Amphiphilic organosilane directed synthesis of iron and aluminum containing mesoporous silicates

Abstract only

Brønsted acidity of Al/SBA-15

To increase the content of well-dispersed aluminium in Al/SBA-15 and its Brønsted acidity, a water-free synthesis method involving a Si-O-Al precursor was employed to preparea series of Al/SBA-15 of widely varying composition. The materials were characterized with ICP, BET, TEM, 27Al MAS NMR and IR spectroscopy and compared to conventionally prepared Al/SBA-15. For low Al content (Si/Al >10),the conventional approach leads to highly dispersed, predominantly isolated Al with well-ordered mesopores.Athigher Al content, the order decreasedor was even completely lost.In general, this led to the agglomeration of Al species on the surface. Although in most cases a substantial part of Al atomsexhibit tetrahedral coordination indicating their high dispersion and interaction with the silica, the overall Brønsted acidity of these Al/SBA-15-type materials is very low. The overall acidity of all Al/SBA-15 is of the same order as amorphous silica-alumina. By IR spectroscopy of H/D exchange with perdeuterobenzene, it was found that the intrinsic acidity of the acid sites in Al/SBA-15 is similar to that in zeolites and amorphous silica-alumina, thus further confirming that acid site concentration dominates differences in acidity of aluminosilicas

In situ synthesis and characterization of a hierarchically structured Al(2)0(3)/Al(3)Ti composite

A hierarchically structured α-Al₂O₃/Al₃Ti composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and TiO₂. The microstructure of the composite was investigated by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. Three transitional phases, specifically TiO, Ti₂O₃, and γ-Al₂O₃, were found to form during the reactive process. Using differential scanning calorimetry, it was found that the reaction between the Al and TiO₂ occurred through three intermediate steps and their corresponding activation energies were 390, 205, and 197 kJ/mol, respectively. Moreover, the reaction rate of the third step was found to be much higher than that of the second step, and the time taken by each reaction step decreased with the increase of the heating rate. The findings are critical to understanding the microstructural development in the synthesis of strong and tough Al₂O₃/Al₃Ti composites.Heguo Zhu, Yaling Jiang, Jinzhu Song, Jianliang Li, Paul Munroe, Zonghan Xi