DISCRIMINATIVE CHARACTERIZATION OF SURFACE PROPERTIES IN THE INTERNAL EXTERNAL SURFACES OF MICROPOROUS CRYSTALS

各种沸石的布朗斯台德酸性质和表面积已经通过吡啶-三烷基胺BDA（碱双吸附）方法、XPS和使用大分子的BET方法用内表面和外表面的区分来表征。沸石是氢形式的丝光沸石、ZSM-5、镁碱沸石、L沸石和菱钾沸石/毛沸石。结果表明：（1）分子筛内、外表面的B酸强度分布有很大差异;在内表面中，强和弱B位点均被定位;而在外表面中，不存在强B位点。外部B位对于L沸石、ZSM-5和菱钾沸石/毛沸石是弱的，或者对于丝光沸石和镁碱沸石是极弱的。(2)随着骨架中Si/Al比的增加，内部布朗斯台德酸强度分布向更高的酸强度移动。这种位移与Si（1Al）单元的浓度有关，而与晶体结构和尺寸无关。(3)外质子酸强度与外表面层的硅铝比无关，而取决于沸石的种类。(4)晶外骨架Al原子的面密度小于晶内骨架Al原子的面密度。因此，外表面中的布朗斯台德酸位点的数量低于从外表面积与内表面积比预期的数量。(5)大分子如全氟三丁胺的吸附可用于测量具有大通道开口的沸石的外表面积。

Bronsted acidic properties and surface areas of various zeolites have been characterized with discrimination of the internal and external surfaces by the pyridine- trialkylanine BDA (Base Dual-Adsorption) method, XPS, and the BET method using bulky molecules. The zeolites were inordenites, ZSM-5, ferrierite, L zeolite, and offretite/erionite in their hydrogen forms. The followings have been proved for all the zeolites:(1) The Bronsted (B) acid strength distribution is quite different between the internal and external surfaces. In the internal surface, both strong and weak B sites are located; whereas, in the external surface no strong B sites are present. External B sites are weak for L zeolite, ZSM-5, and offretitie/erionite or extremely weak for mordenites and ferrierite.(2) The internal Bronsted acid strength distribution shifts to higher acid strength with increasing Si/Al ratios in the framework. This shift is related to the concentration of Si(1Al) units, but not to the micropore structure or size.(3) External Bronsted acid strength has no relation to the Si/Al ratio in the external surface layer and depends on the kind of zeolites.(4) The surface density of framework Al atoms is smaller in extra-crystalline than in intracrystalline. Consequently the population of Bronsted acid sites in the external surface is lower than that expected from the external to internal surface area ratio.(5) Adsorption of bulky molecules such as perfluorotributylamine is useful for measuring the external surface area of zeolites with large channel openings.