Ti-MWW催化烯丙基氯环氧化高效合成环氧氯丙烷

 研究了具有MWW结构的新一代钛硅分子筛Ti-MWW催化剂对烯丙基氯液相环氧化高效合成环氧氯丙烷的催化性能. 结果表明, Ti-MWW的催化活性以及产物选择性均优于传统的钛硅分子筛TS-1. 对于Ti-MWW,合适的溶剂为非质子性溶剂丙酮和乙腈,在该溶剂中环氧化物不易发生溶剂化开环反应; 而对于TS-1,合适的溶剂是质子性溶剂甲醇,但甲醇可导致醇醚副产物的生成. 在Ti-MWW催化剂上烯丙基氯的转化率和环氧氯丙烷的选择性都能达到99%以上.     

Titanosilicate beads with hierarchical porosity: synthesis and application as epoxidation catalysts

Porous titanosilicate beads with a diameter of 0.5-1.5 mm (TiSil-HPB-60) were synthesized from a preformed titanosilicate solution with a porous anion-exchange resin as template. The bead format of this material enables its straightforward separation from the reaction mixture in its application as a liquid-phase heterogeneous catalyst. The material displays hierarchical porosity (micro/mesopores) and incipient TS-1 structure building units. The titanium species are predominantly located in tetrahedral framework positions. TiSil-HPB-60 is a highly active catalyst for the epoxidation of cyclohexene with t-butyl hydroperoxide (TBHP) and aqueous H(2)O(2). With both oxidants, TiSil-HPB-60 gave higher epoxide yields than Ti-MCM-41 and TS-1. The improved catalytic performance of TiSil-HPB-60 is mainly ascribed to the large mesopores favoring the diffusion of reagents and products to and from the titanium active sites. The epoxide yield and selectivity could be further improved by silylation of the titanosilicate beads. Importantly, TiSil-HPB-60 is a stable catalyst immune to titanium leaching, and can be easily recovered and reused in successive catalytic cycles without significant loss of activity. Moreover, TiSil-HPB-60 is active and selective in the epoxidation of a wide range of bulky alkenes.     

Ti-MWW/H2O2体系催化官能化烯烃环氧化

研究了Ti-MWW/H2O2催化体系对多种官能化烯烃液相环氧化的催化性能.结果表明,与钛硅分子筛TS-1相比,Ti-MWW具有更高的催化活性和环氧化产物选择性.溶剂对Ti-MWW催化环氧化反应的活性影响较大,其中水是催化丙烯酸乙酯和乙酸烯丙酯的最佳溶剂,随着C=C双键相邻官能团吸电子能力的增强,环氧化反应的催化活性下降.     

