Cooperative Structure Direction of Diammonium Surfactants and Sodium Ions to Generate MFI Zeolite Nanocrystals of Controlled Thickness

The structure-directing effect of C₁₈H₃₇N⁺(CH₃)₂C₆H₁₂N⁺(CH₃)₂C₆H₁₃(Br^–)₂ surfactant (C_18–6–6) for the formation of MFI zeolite nanosheets was investigated under various synthesis conditions containing a small amount of C_18–6–6 in the presence or absence of Na⁺. Each synthesis mixture after heating for a different period at 413 K was analyzed by X-ray powder diffraction, electron microscopy, and argon adsorption. The synthesis with Na⁺ yielded a small amount of 2.5 nm thick zeolite nanosheets at an early reaction time, while most of the silica source remained as an amorphous phase. As the reaction time increased, the thickness of the zeolite nanosheets gradually increased, along with the depletion of the amorphous silica phase. When Na⁺ was not present, the initial synthesis result also showed a small amount of 2.5 nm zeolite nanosheets, but the zeolite thickness did not change since then on. Hence, the C_18–6–6 surfactant was able to rapidly generate the 2.5 nm zeolite nanosheets and, subsequently, Na⁺ ions gradually participated in the structure-directing process to increase the zeolite thickness. By properly balancing the structure-directing effects of C_18–6–6 and Na⁺, it was possible in the present work to control the thickness of the MFI zeolite nanosheets systematically (e.g., to 20 nm)

Characterization of the Surface Acidity of MFI Zeolite Nanosheets by ³¹P NMR of Adsorbed Phosphine Oxides and Catalytic Cracking of Decalin

MFI zeolite nanosheets tailored to 2.5-nm thickness were synthesized using a surfactant-type zeolite structure-directing agent, [C₂₂H₄₅–N⁺(CH₃)₂–C₆H₁₂–N⁺(CH₃)₂–C₆H₁₃]­(Br^–)₂. The zeolite nanosheets possessed Brønsted acid sites on their external surfaces as well as in the internal micropore walls. The acid strength and concentration was characterized by the ³¹P NMR signals of the adsorbed trimethylphosphine oxide and tributylphosphine oxide. The ³¹P NMR investigation identified three types of Brønsted acid sites with different strengths on external surfaces; there were four types inside the micropores. A linear correlation has been established between the number of the external strongest acid sites and the catalytic activity in decalin cracking for the MFI zeolite catalysts investigated in this work

Anomalously High Lithium Storage in Three-Dimensional Graphene-like Ordered Microporous Carbon Electrodes

Zeolite-templated carbon, having a three-dimensional graphene-like ordered microporous structure with high electrical conductivity, is a fascinating anode material for Li-ion batteries (LIBs). Herein, we report an extremely high Li capacity of 2950 mA h g^–1 (equivalent to Li_1.3/C), which is 7.9 times the maximum capacity of graphite, Li/C₆. This is equivalent to the crowded packing of 20 Li⁺ per pore with 0.9 nm diameter. Approximately 59% of the capacity was reversible. According to the characterizations by electron energy loss spectroscopy, ⁷Li NMR, and ¹³C NMR, most of the Li species existed as Li⁺ within the carbon micropores. Contrary to the often-made assumption, only a small amount of solid–electrolyte interphase layers was detected at the external surface of the carbon particles but not inside the micropores. The anomalously high Li capacity is attributed to the extremely narrow pore environment, where Li⁺ would be difficult to be fully solvated. Tailoring of the carbon pores to a subnanometric range would therefore be exciting for future advancement of LIBs

External Surface Catalytic Sites of Surfactant-Tailored Nanomorphic Zeolites for Benzene Isopropylation to Cumene

Nanomorphic *BEA, MTW, and *MRE zeolites were investigated as catalysts for isopropylation of benzene. From the deactivation pattern of the zeolites, we evaluated the contribution of external and internal active sites. These nanomorphic zeolites exhibited a high activity and long catalytic lifetime. Such catalytic properties can be explained by a large contribution of external sites, which have the advantage of slow deactivation

Mesoporous MFI Zeolite Nanosponge as a High-Performance Catalyst in the Pechmann Condensation Reaction

A zeolite nanosponge possessing <b>MFI</b> framework type was hydrothermally prepared by a seed-assisted synthesis method using C₂₂H₄₅–N⁺(CH₃)₂–C₆H₁₂–N⁺(CH₃)₂–C₆H₁₃ as a structure-directing agent. The nanosponge morphology was composed of a three-dimensional disordered network of <b>MFI</b> nanolayers with 2.5 nm thickness supporting each other. Catalytic performance of the <b>MFI</b> nanosponge was investigated in the Pechmann condensation of bulky reactants (pyrogallol and resorcinol) with ethyl acetoacetate and compared with conventional zeolites <b>MFI</b>, <b>BEA</b>, and USY) and also layered <b>MFI</b>, pillared <b>MFI</b>, and self-pillared <b>MFI</b>. The investigation revealed outstanding catalytic performance of the <b>MFI</b> nanosponge, which can be attributed to the contribution of strong acid sites located on the external surfaces accessible for the reaction of bulky reactants

Mesoporous MFI Zeolite Nanosponge Supporting Cobalt Nanoparticles as a Fischer–Tropsch Catalyst with High Yield of Branched Hydrocarbons in the Gasoline Range

