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, NH3-TPD, FTIR, pyridine-IR, and Al-27 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 degrees 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 degrees C because of the partial hydrophobization of the hydrophilic groups, whereas a high temperature of 70 degrees 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 Al-27 NMR results showed that aluminum was mostly tetrahedrally coordinated. The NH3-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. (C) 2016 Elsevier Inc. All rights reserved.