Nanocasting of Ordered Mesoporous Co₃O₄-Based Polyoxometalate Composite Frameworks

We report the synthesis of highly ordered mesoporous frameworks consisting of nanocrystalline Co 3 O 4 and Keggin-type tungstophosphoric acid (HPW 12 O 40, HPW) compounds using the hard-templating method. The resulting materials feature a Co 3 O 4 /HPW solid solution structure with different HPW loadings, i.e., 6, 11, 15, and 36 wt %. Characterization by small-angle X-ray scattering (SAXS), high-resolution transmission electron microscopy (TEM), and N 2 physisorption measurements reveal that all mesoporous frameworks possess a three-dimensional cubic symmetry with large internal Brumauer−Emmett−Teller (BET) surface area (87−141 m 2 g −1 ) and narrow sized pores (ca. 4 nm). The Keggin structure of the incorporated PW 12 O 40 3− clusters within the composite frameworks was confirmed with X-ray diffused scattering and atomic pair distribution function (PDF) analysis, X-ray photoelectron spectroscopy (XPS), infrared (IR), and diffuse-reflectance UV/vis spectroscopy. Catalytic studies have indicated that these Co 3 O 4 /HPW composites can be effective catalysts, exhibiting remarkable catalytic activity on direct decomposition of N 2 O.