Catalytic reactions on supported metal catalysts often proceed at high adsorbate coverages that can induce structural changes to the catalyst as compared to the clean catalyst. Such restructuring is typically described within an equilibrium picture, where nanoparticle shapes, surface structures, and adsorbate coverages are assumed to find their thermodynamically preferred state. Here, we challenge this assumption and propose that under conditions of high adsorbate coverage and fast turnovers of surface species, common of many industrial catalytic processes, supported metal nanoparticle structures and adsorbate coverages can become kinetically trapped in metastable states. We studied the CO adsorptiondesorption quasi-equilibrium on a Pt/γ-Al2O3 catalyst as a model system via in-situ IR spectroscopy and chemisorption as a function of temperature (300-650 K), CO pressure (10-2-10-4 bar) and visible photon flux (0-2 W/cm 2 440 nm photons). The area of the IR feature associated with adsorbed CO increases as a function of temperature and the inclusion of photon flux, in stark contrast with expectations of decreasing CO coverage from thermodynamic models. Quantitative estimates of apparent dispersion, CO desorption rates, and the reversibility of IR changes support the hypothesis that when CO turnovers are faster than 2 the time scale of Pt atomic rearrangements to their equilibrium state, the catalyst is driven into a metastable state (Pt structure and CO coverage). Based on this analysis, we estimate that atomic rearrangements on CO covered Pt nanoparticle surfaces occur on time scales of 10-1-10-3 s at ~500-600 K, much slower than often expected. Complementary theoretical calculations using grand canonical sampling show that equilibrium Pt-CO structures cannot reproduce the experimental IR trends, implying the presence of off-equilibrium states in coverage, catalyst structure, or both. By matching the experimental IR trend, theory identifies a plausible flat free energy region that does not correspond to equilibrium, and that can facilitate kinetic trapping. These results highlight the need for theoretical and experimental approaches explicitly targeting nonequilibrium structures to establish structure-function relationships in heterogeneous catalysis.

Understanding the stability of TiO2-supported single-atom catalysts (SACs) under H2 reduction conditions, where hydrogen adsorption on the metal/TiO2 surface influences metal-support interactions, diffusion, and aggregation, is important for their long-term applications. Using first-principles density functional theory (DFT) calculations, we investigate the thermodynamic and kinetic stability of Rh, Ag, Pt, and Au-based SACs on pristine, oxygen-defective, and hydroxylated rutile TiO2 (110) surfaces with and without H adsorption on the metal adatom. The thermodynamic driving force for aggregation was assessed by calculating dimerization energies as proxy, while the kinetic stability was quantified in two ways: (i) the total activation energy, Etotal (Ef + Ed), which couples adatom formation (Ef) and diffusion (Ed) energies, serves as a descriptor of ripening kinetics, and (ii) the Ed, used to evaluate diffusion rate constants and characteristic diffusion times, τ. The results show that Pt consistently exhibits the largest Etotal and longest τ, reflecting exceptional resistance to sintering, whereas Ag has the smallest values and is intrinsically unstable. Rh presents a distinctive case: although dimerization is thermodynamically favored, its Etotal is dominated by the formation energy of two separated Rh atoms on support (*Rh*Rh), giving Rh longer lifetimes than expected from its low diffusion barrier for dimer (*Rh2) formation. Au is unstable on oxygen-deficient TiO2 but is kinetically stabilized upon hydroxylation, which significantly increases both Etotal and τ. Hydrogen adsorption further modulates stability in a metal-dependent manner─stabilizing Rh but accelerating the aggregation of Ag and Au. This combined thermodynamic-kinetic framework provides a quantitative basis for predicting SAC sintering behavior and guiding strategies for stabilizing late transition metals under hydrogenation conditions.

Rhodium supported on titania (Rh/TiO 2 ) is an active catalyst for the reverse water gas shift reaction, yet the nature of the active sites for this reaction and others remain under debate due to the dynamic nature of the Rh coordination.

