Elucidating the nature of Mo species on ZSM-5 and its role in the methane aromatization reaction†
The valorization of methane is one of the most important goals during the transition period to the general use of renewable energies. Its transformation into a valuable chemical like benzene by direct aromatization of methane (DAM) reaction has been extensively studied in the past years, mainly using Mo/ZSM-5 catalytic systems. Although viable, this DAM reaction poses a number of issues mainly derived from poor conversion and deactivation processes. Therefore, a deeper knowledge of these systems is needed. Herein, by combining chemical (TPR), spectroscopic (XPS), HAADF and other techniques, we have identified the different Mo precursors stabilized in the calcined ZSM-5 support, their nature (monomers, dimers and bulk Mo oxides), location in the zeolite framework (external surface or micropores), and the partial segregation of aluminum during the preparation of catalysts. The role of each Mo phase promoting or hindering the transformation of methane in aromatics has been also clarified.