We report the results of nonrelativistic and relativistic gradient-corrected density functional calculations on interaction single transition metal atoms with oxygen sites regular MgO(001) surface. The surface has been represented by stoichiometric clusters ions embedded in large arrays point charges. Two adsorption have considered, on-top oxide anion bridge over two adjacent anions; is found to be energetically preferred. considered are Cr, Mo, W; Ni, Pd, Pt; Cu, Ag, Au. These adsorbates...

Adsorption of CO on nanosize Pd particles was studied theoretically by density functional method and spectroscopically means infrared reflection absorption spectroscopy (IRAS) sum frequency generation (SFG). A approach applied to three-dimensional crystallites about 140 atoms. The model clusters were chosen as octahedral fragments the face centered cubic (fcc) bulk, exhibiting (111) (001) facets. Bare adsorbate-decorated cluster models calculated with Oh symmetry constraints. Various types...

With a density functional theory method, we studied computationally the size dependence of adsorption properties metal nanoparticles for CO as probe on Pdn clusters with n = 13–116 atoms. For large particles, values slowly decrease cluster from asymptotic value an (ideal) infinite surface. 13–25 atoms, starting well above value, energies drop quite steeply increasing size. These opposite trends meet in intermediate range, 30–50 yielding lowest energies. computational results help to resolve...

Large octahedral and cuboctahedral palladium clusters, ranging from Pd55 to Pd146, have been investigated by means of all-electron relativistic density functional calculations. Adsorption CO molecules on the (111) facets these clusters was also studied. In particular, we focused interaction (a single molecule per facet) with threefold hollow sites inspect variation calculated adsorption parameters cluster size. We considered how observables for that position relate properties corresponding...

Pyrazole and pyridine adducts of methyltrioxorhenium(VII) form bisperoxo complexes with excess H2O2 (see picture). Density functional calculations reveal that the increased efficiency these as catalysts for olefin epoxidation originates from their stability moderate energies corresponding transition states. Nonaromatic nitrogen-base ligands reduce catalytic performance adducts, in agreement computational results.

Atomic H, C, N and O at the surface in subsurface region of Pd nanoparticles were studied theoretically using an all-electron scalar relativistic density functional approach. We modelled nanosize metal clusters by three-dimensional crystallites Pd79 Pd116 chosen as octahedral fragments bulk Pd; these expose (111) (001) facets. Adsorbed atoms located three-fold hollow sites centre Migration from cluster to (oss) site below was considered. C oss position found be almost isoenergetic; migration...

Interatomic distances in metal nanoparticles are reduced from their values the bulk. We studied computationally how this size-dependent geometry change (from bulk) relates to size-dependence of other properties large clusters, including reactivity. For purpose, using an all-electron scalar-relativistic density-functional approach, we calculated structures and binding energies for example CO adsorption on 3-fold hollow sites at center (111) facets cuboctahedral nanoscale clusters Pdn (n =...

We present calorimetric measurements of the effect cluster size on adsorption enthalpy carbon monoxide Pd nanoclusters sized from 120 to 4900 atoms per particle, which were grown in situ a well-ordered ${\text{Fe}}_{3}{\text{O}}_{4}/\text{Pt}(111)$ film. A substantial decrease initial heat amounting about $20--40\text{ }\text{kJ}\text{ }{\text{mol}}^{\ensuremath{-}1}$ was observed smallest nanoparticles as compared larger clusters and extended Pd(111) single-crystal surface. discuss this...

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 methanol decomposition. To explore this problem computationally, we applied our recently developed approach to realistically metal particles as moderately large three-dimensional crystallites. We present here the first results advanced where comprehensively quantify...

For bimetallic Pd–Au/HOPG model catalysts, reversible enrichment of the surface by Pd under CO oxidation conditions was found using a near-ambient pressure X-ray photoelectron spectroscopy technique. Density functional calculations combined with topological energy expression method were applied to reveal mechanism this phenomenon and quantify stability different arrangements metal atoms in PdAu nanoparticles presence adsorbate. According results computational approach, adsorption already at...

