An Optimized Procedure for the Synthesis of AlSBA-15 with Large Pore Diameter and High Aluminum Content

Abstract

A series of AlSBA-15 materials with different nSi/nAl ratio have been synthesized by simply adjusting the molar water to hydrochloric acid ratio (nH2O/nHCl). It was possible to control the nSi/nAl ratio, location, and coordination of Al atom in the SBA-15 silica matrix by the above method. Moreover, AlSBA-15 with nSi/nAl ratio up to 7 can be successfully prepared by adjusting the nSi/nAl ratio in the synthesis gel at nH2O/nHCl of 276. The effect of the nature of Al source in the AlSBA-15 synthesis has been investigated using different aluminum source, viz., aluminum sulfate, aluminum nitrate, aluminum hydroxide, and aluminum isopropoxide. Aluminum isopropoxide was found to be the good aluminum source for AlSBA-15 material synthesis and enhanced the amount of aluminum incorporation, location, and coordination in the SBA-15 silica walls. The effect of synthesis temperature of AlSBA-15 materials has also been reported. Nitrogen adsorption measurement shows that the pore diameter of AlSBA-15 can be tuned from 9.7 to 12.5 nm by simply adjusting crystallization temperature from 100 to 130 °C. The pore volume increases from 1.35 to 1.55 cm3/g with a concomitant decrease of the surface area from 930 to 783 m2/g. For the first time, the mechanical stability of hexagonal AlSBA-15 materials was studied by applying different pelletizing pressures and subsequent characterization by XRD, N2 adsorption, and mercury porosimetry. n-Heptane adsorption isotherms were recorded to evaluate the uptake of organics of the compressed materials. It has been found that mechanical stability of AlSBA-15 is lower compared to that of pure silica SBA-15 materials.