Ethylene production by direct conversion of methane over isolated single active centers

Non-oxidative conversion of methane over iron atoms on silica can provide a potential catalytic route to directly produce ethylene. However, its mechanism remains elusive. Herein, we perform multiscale simulations to elucidate the key pathways and provide insights into how to tune this process. Extensive density functional theory calculations are conducted for the surface reactions, which are coupled to nearly 10,000 gas-phase reactions. The entire model is assessed with new experimental data. Ab initio phase behavior indicates that iron atoms form isolated carbides under reaction conditions. Unlike decades of prior hypothesis for CH3 radical desorbing from the catalyst and recombining to form ethane in the gas-phase as the sole C2 formation mechanism, ethylene is predominantly produced on the catalyst and is consumed by gas-phase reactions to acetylene and aromatics. Highest ethylene selectivity with high methane one-pass conversion can be achieved by eliminating gas-phase reactions.