Conference Presentations

2024

Imran Abbas, KUL Co-authorsSumant Phadke, Joao Coroa, Jinlong Yin, Olga Safonova, Christophe Copéret, Didier Grandjean, Ewald Janssens

PdZn Bimetallic Clusters-based Catalysts for CO2 Hydrogenation to MethanolAbstractPdZn bimetallic catalysts show significant potential for CO₂ hydrogenation to methanol, but understanding their structure under reaction conditions remains challenging due to the complexity of heterogeneous catalysis processes (1-4). To address this, we synthesized well-defined PdZnOx catalysts using laser ablation-based Cluster Beam Deposition (CBD)(5) under ultra-high vacuum conditions from a Pd_0.5Zn_0.5 alloy target and deposited them on carbon paper. Alloying and oxidation levels were tuned by controlling the O₂ (0-5%) content into the He condensation gas during production. For comparison, Pd nanoparticles were also produced via CBD and deposited on ZnO powder, which was then dry-coated also onto carbon paper. CO₂ hydrogenation activity tests carried out in a high-pressure microreactor with sensitive gas analytics show that a minute concentration of Pd nanoclusters (0.1 wt%) on bulk ZnO enhances methanol formation rates by 10 times while the PdZn alloy produced in 1% O₂/He condensation gas is the most active catalyst with methanol selectivity reaching 90%. Operando X-ray Absorption Fine Structure (XAFS) spectroscopy at Pd and Zn K edges under CO₂ hydrogenation conditions combined with transmission electron microscopy (TEM) of the as-prepared samples revealed strong alloying-dealloying dynamics in the bimetallic catalysts. EXAFS analysis of Pd clusters on ZnO shows that their Pd-Pd coordination increases while their Pd-Zn coordination increases highlighting changes in the nanoalloy composition during the reaction (Fig. 2). Differences in the evolution of Pd-Zn bond distances in PdZn, PdZnO_x and Pd/ZnO catalysts shows the formation of α and/or β phases in the PdZn nanoalloy that could be directly related to their different catalytic activities and selectivities. References: 1. M. Bowker et al., ACS Catal. 12, 5371–5379 (2022); 2. M. Zabilskiy, et al. Angew. Chem. Int. Ed. 202, 17053–17059 (2021); 3. H. Bahruji et al. J. Catal, 133–146 (2016); 4. M. P. Brown and K. Austin, Appl. Phys. Letters 85, 2503-2504 (2004); 5. V. C. Chinnabathini et al. Nanoscale, 15, 6696-6708 (2023).

Imran Abbas, KUL Co-authorsSumant Phadke, Joao Coroa, Jinlong Yin, Olga Safonova, Christophe Coperet, Didier Grandjean, Ewald Janssens

In situ investigation of Pd/ZnO catalysts prepared by Cluster Beam Deposition Technology for CO₂ hydrogenation to methanolAbstractPd/ZnO catalysts show promising CO₂ hydrogenation to methanol activity, yet the metal-support interface and its role in the reaction mechanism remains a topic of ongoing research. One of the reasons for the lack of consensus is the inherent complexity of the heterogeneous catalysts which hinders active site investigation at reaction conditions.To overcome this challenge, we synthesized well-defined Pd, Pd_0.01Zn_0.99O_x, Pd_0.2Zn_0.8O_x, Pd_0.5Zn_0.5O_x and Pd_0.7Zn_0.7O_x nanoparticles under ultra-high vacuum conditions using Cluster Beam Deposition (CBD) technology and soft-landed them onto ZnO or SiO₂. The Pd/Zn composition was efficiently controlled by the ablated target's composition, while the oxidation level was regulated by introducing O₂ (up to 5%) during ablation. Notably, CBD produces catalysts without impurities, ligands, or spectator phases, simplifying the investigation of active phases and interfaces using techniques such as Transmission Electron Microscopy (TEM) and element-specific X-ray Absorption Spectroscopy (XAS). Even a minute concentration of Pd nanoclusters (0.1 wt%) deposited on bulk ZnO exhibits a methanol formation rate ten times higher than that of blank ZnO, with a selectivity exceeding 60%. The activity of bimetallic PdZnO_x nanoclusters follows a volcano-type trend with an optimal Pd:Zn ratio of 50:50, although their selectivity for methanol is lower than Pd/ZnO. Operando XAS shows the formation of a β-PdZn alloy in contact with ZnO, which may be a key factor contributing to the high selectivity of Pd/ZnO. In a selected bimetallic PdZnO_x sample, ZnO is observed to undergo reduction during the reaction, leading to the formation of an α-PdZn alloy, potentially associated with the high activity of bimetallic samples in CO formation. This work is crucial in understanding the catalytic activity of Pd/ZnO in CO₂-to-methanol conversion. It simplifies the investigation of active phases and interfaces through advanced CBD technology, potentially enabling the development of more efficient and selective catalysts for sustainable methanol production, with a significant impact on reducing greenhouse gas emissions and advancing green energy technologies.

Filippo Romeggio, DTU Co-authorsFilippo Romeggio, Rikke E. Tankard, Stefan K. Akazawa, Alexander Krabbe, Olivia F. Sloth, Niklas M. Secher, Sofie Colding-Fagerholt, Stig Helveg, Richard E. Palmer, Christian D. Damsgaard, Jakob Kibsgaard, Ib Chorkendorff

Increasing catalyst stability: AuTiO_x size-selected nanoparticles for CO oxidation AbstractIntroduction Improving catalyst stability is a central challenge for many thermal and electrocatalytic processes which could play a key role in the transition to more sustainable production of fuels and chemicals in the future¹. A catalyst in the form of nanoparticles (NPs) or clusters bound to a support can deactivate, e.g., due to sintering over time, in a reactive environment. From a research perspective, the change in structure of the catalyst during reaction can make it difficult to relate the ex-situ properties to the in situ catalytic performance. More practically, poor stability limits the relevance of an otherwise active catalyst for commercial use. Understanding fundamental ways to stabilize active metal NPs prone to sintering can therefore have a wide-ranging impact. In this work, an enhanced stability of mass-selected AuTiOx alloy NPs on TiO2 for thermocatalytic CO oxidation is demonstrated compared with pure Au NPs. Through a combination of activity tests, spectroscopy, and microscopy methods, the structure of the AuTiOx NPs is investigated in detail and shown to exhibit a reduced mobility and sintering under reactive conditions compared to Au NPs. Results and Discussion The activity and stability of 56k amu Au NPs and 160k amu AuTiOx NPs for thermal CO oxidation were investigated and compared. The AuTiOx NPs were observed to have a core-shell structure withan Au core of 2.1(2) nm and a surrounding Au-TiOx alloy shell. When deposited on TiO2-coated micro-reactors for activity measurements, a deactivation over time was detected for the Au NPs at vtemperatures as low as 50C, and a significant sintering was observed after the reaction for the Au NPs compared to the AuTiOx NPs. The increased stability of the AuTiOx NPs is thought to be caused by a self-anchoring effect of the AuTiOx NP shell on the TiO2 support, similar to stabilization by encapsulation by the support ². The structure of the AuTiOx NPs was observed to be stable under reactive conditions in the electron microscope and after activity tests using depth profiling experiments. On silicon nitride, the AuTiOx NP core-shell structure remained stable under reactive conditions at temperatures up to 400C, whereas the pure Au NPs reacted with the support at temperatures above 200C.The findings presented complement other studies on AuTiOx catalysts synthesized via physical methods ³, and demonstrate how cluster beam methods can allow for fine-tuning of catalyst structures by enabling consistent synthesis of well-defined NP compositions. The work also highlights the importance of obtaining an accurate characterization of the NP structure in evaluating the performance. It lays the groundwork for further research and development of alloy NP catalysts, contributing to the design of more efficient and stable catalysts for a wide range of industrial applications. References: 1. Seh Z. W., et al., Science (2017), 355, 146. 2. Tang H., et al., Sci. Adv. (2017), 3:e170023. 3 Niu, Y.; et al., Nanoscale (2018), 10 (5), 2363–2370.

