Small oxide particles have unique physical and chemical properties and understanding them is virtually important for the design of new heterogeneous catalysts. Our current work concerns Co₃O₄ which is an archetype of spinel oxides, containing metallic sites in two oxidation states Co(III) and Co(II). Unique electronic properties of this oxide have been associated with different structural modifications  including : i) non stoichiometry (surface oxygen excess), ii) location, oxidation state and electronic configuration of metallic sites (inversion and existence of Co(III) high spin), iii) cationic vacancies, iv) electronic transfers. In complement to sophisticated methods (laser deposition, reduction of precursors embedded inside organic micelles) which are not straightforward and uneasy to scale up and for which thermal treatments are difficult to apply without sintering, we have studied Co₃O₄ particles templated inside SBA-15 silica before to reduce them (under an Ar/H₂ flow at 450°C) and to test their activity and selectivity for the selective hydrogenation of conjugated alpha-beta unsaturated aldehyde (cinnamaldehyde). The optical properties of the precursor catalyst, identified by UV visible Diffuse Reflectance Spectroscopy, can be correlated with both its activity and selectivity for the reaction (80% selectivity in unsaturated alcohol).

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