## 2 Theoretical Studies on Heteroatom-Mediated Metal-Support Interactions
### Predicting the Effect of Heteroatom-Mediated SMSI on the Catalytic Performances
#### 2.4.2 SMSI and Metal Dispersion  
The interactions between the metal phase and the support at the interface can also determine the dispersion of metal clusters onto the support surface, and finally the particle sizes. In fact, the nucleation and the growth of metal clusters are governed by a delicate balance between metal cohesion and metal support interactions: if the former prevails over the latter, clustering and agglomeration will preferentially occur. Conversely, when the metal binding energy exceeds the cohesive energy of the bulk metal, metal aggregation is prevented, and a high metal dispersion is achieved. This is the case of some transition metals (Sc, Ti, and V) deposited on nitrogen-doped graphene [65]. When pyridine-like functionalities are introduced on the surface of graphene, highly localized acceptor-like states close to the Fermi level are created, leading to a stronger interaction between graphene and metal atoms, and thus favoring a high metal dispersion. The DFT method has been implemented to determine how far the nucleation and growth of Pt NPs onto a carbon matrix (described by a 4 \(\times\) 4 supercell of graphene) are affected by the presence of nitrogen (pyridinic, pyrrolic, graphitic nitrogen) and and/or sulfur (thiophene defects) [74]. For this purpose, the interaction energy of Pt on doped graphene surfaces was evaluated in terms of adsorption energy. In all of the cases, a higher interaction energy was obtained for nitrogen or sulfur singularly doped surfaces compared to pristine graphene, and in particular, the following interaction order was observed: N pyrrolic > N graphitic > thiophene > N pyridinic > graphene. Surprisingly, a weaker interaction and a lower stabilization of Pt nuclei were predicted on a surface co-doped with nitrogen (pyrrolic defects) and sulfur (thiophene defects). In particular, probing the interaction energy for N and S co-doped surfaces with different dopant location, it appears evident that the interaction and the Pt stabilization decrease by increasing the closeness of the two hetero-defects (nitrogen and sulfur). It seems like sulfur acts as preferential anchoring site for Pt, which is probably due to the electron transfer to the Pt atom.  
Metal phase can be deposited on the support according to several strategies. [PERSON] et al. focused on the influence of a catalyst synthesis strategy on the metal-support interaction of Pt on nitrogen-doped carbon nanotubes (Pt/NCNTs), comparing ethylene glycol (EG) reduction, sodium borohydride reduction, and impregnation H\({}_{2}\) reduction [75].  
In the case of the EG reduction method, neutral Pt NPs preferentially interacted with graphitic nitrogen, whereas in sodium borohydride reduction and impregnation H\({}_{2}\) reduction, the adsorption of charged metal ion precursors is favored on pyridinic nitrogen.  
Figure 5: Structural rearrangement of Pt clusters supported on nitrogen-doped graphene. Reprinted with permission from reference [73]. Copyright 2011 American Chemical Society.