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IR 및 TPD기법을 이용한 불균일계 촉매의 특성연구
A Study on the Characteristics of Heterogeneous Catalysts by IR and TPD
HWAHAK KONGHAK, February 1987, 25(1), 71-80(10), NONE
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Abstract
모더나이트를 전이금속으로 이온교환하거나 수증기처리하여 산의 특성을 변화시키고 헤테로폴리산의 중심원자와 배위원자를 바꿈으로써 산특성을 변화시켰으며 ZSM-5를 여러가지 방법으로 제조하였다. 이들 촉매들에 암모니아 또는 피리딘을 흡착시킨 다음 TPD와 IR분석법에 의해 산의 종류 및 산점의 세기를 측정하였다. 촉매들의 산특성과 반응성간의 관계는 크실렌의 액상 이성화 반응, n-Butene의 이성화 반응, 톨루엔의 불균등화 반응 및 에탄올의 탄화수소에로의 전화반응과 관련지어 해석하였다. 승온탈착실험 결과 모더나이트와 ZSM-5는 두 개의 산점 즉 약산과 강산이 존재함을 확인하였으며 IR실험결과 이들에는 Lewis산과 Brönsted산이 있음을 알았고 헤테로폴리산에는 Brönsted산만이 존재함을 알았다. 크실렌의 이성화 반응 및 톨루엔의 불균등화 반응에서 강산이 생성물 선택성에 중요한 역할을 하며 탄소침적의 원인이 됨을 밝혔고 n-Butene의 이성화반응은 주로 약산에 의해 이루어짐을 밝혔다.
Modified H-Mordenites, ZSM-5, and heteropoly acids were prepared and subjected to reaction studies to gain an insight into their acid roles on the reactions. Modification steps for mordenites include steam-treatment and ion-exchange with transition metals.
Acid properties of the catalysts were investigated by the temperature programmed desorption of ammonia and pyridine and infrared spectra of pyridine adsorbed on the catalysts. TPD experiments showed that there were two kinds of active sites-weak and strong- on mordenite and ZSM-5 surfaces. IR experiments revealed that there were Lewis and Brönsted acids on mordenites and ZSM-5, while there was only Brönsted acid on heteropoly acids.
It was found that strong acids were responsible for the carbon deposits on the catalyst surface. It was also observed that strong acid played an imporatant role on the product selectivity for the xylene isomerization and toluene disproportionation, while weak acids were active for isomerization of n-butene and methanol conversion to dimethyl ether.
Acid properties of the catalysts were investigated by the temperature programmed desorption of ammonia and pyridine and infrared spectra of pyridine adsorbed on the catalysts. TPD experiments showed that there were two kinds of active sites-weak and strong- on mordenite and ZSM-5 surfaces. IR experiments revealed that there were Lewis and Brönsted acids on mordenites and ZSM-5, while there was only Brönsted acid on heteropoly acids.
It was found that strong acids were responsible for the carbon deposits on the catalyst surface. It was also observed that strong acid played an imporatant role on the product selectivity for the xylene isomerization and toluene disproportionation, while weak acids were active for isomerization of n-butene and methanol conversion to dimethyl ether.
