Keynote: Homogeneous Carbonylation Catalysis in Ionic Liquids – Supported, or Not Supported, that is the question
- Prof. Dr. Anders Riisager
In the past 25 years, ionic liquids (ILs) have been established as attractive materials in many diverse and important fields of chemical applications, including homogeneous catalysis. A major reason behind the success is attributed to the physiochemical characteristics and options for alteration of ILs (e.g., negligible vapor pressure, high thermal/chemical stability, solubility for a wide range of compounds, modification with added functionalities), which allows their use in biphasic processes with a recyclable liquid IL-catalyst phase. However, an inherent concern when using (often viscous) ILs in liquid biphasic catalysis is interfacial mass transfer. An innovative approach to avoid such mass transfer is to apply Supported Ionic Liquid-Phase (SILP) technology, where the catalyst is immobilized in a thin IL film in a porous solid material. The large potential of SILP technology has been demonstrated for several homogeneously catalyzed gas-phase process types with high industrial relevance, such as carbonylation, hydroformylation, hydroamination, hydrogenation, oxidation and epoxidation, yielding both excellent catalytic performance and catalyst stability [1]. This presentation will highlight our work on designing new prospective IL catalyst systems and processes for methanol carbonylation into acetic acid and alkoxycarbonylation of alkenes into acrylate precursors using biphasic IL and SILP technology. [1] P. Latos et al., Materials, 2023, 16, 2106, doi.org/10.3390/ma16052106 and cited refs.
Parallel Session 1A: Metal-Organic Frameworks as Functional Catalyst Platform
- Dr. Simon Krause, CRC 1333
Molecular framework materials such as metal-organic frameworks (MOFs) allow to immobilize molecular catalysts into ordered extended materials and make their active sites accessible for chemical transformations via intrinsic porosity. Depending on the size of the pores and the substrate the porous host system itself can play an active role in the selectivity and activity of the catalytic system via confinement effects. From a holistic point of view, the catalytic activity will also depend on the ability of the substrates to enter and leave the pore space. Confinement effects in nanoporous systems can alter the product selectivity and allow for cooperative processes, e.g. when an active organic site is located in close proximity to the inorganic node. However, confinement can also impede the catalytic activity by active site inhibition or hindered substrate diffusion. In my presentation I want to show how molecular transport properties can be impacted by incorporation of active sites into nanoporous framework materials by a series of functionalized metal-organic frameworks. I will demonstrate how reagents such as acidic modulators that are used in the synthesis of Zr-based MOFs can impact the catalytic process beyond defect sites. I will furthermore detail the establishment of multivariate MOFs as an interesting catalysis platform that allows to optimize pore-space, activity and transport properties by mixing different components. I will finally provide an outlook on the ability to utilize and probe local dynamics in these framework materials with low- frequency Raman spectroscopy. This aspect of functional dynamics may allow to overcome transport limitations and result in a new approach towards catalysis in dynamic confinement. [1,2] [1] S. Krause, J.V. Milić, Commun Chem 2023, 6, 151, [2] S. Krause, N. Hosono, S. Kitagawa, Angew. Chem. Int. Ed. 2020, 59, 15325- 15341
Parallel Session 1A: Synthesis and Functionalization of Ordered Mesoporous Silica: Improved Catalyst Carrier Materials through Pore Size Control and Metal Incorporation
- Dr. Johanna Bruckner, CRC 1333
Studying confinement effects in molecular heterogeneous catalysis requires access to mesoporous support materials with well-defined, yet variable, pore sizes. Although ordered mesoporous silica (OMS) - prime candidates for this task - have been studied extensively since the pioneering work of Kresge et al. [1], these materials are not readily available. We demonstrate that direct liquid crystal templating at high surfactant concentrations produces OMS with Gaussian pore size distributions [2], and that this method enables precise tuning of pore sizes between 2.5 and 20 nm when using high-molar mass block copolymers [3]. To enhance the catalytic role of the support material, we study the incorporation of various metal atoms into the OMS, potentially creating Lewis acid sites that offer additional substrate coordination. We will demonstrate that our labor and material efficient synthesis method results in well-defined ordered mesoporous metallo-silicates (OM2S) with high metal loadings and open pores. Furthermore, we will elucidate how synthesis conditions and pore sizes influence the number and strength of the Lewis and Brønsted acid sites. Finally, we will discuss achieving an atomistic understanding of the presented OMS and OM2S through a combined experimental and theoretical approach. [1] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, and J.S. Beck, Nature, 1992 359, 710–712, DOI: 10.1038/359710a0. [2] J.R. Bruckner, J. Bauhof, J. Gebhardt, A.-K. Beurer, Y. Traa, and F. Giesselmann, J. Phys. Chem. B 2021, 125, 3197–3207, DOI: 10.1021/acs.jpcb.0c11005. [3] C. Vogler, S. Naumann, and J.R. Bruckner, Mol. Syst. Des. Eng. 2022, 7, 1318–1326, DOI: 10.1039/D2ME00107A.
Parallel Session 1B: Engineering Artificial Metalloenzymes for Lanthanide Photocatalysis
- Prof. Dr. Cathleen Zeymer, CRC 325
Lanthanide photocatalysis is a powerful tool to activate organic molecules under mild conditions.[1,2] For instance, radical intermediates can be formed using visible light and simple complexes of the earth-abundant lanthanide cerium. However, it remains a major challenge to control the fate of these reactive intermediates to achieve regio- and stereoselectivity. We thus developed an artificial lanthanide-dependent photoenzyme (= PhotoLanZyme) enabling this chemistry in a protein environment.[3] We utilized a de novo designed protein scaffold that we previously engineered to tightly bind lanthanide ions in its central cavity. [4] Upon visible-light irradiation, the cerium-bound enzyme catalyzes the radical C–C bond cleavage of 1,2-diols in aqueous solution. [3] We thoroughly characterized the molecular effects of photodamage and used protein engineering to improve the enzyme’s photostability and metal binding properties. The photoenzyme cleaves a range of aromatic and aliphatic substrates, including lignin surrogates. It exhibits initial stereoselectivity for bulkier substrates. Surface display of the protein scaffold on E. coli and subsequent treatment of the cells with CeCl3 facilitates whole-cell photobiocatalysis. Furthermore, we found that also natural lanthanide-binding proteins have promiscuous enzymatic activity towards cerium photoredox chemistry. [1] A. Prieto, F. Jaroschik, Curr. Org. Chem. 2022, 26, 6-41. [2] Y. Qiao, E.J. Schelter, Acc. Chem. Res. 2018, 51, 2926–2936. [3] A. S. Klein, F. Leiss-Maier, (…), C. Zeymer, ChemRxiv, 2024, doi:10.26434/chemrxiv-2024-6g4px [4] S. J. Caldwell, I. C. Haydon, (…), C. Zeymer, Proc. Natl. Acad. Sci. 2020, 117, 30362-30369
Parallel Session 1B: A Transient Look on Photocatalytic Reactions Involving Preassembly
- Prof. Dr. Patrick Nuernberger, CRC 325
