Program – Day 2
Posters and video chat will be available all day for further individual discussions.
CataLight Project Area B – Functional Polymeric Systems as Matrices for Molecular Components for Photocatalytic Water Splitting
- Dr. Stefan Zechel, CRC/TRR 234 „CataLight”
Functional polymeric systems can be utilized for the (covalent / non-covalent) integration of molecular components, e.g., photosensitizers, catalysts (for OER and HER, respectively. By this manner, the organic matrix can fulfill different functions. For instance, functional copolymers in combination with DNA nanotiles [1] will allow a precise spatial arrangement of different molecular components, which are attached to the functional copolymers. By utilization of these systems as well as block copolymers, a spatial arrangement of the molecular components on the nm-level is possible. Additionally, the functional copolymers can provide additional functionalities. Redox-active moieties can be introduced into the polymeric systems, which can be charged by photosensitizers. Subsequently, these charges can be utilized to drive a catalytic reaction. ______________________________________________________________________ [1] N. Hannewald; P. Winterwerber; S. Zechel; D. Y. W. Ng; M. D. Hager; T. Weil; U. S. Schubert, Angew. Chem. Int. Ed. 2020, Accepted.
CataLight Project Area C - Theoretical and Experimental Mechanistic Studies
- Prof. Dr. Dirk Ziegenbalg, CRC/TRR 234 „CataLight”
The collaborative research center CATALIGHT aims on developing molecular light-driven chromophores and catalysts, and establishing concepts for their integration into soft matter matrices. Hierarchical nanostructuring into membranes, colloids, and thin films will give unprecedented control over substrate and product transport, and will be used to tune catalytic self-regulation, stimuli-responsiveness and triggered repair. In-depth experimental and theoretical studies will provide fundamental insights into the mechanisms which govern catalytic reactivity and stability. CATALIGHT will therefore establish general design concepts for light-driven molecular catalysts in soft matter matrices. Research area C “Theoretical and Experimental Mechanistic Studies” provides a unique set of experimental and theoretical analysis tools to examine the physical and chemical behavior of molecular components in solution and after integration into soft matter matrices. Project area C combines leading expertise in experimental and theoretical materials analysis to provide fundamental understanding of the processes which govern light-driven catalytic reactivity and stability in soft matter matrices. Photophysical and photochemical properties are examined with high temporal and spatial resolution so that the properties of excited states are accessible by absorption and emission spectroscopy, spectroelectrochemistry as well as resonance Raman and time-resolved transient absorption spectroscopy. Reaction kinetics associated with catalytic reactivity and degradation are studied by correlating transient absorption spectroscopy with scanning electrochemical microscopy and in situ Raman/FT-IR spectroscopic studies. The experimental data is examined using homo- and hetero-correlation analysis to establish understanding across several analytical techniques. The experimental analysis of key structures and fundamental reaction steps is combined with theoretical multi-scale modelling to describe catalytic reactivity and understand underlying mechanisms (area A “Molecular Components”) as well as gain insight into molecule-material interactions beyond the molecular level (area B “Integration of Molecular Components into Functional Soft Matter Matrices”). This contribution gives an overview of the current progress in project area C.
Photochemically Driven Redox-Transformations of Small Molecules with Transition Metal Complexes
- Prof. Dr. Sven Schneider, CRC 1073
Hydrogen transfer from transition metal hydride complexes is a key elementary reaction in catalytic chemical and biochemical redox transformations. For example, the hydrogenation of CO2 via transition metal hydrides generally gives formate products (M–O(O)CH), which is pre-determined by the selectivity of the ‘normal’ hydrogen transfer step from the metal to the carbon atom. In this contribution, strategies will be discussed how to control the selectivity of CO2 activation by photochemical excitation of molecular catalysts. For example, the nickel hydride complex 1 (Figure 1) switches the CO2 insertion selectivity from formate-selective ‘normal insertion’ in the thermal regime (2) to the hydroxycarbonyl-selective ‘abnormal insertion’ under photolytic conditions (3).[1] Pump-probe IR and UV absorption spectroscopy and computational results support the relevance of metal-ligand cooperativity for the photochemical reactivity. The ‘abnormal’ CO2 insertion enables CO instead of formic acid selective hydrogenation by photochemically driven reverse water gas shift at room temperature.[2] ______________________________________________________________________ [1] F. Schneck et al., Nat. Commun. 9 (2018) 1161. [2] F. Schneck et al., Angew. Chem. Int. Ed. 57 (2018) 14482.
