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ChemCatChem : the European Society Journal for Catalysis 14(19), e202200300 (2022). doi:10.1002/cctc.202200300 special issue: "Catalysts and Reactors under Dynamic Conditions for Energy Storage and Conversion", Published by Wiley-VCH, Weinheim

Using first-principles density-functional theory calculations combined with ab initio thermodynamics, we introduce a design protocol for RuO2-based core-shell catalysts which exhibit enhanced stability and activity under oxygen evolution reaction (OER) operating conditions. Due to their high activity and favorable stability in acidic electrolytes, Ir and Ru oxides are primary catalysts for the oxygen evolution reaction (OER) in proton-exchange membrane (PEM) electrolyzers. For a future large-scale application, core-shell nanoparticles are an appealing route to minimize the demand for these precious oxides. Here, we employ first-principles density-functional theory (DFT) and ab initio thermodynamics to assess the feasibility of encapsulating a cheap rutile-structured TiO2 core with coherent, monolayer-thin IrO2 or RuO2 films. Resulting from a strong directional dependence of adhesion and strain, a wetting tendency is only obtained for some low-index facets under typical gas-phase synthesis conditions. Thermodynamic stability in particular of lattice-matched RuO2 films is instead indicated for more oxidizing conditions. Intriguingly, the calculations also predict an enhanced activity and stability of such epitaxial RuO2/TiO2 core-shell particles under OER operation.

Supercages of faujasite (FAU)‐type zeolites serve as a robust scaffold for stabilizing dinuclear (Mo2S4) and tetranuclear (Mo4S4) molybdenum sulfide clusters. The FAU‐encaged Mo4S4 clusters have a distorted cubane structure similar to the FeMo‐cofactor in nitrogenase. Both clusters possess unpaired electrons on Mo atoms. Additionally, they show identical catalytic activity per sulfide cluster. Their catalytic activity is stable (>150 h) for ethene hydrogenation, while layered MoS2 structures deactivate significantly under the same reaction conditions., Dinuclear (Mo2S4) and tetranuclear (Mo4S4) molybdenum sulfide clusters were synthesized within the supercages of a faujasite zeolite. Encaged Mo4S4 clusters possess a structure similar to the nitrogenase enzyme's FeMo‐cofactor; both contain unpaired electrons and show identical catalytic activity per cluster. Their activity for ethene hydrogenation is stable, while layered MoS2 deactivates significantly under the same conditions.

A new class of macrocyclic angle-strained alkynes whose size and reactivity can be precisely tuned by modular organic synthesis is disclosed. Detailed analysis of the size-dependent structural and electronic properties provides evidence for considerable distortion of the alkyne units incorporated into the cycloparaphenylene (CPP)-derived macrocycles. The remarkable increase of the alkyne reactivity with decreasing macrocycle size in [2+2]cycloaddition-retrocyclization was investigated by joint experimental and theoretical studies and the thermodynamic and kinetic parameters that govern this reaction were unraveled. Additionally, even the largest, least strained macrocycle in this series was found to undergo strain-promoted azide-alkyne cycloaddition (SPAAC) efficiently under mild conditions, thereby paving the way to the application of alkyne-containing CPPs as fluorescent "clickable" macrocyclic architectures.

Rapid deactivation presently limits a wide spread use of high-temperature solid oxide cells (SOCs) as otherwise highly efficient chemical energy converters. With deactivation triggered by the ongoing conversion reactions, an atomic-scale understanding of the active triple-phase boundary between electrolyte, electrode, and gas phase is essential to increase cell performance. Here, a multi-method approach is used comprising transmission electron microscopy and first-principles calculations and molecular simulations to untangle the atomic arrangement of the prototypical SOC interface between a lanthanum strontium manganite (LSM) anode and a yttria-stabilized zirconia (YSZ) electrolyte in the as-prepared state after sintering. An interlayer of self-limited width with partial amorphization and strong compositional gradient is identified, thus exhibiting the characteristics of a complexion that is stabilized by the confinement between two bulk phases. This offers a new perspective to understand the function of SOCs at the atomic scale. Moreover, it opens up a hitherto unrealized design space to tune the conversion efficiency.

Deliberate doping of oxides is a promising route to further optimize their catalytic performance. To guide corresponding experimental endeavours we perform a density-functional theory based computational screening study for a wide range of metal dopant atoms in rutile RuO2. With a focus on the Deacon process, i.e. the catalytic oxidation of HCl to chlorine and water, we use the rate-controlling Cl desorption energy as a reactivity descriptor. As stability descriptors we employ the dopant surface segregation energy, as well as the dopant thermodynamic stability against precipitation into metal or bulk oxide grains. In the oxygen-rich conditions of the Deacon process, particularly the instability against oxide precipitation represents a strong limitation. In this respect, doping with Cu appears as an optimum compromise between stability and catalytic activity enhancement.

