Identifying Surface Active Sites of SnO₂: Roles of Surface O₂^–, O₂^2– Anions and Acidic Species Played for Toluene Deep Oxidation

Abstract

To elucidate the nature and states of the surface oxygen sites on SnO2 and the relationship between the surface vacancies and the active oxygen sites, a series of SnO2 samples have been fabricated by microwave/ultrasound and KCC-1 hard template. By adjusting the preparation methods, SnO2 samples with varied surface and texture properties were obtained, which display different intrinsic activities for toluene deep oxidation, following the sequence SnO2-Ultra-OH > SnO2-Stir-OH > SnO2-Mic > SnO2-Pre. For the first time, it is discerned clearly with in situ diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance techniques that both superoxide O2– and peroxide O22– anions are present on SnO2 surface as active oxygen species. Generally, these more active SnO2 samples possess richer surface active O2–, O22– anions and acidic sites. The concerted interaction between surface O2–, O22– anions and acidic sites is concluded to be the predominant reason determining the toluene total oxidation activity over SnO2.