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Abstract:
Co3O4 spinel has been widely investigated as a promising catalyst for the oxidation of volatile organic compounds (VOCs). However, the roles of tetrahedrally coordinated Co2+ sites (Co2+ T-d) and octahedrally coordinated Co3+ sites (Co3+ 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 Co2+ and Co3+ in VOC oxidation on the basis of a metal ion substitution strategy, by substituting Co2+ and Co3+ with inactive or low-active Zn2+(d), Al3+(d(0)), and Fe3+(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 Co2+ sites (Co2+ T-d) are more easily oxidized to Co3+ species in comparison to Co2+ T-d, and Co3+ are responsible for the oxidative breakage of the benzene rings to generate the carboxylate intermediate species. CoO with Co2+ o(h), and ZnCo2O4 with Co3+ o(h), species have demonstrated good catalytic activity and high TOFco values at low temperature. Benzene conversions for CoO and ZnCo2O4 are greater than 50% at 196 and 212 degrees C, respectively. However, CoAl2O4 with Co2+ T-d sites shows poor catalytic activity and a low TOFco value. In addition, ZnCo2O4 exhibits good durability at 500 degrees C and strong H2O resistance ability.
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ACS CATALYSIS
ISSN: 2155-5435
Year: 2017
Issue: 3
Volume: 7
Page: 1626-1636
1 1 . 3 8 4
JCR@2017
1 1 . 7 0 0
JCR@2023
ESI Discipline: CHEMISTRY;
ESI HC Threshold:226
JCR Journal Grade:1
CAS Journal Grade:2
Cited Count:
WoS CC Cited Count: 318
SCOPUS Cited Count: 328
ESI Highly Cited Papers on the List: 26 Unfold All
WanFang Cited Count:
Chinese Cited Count:
30 Days PV: 1