Direct synthesis and characterization of pore-broadened Al-SBA-15

A series of pore-broadened Al-SBA-15 samples were synthesized using a direct hydrothermal method . The effects of aluminum incorporation, assembling temperature, and co-solvent (1,3,5-trimethylbenzene (TMB)) content were investigated by low-angle XRD , N 2 adsorption and desorption isotherm analysis, SEM, TEM , NH 3 -TPD, FTIR, pyridine-IR, and 27 Al NMR. The results indicated that aluminum incorporation (Si/Al ratio = 10) increased the pore size of SBA-15 from 5.66 to 10.13 nm. A small pore size of 6.55 nm was observed at a low assembling temperature of 30 °C, attributing to the inadequate stretching of the molecular template. An increased pore size of 8.45 nm was obtained at an assembling temperature of 60 °C because of the partial hydrophobization of the hydrophilic groups , whereas a high temperature of 70 °C resulted in the generation of least ordered pores. The hydrophobic co-solvent TMB showed a significant broadening level as a result of its effective fusion into the hydrophobic micelle cores. A highly ordered pore framework with a pore size of 18 nm was obtained at a TMB/P 123 ratio of 0.25, which was found to be optimum. More or less TMB led to the generation of mesocellular silica-aluminum foams with a complete loss of regularity. The 27 Al NMR results showed that aluminum was mostly tetrahedrally coordinated. The NH 3 -TPD and pyridine-IR detection results indicated that a number of weak and medium acid sites (as Bronsted and Lewis acid sites) existed in Al-SBA-15 pore-broadened by TMB.