†Department of Chemistry, Stanford University, Stanford, California 94305, United States.
‡Center for Surface Chemistry and Catalysis, KU Leuven, Kasteelpark Arenberg 23, 3000 Leuven, Belgium.
J Am Chem Soc. 2015 May 20;137(19):6383-92. doi: 10.1021/jacs.5b02817. Epub 2015 May 7.
Two distinct Cu-O-Cu sites with methane monooxygenase activity are identified in the zeolite Cu-MOR, emphasizing that this Cu-O-Cu active site geometry, having a ∠Cu-O-Cu ∼140°, is particularly formed and stabilized in zeolite topologies. Whereas in ZSM-5 a similar Cu-O-Cu active site is located in the intersection of the two 10 membered rings, Cu-MOR provides two distinct local structures, situated in the 8 membered ring windows of the side pockets. Despite their structural similarity, as ascertained by electronic absorption and resonance Raman spectroscopy, the two Cu-O-Cu active sites in Cu-MOR clearly show different kinetic behaviors in selective methane oxidation. This difference in reactivity is too large to be ascribed to subtle differences in the ground states of the Cu-O-Cu sites, indicating the zeolite lattice tunes their reactivity through second-sphere effects. The MOR lattice is therefore functionally analogous to the active site pocket of a metalloenzyme, demonstrating that both the active site and its framework environment contribute to and direct reactivity in transition metal ion-zeolites.
在沸石 Cu-MOR 中鉴定出具有甲烷单加氧酶活性的两个独特的Cu-O-Cu位点，强调这种具有∠Cu-O-Cu∼140°的 Cu-O-Cu 活性位点几何形状特别在沸石拓扑结构中形成和稳定。虽然在 ZSM-5 中，类似的Cu-O-Cu活性位点位于两个 10 元环的交点处，但 Cu-MOR 提供了两个不同的局部结构，位于侧袋的 8 元环窗口中。尽管通过电子吸收和共振拉曼光谱确定了它们的结构相似性，但在 Cu-MOR 中，两个 Cu-O-Cu 活性位点在选择性甲烷氧化中的动力学行为明显不同。这种反应性的差异太大，不能归因于 Cu-O-Cu 位点的基态的细微差异，这表明沸石晶格通过次级球效应来调节它们的反应性。因此，MOR 晶格在功能上类似于金属酶的活性位点口袋，表明活性位点及其框架环境都有助于并指导过渡金属离子-沸石中的反应性。
