The synergic effect between Mo species and acid sites in Mo/HMCM-22 catalysts for methane aromatization

Abstract

The acid properties of Mo/HMCM-22 catalyst, which is the precursor form of the working catalyst for methane aromatization reaction, and the synergic effect between Mo species and acid sites were studied and characterized by various characterization techniques. It is concluded that Brønsted and Lewis acidities of HMCM-22 are modified due to the introduction of molybdenum. We suggest a monomer of Mo species is formed by the exchange of Mo species with the Brønsted acid sites. On the other hand, coordinate unsaturated sites (CUS) are suggested to be responsible for the formation of newly detected Lewis acid sites. Computer modelling is established and coupling with experimental results, it is then speculated that the effective activation of methane is properly accomplished on Mo species accommodated in the 12 MR supercages of MCM-22 zeolite whereas the Brønsted acid sites in the same channel system play a key role for the formation of benzene. A much more pronounced volcano-typed reactivity curve of the Mo/HMCM-22 catalysts, as compared with that of the Mo/HZSM-5, with respect to Mo loading is found and this can be well understood due to the unique channel structure of MCM-22 zeolite and synergic effect between Mo species and acid sites.

Progress in Developing a Structure‐Activity Relationship for the Direct Aromatization of Methane

“…According to Ma et al . an ideal MDA catalyst should have an appropriate balance between the free Brønsted acid sites and acid sites with anchored Mo . By utilizing Mo/MCM‐22 with different Mo loading, they showed that the best catalyst possessed three Al per unit cell, where one framework Al was associated with aromatization reaction, while other two were used to anchor Mo.…”

“…In conclusion, the separation of these functionalities is not possible . Although some studies address the optimal loading of Mo, given a zeolite with certain acidity and vice versa,,,,, the optimal proximity of BAS to Mo site and the optimal concentration of both sites per zeolite cage is only discussed for MCM‐22 . A careful study is necessary, both varying Mo/Al ratios as well as Si/Al ratios over a wide range while carefully characterizing how many well‐dispersed Mo sites are created inside the pores of the zeolite.…”

Methane Dehydroaromatization on Mo/HMCM-22 Catalysts: Effect of SiO2/Al2O3 Ratio of HMCM-22 Zeolite Supports

“…80% in maximum) as well as a better tolerance to carbonaceous deposits, as compared with Mo/HZSM-5 catalyst under the same experimental conditions [22] MCM-22 zeolite possesses two independent multidimensional channel systems, one system is two-dimensional 10-MR sinusoidal inter-layer channel systems, while the other is inter-layer channel systems contains 12-MR super-cages with inner free space of 0.71 Â 0.71 Â 1.82 nm [23]. The unique catalytic performance of the Mo/HMCM-22 catalyst is probably due to the unusual channel structure of HMCM-22 zeolite [22,24].…”

Elucidating the nature and role of Cu species in enhanced catalytic carbonylation of dimethyl ether over Cu/H-MOR

“…Actually, the synergistic effect between Brønsted acid sites and transition metal sites during reactions has been intensively investigated in the available literature. 6,7 However, it often shows complexity and specificity depending on different reactions and various catalyst systems.…”