2023

Esperanza Sedano Varo, DTUCo-authorsRikke

Tailoring CO₂ electroreduction selectivity with size-controlled Au and Cu nanoparticlesAbstract

Dimitra Papamichail, KU Leuven Co-authorsDeema Balalta, Imran Abbas, Jason Song, Thomas Altantzis, Sara Bals, Deepak Pant, Ewald Janssens, Didier Grandjean, Peter Lievens

Gas-Phase CuPd Bimetallic Cluster-Modified Electrodes as Model Electrocatalysts for CO₂ ConversionAbstractCopper-based electrocatalysts possess the unique ability to convert CO2 to multicarbon products such as ethylene – a precursor in many industrial processes. However, their stability and product selectivity remain insufficient. A promising approach to overcome these
shortcomings and design better CO2RR electrocatalysts is to tune Cu selectivity by forming bimetallic Cu-M systems ¹ while establishing their detailed structure-selectivity relationship.
To achieve this, we used laser ablation Cluster Beam Deposition (CBD) ² to produce well defined bimetallic cluster-modified electrodes ². More specifically, CuPd clusters with an original average size of 2.5 nm and mass loadings of 1-2 µg cm-2 were deposited onto a carbon support. To produce a model catalyst which allows the independent investigation of the electronic and geometric structural effects induced to Cu by the second element, a Cu0.9Pd0.1 composition was selected ³. CuPd cluster-decorated electrodes were tested for CO2 electrolysis and methane (C1), and ethylene (C2) were found among the products. As it is shown from the electrocatalytic activity trends, the evolution of C2 products is correlated with the cluster mass loading. In addition, the cluster coverage influences the onset of the competitive H2 production (HER). High resolution (Scanning) Transmission Electron Microscopy ((S)TEM) coupled with Energy-dispersive X-ray spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS) analyses of the as-prepared cluster-modified electrodes, show that the clusters feature some degree of CuPd alloying in the ambient. CuPd clusterbased systems will then be investigated in-situ using X-ray absorption spectroscopy to unravel their structure-catalytic performance relationship.References (1) X. Zhang et al., Materials Today Advances, 7 (2020) 100074. (2) V. C. Chinnabathini, et al., Nanoscale, 15 (2023) 6696-6708. (3) L. Zaza et al., ACS Energy Letters 7 (2022,), 4, 1284–1291 N

Maximilian Winzely, PSICo-authorsJuan

A novel electrochemical cell for the in situ X-ray absorption spectroscopic investigation of cluster-based CO₂-electroreduction catalystsAbstractThe electrochemical conversion of CO2 into valuable products (e.g., CO or HCOOH) is a promising prospect to slow down global warming. While catalysts with a promising selectivity towards such C1-products have been identified (e.g. Pd) ¹, further improvements in their activity, selectivity and stability are needed. The required design of such improved catalysts can be greatly aided by recent advancements in the synthesis of mass-selected, (sub-) nanometric metal clusters by the so called cluster beam deposition (CBD) method and their subsequent characterization by in situ x-ray absorption spectroscopy (XAS).² However, constraints intrinsic to the CBD method limit the attainable catalyst loadings to ultra-low values below 10 microg_metal/cm_geom². This would in turn translate into unpractically long spectral acquisition times when performing in situ XAS measurements in a standard configuration (i.e., with an Xray beam incidence of 45 or 90° with regards to the electrode plane). To tackle this problem we have developed a new spectro-electrochemical XAS flow cell that enables spectral acquisition in fluorescence mode using an X-ray beam incidence angle of ≤ 0.1° with regards to the working electrode’s substrate plane, i.e., in a so called grazing incidence (GI) configuration (see Figure 1). In this acquisition configuration we successfully recorded an in situ spectrum of palladium in the metallic and full hydride state with a time resolution of 5 minute per spectrum while using a Pd-loading as low as 10 microgPd/cm². References (1) J.S. Diercks, B. Pribyl-Kranewitter, J. Herranz, P. Chauhan, A. Faisnel, T.J. Schmidt, Journal of The Electrochemical Society 168 (2021) 064504. (2) A. Yadav, Y. Li, T.W. Liao, K.J. Hu, J.E. Scheerder, O.V. Safonova, T. Holtzl, E. Janssens, D. Grandjean, P. Lievens, Small 17 (2021) e2004541

Imran Abbas, KU LeuvenCo-authorsSumant Phadke, Joao Coroa, Jinlong Yin, Olga Safonova, Christophe Coperet, Didier Grandjean, Ewald Janssens