With the goal to decipher the underlying reaction mechanism, we discuss the light-induced dynamics observed with time-resolved spectroscopy for several systems where preassembly between a photocatalyst and substrate molecules is decisive. This preassembly may fulfil different roles, on the one hand to circumvent diffusion and hence make short-lived excited states exploitable for photocatalysis, on the other hand to achieve well- defined orientations and facilitate selective reactions. For an octahedrally coordinated bis(diiminopyridine)cobalt complex whose excitation enables the visible-light-driven arylation of pyrroles with chloro- and bromoarenes, spectroscopic studies elucidate that its excited-state lifetime is only a few picoseconds. Ultrafast quenching and computational studies confirm that an interaction within the short excited-state lifetime occurs, owing to a preassembly of the substrate molecules with the complex [1]. Further photochemical reactions involving xanthine derivatives [2], their photochemical rearrangement, and their potential for photocatalysis as a ligand in Ni-xanthine complexes will be discussed. Photoreactions in preassembled species can also be employed for deracemization, as is discussed for hydantoins. The substrate binds to a chiral benzophenone-based photocatalyst by two-point hydrogen bonding, i.e., a pre-complexation exists when the catalyst is excited by light. We show that two criteria have to be met for the reaction to work efficiently: First, light absorption triggers a transfer process that works better (or exclusively) for one of the enantiomers. Second, an achiral intermediate has to be formed whose lifetime exceeds that of the complex, so that the subsequent reformation of the chiral substrate is not enantioselective [3]. [1] J. Märsch et al., Angew. Chem. Int. Ed. 2024, 63, e202405780, 10.1002/anie.202405780 [2] R. E. Rodriguez-Lugo et al., under review, 2024. [3] R.J. Kutta et al., J. Am. Chem. Soc. 2023, 145, 2354, 10.1021/jacs.2c11265
Parallel Session 2A: Structure-resolved computational fluid dynamics simulations in catalytic reactors
- Prof. Dr.-Ing. Gregor Wehinger, CRC 1441
Parallel Session 2A: Role of noble metal-support interaction and in situ/operando spectroscopy in the rational design of active and stable catalysts
- Daria Gashnikova, CRC 1441
Supported noble metal nanoparticles are essential catalytic materials in several application areas such as production of fine chemicals, energy conversion processes and environmental catalysis. Due to the limited availability and high costs of noble metals, maximizing catalyst efficiency is highly anticipated. However, improving the activity and stability of noble metal-based catalysts is only possible with an in-depth understanding of the reaction-induced structural dynamics and identification of the active site motif. [1] In our work, systematic operando X-ray absorption spectroscopy (XAS) and IR spectroscopy investigations in combination with DFT calculations were conducted to track the structure of the active sites in the Pd-based catalysts under transient CO oxidation conditions. For this purpose, a universal concept for the preparation of catalytic materials with a modified, local surface noble metal concentration [2] was developed in a first stage. The threshold of the in situ Pd cluster formation could be increased at a rather low noble metal loading of 0.5 wt.% by using CeO2-Al2O3 support. This is achieved by exploiting the differences in the noble metal-support interaction that appear for CeO 2-Al2O3 materials in comparison to pure CeO2 support. To control the localization of Pd on the CeO2-Al2O3 carrier and ensure the close noble metal-ceria contact, we used flame spray pyrolysis (FSP) in a double nozzle configuration for the catalyst preparation. Based on the findings of our in situ/operando investigations, we were able to determine the crucial role of small PdO x clusters in combination with the Pd-CeO 2- interface for a high CO oxidation activity at low temperatures and propose a strategy for the rational catalyst design.[3] [1] F. Maurer, J. Jelic, J. Wang, A. Gänzler, P. Dolcet, C. Wöll, Y. Wang, F. Studt, M. Casapu, J.-D. Grunwaldt, Nat. Catal. 2020, 3, 824. [2] F. Maurer, A. Beck, J. Jelic, W. Wang, S. Mangold, M. Stehle, D. Wang, P. Dolcet, A. M. Gänzler, C. Kübel, F. Studt, M. Casapu, J.-D. Grunwaldt, ACS Catal. 2022, 12, 2473. [3] D. Gashnikova, F. Maurer, E. Sauter, S. Bernart, J. Jelic, P. Dolcet, C. B. Maliakkal, Y. Wang, C. Wöll, F. Studt, C. Kübel, M. Casapu, J.-D. Grunwaldt, Angew. Chem. Int. Ed. 2024, e202408511.
Parallel Session 2A: Embedded cluster calculations on adsorption at oxide surfaces
- Prof. Dr. Karin Fink, CRC 1441
In the field of heterogeneous catalysis the great majority of quantum chemical calculations are nowadays DFT (density functional theory) slab calculations using periodic boundary conditions and plain wave basis sets. For local processes such as adsorption, the embedded cluster approach is an alternative approach allowing for the usage of higher level quantum chemical methods [DFT with hybrid functionals, MP2 perturbation theory, and coupled cluster singles and doubles with perturbative triples (CCSD(T))] to benchmark the accuracy of the plane wave calculations. For the examples of CO adsorbed on alumina (a-Al2O3) and ceria (CeO2), we compare the adsorption energy and stretching vibrational frequency of CO obtained by different computational methods and by experiment. We discuss the accuracy of the different approaches and their applicability for different experimental conditions.
Parallel Session 2B: X-ray Investigations on the Mechanisms of Homo- and Heterogeneous Catalysis
- Prof. Simone Techert, CRC 1073/1633
In this talk we will present the ultrafast time-resolved, in-situ and / or operando X-ray view on homogeneous and heterogeneous catalysis. The experiments are based on recent developments combining liquid jet microtechnology with different types of soft X-ray spectroscopy coupled to synchrotron and free-electron laser sources. We are particularly interested in multidimensional photon-in / photon-out techniques, such as X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) with high time and energy resolution. As one of the first homogeneous catalysis model systems we studied the ultrafast photocatalysis of Fe(CO)5 i n ethanol with iron L-edge free-electron laser RIXS. The pilot hetero catalytic systems we investigated was the highly efficient oxygen evolution reaction (OER) on perovskites surfaces. Water splitting is intensively studied for sustainable and effective energy storage in green / alternative energy harvesting-storage-release cycles. We will present our different in-situ and time-resolved RIXS studies of the manganese L-edge and oxygen K-edge of perovskites during OER. For that various X-ray photon-in / photon-out spectroscopy techniques, zone plates and gratings have been combined with liquid jet technology. The combination of liquid jet with low-resolution X-ray spectroscopy is sufficient for element- and oxidation-state-specific chemical OER monitoring. For an in-depth study of OER mechanisms, however, including charge-transfer characterization of catalyst-water adsorbates, high-resolution (grating) spectroscopy tools resolving even vibronic couplings, combined with liquid jets bear bigger potential since they allow resolution of otherwise-overlapping, ultrafast X- ray spectroscopy transitions. The impact of polarons and whether they can contribute to OER will be discussed for our latest high-resolution RIXS studies. How they impact proto- coupled electron transfer reaction will be presented on the example of OER on ZnO. The projects are supported by the SFB1073 (“Atomic Scale Control of Energy Conversion”) and the SFB1633 (“Proton Coupled Electron Transfer”). T. Reuss et al. Acc. Chem. Res. 56, 203 (2023). DOI: 10.1021/acs.accounts.2c00525; J. Schlappa et al. arXiv:2403.08461v1. DOI: 10.48550/arXiv.2403.08461; P. Busse et al. JPC C 124, 7893 (2020). DOI: 10.1021/acs.jpcc.0c00840; Ph. Wernet et al. Nat 520 (7545), 78 (2015). DOI:10.1038/nature14296; Z. Yin et al. RSI 86, 093109-1-5 (2015); Z. Yin et al. Opt.Ex.. 25 (10), 10984 (2017). DOI: 10.1364/OE.25.0109 F. Marschall et al. Nat. Sci. Rep. 7(1), 8849-8857 (2017). DOI: 10.1038/s41598-017-09052-0
