Dynamics of weak interactions in the ligand layer of meta-mercaptobenzoic acid protected gold nanoclusters Au68(m-MBA)32 and Au144(m-MBA)40

2020

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. Here, we have performed extensive molecular dynamics simulations, with forces calculated…

Tailoring oxide properties: An impact on adsorption characteristics of molecules and metals

2014

Abstract Both density functional theory calculations and numerous experimental studies demonstrate a variety of unique features in metal supported oxide films and transition metal doped simple oxides, which are markedly different from their unmodified counterparts. This review highlights, from the computational perspective, recent literature on the properties of the above mentioned surfaces and how they adsorb and activate different species, support metal aggregates, and even catalyse reactions. The adsorption of Au atoms and clusters on metal-supported MgO films are reviewed together with the cluster׳s theoretically predicted ability to activate and dissociate O 2 at the Au–MgO(100)/Ag(100…

Chemoselective heterogeneous iridium catalyzed hydrogenation of cinnamalaniline

2020

International audience; Selective hydrogenation of unsaturated imines over heterogeneous catalysts is an ecologically feasible and effective way to produce commercially valuable saturated imines and unsaturated amines under mild conditions, avoiding the utilization of toxic halides. The liquid-phase hydrogenation of a model imine, cinnamalaniline, over Ir, Ru, Pd and Au catalysts was studied in polar protic (methanol, 2-propanol), polar aprotic (methyl tert-butyl ether) and non-polar aprotic (toluene) solvents at 40-80°C under atmospheric hydrogen pressure. Different metal oxides (Al 2 O 3 , ZrO 2 , SiO 2) and carbon composites based on carbon nitrides synthesized by pyrolysis of ethylenedi…

The redox chemistry of gold with high-valence doped calcium oxide.

2012

Gold assisted oxygen dissociation on a molybdenum-doped CaO(001) surface

2016

Using density functional theory (DFT) calculations, we address the adsorption of O2 and the coadsorption of gold species and oxygen molecules on a Mo-doped CaO(001) surface with 1.25% impurity concentration. With the help of the Born–Haber thermodynamic cycle, the enhanced binding of an oxygen molecule on Ca(Mo)O is attributed to energy gain owing to simultaneous electron transfer from the dopant to the molecule and lattice relaxations. We consider three coadsorption structures for an Au atom and O2 molecule with different Au–O2 distances. The calculations demonstrate that the coadsorption structures take one electron from the dopant and the O–Au–O chain structure is thermodynamically more …

The role of polaronic states in the enhancement of CO oxidation by single-atom Pt/CeO2

2023

Single Atom Catalysts (SACs) have shown that the miniaturization of the active site implies new phenomena like dynamic charge transfer between isolated metal atoms and the oxide. To obtain direct proof of this character is challenging, as many experimental techniques provide averaged properties or have limitations with poorly conductive materials, leaving kinetic measurements from catalytic testing as the only reliable reference. Here we present an integrated Density Functional Theory-Microkinetic model including ground and metastable states to address the reactivity of Pt1/CeO2 for CO oxidation. Our results agree with experimentally available kinetic data in the literature and show that CO…

Dissociative adsorption of water on Au/MgO/Ag(001) from first principles calculations

2015

Abstract The molecular and dissociative adsorption of water on a Ag-supported 1 ML, 2 ML and 3 ML-a six atomic layer-thick MgO films with a single Au adatom is investigated using density functional theory calculations. The obtained results are compared to a bulk MgO(001) surface with an Au atom. On thin films the negatively charged Au strengthens the binding of the polar water molecule due to the attractive Au–H interaction. The adsorption energy trends of OH and H with respect to the film thickness depend on an adsorption site. In the case OH or H binds atop Au on MgO/Ag(001), the adsorption becomes more exothermic with the increasing film thickness, while the reverse trend is seen when th…

Selective Acrolein Hydrogenation over Ligand-Protected Gold Clusters : A Venus Flytrap Mechanism

2022

The catalytic partial hydrogenation of α,β-unsaturated aldehydes is an ideal reaction to understand the selectivity between two different functional groups Here the two functional groups are C═C and C═O, and the hydrogenation of C═O is preferentially desired due to the importance of the issuing products, unsaturated alcohols, in fine-chemical industries. Using density functional theory calculations, we investigate the catalytic competency toward this reaction of a Au nanocluster in the presence of protecting ligands that offer higher stability and the possibility for the uniform distribution of size-selected clusters in the catalytic system. meta-Mercaptobenzoic-acid-protected-protected Au …

Computational study of linear carbon chains on gold and silver surfaces

2012

Abstract Density-functional-theory calculations were carried out for hydrogen capped linear carbon chains, polyynes and cumulenes, adsorbed dissociatively on the (1 1 1) and (2 1 1) surfaces of gold and silver. In the studied adsorption reactions, carbon–hydrogen bonds are broken and covalent carbon–metal bonds are created. The adsorption of cumulenes is highly endothermic, whereas the adsorption of polyynes is near thermoneutral. Also, the hydrogenation of adsorbed polyynyl radicals (·C n H) into adsorbed cumulene carbenes (:C n H 2 ) was investigated, which was found to be exothermic on both metals. Vibrational calculations were conducted on the adsorption systems, and the results were co…

Thiolate Adsorption on Au(hkl) and Equilibrium Shape of Large Thiolate-covered Gold Nanoparticles

2013

The adsorption of thiolates on Au surfaces employing density-functional-theory calculations has been studied. The dissociative chemisorption of dimethyl disulfide (CH3S−SCH3) on 14 different Au(hkl) is used as a model system. We discuss trends on adsorption energies, bond lengths, and bond angles as the surface structure changes, considering every possible Au(hkl) with h, k, l ≤ 3 plus the kinked Au(421). Methanethiolate (CH3S-) prefers adsorption on bridge sites on all surfaces considered; hollow and on top sites are highly unfavourable. The interface tensions for Au(hkl)-thiolate interfaces is determined at low coverage. Using the interface tensions in a Wulff construction method, we cons…

Unraveling the Role of the Rh–ZrO2 Interface in the Water–Gas-Shift Reaction via a First-Principles Microkinetic Study

