Ti-HMS和TS-1分子筛结构和催化性能的对比研究

 采用长链十二烷基胺为模板剂,成功合成出含钛中孔分子筛Ti-HMS, 并针对其晶化过程、结构特征以及催化性能与修正经典法制备的微孔分子筛TS-1进行了对比. 结果表明,中孔分子筛Ti-HMS的晶化机理不同于微孔分子筛TS-1的晶化机理. 随着晶化温度的提高, Ti-HMS分子筛的相对结晶度降低,且晶化过程中母液的pH值变化不大. TEM照片显示, Ti-HMS分子筛的孔壁整体上呈无定形,在局部区域可能存在晶态或者类晶态物种. 与TS-1分子筛相比, Ti-HMS分子筛的活性中心(骨架钛)处在畸变的四面体环境中. 中孔分子筛Ti-HMS可以满足大分子硫化物(如苯并噻吩)氧化反应的要求; 对于小分子硫化物(如噻吩)的氧化反应,微孔分子筛TS-1催化剂效果更好.     

介孔分子筛V-MCM-41的水热法制备与合成机理

 以十六烷基三甲基溴化铵为模板剂,廉价的工业级高模数比(3.3)的硅酸钠为硅源,通过水热法合成了V-MCM-41介孔分子筛. 考察了合成条件对产物织构的影响,并采用低温氮吸附法分析探讨了介孔分子筛V-MCM-41的合成机理. 结果表明,模板剂用量、 pH值、加料方式、晶化温度、晶化时间、陈化时间和焙烧气氛等合成条件对介孔分子筛的制备均有影响,其中晶化温度、 pH值和模板剂用量的影响最为明显. X射线衍射谱表明合成的介孔分子筛具有六方晶体结构. 红外光谱和紫外可见光谱表明V进入了介孔分子筛的骨架结构.     

系列硅铝比纳米薄层ZSM-5分子筛的合成和表征

以自制不对称双子季铵盐表面活性剂为模板, 在水热合成体系中控制合成系列硅铝比纳米薄层ZSM-5分子筛.采用X射线衍射(XRD)、N₂吸附-脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)和²⁷Al魔角旋转核磁共振(²⁷Al MAS-NMR)对合成的样品进行了表征. 详细研究了晶化温度、晶化时间、结构导向剂(SDA)用量、碱度等对合成的影响和纳米薄层ZSM-5分子筛的形成过程. 结果表明: 分子筛硅铝比越高, 结构导向剂用量越大, 所需的晶化时间越短; 晶化温度越高, 晶化时间越短; 且不同硅铝比纳米薄层ZSM-5分子筛的形貌规整度、比表面积和介孔/微孔孔容比例随着硅铝比而变化.     

高硅ZSM-5分子筛和二次合成Ti-ZSM-5分子筛的结构

运用度角旋转（MAS）和交叉极化（CP）等核磁共振波谱和红外光谱技术，分别对采用不同模板剂制备的高硅ZSM－5分子筛和以此为母体，经气固同晶取代法得到Ti－ZSM－5分子筛的结构特性进行了研究．结果表明：在水热法合成高硅ZSM-5分子筛过程中，模板剂明显制约着所制得的分子筛的结构特性．通过选用合适的模板剂，可直接获得具有正交晶系结构的高硅ZSM－5分子筛．在随后的气固相同晶取代过程中，钛原子通过占据分子筛骨架中的缺陷位进入骨架，形成具有一定Ti／Si比例的钛硅分子筛（Ti－ZSM－5）。骨架结构中缺陷位的含量直接影响分子筛的载钛量。     

Ti-HMS催化氧化脱除模拟燃料中的硫化物

 将噻吩、苯并噻吩、二苯并噻吩和4,6-二甲基二苯并噻吩(DMDBT)分别溶于正辛烷配成模拟燃料,以Ti-HMS为催化剂,以H2O2为氧化剂,对模拟燃料的氧化脱硫进行了研究,考察了Ti-HMS的催化活性及硅/钛比和结晶度对催化剂活性的影响. 结果表明,在Ti-HMS上硫化物氧化的难易顺序是由噻吩环上硫原子的电子云密度和硫化物分子的空间位阻共同决定的; 氧化反应发生在分子筛孔道内,骨架钛原子为活性中心; DMDBT在Ti-HMS上的氧化脱除效果比在TS-1,Ti-β或Ti-MCM-41上好. 随着Ti-HMS中硅/钛比的增大,DMDBT的脱除率降低; 随着Ti-HMS分子筛结晶度的升高,DMDBT的脱除率升高.     

