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The surface structure and chemical properties of Y‐stabilized zirconia (YSZ) have been subjects of intense debate over the past three decades. However, a thorough understanding of chemical processes occurring at YSZ powders faces significant challenges due to the absence of reliable reference data acquired for well‐controlled model systems. Here, we present results from polarization‐resolved infrared reflection absorption spectroscopy (IRRAS) obtained for differently oriented, Y‐doped ZrO2 single‐crystal surfaces after exposure to CO and D2O. The IRRAS data reveal that the polar YSZ(100) surface undergoes reconstruction, characterized by an unusual, red‐shifted CO band at 2132 cm−1. Density functional theory calculations allowed to relate this unexpected observation to under‐coordinated Zr4+ cations in the vicinity of doping‐induced O vacancies. This reconstruction leads to a strongly increased chemical reactivity and water spontaneously dissociates on YSZ(100). The latter, which is an important requirement for catalysing the water‐gas‐shift (WGS) reaction, is absent for YSZ(111), where only associative adsorption was observed. Together with a novel analysis Scheme these reference data allowed for an operando characterisation of YSZ powders using DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy). These findings facilitate rational design and tuning of YSZ‐based powder materials for catalytic applications, in particular CO oxidation and the WGS reaction. [ABSTRACT FROM AUTHOR]

Hybrid density functional theory calculations are used to investigate different mechanisms of the isomerization of n-butane to isobutane via intermediate formation of olefins. The monomolecular mechanism for isomerization of butene and isobutene is found to be prevalent, with a Gibbs free energy barrier of 155 kJ/mol at 400°C, compared to the bimolecular mechanism (190 kJ/mol) due to less favorable entropy for the latter. Hydrogen transfer reactions that convert olefins into alkanes (and vice versa) are also included in the investigations, and show a free energy barrier of 203 kJ/mol for conversion of isobutene to isobutane. Additionally, a methyl transfer mechanism is discussed as a possible pathway for formation of C3 and C5 side products, in comparison to the bimolecular mechanism; the highest barrier of the initial methyl transfer is calculated to be 227 kJ/mol. We discuss the influence of entropy and anharmonicity on all mechanisms, stating that through the uncertainties in computational methods when calculating these systems, the calculated reaction barriers are likely to be overestimated here. [ABSTRACT FROM AUTHOR]

Due to its outstanding properties, graphene has emerged as one of the most promising 2D materials in a large variety of research fields. Among the available fabrication protocols, chemical vapor deposition (CVD) enables the production of high quality single-layered large area graphene. To better understand the kinetics of CVD graphene growth, multiscale modeling approaches are sought after. Although a variety of models have been developed to study the growth mechanism, prior studies are either limited to very small systems, are forced to simplify the model to eliminate the fast process, or they simplify reactions. While it is possible to rationalize these approximations, it is important to note that they have non-trivial consequences on the overall growth of graphene. Therefore, a comprehensive understanding of the kinetics of graphene growth in CVD remains a challenge. Here, we introduce a kinetic Monte Carlo protocol that permits, for the first time, the representation of relevant reactions on the atomic scale, without additional approximations, while still reaching very long time and length scales of the simulation of graphene growth. The quantum-mechanics-based multiscale model, which links kinetic Monte Carlo growth processes with the rates of occurring chemical reactions, calculated from first principles makes it possible to investigate the contributions of the most important species in graphene growth. It permits the proper investigation of the role of carbon and its dimer in the growth process, thus indicating the carbon dimer to be the dominant species. The consideration of hydrogenation and dehydrogenation reactions enables us to correlate the quality of the material grown within the CVD control parameters and to demonstrate an important role of these reactions in the quality of the grown graphene in terms of its surface roughness, hydrogenation sites, and vacancy defects. The model developed is capable of providing additional insights to control the graphene growth mechanism on Cu(111), which may guide further experimental and theoretical developments. [ABSTRACT FROM AUTHOR]

A frontier challenge in single‐atom (SA) catalysis is the design of fully inorganic sites capable of emulating the high reaction selectivity traditionally exclusive of organometallic counterparts in homogeneous catalysis. Modulating the direct coordination environment in SA sites, via the exploitation of the oxide support's surface chemistry, stands as a powerful albeit underexplored strategy. We report that isolated Rh atoms stabilized on oxygen‐defective SnO2 uniquely unite excellent TOF with essentially full selectivity in the gas‐phase hydroformylation of ethylene, inhibiting the thermodynamically favored olefin hydrogenation. Density Functional Theory calculations and surface characterization suggest that substantial depletion of the catalyst surface in lattice oxygen, energetically facile on SnO2, is key to unlock a high coordination pliability at the mononuclear Rh centers, leading to an exceptional performance which is on par with that of molecular catalysts in liquid media. [ABSTRACT FROM AUTHOR]