富硅壳层结构的无粘结剂MWW钛硅分子筛用作高选择性、 高稳定性的丙烯环氧化

环氧丙烷(PO)是一种重要的高活性丙烯衍生物,被广泛用于生产各种商业化学品(丙二醇、聚氨酯和表面活性剂等).目前,工业生产PO主要有传统的氯醇法(CP),共氧化法(叔丁基过氧化氢法、乙苯过氧化氢法和异丙苯过氧化氢法)和过氧化氢直接氧化法(HPPO).其中,HPPO具有反应条件温和、活性高、选择性好和污染小等特点,被认为是一种极具竞争力的环境友好型PO生产工艺.目前,基于TS-1/H2O2/甲醇催化体系的固定床连续HPPO工艺已经实现了工业化(陶氏/巴斯夫、赢创/伍德和中国石化).但是,溶剂甲醇会导致PO醇解开环,使PO选择性降低,而且甲醇和PO存在共沸问题,使PO纯化分离的操作复杂,能耗和成本增加.本课题组之前报道过Ti-MWW在溶剂乙腈中比TS-1在溶剂甲醇中表现出更好的催化性能(Stud.Surf.Sci.Catal.,2007,170,1236–1243.),尤其是质子型惰性溶剂乙腈的存在可以消除PO醇解副反应,极大地提高了PO选择性.因此,开发和设计以乙腈为溶剂的工业Ti-MWW催化剂具有重要的学术和应用价值.工业HPPO过程通常在固定床反应器中进行,需要具有一定机械强度的催化剂来降低压降,因此需要对催化剂原粉进行成型处理.粘结剂是制备成型催化剂的必要添加剂,通常是催化惰性组分,但是它们的引入会降低催化剂中有效活性组分的比例,而且大量的粘结剂会覆盖在沸石的表面及孔口,导致活性中心的可接近性和利用率降低.因此,设计高性能的工业Ti-MWW催化剂既要消除粘结剂对底物向活性位点扩散的负面影响,又要保持较高的机械强度.本文首次提出了一种可控的二次晶化策略,在双有机结构导向剂N,N,N-三甲基-1-金刚烷基氢氧化铵和六亚甲基亚胺的作用下,成功地将成型SiO2/Ti-MWW催化剂中的粘结剂组分转化为MWW沸石相,形成了具有富硅壳层的整体式无粘结剂Ti-MWW催化剂,提高了扩散效率的同时也保证了机械强度.在二次晶化过程中,母体Ti-MWW发生了部分溶硅,形成了大量的内部硅羟基巢,同时部分骨架TiO4物种转变为了具有更强路易斯酸性(LAS)的开放状态的TiO6物种,提高了催化剂对于H2O2的富集和活化能力,使得PO收率从13.1％提高到48.4％,催化使用寿命从75 h延长到了640 h.为了进一步提高催化性能,我们对催化剂进行了哌啶和氟化处理,提高了催化剂中TiO6物种的比例;将有强拉电子效应的氟引入分子筛骨架,提高了Ti的LAS强度.一方面,具有强LAS的改性催化剂能够促进H2O2的活化形成Ti-OOH中间体,提高Ti-OOH中Oα-Oβ的极化率,从而促进活性Oα转移;另一方面,形成的Si–F基团中的F可以与Ti-OOH中的末端H形成更强的氢键,从而稳定Ti-OOH,促进活性Oα有效转移和环氧化过程,抑制了H2O2的无效分解.此外,大量内部硅羟基巢被淬灭,抑制了PO水解副反应的发生.改性后的无粘结剂Ti-MWW催化剂具有2400 h的超长寿命,PO时空收率达到了543 g kg–1 h–1,每1 kmol H2O2消耗的溶剂乙腈质量仅为194.3 kg.     

Titanosilicate zeolite precursors for highly efficient oxidation reactions

Titanosilicate zeolites are catalysts of interest in the field of fine chemicals. However, the generation and accessibility of active sites in titanosilicate materials for catalyzing reactions with large molecules is still a challenge. Herein, we prepared titanosilicate zeolite precursors with open zeolitic structures, tunable pore sizes, and controllable Si/Ti ratios through a hydrothermal crystallization strategy by using quaternary ammonium templates. A series of quaternary ammonium ions are discovered as effective organic templates. The prepared amorphous titanosilicate zeolites with some zeolite framework structural order have extra-large micropores and abundant octahedrally coordinated isolated Ti species, which lead to a superior catalytic performance in the oxidative desulfurization of dibenzothiophene (DBT) and epoxidation of cyclohexene. It is anticipated that the amorphous prezeolitic titanosilicates will benefit the catalytic conversion of bulky molecules in a wide range of reaction processes.

Titanosilicate zeolite precursors, with open structures of zeolite units and high amounts of catalytically active Ti species, show superior catalytic performance in the oxidative reactions.     

Post-synthesis and catalytic performance of FER type sub-zeolite Ti-ECNU-8

A titanosilicate Ti-ECNU-8 with a FER type sub-zeolite structure was developed by pots-synthesis and applied to the epoxdiation of alkenes with hydrogen peroxide.A controlled acid treatment on the pure silica layered precursor PLS-3 of FER topology gave rise to a sub-zeolite ECNU-8.Composed of a collection of FER sheets without an ordered stacking manner along layer related[100]direction,the structure of ECNU-8 was constructed by a reorientation of interlayer hydrogen bond moieties caused by partial removal of interlayer organic structure directing agent.ECNU-8 possessed an external surface area enlarged by ca.30% in comparison to corresponding three-dimensional FER zeolite.Through a solid-gas reaction with TiCl_4 vapor,tetrahedral Ti active sites were introduced into the framework.The resultant Ti-ECNU-8 retained the structural properties of ECNU-8,and exhibited an excellent catalytic performance for the epoxidation of cycloalkenes owing to the accessible Ti sites located in open reaction space.     

