Co_(1-x)M_xCr2O4 (M = Li, Zr; x = 0-0.2) catalysts were prepared via the citric acid method and investigated for catalytic combustion of methane. Substitution at tetrahedral (A) sites with monovalent (Li) or tetravalent (Zr) metal ions led to a decrease or increase of the catalytic activity, respectively. The Co_(0.95)Zr_(0.05)Cr2O4 catalyst proved to be the most active and its catalytic activity reached 90 of methane conversion at 448 °C, which dropped by 66 °C compared with that of the undoped CoCr2O4 catalyst. XRD and Raman results indicated that lithium or zirconium substitution could modify the spinel structure and electronic properties. For lithium-doped catalysts, oxygen deficiency and a strong surface enrichment in lithium and chromium were detected, Zirconium substitution enhanced the reducibility of zirconium-doped catalysts and decreased the strength constant of both the Co—O band and the Cr—O band, which may contribute to the catalytic activity toward methane combustion. In addition, the prevalent catalytic combustion activity of the zirconium-substituted catalysts could be explained by their higher concentration of suprafacial, weakly chemisorbed oxygen.
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