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As a showcase for experimentally accessible single-site catalysts, well-defined and characterized isolated Ir sites anchored on a covalent triazine framework (CTF) were investigated with computational methods.

Heterogeneous catalysis is key for chemical transformations. Understanding how catalysts' active sites dynamically evolve at the atomic scale under reaction conditions is a prerequisite for accurately determining catalytic mechanisms and predictably developing catalysts. We combine in situ time-dependent scanning tunneling microscopy observations and machine-learning-accelerated first-principles atomistic simulations to uncover the mechanism of restructuring of Pt catalysts under a pressure of carbon monoxide (CO). We show that a high CO coverage at a Pt step edge triggers the formation of atomic protrusions of low-coordination Pt atoms, which then detach from the step edge to create sub-nano-islands on the terraces, where under-coordinated sites are stabilized by the CO adsorbates. The fast and accurate machine-learning potential is key to enabling the exploration of tens of thousands of configurations for the CO-covered restructuring catalyst. These studies open an avenue to achieve an atomic-scale understanding of the structural dynamics of more complex metal nanoparticle catalysts under reaction conditions.

The formation of thin oxide films is of significant scientific and practical interest. In particular, the semiconductor industry is interested in developing a plasma atomic layer etching process to pattern copper, replacing the dual Damascene process. Using a nonthermal oxygen plasma to convert the metallic copper into copper oxide, followed by a formic acid organometallic reaction to etch the copper oxide, this process has shown great promise. However, the current process is not optimal because the plasma oxidation step is not self-limiting, hampering the degree of thickness control. In the present study, a neural network potential for the binary interaction between copper and oxygen is developed and validated against first-principles calculations. This potential covers the entire range of potential energy surfaces of metallic copper, copper oxides, atomic oxygen, and molecular oxygen. The usable kinetic energy ranges from 0 to 20 eV. Using this potential, the plasma oxidation of copper surfaces was studied with large-scale molecular dynamics at atomic resolution, with an accuracy approaching that of the first principle calculations. An amorphous layer of CuO is formed on Cu, with thicknesses reaching 2.5 nm. Plasma is found to create an intense local heating effect that rapidly dissipates across the thickness of the film. The range of this heating effect depends on the kinetic energy of the ions. A higher ion energy leads to a longer range, which sustains faster-than-thermal rates for longer periods of time for the oxide growth. Beyond the range of this agitation, the growth is expected to be limited to the thermally activated rate. High-frequency, repeated ion impacts result in a microannealing effect that leads to a quasicrystalline oxide beneath the amorphized layer. The crystalline layer slows down oxide growth. Growth rate is fitted to the temperature gradient due to ion-induced thermal agitations, to obtain an apparent activation energy of 1.0 eV. A strategy of lowering the substrate temperature and increasing plasma power is proposed as being favorable for more self-limited oxidation.

Dilute Pd-in-Au alloys are valuable materials for selectively hydrogenating alkynes and isomerizing alkenes. By diluting Pd in a Au host, the selectivity toward semihydrogenated alkene isomers can be significantly enhanced and the unfavorable overhydrogenation to alkanes is suppressed. However, a detailed mechanistic study on the origin of the enhanced alkene selectivity over dilute alloy catalysts is still missing. Here, we combine experiment and theory to unravel the reaction mechanism, identifying rate-limiting and selectivity-controlling steps in 1-hexene hydrogenation over dilute Pd-in-Au catalysts. Using isotope-exchange hydrogenation experiments, we show that 1-hexene and hydrogen over a bimetallic Pd4Au96 in silica catalyst preferentially form 1-hexene isomers, (trans and cis) 2- and 3-hexene and only a small amounts of hexane. The reaction is consistent with a Horiuti-Polanyi mechanism, similar to a monometallic Pd nanoparticle catalyst. Computation of the free-energy profiles for 1-hexene hydrogenation and isomerization over a single Pd atom in a Au surface using first principles calculations indicated that the isomerization of 1-hexene to 2-hexene is energetically favorable due to the relatively large barrier for H2 dissociation preventing hydrogenation to n-hexane. Microkinetic modeling established that H2 dissociation on the single-atom Pd sites and H spillover from these sites onto the Au host are rate-limiting and key in steering the selectivity of dilute Pd-in-Au alloys toward the hexene isomers. The mechanistic insights from this study contribute to the rational design of optimized dilute alloy catalysts for selective alkene isomerization.

