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Metal nanoparticles offer a variety of largely independent handles for tailoring catalytic performance - size, shape, and their interaction with the support. DFT calculations, mostly carried out with VASP, allow us to explore this design space, to connect macroscopic activity as well as selectivity trends to specific surface motifs at the atomic scale.
Using CO as probe molecule at Pd, the adsorption energy is determined to depend systematically on the geometry of the local site, with the metal-metal bond lengths at the adsorption site serving as descriptor [1]. Extending this site-resolved picture over particle sizes from 13 to ~150 atoms yields a non-monotonic scaling behavior. A steep drop from very small clusters meets a slow decrease from the asymptotic bulk-surface value, leaving an intermediate-size regime with the weakest CO binding at the intersection of the two competing trends [2]. Particle size thus acts as a first control for adsorption strength.
A second, more subtle role emerges in 1-butene hydrogenation and isomerization on Pd/Al₂O₃ [3]. Selectivity here is not governed by an electronic modification of individual atoms, but by the change in abundance of (111), (100) and edge sites as the particle size varies - a structural effect rationalized by combining DFT with microkinetic modeling.
A third role is played by the support. On graphite-supported Ag, Au and Cu nanoparticles, the carbon is far from innocent. At the metal–carbon three-phase boundary the availability of hydrogen is strongly enhanced, raising the per-atom activity in ethylene hydrogenation by up to two orders of magnitude [4].
Given this many independent levers at hand, the broad deployment of metal nanoparticles in heterogeneous catalysis is hardly a coincidence.
References:
[1] I. V. Yudanov, M. Metzner, A. Genest, N. Rösch, J. Phys. Chem. C 112 (2008) 20269.
[2] I. V. Yudanov, A. Genest, S. Schauermann, H.-J. Freund, N. Rösch, Nano Lett. 12 (2012) 2134.
[3] A. Genest, J. Silvestre-Albero, W.-Q. Li, N. Rösch, G. Rupprechter, Nat. Commun. 12 (2021) 6098.
[4] T. Wicht, A. Genest, L. E. Chinchilla, T. Haunold, A. Steiger-Thirsfeld, M. Stöger-Pollach, J. J. Calvino, G. Rupprechter, ACS Catal. 14 (2024) 16905.