Direct Propylene Epoxidation over CuO x /TiO ₂ : Unveiling the Common Ti–O–Cu Active Interface via DFT and Microkinetic Modeling

The preparation of propylene oxide (PO) by direct epoxidation of propylene with molecular oxygen using a Cu-based catalyst is one of the most important reactions in the chemical industry. Recent experimental studies have shown that the main product of propylene epoxidation catalyzed by rutile TiO2-supported CuOx clusters prepared by ultrahigh temperature calcination is PO. By combining global structural sampling, DFT calculations, and microkinetic modeling, we demonstrate that the high-performance rutile TiO2(110) support can stabilize geometrically diverse yet functionally unified CuOx configurations. Two representative configurations─an isolated cluster (CuOx_cluster/TiO2) and an extended chain (CuOx_chain/TiO2)─were identified. Interestingly, despite their distinct morphologies, both exhibit exceptionally high selectivity toward propylene oxide (PO), and much higher than that of Cu2O(111). Electronic structure analysis reveals that this common selectivity stems from a conserved Ti–O–Cu interface, which modulates the electronic state of adjacent Cu atoms. The strong covalent interaction at this interface pins the Cu d-band center deep below the Fermi level, thereby intrinsically limiting electron transfer to O2. This mechanism ensures the moderate activation of O2 while inhibiting its excessive reduction and dissociation, thereby stabilizing the molecular O2* species conducive to epoxidation and effectively blocking the allyl hydrogen removal (AHS) pathway that leads to combustion. On the other hand, the strong O2 activation on Cu2O(111) results in an O mechanism for DEP, which favors CO2 formation ultimately. This study elucidated the unified mechanism of the high performance of rutile TiO2-supported copper catalysts at the atomic scale, providing new insights for the design of selective oxidation catalysts.