NaOH后处理对多级孔Hβ分子筛上木质素催化热解性能的影响

采用碱性条件下"后处理"脱硅的方法,制备了一系列多级孔Hβ分子筛,考察了Na OH浓度对Hβ分子筛上木质素催化热解性能的影响。结果表明,当Na OH浓度小于0.2 mol/L时,碱处理后的多级孔Hβ分子筛的介孔数量增加,木质素热解液体产物的收率随着Na OH浓度提高而显著增加。当Na OH浓度小于0.5 mol/L时,碱处理可以保持多级孔Hβ分子筛的微孔结构基本不被破坏,木质素催化热解具有较好的脱氧效果;产物以芳烃为主,含氧化合物的收率始终小于3%。当Na OH的浓度增加到1 mol/L时,会造成Hβ分子筛过度脱硅,骨架坍塌;由于Hβ分子筛的多级孔结构被破坏,此时不仅木质素热解液体产物的收率降低,而且脱氧效果变差。     

Y沸石和多级孔Y沸石封装CuPhen配合物催化性能的比较

选用常规Y沸石和经后处理法制备的多级孔Y沸石为主体,采用自由配体法将铜菲咯啉(CuPhen)配合物封装在不同Y沸石中,制备了CuPhen/Y复合催化材料。采用X射线衍射、TEM、紫外-可见光谱、N_2吸附-脱附、ICP和TG等手段对所制备复合催化材料的物化性质进行了较为详细的表征,并对封装在不同Y沸石主体中的铜配合物在不同尺寸大小反应底物中的催化氧化性能进行了比较研究。结果表明,在以双氧水为氧化剂的反应体系中,封装于多级孔Y沸石中的铜配合物在不同环烷烃氧化反应中的催化活性均高于封装在常规Y沸石中的催化活性,体现出多级孔Y沸石更为优越的主体性能。此外,同封装于常规Y沸石中的铜配合物一样,封装在多级孔Y沸石主体中的金属配合物催化剂也具有良好的稳定性。     

Transformations of 5-(2-arylethynyl)-2-methyl-2H-tetrazoles under superelectrophilic activation

Reaction of 5-arylethynyl-2-methyl-2H-tetrazoles (acetylene tetrazoles) with arenes under the action of Brønsted superacid CF₃SO₃H or acidic zeolite HUSY CBV-720 gives rise to E-/Z-5-(2,2-diarylethenyl)-2-methyl-2H-tetrazoles, as products of hydroarylation of acetylene bond, in yields up to 98% with predominant formation of E-isomers. Cationic intermediates of these reactions have been studied theoretically by DFT calculations. Addition of CF₃SO₃H to the triple bond of acetylene tetrazoles leads to the corresponding E-/Z-vinyl triflates in high yields. Hydration of triple bond in these tetrazoles in H₂SO₄ results in the formation of 5-(2-aryl-2-oxoethyl)-2-methyl-2H-tetrazoles. Tandem hydroarylation-ionic hydrogenation of acetylene tetrazoles in the systems acid(CF₃SO₃H or AlCl₃)-arene-cyclohexane affords 5-(2,2-diarylethyl)-2-methyl-2H-tetrazoles.     

Integrated Transmission Electron and Single‐Molecule Fluorescence Microscopy Correlates Reactivity with Ultrastructure in a Single Catalyst Particle

Establishing structure–activity relationships in complex, hierarchically structured nanomaterials, such as fluid catalytic cracking (FCC) catalysts, requires characterization with complementary, correlated analysis techniques. An integrated setup has been developed to perform transmission electron microscopy (TEM) and single‐molecule fluorescence (SMF) microscopy on such nanostructured samples. Correlated structure–reactivity information was obtained for 100 nm thin, microtomed sections of a single FCC catalyst particle using this novel SMF‐TEM high‐resolution combination. High reactivity in a thiophene oligomerization probe reaction correlated well with TEM‐derived zeolite locations, while matrix components, such as clay and amorphous binder material, were found not to display activity. Differences in fluorescence intensity were also observed within and between distinct zeolite aggregate domains, indicating that not all zeolite domains are equally active.     