We report on an inverse model Cu/MgO methanol catalyst modified with 5 % zinc oxide at the Cu surface to element‐specifically probe the interplay of metallic copper and zinc oxide during reductive activation. The structure of copper and zinc was unraveled by in situ X‐ray diffraction (XRD) and in situ X‐ray absorption spectroscopy (XAS) supported by theoretical modelling of the extended X‐ray absorption fine structure and X‐ray absorption near‐edge structure spectra. Temperature‐programmed reduction in H2 during in situ XAS showed that copper was reduced starting at 145 °C. With increasing reduction temperature, zinc underwent first a geometrical change in its structure, followed by reduction. The reduced zinc species were identified as surface alloy sites, which coexisted from 200 °C to 340 °C with ZnO species at the copper surface. At 400 °C Zn−Cu bulk‐alloyed particles were formed. According to in situ XRD and in situ XAS, about half of the ZnO was not fully reduced, which can be explained by a lack of contact with copper. Our experimental results were further substantiated by density functional theory calculations, which verified that ZnO with neighboring Cu atoms reduced more easily. By combining these results, the distribution, phase and oxidation state of Zn species on Cu were estimated for the activated state of this model catalyst. This insight into the interplay of Cu and Zn forms the basis for deeper understanding the active sites during methanol synthesis. [ABSTRACT FROM AUTHOR]

The influence of the confinement imposed by eight different zeotypes on the formation of the alkoxides of 13 primary alcohols is studied using dispersion corrected density functional theory calculations with the PBE‐D3 functional. Adsorption energies of the alcohols are computed along with barriers for formation of the alkoxides, which is the first step of the stepwise dehydration mechanism. We find that variations in the adsorption and transition state energies are largely governed by van der Waals interactions between substrates and the zeolite framework. Trends between different reactants, on the other hand, are largely due to the size of the molecules, which can be described quantitatively by the number of atoms constituting them. We find that the stabilization of adsorbates is largest for frameworks that are neither too small, leading to repulsive interaction, nor too spacious leading only to weak interaction. [ABSTRACT FROM AUTHOR]

In contrast to catalytically active metal single atoms deposited on oxide nanoparticles, the crystalline nature of metal‐organic frameworks (MOFs) allows for a thorough characterization of reaction mechanisms. Using defect‐free HKUST‐1 MOF thin films, we demonstrate that Cu+/Cu2+ dimer defects, created in a controlled fashion by reducing the pristine Cu2+/Cu2+ pairs of the intact framework, account for the high catalytic activity in low‐temperature CO oxidation. Combining advanced IR spectroscopy and density functional theory we propose a new reaction mechanism where the key intermediate is an uncharged O2 species, weakly bound to Cu+/Cu2+. Our results reveal a complex interplay between electronic and steric effects at defect sites in MOFs and provide important guidelines for tailoring and exploiting the catalytic activity of single metal atom sites. [ABSTRACT FROM AUTHOR]

Zeolites are porous materials that are typically studied using periodic density functional theory (DFT). In this work we benchmark commonly used density functionals using cluster models for Brønsted acidic as well as copper substituted SSZ‐13 (H‐SSZ‐13 and Cu‐SSZ‐13). We find that for acid‐catalyzed reactions with relevance for the methanol‐to‐olefins process, barriers are the main challenge as they are commonly underestimated by DFT. For reactions involving Cu‐SSZ‐13 (commonly used for the selective catalytic reduction of NOx, SCR), reaction energies are already a challenge for most density functionals. Our results show that the widely used PBE‐D3 functional leads to mean absolute errors larger than 40 kJ/mol for barrier heights. Hybrid functionals show significant improvements with the best tested functional herein M06 having an error of only 7 kJ/mol. [ABSTRACT FROM AUTHOR]

The reaction mechanism of the synthesis of OMEs with homogeneous Brønsted acid catalysts from dimethoxy methane and trioxane is studied using MP2, density functional theory and implicit solvation models. Additionally, formaldehyde is considered as a reactant and we find its activation barriers for OME‐formation to be comparable with those for trioxane (around 80 kJ/mol). If trioxane is used as a reactant at room temperature, we find that its direct incorporation is more favorable than its decomposition to formaldehyde followed by stepwise reaction of formaldehyde. This is due to the higher stability of trioxane at room temperature. Computational Investigation: The reaction mechanism of the synthesis of OMEs with homogeneous Brønsted acid catalysts from dimethoxy methane and trioxane is studied using MP2, density functional theory and implicit solvation models. [ABSTRACT FROM AUTHOR]

