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HWAHAK KONGHAK,
Vol.31, No.3, 295-302, 1993
Vol.31, No.3, 295-302, 1993
규소산화물이 증착된 HZSM-5촉매와 붕소산화물이 담지된 HZSM-5촉매의 산도와 형상선택성 비교
The Acidity and Shape-selectivity of Silicon Oxide Deposited HZSM-5 Catalysts Compared with Those of Boric Oxide Impregnated HZSM-5 Catalysts
HZSM-5촉매의 기공크기（pore opening size）의 조절 효과를 비교하기 위하여 실리콘메톡사이드[Si(OCH3)4]의 화학증착(CVD)과 붕산의 담지방법을 이용하였다. 제조된 촉매들의 특성을 적외선 분광분석, 암모니아 승온 탈착실험 및 물, p-xylene, o-xylene 등의 흡착실험을 통해 분석한 결과, 붕산을 이용하여 담지시킨 촉매는 소량의 붕소(boron)가 촉매의 기공 내부로 유입되어 촉매의 내부구조와 산도(acidity)에 미세한 변화를 일으키지만 실리콘이 증착된 촉매는 촉매의 내부구조와 산도의 변화없이 외부표면에만 증착되어 실리콘메톡사이드[Si(OCH3)4]의 증착정도에 따라 기공크기가 미세하게 조절됨을 알 수 있었다. 이와 같은 사실을 톨루엔의 메탄올에 의한 알킬화 반응과 여러 흡착질의 흡착실험의 결과들로부터 확인할 수 있었다. 톨루엔의 메탄올에 의한 알킬화 반응시, 규소산화물(silicon oxide)이 증착된 촉매상에서는 규소산화물(silicon oxide)의 증착정도에 따라 m-, o-xylene의 수율과 선택도가 감소하며 p-xylene의 수율과 선택도는 크게 증가하였다. 반면 붕소산화물(boric oxide)이 담지된 촉매상에서는 붕소산화물(boric oxide)의 담지 정도에 따라 규소산화물(silicon oxide)이 증착된 촉매와 같은 경향을 나타내지만 p-xylene의 수율이 감소함을 볼 수 있었다. 담지된 붕소 산화물(boric oxide)과 증착된 규소산화물(silicon oxide)은 모두 촉매의 기공크기를 미세하게 조절하여 p-xylene의 선택도를 향상시키는 역할을 하는 것으로 판단되며, 이 중 규소산화물(silicon oxide)의 화학증착에 의한 기공크기의 조절이 구조적으로 안정한 촉매의 제조와 특정 반응 생상물(p-xylene)의 형상 선택성을 향상시키는데 높은 효율성을 나타내는 것으로 생각되었다.
In order to control the pore-opening size of HZSM-5, boric acid was impregnated on the HZSM-5 catalyst and silicon methoxide was used for Chemical Vapor Deposition（CVD） method. The catalysts were characterized by temperature programmed desorption of ammonia, infrared spectroscopy and adsorption experiments using water, p-xylene and o-xylene as adsorbate. Every result was compared with that of parent HZSM-5 catalyst. It was found that silicon oxide was deposited only on the external surface of the catalysts without changing the internal structure, while in the impregnated catalysts boron oxide was incorporated in the framework of a catalyst and occurred the change of the internal structure of a catalyst. The phenomena of pore-opening size control was tested by the alkylation of toluene with methanol and sorption experiments. From the results of reaction experiments over a series of silicon oxide deposited sample(SiHZSM-5), the yield and selectivity of p-xylene were increased with the contents of deposited silicon oxide. From the results of reaction experiments over a series of boron impregnated samples(BHZSM-5), the selectivity of p-xylene was increased as the above, but the yield of p-xylene was decreased as the contents of impregnated boron oxide was increased. In the aspect of the structural stability and activity of a catalyst, the CVD(chemical vapor deposition)by silicon methoxide was an more effective method to have control of the pore-opening size of a catalyst than the impregnation method by boric acid.
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