Combustion catalysts have been extensively explored to reduce the emission of hydrocarbonsthat are capable of triggering photochemical smog and greenhouse effect. Palladium as themost active material is widely applied in exhaust catalytic converter and combustion units,but its high capital cost stimulates the tremendous research on non-noble metal candidates.Extensive research has been performed in searchingcandidates for noble metal catalysts, but there is still alarge demand for practically useful and acceptable catalystsfor a variety of important reactions. As a cheap candidate to replace noble metals forcatalytic combustion, Co₃O₄ nanoparticles show a pronouncedparticle size effect on the reaction pathway of cyclohexaneconversion. Smaller nanoparticles with more edge and cornersites would lead to more strongly bound oxygen species tomediate the combustion pathway rather than oxidativedehydrogenation one.
Magnetism and Magnetic Materials Division and CatalyticDivision in cooperation with Ningbo Institute of Material Technology and Engineering fabricated highly defective cobalt oxide nanocrystals via a controllable oxidation of carbon-encapsulated cobalt nanoparticles. Strain gradients induced in the nanoconfined carbon shell result in the formation of a large number of active sites featuring a considerablecatalytic activity for the combustion of a variety of hydrocarbons (methane, propane andsubstituted benzenes). For methane combustion, the catalyst displays a unique activity beingcomparable or even superior to the palladium ones. The present work has been published on Nature Communications 6 (2015) 7181.

Fig. Scheme for the transformation process of the Co₃O₄ catalyst.

Fig. Morphological properties of oxidized Co@C nanocapsules. (A) TEM and HRTEM images of the pristine and samples that were oxidized at 200-250 oC. (B) HRTEM images of the residual carbon shells in the oxidized samples at 225℃after washing by hydrochloric acid. (C) XRD spectra of oxidized samples.