Mesoporous MCo 2O 4 (M = Cu, Mn and Ni) spinels: Structural replication, characterization and catalytic application in CO oxidation

Abstract

Mesoporous spinels of MCo 2O 4 (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 m 2 g −1) and large pore volumes (0.35–0.41 cm 3 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 CuCo 2O 4 and MnCo 2O 4 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 NiCo 2O 4 catalyst shows relatively low activity and continuous deactivation during the catalytic life test.