The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H(3)O(+)-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO(2)(110), where water dissociation is a key step in proton diffusion.

Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid-phase catalytic reactions (e.g., hydrogenation of biomass-derived furfural in alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid-phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X-ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ-Al2 O3 . Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under-coordinated copper atoms on the nanoparticle surface.

The drive to reduce consumption of fossil resources, coupled with expanding capacity for renewable electricity, invites the exploration of new routes to utilize this energy for the sustainable production of fuels, chemicals, and materials. Biomass represents a possible source of platform precursors for such commodities due to its inherent ability to fix CO 2 in the form of multi-carbon organic molecules. Electrochemical methods for the valorization of biomass are thus intriguing, but there is a need to objectively evaluate this field and define the opportunity space by identifying pathways suited to electrochemistry. In this contribution we offer a comprehensive, critical review of recent advances in lowtemperature (liquid phase), electrochemical reduction and oxidation of biomass-derived intermediates (polyols, furans, carboxylic acids, amino acids, and lignin), with emphasis on identifying the state-of-the-art for each documented reaction. Progress in computational modeling is also reviewed. We further suggest a number of possible reactions that have not yet been explored but which are expected to proceed based on established routes to transform specific functional groups. We conclude with a critical discussion of technological challenges for scale-up, fundamental research needs, process intensification opportunities (e.g., by pairing compatible oxidations and reductions), and new benchmarking standards that will be necessary to accelerate progress toward application in this still-nascent field.

Reaction pathways are explored for low temperature (e.g., 400 K) reduction of nitric oxide by hydrogen on Pt(111). First-principles electronic structure calculations based on periodic, self-consistent density functional theory (DFT-GGA, PW91) are employed to obtain thermodynamic and kinetic parameters for proposed reaction schemes on Pt(111). The surface of Pt(111) during NO reduction by H2 at low temperatures is predicted to operate at a high NO coverage, and this environment is explicitly taken into account in the DFT calculations. Maximum rate analyses are performed to assess the most likely reaction mechanisms leading to formation of N2O, the major product observed experimentally at low temperatures. The results of these analyses suggest that the reaction most likely proceeds via the addition of at least two H atoms to adsorbed NO, followed by cleavage of the N–O bond.

Ex situ catalytic fast pyrolysis (CFP) is a promising route for producing fungible biofuels; however, this process requires bifunctional catalysts that favor C−O bond cleavage, activate hydrogen at near atmospheric pressure and high temperature (350−500 °C), and are stable under highsteam, low hydrogen-to-carbon environments. Recently, early transition-metal carbides have been reported to selectively cleave C−O bonds of alcohols, aldehydes, and oxygenated aromatics, yet there is limited understanding of the metal carbide surface chemistry under reaction conditions and the identity of the active sites for deoxygenation. In this paper, we evaluated molybdenum carbide (Mo 2 C) for the deoxygenation of acetic acid, an abundant component of biomass pyrolysis vapors, under ex situ CFP conditions, and we probed the Mo 2 C surface chemistry, identity of the active sites, and deoxygenation pathways using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The Mo 2 C catalyst favored the production of acetaldehyde and ethylene from acetic acid over the temperature range of 250−400 °C, with decarbonylation pathways favored at temperatures greater than 400 °C. Little to no ethanol was observed due to the high activity of the carbide surface for alcohol dehydration. The Mo 2 C surface, which was at least partially oxidized following pretreatment and exposure to reaction conditions (possibly existing as an oxycarbide), possessed both metallic-like H-adsorption sites (i.e., exposed Mo and C) and Brønsted acidic surface hydroxyl sites, in a ratio of 1:8 metallic:acidic sites following pretreatment. The strength of the acidic sites was similar to that for H-Beta, H-Y, and H-X zeolites. Oxygen vacancy sites (exposed Mo sites) were also present under reaction conditions, inferred from DRIFTS results and calculated surface phase diagrams. It is proposed that C−O bond cleavage steps proceeded over the acidic sites or over the oxygen vacancy sites and that the deoxygenation rate may be limited by the availability of adsorbed hydrogen, due to the high surface coverage of oxygen under reaction conditions. Importantly, the reaction conditions (temperature and partial pressures of H 2 and H 2 O) had a strong effect on oxygen surface coverage, and accordingly, the relative concentrations of the different types of active sites, and could ultimately result in completely different reaction pathways under different reaction conditions.