Mechanism of Promotion Effects of Ce added to AlPO4 Effective for CFC Decomposition

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  • フロン分解用リン酸アルミニウム系触媒におけるセリウムの助触媒機能の発現機構
  • フロン ブンカイヨウ リンサン アルミニウムケイ ショクバイ ニ オケル セリウム ノ ジョ ショクバイ キノウ ノ ハツゲン キコウ

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Abstract

AlPO4 which was prepared by neutralization of an aqueous solution of Al nitrate was amorphous and has a large specific surface area as much as 130 m2/g after calcination at 1000°C. After the calcination at 1100°C, AlPO4 was slightly crystallized and the crystallite size of AlPO4 was about 16 nm and the catalytic activity was higher than that calcined at 1000°C. But AlPO4 calcined at 1200°C was more crystallized and the activity was decreased. On one hand, AlPO4 promoted by 10 mol% of Ce which was calcined at 1000°C showed a maximum catalytic activity and crystallinity was the same as that of pure AlPO4 calcined at 1100°C. Ce promoted AlPO4 after calcination at 1100°C was well crystallized, and the catalytic activity was decreased.<br>Therefore, it was concluded that Ce as a promoter, creates small AlPO4 particles which was conveniently crystallized to CCl2F2 decomposition by the calcination at 1000°C which is 100°C lower than that in case of pure AlPO4.<br>By treatment with concentrated CCl2F2 at high temperatures such as 800 or 900°C for 8 h, both AlPO4 and Ce promoted catalysts were much crystallized and SSA and the catalytic activity of the catalysts were decreased. The catalytic activity when it will be ultimately inactivated state was estimated using T50% approached at zero SSA, and 550°C will be required to obtain 100% CCl2F2 conversion for Ce promoted AlPO4 catalyst.<br>AlPO4 was crystallized by a steam treatment at 900°C to the same level of that calcined at 1100°C in air and increased the catalytic activity. In case of Ce promoted AlPO4, steam treatment at 1000°C promoted the crystallization of CePO4 but AlPO4 and increased the catalytic activity.<br>The effects of CCl4, CF4, and CCl2F2 treatment were studied and found that AlPO4 was the most crystallized by the treatment by CCl2F2. This may be explained by the formation of chloridefluorides such as AlCl3–nFn and PCl5-mFm which can be sublimated only in the decomposition of CCl2F2.

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