Hierarchically modified Mo/HZSM-5 via alkali treatment for improved activity in methane dehydroaromatization

Considering direct utilization of natural gas, methane dehydroaromatization (MDA) is a promising alternative to produce valuable aromatic hydrocarbons. However, the major limitation of the process is the low catalyst stability and durability due to simultaneous coking. This contribution depicts the modifications of HZSM-5 support via controlled desilication approach using two different kinds of alkaline reagents at two different concentrations. The physicochemical characterizations revealed that after the alkaline treatment, morphological features are modified e.g., pore size distribution, Si/Al ratio, and acidity of HZSM-5. In the catalytic activity results, it was observed that among all the alkali modified catalysts, 0.1 M NaOH modified Mo/HZSM-5 exhibited highest benzene formation rate (2 μmol/gcat.s) as compared to pristine Mo/HZSM-5 (0.4 μmol/gcat.s) in MDA reaction over 90 min of time on stream. The exceptional catalytic performance was attributed to the incorporation of secondary mesopores which in turn facilitated the effective diffusion of Mo species in the pore interiors and subsequently cause the formation of higher number of Mo-anchored active sites. Further, the coke tolerance ability was enhanced, which might be due to the entrapment of coke species in the generated mesopores, thus leaving higher amount of accessible active sites for aromatization.