Unraveling the Cause of Strong Metal‐Support Interaction Formation: Disparities in Metal Nanoparticle Anchoring Mechanisms

Strong metal-support interaction (SMSI) can be normally induced by the surface free energy differences between metal nanoparticles and supports. To gain deeper insights into the effect of SMSI on heterogeneous catalysis, we use prototype Pt, Pd/TiO₂(anatase) systems to demonstrate different reverse water gas shift (RWGS) reaction activity changes, especially with increasing the metal nanoparticle (NP) loading. Our experiments show that the conventional surface-free-energy change law regarding the incremental NP size is no longer applicable to these systems due to the overlook of the change of support properties owing to the disparities of the metal anchoring mechanisms. Both experimental measurements and density functional theory (DFT) calculations show that Pt atoms strongly favor anchoring on the oxygen vacancies (O_v) over the OH-sites on the anatase TiO₂ support. In contrast, Pd atoms lack such O_v-site preference compared to Pt atoms, thereby leaving higher content of O_v on the support than the Pt counterpart. Moreover, high density of residual O_v on the support can cause the Pd NPs to be in higher degree of contact with the support, either in NP-encapsulation state (experiment) or NP-spreading state (simulation). The enhanced CO₂ conversion of Pt/TiO₂A is attributed to the synergistic effect of O_v and hydrogen spillover from Pt sites.