title: Roles of Li+ and Zr4+ cations in the catalytic performances of Co(1-x)M(x)Cr(2)O(4) (M = Li, Zr; x = 0-0.2) for methane combustion.
abstract: Co(1-x)M(x)Cr(2)O(4) (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)Cr(2)O(4) 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 CoCr(2)O(4) 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.
authors.affiliation: School of Environment,  Tsinghua University , Beijing 100084, China.
authors.forename: Jinghuan
authors.initials: J
authors.lastname: Chen
authors.forename: Wenbo
authors.initials: W
authors.lastname: Shi
authors.forename: Xueying
authors.initials: X
authors.lastname: Zhang
authors.forename: Hamidreza
authors.initials: H
authors.lastname: Arandiyan
authors.forename: Dongfang
authors.initials: D
authors.lastname: Li
authors.forename: Junhua
authors.initials: J
authors.lastname: Li
mesh_terms: D000327:Adsorption; D002384:Catalysis; D002412:Cations; D008094:Lithium / Q000737:chemistry*; D008697:Methane / Q000032:analysis*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D056951:Photoelectron Spectroscopy; D013052:Spectrometry, X-Ray Emission; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D013696:Temperature; D014961:X-Ray Diffraction; D015040:Zirconium / Q000737:chemistry*
chemical_list: D002412:Cations; D010087:Oxides; D008094:Lithium; D015040:Zirconium; D008697:Methane; D010100:Oxygen