• 제목/요약/키워드: Shape Selective Catalysis

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Shape-Selective Catalysis over Zeolite. An Attempt in the Alkylation of Biphenyl

  • Sugi, Yoshihiro;Komura, Kenichi;Kim, Jong Ho
    • 공업화학
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    • 제17권3호
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    • pp.235-242
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    • 2006
  • Liquid phase alkylation of biphenyl (BP) was studied over large pore zeolites. Selective formation of the least bulky products, 4,4'-diisopropylbiphenyl (4,4'-DIPB) occurred only in the isopropylation of BP over some large pore molecular sieves. H-mordenites (MOR) gave the highest selectivity among them. The dealumination of MOR enhanced catalytic activity and the selectivity of 4,4'-DIPB because of the decrease of coke-deposition. Non-selective catalysis occurs on external acid sites over MOR with the low $SiO_2/Al_2O_3$ ratio because severe coke-deposition deactivates the acid sites inside the pores by blocking pore openings. The selectivity of DIPB isomers was changed with reaction temperature. Selective formation of 4,4'-DIPB was observed at moderate temperatures such as $250^{\circ}C$, whereas the decrease of the selectivity of 4,4'-DIPB occurred at higher temperatures as $300^{\circ}C$. However, 4,4'-DIPB was almost exclusive isomer in the encapsulated DIPB isomers inside the pores even at high temperatures. These decreases of the selectivity of 4,4'-DIPB are due to the isomerization of 4,4'-DIPB on the external acid sites. Some 12-membered molecular sieves, such as SSZ-24, MAPO-5 (M:Mg, Zn, Si), SSZ-31, and ZSM-12, which have straight channels, gave 4,4'-DIPB with moderate to high selectivity; however; SSZ-55, SSZ-42, and MAPO-36 (M: Mg, Zn) gave lower selectivity because of cages in 12-membered one dimensional channels. Three dimensional H-Y and Beta zeolites also yield 4,4'-DIPB in low yield because of their wide circumstances for the isopropylation of BP. The increasing the size of alkylating agent enhanced the shape-selective alkylaiton even for the zeolites, such as UTD-1. The ethylation of BP to ethylbiphenyls (EBPs) and diethylbiphenyls (DEBPs) over MOR was non-selective. The ethylation of BP to EBPs was controlled kinetically. However, there was difference in reactivity of EBPs and DEBPs for their further ethylation. 4-EBP was ethylated preferentially among the isomers, although the formation of 4,4'-DEBP was less selective. The least bulky 4-EBP and 4,4'-DEBP have the highest reactivity among EBPs and DEBPs for the ethylation to polyethylbiphenyls (PEBPs). These results show that the environments of MOR pores are too loose for shape selective formation of the least bulky isomers, 4-EBP and 4,4'-DEBP in the ethylation of BP, and that MOR pores have enough space for the further ethylation of 4,4'-DEBP.

제올라이트 촉매상에서의 알킬 방향족 화합물 전환 반응기구에 대한 최근 연구 동향 (Recent Advances in the Mechanistic Studies of Alkylaromatic Conversions over Zeolite Catalysts)

  • 민형기;홍석봉
    • Korean Chemical Engineering Research
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    • 제51권1호
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    • pp.1-9
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    • 2013
  • 제올라이트 촉매를 이용한 알킬 방향족 화합물의 전환은 현대 석유화학 산업에서 큰 비중을 차지한다. 본 총설에서는 제올라이트의 구조적 물리화학적 특성에 따른 알킬 방향족 화합물 전환 반응의 기구에 대해 고찰하였다. 제올라이트의 형상선택성은 알킬 방향족 화합물 전환에 있어서 반응중간체의 생성을 조절함으로써 반응 기구 및 생성물 분포에 직접적인 영향을 미친다. 다양한 알킬 방향족 화합물의 전환 반응에 대하여 반응 중간체의 구조 및 역할에 대한 고찰을 통해 지금까지 알려진 반응기구들을 정리하였다. 아울러 제올라이트 촉매를 기초로 하는 향후 석유화학 공정 개발에 대한 전망을 기술하였다.

양이온 교환된 펜타실 제올라이트의 형상 선택적 촉매작용 (Shape Selective Catalysis of Cation-Exchanged Pentasil Zeolites)

  • 안병준;황병우;전학제
    • 대한화학회지
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    • 제28권1호
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    • pp.62-69
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    • 1984
  • 에탄올의 톨루엔에 대한 반응과 방향족 화합물들의 양이온 교환된 펜타실 제올라이트에서의 형상 선택적 촉매작용이 조사되었다. 톨루엔의 에탄올에 의한 알킬화 반응은 $400^{\circ}C$에서 최대가 되고 톨루엔의 동종간 주고 받기 반응에 의한 크실렌 생성은 반응온도에 따라 증가한다. 세슘이온이 교환된 ZSM-5에서 p-에틸톨루엔에 대한 높은 선택성이 나타나고 세슘 교환도에 따라 90% 이상까지 증가한다. 또한 세슘-ZSM-5는 p-크실렌에 대한 m-크실렌의 흡착속도를 감소시킨다. 이러한 현상은 펜타실 제올라이트에 교환된 세슘 이온이 부분적으로 세공을 막아주므로서 나타나는 형상 선택성으로 해석된다.

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Preparation and Pore-Characteristics Control of Nano-Porous Materials using Organometallic Building Blocks

  • Oh, Gyu-Hwan;Park, Chong-Rae
    • Carbon letters
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    • 제4권1호
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    • pp.1-9
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    • 2003
  • Recently, the control of pore-characteristics of nano-porous materials has been studied extensively because of their unique applications, which includes size-selective separation, gas adsorption/storage, heterogeneous catalysis, etc. The most widely adopted techniques for controlling pore characteristics include the utilization of pillar effect by metal oxide and of templates such as zeolites. More recently, coordination polymers constructed by transition metal ions and bridging organic ligands have afforded new types of nano-porous materials, porous metal-organic framework(porous MOF), with high degree and uniformity of porosity. The pore characteristics of these porous MOFs can be designed by controlling the coordination number and geometry of selected metal, e.g transition metal and rare-earth metal, and the size, rigidity, and coordination site of ligand. The synthesis of porous MOF by the assembly of metal ions with di-, tri-, and poly-topic N-bound organic linkers such as 4,4'-bipyridine(BPY) or multidentate linkers such as carboxylates, which allow for the formation of more rigid frameworks due to their ability to aggregate metal ions into M-O-C cluster, have been reported. Other porous MOF from co-ligand system or the ligand with both C-O and C-N type linkage can afford to control the shape and size of pores. Furthermore, for the rigidity and thermal stability of porous MOF, ring-type ligand such as porphyrin derivatives and ligands with ability of secondary bonding such as hydrogen and ionic bonding have been studied.

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