An Extra‐Large‐Pore Zeolite with Intersecting 18‐, 12‐, and 10‐Membered Ring Channels

Zeolites with extra‐large pores have attracted great attention because of their important applications such as in hydrocracking, catalysis, and separation of large molecules. Despite much progress has been made during the past decades, the synthesis of these materials remains a big challenge. A new extra‐large‐pore zeolite NUD‐1 (Nanjing University Du’s group zeolite no. 1) is synthesized by using an approach based on supramolecular self‐assemblies of small aromatic organic cations as structure‐directing agents. NUD‐1 possesses interconnecting 18‐, 12‐, and 10‐membered ring channels, built from the same building units as those of ITQ‐33 and ITQ‐44. There coexist single 3‐membered ring, double‐3‐membered ring and double‐4‐membered ring secondary building units in NUD‐1, which have not been seen in any other zeolites.     

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.     

High‐Silica Zeolite SSZ‐61 with Dumbbell‐Shaped Extra‐Large‐Pore Channels

The synthesis of the high‐silica zeolite SSZ‐61 using a particularly bulky polycyclic structure‐directing agent and the subsequent elucidation of its unusual framework structure with extra‐large dumbbell‐shaped pore openings are described. By using information derived from a variety of X‐ray powder diffraction and electron microscopy techniques, the complex framework structure, with 20 Si atoms in the asymmetric unit, could be determined and the full structure refined. The Si atoms at the waist of the dumbbell are only three‐connected and are bonded to terminal O atoms pointing into the channel. Unlike the six previously reported extra‐large‐pore zeolites, SSZ‐61 contains no heteroatoms in the framework and can be calcined easily. This, coupled with the possibility of inserting a catalytically active center in the channel between the terminal O atoms in place of H⁺, afford SSZ‐61 intriguing potential for catalytic applications.     

An Extra‐Large‐Pore Zeolite with 24×8×8‐Ring Channels Using a Structure‐Directing Agent Derived from Traditional Chinese Medicine

Extra‐large‐pore zeolites have attracted much interest because of their important applications for processing larger molecules. Although great progress has been made in academic science and industry, it is challenging to synthesize these materials. A new extra‐large‐pore zeolite SYSU‐3 (Sun Yat‐sen University no. 3) has been synthesized by using a novel sophoridine derivative as an organic structure‐directing agent (OSDA). The framework structure was solved and refined using continuous rotation electron diffraction (cRED) data from nanosized crystals. SYSU‐3 exhibits a new zeolite framework topology, which has the first 24×8×8‐ring extra‐large‐pore system and a framework density (FD) as low as 11.4 T/1000 ų. The unique skeleton of the OSDA plays an essential role in the formation of the distinctive zeolite structure. This work provides a new perspective for developing new zeolitic materials by using alkaloids as cost‐effective OSDAs.     

EU‐12: A Small‐Pore,High‐Silica Zeolite Containing Sinusoidal Eight‐Ring Channels

Zeolite EU‐12, the framework structure of which has remained unsolved during the past 30 years, is synthesized at a specific SiO₂/Al₂O₃ ratio using choline as an organic structure‐directing agent, with both Na⁺ and Rb⁺ ions present. Synchrotron powder X‐ray diffraction and Rietveld analyses reveal that the EU‐12 structure has a two‐dimensional 8‐ring channel system. Among the two distinct 8‐ring (4.6×2.8 and 5.0×2.7 Å) channels along c axis, the smaller one interconnects with the sinusoidal 8‐ring (4.8×3.3 Å) channel along a axis. The other large one is simply linked up with the sinusoidal channel by sharing 8‐rings (4.8×2.6 Å) in the ac plane. The proton form of EU‐12 was found to show a considerably higher ethene selectivity in the low‐temperature dehydration of ethanol than H‐mordenite, the best catalyst for this reaction.     

An Extra‐Large‐Pore Pure Silica Zeolite with 16×8×8‐Membered Ring Pore Channels Synthesized using an Aromatic Organic Directing Agent

Extra‐large‐pore zeolites for processing large molecules have long been sought after by both the academia and industry. However, the synthesis of these materials, particularly extra‐large‐pore pure silica zeolites, remains a big challenge. Herein we report the synthesis of a new extra‐large‐pore silica zeolite, designated NUD‐6, by using an easily synthesized aromatic organic cation as structure‐directing agent. NUD‐6 possesses an intersecting 16×8×8‐membered ring pore channel system constructed by four‐connected (Q⁴) and unusual three‐connected (Q³) silicon species. The organic cations in NUD‐6 can be removed in nitric acid to yield a porous material with high surface area and pore volume. The synthesis of NUD‐6 presents a feasible means to prepare extra‐large pore silica zeolites by using assembled aromatic organic cations as structure‐directing agents.     

