Direct conversion of methane to oxygenates has attracted numerous research interests from both industrial and academics. However, selective oxidation of methane to value-added chemicals with both high catalytic activity and selectivity under mild conditions still remains a great challenge.

Firstly, selective oxidation of CH₄ to oxygenates with O₂ or O₂/H₂ suffers from low catalytic activity and low oxygenates selectivity, due to the low activity of oxygen and the overoxidation of the oxygenates. Secondly, the high loading (1~5 wt%) of noble metals for supported catalysts used for methane conversion leads to high cost, which is not business-friendly.

Inspired by these challenges, a research team led by Prof. SUN Yuhan and Prof. ZHONG Liangshu at Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences reported a ZSM-5 (Z-5) supported PdCu catalyst for selective oxidation of CH₄ to oxygenates using O₂ in the presence of H₂. The as-obtained PdCu/Z-5 catalyst exhibited a high oxygenates yield of 1178 mmol/g_Pd/h with oxygenates selectivity of 95% at 120 °C. The research results were published in the latest issue of Angew. Chem. Int. Ed.

Based on a combination of control experiments and electron paramagnetic resonance as well as in situ spectroscopic techniques, researchers found that PdO nanoparticles facilitated in situ generation of H₂O₂, while Cu single atoms not only accelerated the generation of abundant ·OH from H₂O₂ decomposition, but also enabled the homolytic cleavage of CH₄ by ·OH to ·CH₃. Subsequently, the ·OH reacted quickly with the ·CH₃ to form CH₃OH with high selectivity. 

These findings may provide valuable insights into selective oxidation of methane to oxygenates, which may also shed light on other highly efficient and low-price catalysts for the selective activation of C-H bonds in light alkanes.

Product yield and oxygenates selectivity for selective oxidation of CH₄ with O₂ and H₂. (Image by SARI)