(182c) Synthesis of Accessible and Catalytically Active Sites on Sub-Nanometer Ru Nanoparticles for CO Oxidation and H2O2 decomposition Reactions

Ruthenium has demonstrated catalytic activity for a wide variety of reactions which include the reduction of C=C and C=O bonds, ammonia synthesis, and Fischer-Tropsch synthesis as several examples. In this work, bulky organic phosphine and thiol ligands are used to synthesize sub-nanometer Ru nanoparticles. The bulky ligands provide a steric barrier against nanoparticle aggregation and enable accessibility of reactants to the nanoparticle surface through inefficient packing on the Ru surface. The particle size distribution is measured by high-angle annular dark field scanning electron microscopy (HAADF-STEM), and the average diameter of the Ru nanoparticles is approximately 0.8 nm. All ligands used in the work give particles of approximately the same size. These are believed to be the smallest ligand-stabilized Ru nanoparticles synthesized in solution in the literature.

The Ru nanoparticles exhibit catalytic activity for CO oxidation and H₂O₂ decomposition with the ligands attached to the Ru surface. All the nanoparticles exhibit the same CO oxidation rates, and the identity of the functional group (thiol versus phosphine) bound to the Ru nanoparticle does not change the CO oxidation rate. However, in H₂O₂ decomposition, the identity of the ligand does play an important role in this reaction. It is observed that the hydrophobicity/hydrophilicity of the ligand has a significant impact on the H₂O₂ decomposition rate with a more hydrophobic ligand layer leading to reduced H₂O₂ decomposition rates. Controlling H₂O₂ decomposition rates is important in reactions which use H₂O₂ as a reactant because the catalysts for these reactions are also often active for H₂O₂ decomposition. Thus, it is demonstrated that bound organic ligands provide a promising approach to achieving control of H₂O₂ decomposition rates.