Parallel Session 2B: Atomic scale dynamics and electric fields at electrocatalyst water interfaces
- Dr. Tobias Meyer, CRC 1073
Interfaces of solids to H 2O are decisive for controlling chemical reactions in heterogeneous catalysis. Despite many decades of research on Helmholtz layers and progress in theoretical modelling, the real structure and dynamics in equilibrium state as well as during electrochemical water oxidation is poorly understood. We present in-situ high-resolution TEM and electron holography studies in H2O vapor that give new and ground-breaking insights into the atomic structure and dynamics at catalyst surfaces including the observation of dynamic adatoms on a manganite perovskite oxide [1], the emergence of dynamic surface sheets in a layered Ca-birnessite [2], and the visualization of an ordered H 2O dipole layer at a Pt(111) surface at different applied electric potentials. These observations will help to understand coordination chemistry at solid-electrolyte interfaces during electro- and photocatalysis, to model chemical reactivity, and give insights into surface dipole fields. [1] G. Lole et al., Comm Mat, 2020, 1, 68, doi.org/10.1038/s43246- 020-00070-6 [2] E. Ronge et al., J Phys Chem C, 2021, 125, 5037-5047, doi.org/10.1021/acs.jpcc.0c09806
Parallel Session 2B: Exploiting the Disulfide/Dithiol Switch for Artificial Photosynthesis and Photoredox Catalysis
- Prof. Franc Meyer, CRC 1073/1633
Light-driven proton-coupled electron transfer (PCET) processes are receiving great attention because they are key to innovative approaches for solar-to-fuel transformations, such as photocatalytic H2 formation. In this context we have equipped bipyridine-ligated photoactive transition-metal complexes with peripheral disulfide/dithiol redox switches (1-3; Figure 1), and we have studied their PCET thermochemistry, excited-state dynamics and photoinduced reactivity.[2] This presentation will focus on a new rhenium photosensitizer 4 decorated with a disulfide moiety,[3] which is capable of storing two electrons and one proton in a light reaction and release these in the form of H-atom transfer (HAT) or hydride transfer in a dark reaction. 4 can also serve as a combined photoredox- and HAT catalyst. The disulfide/dithiol-couple offers interesting perspectives in molecular artificial photosynthetic systems, as 2e− transformations can benefit from potential inversion. [1] M. Cattaneo et al., Chem. Eur. J., 2018, 24, 4864, DOI: 10.1002/chem.201705022 [2] (a) S.-A. Hua et al., Inorg. Chem., 2020, 59, 4972, DOI: 10.1021/acs.inorgchem. 0c00220; (b) M. Heindl et al. Inorg. Chem., 2021, 60, 1672, DOI: 10.1021/acs. inorgchem.0c03163; (c) S.-A. Hua et al., J. Am. Chem. Soc., 2021, 143, 6238, DOI: 10.1021/jacs.1c01763; (d) M. Oelschlegel et al., Inorg. Chem., 2022, 61, 13944, DOI: 10.1021/acs.inorgchem.2c01930 [3] J. Franz et al., J. Am. Chem. Soc., 2024, 146, 11272, DOI: 10.1021/jacs.4c00548
Keynote: Molecular catalytic (electro, photo)reduction of CO2: from C1 to C2+ products
- Prof. Marc Robert
Reduction of carbon dioxide has as main objective the production of useful organic compounds and fuels - renewable fuels - in which solar energy would be stored. Molecular catalysts can be employed to reach this goal, either in photochemical or electrochemical (or combined) contexts. They may in particular provide excellent selectivity thanks to easy tuning of the electronic properties at the metal and of the ligand second and third coordination sphere. Recently we have shown that such molecular catalysts may also be tuned for generating highly reduced products such as formaldehyde, methanol and methane, leading to new exciting advancements. Obtaining C-C coupling products is an additional intriguing possibility. Our recent results will be discussed, using earth abundant metal (Fe, Co) porphyrins and phthalocyanines as well as related complexes as catalysts, being dispersed in solution or assembled at (semi)conductive materials. [1] [2] M. Robert et al. submitted M. Robert, M. Abdinejad, T. Burdyny, Nat. Catal. 2024, in press [3] M. Robert, W. A. Goddard III, R. Ye et al. Nat. Catal. 2023, 6, 818. [4] M. Robert, B. Liu et al. Nat. Commun. 2023, 14, 3401. [5] M. Robert et al. Nat. Commun. 2020, 11:3499 [6] T. F. Jaramillo, M. Robert et al. Angew. Chem. Int. Ed. 2019, 58, 16172. [7] 369. [8] C. Berlinguette, M. Robert et al. Science 2019, 365, 367- J. Bonin, M. Robert et al. Nature 2017, 548, 74.
Parallel Session 1A: Catalytic Functionalization of White Phosphorus
- Prof. Robert Wolf, CRC 325
Organophosphorus compounds are an important class of molecules with numerous industrial uses, e.g. as pharmaceuticals, flame retardants, chemical reagents and catalysts.[1] Nearly all of these valuable compounds are presently synthesized via an atom- inefficient multi-step procedure involving the oxidation of white phosphorus (P 4) with chlorine gas. Catalysis offers the possibility for more atom-efficient transformations. However, catalytic P4 functionalization still is in early stages of development.[2] This lecture will describe our endeavours in catalytic P 4 functionalization. First, we will highlight the utility of photoredox catalysis for transforming P4 into useful monophosphorus compounds. The photocatalytic arylation of P 4 using aryl iodides, bromides and chlorides will be described.[3,4] Mechanistic (31P NMR) investigations revealed major reaction pathways and inspired the development of PH3 arylation.[5] Furthermore, photocatalytic P4 stannylation was found to be a useful method for preparing alkylphosphines and alkylphosphonium salts. [6] Finally, we will describe our ongoing studies into main-group-catalyzed P 4 functionalization, including our first results electrocatalytic P 4 functionalization using disulfide catalysts. [7] [1] D. E. C. Corbridge, Phosphorus 2000. Chemistry, Biochemistry and Technology, Elsevier: Amsterdam, 2000. [2] Review: D. J. Scott, Angew. Chem. Int. Ed 2022, 61, e202205019. [3] a) U. Lennert, P. B. Arockiam, V. Streitferdt, D. J. Scott, C. Rödl, R. M. Gschwind, R. Wolf, Nat. Catal. 2019, 2, 1101–1106; b) P. B. Arockiam, U. Lennert, C. Graf, R. Rothfelder, D. J. Scott, T. G. Fischer, K. Zeitler, R. Wolf, Chem. Eur. J. 2020, 26, 16374– 16382. [4] R. Rothfelder, V. Streitferdt, U. Lennert, J. Cammarata, D. J. Scott, K. Zeitler, R. M. Gschwind, R. Wolf, Angew. Chem. Int. Ed. 2021, 60, 24650–24658. [5] M. Till, J. Cammarata, R. Wolf, D. J. Scott, Chem. Commun. 2022, 58, 8986–8989. [6] M. Till, V. Streitferdt, D. J. Scott, M. Mende, R. M. Gschwind, R. Wolf, Chem. Commun. 2022, 58, 1100–1103. [7] T. M. Horsley Downie, A. Velić, L. A. Coelho, R. Wolf, D. J. Scott, under review.