Gas-phase Pd and PdZn clusters deposited on ZnO and SiO₂ as model catalyst for CO₂ hydrogenation to methanolAbstractSupported Pd nanoparticles have demonstrated promising catalytic activity for the hydrogenation of CO2 into methanol, but the nature of the metal-support interface and its role in the reaction mechanism remains a topic of ongoing research^1-3. In this study, we produced model catalysts by directly depositing well-defined Pd and PdZn clusters onto ZnO and SiO2 powders using the Cluster Beam Deposition (CBD) technology. The clusters were deposited in high vacuum onto one gram of each pre-dried oxide powder placed in a vibrating cup to ensure the uniform deposition of size-controlled clusters containing 500 to 700 atoms. The cluster sizes were determined through in-situ time-of-flight mass spectrometry, and the loading of 0.1 wt% Pd clusters on the oxide powders was confirmed using ICP-OES. For the activity testing, the samples were in situ activated in pure hydrogen at 120°C for 30 minutes before conducting the catalytic tests. The catalytic activity tests for CO2 hydrogenation were performed at 200-250°C and 40 bar, using 0.4g of each sample loaded in a plug flow reactor with a 5 mL/min feed gas mixture of 3H2:1CO2.
A very low concentration of Pd clusters (0.1 wt%) on ZnO was found to promote the hydrogenation of CO2 to methanol and CO, while only minimal activity was observed for Pd/SiO2. Fig. 1 illustrates a four-fold increase in the CO2 hydrogenation rate compared to the sum of blank ZnO and Pd/SiO2, confirming the excellent Pd-ZnO synergy in these model catalysts. To further investigate the Pd-ZnO synergy and uncover the structure-activity relationship, in-situ X-ray absorption spectroscopy was performed under CO2 hydrogenation conditions. The use of well-defined Pd and PdZn catalysts enables a detailed investigation of the Pd-Zn and Pd-ZnO interfaces to unravel their structure-activity relationship.References (1) M. Zabilskiy, et al. Angew. Chem. Int. Ed. 2021, 202, 17053–17059.(2) S.R. Docherty et. al. JACS Au 2021, 1, 450–458.(3) H. Bahruji et al. J. Catal. 2016, 133–146.

Pavol Mikolaj, UUCo-authorsSandra M. Lang, Thorsten M. Bernhardt

Activation of CO₂ by free metal oxide clustersAbstractMotivated by the performance of the industrially employed Cu/ZnO catalyst for direct CO2 hydrogenation ¹, the European training network CATCHY ² seeks to develop new and high performance cluster-based catalysts. As part of this project, we utilize transition metal oxide clusters in the gas phase as model systems to study the fundamental driving forces that
determine the reactive and catalytic properties of such catalysts. So far, we have investigated the interaction of CO2 with small copper oxide, cobalt oxide and yttrium oxide clusters via infrared multiple-photon dissociation (IR-MPD) spectroscopy (collaboration with J. Bakker, FELIX laboratory). Clusters were produced by laser ablation of a metal target in the presence of He carrier gas seeded with O2. Independent of the metal, cluster formation appears to be strongly charge dependent, with cations preferably forming oxygen-rich clusters, while anions tend to form stoichiometric and oxygen-deficient clusters. To study the cluster-CO2 interaction, a CO2/He mixture was subsequently introduced in an adjacent flow tube reactor and the resulting reaction products were investigated via infrared spectroscopy. In the case of cationic copper and cobalt oxide complexes, the characteristic Fermi dyad of CO2 is observed, indicating the presence of physisorbed, unactivated linear CO2. In contrast, all anionic cluster complexes show bands which are characteristic for an activated bent CO2
molecule (cf. Figure 1). Most interestingly, the IR-MPD spectra of yttrium oxide-CO2 complexes
appear to be more complex than the spectra of the copper and cobalt oxide complexes, potentially indicating different CO2 binding motifs. References (1) J. Artz, T.E. Müller, K. Thenert, J. Kleinekorte, R. Meys, A. Sternberg, A. Bardow & W. Leitner, Chem. Rev. 118(2) (2018) 434-504.(2) https://www.catchy-etn.eu/

Bárbara Zamora, BMECo-authorsLászló Nyulászi (BME) and Tibor Höltzl (BME,FETI)

CO₂ and H₂ Activation on Zinc-doped Copper Clusters in a Sputtering Gas Aggregation Source AbstractCopper-based catalysts are commonly used to facilitate the CO₂ hydrogenation into useful chemicals. Here we systematically investigate the CO₂ and H₂ activation and dissociation on small Cu_nZn^0/+ (n=3-6) clusters using Density Functional Theory. Our findings reveal that Cu₆Zn acts as a superatom, exhibiting an enlarged HOMO-LUMO gap and displaying inertness towards the activation or dissociation of CO₂ or H₂. While other neutral clusters exhibit weak CO₂  activation, with the exception of the otherwise unstable Cu₄Zn, the cationic clusters tend to preferentially bind CO₂ in a monodentate, non-activated manner. Generally, CO₂ activation is not favored. Conversely, H₂ dissociation is favored on all investigated clusters, except for Cu₆Zn. We interpreted the bidentate CO₂ binding on the clusters based on the atomic charges and the energy decomposition analysis, which showed that the cluster donates electrons to the antibonding orbital of CO₂, thereby leading to its activation. In contrast to extended surfaces, the frontier orbitals of the clusters contribute mainly to the charge transfer. As the frontier orbital occupations and the orbital energies strongly depend on the number of itinerant electrons, CO₂ binding is also cluster-size dependent.References (1) Zamora, B. Nyulászi, L. Höltzl, T.  CO₂ and H₂ activation on zinc-doped copper clusters. (Manuscript submitted for publication).

Deepak Pradeep, RUCo-authorsBarbara Zamora Yusti, Rutger Zijlstra, Mate Szalay, Tibor Höltzl, László Nyulászi, Joost M. Bakker

3d metal doping of cobalt clusters to tune the activity toward CO₂AbstractThe increasing atmospheric CO2 concentration leads to global warming and climate destabilization. One potential way to mitigate CO2 emissions is by converting CO2 into useful chemicals. In industry, for example, methanol is produced by direct hydrogenation of CO2 over a Cu-ZnO-Al2O3 catalyst.¹ A detailed understanding of the reaction mechanisms is required for a rational design of more active and selective catalysts. Gas-phase metal clusters can form an idealized model system for the active sites of the complex catalysts.² We aim to investigate on a molecular level how the doping of clusters with foreign elements affects their reactivity.³ To test this experimentally, we aim to study the interaction of first-row transition metal-doped clusters with CO2 and H2 using IR photo fragmentation spectroscopy complemented by DFT calculations. For this, we present a newly commissioned dual-laser, dual-target cluster source and show how the doping of cationic cobalt clusters by single vanadium or iron atoms affects the adsorption mode of CO2. References (1) Waugh, K. C. Methanol Synthesis. Catal. Today, 15 (1) (1992), 51–75. (2) Lang, S. M.; Bernhardt, T. M. Phys. Chem. Chem. Phys., 14 (2012), 9255−9269.(3) Szalay, M.; Buzsáki, D.; Barabás, J.; Faragó, E.; Janssens, E.; Nyulászi, L.; Höltzl, T. Phys. Chem. Chem. Phys., 23 (38) (2021), 21738–21747.

