Mechanistic Study on Non-Oxidative Methane Dehydrogenation and C-C Coupling for Ethylene Formation

Sonit Balyan ¹, Sourabh Mishra ¹, Tuhin S. Khan¹, M. Ali Haider¹, K. K. Pant¹

¹Department of Chemical Engineering, IIT Delhi, India

 

DFT calculation have been employed to study the CH₄ activation and C-C coupling for ethylene formation on Mo₄C₂ cluster. Methane is activated on the Mo₄C₂ cluster with an intrinsic activation barrier ~ 116 kJ/mol, related to the second methane activation. The highest intrinsic barrier was obtained for the C-C coupling step forming C₂H₆ (~ 151 kJ/mol). The activation of C₂H₆ (~70 & 95 kJ/mol) was relatively easy and C₂H₄ will be formed easily on the catalyst surface. All the energy barriers observed for these elementary steps have been shown in Figure 1. Also C-H bond activation barrier decreases as the Mo₄C₂ cluster is more reduced in nature (less positive). A detailed mechanistic understanding is developed that correlates the effect of charge on catalyst activity. It dictates that lesser residual charge on Mo_xC_y cluster lowers the barrier for methane dehydrogenation.

Figure 1. Reaction diagram for methane dehydrogenation and C-C coupling to form ethylene on Mo₄C₂ cluster