Degradation via sintering is an ongoing challenge that impedes the broad commercial success of supported metallic nanoparticle catalysts. To mitigate degradation via informed catalyst design and process operations, here we aim to disambiguate the underlying mechanisms of sintering by combining theory and experiment in a quantitative framework. While mechanistic sintering models exist, they only model a single sintering pathway, even though multiple sintering mechanisms can occur simultaneously or dominate at different stages of the process. Data-driven machine learning models have emerged as a means to represent complex processes through data regression. However, machine learning models have very large data needs and lack mechanistic insights due to their black-box encoding. To develop an interpretive model of catalyst degradation via sintering, we constructed a hybrid model combining mechanistic "physics-based" models and data-driven methods to obtain both reliable predictions and mechanistic insights regarding experimentally observed sintering phenomena. Focusing on nanoparticle sintering in the Rh-TiO2 catalyst for the reverse water-gas shift (RWGS) reaction, the hybrid model couples a mechanistic term for Ostwald ripening with energy values calculated via density functional theory (DFT) with a parametric, data-driven discrepancy function term for unmodeled mechanisms. The hybrid model is trained using Bayesian inference with data collected from small-angle X-ray scattering (SAXS) in situ experiments wherein average nanoparticle diameter versus time was measured at three relevant operating temperatures. The calibrated hybrid model results show that an Ostwald ripening-only model parameterized with fixed DFT energies does not fully capture the time and temperature dependence of the SAXS-observed sintering kinetics, and that an additional functional contribution, or DFT energy calibration, is required to reconcile simulation and experiment. Analysis of the hybrid-model error confirms that the hybrid model outperforms both the purely mechanistic and purely data-driven alternatives in terms of expected predictive accuracy for time-evolving average particle sizes. Furthermore, the results support the hypothesis that the Ostwald ripening mechanism is less important for explaining the sintering phenomena as operating temperature increases under an assumed fixed DFT parameterization. This could be explained in one of two ways: either latent, unmodeled sintering mechanisms dominate at higher temperatures, or the DFT uncertainty increases with temperature. The proposed modeling approach directly links theory to experiments and simulations via a statistical hybrid modeling framework and can be extended to other catalytic systems to improve predictive models and mechanistic understanding.

Sub-nanometer supported clusters are of interest in catalysis due to nearly complete precious metal atom utilization, generally high catalytic activity, and attractive tunability via size and clustersupport interactions. The stability of such clusters remains a challenge, however. We demonstrate anchoring and stabilization of size-selected Ptn, n = 2 - 10 clusters soft-landed on HOPG, achieved 2 by modifying the HOPG with 100 eV kinetic energy N(𝑛 1, 2) and Ar+ ions, with and without O2 oxidation of the ion-modified surfaces, prior to Ptn soft-landing. Ion modification is found to significantly improve the sticking probability for soft-landed Ptn, implying increased adsorption energies, and O2 exposure prior to cluster deposition increases the sticking probability to ~unity. DFT finds that Ptn bind preferentially to under-coordinated carbon sites created by the ion impacts, rather than to implanted N atoms, and X-ray photoelectron spectroscopy and scanning tunneling microscopy both show that the defect-anchored clusters are stable against sintering. There is net electron transfer from the defect-bound clusters to the support, and the local defect structure may undergo significant restructuring due to Pt-C bond formation. To probe the effects of ion-modified HOPG on the chemical properties of the adsorbed Ptn clusters, we tested electrodes prepared by Ptn deposition on ion-modified HOPG for the oxygen reduction reaction (ORR). The ion-modified electrodes showed ORR activity consistent with cluster size being maintained, and O2 modification enhanced both cluster anchoring and ORR activity. Thus, ion modification provides means to stabilize sub-nano cluster electrodes, while oxygen functionalization of the anchoring sites tunes the electrocatalytic activity.

Hydrophobic coatings are critical for applications spanning anti-fouling and selfcleaning technologies. Conventional fluorinated materials rely on complex fabrication methods and often lack mechanical robustness and scalability. Here, we report a new class of solution-processable fluorinated coatings based on atomically precise closo-dodecaborate clusters densely functionalized with fluorinated carbon chains. Our approach to fabricating these boron oriented superhydrophobic surfaces (BOSS) coatings is based on flexible chemical design, allowing for tailored functionalization and easy scalability. This molecular design enables unprecedented chain packing density, yielding coating with surface free energy around 13 mJ/m2 and excellent water repellency. The coatings exhibit thermally triggered, controllable degradation, along with electrochemical activity, fire retardancy, and mechanical durability when applied to common substrates, providing a viable alternative to conventional fluoropolymer systems. Our findings establish three-dimensional boron cluster as effective scaffold for high-density functional group incorporation, enabling the design of robust, next-generation advanced coatings.

