Catalytic Asymmetric [8+2] Annulation Reactions Promoted by a Recyclable Immobilized Isothiourea

Higher‐order cycloaddition reactions constitute an efficient approach towards the construction of medium to large ring systems. However, enantioselective versions of these transformations remain scarce, which hampers their deployment in medicinal chemistry, or any other discipline in which homochirality is deemed crucial. Herein, we report a novel method for the production of enantiomerically enriched cycloheptatrienes fused to a pyrrolidone ring on the basis of an isothiourea‐catalyzed periselective [8+2] cycloaddition reaction between chiral ammonium enolates (generated in situ from carboxylic acids) and azaheptafulvenes. The resulting bicyclic compounds can be hydrogenated, but, most remarkably, they can also undergo completely regioselective [4+2] cycloaddition with active dienophiles to give architecturally complex polycyclic compounds in a straightforward manner.     

Self‐Templating Synthesis of Hollow Co3O4 Microtube Arrays for Highly Efficient Water Electrolysis

In spite of recent advances in the synthesis of hollow micro/nanostructures, the fabrication of three‐dimensional electrodes on the basis of these structures remains a major challenge. Herein, we develop an electrochemical sacrificial‐template strategy to fabricate hollow Co₃O₄ microtube arrays with hierarchical porosity. The resultant unique structures and integrated electrode configurations impart enhanced mass transfer and electron mobility, ensuring high activity and stability in catalyzing oxygen and hydrogen evolution reactions. Impressively, the apparent performance can rival that of state‐of‐the‐art noble‐metal and transition‐metal electrocatalysts. Furthermore, this bifunctional electrode can be used for highly efficient overall water splitting, even competing with the integrated performance of Pt/C and IrO₂/C.     

Fractal MTW Zeolite Crystals: Hidden Dimensions in Nanoporous Materials

Screw dislocation structures in crystals are an origin of symmetry breaking in a wide range of dense‐phase crystals. Preparation of such analogous structures in framework‐phase crystals is of great importance in zeolites but is still a challenge. On the basis of crystal‐structure solving and model building, it was found that the two specific intergrowths in MTW zeolite produce this complex fractal and spiral structure. With the structurally determined parameters (spiral pitch h, screw angle θ, and spatial angle ψ) of Burgers circuit, the screw dislocation structure can be constructed by two different dimensional intergrowth sections. Thus the reported complexity of various dimensions in diverse crystals can be unified.     

Preferential Siting of Aluminum Heteroatoms in the Zeolite Catalyst Al‐SSZ‐70

The adsorption and reaction properties of heterogeneous zeolite catalysts (e.g. for catalytic cracking of petroleum, partial oxidation of natural gas) depend strongly on the types and distributions of Al heteroatoms in the aluminosilicate frameworks. The origins of these properties have been challenging to discern, owing in part to the structural complexity of aluminosilicate zeolites. Herein, combined solid‐state NMR and synchrotron X‐ray powder diffraction analyses show the Al atoms locate preferentially in certain framework sites in the zeolite catalyst Al‐SSZ‐70. Through‐covalent‐bond 2D ²⁷Al{²⁹Si} J‐correlation NMR spectra allow distinct framework Al sites to be identified and their relative occupancies quantified. The analyses show that 94 % of the Al atoms are located at the surfaces of the large‐pore interlayer channels of Al‐SSZ‐70, while only 6 % are in the sub‐nm intralayer channels. The selective siting of Al atoms accounts for the reaction properties of catalysts derived from SSZ‐70.     

Redox‐Driven Migration of Copper Ions in the Cu‐CHA Zeolite as Shown by the In Situ PXRD/XANES Technique

Using quasi‐simultaneous in situ PXRD and XANES, the direct correlation between the oxidation state of Cu ions in the commercially relevant deNO_x NH₃‐SCR zeolite catalyst Cu‐CHA and the Cu ion migration in the zeolitic pores was revealed during catalytic activation experiments. A comparison with recent reports further reveals the high sensitivity of the redox‐active centers concerning heating rates, temperature, and gas environment during catalytic activation. Previously, Cu⁺ was confirmed present only in the 6R. Results verify a novel 8R monovalent Cu site, an eventually large Cu⁺ presence upon heating to high temperatures in oxidative conditions, and demonstrate the unique potential in combining in situ PXRD and XANES techniques, with which both oxidation state and structural location of the redox‐active centers in the zeolite framework could be tracked.     

Targeted Synthesis of a Zeolite with Pre‐established Framework Topology

Given their great potential as new industrial catalysts and adsorbents, the search for new zeolite structures is of major importance in nanoporous materials chemistry. However, although innumerable theoretical frameworks have been proposed, none of them have been synthesized by a priori design yet. We generated a library of diazolium‐based cations inspired from the organic structure‐directing agents (OSDAs) recently reported to give two structurally related zeolites (PST‐21 and PST‐22) under highly concentrated, excess‐fluoride conditions and compared the stabilization energies of each OSDA cation in ten pre‐established hypothetical structures. A combination of the ability of the OSDA selected in this way with the excess‐fluoride approach has allowed us to crystallize PST‐30, the targeted aluminosilicate zeolite structure. We anticipate that our approach, which aims to rationally couple computational predictions of OSDAs with an experimental setup, will advance further development in the synthesis of zeolites with desired properties.