水滑石分解物表面酸碱性质微量吸附量热研究

分别在６７３Ｋ、８７３Ｋ和１０７３Ｋ分解Ｍｇ／Ａｌ摩尔比为３的水滑石生成３ＭｇＡｌＯ复合氧化物．ＸＲＤ测定均显示ＭｇＯ物相，８７３Ｋ以上焙烧的样品同时存在ＭｇＡｌ２Ｏ４尖晶石物相．用ＮＨ３和ＣＯ２作探针分子，红外光谱测定其酸碱位，主要存在Ｌ酸，而碱位是氧阴离子．微量吸附量热测定其表面酸碱强度，发现碱强度顺序为：８７３Ｋ＞１０７３Ｋ＞６７３Ｋ，而酸强度顺序是：６７３Ｋ＞１０７３Ｋ＞８７３Ｋ，这种现象可能与１０７３Ｋ样品生成了更多尖晶石及Ａｌ３＋在表面富集有关

MICROCALORIMETRIY STUDIES OF SURFACE ACIDITC AND BASICITY MAGNESIUM- ALUMINUM MIXED OXIDES OBTAINED FROM HYDROTALCITE

Magnesiumaluminum mixed oxides obtained from hydrotalcite compounds upon calcination at 673 K, 873 K and 1 073 K, respectively, show the xray diffraction patterns of MgO. The samples calcined over 873 K also show the patterns of MgAl 2O 4 spinel. NH 3 and CO 2 molecules were used as the probing molecules to investigate the nature of acid and base sites on magnesiumaluminium mixed 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. Microcalorimetric measurements of NH 3 and CO 2 adsorptions were used to determine the number and strength of these sites, It is discovered that the basicity sequence is 873 K>1 073 K>673 K, while acidity order is 673 K>1 073 K>873 K. It is likely that the phenomena is related to the far extra MgAl 2O 4 spinel formed at 1 073 K and the enrichment of Al 3 species on the surface.