Electrocatalytic reactions occur at dynamic, ion-regulated electrochemical interfaces. In electrocatalytic processes such as alkaline hydrogen evolution/oxidation reactions (HER/HOR), which operate at potentials below the electrode's potential of zero charge, electrolyte cations are not mere spectators but profoundly shape reaction behavior. It is generally believed that the alkaline HER and HOR are reversible reactions that share the sluggish Volmer step as their common rate-determining step and therefore exhibit symmetric behavior on Pt-based catalysts. Here, we show that the apparent kinetic symmetry between HER and HOR can be broken on certain transition-metal (TM)-decorated Pt surfaces. Using Ni-decorated Pt as a model system, we show that the formation of Ni-OH species enhances HER kinetics by promoting water dissociation yet paradoxically suppresses HOR kinetics, particularly in highly alkaline electrolytes at potentials above 0.05 V versus the reversible hydrogen electrode. Systematic analyses indicate that abundant TM-OH species drive strong cation accumulation at the outer Helmholtz plane, forming a compact cation layer that pairs with hydroxide anions (OH-) and suppresses their inward diffusion during HOR. Extending this framework across TM-decorated Pt surfaces reveals a systematic trend depending on the TM oxidation potential. Low-oxidation-potential TMs enhance HER but lead to pronounced OH--diffusion-limited HOR. Intermediate TMs promote both HER and HOR, whereas high-oxidation-potential TMs suppress both reactions due to insufficient TM-OH formation. Overall, this work establishes a unified mechanistic framework that links cation accumulation and interfacial OH- transport to distinct HER/HOR kinetics on TM-decorated Pt surfaces in alkaline media, providing design principles for alkaline electrocatalysts.

We report detailed characterization of the vibronic interactions between the first two electronically excited states, à and B̃, in SrOPh (Ph = phenyl, -C6H5) and its deuterated counterpart, SrOPh-d5 (-C6D5). The vibronic interactions, which arise due to non-adiabatic coupling between the two electronic states, mix the B̃,ν0 state with the energetically close vibronic level, Ã,ν21ν33, resulting in extra transition probability into the latter state. This state mixing is more prominent in the deuterated molecule because of the smaller energy gap between the interacting states. We model the mixing of the à and B̃ states using the Köppel-Domcke-Cederbaum (KDC) Hamiltonian parameterized in the diabatic framework of Ichino, Gauss, and Stanton on the basis of equation-of-motion coupled-cluster calculations. The simulation attributes the observed mixing to a second-order effect mediated by linear quasi-diabatic couplings between the Ã-C̃ and B̃-C̃ states. Based on the measured spectra, we deduce an effective coupling strength of ∼0.5 cm-1. Non-adiabatic couplings between different electronic states are an important factor that should be considered in the design of laser-cooling protocols for complex molecules.