2018

The industrially important water–gas-shift (WGS) reaction is a complex network of competing elementary reactions in which the catalyst is a multicomponent system consisting of distinct domains. Herein, we have combined density functional theory calculations with microkinetic modeling to explore the active phase, kinetics, and reaction mechanism of the WGS over the Rh–ZrO2 interface. We have explicitly considered the support and metal and their interface and find that the Rh–ZrO2 interface is far more active toward WGS than Rh(111) facets, which are susceptible to CO poisoning. CO2 forming on the zirconia support rapidly transforms into formate. These findings demonstrate the central role of…

Pd-catalyzed hydrodehalogenation of chlorinated olefins: Theoretical insights to the reaction mechanism

2012

Abstract Density functional theory calculations are applied to study energetics of trichloroethene (TCE) hydrodechlorination over pure Pd(1 1 1), chlorine-covered Pd(1 1 1), and Pd island supported by Au(1 1 1). Our results show that in all cases C Cl bond breakings take place more readily than C H bond formations and that TCE dechlorinates fully producing CCH precursors for the hydrogenations. The reaction pathway through radical-like species provides a possible explanation to the experimental product distributions that show a nominal amount of lesser chlorinated species in the presence of excess hydrogen. The surface chlorine resulted from the TCE decomposition weakens the binding of the …

Adsorption and Activation of Water on Cuboctahedral Rhodium and Platinum Nanoparticles

2017

Rh and Pt are widely used as the components in heterogeneous catalysts for multiple industrial applications. Because the metals are typically in the form of nanoparticles in real catalysts, it is important to carefully select models for the computational prediction of the catalytic properties. Here we report a first-principles study on the water activation, an important step in numerous catalytic reactions, using the finite-size Rh and Pt nanoparticle models and compare them to the extended surface models. We show that regardless of the model, adsorption and activation of water is practically identical for both metals, whereas the dissociation is energetically more favorable on Rh. The expe…

Isophorone on Au/MgO/Ag(001) : Physisorption with Electrostatic Site Selection

2017

We report a computational study of isophorone C9H14O adsorption on a Ag(001)-supported ultrathin MgO film with Au adatoms and clusters employing density functional theory calculations. The calculations show that the keto form of isophorone is more stable than the enol tautomers both in gas phase and on the MgO/Ag(001) surface. The interaction between the keto isophorone and step and terrace sites of MgO/Ag(001) displays long interaction distances, relatively weakly exothermic adsorption energies, lack of charge transfer, and minor changes in the density of states, all of which indicate that the molecule merely physisorbs on the surface. The step sites are energetically preferred adsorption …

DFT Prediction of Enhanced Reducibility of Monoclinic Zirconia upon Rhodium Deposition.

2018

Oxides are an important class of materials and are widely used, for example, as supports in heterogeneous catalysis. In a number of industrial catalytic processes, oxide supports actively participate in chemical transformations by releasing lattice oxygen anions. While this is intuitively understood for reducible oxides, the reducibility of irreducible oxides may be modified via nanoengineering or upon inclusion of foreign species. Our calculations predict that the ability of irreducible monoclinic zirconia to release oxygen improves substantially upon deposition of rhodium. Through a comprehensive screening of Rh/ZrO2 with different size of the rhodium species, we find that a Rh adatom and…

DFT Study on the Complex Reaction Networks in the Conversion of Ethylene to Ethylidyne on Flat and Stepped Pd

2009

Adsorption and conversion of ethylene to ethylidyne on flat (111) and stepped Pd surfaces have been studied with the aim to unravel the complex chemistry of small organic molecules on Pd. These pro...

Au Adsorption on Regular and Defected Thin MgO(100) Films Supported by Mo

2007

Using density functional theory we studied systematically a Au atom adsorption on a Mo-supported regular and defected ultrathin MgO film with 1 to 5 ML thickness. On Mo(100) grown regular MgO Au prefers to adsorb at a hollow site instead of an O site found for single-crystal MgO. The metal support also enhances Au adsorption energy in agreement with the earlier theoretical results. Adsorption energy decreases with increasing film thickness being, however, even in the case of 5 ML thick MgO much higher than that on single-crystal MgO. The Bader analysis was performed to estimate the spatial distribution of charge in different cases. The results show charge transfer (0.7−0.8 e) to the Au atom…

First-principles calculations of the initial incorporation of carbon into flat and stepped Pd surfaces

2010

We employ density-functional-theory calculations to examine carbon adsorption and diffusion in Pd bulk, and on Pd(111) and Pd(211) surfaces. Different possible subsurface and on-surface structures are explored and the most stable structures are analyzed. We calculate various diffusion paths: lateral diffusion on a surface, migration to a subsurface region, and within the first interlayer. Our calculations show in accordance with the earlier theoretical results that on Pd(111) carbon prefers to adsorb on octahedral interstitial sites. On Pd(211) the fourfold hollow site under the step is energetically the most favorable one and the second best sites are the octahedral sites. The calculations…

Charging of atoms, clusters, and molecules on metal-supported oxides: A general and long-ranged phenomenon

2008

The density-functional theory is used to investigate the adsorption of Au atoms, Au clusters, and NO2 molecules on transition-metal-supported oxides. As compared to unsupported oxides, the adsorbates on supported oxide films are charged and experience a higher adsorption energy. The origin of the effect is explored by considering two different oxides (MgO and Al2O3) and a range of supporting metals. Moreover, the limits of the enhancement are probed by explicit calculations for thick MgO films and low coverage. The long-range character of the phenomenon is attributed to electrostatic polarization. The absolute strength depends on several contributions and their relative importance changes w…

Adsorbate-Induced Oxygen Vacancy Mobility in Ultrathin Oxide Films

2013

Oxides at the nanometric scale show a behavior markedly different from that of their bulk counterparts. Ultrathin oxides grown on metals do not reach the full insulator regime, and they cannot decouple the electronic clouds of incoming adsorbates from that of the metal substrate. Although oxygen vacancies control the chemical and physical properties of ultrathin oxide films, the role of intrinsic defects has been overlooked so far. By means of density functional theory methods, we show that the addition of atoms with high electron affinity, such as Au, to ultrathin MgO grown either on a Ag or Mo support, completely reverses the preferential positions of oxygen vacancies, decreases their res…

Structure and dynamics of CaO films: A computational study of an effect of external static electric field

