Exploration of the active phase of the hydrotalcite-derived cobalt catalyst for HCHO oxidation

Abstract A series of Co-based oxide catalysts were prepared by calcining hydrotalcite precursors in different atmospheres and studied for HCHO catalytic oxidation. The N 2 -calcined catalyst exhibits enhanced HCHO oxidation and superior stability. On the basis of H 2 -TPR, X-ray photoelectron spectroscopy, and Raman characterizations, this can be ascribed to better redox ability, octahedrally coordinated Co 2+ ions derived from the CoO phase, and other surface oxygen species, such as O 2 − or O − . The extra octahedrally coordinated Co 2+ ions may reside in a more open framework site than the inactive tetrahedrally coordinated Co 2+ ions. This species of Co 2+ can easily make contact with oxygen and oxidize. The surface oxygen species, along with the octahedrally coordinated Co 2+ ions, and a part of the Co 3+ species constitute the Co 2+ -oxygen species-Co 3+ sites, which enhance the catalytic activities. According to DRIFTS, Co 2+ -oxygen species-Co 3+ makes oxidation of HCHO and conversion of DOM to formate easier.