ZSM—11型Zr—Si分子筛的合成研究

分别以硅溶胶为硅源、氧氯化锆为锆源、四丁基溴化铵的模板剂,采用水热晶化法合成了ZSM-11型的锆硅分子筛。用XRD和SEM等表征了分子筛的结构;考察了硅锆比、晶体温度、碱度、晶化时间、模板剂的用量等对分子筛形成过程的影响。结果表明,ZSM-11型的锆硅分子筛的形成受很多因素的影响,一般晶化温度为120-140℃、硅锆比高于20、碱度控制在4.7左右有利于分子筛晶体的生成,晶化时间一般为约48h,SEM照片显示所合成的Zr-ZSM-11分子筛为结晶完好的棒状晶体;EDX证实了Zr原子在分子筛中的存在。     

直链烷烃对Ti-HMS分子筛合成的影响

以十二胺为模板剂,正硅酸乙酯为硅源,钛酸四丁酯为钛源,直链烷烃正己烷或正辛烷为有机添加剂,在室温下合成出具有较大孔径的Ti-HMS分子筛.研究了烷烃对Ti-HMS分子筛的扩孔作用及对分子筛结晶度和催化性能的影响.结果表明,加入的烷烃越多,分子筛的孔径越大;烷烃链长越长,对Ti-HMS的扩孔作用越显著.与不加烷烃的Ti-HMS相比,加入烷烃后,分子筛的结晶度及四配位骨架钛的含量均有所降低,而且加入的烷烃量越多,影响越明显.将加入烷烃所得的Ti-HMS用于模拟燃料中4,6-二甲基二苯并噻吩的氧化脱除反应,结果发现,Ti-HMS的催化氧化活性有所提高,对4,6-二甲基二苯并噻吩的脱除速率增大.     

超声老化对MCM-49分子筛合成的影响

 以六亚甲基亚胺为模板剂,在静态水热合成条件下,考察了超声老化对MCM-49分子筛合成的影响. 结果表明,凝胶经超声老化处理后,即使使用比表面积小的硅源(硅胶或白碳黑)也能合成出不含杂晶且结晶良好的MCM-49分子筛. 超声老化处理缩短了MCM-49分子筛的晶化时间,扩大了分子筛的晶化范围,同时降低了模板剂的用量. 合成的MCM-49分子筛结晶度高,颗粒度小.     

胆碱和*BEA分子筛在硅锗铝IWR分子筛制备中的协同导向效应

分子筛的制备过程一般需要结构导向剂的参与.结构导向剂主要包括碱(土)金属离子、有机胺或季铵盐为代表的有机模板剂和固体晶种等三类.研究合成凝胶中不同结构导向剂之间的作用对于理解分子筛晶化机理意义重大.以往的研究大都集中在模板剂-模板剂、模板剂-碱(土)金属离子和模板剂-同晶之间的相互作用,迄今尚未有模板剂-异晶之间相互作用研究的报道.我们研究组首次发现模板剂和异晶在分子筛制备中存在协同导向效应.在硅锗铝IWR分子筛的合成中,我们考察了不同的季铵碱模板剂和铝源,发现只有使用胆碱作模板剂、*BEA分子筛作铝源才可以成功制得目标分子筛,相同条件下不加入*BEA分子筛或换用MOR、ZSM-5、MCM-22、USY分子筛及异丙醇铝等铝源都无法合成得到IWR分子筛.这说明*BEA分子筛在IWR分子筛的制备中起到了其他铝源所不具备的结构导向作用,因此我们称之为合成IWR分子筛的"异晶".为了研究胆碱和*BEA分子筛之间的相互作用,进而揭示模板剂-异晶协同导向制备分子筛的一般规律与反应机理,我们制备了不同晶化时间的IWR分子筛样品,使用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、紫外-拉曼光谱(UV-Raman)、固体核磁共振(MAS NMR)和N2物理吸附等手段对这些样品进行了表征.结果显示,加热过程中*BEA分子筛首先发生溶解解离, 72 h后该分子筛相完全消失;12 h开始出现CDO分子筛相,随着晶化时间延长, CDO分子筛先增多后减少,在24 h时达到最大值, 120 h时消失,说明该分子筛是晶化过程的一个中间相;IWR分子筛在12 h开始出现,此后结晶度不断升高,至168 h晶化完全.在上述表征的基础上,我们提出了模板剂-异晶协同导向制备IWR分子筛的晶化机理.IWR分子筛的晶化分为以下5个步骤:(1)*BEA分子筛溶解解离得到硅铝4元环、5元环和6元环等结构单元;(2)胆碱诱导形成硅锗5元环结构单元;(3)硅锗5元环组装生成CDO分子筛;(4)CDO分子筛溶解解离形成硅锗5元环;(5)*BEA分子筛导向的结构单元与胆碱导向的结构单元重组生成IWR分子筛.其中,步骤3和4是一对可逆反应,且可与步骤5同时进行;随着反应物原料的不断消耗,步骤5占据主导,从而导致CDO分子筛完全消失和IWR分子筛的结晶完成.由于胆碱只导向生成5元环结构单元,而构成IWR分子筛骨架结构的4元环和6元环只能由*BEA分子筛提供,因而模板剂和异晶在反应中都不可或缺,二者起到协同导向的作用.分析发现,*BEA分子筛与IWR分子筛具有共同的结构单元(4、5、6元环)和一定的结构相似性是其可以成为异晶、发挥协同导向作用的关键.上述协同导向法的关键在于模板剂和异晶分别导向生成部分结构单元,再经重组得到目标分子筛.这种方法有望用于合成通过传统水热法难以得到的分子筛,并且为新结构分子筛的开发提供新思路.使用协同导向法制备更多种类分子筛的研究正在进行中.     

