Some insights on the negative effect played by silylation of functionalized commercial silica in the direct synthesis of hydrogen peroxide

The surface of sulfonic acid functionalized silica has been modified by silylation, using two silylating agents: (CH3)3SiCl and CF3(CF2)5(CH2)2Si(CH3)2Cl. The modified supports were characterized by different techniques. For these systems, BET specific area was found to decrease upon silylation, but the effect on other textural properties depends on the silylating agent used. Once modified the supports were taken to prepare catalysts by ionic exchange with a palladium salt. The palladium species ratio depends on the used support. Catalyst system of supported palladium nanoparticles deposited on HSO3-functionalized commercial silica produces hydrogen peroxide with a high yield by feeding a non-flammable H2/O2 mixture into a non-acidic catalyst-methanol suspension at 313 K. However, catalysts prepared with silylated supports show a low yield to hydrogen peroxide, due to low H2O2 selectivity. The drop in the selectivity to hydrogen peroxide is related with the different proportion of palladium species present in silylated catalysts as compared to non-silyled sample.