Ag-catalysed ethene epoxidation is the only viable route for making ethene oxide (EO) in industry, but the active site remains elusive due to the lack of tools to probe this reaction under high temperature and high-pressure conditions. Here, aided by advanced machine-learning grand canonical global structure exploration and in situ experiments, we identify a unique surface oxide phase, namely O₅ phase, grown on Ag(100) under industrial catalytic conditions. This phase features square-pyramidal subsurface O and strongly adsorbed ethene, which can selectively convert ethene to EO. The other Ag surface facets, although also reconstructing to surface oxide phases, only contain surface O and produce CO₂. The complex in situ surface phases with distinct selectivity contribute to an overall medium (50%) selectivity of Ag catalyst to EO. Our further catalysis experiments with in situ infra-red spectroscopy confirm the theory-predicted infra-red-active C=C vibration of adsorbed ethene on O₅ phase and the microkinetics simulation results.

银催化乙烯环氧化是工业上制造环氧乙烷（EO）的唯一可行途径，但由于缺乏在高温高压条件下探测该反应的工具，活性位点仍然难以捉摸。在这里，借助先进的机器学习大规范全局结构探索和原位实验，我们确定了一种独特的表面氧化物相，即 O ₅相，在工业催化条件下在 Ag(100) 上生长。该相具有方锥体的地下 O 和强吸附的乙烯，可以选择性地将乙烯转化为 EO。其他Ag表面小面虽然也重建为表面氧化物相，但仅包含表面O并产生CO ₂。具有不同选择性的复杂原位表面相使 Ag 催化剂对 EO 的整体选择性达到中等 (50%)。我们进一步的原位红外光谱催化实验证实了理论预测的O ₅相上吸附乙烯的红外活性C=C振动以及微动力学模拟结果。