Fe-based catalysts are highly selective for the hydrodeoxygenation of biomass-derived oxygenates but are prone to oxidative deactivation. Promotion with a noble metal has been shown to improve oxidative resistance. The chemical properties of such bimetallic systems depend critically on the surface geometry and spatial configuration of surface atoms in addition to their coverage (i.e., noble metal loading), so these aspects must be taken into account in order to develop reliable models for such complex systems. This requires sampling a vast configurational space, which is rather impractical using density functional theory (DFT) calculations alone. Moreover, "DFT-based" models are limited to length scales that are often too small for experimental relevance. Here, we circumvent this challenge by constructing DFT-parametrized lattice gas cluster expansions (LG CEs), which can describe these types of systems at significantly larger length scales. Here, we apply this strategy to Fe(100) promoted with four technologically relevant precious metals: Pd, Pt, Rh, and Ru. The resultant LG CEs have remarkable predictive accuracy, with predictive errors below 10 meV/site over a coverage range of 0 to 2 monolayers. The ground state configurations for each noble metal were identified, and the analysis of the cluster energies reveals a significant disparity in their dispersion tendency.

Single-site copper-based catalysts have shown remarkable activity and selectivity for a variety of reactions. However, deactivation by sintering in high-temperature reducing environments remains a challenge and often limits their use due to irreversible structural changes to the catalyst. Here, we report zeolite-based copper catalysts in which copper oxide agglomerates formed after reaction can be repeatedly redispersed back to single sites using an oxidative treatment in air at 550 degrees C. Under different environments, single-site copper in Cu-Zn-Y/deAlBeta undergoes dynamic changes in structure and oxidation state that can be tuned to promote the formation of key active sites while minimizing deactivation through Cu sintering. For example, single-site Cu2+ reduces to Cu1+ after catalyst pretreatment (270 degrees C, 101 kPa H-2) and further to Cu-0 nanoparticles under reaction conditions (270-350 degrees C, 7 kPa EtOH, 94 kPa H-2) or accelerated aging (400-450 degrees C, 101 kPa H-2). After regeneration at 550 degrees C in air, agglomerated CuO was dispersed back to single sites in the presence and absence of Zn and Y, which was verified by imaging, in situ spectroscopy, and catalytic rate measurements. Ab initio molecular dynamics simulations show that solvation of CuO monomers by water facilitates their transport through the zeolite pore, and condensation of the CuO monomer with a fully protonated silanol nest entraps copper and reforms the single-site structure. The capability of silanol nests to trap and stabilize copper single sites under oxidizing conditions could extend the use of single-site copper catalysts to a wider variety of reactions and allows for a simple regeneration strategy for copper single-site catalysts.

With airlines committed to drastically reduce their carbon footprint by 2050, producing jet fuel from renewable ethanol is of particular interest. Recently, we reported on an Ag/ZrO2/SBA-16 catalyst that is very effective for directly converting ethanol into to n-butene-rich olefins jet fuel precursors (i.e., 88% at full conversion). Here, we report on a Cu/ZrO2/SBA-16 catalyst that presents remarkable olefins selectivity (i.e., 89% at 96% conversion) and enhanced stability as compared to Ag/ZrO2/SBA-16 catalyst. Under severe operating conditions a conversion loss < 10% was observed with the Cu/ZrO2/SBA-16 catalyst as compared to a 50% loss of conversion with the Ag/ZrO2/SBA-16 catalyst. Combined experimental and computational tools revealed that replacing Ag with Cu shifts the reaction pathway of crotonaldehyde hydrogenation from 1,3-butadiene (i.e., coke precursor) production to butyraldehyde formation. Experiments conducted with 4%Cu/4%ZrO2 supported on SBA-16, dealuminated zeolite Beta, and aluminum silicate revealed the performance and stability advantage of the SBA-16-supported catalyst.

