When Fluxionality Beats Size Selection: Acceleration of Ostwald Ripening of Sub‐Nano Clusters

Abstract

Size selection was demonstrated to suppress Ostwald ripening of supported catalytic nanoparticles. When the supported clusters are subnanometer in size and highly fluxional, such as Pt clusters on the rutile TiO2(110) surface, this paradigm breaks down, and the established theory of sintering needs a revision. At temperatures characteristic of catalysis (i.e. 700 K), sub‐nano clusters thermally populate many low‐energy metastable isomers. As these isomers all have different geometric and electronic structures, and thus, formation and dissociation energies (in lieu of surface energy), Ostwald ripening is not suppressed, despite the size‐selection. However, some clusters arise as magic numbers in terms of sintering stability at the ensemble level. Acceleration of sintering by metastable species persists though weakens in polydisperse cluster systems. We propose a competing pathways theory for sintering, which at the atomistic level describes the found size‐specific sintering behavior.

Rate Expressions in Mean Field Microkinetic Models Incorporating Multiple Types of Active Sites

“…This also demonstrates that meta stable sites can dominate the reactive adlayer even though they are weaker binding at low coverages entirely due to macroscopic configurational entropy and realistic coverage effects. This corroborates the recent and ongoing work of Sautet and Alexandrova and co-workers [30][31][32][33][53][54][55][56][57][58][59][60][61][62][63][64] demonstrating the catalytic potential of fluxional and meta-stable sites. Overall, our results are very sensible given the parameters used and substantiate the appropriateness of the rate expressions established here for multiple site types.…”

“…However, it is becoming increasingly clear that multiple active centers exist that are relevant to the kinetics of such systems, 3,4, and recent work has highlighted the critical role of metastable state structures in heterogeneous catalysis. [30][31][32][33] So, a proper formulation is still required.…”

Exploring the materials space in the smallest particle size range: from heterogeneous catalysis to electrocatalysis and photocatalysis

“…A competing pathways theory for sintering, which, at the atomistic level, describes the found size-specific sintering behavior, was proposed in ref. 145.…”

Dynamics of Heterogeneous Catalytic Processes at Operando Conditions

“…80 They found that dynamic fluxionality may break the scaling relationships, 81 cause non-Arrhenius behavior, 82 or accelerate the Ostwald ripening of a supported catalyst. 83 Moreover, a bipartite matching algorithm was introduced to connect low-lying isomers obtained from the GO technique and to build the whole picture of the fluxional behavior, 75 as shown in Figure 4b. More discussion about dynamic fluxionality can be seen in their recently published review.…”