João Coroa, TCL & KU Leuven Co-authorsGiuseppe Sanzone (TCL), Hailin Sun (TCL), Ewald Janssens (KU Leuven), Jinlong Yin (TCL)

Influence of the magnetic field configuration of a magnetron on the cluster growth mechanism in a sputtering gas aggregation source AbstractCluster production using physical methods provides several advantages compared with chemical routes, such as better control of the size distribution and the minimised impact on the environment. On the other hand, their slow deposition rate has inhibited the physical approaches from being used more widely. To address this issue, we have systematically studied the influence of aerodynamics on the efficiency of cluster transportation in a cluster source (1). Another important factor that needs to be considered is the influence of magnetic field configuration on the magnetron sputtering device. In the 1980s, it was found that by tuning the unbalance degree of the magnetic field configuration, one can significantly increase the number of electrons escaping from the plasma sputtering region, increase the ion flux and the associated high ion bombardment on the substrate and thus produce very dense thin films (2). Subsequently, simulations have been carried out to better understand how the unbalanced magnetic field influences the sputtering parameters (3). Although significant progress has been made in the understanding of how the magnetic field influences the magnetron sputtering process, there are very few reports about its influence on cluster formation. An exception is a recent work by Vaidulych et al (4), where it is argued that a decrease in the magnetic field assisted with an increase in the flow of the carrier gas greatly improves the deposition rate of the nanoparticles. However, in this approach, the sputtering rates across experiments were not strictly maintained, which might influence the results in an unexpected way. Furthermore, a concrete explanation of how this magnetic field affects cluster growth is still missing. In this work, preliminary simulation results on the influence of different magnetic field configurations are shown. The electromagnetic modelling software package OPERA was used to optimise the magnetic field configuration, and the configurations of the magnetic field on a magnetron were physically varied to validate the simulation results. Plasma density was measured at different magnetic configurations in an attempt to investigate its influence on the density of charged particles surrounding the target. A hypothesis will be proposed to explain cluster growth mechanisms under the influence of different plasma spatial distributions.References (1) G. Sanzone, J. Yin, K. Cooke, H. Sun, and P. Lievens, Impact of the gas dynamics on the cluster flux in a magnetron cluster-source: Influence of the chamber shape and gas-inlet position, Review of Scientific Instruments, vol. 92, no. 3, p. 033901, 2021; (2) B. Window and N. Savvides, Charged particle fluxes from planar magnetron sputtering sources, Vacuum Science and Technology A Vacuum, Surfaces and Films, vol. 4, pp. 196 – 202, 04 1986; (3) I. Svadkovski, D. Golosov, and S. Zavatskiy, Characterisation parameters for unbalanced magnetron sputtering systems, Vacuum, vol. 68, no. 4, pp. 283–290, 2002; (4) M. Vaidulych, J. Hanus, J. Kousal, S. Kadlec, A. Marek, I. Khalakhan, A. Shelemin, P. Solar, A. Choukourov, O. Kylian, and H. Biederman, Effect of magnetic field on the formation of cu nanoparticles during magnetron sputtering in the gas aggregation cluster source, Plasma Processes and Polymers, vol. 16, 08 2019.

Dimitra Papamichail, KU Leuven Co-authorsDeema Balalta, Imran Abbas, Jason Song, Thomas Altantzis, Sara Bals, Deepak Pant, Ewald Janssens, Didier Grandjean, Peter Lievens

Gas-Phase CuPd Bimetallic Cluster-Modified Electrodes as Model Electrocatalysts for CO₂ ConversionAbstractCopper-based electrocatalysts possess the unique ability to convert CO2 to multicarbon products such as ethylene – a precursor in many industrial processes. However, their stability and product selectivity remain insufficient. A promising approach to overcome these
shortcomings and design better CO2RR electrocatalysts is to tune Cu selectivity by forming bimetallic Cu-M systems ¹ while establishing their detailed structure-selectivity relationship.
To achieve this, we used laser ablation Cluster Beam Deposition (CBD) ² to produce well defined bimetallic cluster-modified electrodes ². More specifically, CuPd clusters with an original average size of 2.5 nm and mass loadings of 1-2 µg cm-2 were deposited onto a carbon support. To produce a model catalyst which allows the independent investigation of the electronic and geometric structural effects induced to Cu by the second element, a Cu0.9Pd0.1 composition was selected ³. CuPd cluster-decorated electrodes were tested for CO2 electrolysis and methane (C1), and ethylene (C2) were found among the products. As it is shown from the electrocatalytic activity trends, the evolution of C2 products is correlated with the cluster mass loading. In addition, the cluster coverage influences the onset of the competitive H2 production (HER). High resolution (Scanning) Transmission Electron Microscopy ((S)TEM) coupled with Energy-dispersive X-ray spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS) analyses of the as-prepared cluster-modified electrodes, show that the clusters feature some degree of CuPd alloying in the ambient. CuPd clusterbased systems will then be investigated in-situ using X-ray absorption spectroscopy to unravel their structure-catalytic performance relationship.References (1) X. Zhang et al., Materials Today Advances, 7 (2020) 100074. (2) V. C. Chinnabathini, et al., Nanoscale, 15 (2023) 6696-6708. (3) L. Zaza et al., ACS Energy Letters 7 (2022,), 4, 1284–1291 N

Deema Balalta, U Antwerpen Co-authorsImran Abbas, Dimitra Papamichail, Didier Grandjean, Ewald Janssens, Peter Lievens, Thomas Altantzis, Sara Bals

In situ (S)TEM Characterization of a Pd/ZnO Catalyst for CO₂ Hydrogenation and Selective Methanol SynthesisAbstractPd/ZnO has been recognized as an effective catalyst for the conversion of CO2 into methanol. While the Pd-Zn alloy phase has traditionally been seen as the key active component, methanol formation does not occur in the presence of an inert oxide support (such as Al2O3 or SiO2), indicating that the presence of both zinc oxide and palladium or palladium-zinc
phases is necessary to achieve high activity and selectivity for methanol under industrial
conditions. To optimize the Pd/ZnO catalytic performance we need a thorough understanding of the
reaction mechanism and active site structure, as well as the nature of active sites during
reaction conditions. In-situ Scanning Transmission Electron Microscopy (S)TEM can provide a
deeper understanding of the changes occurring at the nanometer and atomic scale when
catalytic clusters are exposed to aggressive reaction environments, which in turn have a major
impact on their catalytic behavior¹. In our study, Pd clusters are prepared using a magnetron
sputtering cluster source and are deposited on ZnO powders. The catalyst was drop-casted on
the bottom chip of a MEMS nanoreactor to monitor the reduction process.
In situ reduction in the TEM was carried out at 350 ˚C, using a reactant gas mixture of 5:95
ratio of H2:He with a flow of 0.1 ml/min, and by maintaining the pressure at 500 mbar for 1
hour. High resolution (S)TEM imaging allowed us to track the structural changes of the Pd
clusters on the ZnO support. The measured interatomic distances agree with the PdZn alloy
tetragonal structure, confirming the formation of an alloy during the reduction step.
Currently, the deposition of clusters on powders is limited to very low loadings. In our lab,
we recently designed a chip holder to mount the in situ bottom chip inside the cluster source,
an approach that can allow for higher cluster loadings to be achieved. The chip windows will
accommodate the drop-casted support material and the clusters will be deposited directly on
the support’s surface. Moreover, the holder can house a shadow mask for a more critical
deposition to certain regions of interest. With this improvement, we can study more particles
and perform complementary (S)TEM spectroscopic techniques. This will not only allow for
better statistics on more particles, but also clarify the role of the palladium-zinc alloy phase in
facilitating this reaction.References (1) Matteo Monai et al. ,Restructuring of titanium oxide overlayers over nickel nanoparticles during catalysis.Science 380, 644-651(2023).

