Pore Size Engineering and Mechanical Stability of the Cubic Mesoporous Molecular Sieve SBA-1

Abstract

The influence of HCl/surfactant ratio (nHCl/nS) and synthesis time on the synthesis of the cubic mesoporous molecular sieve SBA-1 were investigated to obtain high-quality materials. The samples prepared at a nHCl/nS ratio of 280 were found to exhibit a higher degree of structural ordering, a higher specific surface area, and a higher specific pore volume as compared to materials prepared at a lower nHCl/nS ratio. The pore diameter of SBA-1 can be tuned from 2.3 to 3.0 nm by simply adjusting the synthesis time between 1 and 72 h. The pore volume increases from 0.7 to 1.03 cm3/g with a concomitant decrease of the surface area from 1430 to 1100 m2/g. Moreover, the stability of the materials toward washing with water was improved by increasing the crystallization time from 1 to 72 h. The mechanical stability of SBA-1 was also investigated using n-heptane and cyclohexane adsorption in addition to nitrogen adsorption. The mechanical stability of SBA-1 is high; by compression of about 217 MPa, the specific pore volume calculated from nitrogen adsorption decreases by 19.7%, whereas the pore volume calculated from the n-heptane and cyclohexane adsorption decreases by 12.5% and 7.5%, respectively. These results together with the large difference between the pore volumes obtained by nitrogen and organics adsorption indicate that the presence of microporosity in the SBA-1 pore walls has to be considered. SBA-1 is mechanically more stable as compared with hexagonal mesoporous materials such as MCM-41 and SBA-15, but exhibits similar mechanical stability as compared to the cubic MCM-48 material.