| Abstract
| - In this study, a novel sol−gel method is used to synthesize amorphous silica−aluminamaterials with a narrow mesoporous distribution and various Si/Al molar ratios withoutusing any templates and pore-regulating agents. During the preparation procedure, onlyinexpensive inorganic salts were used as raw materials, instead of expensive and harmfulalkoxides. The precursor sol was dried at room temperature in a vacuum box kept at 60mmHg until it began to form the gel. The results of a nitrogen sorption experiment indicatethat the synthesized materials with different Si/Al molar ratios have similar mesoporousdistributions (within 2−12 nm). Moreover, it was found that the material's pore sizedistribution remains at a similar value during the heat treatment from room temperatureto 550 °C. On the basis of the nitrogen sorption, TEM, and AFM characterization results, aformation mechanism of mesopores which accounts for the experimental data is alsosuggested. This suggested mechanism involves rearrangement of the primary particles duringthe drying process to form the precursors of the similarly sized mesopores. The synthesizedmaterials were characterized by XRD, thermal analysis (TG/DTA), 27Al and 29Si MAS NMRspectroscopy, SEM, TEM, and AFM. The results of 27Al and 29Si MAS NMR indicate thatthe distribution of silicon and aluminum in the synthesized materials is more uniform andhomogeneous than that in the mixed oxides prepared via the traditional sol−gel methodeven at high alumina contents. The type and density of the acid sites were studied usingpyridine adsorption−desorption FTIR spectroscopy. It was shown that the acidity of thesynthesized materials is higher than that of the silica−alumina materials prepared byconventional methods.
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