Correction: 2D oxides on metal materials: concepts, status, and perspectives.

Correction for '2D oxides on metal materials: concepts, status, and perspectives' by Giovanni Barcaro et al., Phys. Chem. Chem. Phys., 2019, 21, 11510–11536, DOI: 10.1039/C9CP00972H

Editorial: Nanocatalysis

Catalysis by metal and metal oxide nano-sized (and smaller, sub-nanometer) structures such as clusters and nanoparticles represents a consolidated field in chemistry. Shaping metals into the (sub)nano regime allows one to modulate both quantitatively (surface-to-volume ratio) and qualitatively (types of facets and surface atom coordination) the catalytically active regions with respect to extended systems. This increased freedom has been widely exploited in the past to improve/maximize the efficiency and selectivity of many catalytic processes of fundamental interest and industrial relevance. Major challenges however exist in the field, which are not yet fully addressed. The transition from carbon-based to green energy production, storage, and use and the environmental implications in fact requires the development of efficient and selective catalytic processes at lower temperature and less extreme conditions than those currently known e.g. in the conversion of petroleum and biomass, electrochemical and/or photochemical water splitting and fuel cells, CO_2 reduction to fuels, NH_3 synthesis etc

Optical absorption of (Ag-Au)133(SCH3)52 bimetallic monolayer-protected clusters

Abstract The evolution of the optical absorption spectrum of bimetallic Ag-Au monolayer-protected clusters (MPC) obtained by progressively doping Ag into the experimentally known structure of Au 133 (SR) 52 was predicted via rigorous time-dependent density-functional theory (TDDFT) calculations. In addition to monometallic Au 133 (SR) 52 and Ag 133 (SR) 52 species, 5 different (Ag-Au) 133 (SR) 52 homotops were considered with varying Ag content and site positioning, and their electronic structure and optical response were analyzed in terms of Projected Density Of States (PDOS), the induced or transition electron density, and Transition Component Maps (TCM) at selected excitation energies. It was found that Ag doping led to the effects rather different from those encountered in bare metal clusters. And it was also observed that Ag doping could produce structured spectral features, especially in the 3–4 eV range but also in the optical region if Ag atoms were located in the sub-staple region, as rationalized by the accompanying electronic analysis. Additionally, Au doping into the staples of Ag-rich MPC also gave rise to a more homogeneous induced electron density. These findings show the great sensitivity of the electronic response of MPC nanoalloy systems to the exact location of the alloying sites

Optical Activity of Metal Nanoclusters Deposited on Regular and Doped Oxide Supports from First-Principles Simulations

We report a computational study and analysis of the optical absorption processes of Ag20 and Au20 clusters deposited on the magnesium oxide (100) facet, both regular and including point defects. Ag20 and Au20 are taken as models of metal nanoparticles and their plasmonic response, MgO as a model of a simple oxide support. We consider oxide defects both on the oxygen anion framework (i.e., a neutral oxygen vacancy) and in the magnesium cation framework (i.e., replacing Mg++ with a transition metal: Cu++ or Co++). We relax the clusters’ geometries via Density-Functional Theory (DFT) and calculate the photo-absorption spectra via Time-Dependent DFT (TDDFT) simulations on the relaxed geometries. We find that the substrate/cluster interaction induces a broadening and a red-shift of the excited states of the clusters, phenomena that are enhanced by the presence of an oxygen vacancy and its localized excitations. The presence of a transition-metal dopant does not qualitatively affect the spectral profile. However, when it lies next to an oxygen vacancy for Ag20, it can strongly enhance th

Editorial: Nanocatalysis

Catalysis by metal and metal oxide nano-sized (and smaller, sub-nanometer) structures such as clusters and nanoparticles represents a consolidated field in chemistry. Shaping metals into the (sub)nano regime allows one to modulate both quantitatively (surface-to-volume ratio) and qualitatively (types of facets and surface atom coordination) the catalytically active regions with respect to extended systems. This increased freedom has been widely exploited in the past to improve/maximize the efficiency and selectivity of many catalytic processes of fundamental interest and industrial relevance. Major challenges however exist in the field, which are not yet fully addressed. The transition from carbon-based to green energy production, storage, and use and the environmental implications in fact requires the development of efficient and selective catalytic processes at lower temperature and less extreme conditions than those currently known e.g. in the conversion of petroleum and biomass, electrochemical and/or photochemical water splitting and fuel cells, CO_2 reduction to fuels, NH_3 synthesis etc

Structure and diffusion of small Ag and Au clusters on the regular MgO (100) surface