The dissociation of H

Dynamic restructuring of bimetallic catalysts plays a crucial role in their catalytic activity and selectivity. In particular, catalyst pretreatment with species such as carbon monoxide and oxygen has been shown to be an effective strategy for tuning the surface composition and morphology. Mechanistic and kinetic understanding of such restructuring is fundamental to the chemistry and engineering of surface active sites but has remained challenging due to the large structural, chemical, and temporal degrees of freedom. Here, we combine time-resolved temperature-programmed infrared reflection absorption spectroscopy, ab initio thermodynamics, and machine-learning molecular dynamics to uncover previously unidentified timescale and kinetic parameters of in situ restructuring in Pd/Au(111), a highly relevant model system for dilute Pd-in-Au nanoparticle catalysts. The key innovation lies in utilizing CO not only as a chemically sensitive probe of surface Pd but also as an agent that induces restructuring of the surface. Upon annealing in vacuum, as-deposited Pd islands became encapsulated by Au and partially dissolved into the subsurface, leaving behind isolated Pd monomers on the surface. Subsequent exposure to 0.1 mbar CO enabled Pd monomers to repopulate the surface up to 373 K, above which complete Pd dissolution occurred by 473 K, with apparent activation energies of 0.14 and 0.48 eV, respectively. These restructuring processes occurred over the span of ∼1000 s at a given temperature. Such a minute-timescale dynamics not only elucidates the fluxional nature of alloy catalysts but also presents an opportunity to fine-tune the surface under moderate temperature and pressure conditions.

The dynamic restructuring of Cu surfaces in electroreduction conditions is of fundamental interest in electrocatalysis. We decode the structural dynamics of a Cu(111) electrode under reduction conditions by joint first-principles calculations and operando electrochemical scanning tunneling microscopy (ECSTM) experiments. Combining global optimization and grand canonical density functional theory, we unravel the potential- and pH-dependent restructuring of Cu(111) in acidic electrolyte. At reductive potential, Cu(111) is covered by a high density of H atoms and, below a threshold potential, Cu adatoms are formed on the surface in a (4×4) superstructure, a restructuring unfavorable in vacuum. The strong H adsorption is the driving force for the restructuring, itself induced by electrode potential. On the restructured surface, barriers for hydrogen evolution reaction steps are low. Restructuring in electroreduction conditions creates highly active Cu adatom sites not present on Cu(111).

Previously observed formation of sub-stoichiometric titanium oxide dendritic structures across terraces of Au(111) are computationally studied and shown to follow the classical fractal formation mechanism of diffusion limited aggregation (DLA). Globally optimized gas-phase oxide cluster structures were sampled in a variety of landing formations on gold surfaces and shown to favor isomers driving polymerization to Brownian tree fractal structures. Mobility of Ti3O5 monomers is shown to be extremely high, with diffusion barriers of 0.21 eV or less. Through bonding stabilization, polymerization of these monomers is energetically favorable and irreversible on the 111 terrace, but geometrically impossible to propagate along the step edge. Simulated STM images show strong similarity to experiment. By contrast, observation of Ti3O6 aggregating as wires along step edges is explained by affinity of oxygen to step edges and statistical arguments for aggregation entropy at the step, in addition to low barriers for monomer diffusion and polymerization.

Minimally invasive double-level osteotomy (DLP) surgery is performed in severe knee varus, when extra-articular deformity is identified in both the distal femur and proximal tibia. The main advantage is to maintain a horizontal joint line and avoid creating secondary anatomic deformities. This article considers the pearls and pitfalls in performing minimally invasive DLO surgery.