2017

Oxide films play a significant role in a wide range of industrial fields, mostly due to the thickness-dependent variation of their properties. Recently, it has been proposed based on the experimental study that carrier transport in CaO films proceeds via strong phonon excitations with a variable signal depending on the film thickness. In this paper, we report a detailed investigation in the frame of the density functional theory of structural and electronic properties of freestanding and Mo(100)-supported CaO films, as well as phonons therein, as functions of the film thickness and intensity of the external static electric field. Our calculations demonstrate that phonon frequencies negligib…

Formation of Gold(I) Edge Oxide at Flat Gold Nanoclusters on an Ultrathin MgO Film under Ambient Conditions

2010

Many active gold catalysts are prepared onreducible oxides, and strong interactions between the supportand the gold particle may create active sites at the peripheryclose to the particle–support interface. These interactionsmay also include charge transfer to or from the particle. Forpurely geometric reasons, small particles have a high propor-tion of low-coordinated edge and corner atoms that might actas reaction centers. Also, thermal effects from localized softphonon modes at particle edges may contribute to thelowering of critical reaction barriers.Lately, a large amount of work has been conducted toelucidate the properties of gold clusters on ultrathin (a fewmonolayers (ML) thick) MgO …

Electronic and vibrational properties of meso-tetraphenylporphyrin on silver substrates.

2014

The electronic and vibrational properties of meso-tetraphenylporphyrin (mtpp) on silver substrates are investigated using UV–vis and surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Whereas the vibrational signatures associated with the tetrapyrrole backbone exhibit minor variations throughout sequences of consecutively recorded SERRS spectra, the C═C stretching vibrational modes localized on the meso-phenyl moieties of mtpp exhibit noticeable intensity fluctuations, masked in the average SERRS response. We attribute the observed vibrational-state-specific blinking events to conformational changes in mtpp, namely, torsional flexibility which mediates the coupling between th…

Racemization of Secondary-Amine-Containing Natural Products Using Heterogeneous Metal Catalysts

2018

Review: monoclinic zirconia, its surface sites and their interaction with carbon monoxide

2015

This review concerns monoclinic zirconia, its surface sites and their probing with carbon monoxide. The surface sites and their modifications using thermal treatments with vacuum or reactive gases are also included. In this work, we present information on the nature and manipulation of hydroxyl species and their quantities on the surface, the different types of cationic sites where CO is adsorbed linearly and their energetics, as well as the surface sites and dynamics of formate formation. We also compare the surface concentrations of the different surface species to better understand the extent and nature of the interactions. Finally, we discuss some of the remaining open questions and how…

Coadsorption of NRR and HER Intermediates Determines the Performance of Ru-N4 toward Electrocatalytic N2 Reduction

2021

Efficiency of the electrochemical N2 reduction reaction (NRR) to ammonia is seriously limited by the competing hydrogen evolution reaction (HER) but our current atomic-scale insight on the factors controlling HER/NRR competition are unknown. Herein we unveil the elementary mechanism, thermodynamics, and kinetics determining the HER/NRR selectivity on the state-of-the-art NRR electrocatalyst, Ru-N4 using constant potential density functional theory calculations (DFT). The calculations show that NRR and HER intermediates coadsorb on the catalyst where HER is greatly suppressed by the NRR intermediates. The first reaction step leading to either *NNH or *H determines the selectivity towards NRR…

A Density Functional Theory study on gold cyanide interactions: The fundamentals of ore cleaning

2010

We have employed Density Functional Theory calculations to study the adsorption of CN, CN− and KCN on Au(111) and Au(211) surfaces and compare the obtained results to CO. The adsorption of CN, CN−, and KCN are exothermic with respect to the gas-phase moieties, and the adsorption energy increases at steps. Our results show that the binding mechanism of CN− is different from that of CO. The projected LDOS indicates that the bond between the flat surface and CN shows very small overlap between metal and CN states. This overlap increases provided that extra charge is present or low-coordinated Au atoms are available. Charge transfer is analyzed via the Bader method and the Electron Localization…

Carbon Dioxide Activation and Reaction Induced by Electron Transfer at an Oxide-Metal Interface

2015

A model system has been created to shuttle electrons through a metal-insulator-metal (MIM) structure to induce the formation of a CO2 anion radical from adsorbed gas-phase carbon dioxide that subsequently reacts to form an oxalate species. The process is completely reversible, and thus allows the elementary steps involved to be studied at the atomic level. The oxalate species at the MIM interface have been identified locally by scanning tunneling microscopy, chemically by IR spectroscopy, and their formation verified by density functional calculations.

Reducing the irreducible: Dispersed metal atoms facilitate reduction of irreducible oxides.

2021

Oxide reducibility is a central concept quantifying the role of the support in catalysis. While reducible oxides are often considered catalytically active, irreducible oxides are seen as inert supports. Enhancing the reducibility of irreducible oxides has, however, emerged as an effective way to increase their catalytic activity while retaining their inherent thermal stability. In this work, we focus on the prospect of using single metal atoms to increase the reducibility of a prototypical irreducible oxide, zirconia. Based on extensive self-consistent DFT+U calculations, we demonstrate that single metal atoms significantly improve and tune the surface reducibility of zirconia. Detailed ana…

Intrinsic Metal Size Effect on Adsorption of Organic Molecules on Platinum

2008

Di-σ adsorbed ethene, bridge(30) adsorbed benzene (with four di-σ-type and two π-type interactions), and η1 and η2 adsorbed acetone on nanosized platinum clusters consisting of 19 to 38 Pt atoms were studied theoretically by density functional theory (DFT) calculations with general gradient approximation (GGA) utilizing plane wave and local basis sets. The cluster results were compared to plane wave calculations employed with periodic boundary conditions. It was found that the geometries obtained with different methods are very similar but the adsorption energy depends prominently on the cluster size. Adsorption was strongest on the 22- and 26-atom clusters and weakest on the 35- and 38-ato…

Water and carbon oxides on monoclinic zirconia: experimental and computational insights

2014

Zirconium oxide (ZrO2, zirconia) is an interesting catalytic material to be used in biomass conversion, e.g., gasification and reforming. In this work, we show that reducing and hydrating pretreatments affect the surface sites on monoclinic zirconia. The multitechnique approach comprises temperature-programmed surface reactions (TPSR) under CO and CO2 at 100-550 °C, in situ DRIFTS investigations of the surface species and density functional theory (DFT) calculations. The key findings of the work are: (1) formates are formed either directly from gas-phase CO on terminal surface hydroxyls or via the linear CO surface species that are found exclusively on the reduced zirconia without water tre…

Kinetic Modeling of Ethyl Benzoylformate Enantioselective Hydrogenation over Pt/Al2O3

2014

A kinetic model was developed for the enantioselective hydrogenation of ethyl benzoylformate (EBF) on a modified Pt/Al2O3 catalyst. This model was based on the assumption of different numbers of si...

