Synthesis And Thermal Stability Of Ordered Mesoporous Alumina

Mesoporous alumina has been widely used as adsorbents, catalysts and catalyst supports for its excellent structural properties and surface acid/base property, which has been made the synthesis of mesoporous alumina with higher surface area and thermal stability become the research hot-pot. At present, the synthetic methods for mesoporous alumina include sol-gel, precipitation, cation-anion double hydrolysis, solvothermal synthesis, microemulsion templating, spray pyrolysis method. Although some valued progress has been made, the alumina synthesized by above methods has lower surface area (<400 m2/g) and thermal stability. In order to improve the thermal stability, the phase transition under high temperature was investigated. The sintering of alumina is attributed to the dehydration between adjacent alumina particles and the nucleary of a-alumina. The thermal stability of ordered mesoporous alumina has been obviously improved for its ordered mesostructure and large pore volume, which is probably because the ordered mesostructure reduces contact between adjacent alumina particles and nucleary rate of a-alumina. At present, sol-gel and hard templates method are reported to synthesize the ordered mesoporous alumina. However, there are few literatures have been reported, which is due to the hard templates method needs strict and complex conditions and the interface protectors are not easy to choose for the sol-gel method. In this dissertation, sol-gel method was introduced to synthesize the ordered mesoporous alumina and the impacts of interface protectors were investigated.(1) Employing P123 as the structure director, the surface area and thermal stability of ordered mesoporous alumina synthesized by different types of interface protectors were investigated. (2) The ordered mesostructure, surface area and thermal stability of alumina influenced by binary interface protectors were investigated. (3) Base on above results, cerium and cerium-zirconium were supported on synthesized alumina. The impact of above metal oxide on thermal stability of alumina was investigated.Through above research activities, some meaningful results are obtained.1. The surface area and thermal stability of alumina are improved by introducing aniline, benzoic acid, o-diaminobenezene and phthalic acid. However, only the proper amounts of phthalic acid can lead to the formation of ordered mesostructure. When the n(phthalic acid)/n(Al) is 0.25, the surface area of alumina is 432 m2/g (400℃) and 227 m2/g(800℃).2. The surface area and thermal stability of alumina are improved by introducing the mixture of citric acid and salicylic acid. When n(citric acid)/n(Al) is 0.05, n(salicylic acid)/n(Al) is between 0.05-0.15, ordered mesostructured alumina was obtained. Compared with the samples synthesized by citric acid or salicylic acid alone, the samples obtained by addition of binary interface protectors possess more ordered mesostructure and higher surface area and pore volume. When n(citric acid)/n(Al) is 0.05, n(salicylic acid)/n(Al) is 0.1, the obtained sample has a large surface area (521 m2/g), pore volume (0.82 cm3/g). after being calcined at 800℃, surface area is still up to 300 m2/g and pore volume 4.4 cm3/g.3. When n(citric acid)/n(Al) is 0.05, n(salicylic acid)/n(Al) is 0.05, the introduction of different amounts of cerium (n (Ce)/n (Al)=0.02-0.12) can promote the thermal stability of alumina and lead to the formation of highly dispersed ceria supported on ordered alumina.4. When n(citric acid)/n(Al) is 0.05, n(salicylic acid)/n(Al) is 0.1, a series of Ce-Zr/ Al2O3 (n(Ce)/n(Al)=0.02-0.08, n(Ce)= n(Zr)) with ordered mesoporous structure are successfully synthesized. The introduced cerium and zirconium are highly dispersed on the surface of alumina and obviously promote the thermal stability of alumina.