Study On Preparation Of Catalyst Active Alumina

Active alumina has advantages of porosity、high superficial area and good adsorbability, so the products of different surface area and pore volume can be obtained by controlling the preparing condition.Active alumina has been used most widely in the field of catalyst carrier due to the imperfect crystal structure and adjustable pore structure. But in some systems when the reaction temperature is very high, the catalyst may have a sharply down of its surface area and pore volume, which made the active site lost and decrease the catalyst activity suddenly.There are three contents in this paper:The preparation and modification of active alumina;the adsorbability experiment of modified active alumina; the characterization of modified active alumina.La-doped and Ce-doped active alumina was prepared through sol-gel,impregnation,citric acid in this paper. The product of optimal adsorption property was obtained by adsorbability experiment about fluorinion and phosphate in waste water. The effect of different preparation method on the crystal phase, surface areas, pore structure and surface acidity of active alumina was investigated by XRD, BET and IR.The results showed that the sol-gel was the most effective on improving the surface areas and thermal stability of active alumina.5%Ce-doped product had the best adsorbability effect of fluorinion in waste water, adsorbing capacity3.988mg.g-1. Its surface area was268.72m2.g-1, the pore volume was0.2712cm3.g-1and the average pore diameter was103nm after calcination at pH=10,550℃for5h. We speculated that,Ce taken as Ce3+mode filled the vacancy in active alumina and restrained the agglomeration of alumina at high temperature. However, part of Ce3+oxidized Ce4+at high temperature led to Ce separated out in the form of CeO2.Because of different valency between the Ce4+and Al3+, part of the crystalline cell distorted led to decreasing the crystal stability and increasing the crystal transition.5%La-doped product had the best adsorbability of phosphate in wast water,adsorbing capacity50.61mg.g-1.Its surface area was311.07m2.g-1, the pore volume was0.2766cm3.g-1and the average pore diameter was95nm after calcination at pH=8,650℃for6h. We speculated that, the stabilization of La-doped active alumina was mainly because of perovskite-type LaA103formed in the surface of active alumina.Firstly,these stable compounds nucleate,and firmly anchor in corner of Al2O3lattice in the form of interfacial bonding.They prevent sintering and surface diffusion,further restrain the crystal transition.The difference of surface properties and thermal stability of La-doped and Ce-doped active alumina may be due to the different modification mechanism.