Development of CVD Zeolites with Fine Molecular Sieving Function

1. 研究了连续流化学气相沉积（CVD）方法，通过对大量沸石进行均匀改性来控制沸石的开孔尺寸。在593 K温度下，na -丝光沸石上可以均匀沉积二氧化硅，而h -丝光沸石只有在低温条件下才能均匀沉积二氧化硅，并且没有观察到产生甲醇的二次反应。在h -丝光沸石上沉积后，温度的升高使结构恶化，气孔尺寸不均匀。由于焦炭的损失和沉积二氧化硅的细微变化，在673 K时进行水蒸气处理，使沉积二氧化硅的结构发生了改变，气孔大小得到了很好的控制。CVD分子筛的分子筛分性能(1)NaCaA分子筛的孔径大小受分子长度的控制，可以分离乙烯、丙烯、丁烯等低烯烃。(2)对ZSM-5进行改性，获得了辛烷裂化的形状选择性。由于裂解机理的原因，只在高温（773 K）下观察到选择性。(3)对甲基萘进行烷基化反应，提高了CVD沸石的选择性。然而，这种增强是由外表面失活引起的，而不是由孔径控制引起的。

1. Continuous-flow CVD Method to control the Pore-opening Size of ZeolitesA continuous-flow CVD (chemical vapor deposition) method by which a large amount of zeolite could be modified uniformly to control the pore-opening size was studied. Uniformly deposition of silica was possible on the Na-mordenite at 593 K, but on the H-mordenite only at low temperature where no secondary reaction of produced methanol was observed. Subsequent elevation of temperature after the deposition on the H-mordenite deteriorated the structure to obtain the non-homogeneous pore-opening size. The structure of deposited silica was however modified to finely control the pore-opening size by the treatment by water vapor at 673 K due to the loss of coke as well as the subtle change of the deposit silica.2. Molecular Sieving Property of CVD Zeolites(1) The pore-opening size of NaCaA was controlled finely so that the separation of lower olefins such as ethylene, propylene, and butene was possible due to the length of molecules.(2) ZSM-5 was modified to obtain the shape-selectivity of cracking of octane. The selectivity was observed only at high temperature (773 K) because of the mechanism of cracking.(3) Alkylation of methylnaphthalene was carried out, and the beta-selectivity was enhanced on the CVD zeolites. However, the enhancement was caused by the inactivation of external surface rather than by the pore-size control.