Reactive Force Field Development for Propane Dehydrogenation on Platinum Surfaces.

Propane dehydrogenation (PDH) is an on-purpose catalytic technology to produce propylene from propane that operates at high temperatures, 773-973 K. Several key industry players have been active in developing new catalysts and processes with improved carbon footprint and economics, where Pt-based catalysts have played a central role. The optimization of these catalytic systems through computational and atomistic simulations requires large-scale models that account for their reactivity and dynamic properties.

Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations.

Fullerene dimerization inside a peapod is analyzed at DFT level by characterizing the stationary points and deriving the energy profile of the initial and reversible process named phase 1. We find that the barriers for the radical cation mechanism are significantly lower than those found for the neutral pathway. The peapod is mainly providing one-dimensional confinement for the reaction to take place in a more efficient way.

Bringing Selectivity in H/D Exchange Reactions Catalyzed by Metal Nanoparticles through Modulation of the Metal and the Ligand Shell.

Ru and Rh nanoparticles catalyze the selective H/D exchange in phosphines using D as the deuterium source. The position of the deuterium incorporation is determined by the structure of the P-based substrates, while activity depends on the nature of the metal, the properties of the stabilizing agents, and the type of the substituent on phosphorus. The appropriate catalyst can thus be selected either for the exclusive H/D exchange in aromatic rings or also for alkyl substituents.

Peptide Hydrolysis by Metal (Oxa)cyclen Complexes: Revisiting the Mechanism and Assessing Ligand Effects.

The mechanism responsible for peptide bond hydrolysis by Co(III) and Cu(II) complexes with (oxa)cyclen ligands has been revisited by means of computational tools. We propose that the mechanism starts by substrate coordination and an outer-sphere attack on the amide C atom of a solvent water molecule assisted by the metal hydroxo moiety as a general base, which occurs through six-membered ring transition states. This new mechanism represents a more likely scenario than the previously proposed mechanisms that involved an inner-sphere nucleophilic attack through more strained four-membered rings transition states.

A Bridging bis-Allyl Titanium Complex: Mechanistic Insights into the Electronic Structure and Reactivity.

Treatment of the dinuclear compound [{Ti(η-CMe)Cl}(μ-O)] with allylmagnesium chloride provides the formation of the allyltitanium(III) derivative [{Ti(η-CMe)(μ-CH)}(μ-O)] (), structurally identified by single-crystal X-ray analysis. Density functional theory (DFT) calculations confirm that the electronic structure of is a singlet state, and the molecular orbital analysis, along with the short Ti-Ti distance, reveal the presence of a metal-metal single bond between the two Ti(III) centers. Complex reacts rapidly with organic azides, RN (R = Ph, SiMe), to yield the allyl μ-imido derivatives [{Ti(η-CMe)(CHCH═CH)}(μ-NR)(μ-O)] [R = Ph(), SiMe()] along with molecular nitrogen release.

Charge polarization at a Au-TiC interface and the generation of highly active and selective catalysts for the low-temperature water-gas shift reaction.

Au atoms in contact with TiC(001) undergo significant charge polarization. Strong metal-support interactions make Au/TiC(001) an excellent catalyst for the low-temperature water-gas shift (WGS), with turnover frequencies orders of magnitude larger than those observed for conventional metal/oxide catalysts. DFT calculations indicate that the WGS reaction follows an associative mechanism with HOCO as a key intermediate.

O(2) adsorption and dissociation on neutral, positively and negatively charged Au(n) (n = 5-79) clusters.

The adsorption and dissociation of an O(2) molecule on gas-phase gold clusters of size varying from 5 to 79 atoms have been investigated by means of first principles density functional theory calculations. The adsorption energies and dissociation barriers have been determined for neutral, positively and negatively charged gold clusters in order to analyze in a systematic way the role of the charge on the cluster reactivity. While there is beneficial effect on O(2) activation of an extra electron on the small gold clusters (Au(5) and Au(13)), the effect is absent for positively charged clusters.

Critical size for O(2) dissociation by au nanoparticles.

Density functional theory calculations predict that the presence of low-coordination Au atoms is not enough to dissociate O(2), that there is a common pathway for O(2) dissociation on Au nanoparticles and that there is critical size for Au nanoparticles to dissociate O(2) (see figure).Density functional theory calculations carried out for a series of Au nanoparticles as well as for extended systems containing low-coordinated sites show that the presence of low-coordinate Au atoms is not enough to dissociate O(2). Strong adsorption of molecular oxygen on Au nanoparticles is a necessary but not sufficient condition for O(2) dissociation, there is a common pathway for O(2) dissociation on these nanoparticles and there is critical size for Au nanoparticles to dissociate O(2).

Adsorption properties and vibrational spectra of propyne adsorbed on Rh(111). Comparison with other (111) metal surfaces.

We have studied the adsorption properties of propyne on the Rh(111) surface by means of the generalized gradient approach of density functional theory using periodic slab models. The simulation of the vibrational spectra has permitted us to corroborate and complete the experimental band assignment and to confirm the adsorption site preference. Propyne prefers to sit on a 3-fold hollow site, with the C[triple bond]C axis parallel to a Rh-Rh bond and the molecular plane tilted away from the surface normal.

Selectivity control for the catalytic 1,3-butadiene hydrogenation on Pt(111) and Pd(111) surfaces: Radical versus closed-shell intermediates.

The hydrogenation of 1,3-butadiene to different C4H8 species on both Pd(111) and Pt(111) surfaces has been studied by means of periodic slabs and DFT. We report the adsorption structures for the various mono- and dihydrogenated butadiene intermediates adsorbed on both metal surfaces. Radical species are more clearly stabilized on Pt than on Pd.