摘要
探讨了用电负性来表征分子筛的物理化学性质。分子筛平均电负性不仅受分子筛硅铝比的影响,而且也受分子筛组成中阳离子含量和阳离子价数的影响。本文推导了混合阳离子型和多价阳离子型分子筛平均电负性的表达式。从研究分子筛平均电负性S_(int)和脱附活化能Ed间的关系出发,讨论了分子筛吸附作用的强弱,并与TPD图谱分析结果进行了比较。对同系列分子筛吸附体系,Ed与S_(int)间呈线性关系:Ed=a+bS_(int)。因此对给定的吸附体系,S_(int)能用来判断和预测吸附作用的强弱。
Electronegativity is a very useful parameter which can describe the physico-chemical properties of zeolites. According to the Sanderson's electronegativity model, zeolite intermediate electronegativity (Sint ) of the mixed cation type (e.g. Na and H type) is given asand for the multivalent cation type (e.g. Ms+ type) is given asThe influence of the Si/Al ratio, cation content and cation valence of zeolite on the activation energy of desorption is explained by using Sint. For zeolites with different Si/Al ratios or different cation types, the activation energy of desorption (Ed ) increases with the decreasing of Sint. As cation content increases, Sint, decreases and the electrostatic interaction between zeolites and adsorbate molecules increases, therefore, the total adsorption energy increases. There is a linear relation between Ed and Sint, in a homologous zeolite series, it can be represented by Ed = a + bSi ,. The values of a and b are different for different adsorption systems. Above discussion is in agreement with the calculated results from TPD profile. S;, , can also predict the adsorption interaction for the given adsorption system with the use of only the chemical formula of zeolite. The relation between Ed and the net atomic charges in zeolite is the same as that between Ed and Sint.