The nickel-containing carbon monoxide dehydrogenase (CODH) uses a unique heterometallic [NiFe4S4] cluster active site, called the C-cluster, to catalyze the reversible reduction of carbon dioxide (CO2) to carbon monoxide (CO) at low overpotential and with perfect selectivity. Only the properly assembled nickel-bound form is capable of this reactivity, though how the structure of the cluster promotes such selectivity remains poorly understood. We have developed a model of the C-cluster by constructing a [NiFe3S4] cluster in the iron-sulfur cluster binding site of the Pyrococcus furiosus ferredoxin protein (NiFd) that replicates the thiolate ligation and aqueous environment of the native system. In this work, we interrogate the roles of each individual metal site and the whole-cluster covalency across two oxidation states that mirror the C-cluster in the Cox and Cred1 states. We have also studied the system bound to a CODH substrate (CO) and C-cluster inhibitor (CN-). A comprehensive suite of spectroscopic techniques, including pulsed electron paramagnetic resonance (EPR), variable-temperature, variable-field Mössbauer, and high-energy resolution fluorescence-detected X-ray absorption (HERFD-XAS) spectroscopy, have been used in conjunction with quantum mechanics/molecular mechanics (QM/MM) and broken symmetry density functional theory (BS-DFT) calculations to elucidate the electronic properties of these heterometallic clusters. This work reveals that the supporting iron-sulfide subcluster and thiolate ligands play a critical role in buffering charge density as the cluster traverses multiple states. An unusually weak exchange interaction between the Ni site and the iron atoms is found to exist in the CO-bound form, suggesting that substrate binding electronically isolates the nickel site, giving a low-spin ground state that drives localized chemistry to occur at the nickel center. These results have implications for understanding how reactivity is controlled in native CODH to promote CO oxidation and CO2 reduction rather than deleterious hydrogen evolution.

Inverse ZrO2/Cu catalysts, where Zr oxide is deposited on Cu particles, show a high catalytic performance converting CO2 to methanol. We employ density functional theory (DFT) calculations to investigate the CO2 hydrogenation reaction mechanisms on a model of highly dispersed Zr oxide clusters on Cu (111). The exploration is not performed on a single active site configuration but across an ensemble of 83 formate configurations accessible under reaction conditions. Detailed reaction-pathway analysis reveals that structural sensitivity is pronounced, and only 10 of the catalyst configurations are significantly active across the full pathway. The turnover frequency of the studied inverse structures is largely determined by reaction steps after methoxy formation, rather than the formate hydrogenation steps, and the energy of the methoxy intermediate is a key reactivity descriptor. Two hypotheses are presented for the ensemble average activity: where the probabilities of site populations are determined at the formate intermediate, or at the methoxy resting state. The latter, compared to the former, drastically changes the site distribution, eliminating active structures and decreasing the average rate by a factor of 1000. Catalyst rigidity helps maintain activity by slowing down the structural evolution from the more active formate-bound states to the less active methoxy-bound states.

Nonoxidative coupling of methane represents a long-standing challenge in heterogeneous catalysis, as it requires activation of the carbon-hydrogen (C-H) bond, controlled carbon-carbon (C-C) bond formation, and effective hydrogen management without relying on oxidants. Here, we report a low-temperature C-H activation and nonoxidative C-C coupling of methane over atomically dispersed titanium-aluminum-boron nanopowder (Ti-Al-B NP) utilizing a catalytic microreactor coupled to synchrotron single-photon photoionization reflectron time-of-flight mass spectrometry. The soft-ionization, in situ probing method detects the nascent reaction products and radical intermediates under operando conditions, including methyl radical, C2 hydrocarbons, and molecular hydrogen. Methane activation is initiated at 800 K, approximately 700 K below the gas-phase decomposition threshold, leading predominantly to ethylene formation with selectivity reaching up to 78% among the C-C coupled products. Electronic structure calculations on model Ti-Al-B clusters elucidate a cooperative catalytic mechanism in which titanium enables methane adsorption and C-H activation, boron acts as a reversible hydrogen reservoir, and aluminum stabilizes methylene intermediates, thereby facilitating selective C-C coupling and dehydrogenation. These findings establish a distinct catalyst architecture for nonoxidative methane coupling based on earth abundant elements alternative to expensive platinum and other noble metal-containing conventional catalysts and provide molecular-level design principles for controlling dehydrogenation and subsequent C-C bond formation in challenging light alkane conversions.

