Hydrogen‐Atom Abstraction from Methane by Stoichiometric Vanadium–Silicon Heteronuclear Oxide Cluster Cations

Vanadium–silicon heteronuclear oxide cluster cations were prepared by laser ablation of a V/Si mixed sample in an O₂ background. Reactions of the heteronuclear oxide cations with methane in a fast‐flow reactor were studied with a time‐of‐flight (TOF) mass spectrometer to detect the cluster distribution before and after the reactions. Hydrogen abstraction reactions were identified over stoichiometric cluster cations [(V₂O₅)_n(SiO₂)_m]⁺ (n=1, m=1–4; n=2, m=1), and the estimated first‐order rate constants for the reactions were close to that of the homonuclear oxide cluster V₄O₁₀⁺ with methane. Density functional calculations were performed to study the structural, bonding, electronic, and reactivity properties of these stoichiometric oxide clusters. Terminal‐oxygen‐centered radicals (O_t ^. ) were found in all of the stable isomers. These O_t ^. radicals are active sites of the clusters in reaction with CH₄. The O_t ^. radicals in [V₂O₅(SiO₂)_1–4]⁺ clusters are bonded with Si rather than V atoms. All the hydrogen abstraction reactions are favorable both thermodynamically and kinetically. This work reveals the unique properties of metal/nonmetal heteronuclear oxide clusters, and may provide new insights into CH₄ activation on silica‐supported vanadium oxide catalysts.     

Electron impact ionization of ethylene–methanol heteroclusters: Stable configurations and mechanisms in intracluster ion–molecule reactions

Reactions that proceed within mixed ethylene–methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. The ion abundance ratio, [(C₂H₄)_n(CH₃OH)_mH⁺]/[(C₂H₄)_n(CH₃OH)_m⁺], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C₂H₄)_n(CH₃OH)_m⁺ and (C₂H₄)_n(CH₃OH)_m–1CH₃O⁺ ions are interpreted as a consequence of the ion–neutral complex and intracluster ion–molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C₂H₄)_n(CH₃OH)_mH⁺ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion–molecule condensation reactions, leading to the formation of fragment ions, $ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $ and (CH₃OH)H₃O⁺, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C₂H₄)_n(CH₃OH)_mH⁺(n + m ≤ 3) using semi-empirical molecular orbital calculations.     

Catalytic Oxidation of Methane to C2‐C4 Hydrocarbons over CeO2 Promoted W‐Mn/SiO2 Catalysts at Higher Pressure

CeO₂‐promoted Na‐Mn‐W/SiO₂ catalyst has been studied for catalytic oxidation of methane in a micro‐stainless‐steel reactor at elevated pressure. The effect of operating conditions, such as GHSV, pressure and CH₄/O₂ ratio, has been investigated. 22.0% CH₄ conversion with 73.8% C₂‐C₄ selectivity (C₂/C₃/C₄ = 3.8/1.0/3.6) was obtained at 1003 K, 1.5 × 10⁵ h^?;1 GHSV and 1.0 MPa. The results show: Elevated pressure disadvantages the catalytic oxidation of methane to C₂‐C₄ hydrocarbons. Large amounts of C₃ and C₄ hydrocarbons are observed. The unfavorable effects of elevated pressure can be overcome by increasing GHSV; the reaction is strongly dependent on the operating conditions at elevated pressure, particularly dependent on GHSV and ratio of CH₄/O₂. Analyses by means of XRD, XPS and CO₂‐TPD show that CO₂ produced from the reaction makes a weakly poisoning capacity of the catalyst; information of changeful valence on Ce and Mn was detected over the near‐surface of the Ce‐Na‐W‐Mn/SiO₂ catalyst; the existence of Ce³⁺/Ce⁴⁺ and Mn²⁺/Mn³⁺ ion couple supported that the reaction over the catalyst followed the Redeal‐Redox mechanism. Oxidative re‐coupling of C₂H₆ and CH₄ in gas phase or over surface of catalyst produces C₃ or C₄ hydrocarbons.     

