Partially Bonded Aluminum Site on the External Surface of Post-treated Au/ZSM-5 Enhances Methane Oxidation to Oxygenates

Au nanoparticles supported on the exterior surface of the ZSM-5 zeolite (Au/ZSM-5) have shown the ability to partially oxidize methane to methanol and acetic acid. However, further improvements to the catalyst activity are required. This study investigates the effect of modifying the acidic properties of the ZSM-5 support through a desilication-recrystallization (DR) process on the activity of Au/ZSM-5 catalysts toward methane oxidation. A DR treatment of 24 h leads to a 50% higher oxygenate yield compared to the analogous catalyst prepared using the untreated support. Characterization using solid-state Al-27 NMR and FTIR adsorption of pyridine and 2,4,6-trimethylpyridine reveals that DR induces framework dealumination and redistribution of Bronsted acid sites to the zeolite external surface. Two-dimensional Al-27 MQMAS NMR further identifies partially coordinated framework Al sites on the zeolite surface, correlating with a higher oxygenate yield. These external acid sites help stabilize the Au nanoparticles, enhancing catalyst stability for methane partial oxidation.