Maximilian Winzely, PSICo-authorsJuan

A novel electrochemical cell for the in situ X-ray absorption spectroscopic investigation of cluster-based CO₂-electroreduction catalystsAbstractThe electrochemical conversion of CO2 into valuable products (e.g., CO or HCOOH) is a promising prospect to slow down global warming. While catalysts with a promising selectivity towards such C1-products have been identified (e.g. Pd) ¹, further improvements in their activity, selectivity and stability are needed. The required design of such improved catalysts can be greatly aided by recent advancements in the synthesis of mass-selected, (sub-) nanometric metal clusters by the so called cluster beam deposition (CBD) method and their subsequent characterization by in situ x-ray absorption spectroscopy (XAS).² However, constraints intrinsic to the CBD method limit the attainable catalyst loadings to ultra-low values below 10 microg_metal/cm_geom². This would in turn translate into unpractically long spectral acquisition times when performing in situ XAS measurements in a standard configuration (i.e., with an Xray beam incidence of 45 or 90° with regards to the electrode plane). To tackle this problem we have developed a new spectro-electrochemical XAS flow cell that enables spectral acquisition in fluorescence mode using an X-ray beam incidence angle of ≤ 0.1° with regards to the working electrode’s substrate plane, i.e., in a so called grazing incidence (GI) configuration (see Figure 1). In this acquisition configuration we successfully recorded an in situ spectrum of palladium in the metallic and full hydride state with a time resolution of 5 minute per spectrum while using a Pd-loading as low as 10 microgPd/cm². References (1) J.S. Diercks, B. Pribyl-Kranewitter, J. Herranz, P. Chauhan, A. Faisnel, T.J. Schmidt, Journal of The Electrochemical Society 168 (2021) 064504. (2) A. Yadav, Y. Li, T.W. Liao, K.J. Hu, J.E. Scheerder, O.V. Safonova, T. Holtzl, E. Janssens, D. Grandjean, P. Lievens, Small 17 (2021) e2004541

Sumant Phadke, PSICo-authorsJ.

High-Pressure Grazing Incidence Cell for In Situ XAS Characterization of Nanoparticles on Planar Substrates under CO₂ Hydrogenation ConditionsAbstractWell-defined model catalysts studied under realistic CO2-to-methanol hydrogenation conditions offer structure-activity insights, which enables a more profound understanding and a better design of methanol synthesis catalysts. In contrast to conventionally prepared catalysts, physical synthesis methods such as cluster beam deposition (CBD) can produce
model nanoparticles of precise atomic structure and composition¹. Depositing such nanoparticles on various planar substrates at very low metal loadings (0.1 – 10 microg/cm2) provides an opportunity to understand particle size effects and the catalyst's support on the reactivity. However, such model catalysts also present a challenge for in situ structural characterization using bulk-sensitive methods, such as X-ray absorption spectroscopy (XAS), since they are optimized for studying catalysts with about three to four orders of magnitude higher metal loading². To address this, we have developed a grazing incidence (GI) in situ XAS cell that enables the study of the structure of these model catalysts under CO2–to methanol hydrogenation conditions at relevant temperatures and pressures. We have successfully measured in situ XAS data for nanoparticles deposited on flat substrates using fluorescence detection. In particular, we obtained high-quality Pd K- and Au L3-edge XAS data in 30-60 min for Pd and Ag0.7 Au0.3 nanoparticles with ca. 2.5 – 10 microg/cm2 loading at 230°C temperature and 20 bar pressure of reactive gases (CO2:3H2:Ar). With this proof-of-concept, we now intend to investigate innovative bimetallic systems produced by gas-phase cluster deposition and contribute to a rational design of CO2 hydrogenation catalysts.References (1) G. Sanzone, J. Yin, and H. Sun, Front. Chem. Sci. Eng. vol. 15 (2021), pp. 1360 (2) P. J. Chupas, K. W. Chapman, C. Kurtz, J. C. Hanson, P. L. Lee, and C. P. Grey, J. Appl. Crystallogr. vol. 41 (2008), pp. 822

Esperanza Sedano Varo, DTUCo-authorsRikke

Size-studies of Au and Cu nanoparticles for CO₂ electroreduction: every parameter countsAbstractNanoparticles are extensively utilized in various industrial processes due to their enhanced catalytic performance resulting from a high surface-to-bulk ratio. Modulating the size of these nanoparticles allows for manipulation of their activity and selectivity^1,2, which is particularly intriguing in the context of CO2 electroreduction, a process yielding 16 different products
where enhancing selectivity is of significant interest³. However, investigating these minute catalysts in electrochemistry poses considerable challenges, given the multitude of parameters that influence apparent selectivity. In this study, we thoroughly examine the intrinsic selectivity of size-selected nanoparticles by meticulously controlling all relevant parameters, including size, loading, impurities, and shape. Our methodology aims to meticulously manage these variables to establish experimental structure-activity relationships and generate reliable, transferable knowledge applicable to other catalytic studies, both fundamental and experimental. Here, we present several parameters with significant impacts on the selectivity and activity of the nanocatalysts, along with the results demonstrating the influence of these controlled parameters on the accuracy of size-based performance studies of the nanoparticles.References (1) Mistry, H. et al. Exceptional size-dependent activity enhancement in the electroreduction of CO2 over Au nanoparticles. J Am Chem Soc 136, 16473–16476 (2014). (2) Zhu, W. et al. Monodisperse Au Nanoparticles for Selective Electrocatalytic Reduction of CO 2 to CO. J.Am. Chem. Soc 14, 35 (2013).(3) Nitopi, S. et al. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chemical Reviews vol. 119 7610–7672 Preprint at https://doi.org/10.1021/acs.chemrev.8b00705 (2019).

