ZrO2晶相对ZnO/ZrO2+SAPO-34双功能催化剂上合成气制烯烃反应的影响

烯烃是重要的化工原料,目前主要通过石油催化裂化得到.随着石油资源的消耗以及人们对烯烃需求的日益增长,开发非石油路线制取烯烃势在必行.合成气可以从煤、天然气和生物质等获得,由合成气作为重要的C1平台分子一步制取烯烃(STO)的过程受到了广泛关注.将合成气制甲醇/二甲醚的金属催化剂与甲醇制烯烃的分子筛催化剂耦合得到的混合双...     

Single‐Particle Spectroscopy on Large SAPO‐34 Crystals at Work: Methanol‐to‐Olefin versus Ethanol‐to‐Olefin Processes

The formation of hydrocarbon pool (HCP) species during methanol‐to‐olefin (MTO) and ethanol‐to‐olefin (ETO) processes have been studied on individual micron‐sized SAPO‐34 crystals with a combination of in situ UV/Vis, confocal fluorescence, and synchrotron‐based IR microspectroscopic techniques. With in situ UV/Vis microspectroscopy, the intensity changes of the λ=400 nm absorption band, ascribed to polyalkylated benzene (PAB) carbocations, have been monitored and fitted with a first‐order kinetics at low reaction temperatures. The calculated activation energy (E_a) for MTO, approximately 98 kJ mol^?1, shows a strong correlation with the theoretical values for the methylation of aromatics. This provides evidence that methylation reactions are the rate‐determining steps for the formation of PAB. In contrast for ETO, the E_a value is approximately 60 kJ mol^?1, which is comparable to the E_a values for the condensation of light olefins into aromatics. Confocal fluorescence microscopy demonstrates that during MTO the formation of the initial HCP species are concentrated in the outer rim of the SAPO‐34 crystal when the reaction temperature is at 600 K or lower, whereas larger HCP species are gradually formed inwards the crystal at higher temperatures. In the case of ETO, the observed egg‐white distribution of HCP at 509 K suggests that the ETO process is kinetically controlled, whereas the square‐shaped HCP distribution at 650 K is indicative of a diffusion‐controlled process. Finally, synchrotron‐based IR microspectroscopy revealed a higher degree of alkylation for aromatics for MTO as compared to ETO, whereas high reaction temperatures favor dealkylation processes for both the MTO and ETO processes.     

Space‐ and Time‐Resolved In‐situ Spectroscopy on the Coke Formation in Molecular Sieves: Methanol‐to‐Olefin Conversion over H‐ZSM‐5 and H‐SAPO‐34

Formation of coke in large H‐ZSM‐5 and H‐SAPO‐34 crystals during the methanol‐to‐olefin (MTO) reaction has been studied in a space‐ and time‐resolved manner. This has been made possible by applying a high‐temperature in‐situ cell in combination with micro‐spectroscopic techniques. The buildup of optically active carbonaceous species allows detection with UV/Vis microscopy, while a confocal fluorescence microscope in an upright configuration visualises the formation of coke molecules and their precursors inside the catalyst grains. In H‐ZSM‐5, coke is initially formed at the triangular crystal edges, in which straight channel openings reach directly the external crystal surface. At reaction temperatures ranging from 530 to 745 K, two absorption bands at around 415 and 550 nm were detected due to coke or its precursors. Confocal fluorescence microscopy reveals fluorescent carbonaceous species that initially form in the near‐surface area and gradually diffuse inwards the crystal in which internal intergrowth boundaries hinder a facile penetration for the more bulky aromatic compounds. In the case of H‐SAPO‐34 crystals, an absorption band at around 400 nm arises during the reaction. This band grows in intensity with time and then decreases if the reaction is carried out between 530 and 575 K, whereas at higher temperatures its intensity remains steady with time on stream. Formation of the fluorescent species during the course of the reaction is limited to the near‐surface region of the H‐SAPO‐34 crystals, thereby creating diffusion limitations for the coke front moving towards the middle of the crystal during the MTO reaction. The two applied micro‐spectroscopic techniques introduced allow us to distinguish between graphite‐like coke deposited on the external crystal surface and aromatic species formed inside the zeolite channels. The use of the methods can be extended to a wide variety of catalytic reactions and materials in which carbonaceous deposits are formed.     

