CoCr2O4 nanospheres for low temperature methane oxidation

Abstract

Spinel CoCr₂O₄ nanostructured catalysts were prepared by a facile solvothermal method using benzyl alcohol as both a structure-directing agent and a reagent. The growth mechanism of the CoCr₂O₄ nanospheres was studied by Fourier-transform infrared (FTIR) spectroscopy and powder X-ray diffraction (PXRD). The influence of solvothermal reaction time on the morphology, structure, and oxidation states of the products was investigated through scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). It was found that early in the reaction, the CoCr₂O₄ spheres are coated with parasitic Co₃O₄ nanoparticles that disappear after long reaction times to yield smooth CoCr₂O₄ particles. The catalytic performance of the noble metal-free nanospheres was optimized for oxidation of methane to CO₂ as evaluated at a high space velocity of 180 000 mL g⁻¹ h⁻¹, reaching 100% conversion below 500 °C. Importantly, samples prepared with 8 h solvothermal treatment exhibit excellent stability, maintaining 80% conversion in the presence of 10% H₂O and 5 ppm SO₂ after 10 cycles (∼170 h). The high stability gives these nanomaterials valuable potential for application in natural gas vehicles.