响。实验结果表明，在分子筛催化的条件下，反应温度170—180℃、压力8．0MPa、空速0．20h^-l，水／烯摩尔比8：1，正丁烯的单程转化率为35．52％，仲丁醇选择性大于99％。     

动态法、静态法合成MCM-22分子筛

以HMI(六亚甲基亚胺)为模板剂,采用动态法和静态法合成出MCM-22沸石分子筛,并详细考察了反应液配比、晶化温度和晶化时间对MCM-22成晶的影响,同时将这两种方法的差别进行比较.结果表明,当n(Al2O3)/n(SiO2)=30～50时有利于合成出高纯度和高结晶度的MCM-22,温度是影响反应的一个重要因素,反应时间对合成也有影响.一般来说,静态法合成出的微粒直径比动态法大,反应时间较长.     

微孔-介孔复合分子筛的合成及催化应用

综述了近几年微孔-中孔复合分子筛的合成和催化应用,重点介绍了不同复合模式的微孔-中孔复合分子筛的合成方法,包括原位合成法、后合成法和纳米组装法等,并对微孔-介孔复合分子筛的应用前景进行了展望。     

MCM-22和MCM-49分子筛的合成

在Na2O-Al2O3-SiO2-HMI-H2O体系中。对MCM-22和MCM-49分子筛的静态晶化过程进行了研览。结果表明，晶化温度和硅铝比对MCM-22和MCM-49分子舜合成至关重要。晶化温度低（150℃）时，只能合成硅铝比鞋低的MCM-49分子筛；晶化温度高（180℃）时，可以合成较高硅铝比的MCM-49分子筛。同时发现碱庹高有和利于MCM-49分子筛的合成．而Na＋浓度以及模板剂的用量影响不大．     

超细分子筛的合成和应用

综述了近年来超细沸石分子筛的合成及其结构一性能表征方面的进展，并简介超细分子筛材料在催化领域中的应用。     

MCM-41分子筛的合成

以十六烷基三甲基溴化铵(CTAB)为结构模板剂,正硅酸乙酯(TEOS)为硅源,正庚烷(MSDS)为辅助剂,合成出了MCM-41分子筛,并采用傅立叶变换红外光谱仪(FTIR)对分子筛结构进行了表征。探索了pH值、CTAB用量、MSDS用量、晶化温度和晶化时间对分子筛质量吸水率的影响。结果表明:反应体系pH值=10,n(CTAB)∶n(TEOS)=0.06,n(MSDS)∶n(CTAB)=4,晶化温度120℃,晶化时间24h为最佳合成条件。     

Characterization and catalytic properties of MCM-56 and MCM-22 zeolites

We present an investigation of the structure and properties of MCM-56 and MCM-22. These materials have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N₂ adsorption isotherms. DIFFaX was used to simulate pronounced peak broadening in the X-ray diffraction patterns of MCM-56. Toluene disproportionation is used as a test reaction to compare the catalytic activity of MCM-22 and MCM-56. We have found that MCM-56 is made of very thin MWW-type layers. The layers are typically one unit cell along the c direction (with a few of them having two or three unit cells). These very thin layers of MCM-56 become tightly curled upon calcination. The structures thus formed pack very efficiently, and this phenomenon prevents access of organic molecules like toluene to most of the 12 MR cups on the crystal exterior. Although MCM-56 is active for the disproportionation of toluene, its activity is lower than that of MCM-22. A calcination procedure that prevents the curling up of the MCM-56 layers is needed to make MCM-56 a useful catalyst for large organic molecules.     

MCM-22分子筛催化丁烯齐聚反应研究

采用水热法合成了新型多孔材料MCM-22分子筛,并将其用于丁烯齐聚反应。实验结果表明,MCM-22分子筛具有较好的齐聚活性,原料转化率大于80％,C₈^＝烯烃的选择性大于70%。考察了多种因素对反应活性的影响。     

动态法合成MCM-22分子筛及其表征

以六亚甲基亚胺(HMI)为模板剂,采用动态水热晶化法合成出MCM—22沸石分子筛。采用XRD表征对其进行物相分析;采用氨脱附—程序升温脱附(NH3—TPD)法表征其酸性质。结果表明:合成过程中易生成混晶,而适宜的SiO2/Al203比和碱度可以合成出比较纯的MCM—22分子筛。采用常规的离子交换方法可以将其转变为氢型样品。     