Experiments on Vibrational Energy Pooling and Transport in Condensed Phases Using a Mid-Ir Superconducting Nanowire Single Photon Detector
- Prof. Dr. Alec Wodtke, CRC 1073
Superconducting nanowire single-photon detectors (SNSPDs) provide sufficient sensitivity to enable laser induced fluorescence (LIF) experiments in the mid-infrared [1,2]. I will present results of experiments on the vibrational dynamics of monolayers and multilayers of solid CO adsorbed at the surface of a NaCl crystal that show the capabilities of SNSPDs and reveal intriguing phenomena arising from dipole-dipole coupling between molecules. In these experiments, a laser light pulse excites about half of the CO to its v=1 state within a few nanoseconds. The SNSPD detects wavelength and time-resolved mid-infrared emission from CO in vibrational states up to v=27 that are produced by vibration-vibration (V-V) energy transfer—CO(v=m)+CO(v=n)→CO(m-1)+CO(n+1). Kinetic Monte Carlo (kMC) simulations reproduce observed time-dependent population distributions, showing that vibrational energy collects in a few CO molecules at the expense of those up to eight lattice sites away and that NaCl’s transverse surface phonons take up the excess energy of each V-V transfer step. This gives rise to peculiar bottlenecks in the march up the vibrational ladder. The relaxation of these hot molecules is also fascinating. We find that the vibrating CO molecules behave like classical antennae, losing their energy to NaCl lattice-vibrations via the electromagnetic near-field. In fact, the theory that explains this phenomenon is an extension to the atomic-scale, of Sommerfeld’s theory of ground waves that he developed to understand radio wave propagation. This is a weak coupling limit where the anharmonic interatomic forces normally so important to energy flow can be completely neglected [3]. We also observe orientational isomerization—new lines appear in infrared emission spectra when “the right-side up” CO flips to an “up-side down” metastable structure. In its ground vibrational state, CO binds with its C atom adjacent to a Na ion. In vibrationally excited states the electrostatics change and CO binds with its O atom next to the Na+ ion. The lifetime of the metastable state increases dramatically, when buried beneath other adsorbed molecules [4]. Finally, I will show a novel concept of mid-infrared light harvesting, where a thick overlayer absorbs many infrared photons and, due to the properties of V-V energy transfer, it is possible to transport a large fraction of this vibrational energy to the interface, where it drives the CO flipping reaction. The vibrational energy transport seen here is physically similar to Förster energy transfer. ______________________________________________________________________ [1] Accounts of Chemical Research 50, 1400-1409 (2017), [2] Optics Express 26, 14859-14868 (2018). [3] Science 363, 158-161 (2019), [4] Science 367, 175 (2020)
Meet the Speaker Session/ Break
- Dr. Stefan Zechel, CRC/TRR 234 „CataLight” Prof. Dr. Dirk Ziegenbalg, CRC/TRR 234 „CataLight” Prof. Dr. Sven Schneider, CRC 1073 Prof. Dr. Alec Wodtke, CRC 1073
All speakers of the session can be asked more specific questions in individual group chats. Please join the speaker of your choice at the "Meet-the-speaker table".
Atom Probe Tomography: Analysis of Soft Matter, Liquids and Interfaces at the Top of the Tip
- Prof. Dr. Guido Schmitz, CRC 1333
The cutting-edge research goals of the CRC 1333 require a target-oriented development of dedicated experimental and theoretical methods. After a short overview on these activities, I will particularly discuss atom probe tomography, a method of high resolution analysis that stands out by combining single-atom sensitivity with a 3D volume reconstruction. The method is based on laser-assisted field evaporation from nanometric emitter tips. We aim to break the materials boundary towards liquids, softmatter and complex geometries of confinements. To this end, a new instrument has been constructed that joins cryogenic ion beam preparation with a flexible atom probe chamber. Meanwhile, we are able to produce nanometric needles from frozen liquids, even from pure water. Studies are performed with aqueous solutions, liquids of short alkanes, self-assembling monolayers and linker molecules. The talk presents recent measurements of mass spectra, their dependence on field and laser intensities, the development of volume reconstruction algorithms and discusses the potential of measuring individuals bond strengths.