Boron oxide-based catalysts have been shown to be both active and selective for driving the oxidative dehydrogenation of propane (ODHP) without the use of metal promoters. However, this reaction occurs at temperatures where boron oxide melts, challenging experimental identification of the molecular structures within the boron oxide phase under reaction conditions and thus hindering the understanding of its active sites and reaction mechanism(s). By combining density functional theory computations, ab initio molecular dynamics simulations, in situ Raman characterization, and microkinetic modeling, we propose that dimerized di-coordinated boron sites (>B-B<)- dynamically formed in liquid boron oxide-are the active species for O-2 activation under reaction conditions. The resulting peroxylike species (>B-O-O-B<) is then responsible for propane activation but is a moderate oxidant for ODHP and thus inert to propene. These peroxy-like structures rapidly activate propane, homolytically cleaving the >B-O-O-B< bond, producing a propyl radical and a >B-O-center dot dangling bond. These > B-O-center dot originate from the >B-O-O-B< sites as well as the liquid B2O3 structure itself and play a critical role in the abstraction of H atoms from propane and propyl. In fact, microkinetic modeling reveals that the formation of adsorbed C3H7* radicals is the main rate-controlling step due to the highly endergonic adsorption of propane into the system. Otherwise, the only activated processes were found to be the dehydration steps that lead to water formation, which exhibit an intriguing dependence on the concentration of surface hydroxyl species. These findings provide significant insights into the ODHP mechanisms on boron-based catalysts and emphasize the importance of understanding the liquid nature of the oxide to account for its catalytic activity.

Journal Article Investigation of Cu Species in Dealuminated Beta Zeolite Studied by Operando Closed-Cell Gas Reaction STEM Get access Kinga A Unocic, Kinga A Unocic Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA Corresponding author: unocicka@ornl.gov Search for other works by this author on: Oxford Academic Google Scholar Stephen C Purdy, Stephen C Purdy Manufacturing Science Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Search for other works by this author on: Oxford Academic Google Scholar Lawrence F Allard, Lawrence F Allard Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Search for other works by this author on: Oxford Academic Google Scholar Gregory B Collinge, Gregory B Collinge Physical and Computational Sciences, Pacific Northwest National Laboratory, Richland, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Junyan Zhang, Junyan Zhang Manufacturing Science Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Search for other works by this author on: Oxford Academic Google Scholar Shivangi N Borate, Shivangi N Borate The University of Alabama, Tuscaloosa, Alabama, USA Search for other works by this author on: Oxford Academic Google Scholar Qiyuan Wu, Qiyuan Wu National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA Search for other works by this author on: Oxford Academic Google Scholar Evan C Wegener, Evan C Wegener Chemical Sciences and Engineering, Argonne National Laboratory, Argonne, IL, USA Search for other works by this author on: Oxford Academic Google Scholar Nohor “River” Samad, Nohor “River” Samad The University of Alabama, Tuscaloosa, Alabama, USA Search for other works by this author on: Oxford Academic Google Scholar Susan Habas, Susan Habas National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA Search for other works by this author on: Oxford Academic Google Scholar ... Show more Theodore R Krause, Theodore R Krause Chemical Sciences and Engineering, Argonne National Laboratory, Argonne, IL, USA Search for other works by this author on: Oxford Academic Google Scholar James W Harris, James W Harris The University of Alabama, Tuscaloosa, Alabama, USA Search for other works by this author on: Oxford Academic Google Scholar Mal-Soon Lee, Mal-Soon Lee Physical and Computational Sciences, Pacific Northwest National Laboratory, Richland, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Vassiliki A Glezakou, Vassiliki A Glezakou Physical and Computational Sciences, Pacific Northwest National Laboratory, Richland, WA, USAChemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Search for other works by this author on: Oxford Academic Google Scholar Roger Rousseau, Roger Rousseau Physical and Computational Sciences, Pacific Northwest National Laboratory, Richland, WA, USAChemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Search for other works by this author on: Oxford Academic Google Scholar Andrew D Sutton, Andrew D Sutton Manufacturing Science Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Search for other works by this author on: Oxford Academic Google Scholar Zhenglong Li Zhenglong Li Manufacturing Science Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 1614–1615, https://doi.org/10.1093/micmic/ozad067.829 Published: 22 July 2023

