(706f) Investigating the Dynamic Transformations of Mo-Oxides in Mo/H-ZSM-5 Catalysts for Methane Dehydroaromatization (MDA)

Mo-oxide-impregnated H-ZSM-5, the most extensively studied catalyst for methane dehydroaromatization, has not yet been commercialized due to various challenges, notably rapid catalyst deactivation. Despite these challenges, the potential of Mo/H-ZSM-5 for MDA drives interest in optimizing its catalytic performance. Mo/H-ZSM-5 catalysts are prepared by impregnating Mo-oxide precursors into H-ZSM-5, which are understood to reduce to catalytically active (oxy-)carbidic phases during reaction. To comprehend the processes underlying MDA, we have previously studied the nature of the catalyst precursor, which plays a role in establishing the catalyst's structure and composition. This, in turn, affects the activation and deactivation stages of the reaction. In our previous work, we studied the evolution, speciation, and distribution of Mo-oxide species at the initial stages of MDA, demonstrating that a coexistence of oxide species is expected to exist in MoO_x/H-ZSM-5 and that the distribution of species can be rationally controlled.

In this work, to understand the transformations these oxides undergo during and beyond impregnation into the zeolite, we have considered the interconversion of these anchored Mo-oxides under preparation (thermal) conditions as well as under reducing (hydrogen) conditions. Through this work, we have built an understanding of how anchored Mo-oxides of MoO₂OH⁺, MoO₂²⁺, and Mo₂O₅²⁺ stoichiometry may interconvert and reduce, building a foundation on which to more comprehensively understand processes underlying MDA.