A combination of density functional theory (DFT) and experiments with atomically size-selected Ptn clusters deposited on indium-tin oxide (ITO) electrodes was used to examine the effects of applied potential and Ptn size on the electrocatalytic activity of Ptn (n = 1, 4, 7, and 8) for the hydrogen evolution reaction (HER). Activity is found to be negligible for isolated Pt atoms on ITO, increasing rapidly with Ptn size such that Pt7/ITO and Pt8/ITO have roughly double the activity per Pt atom compared to atoms in the surface layer of polycrystalline Pt. Both the DFT and experiment find that hydrogen under-potential deposition (Hupd) results in Ptn/ITO (n = 4, 7, and 8) adsorbing ∼2H atoms/Pt atom at the HER threshold potential, equal to ca. double the Hupd observed for Pt bulk or nanoparticles. The cluster catalysts under electrocatalytic conditions are hence best described as a Pt hydride compound, significantly departing from a metallic Pt cluster. The exception is Pt1/ITO, where H adsorption at the HER threshold potential is energetically unfavorable. The theory combines global optimization with grand canonical approaches for the influence of potential, uncovering the fact that several metastable structures contribute to the HER, changing with the applied potential. It is hence critical to include reactions of the ensemble of energetically accessible PtnHx/ITO structures to correctly predict the activity vs Ptn size and applied potential. For the small clusters, spillover of Hads from the clusters to the ITO support is significant, resulting in a competing channel for loss of Hads, particularly at slow potential scan rates.

Supported Au-Pd nanoparticles are an excellent catalyst for the hydrogenation of alkynes, a crucial step for olefin polymerization. They have better selectivity at a high conversion rate for the hydrogenation of 1-hexyne compared to pure Pd. The size, shape, and composition of the supported catalyst ultimately determine their properties. In this work, a combined scanning transmission electron microscopy (STEM) and density functional theory (DFT) study is used to determine how Pd concentration affects the activity and selectivity of Au-Pd particles for the hydrogenation of acetylene. Atomic resolution microscopy shows the increased probability of Pd-rich islands within particles with increasing Pd concentration. DFT models of the surface concentrations of Pd as monomers, dimers, and trimers allowed insight into the origin of the high activity for ethylene production. Specifically, monomers of Pd were found to be more active than dimers and trimers. This provides insight into why Au1-xPdx particles with low Pd concentration have higher production rates, as Pd monomers are more statistically likely. These combined STEM and DFT results explain the existence of an optimum for Au:Pd ratio, where conversion per gram of Pd is maximized at a concentration of 4 % Pd.

Using CoOx thin films supported on Au(111) single crystal surfaces as model catalysts for the CO oxidation reaction we show that three reaction regimes exist in response to chemical and topographic restructuring of the CoOx catalyst as a function of reactant gas phase CO/O2 stoichiometry a finding that highlights the versatility of catalysts and their evolution in response to reaction conditions. Under oxygen-lean conditions and moderate temperatures (below 150C degrees) partially oxidized films containing CoO were found to be efficient catalysts. In contrast, stoichiometric CoO films containing only Co2+ form carbonates in the presence of CO that poison the reaction below 300 C degrees. Under oxygen-rich conditions a more oxidized catalyst phase forms containing Co3+ species that is effective in a wide temperature range. Resonant photoemission spectroscopy (ResPES) revealed the unique role of Co3+ sites in catalyzing the CO oxidation. DFT calculations provided deeper insights into the pathway and free energy barriers for the reactions on these oxide phases.

