The composite of hierarchical faujasite nanosheets and zeolitic imidazolate framework-8 (Hie-FAU-ZIF-8) has been successfully prepared via a stepwise deposition of ZIF-8 on modified zeolite surfaces. Compared to the direct deposition of metal organic frameworks (MOFs) on zeolite surfaces, ZIF-8 nanospheres were selectively attached to the external surfaces of the MOF ligand-grafted FAU crystals because of the enhancing interaction between the zeolite and MOF in the composite. In addition, the degree of surface functionalization can be greatly enhanced because of the presence of hierarchical structures. This behavior leads to an increase in the deposited MOF content, improving the hydrophobic properties of the zeolite surfaces. Interestingly, the designed hierarchical composite exhibits outstanding catalytic properties as an acid-base catalyst for the aldol condensation of 5-hydroxymethylfurfural with acetone. Compared to the isolated FAU and ZIF-8, a high yield of the product, 4-[5-(hydroxymethyl)furan-2-yl]but-3-en-2-one (67%), can be observed in the composite because of the synergistic effect between the Na-stabilized zeolite framework and the imidazolate linkers bearing basic nitrogen functions. This opens up interesting perspectives for the development of new organic and inorganic hybrid materials as heterogeneous acid-base catalysts.
The superior catalytic performance of amine-grafted hierarchical basic FAU-type zeolite nanosheets for the aldol condensation of 5-hydroxymethylfurfural (5-HMF) and acetone (Ac) has been achieved due to the synergistic effect of hierarchical structures, featuring basic active sites together with surface modification. This results in an unprecedented yield of 4-[5-(hydroxymethyl)furan-2-yl]but-3-en-2-one (HMB) close to 100%. The catalytic activity can be easily tuned by changing the degree of basicity corresponding to the nature of basic sites and surface modification.
As the catalytic performances typically depend on various factors, especially the distribution of Al species in the zeolite framework, in this contribution, hierarchical nanospherical ZSM-5 zeolites have been successfully synthesized using uniform aluminosilicate (AS) nanobeads containing silica and alumina species as a starting material to improve the Al dispersion in the framework. The synthesized zeolites were characterized by means of XRD, TEM, SEM, EDS, N 2 physisorption, 27 Al MAS NMR, and NH 3 -TPD. This example demonstrates that the use of AS nanobeads can effectively control the uniform Al distribution. Subsequently, the synthesized materials were tested for their catalytic activity in the alkylation of benzene with ethanol to ethylbenzene. Interestingly, the designed ZSM-5 nanospheres prepared by using AS nanobeads clearly exhibit an improvement of the catalytic performance in terms of benzene conversion and ethylbenzene selectivity compared with the conventional ZSM-5 and the ZSM-5 nanospheres prepared by using a typical synthesis method. The reason for the improved benzene conversion (60%) and ethylbenzene selectivity (62%) on Hie-SZSM-5-AS relates to the generated mesoporous structure as well as a homogeneous distribution of Al frameworks directed by AS nanobeads. The synthesis approach reported herein illustrates an efficient way to control Al species as well as Al distribution in the zeolite framework, eventually enhancing the catalytic performance in acid catalyzed reaction, such as in the case of benzene alkylation with ethanol.
The development of surfaces with chiral features is a fascinating challenge for modern material science, especially when they are used for chiral separation technologies. In this contribution, the design of hierarchically structured chiral macroporous ZIF-8 electrodes is presented. They are elaborated by an electrochemical depositiondissolution technique, based on the electrodeposition of metal through a colloidal crystal template, followed by controlled electrooxidation. This generates locally metal cations, which can interact with a chiral ligand present in solution to form Metal-Organic Frameworks (MOFs). The macroporous structure facilitates the access of the chiral recognition sites, located in the mesoporous MOF and thus helps to overcome mass transport limitations. The efficiency of the designed functional materials for chiral adsorption and separation can be fine-tuned by applying an adjustable electric potential to the electrode surfaces. This hierarchical chiral ZIF-8 structure was deposited at the walls of a microfluidic device and used as a stationary phase for enantioselective separation. The potential-controlled interaction between the stationary phase and the chiral analytes allows baseline separation of two enantiomers. This opens up interesting perspectives for using hierarchically structured chiral MOF as an efficient material for the selective adsorption and separation of chiral compounds.
The
development of an effective approach for methane utilization,
especially methane conversion to methanol, is a crucial challenge
that has remained unsolved satisfactorily. Herein, we propose an alternative
concept of methane utilization to methanol over Fe-ZSM-5@ZIF-8. The
concept is to use the designed composite as a dual catalyst in which
ZIF-8 and Fe-ZSM-5 act simultaneously as a gas adsorbent and catalyst,
respectively. In this case, methane can be adsorbed on ZIF-8 at 50
°C and subsequently converted to methanol at a moderate temperature
(150 °C) on Fe-ZSM-5. Interestingly, the promising catalytic
performance is observed on Fe-ZSM-5@ZIF-8, whereas only trace amounts
of produced methanol are detected on isolated Fe-ZSM-5 and ZIF-8.
Moreover, the designed composite also facilitates a facile methanol
desorption at the hydrophobic surface of the composite. This first
example opens up new promising horizons in combined perspectives for
gas storage and catalytic process applications.
Over the past decades, the catalytic cracking catalysts for hydrocarbon oil upgrading have been extensively developed to increase the yield of light olefins. In this context, we report the fabrication of the core‐shell ZSM‐5@aqueous miscible organic‐layered double hydroxides prepared by the growth of layered double hydroxides (LDH) precursors on zeolite surfaces. The deposited LDH results in a decrease of the number of strong Brønsted acid sites on zeolite surfaces and its transformation at high temperature leads to produce the highly dispersed metal oxides deposited on external surfaces of zeolites. Therefore, the acid‐base properties of designed surfaces are modified, eventually resulting in the suppression of competing hydride transfers and further side reactions. As a result, there is a significant enhancement in light olefins production compared with the pristine zeolite. In addition, the designed catalysts exhibit high recycling stability and reusability. This first example opens up the new perspectives for the development of modified acid‐base zeolites using zeolite@aqueous miscible organic‐layered double hydroxides for the catalytic upgrading of hydrocarbons.
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