摘要
本文首先报道我们在缩醛反应中发现ＨＺＳＭ－５分子筛催化活性得到增强的现象以及相应的水热处理条件．其次报道用回旋质谱方法对ＨＺＳＭ—５分子筛增强酸位所进行的ＮＨ３－ＴＰＤ表征．最后报道对增强酸性的ＨＺＳＭ－５分子筛进行的核磁共振研究；通过２９Ｓｉ、２７ＡｌＭＡＳＭＭＲ、１Ｈ－２７ＡｌＣｐ／ＭＡＳＮＭＲ观测提供酸增强效应与脱铝程度、铝配位状态变化的关联．这些基本事实将有助于酸增强机制的进一步析解．
AbstractThe cnchanced catalytic activity of the mild hydrothemal dealuminated zeolite HZSM-5 was found in the condensation reaction of aldehyde. The NH3 temperature -programmed desorption experiments(by using a domestic omegatron mass spectroscopic equipment) showed that the NH3 desorption of the mild hydrothermal treated zeolite HZSM-5 was extended to the higher temperature in comparing with the parent material. The fact indicated the presence of the enchanced acidic sites in the hydrothermal treated sample.The framework Si/Al ratios of both parent and hydrothermal treated zeolite HZSM-5 samples were determined by 29Si MAS NMR observations in this way the dealumination degree of the sample with enchanced catalytic activity could be estimated quantitively.In comparing with the parent material, the 27Al MAS NMR spectra of the mild hydrothermal treated zeolite HZSM-5 samples appeared two additional NMR signals around 0ppm and 30ppm. The former was attributed to the sirfold-oxygen coordinahon non-framework aluminium created by the dealuminahon.The 30ppm signal was attributed to extra-lattice aluminium which was probably penta-coordinated. In the 27Al-IH CP / MAS NMR spectra. the 30pmm signal was enhanced.The fact indicated that the extra-lattice aluminium was strongly coupled in same way with protons in its local environment. Since the 30ppm signal didn't change much after impregnation the sample with a solution of acetylacetone(acac) in ethanol, and so this type of penta-coordinated extra-lattice aluminium was not as easy tO be removed by acac as the sixfold-oxygen coordinated non-framework aluminium.The mechanism of the enhanced acidity must be in same way related to those penta-coordinated extra-lattice Al species presenting in the mild hydrothermal treated zeolite HZSM-5 samples.
