Understanding Catalytic Mechanisms of Alkane Oxychlorination from the Perspective of Energy Levels

Identifying surface-active sites and reaction pathways is of great significance in heterogeneous catalysis. However, even for the simplest catalytic reaction, there could exist a myriad of possible active sites and reaction intermediates, rending exhaustive computational and experimental investigations of all possible reaction pathways difficult. For the oxychlorination of C3H8over CeO2catalyst, electron affinity and Brønsted basicity of a variety of surface sites and reaction intermediates have been calculated using density functional theory (DFT), and a diagram of the corresponding energy levels is used to help identify the relevant reaction sites and intermediates. It is found that surface Cl•radicals that are generated from Cl–oxidation by peroxide at oxygen vacancies play an important role in the C–H activation of alkanes. The formation of C3H7Cl and C3H5Cl intermediates regulates reaction channels and prohibits overoxidation. We show that thermodynamic analysis based on energy levels is useful to elucidate reaction sites and mechanisms for oxidative dehydrogenation.