Increasing the propylene epoxidation activity of TS-1 catalysts by hydrothermal treatment of ammonia solution

Summary Treating titanium silicalite (TS-1) with ammonia solution under hydrothermal conditions proves to be an effective post-synthesis modification method for improving TS-1 catalytic activity in propylene epoxidation. Characterizations indicate that the treated TS-1 did not change TS-1 composition and generate more Ti (IV)-superoxide species (g_z = 2.0265, g_y = 2.0090, g_x = 2.0022) when interacting with aqueous H₂O₂(30 wt.%) compared with the as-synthesized one.</o:p>     

Highly efficient olefin oxidation catalysts based on regular nano-particles of titanium-containing mesoporous molecular sieves

Ti-MCM-41 and Ti-MCM-48 are successfully prepared by one step synthesis and post-synthesis at room temperature. The samples have been characterized by X-ray diffraction, SEM, TEM, nitrogen adsorption/desorption isotherms and UV-Vis spectroscopy. The results demonstrate the existence of an ordered mesoporous structure. The Ti species are grafted into the pure silica sieve frameworks without any evidence of the formation of non-skeleton anatase. The post-synthesis Ti-MCM-41 regular nano-particles display a higher conversion and selectivity as compared to that for both the post-synthesis Ti-MCM-48 and Ti-MCM-41 with ordinary particles, in the epoxidation of cis-cyclooctene with aqueous H(2)O(2) as an oxidant. The enhanced catalytic activity may be attributed to the existence of a higher number of isolated tetracoordinated Ti active sites and regular nano-particles, which are conducive to the affinity of the reactants with active sites.     

具有MFI骨架结构的介孔钛硅材料的合成、表征和催化性能

利用介孔碳作硬模板合成出具有MFI骨架结构的介孔钛硅材料. 该样品复制了类似SBA-15的介孔结构, 同时骨架含有MFI微孔结构. 透射电镜表征结果表明, 样品表面还有部分大孔结构. 催化结果证明了该样品既具有介孔材料较大孔道结构, 又保持了微孔钛硅材料的高活性.     

氨基酸辅助合成高活性六配位钛物种的TS-1分子筛

TS-1分子筛是以TO4(T=Si,Ti)四面体为基本单元,通过氧桥连接而形成的具有MFI拓扑结构的微孔晶体材料,其在催化烯烃环氧化、酮类氨肟化、氧化脱硫及芳香烃羟基化等氧化反应中表现出较好的催化活性.目前,提高TS-1分子筛催化性能的方法主要包括:(1)制备纳米和多级孔TS-1分子筛,以提高其扩散传质性能;(2)提高TS-1分子筛的钛含量并抑制锐钛矿相的产生,以增加其催化活性位点.最新研究表明,相比于传统四配位钛物种(TiO4)作为催化活性中心,六配位(TiO6)钛物种在烯烃环氧化反应中具有更高的催化活性,可进一步降低反应活化能,最终实现高效催化转化.然而,TiO6物种结构中的Ti-OH组分,易导致开环反应发生,从而降低环氧化产物的选择性.因此,构筑高活性TiO6物种及调变TiO4/TiO6比例,对提高烯烃转化率及环氧产物选择性具有重要意义.当前,高活性钛物种的结构表征及其构筑已成为研究热点且仍面临挑战.本文协同采用氨基酸辅助合成策略和两步晶化方法,成功地制备出具有TiO4和TiO6物种且无锐钛矿相的多级孔TS-1分子筛.在该协同策略中,两步晶化过程有利于抑制锐钛矿相的形成,而氨基酸的引入对高活性TiO6物种的构筑具有重要作用.氨基酸分子可与钛原料形成螯合物,为TS-1分子筛晶化提供"养料",并有效平衡晶体成核与生长速率及稳定TiO6物种,最终实现制备富含TiO6物种的多级孔TS-1分子筛.相比于传统TiO4物种作为催化活性中心(1-己烯的转化率<25％,环氧化产物选择性>95％),本文所制备的TS-1分子筛(Si/Ti=36.9)因其兼具TiO4和TiO6物种,在1-己烯环氧化反应中表现出更好的催化性能(1-己烯的转化率33％,环氧化产物选择性95％).这是由于TiO4物种不会导致开环反应的发生,因此可以保证较高的环氧产物选择性,而TiO6物种经H2O2活化后,可形成具有更高活性及更小位阻效应的催化中心,极大提高了1-己烯转化率.综上,本文合成策略为构筑具有高活性钛物种及多级孔结构的钛硅分子筛提供了指导作用,为调控硅铝酸盐及硅取代磷酸铝分子筛材料活性位点的含量和分布提供了新思路.     

