RESUMEN
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.
RESUMEN
The development of surfaces with chiral features is a fascinating challenge for modern materials science, especially when they are used for chiral separation technologies. In this contribution, the design of hierarchically structured chiral macroporous zeolitic imidazolate framework-8 (ZIF-8) electrodes is presented. They are elaborated by an electrochemical deposition-dissolution 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 the 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 MOFs as an efficient material for the selective adsorption and separation of chiral compounds.
RESUMEN
The highly selective oxidation of alcohols to aldehydes has been achieved due to the synergic effect of Pt and CeO2 supported on hierarchical zeolites. The combination of Pt and CeO2 strongly enhances the catalytic performance of the oxidation of benzyl alcohol to benzaldehyde with respect to the isolated materials. In addition, the hierarchical zeolite not only increases the fraction of exposed active sites because of its high surface area that can prevent the aggregation of Pt and CeO2 nanoparticles, but also affects the oxidation state of cerium. The presence of a high content of trivalent Ce species (Ce3+) on the hierarchical zeolite benefits the oxidation reaction, eventually leading to almost 100% yield of an aldehyde product. Moreover, the catalytic performance can be further improved by the easily tunable Si to Al ratio of zeolite catalysts.
RESUMEN
The development of bifunctional catalysts is important in the synthesis of materials for multiple sequential reactions in one-pot tandem catalytic processes. In this context, a dealuminated acid-base bifunctional catalyst with a hierarchical aluminum-rich faujasite structure (zeolite Y) has been successfully prepared by the solid-state dealumination of NaX nanosheets with ammonium hexafluorosilicate (AHFS). The characteristic properties of catalysts were examined by means of XRD, SEM, TEM, N2 physisorption technique, ICP-OES, NH3 -TPD, CO2 -TPD, 27 Al NMR, 29 Si NMR, Al K-edge XANES, and Pyridine-FTIR. The materials exhibit a superior catalytic performance for one-pot tandem catalysis, for example, the synthesis of trans-ß-nitrostyrene with a yield close to 100 % in a tandem deacetalization-Henry reaction of benzaldehyde dimethyl acetal with nitromethane. The high catalytic performance is attributed to the facile transfer of bulky molecules between acid and basic sites in the presence of hierarchical structures.
RESUMEN
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.
RESUMEN
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.