Research Of Mesoporous Alumina Synthesized By A Ph Swing Method

Mesoporous 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 andcrystalline phases. In the traditional pH swing method, It always desires to swing many times toobtain high quality alumina, however, with Al(NO3)3·9H2O and NaOH as raw material.Mesoporous γ-alumina was synthesized through a pH swing method with pH swing only twicein this paper, and the synthesis of mesoporous alumina materials with high quantity texturalproperties is investigated in detail.It is investigated that the influence of reaction temperature, aging temperature, aging timeand reaction time on acid side The XRD results showed that pure boehmite was prepared at90°C without aging, furthermore, it could also be obtained at a relatively lower temperature (80℃) by adjusting the aging time to as short as0.5h. Meanwhile, through TG-DSC analysis, wefound that the optimal calcinations condition was that600℃、4h, then the optimal synthesisconditions were given, the reaction temperature was90℃, aging temperature was90℃andthe reaction time on acid side was5min, and the optimal mesoprous γ-Al2O3was obtained withthe specific area of241.95m2.g-1, the pore volume of0.61, and the BJH pore diameter of23.1nm.Noninonic surfactants such as LA and PEG2000, ionic surfactants such as CTAB and SDSwere added to survey the effect on pore structure of mesoporous alumina in the system. Theexperimental results showed that they had different effect on texural properties of mesoporous,especially when PEG2000was added, it can made the BET surface area increased from241.95m2.g-1to270.4m2.g-1, the pore volume increased from0.61cm3.g-1to0.87cm3.g-1, and the BJHpore diameter increased from15nm to23.1nm.In order to to investigate the action mechanism of PEG with precrusor in the process ofalumina synthesis, molecular weight of1000,2000,10000and20000were added into thesystem respectively. The results proved that the BJH pore size remain unchanged, but the BETsurface area and pore vlomne increased sharply with the molecular weight increased. To getoptimal pore parameters, PEG2000was most suitable. Basis on the experimentel results, themutual effect model between PEG moleculars and alumina moleculars was derived. We foundthat the steric hindrance effect of PEG increased with the boost of the molecular weight, however, when molecular weight was too much large, the molecule chains become long, and the molecularvolumne of PEG become large, which resulted to intermolecular entangle mutually, so it is hardto form uniform protective film, finally poor pores was obtained. On the basis ofabove-mentioned results, the model diagram between PEG moleculars and alumina molecularswas derived.