焙烧温度对Mg(Al)O复合物结构和表面酸碱性质影响的研究  

Exploration on Influence of Calcination Temperature on Structure and Surface Acidity and Basicity of Mg (Al)O Composite Oxide

作　　者：李大塘[1] 郭军[1] 沈俭一[2] 屠迈[2] 

机构地区：[1]湘潭师范学院化学系,湘潭411201 [2]南京大学化学化工学院,南京210093

出　　处：《Chinese Journal of Chemical Physics》2000年第2期220-226,共7页化学物理学报（英文）

基　　金：湖南省自然科学基金!(No:98JJY2057);湖南省教委资助课题

摘　　要：分别在 ６７３、 ８７３和 １０７３ Ｋ分解 Ｍｇ／Ａｌ摩尔比为 ３的水滑石生成 Ｍｇ（Ａｌ）Ｏ复合物。ＸＲＤ测定均显示 ＭｇＯ物相。８７３Ｋ以上焙烧的样品同时存在ＭｇＡｌ_２Ｏ_４尖晶石物相。微量吸附量热测定其表面酸碱中心的强度和密度，发现碱中心强度和密度顺序为：ＭＡＯ—２＞ＭＡＯ—３≈ＭＡＯ－１，而酸中心强度和密度顺序是：ＭＡＯ—１＞ＭＡＯ—３≈ＭＡＯ—２．红外光谱表明，Ｍｇ（Ａｌ）Ｏ复合物表面酸碱中心主要存在Ｌ酸，破中心是氧阴离子。焙烧温度对表面碱中心类型几乎没有影响。固态ＭＡＳ^(２７)Ａｌ核磁共振结果展示，这些样品呈现出显著的Ａｌ^(３＋)配位情况的变化．Mg(Al)O composite oxides obtained from hydrotalcite compounds upon calcination at 673、 873 and 1073K, respectively, show the patterns of MgO by X-ray diffraction measurements. The samples calcined over 873K also show the patterns of MgAl_2O_4 spinel. Microcalorimetric measurements of NH_3 and CO_2 adsorptions were used to determine the strength and density of these sites. It is discovered that the basicity sequence is MAO-2>MAO-3 ≈MAO-1, While acidity order is MAO-1 >MAO-3≈MAO-2. NH_3 and CO+2 molecules were used as the probing molecules to investigate the nature of acid and base sites on Magnesium-Aluminium composite oxides. Infrared spectroscopic studies of these adsorped molecules indicated that the acid sites were mainly Lewis acid sites, whereas the base sites were surface oxygen anions. The results showed that the calcination temperature has little influence on the nature of surface base sites. Results of solid-state magic-angel-spinning ~27Al NMR revealed that significant transitions of coordinate state for Al^(3+) occur in the samples upon calcination at 673、873 and 1073K, respectively.

关 键 词：Mg(Al)O复合物 体相结构 焙烧温度 催化剂 

分 类 号：O643.32[理学—物理化学]