IDM‐1: A Zeolite with Intersecting Medium and Extra‐Large Pores Built as an Expansion of Zeolite MFI

IDM‐1 is a new silica zeolite with an ordered and well‐defined framework constructed by alternating pentasil layers and interrupted layers, giving rise to an intersecting system of straight medium pores and undulating extra‐large lobed pores. This unique structure was solved by rotation electron diffraction and refined against synchrotron powder X‐ray diffraction data. Despite the presence of both Si(OSi)₃(OH) and Si(OSi)₂(OH)₂ sites, this new zeolite presents high thermal stability, withstanding calcination even to 1000 °C. The location of defects at specific sites of the structure results in alternating hydrophobic SiO₂ and hydrophilic SiO_(2?x)(OH)_2x intracrystalline regions. This peculiar combination of intersecting medium and extra‐large pores and alternating regions of different chemical character may provide this zeolite with unique catalytic properties.     

A Germanosilicate Structure with 11×11×12‐Ring Channels Solved by Electron Crystallography

Zeolites have been widely used in industry owing to their ordered micropores and stable frameworks. The pore sizes and shapes are the key parameters that affect the selectivity and efficiency in their applications in catalysis, sorption, and separation. Zeolites with pores defined by 10 and 12 TO₄ tetrahedra are often used for various catalytic processes. To optimize the performance of zeolites, it is extremely desirable to fine‐tune the pore sizes/shapes. The first germanosilicate zeolite with a three‐dimensional 11×11×12‐ring channel system, PKU‐16 (PKU, Peking University) is presented. Nanosized PKU‐16 was structurally characterized by the new three‐dimensional rotation electron diffraction (RED) technique. PKU‐16 is structurally related to the zeolite β polymorph C (BEC, 12×12×12‐ring channels) by rotating half of the four‐rings in double mtw units.     

Facile Synthesis,Characterization, and Catalytic Behavior of a Large‐Pore Zeolite with the IWV Framework

Large‐pore microporous materials are of great interest to process bulky hydrocarbon and biomass‐derived molecules. ITQ‐27 (IWV) has a two‐dimensional pore system bounded by 12‐membered rings (MRs) that lead to internal cross‐sections containing 14 MRs. Investigations into the catalytic behavior of aluminosilicate (zeolite) materials with this framework structure have been limited until now due to barriers in synthesis. The facile synthesis of aluminosilicate IWV in both hydroxide and fluoride media is reported herein using simple, diquaternary organic structure‐directing agents (OSDAs) that are based on tetramethylimidazole. In hydroxide media, a zeolite product with Si/Al=14.8–23.2 is obtained, while in fluoride media an aluminosilicate product with Si/Al up to 82 is synthesized. The material produced in hydroxide media is tested for the hydroisomerization of n‐hexane, and results from this test reaction suggest that the effective pore size of zeolites with the IWV framework structure is similar to but slightly larger than that of ZSM‐12 (MTW), in fairly good agreement with crystallographic data.     

A Stable Heterocyclic Amino(phosphanylidene‐σ4‐phosphorane) Germylene

A new stable heterocyclic germylene, in which the divalent germanium atom lies between a nitrogen atom and a phosphanylidene phosphorane group, was synthesized. Experimental and theoretical studies revealed the peculiar effect of phosphanylidene phosphorane substituent, which is a stronger π‐donor towards germanium than an amino group is. Because of the weak phosphorus–germanium π‐bond, this new germylene compound shows an enhanced reactivity compared to classical N‐heterocyclic germylenes.     

PST‐24: A Zeolite with Varying Intracrystalline Channel Dimensionality

Herein we report the synthesis, structure solution, and catalytic properties of PST‐24, a novel channel‐based medium‐pore zeolite. This zeolite was synthesized via the excess fluoride approach. Electron diffraction shows that its structure is built by composite cas‐zigzag (cas‐zz) building chains, which are connected by double 5‐ring (d5r) columns. While the cas‐zz building chains are ordered in the PST‐24 framework, the d5r columns adopt one of two possible arrangements; the two adjacent d5r columns are either at the same height or at different heights, denoted arrangements S and D, which can be regarded as open and closed valves that connect the channels, respectively. A framework with arrangement D only has a 2D 10‐ring channel system, whereas that with arrangement S only contains 3D channels. In actual PST‐24 crystals, the open and closed valves are almost randomly dispersed to yield a zeolite framework where the channel dimensionality varies locally from 2D to 3D.