DFT study of the reactivity of methane and dioxygen with d-L2M complexes

A density functional theory analysis of the reactions of methane and O₂ with d¹⁰-L₂M complexes (M = Pd, Pt; L = N-heterocyclic carbene (NHC), PMe₃) is presented. Computations suggest that reaction of L₂M⁰ with O₂/CH₄ to form cis- (L)₂M(OOH)(CH₃) is only slightly uphill (ΔG ∼ 10-11 kcal/mol). Based on calculated thermodynamics, reaction of (L)₂Pt⁰ with CH₄ and O₂ is predicted to be more favorable by first addition of CH₄ and then reaction of O₂ with the resulting methyl-hydrido complex. However, oxidative addition for either the C-H bond of methane or of O₂ to d¹⁰-L₂M complexes is kinetically prohibitive. If barriers to oxidative addition to d¹⁰-L₂M systems could be reduced, conversion of L₂M(H)(CH₃) to L₂M(OOH)(CH₃) via hydrogen atom abstract/radical rebound is calculated to be thermodynamically and kinetically feasible, particularly for NHC and Pd. As (NHC)₂Pd also has a lower free energy to methane C-H oxidative addition than does (NHC)₂Pt, the former combination would appear to be a promising starting point in the search for catalysts for partial hydrocarbon oxidation.     

Schiff base complexes of silicon(IV)

Reactions of silicon tetraacetate with different types ofSchiff bases have been investigated in anhydrous benzene. Monofunctional bidentate, C₆H₅CHNXOH and HORCHNC₆H₅ [whereX=CH₂CH₂, CH₂CH(CH₃) or o-C₆H₄ and R=o-C₆H₄ or 2,1-C₁₀H₆], bifunctional tridentate, o-HOC₆H₄CHNYOH [whereY=CH₂CH₂ or CH₂CH(CH₃)] and bifunctional tetradentateSchiff bases, o-HOC₆H₄C(CH₃)N(CH₂) _n NC(CH₃)C₆H₄OH-o (wheren=2 or 3) have been shown to yield derivatives of the type, Si(OAc)_4– m L _m, Si(OAc)_4–2 n L _n and Si(OAc)₂ L (wherem=1,2 or 3;n=1 or 2 and HL, H₂ L and H₂ L represent the molecules of monofunctional bidentate, bifunctional tridentate and bifunctional tetradentateSchiff bases resp.) and have been found to be monomeric in boiling benzene. Tentative structures based on IR and in a few cases PMR spectra have been indicated for the resulting derivatives.With 2 Figures     

Effect of sodium cation on the electrochemical reduction of CO<Subscript>2</Subscript> at a copper electrode in methanol

The electrochemical reduction of CO₂ with a Cu electrode in methanol was investigated with sodium hydroxide supporting salt. A divided H-type cell was employed; the supporting electrolytes were 80 mmol dm⁻³ sodium hydroxide in methanol (catholyte) and 300 mmol dm⁻³ potassium hydroxide in methanol (anolyte). The main products from CO₂ were methane, ethylene, carbon monoxide, and formic acid. The maximum current efficiency for hydrocarbons (methane and ethylene) was 80.6%, at −4.0 V vs Ag/AgCl, saturated KCl. The ratio of current efficiency for methane/ethylene, r _f(CH₄)/r _f(C₂H₄), was similar to those obtained in LiOH/methanol-based electrolyte and larger relative to those in methanol using KOH, RbOH, and CsOH supporting salts. In NaOH/methanol-based electrolyte, the efficiency of hydrogen formation, a competing reaction of CO₂ reduction, was suppressed to below 4%. The electrochemical CO₂ reduction to methane may be able to proceed efficiently in a hydrophilic environment near the electrode surface provided by sodium cation.     