We use first-principles calculations and chemical bonding analysis to investigate how the adsorption on topological insulators modifies the chemical properties of thin films of catalytic metals, Pt, Au, and Ag. Topological surface states (TSSs) present at the Fermi level and coinciding with the physical termination of the topological insulators are found to interact with the metal monolayers and themselves become modified by the adhesion, particularly in the case of relatively stronger Pt adhesion. The properties of the monolayers are, in turn, affected by the interaction with TSS. Specifically, the adsorption strengths of the typical catalytic intermediates exhibit important shifts that can lead to an enhanced catalytic reactivity. H is an adsorbate present in the hydrogen evolution reaction (HER) and thermal dehydrogenation, and its adsorption energy is often used as a descriptor of the activity. The bonding to the supported Pt film is slightly weaker than that to the Pt metal due to TSS involvement. This is expected to place the system closer to the apex of the catalytic volcano for the HER than Pt itself. The adsorption of CO on Au and Ag is, in contrast, strengthened by TSS, potentially opening an opportunity to electrochemically reduce CO-a process not achieved by bulk Au or Ag electrodes. We note that all interactions with the TSS play a perturbative role in binding. The metals provide electronic states deep below the Fermi level, facilitating the bonding mechanisms notorious for these adsorbates on the corresponding metals. TSS supply additional bonding and/or antibonding effects that are relatively weak but likely consequential for catalysis.

Boron-doped copper has recently emerged as an active and stable catalyst for the electrochemical reduction of CO2 to value-added C-2 products. Here, we develop a realistic model of CO electroreduction on surface borides of copper under operational conditions, taking into account the effects of electrode potential, electrolyte environment, and pH. We study the possible reconstruction of the electrocatalyst surface using grand canonical DFT and global optimization to obtain a potential-dependent grand canonical ensemble description of metastable, hydrogen-covered catalyst surfaces. Two key surface configurations, low H coverage (LC, -0.6 V-SHE) and high H coverage (HC, -0.8 V-SHE), dominate this ensemble, with the former being kinetically persistent and C-2 selective under strongly reducing conditions. Nonmetallic boron sites on the surface copper boride are found to bind CO more strongly than copper sites, and mechanistic investigation of CO electroreduction pathways presents a surprisingly unconventional case of boron-centered reactivity in contrast to typical copper-centered reactivity. Neighboring boron sites present along boron chains on the surface copper boride are found to facilitate C-C coupling, thereby driving the high C-2 selectivity of this electrocatalyst.

Electrochemical CO2 reduction (CO2RR) offers a promising strategy to recycle carbon by converting CO2 into valuable fuels and chemicals. So far, Cu-based catalysts remain the most effective for producing high-value multi-carbon products from CO2. Under the operating conditions of the CO2RR, Cu is known to undergo significant surface reconstruction. Furthermore, this reconstruction is crucial for creating the active sites for the CO2RR, whereas flat surfaces catalyze only the hydrogen evolution reaction (HER). This poses challenges for accurately elucidating the structure-activity relationship. To address this, recent research has employed CO as a probe molecule, and combined in situ surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) to reveal how surface reconstruction affects not only the macroscopic morphology but also the local active sites, adsorption of key intermediates, and the overall catalytic performance. A specific metric tracked in SERS studies is the intensity ratio of the Cu-CO stretching band to the CO rotational band, as it is believed to be related to the CO coverage. Here, we challenge this assumption. We combine grand canonical genetic algorithm (GCGA) global optimization with grand canonical density functional theory (GCDFT) calculations to find optimal accessible CO coverages under CO2RR conditions. Then, we use these structures to investigate how different surface roughness, facets, and CO adsorption sites influence the Raman spectra, and the intensity ratio of interest. We show that the changes in the Raman intensity ratio are not solely determined by CO coverage. The adsorption site has a significant influence on the spectral signature, while the realistic reconstruction of the Cu surface impacts the available sites in a potential-dependent manner. The local environment of the adsorbed CO, including the site, coverage, and secondary coordination sphere, affect the stretching and rotation mode frequencies and intensities. We conclude that the SERS signature, while it can be exceptionally useful, alone is insufficient to establish a rigorous, quantitative correlation between the surface coverage or density of species and the production rates of target products required for a clear structure-activity relationship.

Abstract Machine-learning-based modeling of molecular crystals is limited by representations that encode geometric structure while overlooking the electronic features that often govern solid-state behavior. We introduce a multimodal learning framework that integrates crystal graphs with solid-state Quantum Theory of Atoms in Molecules (QTAIM)-informed molecular graphs for enhanced predictions of solid-state properties. Our architecture employs modality-specific graph neural network encoders and a bidirectional gated fusion mechanism to capture complementary information between the two representations. When applied to band gap prediction in organic molecular crystals, the fused model outperforms geometry-only and molecular-only baselines. Analysis of the learned representations reveals that QTAIM descriptors contribute interpretable signals associated with intermolecular interactions and density redistribution within the crystal, highlighting the value of quantum-informed learning for advancing data-driven solid-state modeling.

