Size and structure effects on platinum nanocatalysts: theoretical insights from methanol dehydrogenation.

Methanol dehydrogenation on Pt nanoparticles was studied as a model reaction with the focus on size and structure effects employing the density functional theory approach. The effect of cluster morphology is manifested by the higher adsorption energy of COH intermediates on vertexes and edges of model nanoparticles compared to closely packed terraces. Moreover, due to the size effect, the adsorption sites of Pt nanoparticles (1.

Pd Single-Atom Sites on the Surface of PdAu Nanoparticles: A DFT-Based Topological Search for Suitable Compositions.

Structure of model bimetallic PdAu nanoparticles is analyzed aiming to find Pd:Au ratios optimal for existence of Pd1 single-atom surface sites inside outer Au atomic shell. The analysis is performed using density-functional theory (DFT) calculations and topological approach based on DFT-parameterized topological energy expression. The number of the surface Pd1 sites in the absence of adsorbates is calculated as a function of Pd concentration inside the particles.

Size dependence of the adsorption energy of CO on metal nanoparticles: a DFT search for the minimum value.

With a density functional theory method, we studied computationally the size dependence of adsorption properties of metal nanoparticles for CO as a probe on Pd(n) clusters with n = 13-116 atoms. For large particles, the values slowly decrease with cluster size from the asymptotic value for an (ideal) infinite surface. For clusters of 13-25 atoms, starting well above the asymptotic value, the adsorption energies drop quite steeply with increasing cluster size.

Stabilization of Au at edges of bimetallic PdAu nanocrystallites.

Density functional calculations were performed to study the distribution of Au atoms in bimetallic PdAu nanoparticles. A series of Pd(79-n)Au(n) clusters of truncated octahedral shape with different content of Au ranging from n = 1 to 60 was used to model such bimetallic nanosystems. Segregation of Au to the particle surface is found to be thermodynamically favorable.

Theoretical study of carbon species on Pd(111): competition between migration of C atoms to the subsurface interlayer and formation of Cn clusters on the surface.

Subsurface carbon species of Pd catalysts recently attracted considerable attention because they affect the selectivity of hydrogenation reactions. We calculated the migration of C atoms from the Pd(111) surface to interstitial subsurface sites to be energetically favorable. Yet, thermodynamically more stable is a graphene-like phase on the Pd surface.

How the C-O bond breaks during methanol decomposition on nanocrystallites of palladium catalysts.

Experimental findings imply that edge sites (and other defects) on Pd nanocrystallites exposing mainly (111) facets in supported model catalysts are crucial for catalyst modification via deposition of CH(x) (x = 0-3) byproducts of methanol decomposition. To explore this problem computationally, we applied our recently developed approach to model realistically metal catalyst particles as moderately large three-dimensional crystallites. We present here the first results of this advanced approach where we comprehensively quantify the reactivity of a metal catalyst in an important chemical process.

A computational study of H2 dissociation on silver surfaces: the effect of oxygen in the added row structure of Ag110.

We studied computationally the activation of H(2) on clean planar (111), (110) and stepped (221) as well as oxygen pre-covered silver surfaces using a density functional slab model approach. In line with previous data we determined clean silver to be inert towards H(2) dissociation, both thermodynamically and kinetically. The reaction is endothermic by approximately 40 kJ mol(-1) and exhibits high activation energies of approximately 125 kJ mol(-1).

C-O bond scission of methoxide on Pd nanoparticles: a density functional study.

C-O bond scission of methoxide species adsorbed at the surface of Pd nanoparticle was studied by DF calculations for the example of cuboctahedral Pd(79). To investigate different locations of adsorbed intermediates as well as the transition state of C-O bond scission, a substrate model was used, which allows one to consider adsorbates without any local geometry restrictions. In contrast to reaction sites on the flat Pd(111) surface and on extended facets, scission of the C-O bond of methoxide at cluster edges is exothermic by approximately 40 kJ mol(-1) and the decomposition product CH(3) is found to be stabilized there.

Adsorption of carbon on Pd clusters of nanometer size: a first-principles theoretical study.

Adsorbed atomic C species can be formed in the course of surface reactions and commonly decorate metal catalysts. We studied computationally C adsorption on Pd nanoclusters using an all-electron scalar relativistic density functional method. The metal particles under investigation, Pd(55), Pd(79), Pd(85), Pd(116), Pd(140), and Pd(146), were chosen as fragments of bulk Pd in the form of three-dimensional octahedral or cuboctahedral crystallites, exposing (111) and (100) facets as well as edge sites.