Theoretical study on the gas‐phase reaction mechanism between rhodium monoxide and methane for methanol production

The gas‐phase reaction mechanism between methane and rhodium monoxide for the formation of methanol, syngas, formaldehyde, water, and methyl radical have been studied in detail on the doublet and quartet state potential energy surfaces at the CCSD(T)/6‐311+G(2d, 2p), SDD//B3LYP/6‐311+G(2d, 2p), SDD level. Over the 300–1100 K temperature range, the branching ratio for the Rh(⁴F) + CH₃OH channel is 97.5–100%, whereas the branching ratio for the D‐CH₂ORh + H₂ channel is 0.0–2.5%, and the branching ratio for the D‐CH₂ORh + H₂ channel is so small to be ruled out. The minimum energy reaction pathway for the main product methanol formation involving two spin inversions prefers to both start and terminate on the ground quartet state, where the ground doublet intermediate CH₃RhOH is energetically preferred, and its formation rate constant over the 300–1100 K temperature range is fitted by k_CH3RhOH = 7.03 × 10⁶ exp(?69.484/RT) dm³ mol^?1 s^?1. On the other hand, the main products shall be Rh + CH₃OH in the reactions of RhO + CH₄, CH₂ORh + H₂, Rh + CO +2H₂, and RhCH₂ + H₂O, whereas the main products shall be CH₂ORh + H₂ in the reaction of Rh + CH₃OH. Meanwhile, the doublet intermediates H₂RhOCH₂ and CH₃RhOH are predicted to be energetically favored in the reactions of Rh + CH₃OH and CH₂ORh + H₂ and in the reaction of RhCH₂ + H₂O, respectively. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Reactivity and Catalytic Activity of Homobimetallic Vanadium(V) Complex Derived from Bis(5‐chlorosalicylaldehyde)oxaloyldihydrazone Ligand

Homobimetallic vanadium(V) complex of the composition [(CH₃)₂NH₂⁺]₂[(VO₂)₂(sloxCl)].4H₂O was synthesized from the reaction of V₂O₅ with bis(5‐chlorosalicylaldehyde)oxaloyldihydrazone ligand in a 1:1 molar ratio in methanol. The structure of the complex was established by X‐ray crystallography. Reactivity of the complex with H₂O₂ leads to bis (monooxidoperoxidovanadate(V)) [{VO(O₂)}₂(sloxCl)]^2? formation and with HCl, oxidohydroxido complex of composition [(VO (OH)(sloxCl)]^2? was formed. Binding interaction of the complex was also investigated toward protein (BSA) and it was found to be 2.21 x 10⁸ M^?1. The catalytic activity of the complex in the oxidation of alcohols and oxidative bromination of some organic substrates was also studied, and it showed a great potent as a catalyst.     

Reaction‐path dynamics and theoretical rate constants for the reaction CH4 + O3 → HOOO + CH3

We present a direct ab initio dynamics study of thermal rate constants of the hydrogen abstraction reaction of CH₄ + O₃ → HOOO +CH₃. The geometries of all the stationary points are optimized at MPW1K/6‐31+G(d,p), MPWB1K/6‐31+G(d,p), and BHandHLYP/6‐31+G(d,p) levels of theory. The energies are refined at a multi‐high‐level method. The extended Arrhenius expression fitted from the CVT/SCT and μVT/Eckart rate constants of ozonolysis of methane in the temperature range 200–2500 K are k^CVT/SCT(T) = 5.96 × 10^?29T^4.49e^(?17321.3/T) and k^μVT/Eckart(T) = 7.92 × 10^?29T^4.46e^(?17301.7/T), respectively. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

负载型P-Mo-V/SBA-15催化剂上的甲烷选择氧化反应

以磷钼钒杂多酸(H₅PMo₁₀V₂O₄₀)为前驱体、介孔SBA-15为载体, 采用浸渍法制备不同负载量的P-Mo-V氧化物催化剂. 在甲烷选择氧化反应中, 考察了负载量、反应温度、空速等对甲烷转化率和产物选择性的影响. 结果表明, 催化剂对甲烷选择氧化制甲醛具有较高活性, 甲烷转化率随负载量的增大和反应温度的升高而提高, 甲醛的选择性随负载量的增大先升后降. 反应温度为640 ℃、空速为48300 L•kg^－1•h^－1、氧化物负载量w＝2.89%时, 甲醛的时空产率最高(295 g•kg_cat^－1•h^－1). 多种表征表明, 氧化物负载量w≤2.89%时, P-Mo-V氧化物在载体介孔孔道内以高分散形式存在. 催化剂的酸性和氧化还原性质与负载量相关, NH₃-TPD和H₂-TPR的测试结果表明, 较弱的酸性位和较低还原温度的活性组分有利于甲烷选择氧化制甲醛.     

