Waste eggshells to valuable Co₃O₄/CaCO₃ materials as efficient catalysts for VOCs oxidation

Transition metal oxides have excellent catalytic activities for the oxidation of VOCs, in which it is necessary to find new catalysts/supports with cheap and environmentally-friendly properties. Herein, Co₃O₄ nanoparticles decorated eggshell catalysts were firstly synthesized via impregnation method, where the waste eggshell is used as an effective hard template and an excellent support with porous structure. A series of Co₃O₄/Eggshell catalysts were synthesized by changing the different concentration of precursors (different Co₃O₄ loadings), which were defined as Co₃O₄/Eggshell-1 (33.1 %), Co₃O₄/Eggshell-2 (16.7 %) and Co₃O₄/Eggshell-3 (9.1 %) catalysts. Among of them, the Co₃O₄/Eggshell-2 exhibited the best activity with the temperature T_{90 %} = 256 ℃, which is about 90 °C lower than Co₃O₄/oyster shell-2 (benzene catalytic oxidation). And the catalytic activity of Co₃O₄/Eggshell is remarkably improved as compared to commercially pure Co₃O₄ nanoparticles and commercially CaCO₃. The excellent activity can be attributed to the unique structure of the eggshell and the interaction of CaCO₃ and Co₃O₄. In addition, the catalyst has also showed long-term stability. Moreover, the reaction mechanism of benzene catalytic oxidation was further revealed by in-situ FTIR studies.