Ammonia Synthesis: State of the Bellwether Reaction

2013

Catalytic ammonia synthesis has been judged to be one of mankind's greatest scientific achievements during the twentieth century. The socioeconomic implications of producing ammonia industrially have been a strong driving force, and this development has spurred a range of new discoveries within physics, chemistry, and chemical engineering. In this chapter, we describe how it has been possible in recent years to provide a full understanding of the catalytic ammonia synthesis reaction at the atomic level through the combined use of experiments and quantum mechanical electronic structure calculations, thus clearly showing many of the reasons why ammonia synthesis has been, and still is, the be…

Adsorption and activation of O2 at Au chains on MgO/Mo thin films

2010

We have investigated the adsorption of O(2) on Au(n) clusters (n = 1-6) supported by an ultra thin (3ML)MgO(001) film on Mo metal via density functional theory calculations. On thin films, these small clusters have chain like structures and their electronic states resemble 1D quantum well states. The Au(1-3) are charged by one electron whereas the larger Au(4-6) get two electrons from the substrate. This is confirmed both by the symmetries of the HOMO and LUMO states of the clusters and the Bader charge analysis. In contrast to the O(2) adsorption on gas-phase clusters, the adsorption energy of O(2) molecule does not show pronounced oscillations as a function of cluster size. The O(2) is ac…

Cover Feature: Towards Atomically Precise Supported Catalysts from Monolayer‐Protected Clusters: The Critical Role of the Support (Chem. Eur. J. 31/2…

2020

Pd/C-Catalyzed Hydrosilylation of Enals and Enones with Triethylsilane: Conformer Populations Control the Stereoselectivity

2016

The palladium-on-charcoal-catalyzed chemo-, regio-, and stereoselective 1,4-hydrosilylation and transfer hydrogenation reactions of α,β-unsaturated aldehydes and ketones with triethylsilane have been investigated with a combination of experimental and theoretical methods. The reaction mechanism has been studied experimentally by monitoring the reactions by 1H NMR from aliquots withdrawn from the stirred reaction mixtures, labeling experiments, and control experiments. Our density functional theory results indicate that both aforementioned reactions are initiated with a dissociative adsorption of the triethylsilane on the palladium catalyst. In the hydrosilylation reaction, the α,β-unsaturat…

Escaping scaling relationships for water dissociation at interfacial sites of zirconia-supported Rh and Pt clusters

2019

<p>Water dissociation is an important reaction involved in many industrial processes and a good model reaction for probing the activity of catalytic sites. In this computational study, the dissociation of water at interfacial sites of globally optimized ZrO2 sup- ported Pt and Rh clusters is investigated under the framework of density functional theory. Our findings demonstrate that the perimeter sites of these small clusters can activate water, but the dissociation behavior varies considerably between sites. It is shown that the studied clusters break scaling relationships for water dissociation, suggesting these catalysts may achieve activities beyond the maximum imposed by such rel…

Computational Screening of Doped Graphene Electrodes for Alkaline CO2 Reduction

2020

The electrocatalytic CO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR) is considered as one of the most promising approaches to synthesizing carbonaceous fuels and chemicals without utilizing fossil resources. However, current technologies are still in the early phase focusing primarily on identifying optimal electrode materials and reaction conditions. Doped graphene-based materials are among the best CO<sub>2</sub>RR electrocatalysts and in the present work we have performed a computational screening study to identify suitable graphene catalysts for CO<sub>2</sub>RR to CO under alkaline conditions. Several types of modified-graphene frame…

Mechanism of Trichloroethene Hydrodehalogenation: A First-Principles Kinetic Monte Carlo Study

2014

A hydrodehalogenation (HDC) reaction of trichloroethene (TCE) has gained a lot of interest due to its possible application in water purification, but the reaction mechanism has been subject to much controversy. In this work, HDC of TCE on Pd(111) was examined by carrying out kinetic Monte Carlo simulations based on DFT-calculated thermodynamic and kinetic parameters. Obtained kMC results show that the HDC follows a so-called direct pathway, which means that, after adsorption on a catalyst, TCE quickly dechlorinates, producing CH–C and then, more slowly, hydrogenates to form hydrocarbon products. This is reflected in the surface coverage snapshots, where intermediates corresponding to the di…

Gold/Isophorone Interaction Driven by Keto/Enol Tautomerization

2016

The binding behavior of isophorone (C9H14O) to Au adatoms and clusters deposited on MgO/Ag(001) thin films is investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). The STM data reveal the formation of various metal/organic complexes, ranging from Au1/isophorone pairs to larger Au aggregates with molecules bound to their perimeter. DFT calculations find the energetically preferred keto-isophorone to be unreactive toward gold, while the enol-tautomer readily binds to Au monomers and clusters. The interaction is governed by electrostatic forces between the hydroxyl group of the enol and negative excess charges residing on the ad-gold. The activation barrier b…

Globally Optimized Equilibrium Shapes of Zirconia-Supported Rh and Pt Nanoclusters: Insights into Site Assembly and Reactivity

2019

Metal–support interfaces form an active site for many important catalytic reactions. The modeling of these interfacial sites calls for approximations to set up a structure model, which in turn may ...