Variation of atmospheric tritium concentrations in three different chemical forms in Fukuoka, Japan

Atmospheric tritium concentrations of tritiated water vapor (HTO), tritiated hydrogen (HT) and tritiated hydrocarbons (primarily tritiated methane, CH₃T) have been measured in Fukuoka prefecture, Japan from 1984 to the present to establish a general database on the behavior of atmospheric tritium. HTO concentrations expressed in Bq/l-H₂O vary within a range of 1.19 to 2.45, giving an overall average value of 1.86±0.077. HTO concentrations expressed in-mBq/m³-air vary within a range of 7.8 to 46.1 and have a strong correlation with the atmospheric humidity, being high in the summer and low in winter. In the case of HT and CH₃T, no seasonal variations were observed with average monthly values of 23.1 to 61.0 mBq/m³-air and 8.3 to 23.9 mBq/m³-air, respectively. The present HTO concentrations are already close to the tritium level before nuclear testings. However, the present HT and CH₃T concentrations are still higher by a factor of about 140 and 30, respectively, than those before the testings. Specific activities are estimated to be 14.6–16.7 TU for HTO, 5.5·10⁵–1.0·10⁶ TU for HT and 3.2·10⁴–4·10⁴ TU for CH₃T. The apparent difference in the specific activities suggests a very slow transformation of these species in the atmosphere or a continuous supply of HT and CH₃T with high specific activity. Residence time for atmospheric HT was found to be 6.5 years over the period 1988–92 and 10 years for 1988–95. These times are longer than 4.8 years given by Mason and Östlund in the 1970s, and thus indicate a supply to the atmosphere of HT from various tritium sources.     

Mechanisms of Heterogeneous Processes in the System SiO2 + CH4: III. Products of >Si

Permenov  D. G.  Radzig  V. A. 《Kinetics and Catalysis》2004,45(2):273-278

β-d-Xylosidase from Selenomonas ruminantium: Thermodynamics of Enzyme-Catalyzed and Noncatalyzed Reactions

β-d-Xylosidase/α-l-arabinofuranosidase from Selenomonas ruminantium is the most active enzyme known for catalyzing hydrolysis of 1,4-β-d-xylooligosaccharides to d-xylose. Temperature dependence for hydrolysis of 4-nitrophenyl-β-d-xylopyranoside (4NPX), 4-nitrophenyl-α-l-arabinofuranoside (4NPA), and 1,4-β-d-xylobiose (X2) was determined on and off (k _non) the enzyme at pH 5.3, which lies in the pH-independent region for k _cat and k _non. Rate enhancements (k _cat/k _non) for 4NPX, 4NPA, and X2 are 4.3?×?10¹¹, 2.4?×?10⁹, and 3.7?×?10¹², respectively, at 25 °C and increase with decreasing temperature. Relative parameters k _cat ^4NPX/k _cat ^4NPA, k _cat ^4NPX/k _cat ^X2, and (k _cat/K _m)^4NPX/(k _cat/K _m)^X2 increase and (k _cat/K _m)^4NPX/(k _cat/K _m)^4NPA, (1/K _m)^4NPX/(1/K _m)^4NPA, and (1/K _m)^4NPX/(1/K _m)^X2 decrease with increasing temperature.     

Nickel-copper-chromium catalyst for selective methane oxidation to synthesis gas at short residence times

Data on the selective oxidation of methane to synthesis gas on a 9% NiCuCr/2% Ce/(ϑ + α)-Al₂O₃ catalyst in dilute mixtures with Ar at short residence times (2–3 ms) are presented. The composition, structure, morphology, and adsorption properties of the catalyst with respect to oxygen and hydrogen before and after reaction were studied using XRD, BET, electron microscopy with electron microdiffraction, TPR, TPO, and TPD of oxygen and hydrogen. The following optimum conditions for the preparation and pretreatment of the catalyst for selective methane reduction were found: the incipient wetness impregnation of a support with aqueous nitrate solutions; drying; and heating in air at 873 and then at 1173 K (for 1 h at either temperature) followed by reduction with an H₂-Ar mixture at 1173 K for 1 h. At a residence time of 2–3 ms (space velocity to 1.5 × 10⁶ h⁻¹) and 1073–1173 K, the resulting catalyst afforded an 80–100% CH₄ conversion in mixtures with O₂ (CH₄/O₂ = 2: 1) diluted with argon (97.2–98.0%) to synthesis gas with H₂/CO = 2: 1. The selectivity of CO and H₂ formation was 99.6–100 and 99–100%, respectively; CO₂ was almost absent from the reaction products. The catalyst activity did not decrease for 56 h; carbon deposition was not observed. A possible mechanism of the direct oxidation of CH₄ to synthesis gas is considered.     