Growth of High‐Quality,Thickness‐Reduced Zeolite Membranes towards N2/CH4 Separation Using High‐Aspect‐Ratio Seeds

Greatly improved zeolite membranes were prepared by using high‐aspect‐ratio zeolite seeds. Slice‐shaped seeds with a high aspect ratio (AR) facilitated growth of thinner continuous SAPO‐34 membranes of much higher quality. These membranes showed N₂ permeances as high as (2.87±0.15)×10^?7 mol m^?2 s^?1 Pa^?1 at 22 °C while maintaining a decent N₂/CH₄ selectivity (9–11.2 for equimolar mixture). On the basis of these thinner high‐quality SAPO‐34 membranes, fine‐tuning the local crystal structure by incorporating more silicon further increased the N₂ permeance by 1.4 times without sacrificing the N₂/CH₄ selectivity. We expect that application of large AR zeolite seeds might be a viable strategy to grow thin high‐quality zeolite membranes. In addition, fine‐tuning of the crystal structure by changing the crystal composition might be a feasible way for further improving the separating performance of high‐quality zeolite membranes.     

Growth of High‐Quality,Thickness‐Reduced Zeolite Membranes towards N2/CH4 Separation Using High‐Aspect‐Ratio Seeds

Greatly improved zeolite membranes were prepared by using high‐aspect‐ratio zeolite seeds. Slice‐shaped seeds with a high aspect ratio (AR) facilitated growth of thinner continuous SAPO‐34 membranes of much higher quality. These membranes showed N₂ permeances as high as (2.87±0.15)×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 22 °C while maintaining a decent N₂/CH₄ selectivity (9–11.2 for equimolar mixture). On the basis of these thinner high‐quality SAPO‐34 membranes, fine‐tuning the local crystal structure by incorporating more silicon further increased the N₂ permeance by 1.4 times without sacrificing the N₂/CH₄ selectivity. We expect that application of large AR zeolite seeds might be a viable strategy to grow thin high‐quality zeolite membranes. In addition, fine‐tuning of the crystal structure by changing the crystal composition might be a feasible way for further improving the separating performance of high‐quality zeolite membranes.     

A Dynamic Kinetic Model for Methanol to Light Olefins Reactions over a Nanohierarchical SAPO‐34 Catalyst: Catalyst Synthesis,Model Presentation,and Validation at the Bench Scale

This study includes three main parts: synthesizing the hierarchical silicoaluminophosphate (SAPO‐34) catalyst, evaluating the performance of this modified catalyst in the methanol to light olefins (MTO) process, and providing a new dynamic kinetic model for the modified catalyst. At first, a carbon nanotube (CNT) was used as a mesopore template in the sonochemical synthesis of SAPO‐34 hierarchical catalyst. By comparing the performance of this hierarchical catalyst and the common catalyst in the MTO process, it is observed that better performance is obtained on a modified catalysts for a longer period of time. Then, nine process tests were performed in differential fixed bed reactors at different temperatures and space velocities to obtain the kinetic model of the desired catalyst in the MTO process. Finally, the dynamic kinetic model of the modified SAPO‐34 catalyst was considered for main reactions in the MTO process. In this model, the rate equations were assumed elementary and lumped, and the decreasing of the catalyst activity over time on stream was also considered. The reactions constant and catalyst activity coefficient for different reactions were obtained by simultaneous connection of the code related to the reactor model and the genetic algorithm and genetic programming codes. The results obtained from the kinetic model were consistent with the experimental results.     

Direct and Highly Selective Conversion of Synthesis Gas into Lower Olefins: Design of a Bifunctional Catalyst Combining Methanol Synthesis and Carbon–Carbon Coupling

The direct synthesis of lower (C₂ to C₄) olefins, key building‐block chemicals, from syngas (H₂ /CO), which can be derived from various nonpetroleum carbon resources, is highly attractive, but the selectivity for lower olefins is low because of the limitation of the Anderson–Schulz–Flory distribution. We report that the coupling of methanol‐synthesis and methanol‐to‐olefins reactions with a bifunctional catalyst can realize the direct conversion of syngas to lower olefins with exceptionally high selectivity. We demonstrate that the choice of two active components and the integration manner of the components are crucial to lower olefin selectivity. The combination of a Zr–Zn binary oxide, which alone shows higher selectivity for methanol and dimethyl ether even at 673 K, and SAPO‐34 with decreased acidity offers around 70 % selectivity for C₂–C₄ olefins at about 10 % CO conversion. The micro‐ to nanoscale proximity of the components favors the lower olefin selectivity.     