A Zeolite Family Nonjointly Built from the 1,3‐Stellated Cubic Building Unit

From a technological point of view, the synthesis of new high‐silica zeolites is of prime importance owing to their high potential as industrial catalysts and catalyst supports. Two such materials have been synthesized which are made up of the 1,3‐stellated cubic unit (hexahedral ([4²5⁴]) bre unit) as a secondary building unit, with the aid of existing imidazolium‐based structure‐directing agents under “excess fluoride” conditions. One of them, denoted PST‐21, is the first aluminosilicate zeolite consisting of 9‐ring apertures solely; it displays exceptional activity towards steering the skeletal isomerization of 1‐butene to isobutene and bridges the gap between small‐ and medium‐pore structures. A series of hypothetical structures are also described that are nonjointly built from the bre unit; all of these structures are chemically feasible and will thus be helpful in designing the synthesis of novel zeolites containing 9‐ring and/or 10‐ring channels.     

Directing Aluminum Atoms into Energetically Favorable Tetrahedral Sites in a Zeolite Framework by Using Organic Structure‐Directing Agents

The Al location in zeolites can have massive influences on the zeolite properties because it directly correlates with the cationic active sites. Herein, the synthesis of IFR zeolites with controlled Al distribution at different tetrahedral sites (T sites) is reported. The computational calculations suggest that organic structure‐directing agents (OSDAs) used for zeolite synthesis can alter the energetically favorable T sites for Al. Zeolite products synthesized under identical conditions but with different OSDAs are found to have altered fractions of Al at different T sites in accordance with the energies derived from the zeolite–OSDA complexes. Our finding thus provides evidence for the ability of OSDAs to direct Al into more energetically favorable T sites, thereby offering rational synthetic guidelines for the selective placement of Al into specific crystallographic sites.     

Synthesis of Extra‐Large‐Pore Zeolite ECNU‐9 with Intersecting 14*12‐Ring Channels

Highly crystalline and (hydro)thermally stable zeolites with extra‐large pores [≥14‐ring (14‐R)] are desirable as catalysts. A novel zeolite, ECNU‐9, with an intersecting 14*12‐R channel system was rationally designed and synthesized by a building block strategy, in which the interlayer expansion of a two‐dimensional silicate structure was realized by combining organic amine assisted layer‐stacking reorganization and subsequent silylation with a square‐shaped single 4‐ring (S4R) silane, 1,3,5,7‐tetramethylcyclotetrasiloxane (TMCS). The PLS‐3 precursor was disassembled into building blocks and then intercalated with flexible and removable organic amine pillars to offer enough interlayer spacing for accommodating TMCS molecules. The additionally introduced building blocks interconnected the neighboring layers to construct new 14‐R and 12‐R pores. ECNU‐9 possesses a well‐ordered structure with a novel topology. The corresponding Ti‐ECNU‐9, with tetrahedral Ti ions in the framework, showed superior catalytic performance in the selective epoxidation of bulky alkenes.     

Specific Sorption Sites for Nitrogen in Zeolites NaLSX and LiLSX

Specific sorption sites for nitrogen, N₂, in NaLSX and LiLSX zeolites were investigated using a DRIFT spectroscopic method. Sorption of molecular hydrogen, H₂, by NaLSX or LiLSX zeolite at 77 K with DRIFT control of perturbation of sorbed molecules allowed to discriminate two or three different types of specific sorption sites in the respective zeolites. Their H–H stretching frequencies are 4077 and 4081 cm^–1 for NaLSX, and 4061, 4084 and 4129 cm^–1 for LiLSX. With reference to an independent investigation by methods of both sorption thermodynamics and molecular modeling for N₂ sorption on LiLSX, the first two of the corresponding bands were ascribed to H₂ sorption on lithium cations, Li⁺, localized in supercages of the faujasite, FAU, zeolite framework at sites SIII and SIII, while the latter band most likely belongs to H₂ sorption on Li⁺ cations at sites SII, and on hydroxyl groups, OH. Sorption of N₂ by Li⁺ cations at sites SIII and SIII is the strongest, resulting in a decrease of intensity of the corresponding DRIFT bands that stem from subsequent H₂ sorption. Nitrogen sorption by Li⁺ cations at sites SII is much weaker. Sorption of N₂ on Na⁺ cations at sites SIII in NaLSX zeolite is also stronger than by Na⁺ cations at sites SII.     

改性ZSM-5分子筛催化甲苯、甲醇苯环烷基化反应的研究进展

综述了近三十年来国内外有关在改性ＺＳＭ－５沸石催化剂上,甲苯、甲醇苯环烷基化制备对二甲苯反应的研究状况。经过改性的ＸＳＭ－５型沸石具有合适的孔径和适当强度及数量的表面酸中心,有利于反应活性及选择性的提高。参考文献１４５篇。