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.     

Dual‐Mesoporous ZSM‐5 Zeolite with Highly b‐Axis‐Oriented Large Mesopore Channels for the Production of Benzoin Ethyl Ether

Dual‐mesoporous ZSM‐5 zeolite with highly b axis oriented large mesopores was synthesized by using nonionic copolymer F127 and cationic surfactant CTAB as co‐templates. The product contains two types of mesopores—smaller wormlike ones of 3.3 nm in size and highly oriented larger ones of 30–50 nm in diameter along the b axis—and both of them interpenetrate throughout the zeolite crystals and interconnect with zeolite microporosity. The dual‐mesoporous zeolite exhibits excellent catalytic performance in the condensation of benzaldehyde with ethanol and greater than 99 % selectivity for benzoin ethyl ether at room temperature, which can be ascribed to the zeolite lattice structure offering catalytically active sites and the hierarchical and oriented mesoporous structure providing fast access of reactants to these sites in the catalytic reaction. The excellent recyclability and high catalytic stability of the catalyst suggest prospective applications of such unique mesoporous zeolites in the chemical industry.     

Hierarchical mesoporous zeolites: direct self-assembly synthesis in a conventional surfactant solution by kinetic control over the zeolite seed formation

By kinetic control over the zeolite seed formation, we report the direct fabrication of hierarchical mesoporous zeolites using hexadecyl trimethyl ammonium bromide (CTAB) as the soft template in a conventional solution route. Nanometer-sized, subnanocrystal-type zeolite seeds with a high degree of polymerization are essential to prevent the formation of a separate amorphous mesoporous phase and the phase separation between the mesophase and zeolite crystals in the presence of CTAB and a certain amount of ethanol. The mechanisms for the formation of hierarchically porous zeolites in the solution process, including the effect of mother liquid aging, formation of subnanocrystal zeolite seeds and their self-assembly effect with CTAB, and the role of ethanol are proposed and discussed in detail. The prepared mesoporous ZSM-5 zeolite showed much higher catalytic activity than conventional counterparts for aldol condensations involving large molecules, especially in the synthesis of vesidryl.     

Textural manipulation of mesoporous materials for hosting of metallic nanocatalysts

The preparation and stabilization of nanoparticles are becoming very crucial issues in the field of so-called "nanocatalysis". Recent developments in supramolecular self-assembled porous materials have opened a new way to get nanoparticles hosted in the channels of such materials. In this paper, a new approach towards monodisperse and thermally stable metal nanoparticles by confining them in ordered mesoporous materials is presented, and three aspects are illustrated. Firstly, the recent progress in the functional control of mesoporous materials will be briefly introduced, and the rational tuning of the textures, pore size, and pore length is demonstrated by controlling supramolecular self-assembly behavior. A novel synthesis of short-pore mesoporous materials is emphasized for their easy mass transfer in both biomolecule absorption and the facile assembly of metal nanocomposites within their pore channels. In the second part, the different routes for encapsulating monodisperse nanoparticles inside channels of porous materials are discussed, which mainly includes the ion-exchange/conventional incipient wetness impregnation, in situ encapsulation routes, organometallic methodologies, and surface functionalization schemes. A facile in situ autoreduction route is highlighted to get monodisperse metal nanoparticles with tunable sizes inside the channels of mesoporous silica. Finally, confinement of mesoporous materials is demonstrated to improve the thermal stability of monodisperse metal nanoparticles catalysts and a special emphasis will be focused on the stabilization of the metal nanoparticles with a low Tammann temperature. Several catalytic reactions concerning the catalysis of nanoparticles will be presented. These uniform nanochannels, which confine monodisperse and stable metal nanoparticles catalysts, are of great importance in the exploration of size-dependent catalytic chemistry and further understanding the nature of catalytic reactions.     

