Co 3 O 4 spinel has been widely investigated as a promising catalyst for the oxidation of volatile organic compounds (VOCs). However, the roles of tetrahedrally coordinated Co 2+ sites (Co 2+ T d ) and octahedrally coordinated Co 3+ sites (Co 3+ O h ) still remain elusive, because their oxidation states are strongly influenced by the local geometric and electronic structures of the cobalt ion. In this work, we separately studied the geometrical-site-dependent catalytic activity of Co 2+ and Co 3+ in VOC oxidation on the basis of a metal ion substitution strategy, by substituting Co 2+ and Co 3+ with inactive or low-active Zn 2+ (d 0 ), Al 3+ (d 0 ), and Fe 3+ (d 5 ), respectively. Raman spectroscopy, X-ray absorption fine structure (XAFS), and in situ DRIFTS spectra were thoroughly applied to elucidate the active sites of a Co-based spinel catalyst. The results demonstrate that octahedrally coordinated Co 2+ sites (Co 2+ O h ) are more easily oxidized to Co 3+ species in comparison to Co 2+ T d , and Co 3+ are responsible for the oxidative breakage of the benzene rings to generate the carboxylate intermediate species. CoO with Co 2+ O h and ZnCo 2 O 4 with Co 3+ O h species have demonstrated good catalytic activity and high TOF Co values at low temperature. Benzene conversions for CoO and ZnCo 2 O 4 are greater than 50% at 196 and 212 °C, respectively. However, CoAl 2 O 4 with Co 2+ T d sites shows poor catalytic activity and a low TOF Co value. In addition, ZnCo 2 O 4 exhibits good durability at 500 °C and strong H 2 O resistance ability.

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Bismuth tungstate has attracted great attention as a new photocatalyst working under visible irradiation. In this paper, we demonstrate a facile hydrothermal route for controllable synthesis of novel Bi(2)WO(6) hierarchical hollow spheres with an ultrahigh specific surface area in the presence of poly(vinyl pyrrolidone) at a proper C(2)H(5)OH/CH(3)COOH/H(2)O volume ratio. The obtained products are systematically studied by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller (BET) and UV-vis absorption spectroscopy. It is shown that the Bi(2)WO(6) hollow spheres are constructed of numerous nanoplates while the nanoplates consist of a great deal of nanoparticles. UV-vis spectrum is used to estimate the band gap energy (about 2.90 eV) of the Bi(2)WO(6) hollow spheres. The ultrahigh BET specific surface area of ca. 45.0 m(2) g(-1) is displayed for the Bi(2)WO(6) hierarchical hollow spheres, which is much higher than that for all the previously reported Bi(2)WO(6) products. The Bi(2)WO(6) hierarchical hollow spheres are displayed to possess superior photocatalytic activity in the photodegradation of rhodamine B (RhB) under visible light irradiation over other morphological products.