Sunlight-assisted hydrogenation of CO 2 into ethanol and C2+ hydrocarbons by sodium-promoted Co@C nanocomposites

Abstract

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.

Hydrogenation of CO2 on Nickel–Iron Nanoparticles Under Sunlight Irradiation

“…Conversely, iron nanoparticles covered by carbon layers were designed for the transformation of CO2 into CO under similar conditions, also proving that the surface plasmon resonance effect promoted the photogeneration of charges to trigger the reaction [17]. This is consistent with recent results from our laboratories showing that carbon-coated cobalt nanoparticles can promote the hydrogenation of CO2 into hydrocarbons and oxygenates owing to a combination of thermal and photonic effects, as suggested by photo-action spectra, hole-trapping experiments and comparative reactions carried out at identical temperatures either in the dark or under irradiation [18]. Based on all the aforementioned investigations, it seems clear that nanoparticles of certain transition metals can catalyse COx hydrogenation reactions via photothermal activation, that is, local heating originated by light absorption [19][20][21]; notwithstanding this, photonic pathways cannot be ruled out for these solar-driven processes entailing materials with strong UV-vis absorption profiles, via either plasmon effects of metallic nanoparticles [17] or bandgap excitation of semiconductor oxides [15].…”

“…Furthermore, the pure nickel material absorbed light throughout the entire visible range, probably indicating the presence of metallic nickel nanoparticles. It should be pointed out that, although the CO2 hydrogenation activities are likely to be significantly ascribed to photothermal effects, the strong light absorption capabilities of the NiyFe1−yOx materials studied herein might also be partly responsible for the observed performance, as proven for carbon-coated cobalt [18] or iron [17] nanoparticles.…”

Coupling of Solar Energy and Thermal Energy for Carbon Dioxide Reduction: Status and Prospects

“…The research groups of García and Corma reported enhanced ethanol synthesis by coupling solar energy and thermal energy over a Na‐promoted Co@C nanocomposite . The Na‐Co@C catalyst was prepared by H 2 reduction of a Co‐Na‐EDTA precursor, which consisted of metallic Co in the core, CoO x , as well as a Na promoter on the Co surface under C layers (Figure a).…”

FeO–CeO2 nanocomposites: an efficient and highly selective catalyst system for photothermal CO2 reduction to CO

“…Subsequently, Zhang and coworkers reported photothermal CO 2 hydrogenation to C 2+ hydrocarbons using an alumina-supported Co-Fe alloy nanoparticle catalyst 30 . Similarly, Garcia's group demonstrated that Co@C nanocomposites showed excellent photothermal catalytic performance for CO 2 hydrogenation to C 2+ hydrocarbons 32 . However, the photothermal RWGS reaction has received minimal attention to date, justifying a detailed investigation.…”