Dae Sung Kim

Synthesis of MCM-41 using microwave heating with ethylene glycol

Mesoporous material MCM-41 with hexagonal arrangement is obtained by microwave treatment of precursor gel at 100‐ 1208C for 1 h or less, a very short period of time compared with the hydrothermal method. In addition to shorter synthesis time, microwave radiation in the synthesis of MCM-41 provides a way to control its crystallinity and morphology. Especially the addition of small amount of ethylene glycol (EG) in synthetic mixture contributes to improving crystallinity, forming homogeneous particle shape and reducing particle size of MCM-41 under microwave radiation. Attenuated total reflectance (ATR)/FTIR and photoluminescence (PL) spectroscopy have been used to monitor intermediate step of microwave preparation of MCM-41. # 1998 Elsevier Science B.V. All rights reserved.

Metal–oxygen–metal arrays in lamellar hybrid materials: Cobalt and manganese 4-cyclohexene-1,2-dicarboxylates

We have obtained three layered hybrid materials from the hydrothermal reaction of 4-cyclohexene-1,2-dicarboxylic acid with Co and Mn salts: Co(C(8)H(8)O(4))[1], Mn(H(2)O)(C(8)H(8)O(4))[2], and Mn(4)(H(2)O)(C(8)H(8)O(4))(4).0.3(H(2)O)[3]. The structures for all materials were solved by single-crystal XRD ([1]P1, a=4.805(2) A, b=6.650(3) A, c=12.960(6) A, alpha=98.285(7) degrees, beta=98.986(7) degrees, gamma=95.689(7) degrees, V= 401.6(3) A(3), R(1)= 0.0438; [2] P2(1)/c, a=11.151(2) A, b=11.330(2) A, c=7.6560(15) A, beta=108.813(3) degrees , V=915.6(3) A(3), R(1)=0.0412; [3] P1, a= 11.412(3) A, b=12.136(4) A, c=13.809(4) A, alpha=104.703(6) degrees, beta=103.207(6) degrees, gamma=92.468(5) degrees, V=1790.6(9) A(3), R(1)=0.1056). While all three structures are two-dimensional overall, the metal-oxygen-metal dimensionality within the layers varies from isolated metal atoms in the case of [1] to 1D ribbons of vertex sharing MnO(6) octahedra [2] and 2D arrays of edge- and vertex-sharing polyhedra in [3].

Photoinduced activation of CO2 by rhenium complexes encapsulated in molecular sieves

The photochemical activation and reduction of CO 2 over a molecular-sieve-encapsulated rhenium complex was investigated under photo-irradiation (A > 350 nm) at room temperature. Re(CO) 3 (bpy)Cl and [Re(CO) 3 (bpy)(py)] + were respectively encapsulated in the microporous NaY and the mesoporous AIMCM-41 molecular sieve acting as supramolecular heterogeneous host. The molecular-sieve-encapsulated rhenium complexes were characterized by diffuse reflectance (DR) ultraviolet-visible (UV-vis), photoluminescence, and Fourier transform infrared (FTIR) spectroscopy. The interaction between the excited state of encapsulated rhenium complexes and the adsorbed CO 2 was observed in photoluminescence spectra. The radicals of rhenium complexes encapsulated in NaY and AIMCM-41 were produced with photoirradiation and confirmed by DR UV-vis spectra. By monitoring the photoreaction of CO 2 over the molecular-sieve-encapsulated rhenium complexes using FTIR spectroscopy and gas chromatography, the conversion of CO 2 into CO and carbonate species was observed. The molecularsieve-encapsulated rhenium complexes showed photocatalytic activity for the activation and reduction of CO 2 .

Oxidative dehydrogenation of ethylbenzene with carbon dioxide over zeolite-supported iron oxide catalysts

Oxidative dehydrogenation of ethylbenzene with carbon dioxide was carried out over ZSM-5 zeolite-supported iron oxide catalysts. In the presence of carbon dioxide, ethylbenzene was predominantly converted into styrene by oxidation. It was found that carbon dioxide in this reaction plays a role as a soft oxidant to greatly improve catalytic activity. An active phase for the dehydrogenation with carbon dioxide was suggested as rather reduced and isolated magnetite-like phase having oxygen deficiency in zeolite matrix.

MECHANISTIC STUDY OF THE SCR OF NO WITH PROPYLENE OVER CO/ZSM-5 USING IN-SITU FT-IR

The selective catalytic reduction (SCR) of NO with propylene over Co-exchanged ZSM-5 (Co/ZSM-5) was studied using in-situ FTIR. Propylene was activated easily by NO in the absence of oxygen above 200°C, leading to the formation of three different types of surface NCO species; Cobonded (2235 and 2195 cm−1), Si-bonded (2300 cm−1) and Al-bonded (2272 cm−1). These surface NCO species were stable in NO or oxygen atmosphere up to 400°C but in NO+oxygen they were easily converted to the final products of N2 and CO2. It is supposed that the SCR of NO over Co/ZSM-5 occurs through the Co- and Al-bonded NCO intermediates and its conversion is the rate-limiting step.