Understanding the adsorption and reactivity of carboxylic acids on oxide surfaces is of great interest in catalysis for biomass upgrading via ketonization, a carbon–carbon coupling reaction. Herein, we investigate the adsorption and reaction of acetic acid on anatase TiO2(101) using scanning tunneling microscopy, infrared spectroscopy, temperature programmed reaction, and density functional theory calculations. We demonstrate the adsorption of acetic acid can form two intermediates: (1) dissociated, bidentate acetate with an associated bridging hydroxyl, and (2) molecular, monodentate acetic acid. The coexistence of ordered phases with increasing monolayer (ML) saturation coverages consisting of (1) pure acetate (0.5 ML), (2) mixed acetate/acetic acid (0.67 ML), (3) mixed acetate/acetic acid (1.0 ML) and (4) pure acetic acid demonstrates similar energetics for both acetate and acetic acid species. Under ultra-high vacuum conditions, the presence of both monodentate acetic acid and bidentate acetate was observed below room temperature, while solely bidentate acetate was observed up to 575 K. The deprotonation of acetic acid produces water at 280 K, while the thermal decomposition of bidentate acetate produces ketene and acetic acid at 645 K. This model study provides detailed insight into the stability and reactivity of carboxylic acid surface-bound intermediates, which could participate during ketonization reactions for biomass upgrading.

The dynamics of reactive intermediates are important in catalysis for understanding transient species, which can drive reactivity and the transport of species to reaction centers. In particular, the interplay between surface-bound carboxylic acids and carboxylates is important for numerous chemical transformations, including CO2 hydrogenation and ketonization. Here, we investigate the dynamics of acetic acid on anatase TiO2(101) using scanning tunneling microscopy experiments and density functional theory calculations. We demonstrate the concomitant diffusion of bidentate acetate and a bridging hydroxyl and provide evidence for the transient formation of molecular monodentate acetic acid. The diffusion rate is strongly dependent on the position of hydroxyl and adjacent acetate(s). A facile three-step diffusion process is proposed consisting of acetate and hydroxyl recombination, acetic acid rotation, and acetic acid dissociation. This study clearly demonstrates that the dynamics of bidentate acetate could be important in forming monodentate species, which are proposed to drive selective ketonization.

The promise of lattice gas (LG) cluster expansions (CEs) is that they can describe a given system property to any level of accuracy since the orthogonal "cluster basis functions" span the complete space of available configurations. Such an approach can be constructed to an arbitrarily large surface of a finite number of distinct adsorption sites. Unfortunately, this is only true for the case of an ideal, fixed lattice decorated with components at precise lattice points (the lattice "sites") with no distortions or relaxations subsequently allowed. Since most systems, and surfaces specifically, do not conform to such an ideal set of constraints, errors in LG CEs must be expected or CE convergence severely hampered. Beyond this, numerical errors in the provided data can complicate the proper construction of a truly predictive and/or physically significant CE. We show here how reliance on typical statistical tools like confidence intervals cannot be expected to provide an accurate representation of the uncertainty of effective cluster interactions (ECIs) in the CE due to the nature of the target ab initio data and the nature of CEs themselves. We develop a method for estimating these errors that does not rely on statistical assumptions about the model or data. We then use these ECI errors to quantify fundamental consequences on the uncertainty of ECIs in CEs built from O/Fe(100) data whose surface and adsorbates have been allowed to relax in a typical manner and from O/Fe(100) data whose surface and adsorbates are fixed in ideal lattice positions. We also quantify the effect of using a different density functional theory exchange-correlation functional, using these ECI errors to assess the significance in any deviations. In both cases, our method is shown to have remarkable utility in the quantification of errors in the ECIs of CEs. While we stick to the lattice gas convention in this work, the method is equally applicable to the Ising convention or, in principle, any linear model of sufficient complexity.