Parallel Session 1A: Hidden Assemblies Switching Chemoselectivity in Photocatalytic Borylation Reactions of 1,4- Dicyanobenzene
- Prof. Dr. Julia Rehbein, CRC 325
The reaction of Lewis-acid-base adducts obtained of N-heterocylic carbenes and boranes have found application in alkene, arene, and alkyne functionalization under photochemical and photocatalytic conditions.[1] The accessible product scope differs significantly in reactivity and selectivity from thermal hydroboration reactions. Intrigued by the mechanistic postulate of Curran and co-workers on their photocatalytic formal 1,4 hydroboration of electron-deficient alkenes [2], we set out on a mechanistic study and to not only revise that mechanism but also use the gained understanding to derive the originally desired substitution reaction. The talk will provide complementary computational and spectroscopic (transient absorption spectroscopy, NMR) information on the mechanism at hand and will highlight the importance of variance in spatial and temporal evolution of the key open-shell intermediates for chemoselectivity. [1] D. P. Curran et al. Angew. Chem. Int. Ed. 2011, 50, 10294, 10.1002/ anie.201102717. [2] W. Dai et al., J. Am. Chem. Soc. 2020, 142, 6261, 10.1021/jacs.0c00490.
Parallel Session 1B: Homogeneous catalysis in thick films of supported ionic liquids
- Prof. Marco Haumann, CRC 1452
The use of homogeneous catalysts dissolved in ionic liquids (ILs) is an established field of research. Thin IL films containing dissolved catalyst complexes can be immobilized on solid porous supports, thereby creating a heterogenized catalyst material. Aiming at the deliberate positioning of such supported ionic liquid phase (SILP) catalyst, we carried out investigations of two very similar catalyst complexes: depending on the ligand periphery, the first one is homogeneously dissolved in the IL while the second one strongly enriches at the gas/IL interface. To study these different locations within thick IL films of approximately 1 mm thickness, we investigated the hydrogenation of ethene in a continuous pool- reactor setup. The two complexes dissolved in the IL [C 4C1Im][PF6] showed different activity which can be attributed to their different locations. At 313 K and 0.62 MPa total pressure, the surface- enriched complex was approximately two times more active. However, under these conditions the formation of metal (nano)particles could be observed, with the surface-enriched complex exhibiting a stronger tendency for particle formation compared to the one homogeneously distributed in the IL, as derived from XPS and light-scattering measurements.
Parallel Session 1B: Surface and Interface Science Studies of Advanced SCILL and SILP systems
- Dr. Florian Maier, CRC 1452
Over the past two decades, novel catalysis strategies using thin ionic liquid (IL) coatings, such as Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL), have emerged.[1] While a SILP catalyst is homogeneously dissolved in a thin IL film on a high- surface area support, the IL layer in SCILL acts as modifier of a heterogeneous catalyst to enhance selectivity, activity, and stability. We have investigated surfaces and interfaces of model systems to understand surface enrichment/depletion effects, wetting, reactions, and thermal stability in Advanced SILP and SCILL. Recent angle-resolved X-ray photoelectron spectroscopy and molecular beam studies reveal insights into surface enrichment of metal complexes in ILs ("buoy effect")[2] and selective hydrogenation of olefins at IL-platinum interfaces. [3] [1] H.-P. Steinrück et al., Adv. Mater., 2011, 23, 2571, 10.1002/adma.201100211. [2] D. Hemmeter et al., Chem. Eur. J., 2023, 29, e2022033, 10.1002/chem.202203325. [3] L. Winter et al., ACS Catal., 2023, 13, 10866, 10.1021/acscatal.3c02126.
Keynote: Molecular Water Oxidation Catalysts
- Assoc. Prof. Ming-Tian Zhang, CRC 1073
The oxidation of water to oxygen, 2H 2O → O2 + 4H+ + 4e-, is a key step for capturing solar energy in nature. Developing a molecular catalyst that can split water into oxygen and hydrogen is one of the main bottlenecks inhibiting the development of an effective and robust artificial photosynthetic system. The main challenge for catalyst development is that the catalytic process involves accumulative proton coupled electron transfer, multiple bond arrangements and finally the formation of O-O bond. Generally, a high energetic intermediate, M n+=O, was essential to O-O bond formation. On the other hand, the formation of high energetic intermediates needs to be avoided as they can reduce the longevity of the WOC and make the operation potential far away from the thermodynamic potential of water oxidation. In PSII, Mn4Ca cluster distributes charge over multiple metallic centers to avoid charge accumulation on single site and formation of Mn(V) that was proposed as key intermediates for artificial molecular Mn based WOCs. In this presentation, we will introduce our works on the molecular water oxidation catalysts, mainly focus on the redox active ligand- center PCET assisted water oxidation and bimetallic cooperative O-O bond formation in water oxidation. Reference: [1] [2] [3] H.-T. Zhang, M.-T. Zhang et al. Heterobimetallic NiFe Cooperative Molecular Water Oxidation Catalyst. Angew Chem. Int. Ed. 2023, e202218859. X.-H. Zhang et al. Identifying Metal-Oxo/Peroxo Intermediates in Catalytic Water Oxidation by In Situ Electrochemical Mass Spectrometry. J. Am. Chem. Soc., 2022, 144, 17748-17752. Q.-F. Chen, M.-T. Zhang et al. Bioinspired Trinuclear Copper Catalyst for Water Oxidation with a Turnover Frequency up to 20000 s –1. J. Am. Chem. Soc., 2021, [4] [5] 143, 19761–19768. H.-T. Zhang, M.-T. Zhang et al. Iron Catalyzed Water Oxidation: O–O Bond Formation via Intramolecular Oxo–Oxo Interaction. Angew Chem. Int. Ed. 2021, 60, 12467-12474. X.-J. Su et al. Electrocatalytic Water Oxidation by a Dinuclear Copper Complex in a Neutral Aqueous Solution. Angew Chem. Int. Ed. 2015, 54, 4909– 4914.