The development of new catalyst materials for energy-efficient chemical synthesis is critical as over 80% of industrial processes rely on catalysts, with many of the most energy-intensive processes specifically using heterogeneous catalysis. Catalytic performance is a complex interplay of phenomena involving temperature, pressure, gas composition, surface composition, and structure over multiple length and time scales. In response to this complexity, the integrated approach to heterogeneous dilute alloy catalysis reviewed here brings together materials synthesis, mechanistic surface chemistry, reaction kinetics, in situ and operando characterization, and theoretical calculations in a coordinated effort to develop design principles to predict and improve catalytic selectivity. Dilute alloy catalysts─in which isolated atoms or small ensembles of the minority metal on the host metal lead to enhanced reactivity while retaining selectivity─are particularly promising as selective catalysts. Several dilute alloy materials using Au, Ag, and Cu as the majority host element, including more recently introduced support-free nanoporous metals and oxide-supported nanoparticle "raspberry colloid templated (RCT)" materials, are reviewed for selective oxidation and hydrogenation reactions. Progress in understanding how such dilute alloy catalysts can be used to enhance selectivity of key synthetic reactions is reviewed, including quantitative scaling from model studies to catalytic conditions. The dynamic evolution of catalyst structure and composition studied in surface science and catalytic conditions and their relationship to catalytic function are also discussed, followed by advanced characterization and theoretical modeling that have been developed to determine the distribution of minority metal atoms at or near the surface. The integrated approach demonstrates the success of bridging the divide between fundamental knowledge and design of catalytic processes in complex catalytic systems, which can accelerate the development of new and efficient catalytic processes.

Dimethyl methylphosphonate (DMMP), a simulant for toxic sarin, partly desorbs from rutile TiO2(110), and partly decomposes by P–O or C–O bond cleavages. High temperature formation of gaseous methanol and formaldehyde is facilitated at oxygen vacancies.

Resume Introduction Le recours aux cones en metal poreux pour combler les pertes de substance osseuse au cours des arthroplasties du genou est croissant, mais ces dispositifs ne sont pas rembourses en sus des groupes homogenes de sejour (GHS). L’impact economique des cones en metal poreux pourrait etre important pour les hopitaux. Materiel et methodes Etude bicentrique observationnelle incluant tout patient ayant beneficie d’une prothese totale du genou avec reconstruction osseuse par cones en metal poreux entre juin 2014 et juin 2019, dans deux hopitaux universitaires francais. Les couts ont ete evalues a l’aide de l’etude nationale des couts a methodologie commune. Les depenses engagees par les hopitaux ont ete comparees aux montants des groupes homogenes de malades (GHM) et aux recettes percues au titre des GHS. Resultats 96 patients (103 sejours) ont beneficie de l’implantation de 195 cones. Les etablissements ont percu en moyenne 10 970 ± 1401€ /sejour. Les depenses associees aux cones representaient en moyenne 35 % des GHM et 44 % des GHS. Le surcout moyen lie aux cones etait de 2709 ± 1138€ /sejour. Si les reconstructions avaient ete realisees par allogreffe, le gain moyen pour les hopitaux aurait ete de 108€ /sejour. Conclusion Les cones semblent presenter des avantages cliniques pour les chirurgiens en diminuant l’incidence des reprises. Cette etude montre l’inadequation actuelle du financement de ces dispositifs pour les hopitaux francais, suggerant la necessite d’elargir les possibilites de prise en charge des technologies innovantes.

First-principles calculations play a key role in understanding the interactions of molecules with transition-metal surfaces and the energy profiles for catalytic reactions. However, many of the commonly used density functionals are not able to correctly predict the surface energy as well as the adsorption site preference for a key molecule such as CO, and it is not clear to what extent this shortcoming influences the prediction of reaction or diffusion pathways. Here, we report calculations of carbon monoxide diffusion on the Cu(001) surface along the [100] and [110] pathways, as well as the surface energy of Cu(001), and CO-adsorption energy and compare the performance of the Perdew-Burke-Ernzerhof (PBE), PBE + D2, PBE + D3, RPBE, Bayesian error estimation functional with van der Waals correlation (BEEF-vdW), HSE06 density functionals, and the random phase approximation (RPA), a post-Hartree-Fock method based on many-body perturbation theory. We critically evaluate the performance of these methods and find that RPA appears to be the only method giving correct site preference, overall barrier, adsorption enthalpy, and surface energy. For all of the other methods, at least one of these properties is not correctly captured. These results imply that many density functional theory (DFT)-based methods lead to qualitative and quantitative errors in describing CO interaction with transition-metal surfaces, which significantly impacts the description of diffusion pathways. It is well conceivable that similar effects exist when surface reactions of CO-related species are considered. We expect that the methodology presented here will be used to get more detailed insights into reaction pathways for CO conversion on transition-metal surfaces in general and Cu in particular, which will allow us to better understand the catalytic and electrocatalytic reactions involving CO-related species.