Multipore Zeolites: Synthesis and Catalytic Applications

In the last few years, important efforts have been made to synthesize so‐called “multipore” zeolites, which contain channels of different dimensions within the same crystalline structure. This is a very attractive subject, since the presence of pores of different sizes would favor the preferential diffusion of reactants and products through those different channel systems, allowing unique catalytic activities for specific chemical processes. In this Review we describe the most attractive achievements in the rational synthesis of multipore zeolites, containing small to extra‐large pores, and the improvements reported for relevant chemical processes when these multipore zeolites have been used as catalysts.     

二维分子筛的制备及其催化应用研究进展

沸石分子筛是一种具有独特孔道结构的硅铝酸盐晶体,因其具有较大的比表面积、优异的孔道择形性、良好的热稳定性以及适宜的酸性质等特点,被广泛应用于催化、吸附、分离等领域。与常规三维沸石分子筛相比,二维分子筛由于其独特的形貌结构带来的可调变的多级孔结构、适宜的表面酸性以及良好的扩散传质性能等优点,已在吸附和催化领域显示出巨大的应用潜力。本文系统总结了二维MFI、SAPO-34、MCM-n、Y型分子筛等的合成以及此类分子筛催化应用研究方面的最新进展。最后,对二维沸石分子筛材料的新合成方法及新应用领域进行了展望。     

Probing the Different Life Stages of a Fluid Catalytic Cracking Particle with Integrated Laser and Electron Microscopy

While cycling through a fluid catalytic cracking (FCC) unit, the structure and performance of FCC catalyst particles are severely affected. In this study, we set out to characterize the damage to commercial equilibrium catalyst particles, further denoted as ECat samples, and map the different pathways involved in their deactivation in a practical unit. The degradation was studied on a structural and a functional level. Transmission electron microscopy (TEM) of ECat samples revealed several structural features; including zeolite crystals that were partly or fully severed, mesoporous, macroporous, and/or amorphous. These defects were then correlated to structural features observed in FCC particles that were treated with different levels of hydrothermal deactivation. This allowed us not only to identify which features observed in ECat samples were a result of hydrothermal deactivation, but also to determine the severity of treatments resulting in these defects. For functional characterization of the ECat sample, the Brønsted acidity within individual FCC particles was studied by a selective fluorescent probe reaction with 4‐fluorostyrene. Integrated laser and electron microscopy (iLEM) allowed correlating this Brønsted acidity to structural features by combining a fluorescence and a transmission electron microscope in a single set‐up. Together, these analyses allowed us to postulate a plausible model for the degradation of zeolite crystals in FCC particles in the ECat sample. Furthermore, the distribution of the various deactivation processes within particles of different ages was studied. A rim of completely deactivated zeolites surrounding each particle in the ECat sample was identified by using iLEM. These zeolites, which were never observed in fresh or steam‐deactivated samples, contained clots of dense structures. The structures are proposed to be carbonaceous deposits formed during the cracking process, and seem resistant towards burning off during catalyst regeneration.     

Catalytic and Mechanistic Insights of the Low‐Temperature Selective Oxidation of Methane over Cu‐Promoted Fe‐ZSM‐5

The partial oxidation of methane to methanol presents one of the most challenging targets in catalysis. Although this is the focus of much research, until recently, approaches had proceeded at low catalytic rates (<10 h^?1), not resulted in a closed catalytic cycle, or were unable to produce methanol with a reasonable selectivity. Recent research has demonstrated, however, that a system composed of an iron‐ and copper‐containing zeolite is able to catalytically convert methane to methanol with turnover frequencies (TOFs) of over 14 000 h^?1 by using H₂O₂ as terminal oxidant. However, the precise roles of the catalyst and the full mechanistic cycle remain unclear. We hereby report a systematic study of the kinetic parameters and mechanistic features of the process, and present a reaction network consisting of the activation of methane, the formation of an activated hydroperoxy species, and the by‐production of hydroxyl radicals. The catalytic system in question results in a low‐energy methane activation route, and allows selective C₁‐oxidation to proceed under intrinsically mild reaction conditions.