The Direct Partial Oxidation of Methane to Dimethyl Ether over Pt/Y2O3 Catalysts Using an NO/O2 Shuttle

Using a mixture of NO + O₂ as the oxidant enabled the direct selective oxidation of methane to dimethyl ether (DME) over Pt/Y₂O₃. The reaction was carried out in a fixed bed reactor at 0.1 MPa over a temperature range of 275–375 °C. During the activity tests, the only carbon‐containing products were DME and CO₂. The DME productivity (μmol g_cat^?1 h^?1) was comparable to oxygenate productivities reported in the literature for strong oxidants (N₂O, H₂O₂, O₃). The NO + O₂ mixture formed NO₂, which acted as the oxygen atom carrier for the ultimate oxidant O₂. During the methane partial oxidation reaction, NO and NO₂ were not reduced to N₂. In situ FTIR showed the formation of surface nitrate species, which are considered to be key intermediate species for the selective oxidation.     

Syntheses, 95Mo NMR Spectroscopy and Structures of Distorted Cubic Mo4(��3-O)4(��2-O2P(CH2C6H5)2)4O4 and the Open Mixed-Valent Cluster, Mo4(��3-O)2(��2-O2P(CH2C6H5)2)6O6

The reaction of MoO₂(acac)₂ and dibenzylphosphinic acid in ethanol leads to a red distorted cubic tetrameric cluster, Mo₄(??³-O)₄(??²-O₂P(CH₂C₆H₅)₂)₄O₄, and a pink open mixed-valent cluster, Mo₄(??³-O)₂(??²-O₂P(CH₂C₆H₅)₂)₆O₆, when the reduction is carried out at 120 and 75 °C, respectively. ⁹⁵Mo NMR spectroscopy revealed a singlet for Mo₄(??³-O)₄(??²-O₂P(CH₂C₆H₅)₂)₄O₄ (1) at 584.9 ppm (????_1/2 = 4500 Hz) and two resonances for Mo₄(??³-O)₂(??²-O₂P(CH₂C₆H₅)₂)₆O₆ (2) at 238.8 ppm (????_1/2 = 1250 Hz) and 6.4 ppm (????_1/2 = 5999 Hz), which were assigned to the Mo(V) and Mo(VI) sites, respectively. DFT geometries and ⁹⁵Mo DFT-GIAO chemical shifts for Mo₄(??³-O)₄(??²-O₂P(CH₃)₂)₄O₄ (3) and Mo₄(??³-O)₂(??²-O₂P(CH₃)₂)₆O₆ (4) are consistent with X-ray crystallography and ⁹⁵Mo NMR of 1 and 2. The open complex, Mo₄(??³-O)₂(??²-O₂P(CH₂C₆H₅)₂)₆O₆·2(CH₂Cl₂), exhibits a central Mo(V)?CMo(V) single bond at 2.6217(5) Å with each Mo(V) atom bonded to one oxo (trans-disposed) terminal ligand.     

Hydrodechlorination of Dichloromethane by a Metal-Free Triazole-Porphyrin Electrocatalyst: Demonstration of Main-Group Element Electrocatalysis**

In this work, the electrocatalytic reduction of dichloromethane (CH₂Cl₂) into hydrocarbons involving a main group element-based molecular triazole-porphyrin electrocatalyst H2PorT8 is reported. This catalyst converted CH₂Cl₂ in acetonitrile to various hydrocarbons (methane, ethane, and ethylene) with a Faradaic efficiency of 70 % and current density of −13 mA cm⁻² at a potential of −2.2 V vs. Fc/Fc⁺ using water as a proton source. The findings of this study and its mechanistic interpretations demonstrated that H2PorT8 was an efficient and stable catalyst for the hydrodechlorination of CH₂Cl₂ and that main group catalysts could be potentially used for exploring new catalytic reaction mechanisms.     