Resume Introduction Les osteotomies tibiales de valgisation corrigent une deformation du plan coronal et peuvent influencer les parametres du plan sagittal, comme la pente tibiale posterieure et la hauteur patellaire. L’objectif de cette etude etait d’analyser les variations de la hauteur patellaire, apres osteotomie tibiale de valgisation, par ouverture mediale, sur la base des index a reference tibiale et femorale. Materiel et methode Cette etude retrospective monocentrique incluait 129 patients operes par osteotomie tibiale de valgisation « pure », par ouverture posteromediale, sans modification de la pente tibiale, avec guide de coupe personnalise. La hauteur patellaire etait evaluee par les index de Caton et Deschamps, d’Insall–Salvati et de Schroter, la pente tibiale posterieure, ainsi que les angles femoral et tibial, dans le plan coronal, etaient analyses. Les radiographies etaient realisees en preoperatoires et a 12 mois postoperatoires. Les mesures radiographiques etaient realisees par deux observateurs independants. Resultats L’alignement global du membre inferieur (Δ = 6,3 ± 0,95°, p Conclusion Cette serie clinique a permis de montrer que la hauteur patellaire n’etait pas modifiee apres osteotomie tibiale de valgisation posteromediale « pure », sans modification de la pente tibiale, avec guides de coupe personnalises, quelle que soit la reference femorale ou tibiale utilisee. L’index de hauteur femoropatellaire, decrit par Schroter, presente une excellente fiabilite et n’est pas dependant des modifications du tibia proximal pour l’evaluation de la hauteur patellaire ; son utilisation peut etre recommandee pour le suivi des osteotomies tibiales de valgisation. Niveau de preuve III ; etude de cohorte retrospective.

We report the size-dependent activity and stability of FTO-supported Pt1,4,7,8 for electrocatalytic hydrogen evolution reaction, and show that clusters are significantly more active than polycrystalline Pt, but also have stability under HER conditions that is size-dependent. To understand the mechanistic origin of the size effects, we carried out detailed DFT-based theory, accounting for the structural fluxionality under varying potentials. We show that, even under coverage of the simplest adsorbate H, the clusters can undergo drastic changes and populate a grand canonical ensemble of hydride states with diverse distributions of stoichiometry, structure, and thus reactivity. Both experiment and theory find that electrocatalysis mainly results from heavily hydrogenated states of the clusters (~2 H/Pt), and an ensemble-based kinetic model reproduces the experimental activity trend and provides detailed insights into the contributions from metastable configurations. The size-dependent stability trend is rationalized by chemical bonding analysis. The comparison of experiment and theory demonstrates the potential- and adsorbate-coverage-dependent fluxionality of subnano clusters of different sizes and offers a systematic modeling strategy to tackle the complexities.

