Formic Acid Synthesis by CO2Hydrogenation over Single-Atom Catalysts Based on Ru and Cu Embedded in Graphene
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Â© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim At variance with conventional heterogeneous catalysts, where only a small number of transition or noble metal atoms at surfaces play the role of active sites, in the single-atom catalysts (SAC) each metal atom is involved in the catalytic process. Starting from isolated Ru and Cu atoms embedded on defects in graphene, denoted as Ru-dG and Cu-dG, we apply density functional theory (DFT) to examine utilizing these structures to catalyze the conversion of CO2into the formic acid (FA). Our atomistic modeling of this reaction, highly relevant for reducing the CO2level in the atmosphere, includes three different reaction pathways. The first relies on a direct hydrogenation of CO2with protons from the H2molecule. Due to energy barriers higher than 35 kcal/mol on both Ru-dG and Cu-dG, this reaction path does not represent a favorable route for FA synthesis. The other two reaction mechanisms start with the dissociative adsorption of H2and then proceed via completely different paths. At Ru-dG the CO2hydrogenation occurs with the H atoms from the dissociated H2, while the Cu-dG favors the proton transfer from an additional H2, coadsorbed with CO2on hydrogenated SAC. Since we find that these pathways were accompanied with the activation energies smaller than 20 kcal/mol, our DFT study indicates that the Ru adatoms embedded into the defected graphene are promising candidates for designing a SAC enabling an efficient conversion of CO2to FA. Since adsorbed H species markedly decrease Cu binding at the vacancy sites, the Cu-dG is considerably less robust catalyst than Ru-dG.
author list (cited authors)
SredojeviÄ‡, D. N., Å ljivanÄanin, Å. ½., Brothers, E. N., & BeliÄ‡, M. R.