May 15

CO2 Reduction by Nanosecond-Plasma Discharges: Revealing the Dissociation’s Time Scale and the Importance of Pulse Sequence

Power-to-chemical technologies with CO2 as feedstock recycle CO2 and store energy into value-added compounds. Plasma discharges fed by renewable electricity are a promising approach to CO2 conversion. However, controlling the mechanisms of plasma dissociation is crucial to improving the efficiency of the technology. We have investigated pulsed nanosecond discharges, showing that while most of the energy is deposited in the breakdown phase, CO2 dissociation only occurs after an order of microsecond delay, leaving the system in a quasi-metastable condition in the intervening time. These findings indicate the presence of delayed dissociation mechanisms mediated by CO2 excited states rather than direct electron impact. This “metastable” condition, favorable for an efficient CO2 dissociation, can be prolonged by depositing more energy in the form of additional pulses and critically depends on a sufficiently short interpulse time.

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Montesano C., Salden A.P.W., Martini L.M., Dilecce G., and Tosi P.CO2 Reduction by Nanosecond-Plasma Discharges: Revealing the Dissociation’s Time Scale and the Importance of Pulse Sequence The Journal of Physical Chemistry C 127 (21), 10045-10050 (2023) https://pubs.acs.org/doi/10.1021/acs.jpcc.3c02547 

May 15

The Support Can Disguise the Catalytic Effect: the Case of Silver on Alumina in Plasma Ammonia Synthesis

Plasma catalysis combines the high-energy chemistry of plasma with the speed and selectivity of chemical reactions in catalysis. However, unlike well-established thermal catalysis, a better understanding of fundamental mechanisms is needed, as evidenced by the contrasting results reported in the literature. One main challenge is that not only the genuine catalytic effect may play a role, but both the support and the catalyst also impact the plasma, complicating the understanding. In this study, exploring the impact of support by comparing a single metal on various substrates made of the same material is focused on. Herein, silver on γ-alumina is used to investigate ammonia synthesis in N2/H2 plasma discharges. Beyond confirming the beneficial role of silver in ammonia formation, it is also found that the influence of support is crucial and it is affected by the preparation method. These findings contribute to clarifying the discrepancies in the literature results despite using the same materials.

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Spadoni F., Perina S., Castellani G., Tosi P., Fornasiero P., Sglavo V.M. and Martini L.M. The Support Can Disguise the Catalytic Effect: the Case of Silver on Alumina in Plasma Ammonia Synthesis ChemSusChem (2025) https://doi.org/10.1002/cssc.202402778

Nov 01

SASP 2024

XXIV Symposium on Atomic, Cluster and Surface Physics – 28th January – 2nd February 2024, Andalo – TN, Italy

The SASP (Symposium on Atomic, Cluster and Surface Physics) 2024 returns to Italy after the 2000 edition held in Folgaria (Trento)!

This international Symposium is one in a continuing biennial series of conferences which seeks to promote the growth of scientific knowledge and effective exchange of information among scientists in the field of atomic, molecular, cluster, plasma, and surface physics and related areas, including applied topics.

The Symposium deals, in particular, with collisional interactions involving different types of collision partners, i.e., ions, electrons, photons, atoms, molecules, nano-particles, and surfaces.

The XXIV SASP will be held in Andalo (Trento), Italy.

Further information can be found at the conference website: https://event.unitn.it/sasp2024/

We look forward to welcoming you in Andalo!

May 09

Exceeding Equilibrium CO2 Conversion by Plasma-Assisted Chemical Looping

We propose and demonstrate an integrated electrified plasma-assisted chemical looping (PACL) process
that yields supra-equilibrium CO2 conversions unattainable with conventional catalysis at temperatures ≪3000 K. CO2 is first dissociated inside plasma into CO/O at supra-equilibrium conversions (up to 60%) at a bulk gas temperature of 773 K and a 403 kJ/mol energy cost. Supra-equilibrium CO2 conversions
(29% on average) are achieved at the reactor outlet by placing a nanostructured CeO2 /Fe2O3 oxygen scavenger, prereduced by H2 plasma, downstream of the plasma zone, to capture produced oxygen species and suppress CO/O recombination. Without plasma-material synergy, such an average CO2 conversion can only be attained at temperatures ≥ 2775 K, according to chemical equilibrium calculations. This concept of plasma-assisted chemical looping allows reaching 3-fold higher conversions than state-of-the-art plasma technologies.

