Synthesis, Characterization And Catalytic Applications Of Mesoporous Alumina

Alumina is widely used in chemical industry as catalysts, catalyst supports, adsorbents and so on. Its performances in application largely depend on the pore structures, morphologies and crystalline phases. Consequently, we put emphasis on the synthesis of mesoporous alumina materials with controlled textural properties and morphologies in this dissertation.Mesoporous alumina with crystallineγ-Al₂O₃ framework walls was successfully synthesized using boehmite sol as a precursor in the presence of surfactants. The structural properties of the products can be effectively controlled through adjusting the surfactant types, the boehmite precursor or the synthesis conditions. By means of various characterization techniques, it was demonstrated that the nonionic triblock copolymer surfactant acted as a structure-directing agent to direct the formation of alumina mesostructure through inducing the arrangement of rigid boehmite particulates. Such a new structure directing mechanism is quite different from the supramolecular templating mechanism that worked in the ionic surfactant-boehmite reaction system. The obtained mesoporous alumina presents high specific surface areas, large porosities and high thermal stabilities, which should be attributed to their crystalline framework walls and special scaffold-like mesostructures. In addition, we found the cheap and environmental-friendly hydro-carboxylic acids (HCA) can also act as a structure-directing agent for preparation of mesoporousγ-Al₂O₃ via thecoordination interaction between HCA molecules and boehmite particulates.A highly ordered mesoporous alumina with hexagonal symmetric mesostructure and crystallineγ-Al₂O₃ framework walls was firstly synthesized by faithful negative replication from the mesoporous carbon using a nanocasting route. Aluminum precursor with modified infiltration was in situ hydrolyzed and filled into the carbon pores to obtain a stable inorganic framework. The mesoporous carbon not only acted as a rigid template, but also effectively preserved the ordered mesostructure during the crystallization of amorphous framework walls through a stepwise calcination procedure.On the other hand, the morphologically controlled synthesis of mesoporous alumina was conducted in the reaction system Al(NO3)3-NH3-urea-surfactant. The surfactant not only acted as a template for the mesostructure formation, but also controlled the formation of various morphologies.The obtained mesoporous alumina shows good performances as catalyst supports in SO2 reduction with CO and methane low-temperature combustion reactions. The high surface areas, large pore volumes and narrow pore size distributions within the mesopore range of alumina supports can not only give rise to a high dispersion of the loaded active species, but also enhance the mass transfer during reaction processes, which resulted in a great promotion in catalytic performance.