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Shul, Yong Gun,Park, Sang Eon,Yamashita, Hiromi,Anpo, Masakazu,Matsuoka, Masaya,Park, Dal Ryung 한국공업화학회 2000 Journal of Industrial and Engineering Chemistry Vol.6 No.2
Titanium or vanadium oxide species incorporated within the framework of zeolites or mesoporous molecular sieves by an ion-exchange method or hydrothermal synthesis show high and unique photocatalytic activities for various reactions such as the decomposition of NO into O_2 or the reduction activities of CO_2 with H_2O to produce CH_4 and CH_3OH. In situ photoluminescence, XAFS and ESR investigations revealed that titanium as well as vanadium oxide moieties exist in highly dispersed tetrahedral coordination states in the zeolite framework and the charge transfer excited state of these transition metal oxide species play a vital role in the photocatalytic reactions on these zeolite and molecular sieve catalysts. The unique physicochemical properties of porous materials such as pore size, channel structural dimensions, and distribution of ion-exchangeable sites are shown to be important factors in controlling the dispersion and local structures of the metal oxides incorporated within such porous materials as well as the photocatalytic reactivities and selectivities in various photocatalytic reactions.
Photocatalytic Decomposition of NO on Transition Metal Ion-exchanged Zeolite Catalysts
Shul, Yong Gun,Park, Sang Eon,Yamashita, Hiromi,Anpo, Masakazu,Matsuoka, Masaya,Ju, Woo Sung 한국공업화학회 2000 Journal of Industrial and Engineering Chemistry Vol.6 No.3
Transition metal ions (Cu^+, Ag^+) incorporated within the cavities of zeolites by an ion-exchange method show an efficient and unique photocatalytic performance for the decomposition of NO into N₂ and O₂ at 275 K. In situ ESR, UV-VIS, photoluminescence and XAFS (XANES and FT-EXAFS) investigations revealed that the transition metal ions exist in highly dispersed state with linear 2 coordination sphere within the pores of zeolites, the local structures of the metal ions being significantly affected by changing the kinds of zeolites. Detailed studies of the interaction of NO with the excited states of these metal ions clearly indicated that unique inner shell type excitation states of these metal ions play a significant role in the photocatalytic decomposition of NO, i.e., an electron transfer from the s orbital of the excited state of Cu^+ or Ag^+ ions into the π^* antibonding orbital of NO initiates the decomposition reaction of NO.
Synthesis of Organic - Inorganic Composite Membrane by Sol - Gel Process
Shul, Yong Gun,Chun, Kyoung Yong,Kim, Han Sung,Joe, Yung Il,Han, Jung Woo 한국화학공학회 1995 NICE Vol.13 No.6
Silica was succesfully incorpm-ated into canon exchange polymer membranes, CL-25 and Nation 417, utilizing sol-gel process. As dipping time increased, increase in silica uptake in membrane was observed. In Nation 417 membrane, no relationship was found between the silica uptake and the change in ion exchange capacity. But CL-25T which has larger pores than Nation 417 shows proportional decrease in ion exchautge capacity with increasing silica uptake. It suggests that the pore structure of membrane and the size control of silica sol are important to modify- the structure of composite membranes. In CL-25T membranes modified by silica, the transport rate of IPA (isopropyl alcohol) increased with increasing OH concentration on the pore surface.
Crystal Growth of High Silica ZSM -5 at Low Temperature Synthesis Conditions
Shul, Yong Gun,Ihm, Son Ki,Kiyozumi, Yoshinichi,Shin, Shigemitsu,Koo, Kee Kahb 한국화학공학회 1996 NICE Vol.14 No.3
At the temperature of 90 and under atmospheric pressure, growth kinetics of high silica ZSM-5 was investigated through a long induction, nucleation and crystal growth periods. It was found the entire crystallization mechanism of ZSM-5 seems to be the combined process of the nucleation via solid-solid transformation, intergrowth among seed crystals and the normal growth in the reaction mixture. Nuclei were initially formed on the Si-rich surface of the amorphous intermediates, indicating that the reaction of TPA with Si species was prior to that with A1 species. As the reaction time proceeded, various types of intergrowth among the seed crystals were observed along with the crystals growing independently. The intergrowth seems to play a role for forming typical ZSM-5 crystal shapes. And then ZSM-5 crystals further grew in the reaction mixture, so that the bulk Si/Al₂ ratio of crystals approached that of the initial reaction mixture.
DCA(Dichloroacetic acid) Decomposition over Photoreduced Metal Supported TiO_2-SiO_2 Catalysts
Shul, Y.G.,Yang, J.C.,Kim, Y.C.,Yoo, H.J.,Lee, T.K. 전남대학교 촉매연구소 1997 촉매학술발표회 Vol.- No.14
The dichloroacetic acid (DCA) decomposition was studied over photoreduced metal supported TiO_2 and TiO_2-SiO_2 catalysts. The enhancement of photocatalytic activity was achieved by the photoreduction of Pt supported TiO_2 with UV light. The maximum photocatalytic activity was observed at 1.68 wt % of Pt loading. The synergistic effect was observed in the case of doping tungsten and platinum together. TiO_2-SiO_2 mixed oxide was synthesized by sol-gel process and then it was calcined at 400 ℃. When the TiO_2 content was higher than anatase phase found, apparently there was no crystalline peak below 30% of TiO_2 in SiO_2. The photon effiency of DCA decomposition over TiO_2-SiO_2 catalyst also increased when platinum was supported by photoreduction.
Formation of Zeolite A Film on Metal Substrates by Microwave Heating
Shul, Yong Gun,Lee, Kwang Soon,Koo, Kee Kahb,Hwang, Un Yeon,Baek, Dong Ryul 한국공업화학회 2001 Journal of Industrial and Engineering Chemistry Vol.7 No.4
Microwave heating was applied to the formation of zeolite A films on copper (Cu) and stainless steel (SUS) substrates. It was confirmed that crystallization time by microwave heating was much smaller than that by conventional heating due to the rapid dissolution of gel, nucleation and growth of zeolite crystals. It was found that the film formation was primarily influenced by surface properties of the metal substrates: a dense film of zeolite A crystals with the size of about 0.3∼1.0㎛ was formed on Cu substrates. However, no layer-like zeolite film was formed on the SUS substrate. Nucleation of zeolite A crystals on metal substrates was also found to be strongly affected by the heating method and pretreatment of synthesis solution.
Shul, Yong Gun,Yamashita, Hiromi,Anpo, Masakazu,Jung, Kyeong Taek 한국화학공학회 1997 Korean Journal of Chemical Engineering Vol.14 No.3
TS-1 zeolite film has been prepared by using nano sized TS-1 zeolite particles for the photocatalytic isomerization of cis-2-butene. TS-1 zeolite film showed optical transparent property and the thickness of film was 0.7 ㎛. UV irradiation of TS-1 zeolite film in the presence of cis-2-butene leads to the photocatalytic isomerization of cis-2-butene into trans-2-butene at the temperature of 275 K. The yield of trans-2-butene was linearly increased with UV-irradiation time.