MCM-41-HY复合分子筛的合成及其在深度加氢脱硫中的应用

在水热条件下合成了包覆型MCM-41-HY复合分子筛.采用XRD、N2气吸附和SEM等方法对其进行了表征.结果表明,MCM-41-HY复合分子筛和MCM-41与H型Y沸石(HY)的机械混合物明显不同,在复合分子筛MCM-41-HY中,中孔相MCM-41附晶生长在HY沸石上,将HY包覆起来.以二苯并噻吩为模型化合物,考察了该材料担载NiMo催化剂的加氢脱硫活性.结果表明,MCM-41-HY复合分子筛与MCM-41和HY的机械混合物担载NiMo催化剂的加氢脱硫(HDS)活性相当,但MCM-41-HY复合分子筛担载NiMo催化剂的裂化活性较低.其裂化活性不同的原因在于其载体孔道结构和酸性位的分布不同.     

功能化MCM-41在有机合成中的应用

介孔分子筛MCM-41具有较高的比表面和规整的结构以及表面带有羟基,因此可对MCM-41进行官能团化,从而实现均相催化剂在MCM-41中的组装,达到均相催化剂多相化的目的。本文介绍了最近几年以MCM-41为主体,组装均相配合物得到固相化催化剂在氧化、还原、烷基化、氢甲酰化、Heck、环丙烷化等反应中的应用。     

MCM-41-HY复合分子筛的合成及其在深度加氦脱硫中的应用

在水热条件下合成了包覆型MCM-41-HY复合分子筛，采用XRD、N2气吸附和SEM等方法对其进行了表征．结果表明，MCM-11-HY复合分子筛和MCM-41与H型Y沸石（HY）的机械混合物明显不同，在复合分子筛MCM-41-HY中．中孔相MCM-41附晶生长在HY沸石上，将HY包覆起来，以二苯并噻吩为模型化合物，考察了该材料担载NiMo催化剂的加氧脱硫活性．结果表明，MCM-41-HY复合分了筛与MCM-41和HY的机械混合物担载NiMo催化剂的加氯脱硫（HDS）活性相当，但MCM-41-HY复合分子筛担载NiMo催化剂的裂化活性较低．其裂化活性不同的原因在于其载体孔道结构和酸性位的分布不同。     

Study on the Epoxidation of a, β-Unsaturated Ketones Catalyzed by MCM-41 Supported Schiff Base

介孔分子筛MCM-41依次与3-氯丙基三乙氧基硅烷、环己二胺和三唑醛反应,得到席夫碱修饰的新型介孔分子筛MCM-41催化剂.通过傅里叶变换红外光谱（FTIR）和X射线多晶衍射（XRD）等方法对所得催化剂进行表征.以过氧化氢为氧源,介孔分子筛MCM-41负载的席夫碱为催化剂,研究了α,β-不饱和酮的环氧化反应,考察了金属盐、溶剂、催化剂用量、反应时间等因素对环氧化反应的影响.结果表明,在室温下乙腈溶剂中,α,β-不饱和酮的环氧化反应在短时间内均以很高的产率（高达99%）得到了相应的产物.同时,对催化剂的重复利用进行了研究,发现重复使用四次,仍能以较高产率得到环氧化产物.     

MCM-41 负载席夫碱催化α,β-不饱和酮的环氧化反应研究

介孔分子筛MCM-41 依次与3-氯丙基三乙氧基硅烷、环己二胺和三唑醛反应, 得到席夫碱修饰的新型介孔分子筛MCM-41 催化剂. 通过傅里叶变换红外光谱(FTIR)和X 射线多晶衍射(XRD)等方法对所得催化剂进行表征. 以过氧化氢为氧源, 介孔分子筛MCM-41 负载的席夫碱为催化剂, 研究了α,β-不饱和酮的环氧化反应, 考察了金属盐、溶剂、催化剂用量、反应时间等因素对环氧化反应的影响. 结果表明, 在室温下乙腈溶剂中, α,β-不饱和酮的环氧化反应在短时间内均以很高的产率(高达99%)得到了相应的产物. 同时, 对催化剂的重复利用进行了研究, 发现重复使用四次, 仍能以较高产率得到环氧化产物.     