03-P-15-Rapid and mass production of prous materials using a continuous microwave equipment

Publisher Summary This chapter describes a rapid and mass production of porous materials using a continuous microwave equipment (CME). A CME has been developed to achieve a rapid and mass production for ZSM-5 and NaY zeolite. A precursor mixture for the synthesis of ZSM-5 is prepared by mixing aluminosilicate gel with a nanoseed solution obtained under microwave irradiation and pumped into the CME. Duration time in the CME is 5 min to accomplish the crystallization of ZSM-5 under microwave irradiation. For NaY zeolite, the precursor gel without nanoseeds is introduced into the CME, crystallization time is within 30 min. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicate that the structural properties of ZSM-5 and NaY zeolite obtained are similar to those obtained using batch-type microwave instrument and by conventional hydrothermal synthesis.

Para-chlorination activity of solid-state ion-exchanged zeolite KL catalysts

Selective formation of p-dichlorobenzene in the liquid-phase chlorination of monochlorobenzene with Cl2 gas was investigated over zeolite KL catalysts which were modified with various inorganic chlorides having multivalent metals through the solidstate ion-exchange method. Simultaneous enhancement in both conversion of monochlorobenzene and selectivities on p-dichlorobenzene resulted from the solidstate modification, which was attributed to the incorporation of multivalent metal cations due to ion-exchange and the pore modification for the shape-selective control through the remaining metal oxides and/or KCl in pores.

Photocatalytic activation of CO2 under visible light by Rhenium complex encapsulated in molecular sieves

The photocatalytic activation of CO2 over molecular sieve-encapsulated cationic rhenium complex has been investigated under visible light (λ>350 nm). The cationic rhenium complex, [Re(I)(CO)3(bpy)(py)]+(bpy=2,2′bipyridine, py=pyridine), has been encapsulated by ion-exchange method using the aqueous solution of [Re(I)(CO)3 (bpy)(py)]+PF6- into the microporous NaY and the mesoporous A1MCM-41 molecular sieve acting as supramolecular heterogeneous host. To confirm the encapsulation of [Re(IXCO)3(bpy)(py)]+ into the pores of molecular sieve, XeNMR and FT-IR spectroscopies have been applied before and after the [Re(I)(CO)3(bpy)(py)]+ encapsulation. To investigate the photophysical and photochemical properties, molecular sieve-encapsulated cationic rhenium complex has been studied by UV-Visible diffuse reflectance spectroscopy (UV-DRS) with photoirradiation (λ>350 nm) at room temperature. By monitoring the photoreaction of CO2 over the photocatalysts, the conversion of CO2 into CO and carbonate species has been observed by usingin-situ FT-IR and time-resolved mass spectroscopy. From the experimental results, the photocatalytic activation mechanism of CO2 on the catalyst under visible light (λ>350 nm) could be proposed via the photo-induced reaction of two electrons and two protons, resulting from water decomposition.

Spectroscopic monitoring for the formation of mesoporous MCM-41 materials upon microwave irradiation

The mesoporous MCM-41 materials were prepared in very short crystallization time (∼40 min) upon microwave irradiation in comparison with conventional hydrothermal heating method. With both microwave irradiation and hydrothermal heating, the MCM-41 formation via supramolecular templating method has been monitored by fluorescence and electron spin resonance (ESR) spectroscopy. Pyrene as a fluorescence probe and 4-(N,N-dimethyl-N-hexadecyl)ammonium-2,2,6,6-tetramethyl piperidinyloxy iodide (CAT16) as a spin probe were respectively dissolved into the micelle solutions to form the MCM-41 precursor gels. These probes allow the monitoring of the supramolecular interaction between the anionic silicate species and the cationic surfactant molecules during the MCM-41 formation. Analyses of fluorescence and ESR spectra indicate that the fast increase of hydrophobicity and microviscosity at the solubilzation sites of the probes results from the accelerated condensation of silicates onto the micelle surface upon microwave irradiation. The fluorescence change from the silicate L-center in the MCM-41 precursor gel also probes the fast silicate condensation upon microwave irradiation. It seems that the fast formation of MCM-41 upon microwave irradiation is ascribed to the microwave-susceptible head groups of surfactant molecules in addition to fast dissolution of the precursor gel.

13 Nanofabrication of zeolitic crystals with nanoglues by microwave

Microwave irradiation technique can be proposed as a new fabricating method for the fabrication of metallosilicate crystallites into nanostacked form by utilizing metal species as nanoglue. This microwave technique gave births of both the uniform size of hockey puck shaped crystals and the stacking of these crystals into fiber types. The formation of these nanostacked metallosilicate-1 (Ti, Fe) crystals having nanorod shape were, ascribed to the presence of metal species which selectively absorbed microwave irradiation. Metal species seem to play roles as nanoglues, absorb and deliver energy to surface hydroxyl that are supposed to be inorganic linkers that enable the dehydration from hydroxyl group on the crystal surfaces.