Addressing Dynamics at Catalytic Heterogeneous Interfaces with DFT-MD: Anomalous Temperature Distributions from Commonly Used Thermostats.

Density functional theory-based molecular dynamics (DFT-MD) has been widely used for studying the chemistry of heterogeneous interfacial systems under operational conditions. We report frequently overlooked errors in thermostated or constant-temperature DFT-MD simulations applied to study (electro)catalytic chemistry. Our results demonstrate that commonly used thermostats such as Nosé-Hoover, Berendsen, and simple velocity-rescaling methods fail to provide a reliable temperature description for systems considered.

Dynamics of weak interactions in the ligand layer of -mercaptobenzoic acid protected gold nanoclusters Au(-MBA) and Au(-MBA).

Atomically precise metal nanoclusters, stabilized and functionalized by organic ligands, are emerging nanomaterials with potential applications in plasmonics, nano-electronics, bio-imaging, nanocatalysis, and as therapeutic agents or drug carriers in nanomedicine. The ligand layer has an important role in modifying the physico-chemical properties of the clusters and in defining the interactions between the clusters and the environment. While this role is well recognized from a great deal of experimental studies, there is very little theoretical information on dynamical processes within the layer itself.

Support work function as a descriptor and predictor for the charge and morphology of deposited Au nanoparticles.

We show, using density functional theory calculations, that the charge, magnetic moment, and morphology of deposited Au nanoclusters can be tuned widely by doping the oxide support with aliovalent cations and anions. As model systems, we have considered Au (n = 1, 2, or 20) deposited on doped MgO and MgO/Mo supports. The supports have been substitutionally doped with varying concentrations θ of F, Al, N, Na, or Li.

Towards Atomically Precise Supported Catalysts from Monolayer-Protected Clusters: The Critical Role of the Support.

Controlling the size and uniformity of metal clusters with atomic precision is essential for fine-tuning their catalytic properties, however for clusters deposited on supports, such control is challenging. Here, by combining X-ray absorption spectroscopy and density functional theory calculations, it is shown that supports play a crucial role in the evolution of monolayer-protected clusters into catalysts. Based on the acidic nature of the support, cluster-support interactions lead either to fragmentation of the cluster into isolated Au-ligand species or ligand-free metallic Au clusters.

Diffusion barriers, growth pathways, and scaling relations for small supported metal clusters.

Sintering is one of the main causes of degradation of nanocatalysts. With a view to studying the process of sintering, and its relative likelihood across elements, we have used ab initio density functional theory to compute the pathways and energy barriers E for the diffusion of small clusters Pt on MgO(001), n = 1-4. We compare with the corresponding results for Au, Ag, and Pd.

Atomically Precise, Thiolated Copper-Hydride Nanoclusters as Single-Site Hydrogenation Catalysts for Ketones in Mild Conditions.

Copper-hydrides are known catalysts for several technologically important reactions such as hydrogenation of CO, hydroamination of alkenes and alkynes, and chemoselective hydrogenation of unsaturated ketones to unsaturated alcohols. Stabilizing copper-based particles by ligand chemistry to nanometer scale is an appealing route to make active catalysts with optimized material economy; however, it has been long believed that the ligand-metal interface, particularly if sulfur-containing thiols are used as stabilizing agent, may poison the catalyst. We report here a discovery of an ambient-stable thiolate-protected copper-hydride nanocluster [CuH(SPhCl)] that readily catalyzes hydrogenation of ketones to alcohols in mild conditions.

Using first principles calculations to interpret XANES experiments: extracting the size-dependence of the (p , T) phase diagram of sub-nanometer Cu clusters in an O environment.

We have used ab initio density functional theory together with ab initio atomistic thermodynamics, and in situ x-ray absorption near edge spectroscopy (XANES) experiments, to study the oxidation of sub-nanometer clusters of Cu O supported on a hydroxylated amorphous alumina substrate in an O-rich environment. We obtain (p , T) phase diagrams: these differ notably for the nanoclusters compared to the bulk. Both the theory and experiment suggest that in the presence of oxygen, the cluster will oxidize from its elemental state to the oxidized state as the temperature decreases.

Inducing wetting morphologies and increased reactivities of small Au clusters on doped oxide supports.

Au nanoparticles are promising catalysts for industrially important reactions. Their catalytic activity is known to depend on their charge state and morphology. Using density functional theory calculations, we have studied how the induced charge and dimensionality of small Au clusters can be tuned by doping the oxide support that they are deposited on.

Substrate doping: A strategy for enhancing reactivity on gold nanocatalysts by tuning sp bands.

We suggest that the reactivity of Au nanocatalysts can be greatly increased by doping the oxide substrate on which they are placed with an electron donor. To demonstrate this, we perform density functional theory calculations on a model system consisting of a 20-atom gold cluster placed on a MgO substrate doped with Al atoms. We show that not only does such substrate doping switch the morphology of the nanoparticles from the three-dimensional tetrahedral form to the two-dimensional planar form, but it also significantly lowers the barrier for oxygen dissociation by an amount proportional to the dopant concentration.

Trends in the electronic structure of extended gold compounds: implications for use of gold in heterogeneous catalysis.

First-principles electronic structure calculations are presented on a variety of Au compounds and species--encompassing a wide range of formal oxidation states, coordination geometries, and chemical environments--in order to understand the potentially systematic behavior in the nature and energetics of d states that are implicated in catalytic activity. In particular, we monitor the position of the d-band center, which has been suggested to signal catalytic activity for reactions such as CO oxidation. We find a surprising absence of any kind of correlation between the formal oxidation state of Au and the position of the d-band center.

Tuning the morphology of gold clusters by substrate doping.

The morphology of small metal clusters can have a big impact on their electronic, magnetic, and chemical properties. This has been shown earlier, for example, for Au(20) clusters on MgO(001), where planar and tetrahedral geometries are possible for the gold atoms. While the planar geometry is more desirable for catalytic applications, it is disfavored in the usual situation.