Comprehensive understanding of ethylene epoxidation on copper catalysts: a microkinetic study with coverage effects†

Ethylene epoxidation is one of the fundamental industrial reactions, garnering extensive theoretical and experimental studies. While silver has traditionally been the catalyst of choice for this reaction, copper has received comparatively little attention. In this study, we apply a coverage-dependent microkinetic modeling to quantitatively investigate ethylene epoxidation on Cu(111), serving as a model system to study the intrinsic activity and selectivity of Cu catalysts. The coverage-dependent simulation takes into account both self and cross-interactions of adsorbates, as well as the coverage effects on the transition states of each elementary step. In contrast, the coverage-independent modeling is conducted without considering coverage effects. We observe that the coverage-dependent modelling reveals the Cu(111) surface with coverage exceeding 30% oxygen atoms with a high turnover frequency (log(TOF) = 2.65) at 500 K. In contrast, the coverage-independent results indicate the Cu(111) surface being completely covered by oxygen atoms, leading to detrimental poisoning effects (log(TOF) = −2.47). We show that the EO selectivity on Cu(111) can be at a high level of 80% under all studied conditions in contrast to only ∼40% EO selectivity on Ag(111). Detailed structural analyses unveil the fundamental reasons why Cu catalysts are more selective for ethylene epoxidation. Furthermore, we suggest that reducing temperature and increasing oxygen pressure can effectively improve EO selectivity for industrial ethylene epoxidation.