Sol-gel synthesis of micro-mesoporous aluminosilicates using oligoesters of ortho-silicic acid

A method for sol-gel synthesis of micro-meso- and mesoporous aluminosilicates (MAS) was developed using the commercially available raw materials (a mixture of ethylsilicate-40 type oligoesters of ortho-silicic acid and alcohol water solutions of aluminium nitrate). The influence of pH on the porous structure of aluminosilicates with various Si/Al ratios was studied. A variation in pH at the hydrolysis stage was shown to allow both microporous and mesoporous aluminosilicate with a narrow pore size distribution to be synthesized, the specific surface area being varied from 341 to 684 m2/g, specific pore volume from 0,2 to 0,95 cm3/g, pore diameter from 0,17 to 40 nm, total ammonia acidity from 226 to 405 μmol/g. The acidic properties of the samples with different SiO2/Al2O3 ratios and their catalytic activities were studied using the model reaction of α-methylstyrene dimerization (80 °C, 10 wt.% MAC, the initial α-methylstyrene concentration 3.3 mol/l in chlorobenzene). The maximal α-methylstyrene conversion (99,8 %) was observed over the catalysts at the SiO2/Al2O3 ratios equal to 5 and 20 when the concentrations of acid sites are maximal. The micro-mesoporous aluminosilicates are promising catalysts for acid-base transformations of various organic compounds.

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