SAPO-34分子筛合成中的主客体电荷平衡与硅分布(英文)

SAPO-34分子筛的硅磷酸铝组成与菱沸石笼结构孔道促进了甲醇高效转化为乙烯、丙烯(MTO)的反应,以其为催化剂的工业过程不断取得进步.然而,MTO反应过程中SAPO-34分子筛的迅速失活成为困扰该过程的重要问题.研究发现,反应中形成的多环芳烃阻塞了SAPO-34分子筛晶粒表面的笼结构孔道,甲醇分子难以向晶体内部扩散,致使分子筛在其活性中心未曾充分利用之前便己失活.为此,纳米晶粒SAPO-34的合成引起了人们的广泛兴趣,通过提高分子筛晶体的利用率有限地延长了催化剂的MTO反应寿命.但反应后催化剂的结焦量明显增加,说明引起SAPO-34结焦的因素不因晶粒的减小而受到抑制.我们曾研究了无硅A1P04-34分子筛的MTO反应,发现初始活性良好的催化剂在未结焦的情况下却因为活性中心的缺失而失活.显然,SAPO-34的MTO反应活性及其结焦均与其酸性密切相关,而酸性取决于其结构中的硅含量与硅分布.我们通过单晶结构解析获得了二乙胺(DEA)与哌嗪(PIPZ)导向合成SAPO-34的晶体结构,并从文献获得了四乙基氢氧化铵(TEAOH)、三乙胺(TEA)、吗啉(MOR)为模板剂合成SAPO-34的晶体结构.按照SAPO-34结构中菱沸石笼内形成的模板剂阳离子的电荷数(R)对不同模板剂导向合成的SAPO-34加以分类:TEAOH,TEA(R~+);DEA,MOR(2R~+);PIPZ(2R~(2+)).它们不因SAPO-34合成条件的变化而改变.依据分子筛骨架负电荷与SAPO-34菱沸石笼内模板剂阳离子正电荷平衡的原则(主客体电荷平衡),模板剂的类型决定SAPO-34骨架负电荷数,即引入硅形成的酸中心密度;酸中心的强度则取决于合成体系中硅的加入量.由此可以给出不同类型模板剂导向合成SAPO-34骨架中的最低硅含量(形成隔离硅原子).R~+型模板剂SiO_2/Al_2O_3为0.11;2R~+型模板剂为0.22;2R~(2+)型模板剂为0.44.合成体系中硅加入量的增加,会在SAPO-34骨架中形成"硅岛"结构.然而,我们的研究表明,"硅岛"的形成同样受到主客体电荷平衡原则的制约.通过结构分析发现,一个独立的"五硅岛"至少为6个相邻的菱沸石笼所分享,而每个"五硅岛"仅能形成3个负电荷.以R~+型模板剂导向合成的SAPO-34为例,需要6个骨架负电荷来平衡6个菱沸石笼中的R~+电荷,因此,除了"五硅岛"的3个负电荷,还要在这些笼骨架上形成3个"孤立"硅原子.该类模板剂导向合成SAPO-34,形成"五硅岛"的最低SiO_2/Al_2O_3摩尔比(硅含量)为0.45.进一步分析可知,在相邻的7个菱沸石笼之间可以分别形成"八硅岛"、"十一硅岛",而"十四硅岛"只能形成于相邻的10个菱沸石笼之间.同理,每种"硅岛"的形成都要伴随相应数目的"孤立"硅原子共同来平衡菱沸石笼内的R~+电荷.对于以2R~+型模板剂导向合成的SAPO-34,仍然是6个相邻的菱沸石笼分享"五硅岛",但是,每个菱沸石笼内的正电荷阳离子数增加了一倍,为满足主客体电荷平衡,需要形成更多"孤立"硅原子.由此可见,随着菱沸石笼内模板剂电荷数的增加,骨架的负电荷密度增大,给SAPO-34带来了更多酸中心,无论硅以"孤立"硅原子形式分布,还是形成"硅岛".同时,"硅岛"伴随"孤立"硅原子的共同存在也使我们理解了~(29)Si MAS NMR中的一个独特现象:在硅含量很高时形成了"硅岛",可是却存在着很强的属于"孤立"硅原子的谱峰.     

