用正电子湮没技术研究USY沸石的“二次孔”结构

SECONDARY PORE STRUCTURE OF USY ZEOLITES STUDIED BY POSITRON ANNIHILATE TECHNIQUE

测量了ＮａＹ及ＵＳＹ沸石的正电子寿命谱．得到ＮａＹ沸石有四个寿命分量：两个短寿命分量和两个长寿命分量．两个长寿命分量中，τ３，τ４分别是ｏＰｓ在β笼和超笼中的湮没．ＵＳＹ沸石有五个寿命分量：两个短寿命分量和三个长寿命分量，三个长寿命分量中，τ３为ｏＰｓ在笼中的湮没，τ４，τ５分别为ｏＰｓ在“二次微孔”和“二次中孔”中的湮没．与ＮａＹ沸石相比，在真空中，ＵＳＹ的τ４增加到１４ｎｓ，τ５增加到９２ｎｓ．实验证实了离子交换及高温水热处理对沸石的孔结构有很大的影响．还测量了ＵＳＹ沸石在不同大气压力下（０—０１ＭＰａ）的正电子寿命谱，随着ＵＳＹ沸石吸附空气的增加，τ５，Ｉ５明显减少，τ５从（真空中）９２ｎｓ下降５７ｎｓ（０１ＭＰａ），Ｉ５从１５％下降到９％．研究表明，空气中的Ｏ２不仅猝灭了Ｐｓ，抑制了Ｐｓ的生成，而且减小了ｏＰｓ的寿命．另外，空气密度的增加使ｏＰｓ的Ｐｉｃｋｏｆ湮没增加，也抑制了Ｐｓ的生成．

The structures of NaY and ultrastability Y type (USY) zeolite were studied by positron lifetime spectroscopy.Four lifetimes could be obtained in NaY zeolite,the two larger components were assigned to be o Ps annihilation in the β cage and supercage respectively.In USY zeolite,however,an additional lifetime component τ 5 was observed,which was about 92ns in vacuum with continuous distribution from 39ns to 142ns by the Laplace inversion analysis of lifetime spectrum.The second larger lifetimes τ 4 also increased to 14ns,compared to that in NaY zeolite.Existence of the longer lifetimes τ 4 and τ 5 is due to the porous structure of USY.The positron lifetime in USY zeolite was also measured as a function of air pressure ranging from 0 (vacuum) to 0 1MPa.The most interesting was the variation of the largest components τ 5 and I 5.They both decreased with increasing air pressure.The results can be explained as follows.First,the oxygen contained in the air could quench the Ps and reduce its lifetime and intensity.Second,the increasing density of air could also increase the probability of o Ps pick off annihilation and reduce its formation.These would lead to the decrease of its lifetime and intensity.