Direct conversion of captured forms of carbon, or reactive carbon capture (RCC), presents an opportunity to reduce the energy intensity and cost of direct CO2 utilization from dilute sources. While amine-based sorbents effectively capture CO2, their use for RCC presents numerous challenges with typical pure metal catalysts used for electrochemical CO2 reduction (CO2R). Here, using both theory and experiments, we find that Ni-N-C single atom catalysts are effective for RCC conversion to CO using a diethanolamine sorbent, in contrast to pure metal catalysts. Computational analysis reveals that RCC can proceed directly through direct reduction of the sorbent-CO2 adduct or indirectly by C-N bond breaking facilitating CO2 adsorption and subsequent reduction. We find that the latter mechanism is most prevalent at low overpotentials where we experimentally observe RCC selectivity. We also find experimentally that the rate of CO production for RCC with Ni-N-C catalysts can exceed pure bicarbonate solutions at intermediate sorbent concentration (0.1-0.5 M DEA) under dilute (10-25%) streams of CO2 at low overpotentials. The coordination environment of Ni sites and the solution speciation influence their RCC activity, with changes in protonation to coordinating N/C atoms resulting in changing the RCC mechanism and consequent activity. In situ X-ray absorption spectroscopy and computational analysis reveal restructuring under RCC conditions due to hydrogen coadsorption with DEA that limits the stability of Ni-N-C catalysts. This work highlights the importance of carefully controlling the catalyst and solution environment to achieve active and stable RCC electrocatalysis.

Topological materials have recently been proposed as a new class of catalysts, where robust surface states near the Fermi level are expected to influence adsorption and reactivity. In this Letter, using first-principles calculations, we systematically investigate molecular adsorption on bismuth (Bi) slabs across a wide range of adsorbates, spanning both trivial and topological electronic regimes. We find that open-shell adsorbates strongly hybridize with both topological and trivial surface states near the Fermi energy. Although adsorption is primarily governed by conventional chemical bonding, we quantitatively assess how surface states modulate binding energetics by comparing slabs (with surface states) to a monolayer. The COHP analysis further confirms that surface-state hybridization strongly reshapes the bonding and antibonding contributions near the Fermi level, thereby modulating the adsorption energetics. This framework also qualitatively accounts for the distinct catalytic performance between bulk-like slabs and monolayer Bi. Overall, topological character appears to play a more indirect role, while a surface-state-centric perspective may provide a useful framework for understanding catalytic behavior.

Laser cooling of large, complex molecules is a long-standing goal, instrumental for enabling new quantum technology and precision measurements. A primary consideration for the feasibility of laser cooling, which determines the efficiency and technical requirements of the process, is the number of excited-state decay pathways leading to vibrational excitations. Therefore, the assessment of the laser-cooling potential of a molecule begins with estimate of the vibrational branching ratios of the first few electronic excited states theoretically to find the optimum cooling scheme. Such calculations, typically done within the Born-Oppenheimer and harmonic approximations, have suggested that one leading candidate for large, polyatomic molecule laser cooling, alkaline earth phenoxides, can most efficiently be laser cooled via the third electronically excited ( C) state. Here, we report the first detailed spectroscopic characterization of the C state in CaOPh and SrOPh. We find that nonadiabatic couplings between the that enable additional decay pathways. Based on the intensity ratio of these extra decay channels, we estimate a nonadiabatic coupling strength of similar to 0.1 cm-1. While this coupling strength is small, the large density of vibrational states available at photonic energy scales in a polyatomic molecule leads to significant mixing. Only the lowest excited stateA is exempt from this coupling because it is highly separated from the ground state. Thus, this result is expected to be general for large molecules and implies that only the lowest electronic excited state should be considered when judging the suitability of a molecule for laser cooling. A, B, and C states lead to substantial mixing, giving rise to vibronic states