Activation of molecular oxygen over Mn-doped La2CuO4 perovskite for direct epoxidation of propylene

Abstract

Direct epoxidation of propylene (DEP) to propylene oxide (PO) with molecular oxygen is a very desirable reaction but remains a challenge due to the absence of efficient catalysts with high selectivity. The catalytic performance for direct epoxidation of propylene is well related to surface adsorbed electrophilic oxygen species. Herein, we prepared a series of Mn-doped La₂CuO₄ perovskites (LaMn_xCu_1−xO₃) with adjustable valence electronic structure as selective catalysts to explore the impacts of catalyst intrinsic electronic structure evolution on the activation of molecular oxygen. Therein, LaMn_0.5Cu_0.5O₃ performed the best with a PO selectivity of 74.2% at 150 °C. The characterization results and DFT calculations revealed that the excellent catalytic performance of LaMn_0.5Cu_0.5O₃ might be ascribed to the change of molecular oxygen activation sites: from oxygen vacancy active sites on La₂CuO₄ to Cu active sites on LaMn_0.5Cu_0.5O₃. Meanwhile, there was a synergistic interaction between manganese and copper affecting the electron density on Cu sites and ultimately modulating the activated states of surface adsorbed oxygen species. In addition, we employed crystal band theory to associate the oxygen vacancy density with the Cu valence state. This is important for people to understand the bulk electronic structure evolution rules caused by transition metal doping and to design catalysts efficiently for oxygen-based chemical reactions.