Mesoporous MCo2O4 (M = Cu, Mn and Ni) spinels: Structural replication, characterization and catalytic application in CO oxidation

Mesoporous spinels of MCo2O4 (M = Cu, Mn and Ni) with crystalline walls have been synthesized through a nanocasting pathway using concentrated solutions of metal nitrates as precursors and mesoporous silica SBA-15 as the hard template. Characterization of small-angle XRD and TEM confirms that the replica materials retain partially the hexagonal mesostructure of their mother template SBA-15. Wide-angle XRD patterns show that all the products are pure phases with cubic spinel-type structures. HRTEM images reveal that the framework walls of these replica materials are composed of spinel cobaltite nanocrystallites with an average diameter of about 8 nm. Nitrogen physisorption isotherms show that the obtained replicas possess high BET specific surface areas (91–129 m2 g−1) and large pore volumes (0.35–0.41 cm3 g−1). Surface compositions and chemical states of the transition-metal elements in the samples are investigated by XPS technique. Catalytic results suggest that the CuCo2O4 and MnCo2O4 catalysts exhibit high activities and robust stabilities toward the reaction of CO oxidation. Temperatures of 50% CO conversion for copper cobalt oxide and manganese cobalt oxide spinels are 342 and 346 K, respectively. By contrast, the NiCo2O4 catalyst shows relatively low activity and continuous deactivation during the catalytic life test.