ZSM-5/MCM-41复合分子筛的制备及对乙醇脱水的催化活性

以微孔ZSM-5分子筛为母体,采用NaOH溶液对其进行预处理,再在水热条件下以十六烷基三甲基溴化铵（CTMAB）为模板剂制备了ZSM-5/MCM-41介微孔复合分子筛,考察了预处理温度、晶化温度等因素对复合分子筛结构和形貌的影响。进一步考察了该复合分子筛催化剂在乙醇脱水反应中的催化活性。结果表明,ZSM-5分子筛在2.0 mol/L NaOH溶液中于110℃预处理20 h,再于110℃水热晶化20 h制备的分子筛具有良好的介微孔复合结构;该复合分子筛经NH4NO3溶液离子交换制备的氢型催化剂在乙醇脱水催化反应中表现出良好的性能。当乙醇WHSV=0.5 h-1时,最佳反应温度为240～255℃,乙醇转化率〉99%,乙烯选择性〉96%。     

C-radioisotope labeled methanol conversion over H- and Cs- modified ZSM-5, Beta zeolites and MCM-41 mesoporous molecular sieve

The Na–MCM-41 mesoporous molecular sieve, Na–ZSM-5 and Na–Beta zeolites have been modified by Cs- and H- using ion-exchange method and characterized by XRD, SEM and nitrogen adsorption. The conversion of methanol was studied over H- and Cs- modified ZSM-5, Beta zeolites and MCM-41 mesoporous molecular sieve. Methanol was in ¹¹C-radioisotope labeled form in-order to follow its conversion during the catalytic process, since the radioactivity method provides a very sensitive detection possibility to investigate the conversion of small amounts of methanol and some intermediates at different reaction times and temperatures. The understanding of reaction mechanism is important for side-chain methylation over Cs–zeolite catalysts by methanol, as they are more selective than other alkali exchanged zeolites (Li, Na and K). The reaction pathway of the transformation of methanol to hydrocarbons and aldehydes has been elaborated.     

Adsorption of Bovine Serum Albumin and lysozyme on siliceous MCM-41

The adsorption of Bovine Serum Albumin (BSA) and lysozyme on MCM-41 was studied. In particular, characteristics important to the use of this adsorbent as a chromatographic support for protein separations have been examined. These include the effects of external surface area, solution conditions (pH), and rate of adsorption. Comparative studies were performed on MCM-41 of three pore sizes (24.8 Å, 36 Å, 53.5 Å). It has been shown that differences in external surface area can strongly influence the adsorption capacity. This implies that adsorption on the external surface can be misinterpreted as adsorption in the pores of MCM-41. Thus, high adsorption capacities may not necessarily mean high molecular-sieving capacities. This paper also reports a dependence of protein uptake rates on solution conditions. Calorimetry suggests that under certain solution conditions the adsorption of BSA is a combination of two sequential energetic events. These are postulated to be BSA adsorption followed by reorientation/reconformation of the adsorbed protein on the surface. The slow second step affects the attainment of equilibrium.     

微波法合成MCM-41介孔分子筛及吸附性能研究

以十六烷基三甲基氯化铵为模板剂,在微波实验条件下合成MCM-41介孔分子筛,缩短了合成时间,降低产品成本。实验考察了多种因素对MCM-41合成的影响,并通过吸附处理亚甲基蓝溶液能力强弱,得到最佳合成条件：摩尔比1TEOS：0.2CTMACl：160H2O,pH为10,晶化时间15 min。通过红外光谱分析,MCM-41分子筛的主要特征吸收峰均已出现,说明合成分子筛MCM-41成功。     

NaA/MCM-41微介复合分子筛的合成与表征

按n(SiO2)∶n(Na2O)∶n(Al2O3)∶n(H2O)=1∶1.5∶0.5∶100加料,在90℃下水热晶化3 h合成NaA微孔分子筛,再按n(SiO2)∶n(NaOH)∶n(CTAB)∶n(H2O)=1∶0.3∶0.3∶90依次添加到NaA微孔分子筛中,于110℃下水热晶化24 h合成NaA/MCM-41微介复合分子筛,并采用XRD、SEM(EDS)和TEM等方法对其进行了表征。吸附阳离子红X-5GN模拟染料废水结果表明,在50 mLρ(阳离子红X-5GN)=20 mg/L的水溶液中,NaA/MCM-41微介复合分子筛的投加量为0.6 g/L、pH=6、振荡时间为60 min时,脱色率可达到96.4%,比NaA分子筛和MCM-41介孔分子筛独自吸附脱色效果要好。     

Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41

The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrØnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrØnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrØnsted acid sites and exhibits highest catalytic activity.     

