Aromatization of methane over Mo/H-ZSM-5 catalyst: on the possible reaction intermediates

On the Induction Period of Methane Aromatization over Mo-Based Catalysts

“…Thus, this demonstrated that the activation of methane as well as the production of benzene could be conducted at a much lower temperature. Lunsford et al (8) and we (25) had suggested that ethene or something similar is the intermediate of this reaction, whereas some of the authors pointed out that it is acetylene which is the primary product (26). However, both of these substances are easily (could be initiated lower than 673 K) aromatized on a zeolite that possesses Brønsted acidity.…”

Recent progress in methane dehydroaromatization: From laboratory curiosities to promising technology

“…Mériaudeau et al [40,107,108] considered acetylene to be the important intermediate and the bifunctional mechanism to be less important. They reported that (1) the initial product of methane activation is acetylene (and possibly ethylene as well), since the amount of acetylene formed decreases with increased reaction time, while both the yields of ethylene and benzene increase; and (2) according to IR analysis of OH stretching vibrations, the H + sites of HZSM-5 are progressively exchanged during the calcination of Mo/HZSM-5, which are almost completely removed during the induction period of CH 4 reaction at 550 • C. They also found that the rate of benzene formation from ethylene is twice as fast as that over Mo/SiO 2 compared with HZSM-5.…”

“…The accumulation of coke deposits increases with both time-on-stream [92,107] and reaction temperature [63].…”

Direct conversion of methane under nonoxidative conditions

“…Therefore, it was suggested that Mo 2 C is the active component for methane activation and dimerization to C 2 H 4 , and aromatization occurred, catalyzed by protonic acid sites, through the oligomerization/cyclization reactions of C 2 H 4 . However, Mériaudeau and co-workers [68][69][70] challenged this bifunctional description of the reaction mechanism and suggested a monofunctional mechanism, with C 2 H 2 formed from CH 4 on highly dispersed Mo 2 C as the primary product. Moreover, C 6 H 6 was also formed from C 2 H 2 over Mo 2 C. These authors claimed that based on their results of the reactions of CH 4 , C 2 H 2 , and C 2 H 4 over acidic HZSM-5, nonacidic Mo 2 C/SiO 2 and Mo 2 C/HZSM-5 catalysts, and H + ions almost completely removed after the induction period following CH 4 reaction at 623 K, the H + sites are not a prerequisite for C 2 H 2 or C 2 H 4 aromatization.…”