Green Methanation of CO Using New Co-Pt@Flg Nanocomposites

Methanations of CO and CO₂ are reactions of critical importance in the perspective of energy transition [1]. In addition to converting catalytic inhibitors into a useful resource during ammonia synthesis for example, the reaction of CO₂ and hydrogen to methane would provide a strategic way of storing excess electrical power from hydrogen fuel cells into a readily distributable chemical fuel (power to gas). The methanation technology could also potentially be applied to the effluent of the wide-spread cement industry and turn a highly debated greenhouse gas waste into synthetic natural gas on a large scale. Extensive research effort has been devoted to the design of suitable catalysts for this reaction. Typical catalysts involve metal nanoparticles associated with an oxide support. Current processes operate under high pressure, and temperatures above 300°C are required to achieve the targeted conversion levels. Recently, it was shown that reaction rates could be enhanced by using a Co-Pt bimetallic phase [2-4]. In these systems, the reaction was found to be limited by hydrogen spillover across the oxide support [4].

Here we will show that highly efficient Co-Pt-based nanocomposites may be straight-forwardly prepared in one pot by the sonication-assisted NaBH₄-reduction of cobalt nitrate and potassium tetrachloroplatinate in the presence of natural graphite (liquid phase process). The resulting Co-Pt@FLG (FLG=few layer graphene) show unprecedented methanation rates at atmospheric pressure and 320°C. The low temperature synthesis, the readily available metal precursors, the low Pt/Co ratios used (0.01-0.05), the short reaction times and the exfoliation of graphite in the course of metal nanoparticles formation make this process an economically interesting alternative to the high temperature, multi-step syntheses and oxide supports used in previous studies. We will present extensive pre- and post-tests characterization (including temperature programmed reduction and oxidation, thermogravimetric analysis, HRTEM and XRD) to discuss the unique role of the few layer graphene matrix in the methanation process, with regard to hydrogen spillover in particular.

[1] Rönsch, S.; Schneider, J.; Matthischke, S.; Schlüter, M.; Götz, M.; Lefebvre, J.; Prabhakaran, P.; Bajohr, S. Review on methanation – From fundamentals to current projects. Fuel, 2016, 166, 276.

[2] Beaumont, S. K.; Alayoglu, S.; Specht, C.; Michalak, W. D.; Pushkarev, V. V.; Guo, J.; Kruse, N.; Somorjai, G. A. Combining in Situ NEXAFS Spectroscopy and CO₂ Methanation Kinetics To Study Pt and Co Nanoparticle Catalysts Reveals Key Insights into the Role of Platinum in Promoted Cobalt Catalysis. J. Am. Chem. Soc., 2014, 136, 9898.

[3] Shin, H. H.; Lu, L.; Yang, Z.; Kiely, C. J.; McIntosh, S. Cobalt Catalysts Decorated with Platinum Atoms Supported on Barium Zirconate Provide Enhanced Activity and Selectivity for CO₂ Methanation. ACS Catal., 2016, 6, 2811.

[4] Beaumont, S. K.; Alayoglu, S.; Specht, C.; Kruse, N.; Somorjai, G. A. A Nanoscale Demonstration of Hydrogen Atom Spillover and Surface Diffusion Across Silica Using the Kinetics of CO₂ Methanation Catalyzed on Spatially Separate Pt and Co Nanoparticles. Nano Lett., 2014, 14, 4792.