Mesoporous titanosilicates synthesized from TS-1 precursors with enhanced catalytic activity in the alpha-pinene selective oxidation

摘要

Ti-containing mesoporous catalysts have been successfully prepared using zeolite precursors as building blocks of the mesoporous network.Tetrapropylammonium (TPA) cations were used as structure directing agent in the TS-t precursor solutions.The assembly of the polymeric zeolite precursor species into a mesophase was carried out at room temperature assisted by cetyltrimethylammonium bromide as surfactant.Various techniques including XRD,diffuse reflectance UV-vis (DRUV-vis),N2 adsorption,SEM,transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) were employed for the materials characterization.Ti was incorporated into the silica framework in isolated sites,anatase phase was not observed.These materials were catalytically tested in the oxidation of a-pinene with aqueous H2O2,showing an enhanced activity when compared to a conventional mesoporous titanosilicate.Both a catalyst obtained from a precursor gel containing Na and aged at 80 °C for 1 day and one obtained from a precursor gel without Na but aged for 2 days at 80 °C showed the highest activity and selectivity to products arising from epoxidation mechanism.This feature can be attributed to a chemical environment of the Ti species very close to that in titanosilicalite and clearly distinguishable from that in a conventional mesoporous catalyst.An addition of peroxide after the first reaction hour allowed us to increase the conversion values in ~30%.