甲烷在中孔分子筛MCM-41中吸附的计算机模拟

采用巨正则系综Monte Carlo方法研究了甲烷在两个不同孔径的MCM-41中不同温度下的吸附等温线和其在孔中的相行为和排列方式.模拟结果显示,在较小孔径的MCM-41中,流体分子达到毛细凝聚所需的化学位较小,并且观察到两个孔径下计算机模拟得到的亚稳态区域都非常宽,使得层状转变（如果有的话）被包含在这个区域.通过比较两种孔径下达到毛细凝聚后的构型,可以看出,在3.5 nm的孔中流体的分子结构出现非常有序的排列,而在5.0 nm的孔中则没有.在常温300 K时甲烷的吸附的计算机模拟表明,孔壁对流体分子的作用仅仅影响较靠近壁面附近的流体分子的排列,而对孔中间的分子几乎没有影响.     

氮气在MCM－41分子筛中的吸附：实验和分子模拟

用美国Micromeritics公司生产的ASAP2010物理吸附仪测定了低温（77 K） N_2在MCM-41分子筛中的吸附等温线，获得了表征MCM-41特征的BET比表面、BJH孔 容和平均孔径。同时用巨正则Monte Carlo（GCMC）模拟方法考究了N_2在MCM-41中 的吸附，得到了N_2在MCM-41中的模拟吸附等温线，分析了流体在MCM-41分子筛中 的微观结构。GCMC模拟中MCM-41介孔材料模型化为圆柱孔，N_2模型化为Lennard- Jones（LJ）球。N_2和MCM-41介孔墙壁间的相互作用采用Tjatjopoulos-Feke- Mann（TFM）势能模型进行表征。通过使模拟和实验结果有一个好的吻合，确定了 一组有效的MCM-41分子筛的势能参数（σ_(ww) = 0.265 nm，∈_(ww)/k = 190 K ）。这为以后其他吸附质在MCM-41中吸附的预测奠定了基础、提供了依据。     

杂原子介孔MCM-41分子筛的制备及其对含喹啉模拟柴油的吸附脱氮性能

制备了介孔MCM-41分子筛和三种杂原子(Zn、Ba和Ce)介孔MCM-41分子筛,通过X射线衍射(XRD)、红外光谱(FT-IR)、低温N_2吸附-脱附等手段对其进行表征,研究了几种介孔分子筛对氮含量为1732μg/g含喹啉模拟柴油的吸附脱氮性能。结果表明,所制备的几种分子筛均具有典型的介孔结构,且杂原子已进入到分子筛骨架中。利用Materials Studio软件构建介孔分子筛模型,模拟的XRD谱图与实验结果基本相符;进一步模拟了喹啉分子在杂原子介孔分子筛团簇上的吸附,计算了吸附能及被吸附分子和吸附中心的距离(d_((N-M)))。几种分子筛的吸附脱氮性能顺序依次为Zn-MCM-41 Ce-MCM-41 Ba-MCM-41 MCM-41;Zn-MCM-41的吸附性能最好,吸附能最大,吸附分子和吸附中心的距离d_((N-M))最小。吸附时间对杂原子介孔分子筛的吸附脱氮性能具有较大影响,而吸附温度的影响相对较小;Zn-MCM-41、Ba-MCM-41和Ce-MCM-41分子筛的最佳吸附时间分别为40、10和30 min,最佳吸附温度分别为40、30和40℃。     

