we know that the metallic properties of a catalyst are of essential importance for the catalytic factors. Electrons with a well-defined energy are donated from a pool of coordination bond for bond breaking/formation. If a single atom must be strongly bonded on the support (to have a minimal stability), the electron exchange capacity is drastically released so as to the catalytic factors. In this sense, we may question whether single atoms are really the active site, or there is still something blend