Hydrothermal Synthesis of Ruthenium Nanoparticles with a Metallic Core and a Ruthenium Carbide Shell for Low-Temperature Activation of CO2 to Methane

Abstract

[EN] 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 X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) analysis, and transmission electron microscopy (TEM) imaging. According to depth profile synchrotron XPS and X-ray diffraction (XRD) analysis, metallic ruthenium species predominate in the inner layers of the material, ruthenium carbide species being located on the upper surface layers. The ruthenium carbon catalysts presented herein are able to activate both CO2 and H-2, exhibiting exceptional high activity for CO2 hydrogenation at low temperatures (160-200 degrees C) with 100% selectivity to methane, surpassing by far the most active Ru catalysts reported up to now. On the basis of catalytic studies and isotopic (CO)-C-13/(CO2)-C-12/H-2 experiments, the active sites responsible for this unprecedented activity can be associated with surface ruthenium carbide (RuC) species, which enable CO2 activation and transformation to methane via a direct CO2 hydrogenation mechanism. Both the high activity and the absence of CO in the gas effluent confer relevance to these catalysts for the Sabatier reaction, a chemical process with renewed interest for storing surplus renewable energy in the form of methane.The research leading to these results has received funding from the Spanish Ministry of Science, Innovation and Universities through "Severo Ochoa" Excellence Programme (SEV-2016-0683) and the PGC2018-097277-B-100 (MCIU/AEI/FEDER, UE) project. The authors also thank the Microscopy Service of UPV for kind help with measurements. A G.O. thanks "Severo Ochoa" Programme (SEV-2016-0683) for a predoctoral fellowship. C.-H.C. acknowledges financial support from MOST project 107-2112-M-032-005. J.C. thanks the Spanish Government (MINECO) for a "Severo Ochoa" grant (BES-2015-075748). The authors are thankful for the support of the ALBA Synchrotron Light Source staff for the successful performance of the measurements at CIRCE beamline (BL24).Cored-Bandrés, J.; Garcia-Ortiz, A.; Iborra Chornet, S.; Climent Olmedo, MJ.; Liu, L.; Chuang, C.; Chan, T.... (2019). Hydrothermal Synthesis of Ruthenium Nanoparticles with a Metallic Core and a Ruthenium Carbide Shell for Low-Temperature Activation of CO2 to Methane. Journal of the American Chemical Society. 141(49):19304-19311. https://doi.org/10.1021/jacs.9b0708819304193111414