ZrO2 Acting as a Redox Catalyst

2016

Surface defects are discussed and reviewed with regards to the use of ZrO2 in applications involving interactions with CO, H2, CH4, CO2, water and hydrocarbons. Studies of catalytic partial oxidation of methane reveal that part of the surface lattice oxygen in terraces can be removed by methane at high temperatures (e.g. 900 °C). The reaction proceeds via a surface confined redox mechanism. The studies presented here also highlight that defects play a decisive role in the water–gas-shift reaction, since the reaction is likely carried out via OH groups present at defect sites, which are regenerated by dissociating water. Hydroxyl chemistry on ZrO2 is briefly reviewed related to the studies p…

Computational Criteria for Hydrogen Evolution Activity on Ligand-Protected Au25-Based Nanoclusters

2023

The hydrogen evolution reaction (HER) is a critical reaction in addressing climate change; however, it requires catalysts to be generated on an industrial scale. Nanomaterials offer several advantages over conventional HER catalysts, including the possibility of atomic precision in tailoring the intrinsic activity. Ligand-protected metal clusters, such as the thiolate-protected MAu24(SR)18 (where M is Au, Cu, Pd), are of particular interest as not only are they electrocatalytically active toward HER, but the charge state and composition can be precisely tuned. Here, we present a comprehensive computational study examining how the charge state and dopants affect the catalytic activity of [MA…

Adsorption of small Au clusters on MgO and MgO/Mo: the role of oxygen vacancies and the Mo-support

2007

We report a systematic density functional theory investigation of adsorption of small Aun (n = 1-6) clusters on ideal and defected MgO(100) single crystal surfaces and Mo(100) supported thin MgO(100) films. As a model defect, we consider a neutral surface oxygen vacancy (Fs). Optimal adsorption geometries and energies, cluster formation energies and cluster charges are discussed and compared in detail over four different substrates. For a given cluster size, the adsorption energy among these substrates increases in the order MgO, Fs/MgO, MgO/Mo and Fs/MgO/Mo. While cluster growth by association of atoms from gas phase is exothermic on all the substrates, cluster growth by diffusion and aggr…

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

2019

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 [Cu25H10(SPhCl2)18]3- that readily catalyzes hydrogen…

Influence of a Cu–zirconia interface structure on CO2 adsorption and activation

2021

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Strain…

Atomistic Insights into Nitrogen-Cycle Electrochemistry: A Combined DFT and Kinetic Monte Carlo Analysis of NO Electrochemical Reduction on Pt(100)

2017

Electrocatalytic denitrification is a promising technology for the removal of NOx species in groundwater. However, a lack of understanding of the molecular pathways that control the overpotential and product distribution have limited the development of practical electrocatalysts, and additional atomic-level insights are needed to advance this field. Adsorbed NO has been identified as a key intermediate in the NOx electroreduction network, and the elementary steps by which it decomposes to NH4+, N2, NH3OH+, or N2O remain a subject of debate. Herein, we report a combined density functional theory (DFT) and kinetic Monte Carlo (kMC) study of this reaction on Pt(100), a catalytic surface that i…

Selectivity in Propene Dehydrogenation on Pt and Pt3Sn Surfaces from First Principles

2013

Propene can be produced via dehydrogenation of propane on Pt-based catalysts; however, the catalysts are plagued by low selectivity toward propene and high coke formation. The selectivity can be improved and the coke formation reduced by alloying Pt with Sn. The alloying is known to weaken the binding of propene, which in part explains the improved performance. We conducted density functional theory calculations to study the dehydrogenation of propene on flat and stepped Pt and Pt3Sn surfaces. The steps on Pt dehydrogenate propene readily, whereas, on Pt3Sn, the steps are inert because they are decorated with Sn. Our results indicate that the high selectivity and low coking on the Pt–Sn cat…

Effect of atomic layer deposited zinc promoter on the activity of copper-on-zirconia catalysts in the hydrogenation of carbon dioxide to methanol

2023

Funding Information: The work at Aalto University has been financially supported by the Academy of Finland (COOLCAT consortium, decision no. 329977 and 329978 ; ALDI consortium, decision no. 331082 ). This work made use of Aalto University Bioeconomy, OtaNano and RawMatters infrastructure. Hannu Revitzer (Aalto University) is thanked for the ICP-OES analysis, Aalto workshop people (especially Seppo Jääskeläinen) for working on the reactor modifications. The DFT calculations were made possible by computational resources provided by the CSC — IT Center for Science, Espoo, Finland ( https://www.csc.fi/en/ ) and computer capacity from the Finnish Grid and Cloud Infrastructure (urn:nbn:fi:resear…

Mechanistic Origins of the pH Dependency in Au-Catalyzed Glycerol Electro-oxidation: Insight from First-Principles Calculations

2021

Electrocatalytic oxidation of glycerol (EOG) is an attractive approach to convert surplus glycerol to value-added products. Experiments have shown that EOG activity and selectivity depend not only on the electrocatalyst but also on the electrode potential, the pH, and the electrolyte. For broadly employed gold (Au) electrocatalysts, experiments have demonstrated high EOG activity under alkaline conditions with glyceric acid as a primary product, whereas under acidic and neutral conditions Au is almost inactive producing only small amounts of dihydroxyacetone. In the present computational work, we have performed an extensive mechanistic study to understand the pH and potential dependency of …

Electronic structure of MgO-supported Au clusters: quantum dots probed by scanning tunneling microscopy.

2007

We investigate via density functional theory (DFT) the appearance of small MgO-supported gold clusters with 8 to 20 atoms in a scanning tunneling microscope (STM) experiment. Comparison of simulations of ultrathin films on a metal support with a bulk MgO leads to similar results for the cluster properties relevant for STM. Simulated STM pictures show the delocalized states of the cluster rather than the atomic structure. This finding is due to the presence of s- derived delocalized states of the cluster near the Fermi energy. The properties of theses states can be understood from a jellium model for monovalent gold.

Quantum Well States in Two-Dimensional Gold Clusters on MgO Thin Films

2008

The electronic structure of ultra-small Au clusters on thin MgO/Ag(001) films has been analyzed by scanning tunneling spectroscopy and density functional theory. The clusters exhibit two-dimensional (2D) quantum well states, whose shapes resemble the eigen-states of a 2D electron gas confined in a parabolic potential. From the symmetries of the HOMO and LUMO of a particular cluster, its electron filling and charge state is determined. In accordance to a DFT Bader-charge analysis, aggregates containing up to twenty atoms accumulate one to four extra electrons due to a charge transfer from the MgO/Ag interface. The HOMO - LUMO gap is found to close for clusters containing between 70 and 100 a…

A Computational Study of Adsorption of CO2, SO2, and H2CO on Free-Standing and Molybdenum-Supported CaO Films

2018

Oxide films play a significant role in a wide range of fields from catalysis to solar cell materials. CaO films are promising sorbents for many environmentally harmful molecules. Here, we report a systematic investigation of adsorption of CO2, SO2, and H2CO on bulk and Mo-supported CaO(100) films using density functional theory. Significant effects on adsorption energy, charge transfer to the molecules, and degree of the C–O bond activation were demonstrated on Mo-supported CaO films by changing the film thickness, composition, and the strength and direction of an applied external electric field. These findings are relevant for interpreting results from scanning tunneling microscopy of smal…