Immersion calorimetry as a tool to evaluate the catalytic performance of titanosilicate materials in the epoxidation of cyclohexene

Different types of titanosilicates are synthesized, structurally characterized, and subsequently catalytically tested in the liquid-phase epoxidation of cyclohexene. The performance of three types of combined zeolitic/mesoporous materials is compared with that of widely studied Ti-grafted-MCM-41 molecular sieve and the TS-1 microporous titanosilicate. The catalytic test results are correlated with the structural characteristics of the different catalysts. Moreover, for the first time, immersion calorimetry with the same substrate molecule as in the catalytic test reaction is applied as an extra means to interpret the catalytic results. A good correlation between catalytic performance and immersion calorimetry results is found. This work points out that the combination of catalytic testing and immersion calorimetry can lead to important insights into the influence of the materials structural characteristics on catalysis. Moreover, the potential of using immersion calorimetry as a screening tool for catalysts in epoxidation reactions is shown.     

钛硅分子筛催化1-丁烯环氧化研究

自1983年Taramasso等报导TS-1的合成以来,钛硅分子筛的合成及应用一直是分子筛催化领域的热点。经典TS-1合成方法采用四丙基氢氧化铵（TPAOH）为模板剂,合成成本较高、条件苛刻,限制了其应用。用四丙基溴化铵（TPABr）为模板剂代替TPAOH,能够成功地合成TS-1。不同孔道结构的钛硅分子筛,如Ti-β、Ti-MCM-41、Ti-HMS等弥补了TS-1较小孔径的缺点,进一步扩大了钛硅分子筛的应用。本文以不同合成方法得到的TS-1及中孔Ti—HMS为催化剂,双氧水为氧化剂,1-丁烯环氧化合成1,2-环氧丁烷,研究了不同钛硅分子筛对1-丁烯环氧化反应的催化性能。     

自堆积纤维状TS-1分子筛的常规水热合成

<正>研究[1-2]表明分子筛的催化、吸附、分离性能在很大程度上取决于其尺寸和形貌。近年来,人们越来越多的关注于精确控制晶粒的尺寸、形态和取向[3-11]。在所有沸石分子筛中,由于MFI型分子筛具有独特的孔道结构且应用广泛,目前的研究主要集中     

Synthesis, structure, and reactivity of a new Ti-containing microporous/mesoporous material

A new class of porous, mixed phase titanosilicate materials containing a microporous TS-1 phase and a mesoporous Ti-MCM-48 phase has been successfully synthesized. A novel, one-pot synthesis method was used in which the organic templates for the mesoporous and microporous phases were added sequentially to the same reaction mixture, followed by crystallization at 150 degrees C. The gemini surfactant 18-12-18 was used to form the Ti-MCM-48 mesophase; subsequent addition of tetrapropylammonium cation (TPA+) led to the formation of TS-1. The relative amounts of the two phases within the final products were controlled by optimizing the crystallization time. Crystallization times between 12 and 50 h gave materials containing both phases, with an increasing amount of microphase formed at longer crystallization times. These materials, called "Ti-MMM-2" (microporous/mesoporous materials) were characterized using powder XRD, N2 physisorption, TEM, FTIR, DR-UV/Vis spectroscopy, and 29Si MAS NMR. In the epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP), Ti-MMM-2 samples exhibited higher catalytic activity (approximately 61%) than either TS-1 (16%) or Ti-MCM-48 (42%), with a very high selectivity (97%) for formation of cyclohexene oxide.     

Photoluminescence study of mesoporous MCM-41 and Ti-grafted MCM-41

Photoluminescence combined with diffuse reflectance UV—Vis spectroscopy was used to characterise both the pure siliceous MCM-41 and Ti-MCM-41 containing tetrahedral Ti(IV) species anchored onto the inner walls of the siliceous MCM-41. Both Ti-MCM-41 and MCM-41 showed complex photoemission signals and this study allows, for the first time, the distinction of the emission signals of tetrahedral Ti9IV) ions from those due to silica surface centres.     

