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

Abstract

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 T10% = 300 °C and T90% = 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 m2 g−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.