Grand-canonical approach to density functional theory of electrocatalytic systems: Thermodynamics of solid-liquid interfaces at constant ion and elec…

2018

Properties of solid-liquid interfaces are of immense importance for electrocatalytic and electrochemical systems, but modeling such interfaces at the atomic level presents a serious challenge and approaches beyond standard methodologies are needed. An atomistic computational scheme needs to treat at least part of the system quantum mechanically to describe adsorption and reactions, while the entire system is in thermal equilibrium. The experimentally relevant macroscopic control variables are temperature, electrode potential, and the choice of the solvent and ions, and these need to be explicitly included in the computational model as well; this calls for a thermodynamic ensemble with fixed…

ReO as a Brønsted acidic modifier in glycerol hydrodeoxygenation : Computational insight into the balance between acid and metal catalysis

2023

A computational study for the competitive conversion of glycerol to 1,2-propanediol and 1,3-propanediol is presented, considering a two-step sequence of dehydration followed by hydrogenation. The elementary steps for dehydration, i.e., breaking of C–H followed by C–OH or vice versa, were studied computationally both on the Rh metal surface and the acid-modified ReOH–Rh surface in order to understand the role of the acid promoter. While the acid modifier can catalyze the C–OH cleavage, the activation energy for the C–H cleavage was found to be considerably smaller on both pure and acid-doped Rh(111) surfaces, and breaking the secondary C–H bond is kinetically favored over breaking the termin…

On the Mechanistic Origins of the pH-Dependency in Au-Catalyzed Glycerol Electro-Oxidation: Insight from First Principles Calculations

2021

Electrocatalytic oxidation of glycerol (EOG) is an attractive approach to convert surplus glycerol to value-added products. Experiments have shown that EOG activity and selectivity depend on the electrocatalyst, but also on the electrode potential, the pH, and the electrolyte. For broadly employed gold (Au) electrocatalysts, experiments have demonstrated high EOG activity under alkaline conditions with glyceric acid as a primary product, whereas under acidic and neutral conditions Au is almost inactive producing only small amounts of dihydroxyacetone. In the present computational work, we have performed an extensive mechanistic study to understand the pH- and potential- dependency of Au-cat…

Constant inner potential DFT for modelling electrochemical systems under constant potential and bias

2021

Electrochemical interfaces and reactions play a decisive role in e.g. clean energy conversion but understanding their complex chemistry remains an outstanding challenge. Constant potential or grand canonical ensemble (GCE) simulations are indispensable for unraveling the properties of electrochemical processes as a function of the electrode potential. Currently, constant electrode potential calculations at the density functional theory (DFT) level are carried out by fixing the Fermi level of the simulation cell. However, the Fermi level from DFT calculations does does not always reflect the experimentally controlled electrode potential or describe the thermodynamic independent variable in G…

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

2022

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 Nose−Hoover, Berendsen, and simple velocity rescaling methods fail to provide are liable temperature description for systems considered. Instead, nonconstant temperatures and large temperature gradients within the different parts of the system are observed. The errors are not a “feature” of any particular code but …

Aktivierung und Elektronentransfer-induzierte Reaktion von Kohlendioxid an einer Oxid-Metall-Grenzfläche

2015

Es wurde ein Modellsystem realisiert, das mittels Elektronentransfer durch eine Metall-Isolator-Metall(MIM)-Struktur die Bildung eines CO2-Radikalanions von aus der Gasphase adsorbiertem Kohlendioxid induziert, welches anschliesend zu Oxalat weiterreagiert. Dieser reversible Prozess gestattet eine Studie der involvierten Elementarschritte auf atomarer Ebene. Die Oxalatspezies an der MIM-Grenzflache wurden mithilfe der Rastertunnelmikroskopie untersucht, chemisch mittels Infrarotspektroskopie identifiziert und ihre Bildung durch Dichtefunktionalrechnungen verifiziert.

First Principles Calculations for Hydrogenation of Acrolein on Pd and Pt: Chemoselectivity Depends on Steric Effects on the Surface

2016

The chemoselective hydrogenation of acrolein on Pt(111) and Pd(111) surfaces is investigated employing density functional theory calculations. The computed potential energy surfaces together with the analysis of reaction mechanisms demonstrate that steric effects are an important factor that governs chemoselectivity. The reactions at the C=O functionality require more space than the reactions at the C=C functionality. Therefore the formation of allyl alcohol is more favorable at low coverage, while the reduction of the C=C bond and the formation of propanal becomes kinetically more favorable at higher coverage. The elementary reaction steps are found to follow different reaction mechanisms,…

Orbiting Orbitals: Visualization of Vi-Bronic Motion at a Conical Intersection

2013

The Jahn-Teller (JT) active unpaired electron of single metalloporphyrin radical anions is imaged through scanning tunneling microscopy. It is demonstrated that the electron is delocalized over the porphyrin macrocycle and its topographic image is determined by vibronic motion: the orbital of the electron adiabatically follows the zero-point pseudorotation of skeletal deformations. Transformation of the polar graphs of the observed images allows visualization of the adiabatic vibrational density to which the electron is coupled. The vibronic potential at the conical intersection is visualized and the half-integer angular momentum characteristic of the Berry phase is revealed in the radial f…

DFT study on complete ethylene decomposition on flat and stepped Pd

2010

Abstract We applied density functional theory (DFT) calculations to study ethylidyne (CCH 3 ) adsorption and decomposition to C and H over flat and stepped Pd surfaces. Our calculations show that ethylidyne is the most stable molecule among all the possible dehydrogenation or decomposition residues of ethylene. We discuss various possible reaction pathways for ethylidyne decomposition and point out that the most probable one is via ethynyl (CCH) species suggested also by experimental observations. Our calculations indicate that the presence of steps modify the potential energy surface by increasing the binding of most of the species, and also lowering the activation barrier for several reac…

Oxidative Dehydrogenation of Ethanol on Gold : Combination of Kinetic Experiments and Computation Approach to Unravel the Reaction Mechanism

2021

Abstract Selective alcohol dehydrogenation on heterogeneous catalysts is a key industrial reaction for production of aldehydes, ketones, and carboxylic compounds. Design of catalysts with improved activity and selectivity requires understanding of the reaction mechanism and kinetics. Herein, experiments, density functional theory (DFT) and kinetic modelling were combined to elucidate the mechanism and kinetics of ethanol oxidative dehydrogenation to acetaldehyde on gold catalysts. Catalytic experiments clearly emphasized the role of oxygen in this reaction. Ethanol conversion was rather independent on the gold cluster size. Formation of minor products, acetic acid and ethyl acetate was stru…