ZSM-5/MCM-41复合分子筛的微波合成及催化性能

用微孔沸石硅源法微波合成ZSM-5/MCM-41复合分子筛,采用XRD、BET和NH₃-TPD技术对合成分子筛进行表征。结果表明,复合分子筛具有类MCM-41 的典型六方介孔结构,同时具有中孔和微孔结构,复合分子筛的总酸量介于HMCM-41酸量与HZSM-5酸量之间。利用脉冲微反装置考察合成分子筛的邻二甲苯异构化催化性能。结果表明,ZSM-5/MCM-41复合分子筛具有高于同硅铝比的MCM-41、ZSM-5和ZSM-5/MCM-41的机械混合物的催化活性。     

Y-Beta/MCM-41复合分子筛的合成和性能

在酸性水热条件下,通过附晶生长法合成Y-Beta/MCM-41复合分子筛,并对其结构、形貌、水热稳定性及催化性能进行研究。结果表明,合成的Y-Beta/MCM-41复合分子筛比表面积高和水热稳定性好,对α-甲基萘的催化裂解性能明显优于机械混合物,表现出良好的催化性能。     

Methanol oxidation on LaCo mixed oxide supported onto MCM-41 molecular sieve

Lanthanum cobaltate LaCoO_x supported onto MCM-41 mesoporous molecular sieve was prepared by in-situ oxidative decomposition of mixed LaCo citrate complexes inside the mesopores of this support. The prepared materials were characterized by EDX, EPR and UV-Vis DRS techniques as well as by N₂-BET measurements. The nanosized LaCoO_x particles within the mesopores of MCM-41 matrix contains cobalt atoms in lower than Co(III) average oxidation state. Also, the supported cobaltate does not form short-range order species of LaCoO₃ but presents as the highly disordered, oxygen deficient Co oxide nanophase. Catalytic activity in MeOH oxidation was tested using both conventional fixed-bed flow system and “operando” mode of DRIFT technique. The very high activity of MCM-41-supported cobaltate is not only due to highly dispersed LaCoO₃ phase but also because of rather low oxidation state of Co.     

Exploring suitable ZSM-5/MCM-41 zeolites for catalytic cracking of n-dodecane: Effect of initial particle size and Si/Al ratio

In this study, various ZSM-5/MCM-41 micro/mesoporous zeolite composites have been prepared by alkalidesilication and surfactant-directed recrystallization of ZSM-5. The effects of particle size and Si/Al ratio of initial ZSM-5 zeolites on the structure and catalytic performance of ZSM-5/MCM-41 composites are studied. The results of XRD, TEM N₂-adsorption-desorption, NH₃-TPD and in situ FT-IR revealed that ordered hexagonal MCM-41 mesopores with 3-4 nm pore size were formed around ZSM-5 crystals, and the specific surface area and mesopore volume of composites increased with increasing the Si/Al ratio of initial ZSM-5. Catalytic cracking of n-dodecane (550 ℃, 4 MPa) showed that the ZSM-5/MCM-41 composites obtained from the high Si/Al ratio and nano-sized initial ZSM-5 zeolites exhibited superior catalytic performance, with the improvement higher than 87% in the catalytic activities and 21% in the deactivation rate compared with untreated zeolites. This could be ascribed to their suitable pore structure, which enhanced the diffusion of reactant molecules in pores of catalysts.     

MCM-41介孔分子筛改性研究新进展

针对目前研制的MCM-41介孔分子筛因水热稳定性较差、孔径过小、难以用于重油加工等方面的缺陷,综述了国内外对MCM-41介孔分子筛改性研究的新进展,尤其是扩大分子筛孔径、提高水热稳定性、引入杂原子和后处理等方面的最新研究。     

粉煤灰合成中孔分子筛MCM-41及其吸附性能

以粉煤灰为初始原料,十六烷基三甲基溴化铵（CTAB）为模板剂采用水热法合成出中孔分子筛MCM-41,采用小角XRD、TEM、氮气吸附-脱附等对样品的物相、比表面积、孔径、孔体积等进行表征,并研究了样品分子筛对镍离子的吸附性能。结果表明：样品具有典型中孔分子筛MCM-41的特性,比表面积为576 m^2/g,平均孔径为5.53 nm;Ni^2＋能定量吸附在样品分子筛上,最大去除率可达到96%,吸附性能符合Langmuir吸附方程特征,并且随吸附液pH的增大,Ni^2＋去除率也随之增加。     

New acid catalyst comprising heteropoly acid on a mesoporous molecular sieve MCM-41

New solid acid catalysts, consisting of heteropoly acid (HPA) H₃PW₁₂O₄₀ (PW) supported on a mesoporous pure-silica molecular sieve MCM-41, have been prepared and characterized by nitrogen physisorption, X-ray diffraction, FT-IR, and³¹P magic angle spinning NMR. The PW/MCM-41 compositions with PW loadings from 10 to 50 wt% have 30 Å uniformly-sized mesopores. HPA retains the Keggin structure on the MCM-41 surface and forms finely dispersed HPA species. No HPA crystal phase is developed even at HPA loadings as high as 50 wt%. PW/MCM-41 exhibits higher catalytic activity than H₂SO₄ or bulk PW in liquid-phase alkylation of 4-t-butylphenol (TBP) by isobutene and styrene. In the alkylation of TBP by styrene, PW/MCM-41 shows a size selectivity compared to bulk PW and PW/SiO₂, providing higher yields of a 2-(1-phenylethyl)-4-t-butylphenol, at the expense of the more bulky 2,6-bis-(1-phenylethyl)-4-t-butylphenol. The PW/MCM-41 compositions, having strong acid sites and a regular mesoporous system, are promising catalysts for the acid-type conversion and formation of organic compounds of large molecular size.     

