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

微孔晶体内外表面表面性质的判别表征

基本信息

批准号：
63550595
负责人：
TAKE Jun-ichiro
金额：
$ 1.28万
依托单位：
THE UNIVERSITY OF TOKYO
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

项目摘要

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.

用吡啶-三烷基丙氨酸BDA(碱双吸附)法、XPS和大分子BET法表征了各种沸石的Bronsted酸性质和比表面积。沸石有钠沸石、ZSM-5、铁氧体、L沸石和氢型沸石/硅沸石。结果表明：(1)沸石内、外表面的Bronsted(B)酸强度分布有很大差异。内表面既有强B位，也有弱B位；而外表面没有强B位。对于L沸石、ZSM-5沸石和沸石/铁沸石来说，外部B位很弱，而对于丝光沸石和铁沸石来说，外部B位很弱。(2)随着骨架中Si/Al比的增加，内部B酸强度分布向更高的酸强度方向移动。这种位移与Si(1Al)单元的浓度有关，而与微孔结构或尺寸无关。(3)外Bronsted酸强度与外表面层的Si/Al比无关，而与沸石的种类有关。(4)骨架Al原子在晶外的表面密度小于晶内。因此，外表面的布朗斯特酸中心的数量低于外表面积与内表面积之比的预期。(5)大分子如全氟三丁胺的吸附有助于测量具有大孔道的沸石的外表面积。