Ordered Mesoporous Carbons with Controlled Pore Diameters via Organic Self-Assembly of Reverse Pluronics
- Dr. Stefan Naumann, CRC 1333
The usefulness of amphiphilic triblock copolyethers (“Pluronics”) as structure-directing agents in self-assembly processes is dependent on their tunability regarding molar mass, architecture (ABA vs. BAB) and ratio of hydrophilic to lipophilic moieties. By application of a specifically developed organopolymerization catalyst, we were able to expand this property spectrum, now encompassing high-molar-mass copolyethers (> 20.000 g/mol). In particular, this now allows for the generation of highly ordered mesoporous carbons with designed pore diameters based on the so-called “Reverse Pluronics” (PPOn-PEOm-PPOn). Polymer synthesis, carbonization procedure and structure-property relationships will be discussed, alongside a presentation of first results from the application of the thus received carbons as catalyst supports.
Real and Working Structure Analysis of Spinel-Type Catalysts
- Dr. Thomas Lunkenbein, CRC/TRR 247
Heterogeneous oxidation catalysis over metal oxides is a key technology in chemical industry and is used for the efficient production of functionalized short-chain alkanes. This technology usually involves complex and multinary compounds that operate at elevated temperatures. In recent years, much progress has been made in the characterization of these materials focusing on a detailed description of their real structures, and how these influence the structure under working conditions.[1],[2] However, at low reaction temperatures, i.e. below 200 °C, it is still unclear whether chemical dynamics exist and, if they exist, how they influence the surface states of such oxide catalysts. A prospective transition from gas to liquid phase oxidation reactions would benefit from this knowledge and lower the overall energy demand. Due to complexity, low temperature chemical dynamics are difficult to study for industrially relevant catalyst systems. In order to reduce complexity, perovskite- and spinel-type materials are often used as model oxidation catalysts.[3] Here, we present a comparative study that is based on complementary integral (in situ) X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM) and local (scanning) transmission electron microscopy ((S)TEM) coupled with electron energy loss spectroscopy (EELS). This approach allows insights into the geometric and electronic structures of spinel-type catalysts that can operate at low temperatures. Using the cobalt-oxide-system as an example, we will show that the surface is slightly reduced compared to the bulk. Furthermore, we highlight the evolution of the surface during low temperature activation and present atomic scale evidence of surface reconstructions in the temperature regime between 150 °C and 250 °C. In addition, preliminary ESEM experiments reveal direct insights into the surface reactivity of polycrystalline foils during the isopropanol oxidation and allow the correlation of reaction profiles with pre-adjusted surface states and their evolution during reaction. It is, thus, possible to assign surface states relevant for low and high temperature activity regimes that have been discussed before.[4] In summary, the presented results indicate a wide structural variety and dynamic behavior for spinel-type catalysts that have to be considered in modeling. Moreover, these data form a sound basis for further comparative studies, in which the complexity will be gradually enhanced. Such studies are urgently required in order to enhance our understanding of the reaction mechanisms for low temperature oxidation reactions. __________________________________________________________ [1] L. Masliuk, M. Heggen, J. Noack, F. Girgsdies, A. Trunschke, K. E. Hermann, M. G. Willinger, R. Schlögl, T. Lunkenbein, J. Phys. Chem. C 121, 24093 (2017). [2] A. Trunschke, J. Noack, S. Trojanov, F. Girgsdies, T. Lunkenbein, V. Pfeifer, M. Hävecker, P. Kube, C. Sprung, F. Rosowski, R. Schlögl, ACS Catal. 7, 3061 (2017). [3] J. Hwang, R. R. Rao, L. Giordano, Y. Katayama, Y. Yu, Y. Shao-Horn Science 358, 751 (2017). [4] S. Anke, G. Bendt, I. Sinev, H. Hajiyani, H. Antoni, I. Zegkinoglou, H. Jeon, R. Pentcheva, B. Roldan Cuenya, S. Schulz, M. Muhler ACS Catal. 9, 5974 (2019).