Abstract: In this contribution, we investigate the initiation mechanism of the methanol-to-olefins process for the different zeotype materials, H-SSZ-13, H-ZSM-5, H-BEA and H-SAPO-34 using density functional theory. While the energetics differ between these materials, variations are systematic so that the relative ordering of the barriers remains the same. We hence predict that the initiation mechanism follows an identical path in all materials with similar rate-limiting steps. We show that the observed trends that have been found for the reaction barriers can be explained by differences in acidity and van-der-Waals interactions of the materials.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Electrochemical production of hydrogen peroxide (H2O2) from water oxidation could provide a very attractive route to locally produce a chemically valuable product from an abundant resource. Herein using density functional theory calculations, we predict trends in activity for water oxidation towards H2O2 evolution on four different metal oxides, i.e., WO3, SnO2, TiO2 and BiVO4. The density functional theory predicted trend for H2O2 evolution is further confirmed by our experimental measurements. Moreover, we identify that BiVO4 has the best H2O2 generation amount of those oxides and can achieve a Faraday efficiency of about 98% for H2O2 production. [ABSTRACT FROM AUTHOR]

Although large efforts have been dedicated to studying two-dimensional materials for catalysis, a rationalization of the associated trends in their intrinsic activity has so far been elusive. In the present work we employ density functional theory to examine a variety of two-dimensional materials, including, carbon based materials, hexagonal boron nitride ( h-BN), transition metal dichalcogenides (e.g. MoS, MoSe) and layered oxides, to give an overview of the trends in adsorption energies. By examining key reaction intermediates relevant to the oxygen reduction, and oxygen evolution reactions we find that binding energies largely follow the linear scaling relationships observed for pure metals. This observation is very important as it suggests that the same simplifying assumptions made to correlate descriptors with reaction rates in transition metal catalysts are also valid for the studied two-dimensional materials. By means of these scaling relations, for each reaction we also identify several promising candidates that are predicted to exhibit a comparable activity to the state-of-the-art catalysts. Graphical Abstract: Scaling relationship for the chemisorption energies of OH* and OOH* on various 2D materials. [ABSTRACT FROM AUTHOR]

The electrochemical reduction (electroreduction) of CO2 to formic acid (HCOOH) and its competing reactions, that is, the electroreduction of CO2 to CO and the hydrogen evolution reaction (HER), on twenty-seven different metal surfaces have been investigated using density functional theory (DFT) calculations. Owing to a strong linear correlation between the free energies of COOH* and H*, it seems highly unlikely that the electroreduction of CO2 to HCOOH via the COOH* intermediate occurs without a large fraction of the current going to HER. On the other hand, the selective electroreduction of CO2 to HCOOH seems plausible if the reaction occurs via the HCOO* intermediate, as there is little correlation between the free energies of HCOO* and H*. Lead and silver surfaces are found to be the most promising monometallic catalysts showing high faradaic efficiencies for the electroreduction of CO2 to HCOOH with small overpotentials. Our methodology is widely applicable, not only to metal surfaces, but also to other classes of materials enabling the computational search for electrocatalysts for CO2 reduction to HCOOH. [ABSTRACT FROM AUTHOR]

During A–H (A = C, N, O) bond cleavage on O* or OH* pre-covered (111) surfaces, the oxygen species play the role of modifying the reaction energy by changing the species involved in the initial and final states of the reaction. [ABSTRACT FROM AUTHOR]

