The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells.

Biomass conversion to fuels and chemicals provides sustainability, but the highly oxygenated nature of a large fraction of biomass-derived molecules requires removal of the excess oxygen and partial hydrogenation in the upgrade, typically met by hydrodeoxygenation processes. Catalytic transfer hydrogenation is a general approach in accomplishing this with renewable organic hydrogen donors, but mechanistic understanding is currently lacking. Here, we elucidate the molecular level reaction pathway of converting hemicellulose-derived furfural to 2-methylfuran on a bifunctional Ru/RuO x /C catalyst using isopropyl alcohol as the hydrogen donor via a combination of isotopic labeling and kinetic studies. Hydrogenation of the carbonyl group of furfural to furfuryl alcohol proceeds through a Lewis acid-mediated intermolecular hydride transfer and hydrogenolysis of furfuryl alcohol occurs mainly via ring-activation involving both metal and Lewis acid sites. Our results show that the bifunctional nature of the catalyst is critical in the efficient hydrodeoxygenation of furanics and provides insights toward the rational design of such catalysts.

In a previous study (J. Phys. Chem. C, 2009, 113, 10242-10248) we used density functional theory based symmetry-adapted perturbation theory (DFT-SAPT) calculations of water interacting with benzene (C(6)H(6)), coronene (C(24)H(12)), and circumcoronene (C(54)H(18)) to estimate the interaction energy between a water molecule and a graphene sheet. The present study extends this earlier work by use of a more realistic geometry with the water molecule oriented perpendicular to the acene with both hydrogen atoms pointing down. We also include results for an intermediate C(48)H(18) acene. Extrapolation of the water-acene results gives a value of -3.0 +/- 0.15 kcal mol(-1) for the binding of a water molecule to graphene. Several popular dispersion-corrected DFT methods are applied to the water-acene systems and the resulting interacting energies are compared to results of the DFT-SAPT calculations in order to assess their performance.

In the present study we revisit the problem of the interaction of a water molecule with a single graphite sheet. The density fitting-density functional theory-symmetry-adapted perturbation theory (DF-DFT-SAPT; J. Chem. Phys. 2005, 122, 014103) method is used to calculate the individual contributions arising from the interaction of a water molecule with various acenes, including benzene, coronene, and dodecabenzocoronene. These results are combined with calculations of the electrostatic interactions with water and a C 216 H 36 acene to extrapolate to the limit of an infinite graphite sheet, giving a interaction energy of -2.2 kcal/mol for the water-graphite system, with the assumed geometrical structure with one hydrogen atom pointed down toward the ring system. The structure with two hydrogens pointed down is predicted to be more stable, with a net interaction energy of -2.7 kcal/mol.

A distributed point polarizable model (DPP2) for water, with explicit terms for charge penetration, induction, and charge transfer, is introduced. The DPP2 model accurately describes the interaction energies in small and large water clusters and also gives an average internal energy per molecule and radial distribution functions of liquid water in good agreement with experiment. A key to the success of the model is its accurate description of the individual terms in the n-body expansion of the interaction energies.

Localized molecular orbital energy decomposition analysis and symmetry-adapted perturbation theory (SAPT) calculations are used to analyze the two- and three-body interaction energies of four low-energy isomers of (H(2)O)(6) in order to gain insight into the performance of several popular density functionals for describing the electrostatic, exchange-repulsion, induction, and short-range dispersion interactions between water molecules. The energy decomposition analyses indicate that all density functionals considered significantly overestimate the contributions of charge transfer to the interaction energies. Moreover, in contrast to some studies that state that density functional theory (DFT) does not include dispersion interactions, we adopt a broader definition and conclude that for (H(2)O)(6) the short-range dispersion interactions recovered in the DFT calculations account about 75% or more of the net (short-range plus long-range) dispersion energies obtained from the SAPT calculations.

We examine the heterogeneity of the Lewis acidity on the (100) and (110) facets of γ-Al2O3 by computing the binding energies of various oxygenates, in addition to the reaction barriers of dehydration and etherification reactions of ethanol. We show that the ethanol dehydration barrier is moderately affected by site heterogeneity (barriers between 1.2 and 1.6 eV); in contrast, a nearly 3-fold change in the ethanol etherification barrier is found among the various Al3+ sites. In order to rationalize these results, the s-conduction band mean of the Al3+ sites is introduced as a descriptor to characterize the ability to transfer electron charge from the adsorbate to the Lewis acid site. It is shown for the first time that this descriptor quantitatively correlates the oxygenate binding energies and the ethanol dehydration reaction barriers. However, for the ethanol etherification reactions the s-conduction band mean of the Al3+ sites describes barriers only qualitatively due to the bimolecular nature of this reaction, which results in a change in the nucleophilicity of the ethoxy species by a nearby adsorbed ethanol. As a result, the strength of the Lewis acid sites is not the only descriptor for etherification chemistry. Hydration of the (110) facet indicates an increase in Lewis acidity strength as described by the s-conduction band mean that results in stronger binding. However, this increase in Lewis acidity results in either a negligible change of the ethanol dehydration reaction barriers on some sites or an increase due to a reduction in the basicity of the adjacent oxygen by the dissociated water. Similarly, ethanol etherification is slowed down by the presence of water due primarily to the change in nucleophilicity of the ethoxy species. Overall, our results clearly indicate that while the binding energy is an excellent descriptor of Lewis acidity strength and dehydration chemistry on the clean alumina surfaces, cooperative phenomena (i.e., modulation of the nucleophilicity of the ethoxy by the nearby oxygen or water and the basicity of oxygen in the presence of water) are key issues that lead to a breakdown in the correlation between Lewis acid strength in terms of the binding energy or the s-conduction band mean and the reaction barriers.

Graphene oxide, decorated with surface oxygen functionalities, has emerged as an alternative to precious-metal catalysts for many reactions. Herein, we report that graphene oxide becomes superactive for C–C coupling upon incorporation of a highly oxidized surface associated with Brønsted acidic oxygen functionality and defect sites along the surface and edges. The resulting improved graphene oxide (IGO) demonstrates significantly higher activity over commonly used framework zeolites for the upgrade of low-carbon biomass furanics to high-carbon fuel precursors. A maximum 95% yield of C15 fuel precursor with high selectivity is obtained at low temperature (60 °C) and neat conditions via hydroxyalkylation/alkylation (HAA) of 2-methylfuran (2-MF) and furfural. Coupling of 2-MF with carbonyl compounds ranging from C3 to C6 produces precursors of carbon numbers 12 to 21 with a high yield. The catalyst regains nearly full activity upon regeneration. Extensive microscopic and spectroscopic characterization of the fresh and reused IGO carbocatalysts indicates that defects and the enhanced oxygen content are strongly correlated with the high activity of IGO. Density functional theory calculations reveal defects at carbonyl sites as suitable Brønsted acidic oxygen functional groups. A plausible reaction mechanism is also hypothesized.