A DRIFTS study of CO adsorption and hydrogenation on Cu-based core-shell nanoparticles

Core-shell nanoparticles are being considered for various applications due to their controllable atomic structure and improved properties compared to their bulk counterparts. In the present work, we have synthesized Cu@Mn ₃O ₄ and Cu@Co ₃O ₄ (core@shell) nanocatalysts using wet-chemical synthesis methods involving organic surfactants, and probed their surfaces using CO and H ₂ under reaction conditions using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The surfactant ligands used in the synthesis of the nanoparticles must be removed to allow access to the active catalyst sites. These ligands can be removed by oxidation, allowing adsorption of CO and H ₂. This work reports the DRIFTS results of CO adsorption and hydrogenation on Cu@Mn ₃O ₄ and Cu@Co ₃O ₄ nanoparticles after removing the ligands. The CO hydrogenation results were in agreement with the DRIFTS results, which suggested that the Cu@Co ₃O ₄ nanoparticles adsorb CO both dissociatively and associatively, creating a balance between molecular CO required for CO insertion and dissociated surface carbon species required for chain growth. This resulted in higher selectivities towards C ₂₊ alcohols on this catalyst. On the other hand, the Cu@Mn ₃O ₄ nanoparticles showed a higher CO uptake and a lower CO dissociation activity, which resulted in a lower CH _x concentration on the surface, thus limiting the rate of the CO insertion step required to form higher alcohols.