SAPO-5分子筛的可控合成及晶化过程探索

在非醋酸体系下分别通过动态和静态水热晶化方法合成了SAPO-5分子筛, 并考察了转速、 晶化时间及凝胶体系水硅比对SAPO-5分子筛晶相及形貌的影响, 采用X射线衍射(XRD)和扫描电子显微镜(SEM)技术研究了静态、 动态水热条件下SAPO-5分子筛的晶化过程. 结果表明, 静态水热条件下晶化6 h得到的SAPO-5分子筛为球状、 六边形柱状聚集晶体; 而在20 r/min转速下晶化2和6 h得到的SAPO-5分子筛分别为分散的凹面柱状晶体(凹面直径约6~8 μm)及均一分散的球状晶体(直径为16 μm); 在60 r/min转速下晶化3 h即可得到高度分散的六边形柱状晶体(六边形直径约5~8 μm); 提高转速至100和140 r/min时仅需晶化1 h即可得到六边形柱状晶体. 通过考察体系水硅比(H₂O/Si摩尔比)的影响, 确定最佳的水硅比为70, 此条件下所得晶相为纯相且分子筛的分散度最好. 综上可知, 相较于静态晶化, 动态晶化不仅从形貌上改善了晶体的分散度, 通过缩短晶化时间、 降低晶化转速也提高了SAPO-5分子筛的晶化效率. 本文采用较小的水硅比(H₂O/Si摩尔比为70)、 较低的模板剂用量在非醋酸体系下合成了SAPO-5分子筛, 为SAPO-5分子筛的合成提供了一条更简单、 经济的路线.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.     

Catalyst free,visible-light promoted photoaddition reactions between C60 and N-trimethylsilylmethyl-substituted tertiary amines for synthesis of aminomethyl-1,2-dihydrofullerenes

An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene solutions containing fullerene C₆₀ and N-trimethylsilylmethyl-substituted amines by using a 20 W compact fluorescent lamp, leads to formation of aminomethyl-substituted fullerene adducts in a highly efficient manner. The photoaddition reaction takes place via a pathway initiated by visible light absorption by C₆₀, followed by SET from the amine to the triplet excited state of C₆₀. Ethanol-promoted desilylation of the resulting a minimum radical then generates the corresponding α-amino radical which couples with the C₆₀ radical anion to form the anion precursor of the fullerene adducts. The new approach using visible-light takes place under mild conditions and it does not require the use of photocatalysts. Thus, the method developed in this effort could broadens the range of functionalized fullerene derivatives that can be readily prepared.     

Highly efficient and stereoselective cycloaddition of nitrones to indolyl- and pyrrolylacrylates

The reactions of various nitrones with indolyl- and pyrrolylacrylates proceeds regioselectively with high diastereoselectivity in the case of aldonitrones, and represents an effective method for obtaining new indolyl- and pyrrolyl-substituted isoxazolidine carboxylates stabilized by weak (CH?O) and moderate (NH?N) strength intramolecular hydrogen bonding. The resulting cycloadducts exhibit promising in vitro anti-influenza activities.     

Transition metal-free direct amination of benzoxazoles using formamides as nitrogen sources

A transition metal-free method for the direct amination of benzoxazoles using formamides as nitrogen sources is reported, which was mediated by an inexpensive and environmentally friendly tetrabutylammonium iodide/tert-butyl hydroperoxide system and gave the 2-aminobenzoxazole derivatives with moderate to good yields.     

l-Proline-catalyzed five-component domino reaction leading to multifunctionalized 1,2,3,4-tetrahydropyridines

Multifunctionalized 1,2,3,4-tetrahydropyridines are concisely synthesized in good yields via l-proline-catalyzed or l-proline/FeCl₃-cocatalyzed one-pot multicomponent reactions (MCRs). The MCRs involve a domino hydroamination/prins reaction/Mannich-type reaction/intramolecular dehydration-cyclization process. The molecular structure of 5baa, one of multifunctionalized 1,2,3,4-tetrahydropyridines, was confirmed by single-crystal X-ray diffraction.     

Studies of Photoionization of CF3 I by Femtosecond Time-resolved Mass Spectrometry

The multi-photon dissociative photoionization dynamics of CF3I has been studied with femtosecond two-color pump-probe time of flight mass spectra at a pump pulse of 265 nm and a probe pulse of 398 nm. The life constants of CF3I+ and its fragment ions CF3+ and I+ are obtained as (96±7), (198±130) and (167±6)fs, respectively. The multi-photon dynamics leading to these ions differ. CF3I+ corresponds to a (1+2′) transition with one-photon pump excitation to the A band of CF3I. CF3+ are mainly formed by a tow-photon probe excitation to the CF3+ with subsequent dissociation of parent ions. I+ are produced in (2+2′) combined with (1+1′+2′) process. The results provide information on the multi-photon pathways involved.