Development of CVD Zeolites with Fine Molecular Sieving Function

1.连续流化学气相沉积法控制沸石的开孔尺寸研究了一种连续流化学气相沉积的方法，通过对大量沸石进行均匀的改性来控制开孔尺寸。在593K时，在钠系丝光沸石上可以均匀沉积SiO_2，而在H-丝光沸石上只能在低温下均匀沉积SiO_2，没有观察到生成的甲醇发生二次反应。在H-丝光沸石上沉积后温度的随后升高使结构恶化，从而获得了不均匀的开孔尺寸。然而，由于焦炭的损失和沉积二氧化硅的细微变化，通过在673K下用水蒸气处理，沉积的二氧化硅的结构被改变以精细地控制开孔尺寸。CVD沸石的分子筛性能(1)NaCaA分子筛的开孔大小受到分子长度的控制，使乙烯、丙烯、丁烯等低碳烯烃的分离成为可能。(2)对ZSM-5分子筛进行改性，获得了辛烷裂化的择形性能。由于裂化机理的原因，只有在高温(773K)下才能观察到选择性。(3)甲基萘的烷基化反应，提高了分子筛的β-选择性。然而，这种增强是由外表面的失活引起的，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.