Organic‐Free Synthesis of Silicoaluminophosphate Molecular Sieves

Silicoaluminophosphate (SAPO) molecular sieves are an important class of microporous materials and are useful for industrial catalysis and separations. They have been synthesized exclusively by the use of expensive and environmentally unfriendly organic structure‐directing agents. Now the synthesis of SAPO molecular sieves is reported with MER, EDI, GIS, and ANA topologies under wholly inorganic conditions. Multinuclear MAS NMR analyses demonstrate the presence of Si, Al, and P atoms in their frameworks. These SAPO materials all have unusually high framework charge densities (0.25–0.46), owing to the small size of alkali metal cations used as an inorganic structure‐directing agent. A continuous Si increase in the synthesis gel for MER‐type SAPO molecular sieves led to the formation of framework Si(0Al) units, decreasing the number of extra‐framework cations per unit cell and thus making the resulting solid useful for CO₂ adsorption.     

Macroporous Poly(Acrylamide) Hydrogels: Swelling and Shrinking Behaviors

Macroporous poly(acrylamide) hydrogels have been synthesized by using poly(ethylene glycol) (PEG) with three different molecular weights as the pore‐forming agent. Scanning electron microscope graphs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights of PEG during the polymerization reaction. The swelling ratios of the PEG‐modified hydrogels were much higher than those for the same type of hydrogel prepared via conventional method. However, the swelling/deswelling ratios of the PEG‐modified hydrogels were affected slightly by the change in the amount of the PEG. Scanning electron microscopy experiments, together with swelling ratio studies, reveal that the PEG‐modified hydrogels are characterized by an open structure with more pores and higher swelling ratio, but lower mechanical strength, compared the conventional hydrogel. PAAm has potential applications in controlled release of macromolecular active agents.     

Effects of Coke Deposits on the Catalytic Performance of Large Zeolite H‐ZSM‐5 Crystals during Alcohol‐to‐Hydrocarbon Reactions as Investigated by a Combination of Optical Spectroscopy and Microscopy

The catalytic activity of large zeolite H‐ZSM‐5 crystals in methanol (MTO) and ethanol‐to‐olefins (ETO) conversions was investigated and, using operando UV/Vis measurements, the catalytic activity and deactivation was correlated with the formation of coke. These findings were related to in situ single crystal UV/Vis and confocal fluorescence micro‐spectroscopy, allowing the observation of the spatiotemporal formation of intermediates and coke species during the MTO and ETO conversions. It was observed that rapid deactivation at elevated temperatures was due to the fast formation of aromatics at the periphery of the H‐ZSM‐5 crystals, which are transformed into more poly‐aromatic coke species at the external surface, preventing the diffusion of reactants and products into and out of the H‐ZSM‐5 crystal. Furthermore, we were able to correlate the operando UV/Vis spectroscopy results observed during catalytic testing with the single crystal in situ results.     

SAPO-34分子筛晶化过程中硅进入骨架的方式和机理

采用 Ｘ Ｒ Ｄ, Ｓ Ｅ Ｍ, Ｉ Ｒ 和 Ｎ Ｍ Ｒ 等手段考察了 Ｓ Ａ Ｐ Ｏ３４ 分子 筛的晶化过 程,深入研 究了晶化过程中硅进入 Ｓ Ａ Ｐ Ｏ３４ 晶格 骨架的方式和机理． 结果表明 ,在 Ｓ Ａ Ｐ Ｏ３４ 分子筛的整个晶化过程中没有 Ａｌ Ｐ Ｏ３４ 分 子筛晶相生成． 在 初始 凝 胶的 制备 过 程中, 模板 剂 的添 加和 混 合凝 胶的 老 化处 理对 Ｓ Ａ Ｐ Ｏ３４ 晶化过程的进行起着关键性的作用． 晶化前 期（ ＜ ２５ ｈ） , 硅原子直接参与晶核的形成和晶粒的长大过程,形成 Ｓｉ（４ Ａｌ） 结构,此阶段基本上 可以排除硅取代磷机理的作用; 晶化后期（ ＞ ２５ ｈ） ,少量硅以取代方式进入分子 筛骨架形成 Ｓｉ（ ｎ Ａｌ）（ ｎ ＝ ０ ～４） 多种硅结构     