Preparation of B-free Ti-MWW through reversible structural conversion

B-free titanosilicate with the MWW topology, Ti-MWW, has been successfully prepared from its highly siliceous analogue through structural interconversion and simultaneous titanium incorporation in the presence of piperidine or hexamethyleneimine.     

NaPMoO/Ti-MCM-41催化环己烯环氧化反应

采用浸渍法制备了混合氧化物NaPMoO/Ti-MCM-41(n)(n为载体钛硅比)催化剂,考察其在以H2O2为氧化剂的环己烯环氧化反应中的催化性能,并用XRD、UV-Vis、IR、N2吸附-脱附、XPS及H2-TPR等测试技术对催化剂进行表征.结果表明:NPMO/Ti-MCM-41(0.2)的环己烯转化率、环氧环己烷选择性及H2O2利用率达到最高,分别为27.50%、75.31%和78.31%.这归因于负载型NPMO中的MoO3还原能力得到提高;载体Ti-MCM-41中Ti物种进一步促进MoO3的还原能力,从而有利于其与双氧水形成过氧化物活性中间体,使催化性能和双氧水的利用率得到提高.其中负载后的载体Ti-MCM-41孔结构遭到破坏,形成无定形TiOx物种.     

Liquid-phase oxidation of ethylamine to acetaldehyde oximes over tungsten-doped zeolites

The liquid-phase oxidation of ethylamine with hydrogen peroxide was studied over tungsten-doped zeolites to develop a clean and simple route for producing acetaldehyde oxime. The investigations were firstly performed over W/MOR, where the coordinated state as well as the acidity of the W species were characterized. The reaction parameters, including H_2O_2 amount, solvent,temperature, tungsten content as well as catalyst amount, governed the activity and oxime selectivity. Under optimized reaction conditions, W/MOR showed an ethylamine conversion and corresponding oxime selectivity of 18.3% and 88.9%. W/MOR showed a superior performance in comparison to other tungsten-containing zeolites of W/Beta, W/MWW and W/Y. Although W/MOR exhibited lower amine conversion than titanosilicates of TS-1 and Ti-MWW, it gave higher selectivity to the main product of oxime. Moreover, W/MOR proved to be a robust catalyst, exhibiting a stable catalytic performance after being reused at least for 5 times.     

Ti-MWW分子筛上烯丙醇环氧化制环氧丙醇

 以哌啶为模板剂, 硼酸为结构承载助剂,采用动态水热法成功地合成了Ti-MWW层状前体,经酸处理和煅烧后,得到Ti-MWW分子筛. 紫外-可见光谱表明, Ti-MWW层状前体中含有四面体和八面体配位的钛物种. 酸处理可以很容易地将非骨架的八面体钛脱除,煅烧后分子筛不含锐钛矿相; 未经酸处理直接煅烧,部分八面体钛会聚集形成锐钛矿相. Ti-MWW层状前体的红外光谱在960 cm-1处没有骨架钛的特征吸收谱带出现,经酸处理后,该特征吸收峰出现. 以H2O2为氧化剂,考察了Ti-MWW分子筛上的烯丙醇环氧化性能,发现凝胶Si/Ti=20, 15%HNO3处理12～16 h的情况下,制得的Ti-MWW的催化性能最好,在温度为333 K和反应时间为30 min, 转化率为88.7%, 选择性为99%; 但酸处理时间过长可使部分Ti-MWW中的钛生成锐钛矿相,从而导致催化剂活性下降.     

Synthesis of titanium silicalite-1 (TS-1) zeolite with high content of Ti by a dry gel conversion method using amorphous TiO2–SiO2 composite with highly dispersed Ti species

In this study, we have developed a new method to synthesize mesoporous titanium silicalite-1 (TS-1) with a higher content of active titanium in the framework (more than 5%) than that obtained from the conventional hydrothermal synthesis. The new method combines two methods as follows: (1) a sol-gel method in tetrahydrofuran for the synthesis of TiO₂–SiO₂ composite with highly dispersed Ti species and (2) a dry gel conversion method for the crystallization to TS-1. This investigation revealed that the dispersion of Ti in the starting materials was quite important to synthesize mesoporous TS-1 with high content of Ti besides dry conversion method. The obtained mesoporous TS-1 with a high content of titanium showed higher catalytic activity in 1-hexene epoxidation than conventional TS-1. This high activity is likely to originate from the high content of titanium in the framework.