A zeolite nanosponge was obtained by a seed-assisted hydrothermal synthesis route using C₂₂H₄₅–N⁺(CH₃)₂–C₆H₁₂–N⁺(CH₃)₂–C₆H₁₃ as the structure-directing agent. The zeolite was composed of disordered network of 2.5-nm-thick MFI zeolite nanolayers having a narrow distribution of mesopore diameters centered at 4 nm. The highly mesoporous texture (mesopore volume = 0.5 cm³ g^–1) was suitable for supporting cobalt nanoparticles with a narrow distribution of particle diameters centered at 4 nm. The Co/MFI zeolite exhibited high stability of the Co nanoparticles against particle growth, and there was accordingly high catalytic conversion of carbon monoxide to hydrocarbons and long catalytic lifetime in the Fischer–Tropsch synthesis. Furthermore, the Co/MFI catalyst exhibited high selectivity for branched hydrocarbons in the gasoline range (C₅–C₁₁), compared to conventional alumina-based catalysts. This high selectivity could be attributed to hydroisomerization in the extremely thin zeolite frameworks that provided short diffusion path lengths for branched hydrocarbons

Study of Argon Gas Adsorption in Ordered Mesoporous MFI Zeolite Framework

An ordered mesoporous MFI zeolite material (Meso-MFI) was prepared by using CMK-type mesoporous carbons as a hard template. The Meso-MFI exhibits both structural and adsorption differences compared to the conventional bulk MFI zeolite. To study the argon (Ar) adsorption process in Meso-MFI, an in situ gas adsorption powder X-ray diffraction (XRD) analysis was performed using synchrotron X-ray source. Structural rearrangement of the mesoporous MFI zeolite upon Ar adsorption at low temperature (83 K) was intensively studied together with Ar adsorption process in Meso-MFI. We observed that a structural transition of the Meso-MFI zeolite framework from monoclinic (<i>P</i>2₁/<i>n</i>) to orthorhombic (<i>Pnma</i>) occurred at around 126 Pa at 83 K. Positions of Ar atoms are determined as a function of the Ar gas pressure through Rietveld refinement of powder XRD data. Ar atoms are observed at straight channels, sinusoidal channels, and the intersection of these channels at low pressure. As gas pressure increases, Ar atoms in the pore intersection are pulled off from the intersection toward the straight and sinusoidal channels. The pore shape of the straight channel is changed accordingly with the amount of adsorbed Ar atoms within the pores from circular to oval. These results indicate that Ar adsorption induces not only continuous rearrangement of framework atoms but also symmetry change in the Meso-MFI. A molecular simulation study combined with Rietveld refinement of in situ XRD data provided a full understanding of the adsorption process of Ar in Meso-MFI

Nanocage-Confined Synthesis of Fluorescent Polycyclic Aromatic Hydrocarbons in Zeolite

Polycyclic aromatic hydrocarbons (PAHs) attract much attention for applications to organic light-emitting diodes, field-effect transistors, and photovoltaic cells. The current synthetic approaches to PAHs involve high-temperature flash pyrolysis or complicated step-by-step organic reactions, which lead to low yields of PAHs. Herein, we report a facile and scalable synthesis of PAHs, which is carried out simply by flowing acetylene gas into zeolite under mild heating, typically at 400 °C and generates the products of 0.30 g g^–1 zeolite. PAHs are synthesized via acetylene polymerization inside Ca²⁺-ion-exchanged Linde type A (LTA) zeolite, of which the α-cage puts a limit on the product molecular size as a confined-space nanoreactor. The resultant product after the removal of the zeolite framework exhibits brilliant white fluorescence emission in <i>N</i>-methylpyrrolidone solution. The product is separated into four different color emitters (violet, blue, green, and orange) by column chromatography. Detailed characterizations of the products by means of various spectroscopic methods and mainly mass spectrometric analyses indicate that coronene (C₂₄H₁₂) is the main component of the blue emitter, while the green emitter is a mixture of planar and curved PAHs. The orange can be attributed to curved PAHs larger than ovalene, and the violet to smaller molecules than coronene. The PAH growth mechanism inside Ca²⁺-exchanged LTA zeolite is proposed on the basis of mass spectral analyses and density functional theory calculations

Two-Minute Assembly of Pristine Large-Area Graphene Based Films

We report a remarkably rapid method for assembling pristine graphene platelets into a large area transparent film at a liquid surface. Some 2–3 layer pristine graphene platelets temporally solvated with <i>N</i>-methyl-2-pyrrolidone (NMP) are assembled at the surface of a dilute aqueous suspension using an evaporation-driven Rayleigh-Taylor instability and then are driven together by Marangoni forces. The platelets are fixed through physical binding of their edges. Typically, 8-cm-diameter circular graphene films are generated within two minutes. Once formed, the films can be transferred onto various substrates with flat or textured topologies. This interfacial assembly protocol is generally applicable to other nanomaterials, including 0D fullerene and 1D carbon nanotubes, which commonly suffer from limited solution compatibility

Two-Minute Assembly of Pristine Large-Area Graphene Based Films

We report a remarkably rapid method for assembling pristine graphene platelets into a large area transparent film at a liquid surface. Some 2–3 layer pristine graphene platelets temporally solvated with <i>N</i>-methyl-2-pyrrolidone (NMP) are assembled at the surface of a dilute aqueous suspension using an evaporation-driven Rayleigh-Taylor instability and then are driven together by Marangoni forces. The platelets are fixed through physical binding of their edges. Typically, 8-cm-diameter circular graphene films are generated within two minutes. Once formed, the films can be transferred onto various substrates with flat or textured topologies. This interfacial assembly protocol is generally applicable to other nanomaterials, including 0D fullerene and 1D carbon nanotubes, which commonly suffer from limited solution compatibility