This paper reports the use of a combination of density functional theory and microkinetic modelling to establish trends in the hydrodeoxygenation rates and selectivites of transition metal surfaces. Biomass and biomass-derived chemicals often contain large fractions of oxygenates. Removal of the oxygen through hydrotreating represents one strategy for producing commodity chemicals from these renewable materials. Using the model developed in this paper, we predict ethylene glycol hydrodeoxygenation selectivities for transition metals that are consistent with those reported in the literature. Furthermore, the insights discussed in this paper present a framework for designing catalytic materials for facilitating these conversions efficiently. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT calculations of the paring mechanism for H-ZSM-5, H-SSZ-24 and H-SAPO-34. • paring mechanism found relevant for all zeotypes. • lowest barriers found for H-SAPO-34. The paring mechanism, which belongs to the aromatic cycle of the methanol-to-olefins process and produces propene, is investigated for H-ZSM-5 (MFI structure), H-SSZ-24 (AFI structure) and H-SAPO-34 (CHA structure) with the heptamethylbenzylium cation as a co-catalyst using DFT and ab initio calculations. We focus on the mechanistic pathway of the paring mechanism that we have proposed recently for H-SSZ-13 [Catal. Sci. Technol. 12 (2022) 3516–3523.], in which ring contraction occurs from hexamethylmethylenecyclohexadiene and the resulting five-membered ring keeps an unsaturated methylene group throughout the process, leading to tetramethylfulvene as the intermediate after propene elimination. The highest free energy barriers (at 400 °C) for this mechanism are found to be 139 kJ/mol, 156 kJ/mol and 167 kJ/mol for H-SAPO-34, H-SSZ-24 and H-ZSM-5, respectively, compared to 127 kJ/mol for H-SSZ-13. All these barriers are low enough to be kinetically relevant and can thus explain the observed formation of propene as one of the main products of the MTO-process in these zeolites. The barriers for polymethylbenzene methylation to recover the active species are higher than the barriers for the paring mechanism in all zeolites (164 kJ/mol, 187 kJ/mol and 189 kJ/mol for H-SAPO-34, H-SSZ-24 and H-ZSM-5, compared to 163 kJ/mol for H-SSZ-13). The lowest barriers are found for H-SAPO-34, which is often the commercial catalyst in methanol-to-propene plants. [ABSTRACT FROM AUTHOR]

A new method for computational catalyst screening that is based on the concept of the degree of rate control (DRC) is introduced. It starts by developing a full mechanism and microkinetic model at the conditions of interest for a reference catalyst (ideally, the best known material) and then determines the degrees of rate control of the species in the mechanism (i.e., all adsorbed intermediates and transition states). It then uses the energies of the few species with the highest DRCs for this reference catalyst as descriptors to estimate the rates on related materials and predict which are most active. The predictions of this method regarding the relative rates of twelve late transition metals for methane steam reforming, using the Rh(2 1 1) surface as the reference catalyst, are compared to the most commonly-used approach for computation catalyst screening, the Nørskov–Bligaard (NB) method which uses linear scaling relationships to estimate the energies of all adsorbed intermediates and transition states. It is slightly more accurate than the NB approach when the metals are similar to the reference metal (<0.5 eV different on a plot where the axes are the bond energies to C and O adatoms), but worse when too different from the reference. It is computationally faster than the NB method when screening a moderate number of materials (<100), thus adding a valuable complement to the NB approach. It can be implemented without a microkinetic model if the degrees of rate control are already known approximately, e.g., from experiments. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory (DFT) and ab initio thermodynamics are applied in order to investigate the most stable surface and subsurface terminations of Mo2C(001) as a function of chemical potential and in the presence of syngas. The Mo-terminated (001) surface is then used as a model surface to evaluate the thermochemistry and energetic barriers for key elementary steps in syngas reactions. Adsorption energy scaling relations and Brønsted–Evans–Polanyi relationships are established and used to place Mo2C into the context of transition metal surfaces. The results indicate that the surface termination is a complex function of reaction conditions and kinetics. It is predicted that the surface will be covered by either C2H2 or O depending on conditions. Comparisons with transition metals indicate that the Mo-terminated Mo2C(001) surface exhibits carbon reactivity similar to transition metals such as Ru and Ir, but is significantly more reactive toward oxygen. This explains some previous observations for Mo2C catalysts and suggests that Mo2C may exhibit unique and potentially useful reactivity or selectivity patterns. [Copyright &y& Elsevier]

The diffusion barriers of organic molecules through the pores of the zeolite H-SSZ-13 are investigated using periodic DFT calculations at the PBE-D3 level of theory. We calculate the diffusion barriers relative to the most stable adsorbed state on the acid site of the zeolite and find that barriers range from ~70 kJ/mol for smaller molecules such as ethene and propene up to 350 kJ/mol for durene, the largest molecule investigated here. For larger molecules, the diffusion barriers can be correlated with the vdW-radius of the diffusing molecules. For smaller molecules, which generally have smaller diffusion barriers, there is no clear correlation between the barrier and the vdW-radius. Here, the strength of adsorption at the acid site is also extremely important in determining the diffusion barrier. [ABSTRACT FROM AUTHOR]

