Publications by authors named "Felix Studt"

A benchmark model that combines an embedded-cluster approach for ionic surfaces with wavefunction-based methods to predict the vibrational frequencies of molecules adsorbed on surfaces is presented. As a representative case, the adsorption of CO on the lowest index non-polar and most stable facet of CeO2, that is, (111) was studied. The CO harmonic vibrational frequencies were not scaled semiempirically but explicitly corrected for anharmonic effects, which amount to about 25 cm-1 with all tested methods.

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The current state-of-the-art electron-transfer modeling primarily focuses on the kinetics of charge transfer between an electroactive species and an inert electrode. Experimental studies have revealed that the existing Butler-Volmer model fails to satisfactorily replicate experimental voltammetry results for both solution-based and surface-bound redox couples. Consequently, experimentalists lack an accurate tool for predicting electron-transfer kinetics.

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Iron is considered as attractive energy carrier in a carbon-free, circular energy economy. The reduction of iron oxide is crucial for its application as a metal fuel as it determines the efficiency of the cycle. Temperature programmed reduction of α-FeO was monitored by complementary X-ray absorption spectroscopy (XAS) and diffraction (XRD) to obtain the phase composition with high time resolution.

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CeO-supported noble metal clusters are attractive catalytic materials for several applications. However, their atomic dispersion under oxidizing reaction conditions often leads to catalyst deactivation. In this study, the noble metal cluster formation threshold is rationally adjusted by using a mixed CeO-AlO support.

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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 ZrO single-crystal surfaces after exposure to CO and DO.

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Ammonia is a storage molecule for hydrogen, which can be released by catalytic decomposition. Inexpensive iron catalysts suffer from a low activity due to a too strong iron-nitrogen binding energy compared to more active metals such as ruthenium. Here, we show that this limitation can be overcome by combining iron with cobalt resulting in a Fe-Co bimetallic catalyst.

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The study presents an ab-initio based framework for the automated construction of microkinetic mechanisms considering correlated uncertainties in all energetic parameters and estimation routines. 2000 unique microkinetic models were generated within the uncertainty space of the BEEF-vdW functional for the oxidation reactions of representative exhaust gas emissions from stoichiometric combustion engines over Pt(111) and compared to experiments through multiscale modeling. The ensemble of simulations stresses the importance of considering uncertainties.

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Herein we report the one-pot cobalt catalysed synthesis of the dimethylacetal of acetaldehyde from synthesis gas and methanol. The product can be used as a fuel additive either as it is or after transacetalisation with long-chain alcohols. The product is obtained at moderate temperatures in good selectivities and high CO-conversions.

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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.

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For the calculation of anharmonic contributions to free energy barriers, constrained thermodynamic λ-path integration (λ-TI) from a harmonic reference force field to density functional theory is presented as an alternative to the established Blue Moon ensemble method (ξ-TI), in which free energy gradients along the reaction coordinate ξ are integrated. With good agreement in all cases, the λ-TI method is benchmarked against the ξ-TI method for several reactions, including the internal CH group rotation in ethane, a nucleophilic substitution of CHCl, a retro-Diels-Alder reaction, and a proton transfer in zeolite H-SSZ-13. An advantage of λ-TI is that one can use virtually any reference state to compute anharmonic contributions to reaction free energies or free energy barriers.

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Oxide supports play an important role in enhancing the catalytic properties of transition metal nanoparticles in heterogeneous catalysis. How extensively interactions between the oxide support and the nanoparticles impact the electronic structure as well as the surface properties of the nanoparticles is hence of high interest. In this study, the influence of a magnesium oxide support on the properties of copper nanoparticles with different size, shape, and adsorption sites is investigated using density functional theory (DFT) calculations.

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Herein, we propose a novel computational protocol that enables calculating free energies with improved accuracy by combining the best available techniques for enthalpy and entropy calculation. While the entropy is described by enhanced sampling molecular dynamics techniques, the energy is calculated using ab initio methods. We apply the method to assess the stability of isobutene adsorption intermediates in the zeolite H-SSZ-13, a prototypical problem that is computationally extremely challenging in terms of calculating enthalpy and entropy.

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The hydrogenation of CO to methanol over Cu/ZnO-based catalysts is highly sensitive to the surface composition and catalyst structure. Thus, its optimization requires a deep understanding of the influence of the pre-catalyst structure on its evolution under realistic reaction conditions, including the formation and stabilization of the most active sites. Here, the role of the pre-catalyst shape (cubic vs spherical) in the activity and selectivity of ZnO-supported Cu nanoparticles was investigated during methanol synthesis.

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The correct description of catalytic reactions happening on bimetallic particles is not feasible without proper accounting of the segregation process. In this study, we tried to shed light on the structure of large CoCu particles, for which quite controversial results were published before. However, density functional theory (DFT) is challenging to be directly used for the systematic study of nanometer-sized particles.

