Franziska Hess

• Professor
• Professor (Assistant) at Technische Universität Berlin

Perovskite oxides degrade at elevated temperatures while precipitating dopant-rich particles on the surface. A knowledge-based improvement of surface stability requires a fundamental and quantitative understanding of the dopant precipitation mechanism on these materials. We propose that dopant precipitation is a consequence of the variation of dopa...

Deactivation of CeO2‐based catalysts in the HCl oxidation reaction proceeds via selective bulk chlorination of the active CeO2 component to form CeCl3×nH2O. We study the reactivation of two bulk‐chlorinated CeO2‐based Deacon catalysts by oxygen treatment at 430 °C, namely pure CeO2 and 20 mol % of CeO2 supported on preformed ZrO2 particles (20CeO2@...

Perovskite oxides used in heterogeneous catalysis and electrocatalysis are tuned by substitutional doping. Sr-doped LaMnO3 is a popular choice of electrode material for electrochemical energy conversion. At elevated temperatures, relevant to solid oxide fuel or electrolysis cells, Sr enriches at the surface, which leads to fast degradation of the o...

Long-term stability of heterogeneous catalysts is an omnipresent and pressing concern in industrial processes. Catalysts with high activity and selectivity can be searched for by high-throughput screening methods based maybe on educated guesses provided by ab initio thermodynamics or scaling relations. However, high-throughput screening is not feas...

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 react...

Perovskite oxides used in heterogeneous catalysis and electrocatalysis are tuned by substitutional doping. Sr-doped LaMnO3 is a popular choice of electrode material for electrochemical energy conversion. At elevated temperatures, relevant to solid oxide fuel or electrolysis cells, Sr enriches at the surface, which leads to fast degradation of the o...

While lateral interaction models for reactions at surfaces have steadily gained popularity and grown in terms of complexity, their use in chemical kinetics has been impeded by the low performance of current KMC algorithms. The origins of the additional computational cost in KMC simulations with lateral interactions are traced back to the more elabo...

Perovskite materials are widely used as catalysts and electrocatalysts in energy conversion devices. Their bulk transport properties can be tuned flexibly for many applications. While the ion and electron transport properties in their bulk are generally well-understood, the surfaces remain much less explored and challenging. Surface instabilities g...

Mixed Ce1-xZrxO2 nano-rod particles with varying Zr doping levels of up to 20% were exposed to Deacon reaction mixtures with high HCl concentration at a reaction temperature of 430 °C. The mixed Ce1-xZrxO2 nano-rod samples were characterized before and after Deacon reaction by x-ray diffraction (XRD), transmission electron microscopy (TEM), and x-r...

We studied the stability of CeO2 nano-cubes with preferentially (1 0 0)-oriented facets in the HCl oxidation reaction (Deacon process) for various reaction temperatures and the addition of small concentrations of water in the gas feed. For a reaction mixture HCl:O2 = 1:2 we find that CeO2 is substantially chlorinated below 380 °C, revealing a low c...

Transient spectroscopic surface chemistry experiments in combination with spatially resolved kinetic Monte Carlo (KMC) simulations offer great potential to gain a wealth of molecular information on the kinetics of a catalytic surface reaction as exemplified with the CO oxidation reaction over RuO2(110). This approach surpasses the common problem th...

Ab-initio kinetic Monte Carlo (KMC) is successfully applied to simulate the experimentally observed promoting effect of O2 on the HCl oxidation reaction (Deacon process) catalyzed by RuO2(110). Density functional theory (DFT) calculations provide besides the adsorption energies of reaction intermediates and activation energies, also interaction ene...

In this perspective we discuss how an intimate interaction of experiments with theory is able to deepen our insight into the catalytic reaction system on the molecular level. This strategy is illustrated by discussing various examples from our own research of surface chemistry and model catalysis. The particular examples were carefully chosen to ba...

In this perspective, we focus on the catalyzed oxidation of CO and HCl over the model catalyst RuO2(110) and how the kinetics of these reactions can be modeled by kinetic Monte Carlo (kMC) simulations. Assuming the reaction mechanism is known, the critical parameters entering the kMC simulations include the activation and adsorption energies as wel...

In this perspective, we focus on the catalyzed oxidation of CO and HCl over the model catalyst RuO 2 (110) and how the kinetics of these reactions can be modeled by kinetic Monte Carlo (kMC) simulations. Assuming the reaction mechanism is known, the critical parameters entering the kMC simulations include the activation and adsorption energies as w...

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 catalys...

With temperature programmed reaction (TPR) experiments and kinetic Monte Carlo (kMC) simulations of coadsorbed oxygen and HCl on the RuO2(110) surface we studied the thermal stabilization of dissociatively adsorbed oxygen. Due to one-dimensional confinement single surface O atoms can be trapped by surface chlorine atoms so that surface oxygen is no...

With temperature programmed reaction (TPR) experiments and kinetic Monte Carlo (kMC) simulations of coadsorbed oxygen and HCl on the RuO 2 (110) surface we studied the thermal stabilization of dissociatively adsorbed oxygen. Due to one-dimensional confinement single surface O atoms can be trapped by surface chlorine atoms so that surface oxygen is...

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 resu...

Chlorine adsorption on Ru(0001) surface has been studied by a combined density functional theory (DFT) and quantitative low energy electron diffraction (LEED) approach. The (√3 × √3)R30°-Cl phase with ΘCl = 1/3 ML and chlorine sitting in fcc sites has been identified by DFT calculations as the most stable chlorine adsorbate structure on Ru(0001) wi...

Kinetic Monte Carlo (kMC) simulations of the CO oxidation over RuO2(110) have been performed for a variety of different reaction conditions ranging from 10–7 to 10 mbar and temperatures from 300 to 600 K. The kMC simulations are based on reaction rates of elementary steps including diffusion, adsorption/desorption, and recombination of surface CO a...