Enhanced sampling ab initio simulations enable to study chemical phenomena in catalytic systems including thermal effects & anharmonicity, & collective dynamics describing enthalpic & entropic contributions, which can significantly impact on reaction free energy landscapes.

When chemical reactions are accelerated by a catalyst, entropy differences between reactants and their transient intermediates can be the driving force behind the promotion or inhibition of desired and parasitic chemical pathways. Understanding and controlling catalytic processes therefore requires both a fundamental and practicable understanding of entropy in addition to enthalpy. In unstructured media such as the vapor phase equilibrated with sparsely covered surfaces, entropy can be adequately accounted for by well-established approaches based on translational, rotational, and harmonic vibrational partition functions. However, these approximations become inadequate in more complex condensed phase environments, e.g., solid-liquid interfaces of confined reaction spaces. In this chapter, we provide an overview of the state-of-art in the computational quantification of entropy and its known ramifications on catalysis. The fundamental roles of thermodynamics and kinetics in catalysis are covered in enough detail to appreciate and contextualize the computational methods employed to compute chemically accurate estimates of entropy. These methods are discussed in appropriate detail and range from the ubiquitous harmonic oscillator approximation where entropy unrelated to high frequency oscillations is typically underestimated, to enhanced free energy sampling with molecular dynamics where the desired accuracy must be weighed against the associated computational cost of obtaining it. The rising importance of machine learning and artificial intelligence in accelerating methodological progress in this field is touched upon, as well. Finally, applications, successes, and pitfalls of using these methods are provided to showcase past and present accomplishments while clarifying where improvements in both understanding and methodology are still needed.

It is well known that heterogenous catalysts exhibit a distribution of sites/structures, some more active than others but more than one often being important to the underlying reaction mechanism(s). The inclusion of this reality in mean field microkinetic models has been largely avoided in favor of lattice-based models like cluster expansions where in principle different types of sites can be explicitly defined. Here, we develop a thermodynamically self-consistent theory of multi-site microkinetics from the first principles of statistical mechanics to show how multiple site types can be represented in mean field microkinetic models. The theory incorporates local enthalpies and entropies, lateral molecular interactions, and global entropy; generating thermodynamic activities for any number of site types that deviate significant from those of idealized models. We provide the resultant rate expressions for rates of adsorption/desorption and surface diffusion between the site types. Contrary to what is typically assumed, even when a species has access to many different sites or binding configurations, only one rate, which is driven by the average adlayer chemical potential, can be defined for desorption from the surface. The approach in this work correctly describes adsorption/desorption and diffusion for a multi-site model of a heterogenous catalyst and differs from the commonly used law of mass action.

Requiring catalysts to be both active yet stable over long periods of time under variable reaction conditions including high and low temperatures is a daunting challenge due to the almost mutual exclusivity of these constraints. Using CO oxidation as a probe reaction, we demonstrate that thermally stable single atom copper catalysts prepared by high-temperature synthesis (atom trapping) on ceria can achieve this feat by allowing modulation of the Cu charge state through facile charge transfer between the active site and the support. This provides the catalysts with an ability to activate either lattice or adatom oxygen atoms, accessing additional reaction channels as the catalyst environment changes. Such adaptability allows dynamic response of such catalysts, enabling them to remain active under variable reaction conditions. The inherent stability of the catalyst arises from the enhanced strength of the Cu-O interactions established by high-temperature synthesis and remains stable even as the Cu oxidation state varies, effectively halting sintering and deactivation. As we show here, one can circumvent the dilemma of designing catalysts that are simultaneously active and stable by matching the redox properties of the active site and support and establishing an environmental adaptability into the active sites.

