The evolution of surface species by steam pre-treatment on CrOx/Al2O3 catalysts for propane dehydrogenation

Propane dehydrogenation (PDH) has emerged as an efficient complementary process for producing propylene. The fundamental understanding of reaction mechanism of traditional CrOx-based catalysts is important for designing novel PDH catalysts. Here, the evolution of surface Cr species was investigated by means of steam pre-treatment to introduce a certain amount of hydroxyl groups on deeply reductive Cr2O3/Al2O3 catalysts without influencing the valence states and aggregated states. The surface structural features of CrOx/Al2O3 catalysts were investigated by FT-IR, TGA, XPS, NH3-TPD, and Py-IR characterization techniques. It demonstrated that more hydroxyls were produced on the surface of catalysts under steam treatment. Subsequently, hydroxyl groups were mostly removed during the H2 thermal treatment and abundant oxygen defect sites were generated. These defect sites showed an increasing number of acidic sites, thus exhibiting a relatively high PDH activity. This strategy of introducing hydroxyl groups to construct oxygen defect sites is also applicable to other oxide materials, which offers a novel perspective for rational catalyst design.