Effect of pretreatment conditions on catalytic activity of Ag/SBA-15 catalyst for toluene oxidation

Abstract

The catalytic oxidation of toluene over Ag/SBA-15 synthesized under different pretreatment conditions, including O2 at 500 °C (denoted O500), H2 at 500 °C (H500), and O2 at 500 °C followed by H2 at 300 °C (O500-H300) was studied. The pretreated samples were investigated by N2 physisorption, X-ray diffraction, and ultraviolet-visible diffuse reflectance. The pretreatment atmosphere greatly influences the status of the Ag and O species, which in turn significantly impacts the adsorption and catalytic removal of toluene. Ag2O and amorphous Ag particles, as well as a large amount of subsurface oxygen species, are formed on O500, and the subsurface oxygen enhances the interaction between Ag species and toluene, so O500 shows good activity at higher temperature. However, its activity at lower temperature is not as high as expected, with a reduced presence of Ag2O and lower adsorption capacity for toluene. H2 pretreatment at 500 °C is conducive to the formation of large Ag particles and yields the largest adsorption capacity for toluene, so H500 exhibits the best activity at lower temperatures; however, because of poor interaction between Ag and toluene, its activity at higher temperature is modest. The O500-H300 sample exhibits excellent catalytic activity during the whole reaction process, which can be attributed to the small and highly dispersed Ag nanoparticles as well as the existence of subsurface oxygen.