First principles investigations of Pd-on-Au nanostructures for trichloroethene catalytic removal from groundwater

2010

Catalytic groundwater remediation from chlorinated organic solvents like trichloroethene (TCE) has been found to be more effective and sustainable than traditional non-destructive methods. Among the experimentally studied catalyst materials, Pd-decorated Au nanoparticles show the highest activity and selectivity combined with the best resistance towards poisoning by chemicals present in groundwater. In this study the thermochemistry and adsorption geometries of TCE and its hydrodechlorination products are investigated via density functional theory calculations. Various model systems for Pd-supported Au nanoparticles are addressed. The adsorption of TCE is endothermic on bare Au(111), almost…

Adsorption of gold clusters on metal-supported MgO: Correlation to electron affinity of gold

2007

Adsorption of ${\mathrm{Au}}_{N}$ clusters $(N=1\char21{}6)$ on a bulk MgO(001) surface and on an ultrathin (3 ML) MgO(001) film supported by Mo metal is investigated via density-functional theory calculations. Comparison of the two substrates unambiguously shows that the gold clusters adsorbed on $\mathrm{Mg}\mathrm{O}∕\mathrm{Mo}$ turn into singly charged cluster anions ${\mathrm{Au}}_{N}^{\ensuremath{\delta}}$, $\ensuremath{\delta}\ensuremath{\approx}\ensuremath{-}1$. Their structures and internal charging patterns are analogous to singly charged, planar, gas-phase cluster anions ${\mathrm{Au}}_{N}^{\ensuremath{-}}$. The adsorption energy has prominent size-dependent odd-even oscillation…

Atomic Layer Deposition of Aluminum Oxide on TiO2 and Its Impact on N3 Dye Adsorption from First Principles

2011

The atomic layer deposition of aluminum oxide on an OH-terminated TiO2(101) anatase surface was studied employing density functional theory calculations. The formation of the Al2O3−TiO2 interface during the first atomic layer deposition cycle was modeled by studying the dissociative adsorption of an Al(CH3)3 precursor, followed with a H2O-pulse reaction step that changes the surface termination. Calculations provide evidence for the formation of a discontinuous, atomically rough aluminum oxide layer after the first cycle. To explore the role of the aluminum oxide layer on adsorption of a ruthenium-based N3 dye molecule, various adsorption geometries were investigated. Calculations show that…

Screening the bulk properties and reducibility of Fe-doped Mn2O3 from first principles calculations

2017

Abstract Manganese oxides, particularly Mn 2 O 3 , have demonstrated great potential for oxygen carrier materials in chemical looping applications. The application of these materials in the industrial scale is hindered by thermodynamic restrictions related to the reoxidation process. This disadvantage can be overcome by doping the oxide with a guest cation. Iron is one of the most promising dopants, but the atomic-level understanding of its effects on the properties of α-Mn 2 O 3 is incomplete. Herein, we report a systematic GGA+U study of the bulk properties and reducibility of Fe x Mn 2-x O 3 (0 ≤ x ≤ 2) as a function of Fe dopant concentration. In particular, we focus on a representative…

Density Functional Theory Study on Propane and Propene Adsorption on Pt(111) and PtSn Alloy Surfaces

2011

Density functional theory calculations were performed to investigate the adsorption of propane, propene, and C and H atoms on Pt and PtSn surfaces employing the revised Perdew–Burke–Ernzerhof (RPBE) and vdW-DF functionals. Propane adsorption was found to be mediated by van der Waals interactions without significant site preference on any of the studied surfaces. The adsorption characteristics of propene are different: On the Pt(111) and Pt3Sn(111) surfaces, propene adsorption is covalent, and the molecule prefers a di-σ site to a π site. Alloying Pt(111) with Sn leads to weaker adsorption owing to geometric and relaxation effects, whereas electronic effects are found to be small. On the PtS…

Binding Behavior of Carbonmonoxide to Gold Atoms on Ag(001)

2020

AbstractThe adsorption behavior of single CO molecules at 4 K bound to Au adatoms on a Ag(001) metal surface is studied with scanning tunneling microscopy (STM) and inelastic electron tunneling spectroscopy (IETS). In contrast to earlier observations two different binding configurations are observed—one on top of a Au adatom and the other one adsorbed laterally to Au on Ag(001). Moreover, IETS reveals different low-energy vibrational energies for the two binding sites as compared to the one for a single CO molecule bound to Ag(001). Density functional theory (DFT) calculations of the adsorption energies, the diffusion barriers, and the vibrational frequencies of the CO molecule on the diffe…

Ligand assisted hydrogenation of levulinic acid on Pt(111) from first principles calculations

2021

In this study, we investigate the hydrogenation reaction of levulinic acid to 4-hydroxypentanoic acid on ligand-modified Pt(111) using DFT. Modifying nanoparticle surfaces with ligands can have beneficial effects on the desired reaction such as improved selectivity or lower activation energies. The N3,N3-dimethyl-N2-(quinolin-2-yl)propane-1,2-diamine (AQ) ligand was selected to modify the surface, since it combines good surface adsorption properties with functional groups that can influence the reaction. The adsorption geometry of the AQ ligand was studied as well as the co-adsorption of a second AQ ligand for the possibility of self-assembly. We found that dissociated hydrogen from the Pt(…

On the Mechanistic Origins of the pH-Dependency in Au-Catalyzed Glycerol Electro-Oxidation: Insight from First Principles Calculations

2021

Electrocatalytic oxidation of glycerol (EOG) is an attractive approach to convert surplus glycerol to value-added products. Experiments have shown that EOG activity and selectivity depend on the electrocatalyst, but also on the electrode potential, the pH, and the electrolyte. For broadly employed gold (Au) electrocatalysts, experiments have demonstrated high EOG activity under alkaline conditions with glyceric acid as a primary product, whereas under acidic and neutral conditions Au is rather inactive producing only small amounts of dihydroxyacetone. In the present computational work, we have performed an extensive mechanistic study to understand the pH- and potential-dependency of Au-cata…

First-principles insight into CO hindered agglomeration of Rh and Pt single atoms on m-ZrO2