Keynote: Insights into the mechanism of simultaneous N 2O and NO abatement over iron-zeolites by modulated excitation spectroscopy
- Prof. Dr. Oliver Kröcher
Nitrous oxide (N2O) and nitric oxide (NO) are air pollutions that strongly affect human health and the environment. Scientific research on the abatement of both exhaust gas components has experienced a tremendous interest due to industrial processes and the forthcoming advent of ammonia-fueled ship engines, which will result in increasing emissions of these pollutants. Iron-exchanged zeolites proved to be suitable for either the individual abatement of N2O and NO or the combined selective catalytic reduction (SCR) of N2O and NO by NH3 (N2O-NO-SCR).[1] For the identification and monitoring of the redox processes and dynamics of adsorbed species on iron-zeolites in these processes, we combined catalytic experiments with transient spectroscopic methods using the modulated excitation (ME) approach[2] (ME-XAS, ME-EPR, ME-DRUV, ME-DRIFTS). The application of these methods allowed to develop a mechanistic understanding of the N 2O decomposition reaction over iron-zeolites and embed it into a comprehensive understanding of N2O-NO-SCR chemistry: i) N 2O is activated on square planar isolated Feb2+ sites in form of Feb3+-OH, ii) Feb2+-NO species drives utilization of Feb3+-OH, promoting iii) the Feb3+-OH/ Feb2+ redox transition and the oxidative activation of Fe b2+-NO to Feb3+-HONO. Finally, iv) Fe b3+-HONO is reduced by reactive NH 3,BAS producing N 2 and water through NH4NO2 and closing the catalytic cycle.[3] [1] F. Buttignol et al., Catal. Sci. Technol. 2022, 12, 7308, DOI: 10.1039/d2cy01486f. [2] V. Marchionni et al., Anal. Chem. 2017, 89, 5801-5809, DOI: 10.1021/acs.analchem.6b04939. [3] F. Buttignol et al., Nat. Catal. 2024, accepted.
Parallel Session 2A: Ligand-field/redox potential correlation in Co-Fe oxides investigated by 2p3d resonant inelastic X- ray emission spectroscopy
- Dr. Olaf Rüdiger, CRC 247
Development of new anode materials based on earth abundant transition metals for water splitting is strategically important for industrial and large-scale applications. 1 Especially significant has been the development of mixed-metal oxides, where a synergistic effect has been found in many cases resulting in dramatic improvement of the catalytic performance of the material. 2-3 Nevertheless, we still lack of understanding of these observed synergistic effects. Specifically, the Co3O4 spinel structure has shown a high catalytic activity for OER reactions and can be further improved by substitution of Fe into Co3O4 at varying concentrations. 3 Here, we studied a series of Fe substituted Co spinels with different Co/Fe ratios, using 2p3d resonant inelastic X-ray scattering spectroscopy (RIXS). This technique allows to characterize the electronic structure of the Co frontier orbitals, which should be responsible for the redox properties of the material, by interrogating the d-d transitions, including spin-forbidden transitions, which are very weak, broad, or completely silent in other spectroscopies. 4 Analysis of the spectra in combination with ligand-field theory (LFT) calculations, allowed us to assign the different features to d-d transitions of each Co site in the spinel. The measured 2p3d RIXS allows to clearly differentiate the degree of spinel inversion as the Fe loading in the Co spinel increases. Interestingly, we have found a strong correlation between the lowest energy transfer feature (~0.5eV), assigned to the Td Co2+ site, and the potential of the pre- catalytic wave, which indicates that the Fe content modulates the ligand-field splitting of the Co, and consequently the redox potential of the material. This study describes how 2p3d RIXS can be used to investigate in detail the electronic structure of electrocatalysts, being one of the first examples to provide evidence of the modulation of the electronic structure of the Co by Fe doping, even at low-doping levels, and how this modulation is correlated to the redox potential of the material. [1] Fabbri, E., et al. ACS Catalysis 2018, 8, 9765-9774. [2] Song, F., et al. J. Am. Chem. Soc. 2018, 140, 7748-7759. [3] Budiyanto, E. et al. ACS Applied Energy Materials 2020, 3, 8583-8594. [4] Hahn, A. W. et al. Inorg. Chem. 2017, 56, 8203-8211.
Parallel Session 2A: Neural Network Potentials for Catalysis
- Prof. Jörg Behler, CRC 247
Interatomic potentials relying on machine learning have become a promising tool for atomistic simulations of complex systems. Neural network potentials (NNP) are an important class of machine learning potentials, and to date four generations of NNPs have been proposed [1]. While the first generation of NNPs has been restricted to small molecules, the second generation extended the applicability of NNPs to high-dimensional systems containing thousands of atoms by constructing the total energy as a sum of environment-dependent atomic energies. Long-range electrostatic interactions can be included in third-generation NNPs employing environment-dependent charges, while the limitations of this locality approximation could be overcome by the introduction of fourth-generation NNPs, which are able to describe non-local charge transfer using a global charge equilibration step. In this talk an overview about the evolution of high-dimensional neural network potentials will be given along with a discussion of applications relevant for heterogeneous catalysis. [1] J. Behler, Chem. Rev., 2021, 121, 10037, DOI: 10.1021/acs.chemrev.0c00868.
Parallel Session 2B: Can Polymers do Magic? – The Role(s) of Soft Matter Matrices in Light-Driven Catalysis
- Prof. Felix Schacher, TRR 234
Polymers are a versatile class of materials with almost unlimited combinations of functional groups being present in close proximity. This in combination with a widely tunable solubility has enabled quite a range of examples where building blocks for light-driven catalysis (i.e., photosensitizers and catalysts) are immobilized using either covalent anchoring or non-covalent interactions. During recent years, we have developed different soft matter matrices for either light-driven hydrogen evolution (HER) or water oxidation (WOC) based on unimolecular graft copolymers, block copolymer micelles, hydrogels, or nanoporous block copolymer membranes. In all cases, close proximity of the immobilized building blocks facilitated light-driven reactivity, but we also observed additional effects during our studies, such as prolonged lifetime of photosensitizers, altered degradation pathways, or the possibility to repair / exchange catalysts or sensitizers. In addition, some effects imply that – especially in case of polyampholytic graft copolymers – the polymeric matrix is also involved in charge transport, presumably due to the high charge density present along the polymer backbone. Altogether, in this contribution we try to derive some general guidelines for the design of (charged) soft matter matrices for light-driven catalysis.
