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

The catalytic oxidation of toluene over Ag/SBA-15 synthesized under different pretreatment condidons, including 02 at 500 degrees C (denoted 0500), H-2 at 500 degrees C (H500), and O-2 at 500 degrees C followed by H-2 at 300 degrees C (0500-H300) was studied. The pretreated samples were investigated by N-2 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 Ag-20 and lower adsorption capacity for toluene. H-2 pretreatment at 500 degrees 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 nanopartides as well as the existence of subsurface oxygen. (C) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.