有机弱碱体系中介孔分子筛MCM-41的合成与表征

在有机弱碱无水乙二胺为碱介质的条件下(pH≈10) ,以阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为模板剂,以正硅酸乙酯(TEOS)为硅源,在室温下合成了介孔分子筛MCM-41。与在强碱水热体系中合成的样品相比,室温弱碱体系中合成的样品具有孔道短程有序度高等特点。详细考察了晶化时间、表面活性剂浓度和晶化温度对产物结构的影响。用XRD对所合成的产物进行表征,结果表明,晶化时间越长,所得到产物的有序度越高;随着表面活性剂质量分数的增加,所合成产物的结构和晶型的完整性越高,但并不是表面活性剂的质量分数越大越好,当表面活性剂的质量分数大于6%时,就呈现下降的趋势;随着晶化温度的升高,所得样品的规整性变差,但晶格参数a₀随温度的升高而呈现变大的趋势。     

以离子液体为模板剂合成MCM-41介孔分子筛

以离子液体1-十六烷基-3-甲基溴代咪唑为模板剂,合成介孔分子筛MCM-41。考察了不同硅源[、C16mim]Br/SiO2配比、pH值、晶化时间等条件对合成MCM-41的影响。采用XRD和低温氮吸附对产物进行表征,结果表明该方法合成的样品具有较大比表面积和规整介孔孔道结构。     

改性MCM-41分子筛的合成与亚甲基蓝吸附性能

选用TEOS（正硅酸乙酯）做为硅源,CTAB（十六烷基三甲基溴化铵）做为表面活性剂,在碱性条件下水热合成MCM-41。实验采用3-氨丙基三甲基硅烷对MCM-41进行改性,成功得到氨基改性介孔材料NH₂-MCM-41吸附剂,并使用X射线衍射（XRD）对其做了表征。考察了各种实验条件下,比如温度、吸附剂的量、pH、亚甲基蓝初始浓度等条件下MCM-41和NH₂-MCM-41对水溶液中亚甲基蓝（MB）的吸附能力。MCM-41和氨基改性介孔材料NH₂-MCM-41均为平面六方介孔结构。结果表明,温度和pH是影响MCM-41和NH₂-MCM-41对亚甲基蓝吸附的最主要的因素。随着温度的升高,材料吸附能力增强,而过高或者过低的pH都会降低MCM-41和NH₂-MCM-41对亚甲基蓝的吸附能力。     

用于氧化反应的改性介孔分子筛MCM-41研究进展

主要从金属掺杂、杂多酸负载和有机官能化等方面详细介绍了改性的MCM-41分子筛作为催化剂在氧化反应中的应用情况,分析了其优缺点。今后的研究重点将是进一步提高改性材料MCM-41分子筛的活性,解决活性组分溶脱现象以及水热稳定性等问题。     

环己烷催化氧化制环己酮的MCM-41催化剂研究

以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯为硅源,采用水热合成法制备纯MCM-41分子筛和掺杂不同金属离子的MCM-41分子筛,并采用等体积浸渍法将一定量的金属离子负载在纯MCM-41分子筛内表面上,制备了负载型和掺杂型2类不同的MCM-41分子筛催化剂.分别考察了负载和掺杂的金属种类、金属Cr负载和掺杂量等对环己烷氧化制环己酮中的催化活性和选择性的影响.研究表明:采用掺杂制备的MCM-41分子筛催化剂活性明显高于负载型MCM-41分子筛催化剂;Cr掺杂量增加,虽然环己烷氧化转化率增加,但产物选择性下降;掺杂Cr的MCM-41分子筛催化剂,用于环己烷氧化制环己酮,在Si与Cr摩尔比为50以下、反应温度75℃、H2O2与环己烷摩尔比为1.2的条件下,环己烷的转化率可达60%左右,环己酮和环己醇的总选择性可达94%以上.     

有机胺改性MCM-41吸附富集CO2

采用浸渍法分别将二乙烯三胺(DETA),二乙醇胺(DEA),乙醇胺(MEA),三乙烯四胺(TETA),羟乙基乙二胺(AEE)负载到MCM-41介孔硅材料上,制成各种吸附剂,考察不同胺负载量的吸附剂对CO2的吸附和再生性能;结果表明质量负载量为50%的AEE/MCM-41吸附效果最佳,在80℃下具有很好的再生性能。     

以聚乙二醇/十六烷基三甲基溴化铵为模板剂制备MCM-41分子筛

通过将聚乙二醇(PEG)直接引入MCM-41分子筛合成模板剂十六烷基三甲基溴化铵溶液中,经脱洗和焙烧处理得到厚孔壁有序介孔材料.选用X射线衍射(xRD)、透射电子显微镜(TEM)和等温吸附(BET)对样品进行了表征,结果显示,添加PEG的合成产物孔壁厚度增加,孔壁厚度可达1.45 nm,孔径尺寸和比表面积减小,有序性降低,低相对分子质量PEG的添加有助于厚孔壁产物生成.