Liquid-phase thiophene adsorption on MCM-22 zeolite and activated carbon

The liquid-phase adsorption of thiophene from thiophene/iso-octane and toluene-rich thiophene/toluene/iso-octane solutions has been investigated in batch conditions at room temperature and atmospheric pressure on MCM-22 zeolite and activated carbon. The adsorption of toluene from toluene/iso-octane solutions has also been investigated on both the adsorbents. These were characterised by X-ray diffraction, nitrogen physisorption, scanning electron microscopy and adsorption microcalorimetry of ammonia. Both MCM-22 and activated carbon were able to adsorb thiophene and toluene from the corresponding single-adsorptive iso-octane solutions. MCM-22 appeared superior to activated carbon for the adsorption of thiophene from toluene-rich thiophene/toluene/iso-octane mixtures. The adsorption data for MCM-22 were correlated with the acid sites and silanol groups concentrations, as determined by microcalorimetric experiments. No such correlation was found for activated carbon. Apparently, on MCM-22 thiophene adsorption occurs first on the acid sites until they are saturated and then continues on the silanol groups. Toluene adsorption also occurs on the acid sites of MCM-22 until saturation, but no further adsorption by interaction of toluene with the silanol groups takes place. GC/MS investigation of the nature of the organosulphur material retained by the adsorbent revealed that the tiophene adsorbed on MCM-22 undergoes transformation into heavy products. Besides thiophene trimers and tetramers, these include other compounds formed by two and three thiophenic rings linked by alkyl groups, as well as a rather high molecular weight product where a trimer is linked to thiophenic ring by a cyclohexadienic ring. Reaction pathways leading to these products have been tentatively outlined.     

新型MCM-22/MCM-41复合分子筛上FCC汽油降烯烃芳构化反应

采用纳米组装法合成MCM-22/MCM-41微孔/介孔复合分子筛,分别以H-MCM-22和H-MCM-22/MCM-41为催化剂,在固定床微反装置上对FCC汽油进行降烯烃芳构化的对比考察。结果表明,在反应时间2 h内,与MCM-22相比, MCM-22/MCM-41具有高的芳构化性能和持久的初始活性,复合分子筛汽油改质的产物中,芳烃体积分数由28.58%上升至51.1%,烯烃体积分数由34.04％降至5.8％。探讨了新型H-MCM-22/MCM-41复合分子筛用于FCC汽油改质的操作条件以及催化剂失活再生性能。结果表明,最佳反应条件为：反应温度400 ℃,压力2 MPa,空速3 h^-1。失活催化剂经过两次再生,降烯烃芳构化性能基本不变。     

Synthesis,characterization and catalytic properties of mesoporous MCM-48 containing zeolite secondary building units

Mesoporous aluminosilicate MCM-48 containing zeolite secondary building units in the pore wall has been synthesized in alkaline media with a two-step procedure. The aluminosilicate precursors comprising zeolite secondary building units were first synthesized by carefully controlling reaction conditions and then were assembled using co-templates of gemini surfactant [C₁₈H₃₇N(CH₃)₂(CH₂)₃-N(CH₃)₂C₁₈H₃₇]²⁺ (18-3-18) and triethanolamine (TEA). X-ray Diffraction (XRD) patterns of the as-made samples indicated that highly ordered mesostructured MCM-48 was formed. Transmission Electron Microscopy (TEM) images further verified the formation of MCM-48 with uniform cubic pore channel system having the pore opening diameter of about 25 ?. Compared with the conventionally synthesized MCM-48, the as-synthesized MCM-48 sample showed an adsorption band at 520–600 cm⁻¹ in its FT-IR spectrum, which was assigned to five-membered ring vibration from zeolite structure. This suggested the presence of zeolite building units in the pore wall. N₂ adsorption data showed that the material had a much higher specific surface area (1 200 m²/g) than the conventional MCM-48(1 100 m²/g). Finally, the catalytic performance of the as-made MCM-48 was evaluated by hydrogenation dealkylation reaction of heavy aromatic hydrocarbons. Catalytic results showed that the as-made MCM-48 catalyst exhibited higher conversion than the conventional MCM-48 catalyst. The as-made mesostructured MCM-48 may have a potential catalytic application in the conversion of bulky molecules. Translated from Journal of Fuel Chemistry and Technology, 2006, 34(1): 105–108 [译自: 燃料化学学报]     

Enantioselective epoxidations catalyzed by zeolite MCM-22 encapsulated Jacobsen's catalyst

A novel method for the encapsulation of homogeneous catalysts within the supercages (7.1×18.2 Å) of zeolite MCM-22 has been developed. By way of example, the well known asymmetric oxidation catalyst (R,R)-N,N-bis(3,5-di-tert-butylsalicylidedene)-1,2-cyclohexanediaminemanganese(III) chloride, a.k.a Jacobsen's catalyst, was occluded in MCM-22 during the zeolite synthesis. This ship-in-a-bottle complex exhibited both higher activity and enantioselectivity for the epoxidation of -methylstyrene compared with the homogeneous catalyst.     

采用二元模板剂合成MCM-22分子筛的研究

以硅溶胶和偏铝酸钠分别为硅源和铝源制备MCM-22,采用动态水热法合成MCM-22分子筛,考察了以六亚甲基亚胺和哌嗪二元模板剂对合成MCM-22分子筛的影响。XRD和SEM分析表明：采用二元模板剂能够合成较纯的MCM-22分子筛,并且表面形貌基本相同。     

Shape-selective alkylation of isopropylnaphthalene on MCM-22 zeolite

An MCM-22 zeolite with an Si/Al ratio 13 was found to exhibit higher selectivity to β,β-diisopropylnaphthalene in the alkylation of isopropylnaphthalene with isopropylalcohol, as compared with other zeolites such as mordenite, Y and beta having similar Si/Al ratios. This high selectivity is ascribed to the specific pore shape of MCM-22 zeolite. The gradual increase in the selectivity with reaction time is due to its pore modification by coke deposit.