Monolayer Two‐dimensional Molecular Crystals for an Ultrasensitive OFET‐based Chemical Sensor

The sensitivity of conventional thin‐film OFET‐based sensors is limited by the diffusion of analytes through bulk films and remains the central challenge in sensing technology. Now, for the first time, an ultrasensitive (sub‐ppb level) sensor is reported that exploits n‐type monolayer molecular crystals (MMCs) with porous two‐dimensional structures. Thanks to monolayer crystal structure of NDI3HU‐DTYM2 (NDI) and controlled formation of porous structure, a world‐record detection limit of NH₃ (0.1 ppb) was achieved. Moreover, the MMC‐OFETs also enabled direct detection of solid analytes of biological amine derivatives, such as dopamine at an extremely low concentration of 500 ppb. The remarkably improved sensing performances of MMC‐OFETs opens up the possibility of engineering OFETs for ultrasensitive (bio)chemical sensing.     

晶种存在形态对所合成的SAPO-34分子筛性质及其甲醇转化催化性能的影响

采用常规水热合成法、添加粉末晶种和添加含有分子筛前驱体的液相晶种等方法制备了低硅铝比的SAPO-34分子筛。采用XRD、SEM、FT-IR及TPD等表征手段研究了合成方法对晶体结构、形貌、晶粒粒径及酸性的影响。并在固定床上对比了其甲醇转化制烯烃的催化性能差异。结果表明,晶种存在形态对分子筛的结晶度影响不大,但影响了硅在骨架中的分布、晶粒粒径和酸性等。与添加粉末晶种相比,采用含有分子筛前驱体的液相晶种法更有利于减小分子筛晶粒粒径,降低分子筛酸性,提高低碳烯烃选择性。     

Seed‐Assisted,One‐Pot Synthesis of Hollow Zeolite Beta without Using Organic Structure‐Directing Agents

Hollow aluminosilicate zeolite beta was successfully synthesized by adding CIT‐6, that is, zincosilicate zeolite, which has the same topology as beta, as seeds to the Na‐aluminosilicate gel without the need for organic structure‐directing agents. One important factor in the successful organic structure‐directing agent (OSDA)‐free synthesis of hollow beta crystals is the solubility of the seed crystals in alkaline media. CIT‐6 was less stable than aluminosilicate zeolite beta in alkaline media and the solubility changed depending on whether the crystals were calcined or not. The hollow beta could be obtained by using the uncalcined CIT‐6 seed crystals. The volumes of intra‐crystalline voids were tuned by changing the reaction time and the initial gel compositions, such as the SiO₂/Al₂O₃ and Na₂O/SiO₂ ratios. We estimated that the intra‐crystalline voids were formed through the dissolution of the seed crystals, just after the crystal growth of new beta on the outer surface of the seeds. In addition, new crystal growth toward inside of the void was also observed by TEM. On the basis of the characterization data, such as chemical analysis, N₂‐adsorption/desorption measurements, and TEM observation, a formation mechanism of the intra‐crystalline voids is proposed and discussed.     