Ptn/FTO HER Datasets This is the dataset of the manuscript: *"Hydrogen Evolution on FTO-Supported Ptn Clusters: Ensemble of Hydride States Governs the Size Dependent Reactivity"* Structure of the hydroxylated FTO support In VASP format, including the constraints. FTO.cif All unique bare Ptn/FTO structures from BLDA sampling They are sorted from BLDA searches, with all duplicates removed. The structures and associated metadata are stored in ASE database format. In the subdirectory: ensemble_Ptn Pt01.db Pt04.db Pt07.db Pt08.db All unique H-covered Ptn/FTO structures from GCGA sampling They are merged and sorted from multiple GCGA searches at different chemical potential of H, with all duplicates removed. The structures and associated metadata are stored in ASE database format. In the subdirectory: ensemble_PtnHx Pt01-GM.db Pt04-GM.db Pt04-LM1.db Pt07-GM.db Pt07-LM1.db Pt08-GM.db GCDFT results of low-energy minima The fitted "electronic grand canonical free energy \Omega vs. electrode potential U_\mathrm{SHE}" relations from surface charging calculations: \Omega = a U_\mathrm{SHE}^2 + b U_\mathrm{SHE} + c Each line gives the name, a value, b value, and c value of a structure. In the subdirectory: gcdft_fitting sc-Pt01-GM.dat sc-Pt04-GM.dat sc-Pt04-LM1.dat sc-Pt07-GM.dat sc-Pt07-LM1.dat sc-Pt08-GM.dat Bonding analysis data The Bader analysis and COHP analysis results of low-energy PtnHx/FTO structures. In the subdirectory: bonding_analysis Each sub-subdirectory contains: CONTCAR chg.xyz ICOHPLIST.lobster

The oxygen reduction reaction (ORR) plays a key role in renewable energy transformation processes. Unfortunately, it is inherently sluggish, which greatly limits its industrial application. Sub-nano cluster decorated electrode interfaces are promising candidate ORR electrocatalysts. However, understanding the nature of the active sites on these catalysts in electrocatalytic conditions presents a formidable challenge for both experiment and theory, due to their dynamic fluxional character. Here, we combine global optimization with the electronic Grand Canonical DFT, to elucidate the structure and dynamics of sub-nano Ptn clusters deposited on electrified graphite. We show that under electrochemical conditions, these clusters exist as statistical ensembles of multiple states, whose fluxionality is greatly affected by the applied potential, electrolyte, and adsorbate coverage. The results reveal the presence of potential-dependent active sites, and hence, reaction energetics.

Heterogeneous catalysis is key for chemical transformations. Understanding how catalyst active sites dynamically evolve at the atomic scale under reaction conditions is a prerequisite for accurate determination of catalytic mechanisms and predictably developing catalysts. We combine in-situ time-dependent observation and machine learning-accelerated first-principle atomistic simulations to uncover the mechanism of restructuring of Pt catalysts under a pressure of carbon monoxide (CO). We show that a high CO coverage at a Pt step edge triggers the formation of atomic protrusions of low-coordination Pt atoms, which then detach from the step edge to create subnano-islands on the terraces, where undercoordinated sites are stabilized by the CO adsorbates. The fast and accurate machine learning potential is key to enable the exploration of ten of thousands of configurations for the CO covered restructuring catalyst. These studies open an avenue to achieve atom-scale understanding of structural dynamics of more complex metal nanoparticle catalysts under reaction.

Copper (Cu) remains the most important metal catalyst for the carbon dioxide reduction reaction (CO2 RR) into C2 products. Due to limited evidence from in situ experiments, mechanistic studies are often performed in the framework of density functional theory (DFT), using functionals at the generalized gradient approximation (GGA) level, which have fundamental difficulties to correctly describe CO adsorption and surface stability. We employ the adiabatic connection fluctuation dissipation theorem within the random phase approximation (RPA), in combination with the linearized Poisson-Boltzmann equation to describe solvation effects, to investigate the mechanism of CO2 RR on the Cu(100) facet. Qualitatively different from the DFT-GGA results, RPA results propose the formation of *OCCHO as the potential determining step towards C2 products. The results suggest that it is important to use more accurate methods like RPA when modeling reactions involving multiple CO-related species like CO2 RR.