The epoxidation of olefins by peroxo complexes Cr(VI), Mo(VI) and W(VI) was investigated using the B3LYP hybrid density functional method. For mono- bisperoxo model with structures (NH(3))(L)M(O)(2)(-)(n)()(eta(2)-O(2))(1+)(n)() (n = 0, 1; L none, NH(3); M Cr, Mo, W) ethylene as olefin, two reaction mechanism were considered, direct oxygen transfer a two-step insertion into metal-peroxo bond. calculations reveal that attack nucleophilic olefin on an electrophilic center via transition state...

Density functional calculations were performed to study the distribution of Au atoms in bimetallic PdAu nanoparticles. A series Pd(79-n)Au(n) clusters truncated octahedral shape with different content ranging from n = 1 60 was used model such nanosystems. Segregation particle surface is found be thermodynamically favorable. The most stable sites for substitution are located at edges nanoclusters. stabilization rationalized by their higher flexibility relaxation which minimizes strain induced...

With density functional calculations, we studied the size dependence of adsorption properties metal nanoparticles (NPs) via example CO as a probe on Ptn clusters with n = 38–260 atoms. For largest NPs considered, calculated energies lie below corresponding value for (ideal) infinite surface Pt(111). 38–116 atoms, sharp increase energy decreasing cluster size. These opposite trends meet in an intermediate range, about 200 yielding lowest energies. computational results suggest that nanosized...

A density functional study on olefin epoxidation by rhenium and molybdenum peroxo complexes has been carried out. Various intermediates transition structures of the systems CH3ReO3/H2O2, H3NMoO3/H2O2, H3NOMoO3/H2O2 were characterized, including ligated unligated mono- bisperoxo as well hydroperoxo derivatives. For system complex CH3ReO(O2)2*H2O was found to be most stable one with lowest state for ethylene (activation barrier 16.2 kcal/mol), in line experimental findings. However,...

Ionic materials can be conveniently described by quantum mechanical cluster models. In these models the electrostatic field of crystal surrounding is often taken into account embedding in an array point charges (PCs). However, anions at boundary strongly polarized neighboring positive PCs. These artifacts significantly reduced if a model potential description employed for nearest-neighbor cations surrounding. We have implemented scheme total ion potentials (TIMP) density functional code...

Supported silver catalysts exhibit a remarkably high selectivity in the industrially important hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols. We carried out density functional calculations clarify factors that affect catalytic function hydrogenating aldehydes. examined activity and model for acrolein, simplest, yet most difficult aldehyde be selectively hydrogenated. focused on describing bulky catalyst particles, represented by sites extended surfaces, regular clean...

Epoxidation of olefins by TiIV peroxo and hydroperoxo (alkylperoxo) complexes was investigated using a hybrid DFT method (B3LYP). Reaction energies activation barriers for direct oxygen transfer to ethylene as model olefin were computed various compare the epoxidation activity Ti(η2-O2) TiOOR (R = H, CH3) moieties. The with Ti(O2) group is shown be essentially quenched when coordination sphere complex saturated strongly basic (σ-donor) ligands. In contrast, TiOOH functional depends only...

We studied computationally the activation of H2 on clean planar (111), (110) and stepped (221) as well oxygen pre-covered silver surfaces using a density functional slab model approach. In line with previous data we determined to be inert towards dissociation, both thermodynamically kinetically. The reaction is endothermic by ∼40 kJ mol−1 exhibits high energies ∼125 mol−1. However, surface, modeled reconstructed surface p(2 × 1)O/Ag(110) that –O–Ag–O– added rows, renders dissociation clearly...

Clean silver is known to be inert toward H2 dissociation. Nevertheless, catalysts recently have been found exhibit a noteworthy selectivity in the hydrogenation of unsaturated aldehydes alcohols. Experimental studies indicate that pretreatment oxygen atmosphere activates catalyst. To examine role activation catalysts, we carried out density functional study on periodic slab models dissociation at various species surfaces, including subsurface oxygen. According our calculations all forms...

Subsurface carbon species of Pd catalysts recently attracted considerable attention because they affect the selectivity hydrogenation reactions. We calculated migration C atoms from Pd(111) surface to interstitial subsurface sites be energetically favorable. Yet, thermodynamically more stable is a graphene-like phase on surface. Applying density functional method periodic models, we explored formation Cn (n = 2–4) clusters Pd(111). At low coverage, monomers and at octahedral were than dimer...