Filippo Romeggio, DTUCo-authorsRikke

Stable mass-selected AuTi nanoparticles for CO oxidationAbstractAddressing stability in reactive conditions is a big challenge when working with clusters and nanoparticles¹ . The stability of < 5 nm gold nanoparticles has been a central focus since their catalytic properties were discovered. To enhance their stability during CO oxidation at high temperatures, one common approach involves modifying their interactions with the supporting material, while another approach involves incorporating another metal into the nanoparticles themselves, forming an alloy with gold. Previous studies have suggested that AuTi alloy nanoparticles could offer improved stability^2,3. This research presents direct observations that demonstrate the enhanced stability of AuTi alloy nanoparticles compared to pure Au nanoparticles during CO oxidation. The alloyed nanoparticles exhibited activity comparable to that of the pure Au nanoparticles, but they displayed significantly higher stability at elevated temperatures. Detailed investigations employing Low Energy Ion Scattering, X-ray Photon Spectroscopy, and Environmental Transmission Electron Microscopy unveiled the structure of the AuTi nanoparticles. These characterizations revealed an Au core surrounded by an alloy shell consisting of AuTi. Remarkably, this structure remained stable even under reactive conditions at 320°C, and an incremental increase in activity was observed over a duration of more than 140 hours. This work reaffirms the potential of nanoparticle alloying as a mean to tune both catalytic activity and stability, emphasizing the importance of employing complementary and in-situ characterization techniques to advance the optimization of nanoparticle catalyst design.References (1) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Nørskov, J. K.; Jaramillo, T. F., Science 355 (2017).
(2) Liu, S.; Xu, W.; Niu, Y.; Zhang, B.; Zheng, L.; Liu, W.; Li, L.; Wang, J, Nat Commun 10 (2019).
(3) Niu, Y.; Schlexer, P.; Sebok, B.; Chorkendorff, I.; Pacchioni, G.; Palmer, R. E., Nanoscale 10 (2018).
(4) Tankard R. E., Romeggio F., Akazawa S. k., Krabbe A., Sloth O. F., Secher N. M., Colding-Fagerholt S., Helveg S., Palmer R. E., Damsgaard C. D., Kibsgaard J., Chorkendorff I., ACS Catalysis (2023, in preparation).

Wenjian Hu, VITOCo-authorsDeema

Structure-selectivity of Cu_2-xSe towards CO₂ electroreductionAbstractCopper selenides, forming both non-stoichiometric and stoichiometric phases, are an important family of transition metal chalcogenides (TMCs) ¹. Despite their promising electrocatalytic performance, active site identification in Cu2-xSe nanostructures remains a challenge. The varying product selectivity among similar nanostructures, yielding products like formic acid ², CO ³, and methanol ⁴, highlights the need to understand structure performance relationships for improved Cu2-xSe electrocatalyst design. This work highlights the structure-selectivity relationship in Cu2-xSe under CO2 electroreduction at -1.4 VRHE yielding 23% of methanol in its pristine form and 82.1% CO at partial current density of 27.7 mA cm-2 after chemical- (H2O2 etching) and electro-activation. Low and high magnification STEM images reveal that the pristine Cu2-xSe catalyst is comprised of Cu1.71Se wires with a cubic structure while the chemically activated one Cu2-xSeOy displays wire-like characteristics enveloped by thin, folded oxide layers. In situ Raman under electro activation of Cu2-xSeOy at -1.6 V shows a drastic reduction of the Cu-Se bond signal with time suggesting a degradation of the CuSe while a Cu2O signal appearing and constantly growing once the potential is returned to OCP suggests that metallic Cu segregated under electro-activation is then oxidized into Cu1+ after activation. Ex situ EXAFS of Cu2-xSeOy confirms the progressive transformation of the Cu2-xSe into Cu1-zSe phase through segregation of Cu that forms a mixture of Cu1+ and Cu2+ after reaction. A more moderate Cu segregation also occurs in pristine Cu2-xSe as no Cu1-zSe phase transformation is detected. In good agreement with EXAFS, post-activated catalysts reveal the presence of agglomerates of Cu2O cubes (cubic, Pn-3m) with 50 to 90 nm edges amidst smaller Cu2-xSe particulates. The copper selenide system's changing selectivity, which depends on activation, could be explained by the combined impact of copper segregation and the interactive effects between metallic Cu and the residual structures of Cu2-xSe or Cu1-zSe. References (1) Shaohua Zhang, Zhen Li., et al., Advanced Materials 28 (2016) 8927
(2) Junyuan Duan, Tiaoyou Zhai., et al., Nature Communications 13 (2022) 2039
(3) Jiajun Wang, Wenbin Hu., et al., Advanced Materials 34 (2022) 2106354
(4) Dexin Yang, Buxing Han., et al., Nature Communications 10 (2019) 677

Imran Abbas, KU LeuvenCo-authorsSumant Phadke, Joao Coroa, Jinlong Yin, Olga Safonova, Christophe Coperet, Didier Grandjean, Ewald Janssens

Gas-phase Pd and PdZn clusters deposited on ZnO and SiO₂ as model catalyst for CO₂ hydrogenation to methanolAbstractKeywords: CO2 hydrogenation, methanol synthesis, metal-support interface, heterogeneous catalysis, gas-phase clusters
Introduction. Supported Pd nanoparticles have demonstrated promising catalytic activity for the
hydrogenation of CO2 into methanol but the nature of the metal-support interface and its role in the
reaction mechanism remains a topic of ongoing research ^1-3. We have produced model catalysts by
depositing well-defined Pd and PdZn clusters directly onto ZnO and SiO2 powders using the Cluster Beam Deposition (CBD) technology. Well defined Pd and PdZn catalysts will facilitate the investigation of the Pd-Zn and Pd-ZnO interface to unravel their structure-activity relationship.
Experimental/methodology. Pd and PdZn clusters of different compositions were produced in high vacuum using a magnetron sputtering-based CBD at Teer Coatings Limited, UK and deposited onto one gram of each pre-dried oxide powder placed in a vibrating cup for uniform deposition of size-controlled clusters containing 500 to 700 atoms. 0.1 wt% Pd clusters loading on oxide powders was confirmed using ICP-OES and the size of clusters deposited on TEM grid was found to be 3-4nm (figure 1). The samples were activated in situ in pure hydrogen at 120°C for 30 minutes before catalytic tests. Catalytic activity tests for CO2 hydrogenation were performed at 210°C and 40 bar on 0.4 g of each sample loaded in a plug flow reactor in a 5 mL/min feed gas of 3H2:1CO2.
Results and discussion. A very small concentration of Pd clusters (0.1wt%) on ZnO is found to promote the CO2 hydrogenation to methanol and CO while only a very small activity is observed for Pd/SiO2. A four-time increase of the CO2 hydrogenation rate compared to sum of blank ZnO and Pd/SiO2 is reported in Figure 1, confirming the excellent Pd-ZnO synergy in these model catalysts.References (1) M. Zabilskiy, et al. Angew. Chem. Int. Ed. 2021, 202, 17053–17059.(2) S.R. Docherty et. al. JACS Au 2021, 1, 450–458.(3) H. Bahruji et al. J. Catal. 2016, 133–146.

Sumant Phadke, PSICo-authorsC.

