NaHY沸石中结构羟基与积碳的关系

Correlation Between the Coke Formation and Structural Hydroxyl in NaHY Zeolite

Uylterhoevn^([1])和Ward^([2])等人已经证明了: 1.NaHY沸石中的结构羟基,是NH_(4)NaY脱氨后余下的氢附连于邻近的骨架氧而形成的。对应红外光谱3643cm^(-1)吸收峰的结构羟基具有Brönsted酸性。 2.这种Brönsted酸是异丙苯裂解反应的主要活性中心。 3.NaHY中的结构羟基,在大约500℃吋开始脱除。脱除的程度与焙烧温度及时间有关。脱除羟基中,两个质子酸转变为一个Lewis酸中心。

In this article the correlation between the coke formation and structural hydroxyls in NaHY zeolite was investigated by using ESR technique in cumcne cracking, and the following were observed.1.With the pretrcatmcnt temperature of zeolite increasing the cumcne cracking activity decreased and the coke formation declined.2.Also with the calcination time being prolonged the cumcne cracking activity decreased and the coke formation declined.3.The higher the exchange degree of zeolite, the higher the cracking activity of zeolite and the more the coke formation.The tendency of changes of both the cracking activity and the coke formation was in accordance with that of changes of the amount of the structural hydroxyls in NaHY zeolite as function of the prctrcatment temperature, time and the exchange degree of zeolite. On those results above it was concluded that the coke formation was a secondary reaction for the cracking of cumene,that is, not only the structural hydroxyls in NaHY were active sites for the cracking, but also for the coke formation.