2020

In this first-principles study we evaluate the thermodynamic and kinetic stability of Rh and Pt single-atoms (SAs) and subnano clusters on the monoclinic zirconia surface with and without a CO atmosphere. To address the kinetic stability and agglomeration of SAs to clusters and nanoparticles, a non-equilibrium nanothermodynamic approach is developed and parametrised using data computed with density functional theory. The bare subnano clusters are more stable than SA and become more so with increasing size, which means the agglomeration is always favoured. CO binds strongly to the single atoms and clusters, and our atomistic thermodynamics treatment indicates that some CO will be present eve…

Oxidative dehydrogenation of alcohols on gold : An experimental and computational study on the role of water and the alcohol chain length

2023

The oxidative dehydrogenation of primary alcohols promoted by gold nanoparticles was investigated from an experimental and computational viewpoint to derive a plausible reaction mechanism and to understand the role of water and alcohol chain length in the elementary steps. The influence of water in reaction kinetics and product distribution was determined in a laboratory-scale microreactor adding water to the reaction mixture in different amounts. DFT calculations revealed that the presence of water on the catalyst surface is beneficial to assist the key step in alcohol oxidation i.e., oxygen activation by protonation. The calculations were performed for primary alcohols ranging from methan…

Exploring CO2 hydrogenation to methanol at a CuZn–ZrO2 interface via DFT calculations

2023

Multi-component heterogeneous catalysts are among the top candidates for converting greenhouse gases into valuable compounds. Combinations of Cu, Zn, and ZrO2 (CZZ) have emerged as promisingly efficient catalysts for CO2 hydrogenation to methanol. To explore the catalytic mechanism, density functional theory (DFT) calculations and the energetic span model (ESM) were used to study CO2 conversion routes to methanol on CuZn–ZrO2 interfaces with a varying Zn content. Our results demonstrate that the presence of Zn sites at the interface improves CO2 binding. However, the adsorption and activation energies are insensitive to Zn concentration. The calculations also show that the hydrogenation of …

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

2020

Abstract 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 Au0 clusters. On Lewis acidic supports that bind metals strongly, the latter transformation occurs while pre…

Understanding Structure and Stability of Monoclinic Zirconia Surfaces from First-Principles Calculations

2017

Under the water-rich pre-treatment and/or reaction conditions, structure and chemistry of the monoclinic zirconia surfaces are strongly influenced by oxygen vacancies and incorporated water. Here, we report a combined first-principles and atomistic thermodynamics study on the structure and stability of selected surfaces of the monoclinic zirconia. Our results indicate that among the studied surfaces, the most stable (111) surface is the least vulnerable towards oxygen vacancies in contrast to the less stable (011) and (101) surfaces, where formation of oxygen vacancies is energetically more favorable. Furthermore, we present a vigorous, systematic screening of water incorporation onto the s…

A Computational Study of Adsorption of CO2, SO2, and H2CO on Free-Standing and Molybdenum-Supported CaO Films

2019

Oxide films play a significant role in a wide range of fields from catalysis to solar cell materials. CaO films are promising sorbents for many environmentally harmful molecules. Here, we report a systematic investigation of adsorption of CO2, SO2, and H2CO on bulk and Mo-supported CaO(100) films using density functional theory. Significant effects on adsorption energy, charge transfer to the molecules, and degree of the C−O bond activation were demonstrated on Mo-supported CaO films by changing the film thickness, composition, and the strength and direction of an applied external electric field. These findings are relevant for interpreting results from scanning tunneling microscopy of smal…

Unraveling the prominent role of the Rh/ZrO2-interface in the water-gas shift reaction via a first principles microkinetic study

2018

The industrially important water–gas-shift (WGS) reaction is a complex network of competing elementary reactions in which the catalyst is a multicomponent system consisting of distinct domains. Herein, we have combined density functional theory calculations with microkinetic modeling to explore the active phase, kinetics, and reaction mechanism of the WGS over the Rh–ZrO2 interface. We have explicitly considered the support and metal and their interface and find that the Rh–ZrO2 interface is far more active toward WGS than Rh(111) facets, which are susceptible to CO poisoning. CO2 forming on the zirconia support rapidly transforms into formate. These findings demonstrate the central role of…

Globally Optimized Equilibrium Shapes of Zirconia-Supported Rh and Pt Nanoclusters : Insights into Site Assembly and Reactivity

2019

Metal−support interfaces form an active site for many important catalytic reactions. The modeling of these interfacial sites calls for approximations to set up a structure model, which in turn may significantly have an impact on studied chemistry and obtained atomistic understanding. Herein, we have employed a density functional theory-based genetic approach to obtain globally optimized nanostructures for Rh and Pt clusters on a ZrO2 support. The analysis of the obtained structures shows that Rh clusters take more compact shapes, whereas Pt prefers elongated and low-symmetry structures. We find that metal−oxide perimeter sites are structurally different, presenting varying Pt and Rh coordin…

Influence of a Cu–zirconia interface structure on CO2 adsorption and activation

2021

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Strain…

DFT Prediction of Enhanced Reducibility of Monoclinic Zirconia upon Rhodium Deposition

2018

Oxides are an important class of materials and are widely used, for example, as supports in heterogeneous catalysis. In a number of industrial catalytic processes, oxide supports actively participate in chemical transformations by releasing lattice oxygen anions. While this is intuitively understood for reducible oxides, the reducibility of irreducible oxides may be modified via nanoengineering or upon inclusion of foreign species. Our calculations predict that the ability of irreducible monoclinic zirconia to release oxygen improves substantially upon deposition of rhodium. Through a comprehensive screening of Rh/ZrO2 with different size of the rhodium species, we find that a Rh adatom and…

Dynamics of weak interactions in the ligand layer of meta-mercaptobenzoic acid protected gold nanoclusters Au68(m-MBA)32 and Au144(m-MBA)40

2020

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. Here, we have performed extensive molecular dynamics simulations, with forces calculated…

CCDC 1851619: Experimental Crystal Structure Determination

2019

Related Article: Cunfa Sun, Nisha Mammen, Sami Kaappa, Peng Yuan, Guocheng Deng, Chaowei Zhao, Juanzhu Yan, Sami Malola, Karoliina Honkala, Hannu Häkkinen, Boon K. Teo, Nanfeng Zheng|2019|ACS Nano|13|5975|doi:10.1021/acsnano.9b02052