Discovery of shale gas has generated huge industrial attention towards catalytic conversion of methane (85% of shell gas) to aromatics. MoxCy/H-ZSM-5 is one of the suitable catalyst for the methane to aromatics (MTA) process. Electronic and geometrical changes over MoxCy cluster found to have drastic effect on the catalyst activity and stability. Density functional theory (DFT) calculations have been employed to study the effect of charge on two catalytically active molybdenum carbide (MoxCy) nanoclusters, Mo4C2 and Mo2C6 grafted over Al-O-(Si-O)2-Al-O active site of zeolite channel for methane C-H bond activation. Effect of electron density on the MoxCy clusters in methane C-H bond activation is analyzed by varying the charge on the Mo4C2 and Mo2C6 clusters (Figure 1(c)). Methane C-H bond activation barrier decreases as the MoxCy clusters are more reduced in nature (less positive). Mo2C6 cluster is more active than Mo4C2 cluster for all the charges studied here. DFT calculation have been employed to study the CH4 activation on both the above mentioned clusters all the way up-to the formation of C2H4, one of the most important intermediate for methane dehydroaromatization process (Figure 1(d)). Methane is activated on the Mo2C6 cluster with an intrinsic activation barrier ~ 115 kJ/mol, related to the second methane activation. The highest intrinsic barrier is obtained for the C-C coupling step forming C2H6 (~ 150 kJ/mol). The activation of C2H6 (~89 kJ/mol) is relatively easy than CH4 and will be formed easily on the catalyst surface as also observed experimentally.

Methane dehydroaromatization over Mo/ZSM-5 catalyst: Effect of residual charge on reaction energy profiles of Mo4C2 and Mo2C6 nanoclusters

254th National Meeting (2017)

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