The hydrogenation of CO2 into hydrocarbons promoted by the action of sunlight has been studied on Co nanoparticles covered by thin carbon layers. In particular, nearly 100% selectivity to hydrocarbons is obtained with increased selectivity's towards C2+ hydrocarbons and alcohols (mainly ethanol) when using nanostructured materials comprising metallic cobalt nanoparticles, carbon layers, and sodium as promoter (Na-Co@C). In the contrary, larger amount of CH4 and lower selectivity to C2+ hydrocarbons and alcohols were obtained in the conventional thermal catalytic process. When using Co@C nanoparticles in the absence of Na or bare Co3O4 as catalyst, methane is essentially the main product (selectivity >96%). Control experiments in the presence of methanol as a hole scavenger suggest the role of light in generating charges by photon absorption via surface plasmon resonance as promoting factor. The reaction mechanism for photoassited CO2 hydrogenation on the Co-based catalysts were investigated by near ambient-pressure X-ray photoelectron (AP-XPS) and in situ Raman spectroscopies, which provided information on the role of light and Na promotor in the modulation of product distribution for CO2 hydrogenation. Spectroscopic studies suggested that surface CO2 dissociation to CO, the stabilization of CO adsorbed on the surface of Na-Co@C catalyst and the easy desorption of reaction products is a key step for photoassisted CO2 hydrogenation to ethanol and C2+ hydrocarbons.

Ruthenium nanoparticles with a core-shell structure formed by a core of metallic ruthenium and a shell of ruthenium carbide have been synthesized by a mild and easy hydrothermal treatment. The dual structure and composition of the nanoparticles have been determined by synchrotron XPS and NEXAFS analysis and TEM imaging. At increasing sample depth, metallic ruthenium species start to predominate, according to depth profile synchrotron XPS and XRD analysis. The herein ruthenium carbon catalyst is able to activate both CO2 and H2 showing exceptional high activity for CO2 hydrogenation at low temperatures (160-200 °C) with 100% selectivity to methane, surpassing by far the most active Ru catalysts reported up to now. Based on catalytic studies and isotopic 13 CO/ 12 CO2/H2 experiments, the active sites responsible for the unprecedented activity can be associated to those surface ruthenium carbide (RuC) species, enabling CO2 activation and transformation to methane via direct CO2 hydrogenation mechanism. The high activity and absence of CO in the gas effluent confers this catalyst interest for the Sabatier reaction, a reaction with renewed interest for storing surplus renewable energy in the form of methane.