Reactivity of Single-Atom Alloys as Easy as Counting to Ten

Abstract

Single-Atom Alloys (SAAs) have recently emerged as highly active and selective alloy catalysts. Unlike pure metals, SAAs escape the well-established conceptual framework developed nearly three decades ago for predicting catalytic performance. Here, based on high throughput density functional theory calculations, we reveal a 10-electron count rule for the binding of adsorbates on the dopant of SAA surfaces. A simple molecular orbital approach rationalises this rule and the nature of the adsorbate/dopant interaction. In addition, our intuitive model can accelerate the rational design of SAA catalysts. Indeed, we illustrate how the unique insights provided by the electron count rule help identify the most promising dopant for an industrially relevant hydrogenation reaction, thereby reducing the number of potential materials by more than one order of magnitude.

Challenges and Opportunities in Engineering the Electronic Structure of Single-Atom Catalysts

“…Although all the above-mentioned approaches are valuable for understanding SAC reactivity, they still require expensive and complex simulations that are not easily accessible to researchers attempting to design efficient SACs for a specific reaction. Lately, an uncommonly simple molecular orbital approach has been proposed for SAAs based on the key concept that the interaction of adsorbates at their surface can be described in terms of an electron counting rule . By combining machine learning and DFT analyses, a variety of catalytically relevant adsorbates was screened on a large set of SAA surfaces, showing that the adsorbate interaction with the isolated metal site is maximized when the n d valence electrons of the dopant and the k valence electrons of the adsorbates sum up to 10: n d + k = 10.…”

“…Lately, an uncommonly simple molecular orbital approach has been proposed for SAAs based on the key concept that the interaction of adsorbates at their surface can be described in terms of an electron counting rule. 17 By combining machine learning and DFT analyses, a variety of catalytically relevant adsorbates was screened on a large set of SAA surfaces, showing that the adsorbate interaction with the isolated metal site is maximized when the n d valence electrons of the dopant and the k valence electrons of the adsorbates sum up to 10: n d + k = 10. Undoubtedly, this simple 10-electron rule provides experimentalists with a straightforward tool to identify suitable metal combinations when designing SAAs for targeted applications.…”

“…Nonetheless, as highlighted by several recent works, ,− the performance of SACs can significantly differ from that of extended metal surfaces, calling for a reanalysis of the suitability of existing general models, e.g., to account for local charges or spin polarization. Beyond heterogeneous catalysts, researchers frequently highlight the resemblance of SACs to organometallic complexes and have explored descriptors such as molecular orbitals and oxidation states. , However, it has also been shown that the coordination of metal atoms to solid supports can differ in nature, compared to ligands, , and the impacts are not yet fully understood.…”

“…Beyond heterogeneous catalysts, researchers frequently highlight the resemblance of SACs to organometallic complexes and have explored descriptors such as molecular orbitals and oxidation states. 17 , 18 However, it has also been shown that the coordination of metal atoms to solid supports can differ in nature, compared to ligands, 18 , 19 and the impacts are not yet fully understood.…”

Investigating Spillover Energy as a Descriptor for Single-Atom Alloy Catalyst Design

“…When coverage effects are negligible, two factors influence the binding energies of adsorbates at the dopant site on SAAs: the atomic charge of the dopant and the number of valence electrons of the dopant. 27 In the limiting case of adsorption governed by electrostatic contributions (e.g., H 2 O and OH), the atomic charge of the dopant is, on its own, a good qualitative descriptor for the SOE. Because of the negative partial charges of the oxygen atoms with which the formate binds to the surface, we would expect that dopants with less negative charges would interact more favorably with formate.…”