Influence of ethylene and acetylene on the rate and reversibility of methane dehydroaromatization on Mo/H-ZSM-5 catalysts

Acetylene is identified as a key intermediate in methane dehydroaromatization (DHA) reactions present in concentrations O(1) Pascal. The rank of acetylene and other C₂ hydrocarbon intermediates is determined by conversion-selectivity profiles collected from 0.01% to 8% methane conversion varied by extent of “non-selective” deactivation of Mo/H-ZSM-5 catalysts. Ethane is shown to be the sole primary product of methane pyrolysis and is sequentially dehydrogenated to ethylene and acetylene – which aromatizes to benzene with rates similar to direct acetylene aromatization measured in the absence of methane. The influence of C[sbnd]H cleavage and C[sbnd]C coupling events to control the rate and reversibility of DHA is assessed by the degree of reversibility control, introduced here for the first time, and the degree of rate control. The approach to equilibrium of the methane to benzene synthesis reaction is length averaged and affinity averaged by the degree of reversibility control of each intervening elementary step to rigorously calculate forward rates of benzene synthesis by use of De Donder relations. Forward rates are found to be invariant along the catalyst bed once the DHA network reaches a pseudo-steady state and methane, ethane, and ethylene form an equilibrated pool.