From Ensemble to Single Entity Electrochemistry or how to Determine Intrinsic Electrocatalytic Activity of Nanoparticle Electrocatalysts
- Prof. Dr. Wolfgang Schuhmann, CRC/TRR 247
Determination of the intrinsic electrocatalytic activity of catalyst particles is an impossible using ensemble methods in which a large number of catalyst particles are together coated on a macroscopic electrode surface typically in presence of (conducting) binder materials and ionomers such as Nafion. If reactions are investigated in which multiple coupled electron/pro-ton transfer reactions occur such as the oxygen reduction reaction, the oxygen evolution reaction, alcohol oxidation or CO2 reduction reaction the catalytic turnover is not only limited by mass transport reactions but also by changes in the local pH value within the catalyst film. This is leading to a challenging situation in which the comparison of different electrocatalysts with respect of the catalytic activity is impossible and the definition of overpotentials for a given reaction does not provide insight into the reaction itself, even more due to the fact that normalization of the measured current to the footprint of the electrode does not provide evidence of the electrochemically active surface area [1]. Hence, new electrochemical methods have to be developed which are addressing single nanoparticle electrocatalysts in absence of any binder materials, preventing diffusion limita-tions and local pH value changes. The presentation will show examples of such investiga¬tions using the nanoparticle-on-the-stick method in which individual catalyst nanoparticles are immobilized [2], placed or grown [3] on nanoelectrodes, as well as the determination of the electrocatalytic activity of nanoparticles using scanning electrochemical cell microscopy (SECCM) [4]. Single entity electrochemistry is considered the basis for accurate determination of electro-catalytic activity of nanoparticle electrocatalysts. __________________________________________________________ [1] J. Masa, C. Andronescu, W. Schuhmann, Angew. Chem. Int. Ed., 2020 (in press) [2] T. Löffler, H. Meyer, A. Savan, P. Wilde, A. Garzón Manjón, Y.-T. Chen, E. Ventosa, C. Scheu, A. Ludwig, W. Schuhmann, Adv. Energy Mater. 8 (2018) 1802269 [3] H. Barike Aiyappa, P. Wilde, T. Quast, J. Masa, C. Andronescu, Y.-T. Chen, M. Muhler, R. A. Fischer, W. Schuhmann, Angew. Chem. Int. Ed. 58 (2019) 8927-8931 [4] a) C. L. Bentley, C. Andronescu, M. Smialkowski, M. Kang, T. Tarnev, B. Marler, P. R. Unwin, U.-P. Apfel, W. Schuhmann, Angew. Chem. Int. Ed. 57 (2018) 4093-4097. b) T. Tarnev, H. Barike Aiyappa, A. Botz, T. Erichsen, A. Ernst, C. Andronescu, W. Schuhmann, Angew. Chem. Int. Ed. 58 (2019) 14265-14269. __________________________________________________________ Acknowledgement. The presenting author is grateful to all coworkers and cooperation part-ners who contributed to this research topic especially to Tsvetan Tarnev, Harshitha Barike Ayappa, Corina Andronescu, Justus Masa, Thomas Quast, Swapnil Varhade, Emmanuel Tetteh, Thomas Erichsen, Nivedita Sikdar, Tobias Löffler, Patrick Wilde, Denis Öhl, Tim Bo-browski, Stefan Dieckhöfer, Joao Junquiera, Jonas Weidner. This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Re-search Foundation) in the framework of the TRR 247 [388390466] within the collaborative research centre/transregio 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase", under Germany´s Excellence Strategy – EXC 2033 – 390677874 – RESOLV, FOR 2982 [433304633; 433304666] within the research unit "UNODE - unusual anode reactions" as well as from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement CasCat [833408]).
Meet the Speaker Session/ Break
- Prof. Dr. Guido Schmitz, CRC 1333 Dr. Stefan Naumann, CRC 1333 Dr. Thomas Lunkenbein, CRC/TRR 247 Prof. Dr. Wolfgang Schuhmann, CRC/TRR 247
All speakers of the session can be asked more specific questions in individual group chats. Please join the speaker of your choice at the "Meet-the-speaker table".
Closing Remarks
- Prof. Dr. Sven Rau, CRC/TRR 234 „CataLight” Prof. Dr. Michael R. Buchmeiser, CRC 1333 Prof. Dr. Malte Behrens, CRC/TRR 247 Prof. Dr. Christian Jooss, CRC 1073
Closing statements of the spokespersons of the four participating CRCs.