The specific aim of this project is to develop a comprehensive understanding of cheaper and more stable methane and carbon dioxide reforming catalysts with an optimal introduction of steam to reduce carbon deposits that typically prevent the catalytic systems from transferring to commercial implementation. The work was proposed as a two-year project with the end goal of to show a reliable catalyst system run for at least 400 hours at temperatures less than 800 °C with less than 5% loss of activity of the catalyst and a carbon monoxide to hydrogen product ratio of at least 1:1. The project went for one-year and met the end of year milestone by developing two strategies (use of a cerium co-catalyst and introducing 5% water) that reduced the carbon deposition rates by at least 20% relative to the baseline 10% Ni MgAlO methane reforming of CO2 at < 800 °C in order to shown technical feasibility of the concept.

Hierarchically ordered oxides are of critical importance in material science and catalysis. Unfortunately, the design and synthesis of such systems remains a key challenge to realizing their potential. In this study, we demonstrate how the deposition of small oligomeric (MoO3)1-6 clusters-formed by the facile sublimation of MoO3 powders-leads to the self-assembly of locally ordered arrays of immobilized mono-oxo (MoO3)1 species on anatase TiO2(101). Using both high-resolution imaging and theoretical calculations, we reveal the dynamic behavior of the oligomers as they spontaneously decompose at room temperature, with the TiO2 surface acting as a template for the growth of this hierarchically structured oxide. Transient mobility of the oligomers on both bare and (MoO3)1-covered TiO2(101) areas is identified as key to the formation of a complete (MoO3)1 overlayer with a saturation coverage of one (MoO3)1 per two undercoordinated surface Ti sites. Simulations reveal a dynamic coupling of the reaction steps to the TiO2 lattice fluctuations, the absence of which kinetically prevents decomposition. Further experimental and theoretical characterizations demonstrate that (MoO3)1 within this material are thermally stable up to 500 K and remain chemically identical with a single empty gap state produced within the TiO2 band structure. Finally, we see that the constituent (MoO3)1 of this material show no proclivity for step and defect sites, suggesting they can reliably be grown on the (101) facet of TiO2 nanoparticles without compromising their chemistry.

Significance The design and synthesis of hierarchically ordered oxides remains a critical challenge in material science and catalysis. Here, we demonstrate that well-ordered homotopic arrays of mono-oxo (MoO 3 ) 1 can be easily prepared on anatase TiO 2 (101) via the deposition of (MoO 3 ) n oligomers. As revealed by our combined experiential and theoretical studies, the oligomers spontaneously decompose and self-assemble into chemically identical and thermally stable monomers. The oligomer decomposition is permitted at room temperature due to the dynamic coupling of decomposition steps to the lattice phonons of TiO 2 . We identify transient mobility of the oligomers as key to the self-assembly of the complete overlayer. The ease of preparation and thermal stability of this atomically precise system makes it highly suitable for a broad range of applications.

The analogy between single atom catalysts (SACs) and molecular catalysts predicts that the specific catalytic activity of these systems is constant. We provide evidence that this prediction is not necessarily true. As a case in point, we show that the specific activity over ceria5 supported single Pd atoms linearly increases with metal atom density, originating from the cumulative enhancement of lattice oxygen mobility. The long-range electrostatic fingerprints (~1.5 nm) around each Pd site overlap with each other as surface Pd density increases, resulting in the observed deviation from constant specific activity. These cooperative effects exhaust previously active O atoms above a certain Pd density, leading to their permanent 10 removal and consequent drop in reaction rate. The findings of our combined experimental and computational study show that the specific catalytic activity of reducible oxide-supported single atom catalysts can be tuned by varying the surface density of single metal atoms.

Wie bei einem Billardspiel können Einzelatomkatalysatoren zu neuen und aufregenden katalytischen Reaktionspfaden führen. Ähnlich wie im Spiel beeinflussen das Substrat, die Einzelatomdichte und die Atomposition den Reaktionspfad und das Ergebnis. Sung June Cho, Roger Rousseau, Janos Szanyi, Ja Hun Kwak et al. stellen in ihrem Forschungsartikel auf S. 22951 eine kombinierte experimentelle und theoretische Studie vor, die die Rolle von Pd-Einzelatomen auf CeO2 und die elektronischen Effekte in der CO-Oxidation beleuchtet. Graphik: C. Johnson und V.-A. Glezakou (PNNL).

