Molecular-level investigation on supported CrOx catalyst for oxidative dehydrogenation of propane with carbon dioxide

• Highly dispersed CrSiβ catalyst is prepared via a two-step post-synthesis method. • The 3CrSiβ catalyst shows the best performance for CO 2 -ODP. • The amount of Cr 6+ oxides is responsible for the activity of CrSiβ for CO 2 -ODP. • In-situ formed coordinatively unsaturated Cr 3+ oxides are active sites for CO 2 -ODP. • A detailed redox mechanism including the formation of active sites is proposed. Although the supported CrO x is widely applied as an important industrial catalyst for oxidation processes (such as propane dehydrogenation), the molecular-level understanding of its catalytic mechanism is still limited. In this work, the oxidative dehydrogenation of propane with carbon dioxide (CO 2 -ODP) was exploited as a probe reaction to investigate CrO x highly dispersed over dealuminated β zeolite (CrSiβ). It was revealed that the activity of the CrSiβ catalyst was dependent on the dispersion of Cr species and the content of initial highly-dispersed Cr 6+ oxides. Namely, the oxygen of terminal Cr = O bonds in initial Cr 6+ oxides could rapidly react with propane molecules, thus generating the coordinatively unsaturated Cr 3+ oxides as active sites for the redox cycles of CO 2 -ODP. In this redox cycle, the unsaturated Cr 3+ site takes an oxygen from a CO 2 molecule and then the activated oxygen reacts with propane to produce H 2 O and propene . This finding is not only important for the molecular understanding of the CrO x catalytic properties, but also is beneficial for the rational design of more efficient CrO x catalysts for dehydrogenation reactions including CO 2 -ODP.