<p>Cobalt-containing spinel oxides are promising platforms to fine-tune the intrinsic activity/selectivity of their geometric sites in catalysis. However, the role of tetrahedrally occupied Co²⁺ (Co²⁺_Td) and Co³⁺ in an octahedral site (Co³⁺_Oh) in controlling the catalytic activity remains controversial. Herein, we investigated a geometrical-site-dependent catalytic activation of ozone respectively on the Co²⁺_Td and Co³⁺_Oh sites. The same exposure of [111] crystal facet is achieved by substituting those undesired sites with catalytically inactive cations. The highly spin-polarized Co²⁺_Td sites invoke strong orbital interactions and intensive electron transfer with the adsorbed O₃ and become the active sites for selectively producing surface-bound hydroxyl radicals (^•OH) and avoiding the formation of unfavorable singlet oxygen (¹O₂), resulting in a 17.6-fold increase in turnover frequency (TOF). This work enlightens the spin-polarized electronic states into regulating the reaction thermodynamics in transition metal oxide-induced catalysis and envisages the practical application potentials of geometric site engineered spinel oxides.</p>