Parallel Session 2B: Enhanced H2O2 Production via Photocatalytic O2 Reduction over Tailored Poly(heptazine imides) Spheres
- Dr. Lingli Ni, TRR 234
The utilization of carbon nitride materials is significantly constrained by their inherently low surface area (SA), low charge carrier mobility between adjacent layers and low electronic conductivity.[1] Specifically, introducing porosity to the ionic derivatives of carbon nitrides, such as poly(heptazine) imides, proves challenging due to the high-temperature ionothermal process yielding more regular structure during its synthesis.[2] This study introduces a novel synthetic strategy for porous hollow poly(heptazine) imide spheres (KPHIS) via a hard-templating method.[3,4] KPHIS exhibit significantly higher SA with tunable shell thickness, improved visible light absorption, and enhanced hydrophilicity compared to the bulk material. The increased SA facilitates the intercalation of metal cations with a higher content and the channel system of PHIS is able to accommodate various cations into the structure, resulting in the changes in morphology, structure and optical properties. It allows for enhancing the catalytic performance for H2O2 production from O2 reduction under visible light. [1] X. Wang et al., ACS Catal. 2012, 2, 1596. DOI. 10.1021/cs300240x [2] Y. Wang et al., Angew. Chem. Int. Ed. 2012, 51, 68. DOI. 10.1002/anie.201101182 [3] J. Sun et al., Nat. Commun. 2012, 3, 1139. DOI. 10.1038/ncomms2152 (2012) [4] J. Kröger et al., Adv. Mater. 2022, 34, 2107061. DOI. 10.1002/adma.202107061
Parallel Session 3A: Design of hierarchical SCALMS systems via spray-drying
- Dr. Susanne Wintzheimer, CRC 1452
In the last 15 years, nanoparticles have been considered as building blocks[1] to create more complex particulate units from them, i.e. supraparticles. Supraparticles not only conserve nanoparticulate properties and lift the overall particle sizes to the microscale range but also provide additional functionalities exceeding the sum of properties of their constituent building blocks. [2] Concerning supraparticles for catalysis, this for example means providing beneficial coupling between the supraparticle components or an emerging inner porosity of the catalyst material. [3] Supraparticles can consequently provide nanoparticle-based catalytic activity and serve at the same time as support material. This permits the creation of complex catalytic materials with enhanced activity, selectivity, or stability. [4] In this talk, the tunability of spray-dried supraparticles regarding their pore structure and catalyst distribution within the support matrix is highlighted[5]. Furthermore, their high potential as hierarchical SCALMS (Supported Catalytically Active Liquid Metal Solutions) systems is demonstrated.[6] [1] S. C. Glotzer, et al., Nature Mater, 2007, 6, 557, 10.1038/nmat1949 [2] S. Wintzheimer, et al., ACS nano, 2018, 12, 5093, 10.1021/acsnano.8b00873 [3] S. Wintzheimer, et al., Adv. Funct. Mater., 2021, 31, 2011089, 10.1002/adfm.202011089 [4] S. Wintzheimer, et al., Adv. Mater., 2023, 35, 2306648, 10.1002/adma.202306648 [5] P. Groppe, et al., Small, 2024, 2310813, 10.1002/smll.202310813 [6] T. Zimmermann, et al., Mater. Horiz., 2023, 10, 4960, 10.1039/d3mh01020a
Parallel Session 3A: Predicting catalytic activity and phase transitions in liquid metal alloys by molecular dynamics with machine-learned force fields
- Prof. Dr. Andreas Görling, CRC 1452
Supported catalytically active metal solutions (SCALMS) constitute a promising new catalyst concept. SCALMS are droplets of a low melting metal matrix metal (Ga, In, Sn, GaIn, GaSn, GaCu, GaAg) with a small amount of dissolved active metal, here Pt, on a support. At reaction temperatures, the droplets are liquid and the dissolved active metal atoms frequently appear at the surface of the droplet. In this way, dynamically single atoms are provided for catalysis. SCALMS turned out to be highly active catalysts for direct alkane dehydrogenation, which show high coking resistance. Coking has been a major obstacle for large-scale industrial applications of direct alkane dehydrogenation. Predicting the catalytic activity of SCALMS by theory requires the determination of the distribution of elements at the surface of SCALMS. Molecular dynamics (MD) simulation of slab models of SCALMS can yield this information. However, classical MD is not suited for the description of liquid metals that do not exhibit stable bonds between individual atoms. Ab-initio MD based on density- functional theory is able to describe with high accuracy liquid metals but is computationally too expensive to be applied to more than the simplest systems. Here we present MD with force fields generated by machine learning from ab-initio MD runs. The resulting approach has almost the quality of ab-initio MD but requires only a fraction of the computational costs and thus enabled a screening of SCALMS with various compositions. In combination with the calculation of the position of the d-band of the active metal, the catalytic activity of SCALMS for propane dehydrogenation could be predicted. Furthermore, MD with machine-learned force fields turned out to be capable to describe the formation of intermetallic phases, which are frequently observed in liquid metal mixtures and therefore are highly relevant for SCALMS. [1] M. Moritz, et al., ACS Catal. 2024, 14, 6440-6450, 10.1021/acscatal.4c01282 [2] A. Shahzad, et al., J. Phys.: Condens. Matter 2024, 36, 175403, 10.1088/1361-648X/ad1e9f
Parallel Session 3A: Heterogenized catalysts – at the interface of molecular and solid-state chemistry
- TT.-Prof. Schirin Hanf, CRC1441
Extensive research has been directed towards heterogenizing molecular catalysts, effectively erasing the distinctions between homogeneous and heterogeneous catalysis.[1] One approach in this context involves the anchoring of molecular metal complexes onto solid supports to obtain highly dispersed metal catalysts. We have therefore utilized gold phosphine complexes as precursors for the in-situ generation of CO oxidation catalysts. We found that the type and number of ligands significantly affect the catalyst activity and stability. By employing a variety of ex-situ and operando characterization techniques, we witnessed the formation of P- containing binding pockets for the stabilization of small Au particle.[2] We have also extended our work in the field of heterogenized catalysts towards the combination of a d-metal with a p-block element to afford a main group stabilized metal phase, such as a metal phosphide or sulphide. Through the incorporation of a p-block element into the metal matrix, highly defined and uniformly distributed active sites can be formed, which are highly active catalysts in C–C bond formation reactions.[4] [1] S. Hanf, Nachr. Chem., 2021, 69, 75. [2] F. Rang, T. Delrieux, F. Flecken, F. Maurer, J. Grunwaldt, S. Hanf, ChemRxiv 2024, DOI: 10.26434/chemrxiv-2024-0vzrw. [3] F. Flecken, T. Grell, S. Hanf, Dalton Trans, 2022, 51, 8975. [4] A. Neyyathala, E. Fako, S. De, D. Gashnikova, F. Maurer, J.-D. Grunwaldt, S. A. Schunk, S. Hanf, ChemRxiv 2024, DOI: 10.26434/chemrxiv-2024-8cxlz-v2, and under review.
Parallel Session 3B: Chemical and functional DYEversity: noble metal-free photosensitizers for light driven hydrogen production
- Prof. Dr. Kalina Peneva, TRR 234
The inexpensive cost, earthly abundance, and chemical tunability of organic photoactive materials make them interesting candidates for molecular artificial photosynthetic systems. Our research focuses on the development and synthesis of organic photosensitizers that are photostable, such as perylene monoimides, BODIPY dyes as well as ketocoumarins for use in light-driven hydrogen evolution[1,2]. We will present the synthetic approach we have developed to prepare photostable rylene monoimides that can sensitise [Mo 3S 13]2-clusters in aqueous solution for hydrogen evolution driven by visible light and demonstrate the remarkable influence of the substituents on the nature of the excited state and its longevity upon excitation by visible light. Furthermore, we will demonstrate how the photocatalytic activity of photosensitizers and catalysts can be greatly enhanced by including them into macromolecular templating agents such as soft matter matrices[3,4]. [1] D. Costabel, R. T. D. De, F. Jacobi, J. Eichhorn, K. Hotzel, A. Nabiyan, C. Neumann, A. Turchanin, S. Kupfer, F. H. Schacher, S. Rau, B. Dietzek-Ivansic, K. Peneva, ACS Catalysis 2023, 13, 7159-7169. [2] D. Costabel, A. Nabiyan, A. Chettri, F. Jacobi, M. Heiland, J. Guthmuller, S. Kupfer, M. Wächtler, B. Dietzek- Ivansic, C. Streb, F. H. Schacher, K. Peneva, ACS Applied Materials & Interfaces 2023, 15, 20833-20842. [3] G. Knorr, K. Hotzel, A. Chettri, A. Skabeev, M. Wächtler, B. Dietzek-Ivansic, K. Peneva, J Mater Chem A 2023, 11, 23260-23269 [4] D. Kowalczyk, G. Knorr, K. Peneva, D. Ziegenbalg, React Chem Eng 2023, 8, 2941-3212.