Multiphotonenabsorption (MPA) ist eine der wichtigsten nichtlinear-optischen (NLO) Effekte und hat verschiedene Anwendungen, z. B. in Telekommunikation, Verteidigung, Photonik und Biomedizin. Bekannte MPA-Materialien sind Farbstoffe, Quantenpunkte, metallorganische Verbindungen und konjugierte Polymere, die oft als Dispersion in Losung verwendet werden. Wir zeigen wie Metall-organische Gerusteverbindungen (MOFs), eine neuartige NLO-Festkorpermaterialklasse, so entworfen werden konnen, dass sie ausergewohnlich starkes MPA-Verhalten zeigen. MOFs, die aus Zirconium- und Hafnium-Oxo-Clustern bestehen und einen Tetraphenylethen(TPE)-basierten Chromophor-Linker beinhalten, zeigen rekordverdachtig hohe Zweiphotonenabsoptionsquerschnitte mit bis zu 3600 GM. Das einzigartige, modulare Baukastenprinzip von MOFs erlaubt eine Optimierung und Verbesserung ihrer MPA-Eigenschaften, gestutzt auf einen theoriebasierten Ansatz, durch die Berucksichtigung von masgeschneiderter Ladungspolymerisation, konformativer Spannung, dreidimensionaler Anordnung und Ausrichtung der Chromophore im Kristall.

Wir prasentieren eine Einbettungstechnik fur metallische Systeme, die es ermoglicht, Energiedissipation in Substratphononen wahrend chemischer Reaktionen ausgehend von ersten Prinzipien zu modellieren. Die Trennung von chemischen und elastischen Beitragen zum Wechselwirkungspotential liefert eine quantitative Beschreibung von elektronischer und phononischer Bandstruktur. Eine Anwendung auf O2-Dissoziation auf Pd(100) sagt in ihren Translationsfreiheitsgraden “heise” Sauerstoffadatome als eine Folge der dabei freigesetzten Energie (rund 2.6 eV) voraus. Dies stellt die instantane Thermalisierung von Reaktionsenthalpien in Frage, die sonst in der Modellierung von heterogener Katalyse angenommen wird.

The fabrication of highly active and robust hexagonal ruthenium oxide nanosheets for the electrocatalytic oxygen evolution reaction (OER) in an acidic environment is reported. The ruthenate nanosheets exhibit the best OER activity of all solution-processed acid medium electrocatalysts reported to date, reaching 10 mA cm(-2) at an overpotential of only approximate to 255 mV. The nanosheets also demonstrate robustness under harsh oxidizing conditions. Theoretical calculations give insights into the OER mechanism and reveal that the edges are the origin of the high OER activity of the nanosheets. Moreover, the post OER analyses indicate, apart from coarsening, no observable change in the morphology of the nanosheets or oxidation states of ruthenium during the electrocatalytic process. Therefore, the present investigation suggests that ruthenate nanosheets are a promising acid medium OER catalyst with application potential in proton exchange membrane electrolyzers and beyond.

An asymmetric turn: Scanning tunneling spectroscopy has been used to analyze the structure of tris[4-(phenylazo)phenyl)]amine on a Au(111) surface. A degenerate marker state serves as a sensitive probe for the structure of the adsorbed molecules.

We present a DFT-based Wulff construction of the equilibrium shape of RuO2 particles in an oxygen environment. The obtained intricate variations in the crystal habit with the oxygen chemical potential allow for a detailed discussion of the dependence on the oxidising pretreatment used in recent powder catalyst studies. The analysis specifically indicates an incomplete particle shape equilibration in previously used low-temperature calcination. Equilibrated particles could be active CO oxidation catalysts with long-term stability in oxidising feed and then represent an interesting alternative to the previously suggested core–shell concept.