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Article Synopsis
  • A key challenge in single-atom (SA) catalysis is creating fully inorganic sites that can achieve the high reaction selectivity typically seen in organometallic catalysts used in homogeneous catalysis.
  • Researchers have found that isolated rhodium (Rh) atoms on oxygen-defective SnO can achieve high turnover frequency (TOF) and excellent selectivity for gas-phase hydroformylation of ethylene while preventing unwanted olefin hydrogenation.
  • The study demonstrates that a significant reduction of lattice oxygen in the SnO surface allows for greater flexibility in the coordination of Rh atoms, resulting in exceptional catalytic performance comparable to liquid-phase molecular catalysts.
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Although the CVD synthesis of graphene on Cu(111) is an industrial process of outstanding importance, its theoretical description and modeling are hampered by its multiscale nature and the large number of elementary reactions involved. In this work, we propose an analytical model of graphene nucleation and growth on Cu(111) surfaces based on the combination of kinetic nucleation theory and the DFT simulations of elementary steps. In the framework of the proposed model, the mechanism of graphene nucleation is analyzed with particular emphasis on the roles played by the two main feeding species, C and C2.

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Converting CO into value-added chemicals and fuels, such as methanol, is a promising approach to limit the environmental impact of human activities. Conventional methanol synthesis catalysts have shown limited efficiency and poor stability in a CO/H mixture. To design improved catalysts, crucial for the effective utilization of CO, an in-depth understanding of the active sites and reaction mechanism is desired.

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Water influences critically the kinetics of the autocatalytic conversion of methanol to hydrocarbons in acid zeolites. At very low conversions but otherwise typical reaction conditions, the initiation of the reaction is delayed in presence of HO. In absence of hydrocarbons, the main reactions are the methanol and dimethyl ether (DME) interconversion and the formation of a C reactive mixture-which in turn initiates the formation of first hydrocarbons in the zeolite pores.

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Cobalt-copper (CoCu) catalysts have industrial potential in CO/CO hydrogenation reactions, and CoCu alloy has been elucidated as a major active phase during reactions. However, due to elemental surface segregation and dealloying phenomena, the actual surface morphology of CoCu alloy is still unclear. Combining theory and experiment, the dual effect of surface segregation and varied CO coverage over the CoCu(111) surface on the reactivity in CO hydrogenation reactions is explored.

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Article Synopsis
  • The study explores how improving bimetallic catalysts, specifically Au-Pd, can enhance chemical processes, particularly in hydrogenating butadiene.
  • By manipulating the atomic structure of these catalysts, researchers achieved up to 50 times greater activity compared to traditional methods, while maintaining selectivity.
  • The findings suggest that not just the outer layer but also subsurface structures impact catalytic performance, paving the way for new designs in bimetallic catalysts.
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Adsorption processes are often governed by weak interactions for which the estimation of entropy contributions by means of the harmonic approximation is prone to be inaccurate. Thermodynamic integration (TI) from the harmonic to the fully interacting system (λ-path integration) can be used to compute anharmonic corrections. Here, we combine TI with (curvilinear) internal coordinates in periodic systems to make the formalism available in computational studies.

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In ceria-based catalysis, the shape of the catalyst particle, which determines the exposed crystal facets, profoundly affects its reactivity. The vibrational frequency of adsorbed carbon monoxide (CO) can be used as a sensitive probe to identify the exposed surface facets, provided reference data on well-defined single crystal surfaces together with a definitive theoretical assignment exist. We investigate the adsorption of CO on the CeO_{2}(110) and (111) surfaces and show that the commonly applied DFT(PBE)+U method does not provide reliable CO vibrational frequencies by comparing with state-of-the-art infrared spectroscopy experiments for monocrystalline CeO_{2} surfaces.

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A methodology is introduced for controlled postsynthetic thermal defect engineering (TDE) of precious group metal-organic frameworks (PGM-MOFs). The case study is based on the Ru/Rh analogues of the archetypical structure [Cu(BTC)] (HKUST-1; BTC = 1,3,5-benzenetricarboxylate). Quantitative monitoring of the TDE process and extensive characterization of the samples employing a complementary set of analytical and spectroscopic techniques reveal that the compositionally very complex TDE-MOF materials result from the elimination and/or fragmentation of ancillary ligands and/or linkers.

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Understanding and tuning the catalytic properties of metals atomically dispersed on oxides are major stepping-stones toward a rational development of single-atom catalysts (SACs). Beyond individual showcase studies, the design and synthesis of structurally regular series of SACs opens the door to systematic experimental investigations of performance as a function of metal identity. Herein, a series of single-atom catalysts based on various 4d (Ru, Rh, Pd) and 5d (Ir, Pt) transition metals has been synthesized on a common MgO carrier.

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