MCr2O4 (M=Co, Cu, and Zn) nanospinels for 2-propanol combustion: Correlation of structural properties with catalytic performance and stability

The correlation between structure and activity of MCr2O4 nanospinels (M=Co, Cu, and Zn) synthesized by a sol-gel combustion method was investigated for the oxidation of 2-propanol. The catalysts were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), N2 adsorption/desorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Wide-angle XRD patterns show that the samples are pure spinel phases with cubic structure for CoCr2O4 and ZnCr2O4, and tetragonal structure for CuCr2O4. FTIR spectra confirmed the spinel structure of samples. The spinels were tested for total oxidation of 2-propanol as a model reaction for the catalytic combustion of oxygenated organic pollutants. ZnCr2O4 exhibited the highest activity and stability than the others toward the combustion of 2-propanol. The higher activity of ZnCr2O4 was ascribed to existence of excess surface oxygen on catalyst, active Cr3+-Cr6+ pair sites, and synergistic effect between ZnO and ZnCr2O4 confirmed by TPR and XPS techniques. The high stability of ZnCr2O4 and CuCr2O4 was explained by the existence of stable Cr6+ species on the surface of catalysts. The study showed that ZnCr2O4 could be used as a promising catalyst in the catalytic conversion of organic compounds.