Abstract：
Copper-exchanged zeolite omega (Cu-omega) is a potent material for the selective conversion of methane-to-methanol (MtM) via the oxygen looping approach. However, its performance exhibits substantial variation depending on the operational conditions. Under an isothermal temperature regime, Cu-omega demonstrates subdued activity below 230 °C, but experiences a remarkable increase in activity at 290 °C. Applying a high-temperature activation protocol at 450 °C causes a rapid deactivation of the material. This behavioral divergence is investigated by combining reactivity studies, neutron and in situ high-resolution anomalous X-ray powder diffraction (HR-AXRPD), as well as electron paramagnetic resonance spectroscopy, to reveal that the migration of Cu throughout the framework is the primary cause of these behaviors, which in turn is governed by the degree of hydration of the system. This work suggests that control over the Cu migration throughout the zeolite framework may be harnessed to significantly increase the activity of Cu-omega by generating more active sites for the MtM conversion. These results underscore the power of in situ HR-AXRPD for unraveling the behavior of materials under reaction conditions and suggest that a re-evaluation of Cu-zeolites priorly deemed inactive for the MtM conversion across a broader range of conditions and looping protocols may be warranted.
摘要：
铜交换的omega沸石（Cu-omega）是通过氧气循环方法将甲烷选择性转化为甲醇（MtM）的有效材料。然而,其性能表现出很大的变化取决于操作条件。在等温温度制度下，Cu-omega在230°C以下表现出减弱的活性，但在290°C下的活性显着增加。在450°C下应用高温活化方案导致材料的快速失活。通过结合反应性研究来研究这种行为差异，中子和原位高分辨率反常X射线粉末衍射（HR-AXRPD），以及电子顺磁共振波谱，为了揭示铜在整个骨架中的迁移是这些行为的主要原因，这又受系统水合程度的控制。这项工作表明，对整个沸石骨架中Cu迁移的控制可以通过产生更多的MtM转化活性位点来显著增加Cu-ω的活性。这些结果强调了原位HR-AXRPD在反应条件下揭示材料行为的能力，并表明在更广泛的条件和循环方案中重新评估以前被认为对MtM转化无活性的Cu-沸石可能是必要的。
