Single Atom Catalysts: What Matters Most, the Active Site or The Surrounding?

Single atom catalysts (SACs) consist of isolated metal atoms stabilized on a solid support. The name suggests that the catalytic activity is due to the nature of the metal atom, but of course the interaction with the substrate plays a role as well. But what is more important? The metal atom or its surrounding? To answer this question, we have performed numerical experiments based on density functional theory (DFT). 24 transition metal atoms have been incorporated in Nitrogen-doped graphene, and the catalytic activity in the hydrogen evolution reaction (HER) has been studied changing the metal and keeping the N-doped graphene matrix fixed. Then, one specific atom, Pt, has been embedded in the same matrix but the nitrogen neighbors of Pt have been systematically replaced by carbon or oxygen atoms generating more than 20 structures. The HER has thus been studied by keeping the metal center fixed but changing the surrounding. It turns out that the same great variability in chemical behavior can be achieved by changing the active site or the surrounding environment. This shows the importance of the local coordination in determining the catalytic activity. The consequences of this conclusion for modeling studies of SACs are discussed.