Elucidating the Reactivity of Oxygenates on Single-Atom Alloy Catalysts

Doping isolated transition metal atoms into the surface of coinage-metal hosts to form single-atom alloys (SAAs) can significantly improve the catalytic activity and selectivity of their monometallic counterparts. These atomically dispersed dopant metals on the SAA surface act as highly active sites for various bond coupling and activation reactions. In this study, we investigate the catalytic properties of SAAs with different bimetallic combinations [Ni-, Pd-, Pt-, and Rh-doped Cu(111), Ag(111), and Au(111)] for chemistries involving oxygenates relevant to biomass reforming. Density functional theory is employed to calculate and compare the formation energies of species such as methoxy (CH3O), methanol (CH3OH), and hydroxymethyl (CH2OH), thereby understanding the stability of these adsorbates on SAAs. Activation energies and reaction energies of C–O coupling, C–H activation, and O–H activation on these oxygenates are then computed. Analysis of the data in terms of thermochemical linear scaling and Bro̷nsted–Evans–Polanyi relationship shows that some SAAs have the potential to combine weak binding with low activation energies, thereby exhibiting enhanced catalytic behavior over their monometallic counterparts for key elementary steps of oxygenate conversion. This work contributes to the discovery and development of SAA catalysts toward greener technologies, having potential applications in the transition from fossil to renewable fuels and chemicals

Structuration and Dynamics of Interfacial Liquid Water at Hydrated γ‑Alumina Determined by ab Initio Molecular Simulations: Implications for Nanoparticle Stability

Liquid water/solid interfaces are central in catalytic nanomaterials, from their preparation to their chemical stability under harsh catalytic conditions such as the hot aqueous medium used in biomass valorization. Here we report an ab initio molecular dynamics (AIMD) study of the γ-Al₂O₃ (110)/water interface using the most recent surface model available in the literature. The size of the simulation box and the duration of the AIMD simulation enables us to characterize the whole interface at the atomic scale. The simulation evidences a redistribution of protons within the chemisorbed water layer. The influence of γ-Al₂O₃ (110) is also important on the water molecules that are not bound to the surface: it is only above 10 Å that water recovers its bulk liquid behavior. The influence of alumina is structural, with preferred angular orientations for water molecules, and also dynamical. The translational self-diffusivity of water is diminished by up to 2 orders of magnitude, and the angular relaxation time increased up to a factor of 6. The influence of the interface on chemisorbed water molecules is also characterized with an infrared spectrum (fully simulated at the density functional theory level) that shows two distinct regions (3500 and 3200 cm^–1) assigned to two different interfacial environments. This full characterization of the nanoscale interfacial zone highlights the specific physicochemical features of water that arise in contact with γ-Al₂O₃ and opens the door to an improved preparation of supported catalysts (from templating agents to protective coatings)

Structuration and Dynamics of Interfacial Liquid Water at Hydrated γ‑Alumina Determined by ab Initio Molecular Simulations: Implications for Nanoparticle Stability

Liquid water/solid interfaces are central in catalytic nanomaterials, from their preparation to their chemical stability under harsh catalytic conditions such as the hot aqueous medium used in biomass valorization. Here we report an ab initio molecular dynamics (AIMD) study of the γ-Al₂O₃ (110)/water interface using the most recent surface model available in the literature. The size of the simulation box and the duration of the AIMD simulation enables us to characterize the whole interface at the atomic scale. The simulation evidences a redistribution of protons within the chemisorbed water layer. The influence of γ-Al₂O₃ (110) is also important on the water molecules that are not bound to the surface: it is only above 10 Å that water recovers its bulk liquid behavior. The influence of alumina is structural, with preferred angular orientations for water molecules, and also dynamical. The translational self-diffusivity of water is diminished by up to 2 orders of magnitude, and the angular relaxation time increased up to a factor of 6. The influence of the interface on chemisorbed water molecules is also characterized with an infrared spectrum (fully simulated at the density functional theory level) that shows two distinct regions (3500 and 3200 cm^–1) assigned to two different interfacial environments. This full characterization of the nanoscale interfacial zone highlights the specific physicochemical features of water that arise in contact with γ-Al₂O₃ and opens the door to an improved preparation of supported catalysts (from templating agents to protective coatings)

Elucidating the Stability and Reactivity of Surface Intermediates on Single-Atom Alloy Catalysts

Doping isolated single atoms of a platinum-group metal into the surface of a noble-metal host is sufficient to dramatically improve the activity of the unreactive host yet also facilitates the retention of the host’s high reaction selectivity in numerous catalytic reactions. The atomically dispersed highly active sites in these single-atom alloy (SAA) materials are capable of performing facile bond activations allowing for the uptake of species onto the surface and the subsequent spillover of adspecies onto the noble host material, where selective catalysis can be performed. For example, SAAs have been shown to activate C–H bonds at low temperatures without coke formation, as well as selectively hydrogenate unsaturated hydrocarbons with excellent activity. However, to date, only a small subset of SAAs has been synthesized experimentally and it is unclear which metallic combinations may best catalyze which chemical reactions. To shed light on this issue, we have performed a widespread screening study using density functional theory to elucidate the fundamental adsorptive and catalytic properties of 12 SAAs (Ni-, Pd-, Pt-, and Rh-doped Cu(111), Ag(111), and Au(111)). We considered the interaction of these SAAs with a variety of adsorbates often found in catalysis and computed reaction mechanisms for the activation of several catalytically relevant species (H₂, CH₄, NH₃, CH₃OH, and CO₂) by SAAs. Finally, we discuss the applicability of thermochemical linear scaling and the Brønsted–Evans–Polanyi relationship to SAA systems, demonstrating that SAAs combine weak binding with low activation energies to give enhanced catalytic behavior over their monometallic counterparts. This work will ultimately facilitate the discovery and development of SAAs, serving as a guide to experimentalists and theoreticians alike