Understanding Intermolecular Forces: DFT-SAPT studies on graphite-like acenes interacting with water

The interaction of water with graphene has been a quintessential example of hydrophobic interactions for many years. However, no reliable experimental or theoretical value exists for the water-graphene interaction energy. In the current document, the water-graphene interaction energy is explored using high-level ab initio methods. In addition, the water-graphene interaction energy is decomposed into its physical components in order to give further physical insight into the water-graphene interaction.Water is found in a variety of environments, ranging from small clusters to the bulk. Because of this, the development of accurate models capable of describing water in a wide range of environments has been an active area of research. In the second part of this document, the nature of the water--water interaction is explored and a new polarizable water model is presented

DFT Study of the Conversion of Furfuryl Alcohol to 2‑Methylfuran on RuO₂ (110)

Recently, our group proposed the catalytic transfer hydrogenation for refining biomass-derived 5-hydroxymethylfurfural and furfural to 2,5-dimethylfuran and 2-methylfuran, respectively. With a metallic Ru/C catalyst, a selectivity of ∼30% was achieved. The promotion of the Ru/C catalyst with the Lewis acid RuO_<i>x</i> resulted in a selectivity of ∼80%. In the current study, we employ density functional theory calculations on the RuO₂ (110) surface in order to elucidate the role of the Lewis acidity in the reduction of the biomass-derived furfuryl alcohol to 2-methylfuran. We identify the rate-limiting step to be the scission of the C–O bond of the side chain. In addition, we find evidence for the activation of the furan ring via an insertion of a hydrogen atom. However, the Lewis basicity of a neighboring bridging oxygen results in the furan ring being deactivated. Finally, the formation of water from the reduction process is facile. However, owing to the strong binding energy between the RuO₂ surface and the water molecule, poisoning of the catalytic surface by adsorbed water is possible. Finally, we show that the RuO₂ (110) carries out the reduction of furfural to furfuryl alcohol via the Meerwin–Ponndorf–Verley (MPV) reaction fairly easily, consistent with published experimental data

A second generation distributed point polarizable water model

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. © 2010 American Institute of Physics

Reaction Pathways and Intermediates in Selective Ring Opening of Biomass-Derived Heterocyclic Compounds by Iridium

While the catalytic hydrogenolysis of biomass-derived aromatic cyclic compounds to functionalized long chain alcohols and polyols has been known for decades, the factors that control the selectivity remain either unknown or controversial. Previous reports have hypothesized full ring saturation of the aromatic ring is necessary prior to hydrogenolysis. Contradictorily, recent studies have shown hydrogenolysis occurs prior to the saturation of the conjugated bonds. Furthermore, it has been assumed the functional groups present are fully reduced prior to hydrogenolysis; however, this has not been shown a priori. In order to resolve these controversies, we combine density functional theory and high-resolution electron energy loss spectroscopy (HREELS) to probe the catalytic hydrogenolysis of saturated and unsaturated heterocyclic molecules (furan, furfural, furfuryl alcohol, and tetrahydrofurfuryl alcohol) on iridium. Our results reveal that full saturation of the aromatic ring is not only unnecessary but leads to slower kinetics and differing selectivities. In contrast to previous studies, we show selective partial ring saturation can enhance the kinetics of the hydrogenolysis process. Reduction/oxidation of the functional group leads to a change in the electronegativity, resulting in a change in selectivity. These results provide important mechanistic insights allowing for further improvement of catalysts for the effective transformations of biomass-derived oxygenates to value-added products

Reaction Pathways and Intermediates in Selective Ring Opening of Biomass-Derived Heterocyclic Compounds by Iridium

While the catalytic hydrogenolysis of biomass-derived aromatic cyclic compounds to functionalized long chain alcohols and polyols has been known for decades, the factors that control the selectivity remain either unknown or controversial. Previous reports have hypothesized full ring saturation of the aromatic ring is necessary prior to hydrogenolysis. Contradictorily, recent studies have shown hydrogenolysis occurs prior to the saturation of the conjugated bonds. Furthermore, it has been assumed the functional groups present are fully reduced prior to hydrogenolysis; however, this has not been shown a priori. In order to resolve these controversies, we combine density functional theory and high-resolution electron energy loss spectroscopy (HREELS) to probe the catalytic hydrogenolysis of saturated and unsaturated heterocyclic molecules (furan, furfural, furfuryl alcohol, and tetrahydrofurfuryl alcohol) on iridium. Our results reveal that full saturation of the aromatic ring is not only unnecessary but leads to slower kinetics and differing selectivities. In contrast to previous studies, we show selective partial ring saturation can enhance the kinetics of the hydrogenolysis process. Reduction/oxidation of the functional group leads to a change in the electronegativity, resulting in a change in selectivity. These results provide important mechanistic insights allowing for further improvement of catalysts for the effective transformations of biomass-derived oxygenates to value-added products

Site-Dependent Lewis Acidity of γ‑Al₂O₃ and Its Impact on Ethanol Dehydration and Etherification

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 <i>s</i>-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 <i>s</i>-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 <i>s</i>-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 <i>s</i>-conduction band mean and the reaction barriers

Mechanistic Insights into Metal Lewis Acid-Mediated Catalytic Transfer Hydrogenation of Furfural to 2‑Methylfuran

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_<i>x</i>/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

Solventless C–C Coupling of Low Carbon Furanics to High Carbon Fuel Precursors Using an Improved Graphene Oxide Carbocatalyst

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