Synthesis, Characterization And Catalytic Performances Of Nanosized Al-kit-1Mesoprous Molecular Sieve

The disordered KIT-1is a three-dimensional mesoporous molecular sieve with uniform "wormlike" pore structure. These unique properties provide it high surface area and excellent transportation ability. Nanosized mesoporous silica nanoparticles have drawn particular attention due to its controllable size, morphologies and fast mass transport. They show excellent performace in the helds of catalysis, nanoreactors, sensors, separation, chromatography and inclusion chemistry etc.The formation mechanisms of mesoporous molecular sieves have been studied extensively. Two main mechanisms, liquid-crystal template mechanism and cooperative self-assembly formation mechanism have been put forward. In this study, UV Raman spectroscopy, combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM), were used to study the formation process of mesoporous molecular sieve and short-range interactions between surfactant, silica species and salts. The obvious change of the Raman bands related to the surfactants supports a cooperative interaction between surfactant and inorganic species during self-assembly process. The addition of EDTANa4to the system induces the interaction between the COO-groups of EDTA4-and sianol groups of silica and a strong interaction between the EDTA4-and the N+(CH3)3groups of the surfactant. The above interactions may be the main reason for the salt effect.The mophorlogy, structure, acid property and catalytic performance of nanosized Al-KIT-1have been systematic studied. It is found that the morphology can be controlled by alkali addition sequence and the type of alkali. The samples used basic media with buffering capacity (ammonia, triethanolamine and diethanolamine) as base media display sphere-like shape nanoparticle with sizes of40-80nm. When NaOH is used as the basic media, such nanoparticle can be obtained only after adjusting pH value twice. This indicates that stabilizing pH value during self-assembly is significant for the formation of the sphere-like shape nanoparticle. An increase in aluminum content in a proper range leads to less uniform particle size distribution, a decrease in pore size, an increase in framework aluminum concentration and the presence of strong acid sites. Cumene dealkylation is a strong acid-catalyzed reaction. The samples with strong acid sites exhibit higher activity. In contrass1, weak to medium acid sites are required for the cracking of1,3,5-triisopropylbenzene. All the samples exhibit very high activity in1,3,5-triisopropylbenzene cracking. The cracking extent of cumene and1,3,5-triisopropylbenzene becomes deeper with decreasing the Si/Al ratios. The above results provide useful information on the synthesis and application of nanozised Al-KIT-1.