Non-oxidative Coupling of Methane via Selective Passivized Catalysis

Abstract

Methane activation remains a grand challenge in catalysis science and reaction engineering. Under nonoxidative conditions, this is likely not due to the intrinsic inertness of CH4 molecules, but because activity must be balanced with selectivity and long-term stability of catalysts. We clarify that the C–H bond dissociation enthalpy (BDE) of methane, while large, is a poor metric for the catalytic reactivity of methane: BDE is a gas-phase quantity that neither dictates the reaction free energy nor the site-specific activation free energy relevant to reaction pathways. Guided by thermodynamic analysis of non-oxidative coupling of methane (NOCM) and kinetic evidence on Pt-based catalysts, we show that rapid deactivation via deep dehydrogenation and coking dominates catalytic performance limits. We advance Selective Passivized Catalysis (SPC) as a differentiated catalyst design strategy in which a fraction of overly active sites is deliberately shielded, ex-situ (e.g., alloying, support modification, geometric confinement) or in-situ (reaction-induced passivation), to suppress undesired pathways while preserving sites that promote desired products. SPC reconciles activity with stability and has delivered sustained NOCM performance with C2 selectivities >90% on Pt–Bi/ZSM-5 and stable operation using Pt nanolayers on Mo2TiC2Tx MXene. We outline mechanistic scenarios for solely heterogeneous NOCM and highlight operando characterization (EPR, MBMS) to resolve radical vs. surface-mediated routes. In this Feature Article, we review that Selective Passivized Catalysis provides a rational blueprint to stabilize methane activation and bring NOCM closer to practical relevance.