The rationale of the catalytic activity observed in experiments is a crucial task in fundamental catalysis studies. Efficient catalyst design relies on an accurate understanding of the origin of the activity at the atomic level. Theoretical studies have been widely developed to reach such a fundamental atomic scale understanding of catalytic activity. Current theories ascribe the catalytic activity to the geometric and electronic structure of the active site, in which the geometrical and electronic structure effects are derived from the equilibrium geometry of active sites characterizing the static property of the catalyst; however catalysts, especially in the form of nanoclusters, may present fluxional and dynamic structure under reaction conditions, and the effect of this fluxional behavior is not yet widely recognized. Therefore, this Account will focus on the fluxionality of the active sites, which is driven by thermal fluctuations under finite temperature.Under reaction conditions, nanocluster catalysts can readily restructure, either being promoted to another metastable isomer (named as plastic fluxionality) or presenting ample deformations around their equilibrium geometry (named as elastic fluxionality). This Account summarizes our recent studies on the fluxionality of the nanoclusters and how plastic and elastic fluxionalities play roles in highly efficient reaction pathways. Our results show that the low energy metastable isomers formed by plastic fluxionality can manifest high reactivity despite their minor occurrence probability in the mixture of catalyst isomers. In the end, the highly active metastable isomer may dominate the total observed reactivity. In addition, the isomerization between the global minimum structure and the highly active metastable isomer can be a central step in catalytic transformations in order to circumvent some difficult reaction steps and may govern the overall mechanism. In addition, the thermal fluctuation driven elastic fluxionality is also found to play a key role, complementary to plastic fluxionality. The elastic fluxionality creates substantial structural deformations of the active site, and these deformed geometries enable low activation energies and high catalytic activity, which cannot be found from the static equilibrium geometry of the catalyst. A dedicated global activity search algorithm is proposed to search for the optimal reaction pathway on fluxional nanoclusters. In summary, our studies demonstrate that thermal-driven fluxionality provides a different paradigm for understanding the high activity of nanoclusters under reaction conditions beyond the static description of geometric and electronic structure. We first summarize our previous results and then provide a perspective for further studies on how to investigate and take the advantage of the fluxional geometry of nanoclusters. We will defend in this Account that the static picture for the active site is not complete and might miss critical reaction pathways that are highly efficient and only open after thermally induced restructuring of the active site.

The decomposition of dimethyl methylphosphonate (DMMP, (CH

The relative stability of reactive intermediates and reactants on a surface, which dictates the rate and selectivity of catalytic reactions in both gas and liquid phases, is dependent on numerous factors. One well-established example is secondary interactions, such as van der Waals interactions between the catalyst surface and the pendant group of the intermediate, which can govern reaction selectivity for coupling reactions. Herein, we directly show that interactions between adsorbed reaction intermediates and reactant molecules increase the binding energy and affects the geometrical arrangement of coadsorbed reactant/solvent molecules. Evidence for this effect is demonstrated for the oxidative coupling reaction of methanol on a single crystal gold (Au(110)) surface. The rate-limiting reaction intermediate for methanol self-coupling, methoxy, stabilizes excess adsorbed methanol, which desorbs as a result of beta-hydride decomposition of the adsorbed methoxy. Direct molecular-scale imaging by scanning tunneling microscopy, supplemented by density functional theory, revealed interactive structures formed by methoxy and coadsorbed methanol. Interactions between the methoxy intermediate and coadsorbed methanol stabilizes a hydrogen-bonded network comprising methoxy and methanol by a minimum of 0.13 eV per methanol molecule. Inclusion of such interactions between reaction intermediates and coadsorbed reactants and solvents in kinetic models is important for microkinetic analysis of the rates and selectivities of catalytic reactions in both the gas and liquid phases whenever appreciable coverages of species from the ambient phase exist.

