MgO Facets as Regenerable Molecular Oxygen Reservoirs in Oxidative Coupling of Methane.

Abstract

Optimizing the performance of metal oxide catalysts centers upon the ability to engineer crystal facets to elicit improved activity and selectivity. Here, we advance the structure-performance relationships in MgO catalysts exposing {100}, stepped {100}, and {111} facets using oxidative coupling of methane as a benchmark reaction to probe surface-sensitive chemistries. The transient catalytic behavior of the structurally robust {111}-faceted MgO octahedra consistently outperforms their conventional counterparts over a range of reaction conditions. Kinetic analysis, operando Raman spectroscopy, and ab initio calculations indicate that surface-bound molecular oxygen on MgO{111} assists methane C-H activation and contributes to enhanced C2+ formation, while the transient behavior is attributed to its consumption during reaction. Facile oxidative regeneration replenishes these species and restores the initial reactive state, enabling sustained reaction-regeneration cycling. These findings show a distinctive catalytic function of MgO{111} surfaces as dynamic molecular oxygen reservoirs, underscoring the advantages of engineering metal oxides with well-designed surface structures.

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