Parallel Session 3B: Raman spectroscopy´s role in understanding photocatalytic systems
- apl. Prof. Dr. Michael Schmitt, TRR 234
In light of the growing demand for energy resources and the constrained supply, renewable energy represents a prospective and sustainable solution. In this context, the utilization of solar energy via novel photocatalytically active materials represents a promising avenue of research. The development of new photocatalysts necessitates the utilization of analytical techniques that can be employed in situ, with the objective of elucidating the underlying photocatalytic processes that occur following exposure to light at the molecular level. A comprehensive grasp of photochemical reactivity is a fundamental prerequisite for regulating photocatalytic activity and implementing novel repair mechanisms at the molecular or material level, for instance. Here, we will show that Raman spectroscopy is an effective method for analyzing photocatalytic processes at the molecular level. We are investigating in operando photo-catalytic activity for homo- and heterogeneous systems. Processes such as degradation of the photosensitizer, optimization, and stability of the system are investigated. The impact of dynamic irradiation on water oxidation catalysis was investigated with the objective of elucidating the underlying limitations in artificial photosynthesis and developing strategies to circumvent deactivation pathways. Furthermore, the binding conditions of photocatalysts integrated into matrices such as polymers have been investigated. For the analysis of the observed Raman spectra tailored 2D correlation analysis routines have been developed.
Parallel Session 3B: Mimicking Copper Active Sites with Cage Ligands
- Dr. Matthias Otte, CRC 1633
Imidazole units are a reoccurring motive in the active sites of copper enzymes e.g. tyrosinase (Tyr) or the Cu B site of particulate methane monooxygenase (pMMO). Heteroleptic coordination environments are known, where copper is additionally coordinated by other ligands such as carboxylates, like in the Cu C site of pMMO. Endo- Functionalized cage compounds have been shown to act as ligands towards transition metals, leading to catalysts with interesting properties for example unusual selectivity, increased turnover number or a switchable behavior.[1] Here, endo-functionalized organic cages are presented, that mimic the ligand spheres found in enzymes. For instance, they offer three imidazole units, coordinating to copper in a mode, which is reminiscent to the ones occurring at enzymatic active sites.[2] These can be used as catalysts for the aerobic oxidation of organic substrates. We could expand this strategy of cages to coordinate to metal centers in a bio-inspired fashion towards a heteroleptic ligation.[3] Such cages can be used to mimic the coordination in the CuC site of pMMO. [4] [1] M. Otte, Eur. J. Org. Chem. 2023, e202300012. [2] S.C. Bete, M. Otte, Chem. Commun. 2019, 55, 4427-4430. [3] S.C. Bete, M. Otte, Angew. Chem. Int. Ed. 2021, 60, 18582- 18586. [4] S.C. Bete, L.K. May, P. Woite, M. Roemelt, M. Otte, Angew. Chem. Int. Ed. 2022, 61, e202206120.
CRC 1633: Pushing Electrons with Protons
- Prof. Dr. Sven Schneider, CRC 1633
The new CRC 1633 examines proton-coupled electron transfer as a key phenomenon to control catalysis in solution, biological environments, and at interfaces. We will present the structure of the CRC (Figure 1), the scientific goals and resources, as well as selected examples for PCET research within the CRC.
Keynote: Choose Your Own Adventure in Metal-Hydride Catalysis
- Prof. Vy M. Dong
Metal hydrides promote a wide-range of organic transformations that include both C-C bond making and C-C bond breaking processes. This lecture will highlight the development of Rh and Co- catalysts for use in enantioselective hydrofunctionalizations (e.g., hydroacylation, hydroamination, hydrothiolation, and/or hydrogenation). In addition, a unique transfer hydroformylation will be described that allows conversion of aldehydes/alcohols to olefins. The presentation emphasizes mechanistic studies that showcase the role of counter-ions for controlling selectivities. Lastly, we disclose applications of these catalysts for transforming feedstocks into more complex building blocks and natural products. [1] Davison, R. T.; Kuker, E. L.; Dong, V. M. Teaching Aldehydes New Tricks Using Rhodium- and Cobalt-Hydride Catalysis. Acc. Chem. Res. 2021, 54 (5), 1236–1250, https://doi.org/10.1021/acs.accounts.0c00771 [2] Parker, P. D.; Hou, X.; Dong, V. M. Reducing Challenges in Organic Synthesis with Stereoselective Hydrogenation and Tandem Catalysis. J. Am. Chem. Soc. 2021, 143 (18), 6724–6745, https://doi.org/10.1021/jacs.1c00750
Parallel Session 1A: Tailoring Selectivity With Confinement-Governed Transition States
- Prof. Dr. Michael R. Buchmeiser, CRC 1333
Catalytic reactions under steric confinement mimic enzymes and benefit from the proximity of the catalyst to a pore wall with a defined geometry and polarity, thereby offering access to tailored selectivities, productivities, and activities. Here, the concepts of tailoring transition states of catalytic reactions with organometallic catalysts by confinement are presented. The concept was successfully used in the size-specific macrocyclization by tethered and surface-bound neutral ruthenium and cationic molybdenum and tungsten imido alkylidene N-heterocyclic carbene (NHC) complexes, [1-5] in Z-selective ring-opening cross-metathesis reactions, [6]in Z- selective hydrosilylation and hydroboration reactions of alkynes by Rh-NHC complexes,[7] in the alkene-selective oligomerization of ethylene with Cr(II) and Cr(III) complexes as well as in the ring- expansion metathesis polymerization with cationic molybdenum alkylidyne NHC complexes to yield low-molecular weight cyclic polymers[8]. Also, the concept of liquid confinement in biphasic supported ionic liquid phase (SILP) conditions[9] will be outlined. [1][2][3][4][5]F. Ziegler, et al., J. Am. Chem. Soc. 2019, 141, 19014, doi: 10.1021/jacs.9b08776 A. Böth, et al., ChemCatChem 2022, 15, e202201268, doi: 10.1002/cctc.202201268 F. Ziegler, et al., ChemCatChem 2023, 15, e202300871, doi: 10.1002/cctc.202300871 F. Ziegler, et al., ACS Catal. 2021, 11, 11570, doi: 10.1021/acscatal.1c03057 F. Ziegler, et al., ChemCatChem 2021, 13, 2234, doi: 10.1002/cctc.202001993 [6][7][8][9]E. L. Goldstein, et al., ChemCatChem 2022, 14, e202201008, doi: 10.1002/cctc.202201008 P. K. R. Panyam, et al., Chem. Eur. J. 2021, 27, 17220, doi: 10.1002/chem.202103099 P. Probst, et al., J. Am. Chem. Soc. 2024, 146, 8435, doi: 10.1021/jacs.3c14457 P. K. R. Panyam, et al., Faraday Disc. 2023, 244, 39, doi: 10.1039/D2FD00152G
Parallel Session 1A: Computational Modeling of Catalytic Reactions
- Prof. Dr. Johannes Kästner, CRC 1333
