Illuminating Initial Carbon-Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization.

Abstract

Still in 2020, methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science due to the inherent harsh reaction conditions and fast catalyst deactivation. To improve it further, understanding the initial C-C bond formation mechanism is sine qua non. However, consensus about the actual reaction mechanism is still to be achieved. In this work, using advanced magic angle spinning (MAS) solid-state NMR spectroscopy, we study in detail the early stages of the reaction over a well-dispersed Mo/H-ZSM-5 catalyst. Simultaneous detection of acetylene (i.e., presumably the direct C-C bond forming product from methane), methylidene, allenes, acetal and surface-formate species along with the typical olefinic/aromatic species allow us to conclude the existence of two independent C-H activation pathways. Moreover, this study emphasizes the significance of mobility-dependent host-guest chemistry between inorganic zeolite and its organic trapped species during heterogeneous catalysis.