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First principles-based kinetic Monte Carlo (kMC) simulations are performed for the CO oxidation on RuO(2) (110) under steady-state reaction conditions. The simulations include a set of elementary reaction steps with activation energies taken from three different ab initio density functional theory studies. Critical comparison of the simulation results reveals that already small variations in the activation energies lead to distinctly different reaction scenarios on the surface, even to the point where the dominating elementary reaction step is substituted by another one. For a critical assessment of the chosen energy parameters, it is not sufficient to compare kMC simulations only to experimental turnover frequency (TOF) as a function of the reactant feed ratio. More appropriate benchmarks for kMC simulations are the actual distribution of reactants on the catalyst's surface during steady-state reaction, as determined by in situ infrared spectroscopy and in situ scanning tunneling microscopy, and the temperature dependence of TOF in the from of Arrhenius plots.

Segregation of aliovalent dopant cations is a common degradation pathway on perovskite oxide surfaces in energy conversion and catalysis applications. Here we focus on resolving quantitatively how dopant segregation is affected by oxygen chemical potential, which varies over a wide range in electrochemical and thermochemical energy conversion reactions. We employ electrochemical polarization to tune the oxygen chemical potential over many orders of magnitude. Altering the effective oxygen chemical potential causes the oxygen nonstoichiometry to change in the electrode. This then influences the mechanisms underlying the segregation of aliovalent dopants. These mechanisms are (i) the formation of oxygen vacancies that couples to the electrostatic energy of the dopant in the perovskite lattice and (ii) the elastic energy of the dopant due to cation size mismatch, which also promotes the reaction of the dopant with O2 from the gas phase. The present study resolves these two contributions over a wide range of effective oxygen pressures. Ca-, Sr-, and Ba-doped LaMnO3 are selected as model systems, where the dopants have the same charge but different ionic sizes. We found that there is a transition between the electrostatically and elastically dominated segregation regimes, and the transition shifted to a lower oxygen pressure with increasing cation size. This behavior is consistent with the results of our ab initio thermodynamics calculations. The present study provides quantitative insights into how the elastic energy and the electrostatic energy determine the extent of segregation for a given overpotential and atmosphere relevant to the operating conditions of perovskite oxides in energy conversion applications.

Ab initio kinetic Monte Carlo (KMC) is successfully applied to simulate the experimentally observed promoting effect of O 2 on the HCl oxidation reaction (Deacon process) catalyzed by RuO 2 (110). Density functional theory (DFT) calculations provide, in addition to the adsorption energies of reaction intermediates and activation energies, also interaction energies between the adsorbates within the cluster expansion approach. KMC simulations with this extended set of energy parameters were analyzed employing the concept of "degree of rate control". In contrast to previous propositions, our simulations indicate that neither the dissociative O 2 adsorption (the sterically hindered first reaction step) nor the associative desorption of chlorine (the step with the highest activation energy) are rate determining under typical Deacon conditions. Instead, the hydrogen transfer in the water formation determines the rate of the overall reaction. These hydrogen transfer processes are not highly activated but turn out to be strongly configuration controlled.

Long‐term stability is a major issue in heterogeneous catalysis and is often related to structural instabilities, which are difficult to assess in the early stage of catalyst screening. However, studies of morphological transformations in catalytic systems can greatly benefit from a well‐defined starting morphology and microstructure of the catalyst to be analysed. The present study suggests the use of catalysts in the form of 1 D nanofibres (NFs) as a conceptual methodology to assess catalyst stability, which is exemplified for the HCl oxidation reaction. These nanostructured model catalysts are synthesised by electrospinning, a versatile method to produce metal oxide NFs. We have studied the stability of RuO2‐ and CeO2‐based materials in the harsh HCl oxidation reaction (Deacon process). At 573 K pure RuO2 NFs have shown to be morphologically unstable, whereas mixed RuO2‐TiO2 NFs are stable. The stability of CeO2‐based NFs in the HCl oxidation was studied at 703 K. Under HCl lean conditions CeO2 NFs are stable, whereas under HCl rich conditions pure CeO2 NFs disintegrate by recrystallisation, forming (hydrated) Ce‐chloride. If CeO2 is doped with 20 % of Zr, the resulting mixed oxide Zr0.20Ce0.80O2 NFs have shown to be stable even under HCl rich reaction conditions and are similarly active as pure CeO2. These are the first activity experiments of mixed oxide ZrxCe1−xO2 in the Deacon process. The versatility of electrospun NFs as model catalysts has been demonstrated for testing catalyst stability in terms of morphology changes, thus serving as a proof‐of‐principle study.