From Anti-Sintering to Anti-Dispersion: Preserving Reactive Metallic Pt Ensembles in Light-Alkane Oxidation

Conspectus

A long-standing principle in supported noble-metal catalysis is to maximize metal dispersion and prevent nanoparticle sintering. This dispersion-centered, anti-sintering paradigm is rational because highly dispersed species increase apparent metal utilization and often expose low-coordinated sites with distinct electronic structures. For low-temperature oxidation of C2+ light alkanes, however, dispersion alone does not define the working catalyst. Propane is considered here as a representative model because its complete oxidation couples initial alkane adsorption and C–H activation with subsequent dehydrogenation, C–C bond cleavage, and deep oxidation of Cx intermediates. These functions require a balance between alkane-accessible metallic Pt ensembles and oxygen or interfacial functions that sustain complete oxidation. Excessive dispersion can disrupt this balance by promoting Pt oxidation, strong oxygen binding, or stabilization of isolated species, whereas less-dispersed Pt can preserve the contiguous metallic sites needed for alkane activation under suitable reaction conditions.

In this Account, we propose anti-dispersion as a design concept for constructing and preserving the appropriate working Pt ensemble. Pt dispersion is treated not as a monotonic activity descriptor but as a reaction-dependent variable coupled to metallic character, ensemble availability, oxygen coverage, accessible-site density, and support anchoring. Anti-dispersion therefore encompasses both controlled restructuring of over-dispersed Pt into reactive metallic ensembles and prevention of their subsequent fragmentation under working conditions. Our studies reveal these two complementary dimensions. Size-controlled Pt/CeO2 model catalysts show that increasing Pt size can enhance metallic character and intrinsic activity for propane oxidation, while the overall rate reflects a trade-off between ensemble reactivity and exposed-site density. Controlled sintering of Pt on MgAl2O4 further demonstrates that lower dispersion can be beneficial when it generates metallic surfaces that remain alkane-accessible within the relevant oxygen-coverage window. Conversely, active metallic Pt ensembles on CeO2 can fragment during propane oxidation and become stabilized as isolated Pt spectators. Selective blocking of the corresponding atom-trapping sites suppresses this reaction-induced redispersion and preserves metallic Pt ensembles. Extending this concept across oxide supports shows that anti-dispersion must be adapted to the dominant anchoring environment. Depending on the support, the relevant strategy may involve blocking support-templated Pt oxide formation, moderating acid-site-mediated anchoring, or competitively occupying hydroxyl sites that otherwise over-disperse Pt. The unifying objective is to regulate the anchoring landscape selectively while retaining useful interfacial functions for oxygen management, Cx-intermediate conversion, water tolerance, and durability.

Together, these results shift catalyst design from maximizing Pt dispersion to controlling the working ensemble. The optimum state is defined not by particle size alone but by whether the Pt ensemble remains metallic, contiguous, and alkane-accessible under the relevant feed and support environment. This perspective complements conventional anti-sintering and may guide other catalytic reactions in which isolated atoms are insufficient and contiguous metallic ensembles are required for bond activation.