Synergetic Activity of Ag and Zn in CO₂ Hydrogenation to MethanolAbstractIntroduction: The search for a highly-efficient CO2-to-methanol hydrogenation catalyst has led scientists to screen different bimetallic compositions, mainly consisting of Cu, Pd, Ni and Au nanoparticles promoted with various promoters such as Zn, Ga, Zr, etc. However, Ag, the element sandwiched between Cu and Au, has been much less considered among the coinage metals. In this work, we attempt to uncover the activity of Ag in combination with Zn for the selective hydrogenation of CO2 to methanol.
Experimental/Methodology: In contrast to Cu-Zn bimetallic system, very little is known about the synergy of zinc and silver. We synthesized a series of Ag-Zn catalysts supported on silica with constant Ag and varied Zn loading. The catalysts were tested in a flow reactor at 40 bar CO2:H2:Ar = 1:3:1 at 250°C. Quasi in situ XAS analysis was performed at Zn and Ag K-edges for the calcined and H2 activated (at 350°C) catalysts. (S)TEM and EDX mapping were implemented to visualize the distribution of Ag and Zn.Results and Discussion: Neither Ag nor Zn are very active in CO2 hydrogenation and selective for the formation of methanol. Adding Zn to Ag/SiO2 steadily increases the methanol formation rates. The methanol selectivity, the other product being CO, seems to plateau after 2 Zn/nm2 support coverage. According to XAS and TEM, Ag is easily reducible and forms Ag nanoparticles of ca. 2.8 nm without evidence of alloying with Zn. From XAS, it is also apparent that Zn exists only in a cationic ZnII state, even after H2 activation at 350°C. This cationic ZnII is composed of a mixture of isolated ZnII sites on silica and highly dispersed ZnO oligomers with an incomplete second Zn-O-Zn coordination shell. The latter is visible in HAADF-STEM images of the catalyst with the highest Zn loading (Ag:Zn = 0.2), and its location coincides with the Ag nanoparticles. For the lower Zn loading (Ag:Zn = 1), crystalline domains of ZnO are not detectable. We hypothesize that the ZnO phase presenting at higher Zn loading and its characteristic interface with the Ag nanoparticles are crucial for catalyzing the hydrogenation of CO2 and the formation of methanol. We are currently probing the structure of the Ag-Zn system using in situ XAS and IR spectroscopy to further elucidate the specific function of each
phase, clarify the reaction mechanism of methanol formation, and compare the reactivity of Ag-Zn and Cu- Zn systems.
Acknowledgments: This work is financially supported by the Europan Union’s Horizon 2020 research and innovation program under the Marie-Curie ITN project “CATCHY” (GA No. 955650). References: (1) G. Sanzone, J. Yin, and H. Sun, Front. Chem. Sci. Eng. vol. 15 (2021), pp. 1360 (2) P. J. Chupas, K. W. Chapman, C. Kurtz, J. C. Hanson, P. L. Lee, and C. P. Grey, J. Appl. Crystallogr. vol. 41 (2008), pp. 822

Deepak Pradeep, RUCo-authorsTooltip content

CO₂ hydrogenation on bimetallic clustersAbstractThe increasing atmospheric CO₂ concentration leads to global warming and climate destabilization. One potential way to mitigate  CO₂ emissions is by converting them into useful chemicals. In industry, for example, methanol is produced by direct hydrogenation of CO₂ over a Cu/ZnO/Al₂O₃ catalyst. However, this process occurs at high temperatures and pressure and is thus energy-intensive. Because the catalyst has a relatively low conversion efficiency, new catalysts for CO₂ reduction are desirable. For a rational design of such new catalysts, a detailed understanding of the reaction mechanisms is required.Gas-phase metal clusters represent an idealized model system for the active sites of the complex catalysts. Because pure Cu catalysts are not sufficiently active in CO₂ reduction, we investigate on a molecular level how the doping of Cu clusters with foreign elements affects their reactivity. For this, we study the interaction of transition metal-doped Cu clusters with CO₂ and H₂ using IR photo fragmentation spectroscopy complemented by DFT calculations. We will present our initial steps in forming 3d metal-doped Cu clusters obtained from a newly commissioned dual-laser, dual-target cluster source.

Deema Balalta, UACo-authorsDeema Balalta, Imran Abbas, Dimitra Papamichail, Didier Grandjean, Ewald Janssens, Peter Lievens, Thomas Altantzis, Sara Bals

In situ (S)TEM Characterization of bimetallic atomic cluster catalystsAbstractThe use of bimetallic clusters has emerged as an effective approach for controlling and fine-tuning reaction selectivity and activity in catalysis. The coexistence of different materials on the same nano-object increases its functionalities because the individual properties of each component can be present on a single cluster, and even more interestingly, opens the way to the discovery of new properties, such as enhanced catalytic activity and increased stability, stemming from an interaction between the different materials. The optimization of the clusters’ catalytic performance requires a deep understanding of their structure, composition and morphology as well the way these parameters are tuned during actual catalytic reactions. Indeed, only little is known about the changes occurring at the nanometer and atomic scale when catalytic atomic clusters are exposed to aggressive reaction environments, which in turn have a major impact on their catalytic behavior. A detailed characterization of these parameters ex and in situ is of utmost importance if one wants to obtain a better insight concerning the structure-function relationship. Transmission Electron Microscopy (TEM) is an ideal technique to investigate atomic clusters at a very local scale. By using dedicated in situ holders which are nowadays commercially available and utilize MEMS chips with electron transparent SiNx membranes to build a nanoreactor, one can also reach higher pressures and temperatures and also introduce liquids in the TEM, creating an environment which is identical to that during actual catalytic reactions.^1,2 In our study, bimetallic clusters are prepared using a magnetron sputtering cluster source and are deposited directly on the MEMS chips. In order to assure a selective deposition of the clusters on the region of interest on the chips (i.e. the working electrode and the thin SiNx window on the chips of the liquid and gas systems respectively) and avoid any unwanted contamination of the other electrodes, a mounting system was designed that can hold the bottom chip and allows for a shadow mask, which was fabricated by focused ion beam (FIB) milling, to be secured on top of it. By using a combination of in situ aberration-corrected STEM imaging and spectroscopy with statistically based approaches and molecular dynamic simulations, we were able to determine in a quantitative manner in 3D the structure, number of atoms, shape and composition of bimetallic clusters during the CO2 reduction reaction (CO2 RR). This way, it is possible to observe the dynamics of catalyst transformation during reaction conditions and obtain useful insight on the activation/deactivation mechanisms. References: 1. Hector Hugo Pérez Garza et al., Micro & Nano Letters, 2017, 12, 69-75. 2. Thomas Altantzis et al., Nano Lett., 2019, 19, 477-481.

