Maxima were observed for the d 4 (Mn 3+ , Fe 4+ ) and d 6 (Co 3+ ) configurations, while minima were observed for the d 5 (Fe 3+ ) configuration. These authors conclude that the local surface symmetry strongly influences the adsorption and catalytic properties of perovskites. In this sense, it is commonly assumed that the eg orbitals of the B cation present the optimal geometry (vertically oriented) for interacting with the molecular orbitals of CO and O2 molecules. Moreover, the binding strength of adsorbates depends on the occupancy of the eg orbital, being optimal (neither too strongly nor too weakly) for an eg filling of 1, as in the case of Fe .