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

Mg(A1)O composite oxides obtained from hydrotalcite compounds upon calcination at 673、 873 and 1073K, respectively, show the pattems of MgO by X-ray difffraction measurements. The samples calcined over 873K also show the patterns of MgA12O4 spinel.Microcalorimetric measurements of NH3 and CO2 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. NH3 and CO2 molecules were used as the probing molecutles 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 Al3+occur in the samples upon calcination at 673、873 and 1073K, respectively.