Grafting of iron on amorphous silica surfaces from ab initio calculations.

Iron over silica catalytic systems have attracted considerable attention due to their activity and selectivity in different reactions, for instance, in the hydrodeoxygenation process. Here, the grafting mechanisms of iron under various forms (one atom, two atoms, or a cluster) on silica surfaces are studied using ab initio calculations. Various geometries with different locations of iron on the silica structure have been investigated, and it is found that a strong interaction between iron and the silanol groups takes place, mostly driven by the formation of Fe-O-Si bonds, and in few cases by nearby surface OH groups, creating Fe-OH-Si bonds. For the cluster, we show that the most favorable adsorption mode induces a strong effect on the silica surface accompanied with a large charge transfer, making it very stable and promising for a large panel of applications.