磷铝系列分子筛催化剂的制备、表征及催化丁烷转化反应的研究

 合成了AlPO－11,SAPO－11及其含杂原子Co或Mn的磷铝系列分子筛．XRD结果证实,合成产物均具有AEL分子筛晶体结构．用X射线荧光光谱测定了晶体的元素组成,并用NH3－TPD考察了样品的酸性和酸分布．在以合成的分子筛为基质所制备的催化剂上进行了丁烷异构化和一步异构脱氢反应．结果表明,载0．3％Pd的SAPO－11分子筛催化剂具有最高的丁烷异构化选择性,而在丁烷一步异构脱氢反应中,含金属杂原子的催化剂具有更高的异丁烯选择性．     

Melt crystallization and morphology of poly(ε‐caprolactone)‐poly(ethylene glycol) diblock copolymers with different compositions and molecular weights

Ring opening polymerization of ε‐caprolactone was realized in the presence of monomethoxy poly(ethylene glycol) with M_n = 1000 and 2000, using Zn(La)₂ as catalyst. The resulting PCL‐PEG diblock copolymers with CL/EO repeat unit molar ratios from 0.2 to 3.0 were characterized by using DSC, WAXD, SEC, and ¹H NMR. The crystal phase of PCL blocks exist in all polymers, and the crystallization ability of PCL blocks increases with CL/EO ratio. PEG blocks are able to crystallize for copolymers with CL/EO below 1.0 only. Melt crystallization results were analyzed with Avrami equation. The Averami exponent n is around 3.0 in most cases, in agreement with heterogeneous nucleation with three dimensional growth. The morphology of the crystals was observed by using POM. Rod‐like crystals were found to grow in 1, 3 or 2, 4 quadrants for samples with low molecular weights. In the case of a copolymer with M_n,PEG = 2000 and M_n,PCL = 800, PEG blocks could crystallize and grow on PCL crystals after PCL finished to form rod‐like crystals, leading to formation of poorly or well structured spherulites. The spherulite growth rate (G) was determined at different crystallization temperatures (T_c) ranging from 9 to 49 °C. All the copolymers present a steady G decrease with increasing crystallization temperature due to lower undercooling. On the other hand, increase of CL/EO ratio leads to increase of G in the same T_c range. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 286–293, 2010     

Theoretical study of the CO catalytic oxidation on Au/SAPO‐11 zeolite

Quantum chemistry calculations were carried out, using ONIOM2 methodology, to investigate the CO adsorption and oxidation on gold supported on Silicoaluminophospates (SAPO) molecular sieves Au/SAPO‐11 catalysts. Two models were studied, one containing one Au atom per site (Au? SAPO‐11), and the other with two Au atoms per site (Au₂? SAPO‐11). The results reveal that the CO adsorption and oxidation are exothermic on Au/SAPO11 with an ΔE of ?41.0 kcal/mol and ΔE = ?52.0 kcal/mol, for the adsorption and oxidation, respectively. On the Au₂? SAPO‐11 model, the CO adsorption and oxidation reaction occur, with a ΔE of ?29.7 kcal/mol and ?52 kcal/mol, respectively. According to our results, the oxidation reaction exhibits an Eley‐Rideal type mechanism with adsorbed CO. The theoretical calculations reveal that this type of material could be interesting to disperse Au and consequently to strengthen its catalytic use for different reactions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2573–2582, 2010     

Catalytic conversion of methanol to olefins over rare earth (La, Y) modified SAPO-34

SAPO-34 modified with lanthanum and yttrium exhibited higher selectivity to light olefins, lower methane formation, and longer lifetime (prolonged by 20%) than the parent SAPO-34 in the process of methanol conversion to olefins. The modified catalytic performance could be ascribed to the incorporation of La³⁺ and Y³⁺ into the framework of SAPO-34.     

Transition Metal Complexes Containing Functionalized Organoimido and Phosphaneiminato Ligands

Two different types of modified imido and phosphaneiminato ligands are investigated, namely chelate ligands and redox‐functionalised ligands. The first examples of di(organoimido)chromium as well as di(phosphaneiminato)titanium and niobium chelates are described. Furthermore, the first complexes containing redox‐functionalised organoimido ligands are presented, together with the first structurally characterised redox‐functionalised phosphaneiminato complex. Compounds of the type [(RN)₂M(CH₂Ph)₂] (M = Cr, Mo) are used as catalysts for the (co‐)polymerisation of the polar olefins methyl methacrylate, acrylonitrile and vinyl acetate. A range of X‐ray crystal structure determinations provide clear evidence for the quantum‐chemical result that, similar to organoimido complexes, the potential energy well for the angle at the nitrogen atom is very shallow for phosphaneiminato complexes.