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Delikonstantis E., Scapinello M., Singh V., Poelman H., Montesano C., Martini L.M., Tosi P., Marin G. B., Van Geem K. M., Galvita V. V. and Georgios D. Exceeding Equilibrium CO2 Conversion by Plasma-Assisted Chemical Looping. ACS Energy Letters 7, 6, 1896–1902 (2022). https://doi.org/10.1021/acsenergylett.2c00632

Sep 06

Time-resolved optical emission spectroscopy in CO2 nanosecond pulsed discharges

Nanosecond repetitively pulsed discharges at atmospheric pressure have shown comparatively high performances for CO2 reduction to CO and O2. However, mechanisms of CO2 dissociation in these transNanosecond repetitively pulsed discharges at atmospheric pressure have shown comparatively high performances for CO2 reduction to CO and O2. However, mechanisms of CO2 dissociation in these transient discharges are still a matter of discussion. In the present work, we have used time-resolved optical emission spectroscopy to investigate the CO2 discharge progression from the initial breakdown event to the final post-discharge. We discover a complex temporal structure of the spectrally resolved light, which gives some insights into the underlying electron and chemical kinetics. We could estimate the electron density using the Stark broadening of O and C lines and the electron temperature with C+ and C++ lines. By adding a small amount of nitrogen, we could also monitor the time evolution of the gas temperature using the Second Positive System bands of N2. We conclude that the discharge evolves from a breakdown to a spark phase, the latter being characterised by a peak electron density around 1018 cm−3 and a mean electron temperature around 2 eV. The spark phase offers beneficial conditions for vibrationally enhanced dissociation, which might explain the high CO2 conversion observed in these plasma discharges.

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M. Ceppelli*, T.P.W. Salden*, L. M. Martini, G. Dilecce and P. Tosi, Time-Resolved Optical Emission Spectroscopy in CO2 Nanosecond Pulsed Discharges, Plasma Sources Sci. Technol. https://doi.org/10.1088/1361-6595/ac2411 (2021).

*M. Ceppelli and T. P. W. Salden have equally contributed to the paper.

Aug 16

The reactivity of methanimine radical cation (H2CNH•+) and its isomer aminomethylene (HCNH2•+) with C2H4

Experimental and theoretical studies are presented on the reactivity of H2CNH•+ (methanimine) and HCNH2•+ (aminomethylene) with ethene (C2H4). Selective isomer generation is performed via dissociative photoionization of suitable neutral precursors and reactive cross sections and branching ratios are measured as a function of photon and collision energies. Differences between isomers’ reactivity are discussed in light of ab-initio calculations on reaction mechanisms. The main products, for both isomers, are H-elimination, most likely occurring from covalently bound adducts (giving c-CH2CH2CHNH+/ CH2NHCHCH2+) and H• atom transfer to yield H2CNH2+. The astrochemical implications of the results are briefly addressed.

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Sundelin D., Ascenzi D., Richardson V., Alcaraz C., Polášek M., Romanzin C., Thissen R., Tosi P., Žabka J., Geppert W. The reactivity of methanimine radical cation (H2CNH•+) and its isomer aminomethylene (HCNH2•+) with C2H4. Chemical Physics Letters 777, 138677 (2021). https://doi.org/10.1016/j.cplett.2021.138677

Aug 06

CH44 reforming with CO2 in a nanosecond pulsed discharge. The importance of the pulse sequence

The plasma dry reforming reaction of methane with carbon dioxide is investigated in a nanosecond repetitively pulsed discharge, a type of plasma that offers some of the highest performance and non-equilibrium characteristics. The experiment’s purpose was to examine the effect of varying the sequence of high-voltage pulses. We find that when successive pulses are closer than 500 μs, a memory-dominated regime gradually develops, which influences subsequent breakdown events. While reactant conversions increase with the plasma energy, both energy efficiency and conversions increase by shortening the inter-pulse time at the same plasma energy. This finding suggests that plasma power is not the only thing that matters to achieve better performance. How it is delivered can make a significant difference, in particular for CO2, whose conversion doubles at the maximum energy for molecule investigated, 1.6 eV molecule-1.en start writing!

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C. Montesano, M. Faedda, L.M. Martini, G. Dilecce, P. Tosi, CH4 reforming with CO2 in a nanosecond pulsed discharge. The importance of the pulse sequence, Journal of CO2 Utilization 49, 101556 (2021).