Sumant Phadke, PSICo-authorsTooltip content

In situ high-pressure GI-XAS cell for structural studies of physically deposited nanoparticles under CO₂ hydrogenation conditionsAbstract

Filippo Romeggio, DTU Co-authorsJakob Kibsgaard (DTU), Ib Chorkendorff (DTU), Christian Danvad Damsgaard (DTU)

Ni_5-xGa_3+x Catalyst for Selective CO₂ Hydrogenation to MeOH : Investigating the Activity at Ambient Pressure and Low Temperature with Microreactors AbstractMethanol obtained from the direct hydrogenation of CO₂ at low pressures and temperatures can be used as a fuel/chemical feedstock and, if paired with renewable energy sources, could strongly contribute to reach a more sustainable society. We have studied the catalytic performance of the intermetallic compound Ni_5-xGa_3+x for methanol production. The catalyst shows outstanding activity and selectivity at low temperatures, outperforming the conventional Cu/ZnO. At higher T, the selectivity promptly shifts towards the production of methane and CO, leading to surface poisoning. Nevertheless, the experiments demonstrate the possibility of full regeneration of the catalyst by hydrogen reduction. Lastly, high stability over time under reaction conditions makes it an interesting candidate for scale-up and future industrial application. A variety of techniques are used to characterize the surface before and after reaction, including XPS, HR-SEM/STEM, XRD, etc., along with close collaboration with computational theoreticians for DFT calculations. All the experiments are performed in state-of-the-art equipment: microreactors of 236 nL are used for catalytic testing. The inlet flow rate is in the order of magnitude of nanomoles/min, making it possible for all the gases to enter directly the QMS, leading to extremely high product detection sensitivity. This, together with an almost immediate temperature control, makes our system ideal for further fundamental studies about CO₂ hydrogenation.

Pavol Mikolaj, UUCo-authorsTooltip content

Activation of CO₂ and H₂ by free copper oxide clustersAbstract

2022

João Coroa, TCLCo-authorsJoao Coroa, Giuseppe Sanzone, Hailin Sun, Ewald Janssens, Jinlong Yin

Influence of the Magnetic field configuration of a Magnetron on the cluster growth mechanism in a GASAbstractCluster production using physical methods provides several advantages compared with chemical routes, such as better control of the size distribution and
the minimised impact on the environment. On the other hand, their slow deposition rate has inhibited the physical approaches from being used more widely.To address this issue, we have systematically studied the influence of aerodynamics on the efficiency of cluster transportation in a cluster source ¹. Another important factor that needs to be considered is the influence of magnetic field configuration on the magnetron sputtering device. In the 1980s, it was found that by tuning the unbalance degree of the magnetic field configuration, one can significantly increase the number of electrons escaping from the plasma sputtering region, increase the ion flux and the associated high ion bombardment on the substrate and thus produce very dense thin films ². Subsequently, simulations have been carried out to better understand how the unbalanced magnetic field influences the sputtering parameters ³.
Although significant progress has been made in the understanding of how the magnetic field influences the magnetron sputtering process, there are very few reports about its influence on cluster formation. An exception is a recent work by Vaidulych et al ⁴, where it is argued that a decrease in the magnetic field assisted with an increase in the flow of the carrier gas greatly improves the
deposition rate of the nanoparticles. However, in this approach, the sputtering rates across experiments were not strictly maintained, which might influence the results in an unexpected way.
In this poster, we will present the plans and preliminary simulation results on the influence of the magnetic field and its impact on cluster growth. The electromagnetic modelling software package OPERA will be used to optimise the magnetic field configuration, and several magnetrons will be built to validate the simulation results. The objective is to reveal the physical mechanism of the impact of a varying magnetic field on cluster growth. References: 1. G. Sanzone, J. Yin, K. Cooke, H. Sun, and P. Lievens, Impact of the gas dynamics on the cluster flux in a magnetron cluster-source: Influence of the chamber shape and gas-inlet position, Review of Scientific Instruments, vol. 92, no. 3, p. 033901, 2021. 2. B. Window and N. Savvides, Charged particle fluxes from planar magnetron sputtering sources, Vacuum Science and Technology A Vacuum, Surfaces and Films, vol. 4, pp. 196 – 202, 04 1986. 3. I. Svadkovski, D. Golosov, and S. Zavatskiy, Characterisation parameters for unbalanced magnetron sputtering systems, Vacuum, vol. 68, no. 4, pp. 283–290, 2002. 4. M. Vaidulych, J. Hanus, J. Kousal, S. Kadlec, A. Marek, I. Khalakhan, A. Shelemin, P. Solar, A. Choukourov, O. Kylian, and H. Biederman, Effect of magnetic field on the formation of cu nanoparticles during magnetron sputtering in the gas aggregation.

Esperanza Sedano Varo, DTUCo-authorsChristian

Electrochemical CO₂ reduction with clusters real-time detection of productsAbstract

Maximilian Winzely, PSICo-authorsJuan

A novel electrochemical cell for the in situ X-ray absorption spectroscopic investigation of cluster-based CO₂-electroreduction catalystAbstract

Bárbara Zamora Yusti, BMECo-authorsTooltip content

DFT-based investigation of structure and CO₂ adsorption on Cu₄Zn clustersAbstractA promising approach to the emission control of carbon dioxide (CO2) into the atmosphere is the catalytic conversion of this greenhouse gas into valuable compounds. ¹ For example, the syngas (mixture of CO/CO2/H2) has been converted to methanol using heterogeneous copper catalysts. ^1,2  Copper, as well as doped copper clusters, have proven to be promising candidates for CO2 reduction. ^3,4   By comparing zinc dopped copper clusters with pure copper clusters, zinc dopped copper clusters show a higher CO2 reduction activity due to lower activation barriers for CO2 dissociation. In addition, zinc-doped copper clusters demonstrate easier catalyst regeneration. ⁴ In the present contribution, we have generated a protocol to study these systems using methods based on density functional theory (DFT). We have determined computationally the lowest energy (most stable) structures for the Cu4Zn cluster as well as the different binding modes of CO2 on the metal cluster. Calculations for Cu4Zn revealed that the dissociative adsorption of CO2 into CO and O is energetically more favourable than non-dissociative adsorption. References: 1. Yu, K. M. K.; Curcic, I.; Gabriel, J.; Tsang, S. C. E. ChemSusChem., 2008, 1,893−899.2. K. C. Waugh, Catal. Today., 1992, 15, 51–75. 3. C. Liu, B. Yang, E. Tyo, S. Seifert, J. DeBartolo, B. Von Issendorff, P. Zapol, S. Vajda and L. Curtiss, J. Am. Chem. Soc., 2015, 137, 8676–8679.4. Szalay, M., Buzsáki, D., Barabás, J., Faragó, E., Janssens, E., Nyulászi, L., & Höltzl, T., Phys. Chem. Chem. Phys., 2021, 23(38), 21738-21747.