| As the catalyst carrier, activity alumina has the characteristic of thermo stability and ant oxidation. In domestic and foreign, it widely serves as the carrier of automobile exhaust catalyst, petroleum refining catalyst, hydrogenation and hydrodesulfurizing catalyst and so on. Alumina is a ionic bond compound with strong chemical bond. It can divide into quality different various crystal such as delta-, chi-, kappa-, eta-, beta-, gamma- and alpha-alumina according to different crystal texture. Gamma-alumina, beta-alumina and alpha-alumina are mainly and obtain the important application in the actual industry.At present the application of gamma-alumina is the most widely as a coating material, and the effect of it to expand the surface is good. Gamma-alumina is often obtained through burning hydrate of alumina. However, gamma-alumina which usually constitutes the activation coating will chang into alpha-alumina in above of 800℃, it can cause density increase, suface area reduced and pore structure collapsed. And in above of 1200℃, the activation coating will expoliated from the vector, and will caused gas resistance and activity decreased. Adds lanthanum can stabilize the crystal structure of alumina, causes the activation coating keep stable under high temperature, and suppresses the active lost.In this paper, for the above-mentioned the existence of activated alumina problem, research of preparation for high temperature high surface area activated alumina was system carry on.In the course of heat stabilizer he study, La3+ was found that have the best the modified effect, Ce4+ lies the second, and, Pr3+, Nd3+, Sm3+ perform poor and performance of Er3+, Y3+is the worst. This order is the same to the added the size order of ionic radius of rare earth elements La3+> Ce3+> Pr3+> Nd3+> Sm3+>Er3+> Y3+, which indicating that the greater of ionic radius, the better the stability. At the same time, valence of ions also have affect on the stability results, this was mainly due to large ionic radius and the valence state would reduce ion mobility, which can prevent the sintering of alumina at the surface of alumina at a fixed high temperature.As a prominent impact of La2O3, at the same time, its price are relatively low (30 yuan per kg), so the application prospects will be more promising. The author confirm that the lanthanum carrier as the best heat oxide alumina stabilizer.As to the preparation methods of activated alumina, study mainly on the AICl3, A12(SO4)3, Al(NO3)3 sol method and (NH4)Al(SO4)2,(NH4)Al(CO3)2 decomposition method. Under the same conditions, that is,heat stabilizer for La2O3,pore-expanding agent were PEG, activated carbon,EDTA,the preparation of alumina particles calcined at 1200℃for 1 hour. And then use DAT, SEM to analyze the activity of alumina particles, the study found that using the sol method with AICl3, Al2(SO4)3 and Al(NO3)3,the size, pore volume,pore size and surface area of production alumina particle is more or less the same; as a new type of pollution-free raw materials (NH4)Al(CO3)2 has become a recent research hotspot,in the (NH4)Al(CO3)2 decomposition method, as a result of low decomposition temperature of CO32+ than SO42-,although small particles of alumina generate in calcined, but bubble-like alumina could not generated,so high-temperature decomposition of the activity of alumina the formation by the (NH4)Al(CO3)2 decomposition method is of slightly higher than the sol method;and during (NH4)Al(SO4)2 decomposition process at high temperature formed a bubble-like structure of the alumina,compared with other preparation methods,the high-temperature alumina prepared by (NH4)Al(SO4)2 decomposition method has the smallest particles size,the highest activity, the largest surface area,so to determine ammonium aluminum sulfate as the best preparation agents of high temperature high surface area activated alumina.During the preparation process of activity alumina at low temperatures,phosphate and silicate additives can effectively improve the activity of alumina.Therefore,in the preparation process of high temperature of high surface area activated alumina,adding phosphate and silicate additives through DAT,SEM to analyze the activity of alumina particles.The experimental results show that after the adding of phosphate and silicate additives,although increased alumina surface area, but the level of increase is very small, did not meet the specific surface area activated alumina it should have.Therefore,the method of use of additives does not suit for preparation process of high temperature activated alumina.Although commonly used pore-expanding agent such as (NH4)2CO3,PEG,activated carbon,EDTA,etc.can effectively raise the activity of activated alumina,but have very little influence on the process of preparation the high temperature high surface area activated alumina,which mainly because that most pore-expanding agent’s decomposition temperature is too low.Through this experiment the synthesis solid contains [La(EDTA)]- used as the pore-expanding agent,by reaming ammonium aluminum sulfate experiment and the following DAT,SEM analysis,we draw such conclusions:synthesis containing high-temperature solid containing [La(EDTA)]-pore-expanding agent,using a method of solids-solid mixture,the large pore structure of all the experimental samples increase,resulting in the same larger specific surface area a high temperature of 1200℃. Scanning electron microscopy showed that under high temperature alumina has a large diameter 10-30nm porous network structure.,the four samples synthesized which calcined at 1200℃for 1h have 120m2/g or more specific surface area, in which the sample of x([La(EDTA)]-)=1% have surface area of 150.36 m2/g, much higher compared to the literature information under same condition.Method for preparation for activated alumina with high specific surface area. Heat stabilizer is La2O3 and molar ratio of La2O3 and Al2O3 is 1:100; pore-expanding agent is H[La(EDTA)]·16H2O crystals which synthesis by EDTA and heat stabilizer with the molar ratio of 1:1. |
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