Heterogeneous catalysis is key for chemical transformations. Understanding how catalyst active sites dynamically evolve at the atomic scale under reaction conditions is a prerequisite for accurate determination of catalytic mechanisms and predictably developing catalysts. We combine in-situ observation and Machine Learning accelerated first-principle atomistic simulations to uncover the mechanism of restructuring for Pt catalysts under a pressure of carbon monoxide CO. We show that a high CO coverage at a Pt step edge triggers the formation of atomic protrusions of low-coordination Pt atoms, that then detach from the step edge to create sub-nano-islands on the terraces, where undercoordinated sites are stabilized by the CO adsorbates. These studies open an avenue to achieve an atom-scale understanding of structural dynamics of more complex metal nanoparticles under reaction.

The dissociation of H2 is an essential elementary step in many industrial chemical transformations, typically requiring precious metals. Here, we report a hierarchical nanoporous Cu catalyst doped with small amounts of Ti (npTiCu) that increases the rate of H2-D2 exchange by approximately one order of magnitude compared to the undoped nanoporous Cu (npCu) catalyst. The catalysts were prepared by dealloying of bulk alloys, Al80Cu20 and Al80Cu19Ti1, to produce the npCu and npTiCu catalysts, respectively. The promotional effect of Ti was measured via steady-state H2-D2 exchange reaction experiments under atmospheric pressure flow conditions in the temperature range of 300─523 K. Pretreatment with flowing H2 is required for stable catalytic performance. Two pretreatment temperatures, 573 K and 673 K, were investigated for both the undoped and Ti-doped npCu catalysts. The experimentally-determined H2-D2 exchange rate is 5-7 times greater for npTiCu vs. the undoped material under optimized pretreatment and reaction temperatures. The H2 pretreatment leads to full reduction of Cu oxide and partial reduction of surface Ti oxide species present in the as-prepared catalyst as demonstrated using in-situ ambient pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Both catalysts also contained similar, small amounts of residual aluminum from the dealloying which is present in the form of alumina nanoparticles that did not contribute to the differences in catalytic activity. The apparent activation energy and pre-exponential factors measured for H2-D2 exchange are substantially different for Ti-doped vs. undoped npCu catalysts. DFT calculations suggest that isolated, metallic Ti atoms on the surface of the Cu host can act as the active surface sites for hydrogen recombination. The increase in the rate of exchange above that of pure Cu is caused primarily by a shift in the rate-determining step from dissociative adsorption starting from gas phase H2 or D2 on Cu to H/D atom recombination towards chemisorbed H2/HD/D2 on Ti-doped Cu, with the corresponding decrease in activation entropy that it produces.

Copper (Cu) remains the most important metal catalyst for the carbon dioxide reduction reaction (CO

Author(s): van der Hoeven, Jessi ES; Ngan, Hio Tong; Taylor, Austin; Eagan, Nathaniel M; Aizenberg, Joanna; Sautet, Philippe; Madix, Robert J; Friend, Cynthia M

To understand the nature and structure of N-doping centers in carbon materials, we combine two-dimensional (2D) solid-state NMR experiments and chemical shift calculations for 15N, 13C, and 1H nucl...

Heterogeneous thermocatalytic hydrogenation is widely believed to occur via co-adsorption of H2 and other reactants, but in aqueous phase an ionic or electrochemical mechanism was also proposed. Herein, we conduct 4-nitrophenol hydrogenation in an unbiased H-cell, where H2 and substrate are separately supplied into two chambers connected by a proton exchange membrane, in comparison with the same reaction in a single-cell in which H2 and 4-nitrophenol are co-fed. Based on the observation of the almost identical hydrogenation performance between the H-cell and the single cell, we conclude that co-adsorption of H2 and 4-nitrophenol is not a prerequisite for hydrogenation in aqueous phase in the tested pH range. Isotope experiments, scavenger test, DFT calculations and reaction kinetics suggest that a coupled electrochemical half-reaction mechanism for 4-nitrophenol hydrogenation in acidic aqueous phase is predominant. Importantly, while H2 oxidation primarily occurs on metal sites, 4-nitrophenol reduction occurs on both metal sites and conductive support, highlighting the non-innocent role of the support if the hydrogenation reaction follows the electron-proton transfer pathway.