Methane Activation by Diatomic Molybdenum Carbide Cations

Metal carbide species have been proposed as a new type of chemical entity to activate methane in both gas‐phase and condensed‐phase studies. Herein, methane activation by the diatomic cation MoC⁺ is presented. MoC⁺ ions have been prepared and mass‐selected by a quadrupole mass filter and then allowed to interact with methane in a hexapole reaction cell. The reactant and product ions have been detected by a reflectron time‐of‐flight mass spectrometer. Bare metal Mo⁺ and MoC₂H₂⁺ ions have been observed as products, suggesting the occurrence of ethylene elimination and dehydrogenation reactions. The branching ratio of the C₂H₄ elimination channel is much larger than that of the dehydrogenation channel. Density functional theory calculations have been performed to explore in detail the mechanism of the reaction of MoC⁺ with CH₄. The computed results indicate that the ethylene elimination process involves the occurrence of spin conversions in the C?C coupling (doublet→quartet) and hydrogen atom transfer (quartet→sextet) steps. The carbon atom in MoC⁺ plays a key role in methane activation because it becomes sp³ hybridized in the initial stages of the ethylene elimination reaction, which leads to much lower energy barriers and more stable intermediates. This study provides insights into the C?H bond activation and C?C coupling involved in methane transformation over molybdenum carbide‐based catalysts.     

Kinetics of the reactions of CH3 with O(3P) and O2 at 295 K

The reactions of CH₃ radicals with O(³P) and O₂ have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. For the reaction between CH₃ and O, conditions were such that [O] » [CH₃] and the methyl radicals decayed under pseudo-first-order conditions giving a rate coefficient of (1.14 ± 0.29) × 10^?10 cm³/s. The reaction between CH₃ and O₂ was studied in separate experiments in which CH₃ decayed under pseudo-first-order conditions. In this case, the rate coefficient obtained increased with increasing concentration of the helium carrier gas. This was varied over the range of 2.5–25 × 10¹⁶ cm^?3, resulting in values for the apparent two-body rate coefficient ranging from 1 × 10^?14 to 5.2 × 10^?14 cm³/s. No evidence was found for the production of HCHO by a direct two-body process involving CH₃ + O₂, and an upper limit of 3 × 10^?16 cm³/s was placed on the rate coefficient for this reaction. The experimental results for the apparent two-body rate coefficient exhibit the curvature one would expect for an association reaction in the fall-off region. Calculations used to extrapolate these measurements to the low-pressure limit yield a value for k₀ of (3.4 ± 1.1) × 10^?31 cm⁶/s, which is more than a factor of 2 higher than previous estimates.     

The effect of active oxygen species in nano-ZnCr2O4 spinel oxides for methane catalytic combustion

The nano-ZnCr₂O₄ spinel oxides was synthesized by a ethylene glycol mediated solvothermal method. Catalytic combustion of methane test showed that an excellent activity over nano-ZnCr₂O₄ with T_10% = 300 °C and T_90% = 400 °C. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption-desorption measurements (BET) indicated that a uniform nano-ZnCr₂O₄ spinel oxides particles with the high surface area (96.2 m²g⁻¹) was successfully synthesized. Oxygen temperature programmed desorption (O₂-TPD) profile revealed there were two obvious desorption of oxygen species from nano-ZnCr₂O₄ in the range of 300–400 °C and 500–700 °C. It was clear that the desorption temperature range of the first oxygen species coincided with the methane catalytic combustion temperature. X-ray photoelectron spectroscopy (XPS) analysis exhibited that Cr⁶⁺ was present in the lattice of ZnCr₂O₄ apart from Cr³⁺. High valence cations of chromium in crystal lattice probable caused the presence of interstitial oxygen species in the structure to maintain the electroneutrality. Additionally, Raman spectra proved that there is the interstitial oxygen species in the crystal lattice of ZnCr₂O₄. Therefore, the excellent catalytic activity for methane combustion was contributed to the flexible interstitial oxygen in the ZnCr₂O₄.