Conference Presentations

2023

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).

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.

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.