Reactivity of Methoxy species towards Methylation and Oligomerization in Cu-Zeolite systems

Ethylene, propylene, and benzene were investigated as molecules for extracting methoxy intermediate species formed during the cyclic partial oxidation of methane in Cu-exchanged zeolites, promising materials for the step-wise methane-to-methanol (MTM) reaction. 13C-labeled reaction studies reveal that alkenes preferentially undergo oligomerization followed by cracking, while benzene is successfully methylated, forming toluene. Benzene methylation further showcases the methyl species to behave similar to surface methoxy species formed on Brønsted acid sites in methanol-to-hydrocarbon (MTH) reaction. However, benzene is only able to extract a fraction of the methyl species compared to the methanol produced with water extraction, indicating either steric or intrinsic mechanistic effects to limit the full potential of the methyl pool inside the framework. We infer the presence of reactive methoxy species on Brønsted acid sites generated under reaction conditions, revealing their potential as a synthetic platform to form additional products from methane.