Characterization and Stability of Metal Oxide Supported Cobalt Nanorod Catalysts for CO2 Hydrogenation

Converting carbon dioxide to useful chemicals, such as hydrocarbons, through hydrogenation processes has attracted great deal of interests recently amid the global rising of CO₂ levels. Cobalt nanorods are recently found by our group to have high activity to CO₂ hydrogenation and high selectivity towards hydrocarbons due to their preferentially exposed {110} facet on the surface. To translate these cobalt nanorods into a practical catalyst for industrial plants, we developed a method to preserve the surface faceting when supporting the nanorods with a metal oxide. Charged ligands were grafted onto the nanorods to enable the metal oxides to grow around the nanorods. Three different metal oxides – silica, alumina, and titania – were grafted as different supports onto cobalt nanorods. The mesoporous structure of the supports also allows for improved heat and mass transfer during hydrogenation. Using Induced Coupled Plasma (ICP), the synthesized catalysts were determined to be equal parts metal oxide support and cobalt oxide catalyst. The alumina and titania supported cobalt nanorods indicated improved activity toward hydrogenation over pure cobalt nanorods, and the silica supported nanorods exhibited the same catalytic performance. The enhancement of catalytic activity was further investigated with Temperature Programmed Reduction (TPR) experiments, which indicate that a strong interaction between cobalt nanorods and oxide support is the main cause of activity increase. The reactivity and selectivity toward hydrocarbon formation were not hindered by supporting the cobalt nanorods. Furthermore, the structures of the pure and supported catalysts were characterized before and after the reaction to determine stability and preservation of the {110} facet. From X-Ray Diffraction (XRD) analysis and Raman spectroscopy, the supported catalysts were determined to have the cobalt oxide spinel structure before and after the reaction. The Raman spectra also revealed there was coke formation during the reaction. From nitrogen adsorption/desorption data, the coking resulted in the surface area and the pore size of the unsupported and supported catalysts decreasing.