Lattice-Matched Bimetallic CuPd-Graphene Nanocatalysts for Facile Conversion of Biomass-Derived Polyols to Chemicals

A bimetallic nanocatalyst with unique surface configuration displays extraordinary performance for converting biomass-derived polyols to chemicals, with potentially much broader applications in the design of novel catalysts for several reactions of industrial relevance. The synthesis of nanostructured metal catalysts containing a large population of active surface facets is critical to achieve high activity and selectivity in catalytic reactions. Here, we describe a new strategy for synthesizing copper-based nanocatalysts on reduced graphene oxide support in which the catalytically active {111} facet is achieved as the dominant surface by lattice-match engineering. This method yields highly active Cu-graphene catalysts (turnover frequency = 33–114 mol/g atom Cu/h) for converting biopolyols (glycerol, xylitol, and sorbitol) to value-added chemicals, such as lactic acid and other useful co-products consisting of diols and linear alcohols. Palladium incorporation in the Cu-graphene system in trace amounts results in a tandem synergistic system in which the hydrogen generated <i>in situ</i> from polyols is used for sequential hydrogenolysis of the feedstock itself. Furthermore, the Pd addition remarkably enhances the overall stability of the nanocatalysts. The insights gained from this synthetic methodology open new vistas for exploiting graphene-based supports to develop novel and improved metal-based catalysts for a variety of heterogeneous catalytic reactions

Pyrazinetetracarboxamide: A Duplex Ligand for Palladium(II)

Tetraethylpyrazine-2,3,5,6-tetracarboxamide forms a dipalladium­(II) complex with acetates occupying the fourth coordination sites of the two bound metal ions. Crystallographic results indicate that the “duplex” dipincer has captured two protons that serve as the counterions. The protons lie between adjacent amide carbonyl groups with very short O···O distances of 2.435(5) Å. In the free base, the adjacent carbonyl groups are farther apart, averaging 3.196(3) Å. While the dipalladium­(II) complexes stack in an ordered stepwise fashion along the <i>a</i> axis, the free base molecules stack on top of each other, with each pincer rotated by about 60° from the one below

Nanocarbon-Based Photovoltaics

Carbon materials are excellent candidates for photovoltaic solar cells: they are Earth-abundant, possess high optical absorption, and maintain superior thermal and photostability. Here we report on solar cells with active layers made solely of carbon nanomaterials that present the same advantages of conjugated polymer-based solar cells, namely, solution processable, potentially flexible, and chemically tunable, but with increased photostability and the possibility to revert photodegradation. The device active layer composition is optimized using <i>ab initio</i> density functional theory calculations to predict type-II band alignment and Schottky barrier formation. The best device fabricated is composed of PC₇₀BM fullerene, semiconducting single-walled carbon nanotubes, and reduced graphene oxide. This active-layer composition achieves a power conversion efficiency of 1.3%a record for solar cells based on carbon as the active materialand we calculate efficiency limits of up to 13% for the devices fabricated in this work, comparable to those predicted for polymer solar cells employing PCBM as the acceptor. There is great promise for improving carbon-based solar cells considering the novelty of this type of device, the high photostability, and the availability of a large number of carbon materials with yet untapped potential for photovoltaics. Our results indicate a new strategy for efficient carbon-based, solution-processable, thin film, photostable solar cells

Characterizing Hydrogen-Bond Interactions in Pyrazinetetracarboxamide Complexes: Insights from Experimental and Quantum Topological Analyses

Experimental and topological analyses of dipalladium­(II) complexes with pyrazinetetracarboxamide ligands containing tetraethyl (<b>1</b>), tetrahexyl (<b>2</b>), and tetrakis­(2-hydroxyethyl) ethyl ether (<b>3</b>) are described. The presence of two very short O---O distances between adjacent amide carbonyl groups in the pincer complexes revealed two protons, which necessitated two additional anions to satisfy charge requirements. The results of the crystal structures indicate carbonyl O---O separations approaching that of low barrier hydrogen bonds, ranging from 2.413(5) to 2.430(3) Å. Solution studies and quantum topological analyses, the latter including electron localization function, noncovalent interaction, and Bader’s quantum theory of atoms in molecules, were carried out to probe the nature of the short hydrogen bonds and the influence of the ligand environment on their strength. Findings indicated that the ligand field, and, in particular, the counterion at the fourth coordination site, may play a subtle role in determining the degree of covalent association of the bridging protons with one or the other carbonyl groups