负载型铜系分子筛催化剂在苯酚羟基化反应中的应用

以介孔分子筛MCM-41、MCM-48和AIMCM-41以及微孔分子筛Naβ和MOR为载体,分别采用有机官能团化法和分步水热合成法制备了系列负载型催化剂,考察了其在苯酚羟基化反应中的活性;得到了不同载体类型、不同负载方法及不同助剂与反应活性的对应关系．结果表明：以微孔分子筛为载体的催化剂对副产物有明显的抑制作用．介孔分子筛AIMCM-41,MCM-41,MCM--48为载体时,催化剂在苯酚羟基化反应中的活性顺序为AIMCM-41〉MCM-48〉MCM-41,助剂镧和钴的引入可以有效抑制副产物的产生．     

乙二胺基和2，4-戊二酮官能化介孔分子筛固载钼（Ⅵ）：新型的环己烯环氧化催化剂

通过对介孔分子筛HMS和MCM-41表面修饰，将乙二胺基和2，4-戊二酮引入到介 孔分子筛孔道内，制备出乙二胺基和戊二酮官能化介孔分子筛。首次将烯烃环氧化 均相催化剂MoO_2(acac)_2固载到乙二胺基和戊二酮官能化介孔分子筛孔道内，制 备出新型的、易回收、可重复使用的烯烃环氧化多相催化剂。环已烯催化环氧化表 明，该催化剂的催化活性与均相催化剂MoO_2(acac)_2相当，选择性大于80%。     

Gas adsorption in mesoporous micelle-templated silicas: MCM-41, MCM-48, and SBA-15

This paper reports a molecular simulation and experimental study on the adsorption and condensation of simple fluids in mesoporous micelle-templated silicas MCM-41, MCM-48, and SBA-15. MCM-41 is described as a regular cylindrical silica nanopore, while SBA-15 is assumed to be made up of cylindrical nanopores that are connected through lateral channels. The 3D-connected topology of MCM-48 is described using a gyroid periodic minimal surface. Argon adsorption at 77 K is calculated for the three materials using Grand Canonical Monte Carlo simulations. Qualitative comparison with experiments for nitrogen adsorption in mesoporous micelle-templated silicas is made. The adsorption isotherm for SBA-15 resembles that for MCM-41. In particular, capillary condensation and evaporation are not affected by the presence of the connecting lateral channels. In contrast, the argon adsorption isotherm for MCM-48 departs from that for MCM-41 having the same pore size. While condensation in MCM-41 is a one-step process, filling of MCM-48 involves two successive jumps in the adsorbed amounts which correspond to condensation in different domains of the porosity. The condensation pressure for MCM-48 is larger than that for MCM-41. We attribute this result to the morphology of the MCM-48 surface (made up of both concave and convex regions) that differs from that for MCM-41 (concave only). Our results suggest that the pore connectivity affects pore filling when the size of the connections is comparable to that of the nanopores.     

Nature of adsorption and desorption branches in cylindrical pores

To examine the nature of the adsorption and desorption branches in hysteretic adsorption isotherms of gases on mesoporous materials, we measured the temperature dependence of the adsorption and desorption isotherms of argon, oxygen, and carbon dioxide onto MCM-41 with a pore diameter of 4.4 nm. The results clearly show that in the open-ended cylindrical pores of MCM-41, capillary condensation rather than evaporation takes place near a thermodynamical equilibrium transition, as opposed to the general statement that capillary evaporation can occur via a meniscus formed at the pore mouth, and, thus, takes place at equilibrium.     