The lowest energy structures and the diffusion energy barriers of small MN (N = 1–4) Ag and Au clusters absorbed on the regular MgO (100) surface are investigated via density-functional (DF) calculations, using two different xc-functionals (PBE and LDA). In agreement with previous work, it is found that the lowest-energy structures of Ag and Au clusters in this size-range exhibit a strong 'metal-on-top' effect, by which the clusters are absorbed atop oxygen ions in a linear (dimer) or planar (trimer and tetramer) configuration perpendicular to the surface. The corresponding diffusion mechanisms range from monomer hopping, to dimer leapfrog (Ag2) or hopping (Au2), trimer walking, tetramer walking (Ag4) or rocking and rolling (Au4), exhibiting interesting differences between Ag and Au. An analysis of the corresponding energy barriers shows that trimers can diffuse at least as fast as monomers, while tetramers and (especially in the case of gold) dimers present somewhat higher barriers, but are anyway expected to be mobile on the surface at the temperatures of molecular beam epitaxy (MBE) experiments. The calculated PBE diffusion energy barriers compare reasonably well with the values extracted from the analysis of recent MBE experimental data, with the LDA predicting slightly higher barriers in the case of gold

Reaction intermediates during operando electrocatalysis identified from full solvent quantum mechanics molecular dynamics

Electrocatalysis provides a powerful means to selectively transform molecules, but a serious impediment in making rapid progress is the lack of a molecular-based understanding of the reactive mechanisms or intermediates at the electrode–electrolyte interface (EEI). Recent experimental techniques have been developed for operando identification of reaction intermediates using surface infrared (IR) and Raman spectroscopy. However, large noises in the experimental spectrum pose great challenges in resolving the atomistic structures of reactive intermediates. To provide an interpretation of these experimental studies and target for additional studies, we report the results from quantum mechanics molecular dynamics (QM-MD) with explicit consideration of solvent, electrode–electrolyte interface, and applied potential at 298 K, which conceptually resemble the operando experimental condition, leading to a prototype of operando QM-MD (o-QM-MD). With o-QM-MD, we characterize 22 possible reactive intermediates in carbon dioxide reduction reactions (CO_2 RRs). Furthermore, we report the vibrational density of states (v-DoSs) of these intermediates from two-phase thermodynamic (2PT) analysis. Accordingly, we identify important intermediates such as chemisorbed CO_2 (b-CO_2), *HOC-COH, *C-CH, and *C-COH in our o-QM-MD likely to explain the experimental spectrum. Indeed, we assign the experimental peak at 1,191 cm^(−1) to the mode of C-O stretch in *HOC-COH predicted at 1,189 cm^(−1) and the experimental peak at 1,584 cm^(−1) to the mode of C-C stretch in *C-COD predicted at 1,581 cm^(−1). Interestingly, we find that surface ketene (*C=C=O), arising from *HOC-COH dehydration, also shows signals at around 1,584 cm^(−1), which indicates a nonelectrochemical pathway of hydrocarbon formation at low overpotential and high pH conditions

Catalytic activity of Pt_(38) in the oxygen reduction reaction from first-principles simulations

The activity of truncated octahedral Pt_(38) clusters as a catalyst in the oxygen reduction reaction (ORR) is investigated via first-principles simulations. Three catalytic steps: O_2 dissociation (O_(2ads) → 2_O_(ads)), O hydration (O_(ads) + H_2O_(ads) → 2OH_(ads)), and H_2O formation (OH_(ads) + H_(ads) → H_2O_(ads)) are considered, in which all reactant species are co-adsorbed on the Pt_(38) cluster according to a Langmuir–Hinshelwood mechanism. The minimum structures and saddle points for these different steps are then calculated at the density-functional theory (DFT) level using a gradient-corrected exchange–correlation (xc-)functional and taking into account the effect of the solvent via a self-consistent continuum solvation model. Moreover, first-principles molecular dynamics (AIMD) simulations in which the H_2O solvent is explicitly described are performed to explore dynamic phenomena such as fast hydrogen transfer via meta-stable hydronium-type configurations and their possible role in ORR reaction paths. By comparing the present findings with previous results on the Pt(111) surface, it is shown that in such a nanometer-size cluster the rate-determining-step (rds) corresponds to H_2O formation, at variance with the extended surface in which O hydration was rate-determining, and that the overall reaction barrier is actually increased with respect to the extended system. This is in agreement with and rationalizes experimental results showing a decrease of ORR catalytic activity in the nanometer-size cluster range