Direct dehydrogenation of methanol to produce anhydrous formaldehyde is investigated using periodic density functional theory (DFT) and combining the microkinetic model to estimate rates and selectivities on stepped (211) surfaces under a desired reaction condition. Binding energies of reaction intermediates and transition state energies for each elementary reaction can be accurately scaled with CHO and OH binding energies as the only descriptors. Based on these two descriptors, a steady-state microkinetic model is constructed with a piecewise adsorbate–adsorbate interaction model that explicitly includes the effects of adsorbate coverage on the rates and selectivities as well as the volcano plots are obtained. Our results show that most of the stepped (211) pure-metallic surfaces such as Au, Pt, Pd, Rh, Ru, Ni, Fe, and Co are located in a region of low activity and selectivity toward CH 2 O production due to higher rate for CH 2 O dehydrogenation than CH 2 O desorption. The selectivities toward CH 2 O production on Zn, Cu, and Ag surfaces are located on the boundary between the high and low selectivity regions. To find suitable catalysts for anhydrous CH 2 O production, a large number of A 3 B-type transition metal alloys are screened based on their predicted rates and selectivities, as well as their estimated stabilities and prices. We finally propose several promising candidates for the dehydrogenation of CH 3 OH. [ABSTRACT FROM AUTHOR]

We present a literature collection of experimental adsorption energies over late transition metal surfaces for systems where we believe the energy measurements are particularly accurate, and the atomic-scale adsorption geometries are particularly well established. We propose that this could become useful for benchmarking theoretical methods for calculating adsorption processes. We compare the experimental results to six commonly used electron density functionals, including some (RPBE, BEEF-vdW) which were specifically developed to treat adsorption processes. The comparison shows that there is ample room for improvements in the theoretical descriptions. [ABSTRACT FROM AUTHOR]

We introduce a general method for estimating the uncertainty in calculated materials properties based on density functional theory calculations. We illustrate the approach for a calculation of the catalytic rate of ammonia synthesis over a range of transition-metal catalysts. The correlation between errors in density functional theory calculations is shown to play an important role in reducing the predicted error on calculated rates. Uncertainties depend strongly on reaction conditions and catalyst material, and the relative rates between different catalysts are considerably better described than the absolute rates. We introduce an approach for incorporating uncertainty when searching for improved catalysts by evaluating the probability that a given catalyst is better than a known standard. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we examine the thermochemistry of methanol synthesis intermediates using density functional theory (DFT) and analyze the methanol synthesis reaction network using a steady-state micro-kinetic model. The energetics for methanol synthesis over Zn-terminated ZnO (0001) are obtained from DFT calculations using the RPBE and BEEF-vdW functionals. The energies obtained from the two functionals are compared and it is determined that the BEEF-vdW functional is more appropriate for the reaction. The BEEF-vdW energetics are used to construct surface phase diagrams as a function of CO, H2O, and H2 chemical potentials. The computed binding energies along with activation barriers from literature are used as inputs for a mean-field micro-kinetic model for methanol synthesis including the CO and CO2 hydrogenation routes and the water–gas shift reaction. The kinetic model is used to investigate the methanol synthesis rate as a function of temperature and pressure. The results show qualitative agreement with experiment and yield information on the optimal working conditions of ZnO catalysts. [Copyright &y& Elsevier]

Highlights: [•] Trends in catalytic activity for CO methanation are examined for transition metal surfaces. [•] We model adsorbate–adsorbate interactions between methanation intermediates on multiple sites. [•] DFT and microkinetic modeling predicts the CO methanation rates of transition metals. [•] Trends in methanation rates are preserved when interaction effects are included. [•] Interactions were found to increase the rates of the most reactive metals. [Copyright &y& Elsevier]

Abstract: The absorption of sulfur on the Ni(100) surface has been reported to influence its product selectivity for methanol dehydrogenation. While dehydrogenation on the clean Ni(100) surface primarily produces a mixture of carbon monoxide and hydrogen, preadsorption of 0.25–0.33 monolayers of sulfur shifts the selectivity to mainly formaldehyde and hydrogen. Density functional theory calculations of clean and sulfur-modified Ni(100) surfaces demonstrate that sulfur destabilizes methanol dehydrogenation reaction intermediates in a manner consistent with this shift in selectivity. Microkinetic modeling of the reaction system further indicates that these changes alter the reaction selectivities from CO to CH2O production in the steady state. The reaction selectivities of metal alloy surfaces, which also have heterogeneous surface morphologies, are hypothesized to be influenced in a similar manner as these S/Ni(100) surfaces. [Copyright &y& Elsevier]

Abstract: This paper demonstrates the utility of a new tool for mapping out the activities and selectivities of transition metals for catalytic reactions. A database of reaction and activation energies has recently been made available to the public via a web-based application called “CatApp”. Combined with microkinetic modeling, CatApp allows researchers to gain insights into the energetics and mechanisms of a given catalytic reaction. This paper illustrates this utility using the anhydrous dehydrogenation of methanol to formaldehyde as an example. There are presently no stable catalysts for this potentially important process. The model developed in this paper presents possible explanations for this observation and suggests certain properties that would be needed to design a good catalyst. [Copyright &y& Elsevier]