Synthesis and characterization of mesoporous Si-modified alumina with high thermal stability

Abstract

Mesoporous alumina with pseudo-boehmite phase modified by water glass was prepared by using the cation–anion double hydrolysis method from mixed aqueous solution of aluminum sulfate and sodium aluminate. The texture structure and acidity of these samples was studied with the assistance of characterization techniques, such as X-ray diffraction (XRD), N2 adsorption–desorption isotherms, 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) and Fourier transform infrared (FTIR) spectroscopy. The XRD and N2 adsorption–desorption results show that the addition of sodium silicate can decrease the crystallinity of alumina, but greatly improve pore volume and surface area. The highest pore volume (1.46 cm3/g) and surface area (427.69 m2/g) can be simultaneously obtained when the adding amount of silica is up to 12 wt%. The NMR and FTIR results display that the presence of a certain amount of silicon can generate AlV in alumina, which is considered to be related with strong acid sites. In addition, the acidity of the Si-modified alumina samples can be adjusted by changing the amount of silica.