CoCr2O4 nanospheres for low temperature methane oxidation†
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.