Porous Texture and Surface Character of Dehydroxylated and Rehydroxylated MCM-41 Mesoporous Silicas-Analysis of Adsorption Isotherms of Nitrogen Gas and Water Vapor

Four samples of MCM-41 mesoporous silicas whose average pore diameters are 2.4, 2.8, 3.2, and 3.6 nm were prepared using sodium orthosilicate and cationic surfactants of [CH(3)(CH(2))(n)N(CH(3))(3)]X (n=11, 13, 15, 17). These four samples were calcined at 1123 K in vacuo to obtain the dehydroxylated samples, which were further rehydroxylated at 298 K to obtain the rehydroxylated samples. The adsorption isotherms of nitrogen gas (77 K) for the 12 MCM-41 mesoporous silicas are of Type IVc, giving no adsorption hysteresis. On the other hand, the first adsorption isotherms of water vapor (298 K) for the dehydroxylated MCM-41 samples are quite different from those of nitrogen gas, giving the remarkable adsorption hysteresis. The second water isotherms for the rehydroxylated MCM-41 samples are of Type IV, showing slight hysteresis. Using the nitrogen isotherms, the relation between the pore size and carbon chain length of the surfactant has been determined, and the effect of dehydroxylation and rehydroxylation on the porous texture has been examined. Using the first and second water isotherms, the adsorption model of physisorbed waters adsorbed on the surface silanol groups has been proposed. From the pore size distribution curves of nitrogen and water, the presence of constrictions in the cylindrical pores has been predicted. Copyright 2000 Academic Press.     

介孔材料氨基表面修饰及其对CO2的吸附性能

采用接枝方法在介孔材料MCM-41和SBA-15的孔道内表面进行氨基化修饰, XRD、29Si-NMR、FT-IR、TGA、BET等测试结果表明, 氨丙基三乙氧基硅烷(APTS)和氨乙基氨丙基甲基二甲氧基硅烷(AEAPMDS)都分别接枝在介孔材料的孔道内, 表面氨基修饰量约为1.5-2.9 mmol·g-1. 表面修饰后介孔材料的孔道仍高度有序, 但比表面积减小. 表面修饰前后介孔材料对CO2的吸附性能发生显著变化, 由于物理吸附转化为以氨基为活性中心的化学吸附, 吸附量从修饰前的0.67 mmol·g-1提高到2.20 mmol·g-1.     

Adsorption of Carbon Tetrachloride by 3.4 nm Pore Diameter Siliceous MCM-41: Isotherms and Neutron Diffraction

Adsorption isotherms of carbon tetrachloride at temperatures between 273 and 323 K have been determined on the pure silica form of MCM-41 of pore diameter ca. 3.4 nm. All isotherms were of Type V, the isotherms at 273, 288 and 303 K showing hysteresis loops, whereas the isotherm at 323 K was completely reversible. Despite the questionable validity of the Kelvin equation when applied to narrow mesopores, changes in the relative pressure positions of capillary condensation and evaporation as a function of the temperature appear to be well described. Neutron diffraction measurements at 200 and 273 K show significant changes in the physical properties of the adsorbed CCl4 in the MCM-41 from those of bulk adsorbate. The results also suggest a highly heterogeneous surface and appear to show some flexibility in the pore walls upon pore filling. The conditions required for first order reversible capillary condensation are discussed.     

Adsorption of simple gases in MCM-41 materials: the role of surface roughness

This paper reports the development and testing of atomistic models of silica MCM-41 pores. Model A is a regular cylindrical pore having a constant section. Model B has a surface disorder that reproduces the morphological features of a pore obtained from an on-lattice simulation that mimics the synthesis process of MCM-41 materials. Both models are generated using a similar procedure, which consists of carving the pore out of an atomistic silica block. The differences between the two models are analyzed in terms of small angle neutron scattering spectra as well as adsorption isotherms and isosteric heat curves for Ar at 87 K and Xe at 195 K. As expected for capillary condensation in regular nanopores, the Ar and Xe adsorption/desorption cycles for model A exhibit a large hysteresis loop having a symmetrical shape, i.e., with parallel adsorption and desorption branches. The features of the adsorption isotherms for model B strongly depart from those observed for model A. Both the Ar and Xe adsorption branches for model B correspond to a quasicontinuous pore filling that involves coexistence within the pore of liquid bridges and gas nanobubbles. As in the case of model A, the Ar adsorption isotherm for model B exhibits a significant hysteresis loop; however, the shape of the loop is asymmetrical with a desorption branch much steeper than the adsorption branch. In contrast, the adsorption/desorption cycle for Xe in model B is quasicontinuous and quasireversible. Comparison with adsorption and neutron scattering experiments suggests that model B is too rough at the molecular scale but reproduces reasonably the surface disorder of real MCM-41 at larger length scales. In contrast, model A is smooth at small length scales in agreement with experiments but seems to be too ordered at larger length scales.     

