Enhancing Selectivity Towards CO over Co/CeO₂ Catalyst for CO₂ Hydrogenation by Calcination

Seeking energy sources to supplant fossil fuel is a confronted task to mitigate atmospheric CO₂ concentration and suppress global warming problem. Electricity-based fuel (E-fuel), synthesized from green H₂ and CO₂, is one of solutions. Due to a thermodynamic unfavourability of C-C bond formation through direct CO₂ hydrogenation, synthetic fuels are usually generated by CO hydrogenation, i.e., Fischer Tropsch synthesis, which requires selective CO production by electro-catalytic CO₂ reduction or thermos-catalytic CO₂ hydrogenation. Here, we demonstrated a simple preparation method of Co/CeO₂ catalyst to increase the selectivity towards CO during CO₂ hydrogenation. Generally, Co-based catalysts of metallic Co nanoparticles with metal oxide support material are well-known for its selective production towards CH₄. However, we found that by using CeO₂ support calcined at an unusually high temperature, the CO selectivity significantly increased over Co/CeO₂ catalyst under atmospheric pressure at a wide range of reaction temperature. We investigated the microstructure of catalysts and identified the formation of reduced CeO_2-x surface layer in the CO-selective catalyst, corroborated by <i>in-situ </i>X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy with electron energy loss spectroscopy. Based on the catalyst structure, we suggested that CO-production is correlated to an enhanced reduction of CeO₂ support and the reduced CeO_2-x may be preserved during CO₂ hydrogenation without sacrificial oxidation instead of metallic Co due to a weak metal-support interaction. In addition, the CO-selectivity further enhanced upon the additional pretreatment over the reduced catalyst, which is attributed to the formation of carbon structures encapsulating the Co surface.