Precise determination of the structure-property relationship of zeolite-based metal catalysts is critical for the development toward practical applications. However, the scarcity of real-space imaging of zeolite-based low-atomic-number (LAN) metal materials due to the electron-beam sensitivity of zeolites has led to continuous debates regarding the exact LAN metal configurations. Here, a low-damage high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging technique is employed for direct visualization and determination of LAN metal (Cu) species in ZSM-5 zeolite frameworks. The structures of the Cu species are revealed based on the microscopy evidence and also proved by the complementary spectroscopy results. The correlation between the characteristic Cu size in Cu/ZSM-5 catalysts and their direct oxidation of methane to methanol reaction properties is unveiled. As a result, the mono-Cu species stably anchored by Al pairs inside the zeolite channels are identified as the key structure for higher C1 oxygenates yield and methanol selectivity for direct oxidation of methane. Meanwhile, the local topological flexibility of the rigid zeolite frameworks induced by the Cu agglomeration in the channels is also revealed. This work exemplifies the combination of microscopy imaging and spectroscopy characterization serves as a complete arsenal for revealing structure-property relationships of the supported metal-zeolite catalysts.

Direct oxidation of methane (DOM) to value-added chemicals is of great significance but still challenging under mild conditions. Herein, we report that Cr1-O4 as an active site in ZSM-5 anchored...

Rationally constructing atom‐precise active sites is highly important to promote their catalytic performance but still challenging. Herein, this work designs and constructs ZSM‐5 supported Cu and Ag dual single atoms as a proof‐of‐concept catalyst (Ag1−Cu1/ZSM‐5 hetero‐SAC (single‐atom catalyst)) to boost direct oxidation of methane (DOM) by H2O2. The Ag1−Cu1/ZSM‐5 hetero‐SAC synthesized via a modified co‐adsorption strategy yields a methanol productivity of 20,115 µmol gcat−1 with 81% selectivity at 70 °C within 30 min, which surpasses most of the state‐of‐the‐art noble metal catalysts. The characterization results prove that the synergistic interaction between silver and copper facilitates the formation of highly reactive surface hydroxyl species to activate the C−H bond as well as the activity, selectivity, and stability of DOM compared with SACs, which is the key to the enhanced catalytic performance. This work believes the atomic‐level design strategy on dual‐single‐atom active sites should pave the way to designing advanced catalysts for methane conversion.

The performance of the direct oxidation of methane to methanol (DMTM) is significantly influenced by the oxidant. It is still incredibly challenging to realize one-pot DMTM using dioxygen. So far, hydrogen peroxide is still the most frequently reported green oxidant for DMTM with a high selectivity for methanol. To achieve insights into the influence of oxidants on the DMTM performance, we computationally investigated the reaction mechanisms of DMTM using hydrogen peroxide at mono-copper sites in three kinds of Cu-exchanged zeolites with different sizes of the micropores. We identified the common advantages and limitations of hydrogen peroxide as the oxidant. In contrast to dioxygen, the O-O bond of hydrogen peroxide could be easily broken to produce reactive surface oxygen species, which enables the facile C-H bond activation of methane at a lower temperature. However, because of the radical-like process for C-H bond activation at mono-copper sites, it is kinetically challenging to actualize the preferential C-H bond activation of methane as compared to that of methanol. Moreover, the lower O-H bonding energy of hydrogen peroxide would result in the self-decomposition of hydrogen peroxide. Despite the bottlenecks, the kinetic analysis shows that it is still promising to improve catalysts to boost the performance of DMTM using hydrogen peroxide.