Computational modeling can provide insight into catalytic processes that augment experimental measurements. DFT calculations, combined with microkinetic modeling, provide detailed information on the elementary reaction steps. Combined with kinetic measurements, it allows the identification of side paths and alternative routes. Computational modification of the catalyst allows us to make predictions on improving catalytic performance. I will cover examples from metathesis [1], boron chemistry [2], and cooperative catalysis [3]. [1] P. Probst, J. Groos, D. Wang, A. Beck, K. Gugeler, J. Kästner, W. Frey and M. R. Buchmeiser J. Am. Chem. Soc. 2024, 146, 8435– 8446, 10.1021/jacs.3c14457 [2] Y. Stöckl, K. Gugeler, C. M. Holzwarth, W. Frey, S. Wegner, B. Claasen, A. Zens, D. Gudat, Ch. P. Sindlinger, J. Kästner and S. Laschat Organometallics 2024, 43, 330–340, 10.1021/acs.organomet.3c00472 [3] D. M. Wanner, P. M. Becker, S. Suhr, N. Wannenmacher, S. Ziegler, J. Herrmann, F. Willig, J. Gabler, K. Jangid, J. Schmid, A. C. Hans, W. Frey, B. Sarkar, J. Kästner and R. Peters Angew. Chem. Int. Ed. 2023, 62, e202307317, 10.1002/anie.202307317
Parallel Session 1B: Evaluation of electrocatalytic activity of OER electrocatalysts using scanning electrochemical cell microscopy (SECCM)
- Prof. Dr. Corina Andronescu, CRC 247
Structural activity correlations are essential to understanding catalyst materials that would allow a rational design of new performant electrocatalyst materials. Catalyst materials often possess an intrinsic structural complexity, for example, by having different crystal orientations. Scanning electrochemical cell microscopy (SECCM) allows local measurements to be performed at the nanoscale, thus evaluating their local electrocatalytic activity that can be correlated with different structural features when correlated with additional characterization techniques. Due to its configuration, in which a nanopipette having a hanging meniscus is approached to the catalyst surface and upon contact, an electrochemical cell is formed that is used to probe the local electrocatalytic activity, the size of the formed cell strongly depends on the surface characteristics. Electrowetting often occurs when using alkaline electrolytes and testing electrocatalysts in the oxygen evolution reaction regime, leading to measured areas of hundreds of nanometers that prevent measurements with high lateral resolution from being performed. In the present talk, I will highlight important aspects to be considered when testing oxygen evolution catalysts using SECCM, focusing in particular on the impact of the atmosphere used during the SECCM measurement on the recorded electrocatalytic activity. Correlation of the electrocatalytic activity of a Ni2/Ni3 ingot sample with the catalyst composition will be done considering the atmosphere composition, nanopipette size, and electrolyte concentration.
Parallel Session 1B: Synthesis of Mixed Metal Oxides with tailored Composition, Size, and Morphology and their Activity in OER and Thermal Oxidation Catalysis
- Prof. Dr. Stephan Schulz, CRC 247
Perowskite- and spinel-type oxides are promising catalysts in oxygen evolution reaction (OER) and alcohol oxidation. To develop a mechanistic understanding of the reactions and to improve the activity of the catalyst, the knowledge of the solid-liquid-interphase is crucial. We will report on synthetic routes for such mixed-metal nanoparticles with defined composition, size, and shape, which may help to identify structure-property relationships. The catalytic properties of the nanoparticles both in OER and alcohol oxidation were studied in ensemble measurements, revealing the influence of the particle surface on the activity. In addition, results from single particle experiments are presented, which improve our understanding of the influence of distinct crystallographic sites on the catalytic behavior in OER. References C. Placke-Yan, G. Bendt, S. Salamon, J. Landers, H. Wende, U. Hagemann, S. Schulz, Mater. Adv. 2024, 5, 3482, DOI: 10.1039/D4MA00088A. T. Quast, S. Varhade, S. Saddeler, Y.-T. Chen, C. Andronescu, S. Schulz, W. Schuhmann, Angew. Chem. Int. Ed. 2021, 60, 23444. DOI: 10.1002/anie.202109201
Keynote: Understanding Structure to Property Relations for IrOx Amorphous and Crystaline Catalysts for PEM Water Electrolyzers
- Prof. Iryna Zenyuk, CRC 247
Proton exchange membrane (PEM) water electrolyzers carry a promise to decarbonize hydrogen production sector. One of the largest cost components of these technologies is the PEM water electrolyzer stack. Within the stack membrane electrode assemblies (MEAs) rely on expensive and rare IrOx catalyst for oxygen evolution reaction. To reduce the cost of the stack and use of IrOx the loadings have to be reduced. However, there are many challenges associated with reduction of the IrOx loadings [1]: durability challenge, poor in-plane electric conductivity, poor contact with the porous transport layers. Micro-porous layers (MPLs) that consist of finer titanium particles can alleviate contact resistance problems but these layers are not yet commercially available. Another approach consists of supporting IrOx onto a metal oxide support to enable thicker catalyst layers to ensure good in-plane electric conductivity. However, degradation mechanisms of IrOx, whether it is dissolution or nanoparticle precipitation into membrane or cathode for the low-loading catalyst layers are not well understood. In this study we perform thorough MEA evaluation of low-loading catalyst layers consisting of various commercially-available IrOx catalysts and present results for beginning of life and end of life. We correlate the electrolyzer-level testing results with the structure to property relations of these catalysts. Through various x-ray and electron characterization methods combined with electrochemical methods we unveil the important structural parameters that control the layer durability. References 1. C. Wang, K. Lee, C.P. Liu, D. Kulkarni, P. Atanassov, X. Peng, I.V. Zenyuk, “Design of PEM Electrolyzers with Low Iridium Content”, International Materials Review, 09506608231216665, 2023
Keynote: Hybrid Molecular Materials for Energy Applications
- Prof. Antoni Llobet, TRR 234
The replacement of fossil fuels by a clean and renewable energy source is one of the most urgent and challenging issues our society is facing today, which is why intense research is devoted to this topic.[1] Nature has been using sunlight as the primary energy input to oxidize water and reduce CO2 to generate carbohydrates (a solar fuel) for over a billion years. Inspired but not constrained by nature, artificial systems can be designed to capture light and oxidize water and reduce protons or other useful substrates such as CO2 to generate chemical fuels. One of the key aspects for the efficient design of devices for the making solar fuels is the understanding and mastering of the catalysts involved in both the anodic and cathodic reactions. The talk will describe the initial developments up to the state of the art, of molecular catalysts and their anchoring on conductive and semiconductive surfaces. The latter is crucial for the generation of powerful hybrid molecular anodes and cathodes for the production of solar fuels.[2] [1] (a) Llobet, A. et al. Nat. Rev. Chem. 2019, 3, 331–341. (b) Llobet, A. et al. Chem. Soc. Rev. 2023, 52, 196-211. [2] (a) Llobet, A. et al. Nat. Chem. 2020, 12, 1060–1066. (b) Llobet, A. et al. Adv. Energy Mater. 2020, 2002329. (c) Llobet, A. et al. J. Am. Chem. Soc. 2021, 143, 11651–11661. (d) Llobet, A. Nat. Catal. 2022, 5, 79-82, (e) Llobet, A. et al. ACS Energy Lett. 2023, 8, 1, 172–178. (f) Llobet, A. et al., Adv. Mater. 2024, 36, 2308392. (g) Llobet, A. et al., Adv. Energy Mat. 2024, in press.