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Direct non‐oxidative methane conversion (DNMC) has been recognized as a single‐step technology that directly converts methane into olefins and higher hydrocarbons. High reaction temperature and low catalyst durability, resulting from the endothermic reaction and coke deposition, are two main challenges. We show that a millisecond catalytic wall reactor enables stable methane conversion, C2+ selectivity, coke yield, and long‐term durability. These effects originate from initiation of the DNMC on a reactor wall and maintenance of the reaction by gas‐phase chemistry within the reactor compartment. The results obtained under various temperatures and gas flow rates form a basis for optimizing the process towards lighter C2 or heavier aromatic products. A process simulation was done by Aspen Plus to understand the practical implications of this reactor in DNMC. High carbon and thermal efficiencies and low cost of the reactor materials are realized, indicating the technoeconomic viability of this DNMC technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developed detailed surface reaction mechanism for methane non-oxidative coupling. • Elucidated the interplay between catalytic and gas-phase chemistry. • Demonstrated catalytic generation of ethylene during methane coupling. • Showcased enhanced selectivity to ethylene by minimizing gas-phase reactions. 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 CH 3 radical desorbing from the catalyst and recombining to form ethane in the gas-phase as the sole C 2 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. [ABSTRACT FROM AUTHOR]