Morphology-Dependent Catalysis by Co₃O₄ Nanostructures in Atmospheric Pressure Carbon Dioxide Hydrogenation

In this work, three Co 3 O 4 nanostructures with different morphologies (cubes, rods, and sheets) were synthesized using a hydrothermal method and tested for the CO 2 hydrogenation reaction. The physicochemical properties of the structured Co 3 O 4 were well characterized by X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), hydrogen temperature-programmed reduction (H 2 -TPR), and X-ray photoelectron spectroscopy (XPS) techniques. Based on the characterization, cube, rod, and sheet Co 3 O 4 nanostructures were found to expose the (100), (110), and (112) planes, respectively. The effect of cobalt oxide morphologies with different exposed surfaces on the activity and selectivity toward CO 2 hydrogenation reaction in a plug-flow reactor operated between 200 and 400 °C under atmospheric pressure conditions was explored. The results establish a correlation of the catalytic activity with morphological structures in the order rods > sheets > cubes. H 2 -TPR and XPS studies demonstrated that the high reducibility of Co 3 O 4 rod makes it an excellent catalyst for CO 2 hydrogenation.