Initial Carbon−Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization

Abstract

Methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science owing to the inherent harsh reaction conditions and fast catalyst deactivation. To improve this process, understanding the mechanism of the initial C−C bond formation is essential. 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 at least two independent C−H activation pathways. Moreover, this study emphasizes the significance of mobility‐dependent host–guest chemistry between an inorganic zeolite and its trapped organic species during heterogeneous catalysis.

Transitioning from Methanol to Olefins (MTO) toward a Tandem CO2 Hydrogenation Process: On the Role and Fate of Heteroatoms (Mg, Si) in MAPO-18 Zeotypes

“…Experiments carried out under 13 C-labeled methanol and similar conditions allowed us to confirm the same performance of the two zeotypes by solid-state 13 C NMR (Figure S11). For MgAPO-18 and SAPO-18, the NMR spectra were almost superimposable, suggesting the formed hydrocarbon pool species in the zeotypes are identical in the absence of CO. − Moreover, the presence of aromatics and alkyl groups was confirmed after 30 min on stream, as one would expect from the methanol-to-hydrocarbons chemistry.…”