The high activity and selectivity of Fe-based heterogeneous catalysts toward a variety of reactions that require the breaking of strong bonds are offset in large part by their considerable instability with respect to oxidative deactivation. While it has been shown that the stability of Fe catalysts is considerably enhanced by alloying them with precious metals (even at the single-atom limit), rational design criteria for choosing such secondary metals are still missing. Since oxidative deactivation occurs due to the strong binding of oxygen to Fe and reduction by adsorbed hydrogen mitigates the deactivation, we propose here to use the binding affinity of oxygen and hydrogen adatoms as the basis for rational design. As it would also be beneficial to use cheaper secondary metals, we have scanned over a large subset of 3d-5d mid-to-late transition metal single atoms and computationally determined their effect on the oxygen and hydrogen adlayer binding as a function of chemical potential and adsorbate coverage. We further determine the underlying chemical origins that are responsible for these effects and connect them to experimentally tunable quantities. Our results reveal a reliable periodic trend wherein oxygen binding is weakened greatest as one moves right and down the periodic table. Hydrogen binding shows the same trend only at high (but relevant) coverages and otherwise tends to have its binding slightly increased in all systems. Trends with secondary metal coverage are also uncovered and connected to experimentally tunable parameters.

In catalysis, MgO is often used to modify the acid-base properties of support oxides and to stabilize supported metal atoms and particles on oxides. In this study, we show how the sublimation of MgO powder can be used to deposit MgO monomers, hither on anatase TiO2(101). A combination of x-ray electron spectroscopy, high-resolution scanning tunneling microscopy, and density functional theory is employed to gain insight into the MgO monomer binding, electronic and vibrational properties, and thermal stability. In the most stable configuration, the Mg and O of the MgO monomer bind to two surface oxygens and one undercoordinated surface titanium, respectively. The additional binding weakens the Mg-O monomer bond and makes Mg more ionic. The monomers are thermally stable up to 600 K, where the onset of diffusion into the TiO2 bulk is observed. The monomeric MgO species on TiO2(101) represent an ideal atomically precise system with modified acid-base properties and will be employed in our future catalytic studies.

Ethanol is an important C-2 platform molecule for producing value-added chemicals and distillate hydrocarbon fuels (e.g., jet and diesel). Among these, catalytic upgrading of ethanol to butenes can generate valuable commodity chemicals (e.g., 1-butene) and provide C-4 olefin intermediates that can be further upgraded to jet/diesel fuels. Two-dimensional (2D) zeolites offer hierarchical mesoporous structures, leading to improved mass transport and reduced diffusion length, which can help to address the coking challenges faced by ethanol conversion to hydrocarbons over three-dimensional (3D) zeolites. In this study, we investigate the acidcatalyzed conversion of ethanol to 1-butene over the Bronsted acid sites (BAS) in 2D-pillared MFI zeolite (2D-PMFI) using ab initio molecular dynamics (AIMD) simulations, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and calorimetric measurements. A detailed thermodynamic analysis, using quasi-harmonic approximation (QHA), on the Gibbs free-energy pathway of ethanol conversion shows that the consideration of entropy is critical to accurately capture the detailed thermodynamic profiles. Employing the Blue Moon ensemble method, the formation of framework-bound butoxide from ethoxy and ethene is found to be the likely rate- determining step (RDS), proceeding via a stepwise mechanism. The reactivity of 2D-PMFI can be further tuned by manipulating RDS through careful control of the number of BAS and operating temperatures. The calculated vibrational density of states (VDOS) validate the structural models of adsorbed ethanol by comparing with the experimental DRIFTS measurements. Overall, our study provides mechanistic insights into ethanol upgrading over the 2D-PMFI and shows the importance of evaluating entropic effects in such a confined system.