A density functional theory for Lennard-Jones fluids in cylindrical pores and its applications to adsorption of nitrogen on MCM-41 materials

A density functional theory (DFT) constructed from the modified fundamental-measure theory and the modified Benedict-Webb-Rubin equation of state is presented. The Helmholtz free energy functional due to attractive interaction is expressed as a functional of attractive weighted-density in which the weight function is a mean-field-like type. An obvious advantage of the present theory is that it reproduces accurate bulk properties such as chemical potential, bulk pressure, vapor-liquid interfacial tension, and so forth when compared with molecular simulations and experiments with the same set of molecular parameters. Capabilities of the present DFT are demonstrated by its applicability to adsorption of argon and nitrogen on, respectively, a model cylindrical pore and mesoporous MCM-41 materials. Comparison of the theoretical results of argon in the model cylindrical pore with those from the newly published molecular simulations indicates that the present DFT predicts accurate average densities in the pore, slightly overestimates the pore pressure, and correctly describes the effect of the fluid-pore wall interaction on average densities and pressures in the pore. Application to adsorption of nitrogen on MCM-41 at 77.4 K shows that the present DFT predicts density profiles and adsorption isotherms in good agreement with those from molecular simulations and experiments. In contrast, the hysteresis loop of adsorption calculated from the mean-field theory shifts toward the low pressure region because a low bulk saturated pressure is produced from the mean-field equation of state. The present DFT offers a good way to describe the adsorption isotherms of porous materials as a function of temperature and pressure.     

萘在介孔分子筛MCM-41与SBA-15上的吸附特性研究

对低浓度气相萘在两种常见介孔分子筛MCM-41和SBA-15上的吸附特性进行研究。得到了萘在两种吸附剂上的吸附等温线和不同初始浓度下的穿透曲线,并分别与吸附等温线模型(Langmuir、Freundlich、D-R)和恒定浓度波动力学模型进行了拟合。结果表明, Langmuir模型能很好描述低浓度气相萘的吸附等温线(R²均在99%以上);具有微孔结构的SBA-15对萘的吸附能力要优于仅具备介孔结构的MCM-41。动力学模型在初始浓度较低时能较好地预测萘在吸附剂上的穿透曲线,且在SBA-15上的相关系数高于MCM-41;萘在2.76 mol/L时具有较大介孔的SBA-15的总传质系数K_a更高,表明萘在SBA-15上的总传质阻力更低,更能较快达到传质平衡。     

Water adsorption-desorption isotherms of two-dimensional hexagonal mesoporous silica around freezing point

Zr-doped mesoporous silica with a diameter of approximately 3.8 nm was synthesized via an evaporation-induced self-assembly process, and the adsorption-desorption isotherms of water vapor were measured in the temperature range of 263-298 K. The measured adsorption-desorption isotherms below 273 K indicated that water confined in the mesopores did not freeze at any relative pressure. All isotherms had a steep curve, resulting from capillary condensation/evaporation, and a pronounced hysteresis. The hysteresis loop, which is associated with a delayed adsorption process, increased with a decrease in temperature. Furthermore, the curvature radius where capillary evaporation/condensation occurs was evaluated by the combined Kelvin and Gibbs-Tolman-Koening-Buff (GTKB) equations for the modification of the interfacial tension due to the interfacial curvature. The thickness of the water adsorption layer for capillary condensation was slightly larger, whereas that for capillary evaporation was slightly smaller than 0.7 nm.