Forming the basis for the production of virtually all every-day products, catalysis has always been the driving force for chemical industries. In the 21st century, the concomitant importance of catalysis research is even further increased by the worldwide rapidly growing demand for more efficient exploitation of energy and materials resources. As in many other areas of materials science, modern computational science is becoming a key contributor in the quest to quantitatively understand the molecular-level mechanisms underlying the macroscopic phenomena in chemical processing, envisioned to ultimately enable a rational design of novel catalysts and improved production strategies. Of particular relevance are hierarchical approaches that link the insights that modeling and simulation can provide across all relevant length and time scales. At the molecular level, first-principles electronic-structure calculations unravel the making and breaking of chemical bonds. At the mesoscopic scale, statistical simulations account for the interplay between all elementary processes involved in the catalytic cycle, and at the macroscopic scale continuum theories yield the effect of heat and mass transfer, ultimately scaling up to a plant-wide simulation. A comprehensive control of catalytic processes requires to address all of these facets and will thus ultimately necessitate novel methodological approaches that integrate the various levels of theory into one multi-scale simulation. With the focus on the surface chemistry, first-principles kinetic Monte Carlo (kMC) simulations for heterogeneous catalysis represent precisely one step in this direction. A proper evaluation of the surface kinetics also dictates to unite two distinctly different aspects and in turn two distinct methodologies: The first important part is an accurate description of the involved elementary steps, typically comprising adsorption and desorption processes of reactants and reaction intermediates, as well as surface diffusion and surface reactions. When aiming at a material-specific modeling that is at best of predictive quality, the computation of the corresponding kinetic parameters is the realm of electronic structure theories that explicitly treat the electronic degrees of freedom and thus the quantum-mechanical nature of the chemical bond. Even though such a set of first-principles kinetic parameters constitutes already an (even for the most simple model systems hitherto barely achieved) important intermediate goal and highly valuable result, it does not suffice for a description of the surface catalytic function. For this, a second key ingredient is the occurrence (and thus relevance) of the individual elementary processes, in particular of the different reaction mechanisms. An evaluation of this statistical interplay within the manifold of elementary processes obviously needs to go beyond a separate study of each microscopic process. Taking the interplay into account naturally necessitates the treatment of larger surface areas. Much more challenging than this size, however, is the fact that the surface catalytic system is of course “open” in the sense that reactants, reaction intermediates and products continuously impinge from and desorb into the surrounding gas phase. Due to the highly activated nature of many of the involved elementary steps, the correspondingly required evaluation of the chemical kinetics faces the problem of a so-called “rare-event dynamics”, which means that the time between consecutive events can be orders of magnitude longer than the actual process time itself. Instead of the typical picosecond time scale on which say a surface diffusion event takes place, it may therefore be necessary to follow the time evolution of the system up to seconds and longer in order to arrive at meaningful conclusions concerning the statistical interplay.

The need for greater fuel economy in automotive vehicles has driven a surge in the development of diesel and lean-burn gasoline engines. Coupled with the increase in fuel efficiency, an increase in the air to fuel ratio also results in heightened production of NOx. [1] Several different strategies have been proposed for the handling of the higher NOx levels in lean-burn automotive emissions. One such strategy is the NOx storage reduction (NSR) system whereby excess NO is further oxidized to NO2 over the exhaust catalyst, which is typically platinum, and then NO2 is stored on a carrier material, such as BaO. [2] The catalyst system operates in this fashion for some minutes until the storage material has been fully converted. The system then cycles to a rich mode, during which a reductant is injected into the exhaust stream and reacts with the stored NOx, possibly at the interface between the carrier material and the metal particle, to produce the traditional exhaust products of N2, H2O, and CO2, all in a matter of seconds. Therefore, a requirement of a successful NSR catalyst is that the catalyst must be active for both NO oxidation and NOx reduction. In recent years, a debate has emerged as to the role of metal oxides in oxidation catalysis. [3–6] Although there have been some indications that oxide surfaces may be more active in simple oxidation reactions such as CO oxidation, [7] platinum catalysts have been preferred as the metal component in the NOx storage reduction system for their combination of high activity and ability to resist deactivation through oxidation. Ribeiro et al. have studied Pt NO-oxidation catalysts for NSR applications in considerable detail. They determined that large Pt particles are more active and that single crystal Pt(111) and Pt(100) outperform disperse Pt particles. [8, 9] One possible explanation for the higher activity of the single crystal surfaces is that oxygen is bound less strongly and that the catalysts do not deactivate due to oxide formation. Reports of platinum deactivation as a NO oxidation catalyst, however, concern catalysts that have been exposed to oxygen (and NO) for long periods. [9] As NSR systems operate under a cyclic operation

Electronic structure calculations have emerged as a key contributor in modern heterogeneous catalysis research, though their application in chemical reaction engineering remains largely limited to academia. This perspective aims at encouraging the judicious use of first-principles kinetic models in industrial settings based on a critical discussion of present-day best practices, identifying existing gaps, and defining where further progress is needed.