碱处理法改善Pt／ZSM-5异构化性能

Alkali Treatment for Improving Isomerization Performance of Pt/ZSM-5

制备了一系列不同条件下碱处理的ZSM-5样品,以调控其酸性和孔道结构.考察了酸性和孔道结构对Pt/ZSM-5的异构化性能的影响.样品的晶相、酸性及结构分别通过X射线衍射、NH3程序升温脱附及N2吸附-脱附表征.结果表明,缓和的碱处理导致ZSM-5上强酸中心减少,催化剂异构化活性下降;而苛刻条件下的碱处理使得ZSM-5上强酸中心增加、大量中孔产生及催化剂异构化活性明显提高.催化剂的异构化活性取决于分子筛上强酸中心的量,与孔道结构无关;而异构体的分布不仅与孔道结构有关,而且与正己烷转化率密切相关,与分子筛的酸性无关.

A series of alkali-treated ZSM-5 samples were prepared in order to adjust acidity and pore structure of ZSM-5. The effects of acidity and pore structure on n-hexane isomerization performance of Pt/ZSM-5 were investigated. The crystalline structure, acidity, and textural properties were measured by X-ray diffraction, NH3 temperature-programmed desorption, and N2 adsorption-desorption, respectively. The results indicated that the mild alkali treatment led to a distinct decrease in the strong acid sites on ZSM-5 and the isomerization activity of Pt/ZSM-5. However, severe alkali treatment resulted in the increase of the strong acid sites, as well as the formation of new mesopores, accompanied by the significant increase in the isomerization activity. It was proposed that the iso- merization activity was dependent on the amount of strong acid sites over ZSM-5 and irrelevant to its pore structure, while the distribution of isomers was related to the pore structure, the conversion of n-hexane, and independent of the acidity of ZSM-5.