Plasma-catalytic ammonia synthesis: Packed catalysts act as plasma modifiers

Ndayirinde, Callie; Gorbanev, Yury; Ciocarlan, Radu-George; Meyer, Robin De; Smets, Alessandro; Vlasov, Evgenii; Bals, Sara; Cool, Pegie; Bogaerts, Annemie

doi:10.1016/j.cattod.2023.114156

Cited by 22 publications

(5 citation statements)

References 59 publications

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“…In a later study by Gorbanev et al, the model was validated with experiments, where it was also found that different metals show a similar activity. The same observations were also made in other experiments. − …”

Section: Modeling Of Eley–rideal Reactionssupporting

confidence: 80%

“…It is worth noting that some studies ,, clearly mention that this is only true under certain conditions or assumptions, e.g., if the barriers for ER reactions are 0 eV. We need to make some remarks on how these ER reactions were modeled: The parameters to determine the ER rate coefficients were nearly always estimated or derived from experimental fits. − ,, Fitting to experiments is difficult in plasma catalysis, as there are many possible underlying mechanisms that could have the same effect, e.g., the lack of a difference in metal activity found in NH 3 synthesis could also be caused by the fact that all metals modulate the physical plasma characteristics in a similar way . This also explains why experimental validation of the kinetic models is difficult.…”

Section: Modeling Of Eley–rideal Reactionsmentioning

confidence: 99%

“…[9][10][11][12]22,23 Fitting to experiments is difficult in plasma catalysis, as there are many possible underlying mechanisms that could have the same effect, e.g., the lack of a difference in metal activity found in NH 3 synthesis could also be caused by the fact that all metals modulate the physical plasma characteristics in a similar way. 17 This also explains why experimental validation of the kinetic models is difficult. The above estimations are of course necessary due to a lack of fundamental studies.…”

Section: Modeling Of Eley−rideal Reactionsmentioning

confidence: 99%

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Plasma Catalysis Modeling: How Ideal Is Atomic Hydrogen for Eley–Rideal?

Michiels,

Gerrits,

Neyts

et al. 2024

J. Phys. Chem. C

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Plasma catalysis is an emerging technology, but a lot of questions about the underlying surface mechanisms remain unanswered. One of these questions is how important Eley−Rideal (ER) reactions are, next to Langmuir−Hinshelwood reactions. Most plasma catalysis kinetic models predict ER reactions to be important and sometimes even vital for the surface chemistry. In this work, we take a critical look at how ER reactions involving H radicals are incorporated in kinetic models describing CO 2 hydrogenation and NH 3 synthesis. To this end, we construct potential energy surface (PES) intersections, similar to elbow plots constructed for dissociative chemisorption. The results of the PES intersections are in agreement with ab initio molecular dynamics (AIMD) findings in literature while being computationally much cheaper. We find that, for the reactions studied here, adsorption is more probable than a reaction via the hot atom (HA) mechanism, which in turn is more probable than a reaction via the ER mechanism. We also conclude that kinetic models of plasma-catalytic systems tend to overestimate the importance of ER reactions. Furthermore, as opposed to what is often assumed in kinetic models, the choice of catalyst will influence the ER reaction probability. Overall, the description of ER reactions is too much "ideal" in models. Based on our findings, we make a number of recommendations on how to incorporate ER reactions in kinetic models to avoid overestimation of their importance.

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Section: Modeling Of Eley–rideal Reactionssupporting

confidence: 80%

Section: Modeling Of Eley–rideal Reactionsmentioning

confidence: 99%

Section: Modeling Of Eley−rideal Reactionsmentioning

confidence: 99%

See 1 more Smart Citation

Plasma Catalysis Modeling: How Ideal Is Atomic Hydrogen for Eley–Rideal?

Michiels,

Gerrits,

Neyts

et al. 2024

J. Phys. Chem. C

Self Cite

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“…Conventional thermal catalytic ammonia synthesis commonly employs the stoichiometric N 2 /H 2 ratio (1:3), whilst under NTP conditions relevant studies showed that the N 2 -rich environment is beneficial to promote the ammonia production rate [27,39,54,57,[70][71][72]. For example, Patil et al conducted a comparative investigation of the N 2 /H 2 ratio on NH 3 formation over various metals supported on Al 2 O 3 , showing the optimal N 2 /H 2 ratio in the NTP-catalysis was either 1 or 2 depending the type of metals [27].…”

Section: N 2 -To-h 2 (N 2 /H 2 ) Ratio and Flowratementioning

confidence: 99%

Ammonia synthesis by nonthermal plasma catalysis: a review on recent research progress

Zhang,

Niu,

Chen

et al. 2024

J. Phys. D: Appl. Phys.

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Ammonia is one of the most important industrial chemicals which is commonly used for producing fertilizers and cleaning solutions and as the refrigerant gas and precursors for making various chemicals. And with the goal of sustainable development, ammonia is also proposed as the clean fuel for decarbonized transportation. The current the Haber-Bosch process for ammonia synthesis has large footprint and operates under harsh conditions using fossil fuels as the feedstock, being recognized as the major carbon emission source. Accordingly, call for sustainable production of green ammonia using renewable energies is proposed. Ammonia synthesis assisted by nonthermal plasmas has emerged in recent years as a novel and mild electrified technology, which can potentially be coupled with intermittent renewable energies and green hydrogen. Although being promising, significant development is still needed to advance the technology towards practical applications at scales. Hence, this review comments the progression of key aspects of the plasma-assisted ammonia synthesis such as catalyst and reactor design, mechanistic understanding, and process parameters. The snapshot of the current developments and proposed perspectives hope to provide guidance for the future research efforts to drive the technology towards higher technology readiness levels.

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“…As collected information about the identity and concentration of species in the plasma bulk is not necessarily reflective of what the catalyst surface “sees”, the major obstacle in addressing the mechanistic questions above is the exceptional difficulty in characterizing the plasma–catalyst interface under operando conditions. Thus, clever reactor setups and experiments need to be designed to indirectly infer mechanistic aspects. ,,− For instance, from mass balances and measurements in reactors of various lengths with plasma jets characterized by molecular beam mass spectroscopy (MBMS), Bruggeman and co-workers recently obtained evidence suggesting that N 2 ( v ) did not contribute toward NH 3 formation, suggesting N and H radicals to be involved …”

Section: Introductionmentioning

confidence: 99%

Plasma Radicals as Kinetics-Controlling Species during Plasma-Assisted Catalytic NH₃ Formation: Support from Microkinetic Modeling

Liu,

Gorky,

Carreon

et al. 2023

ACS Sustainable Chem. Eng.

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About 1% of the world’s CO2 emissions are tied to the standard method to produce NH3 (i.e., Haber–Bosch process); hence, there is a need to decarbonize the production of this chemical. To this end, plasma-assisted catalysis is emerging as a “green” alternative to synthesize NH3. However, the insufficient mechanistic understanding of this process has hindered significant improvements in its cost-effectiveness. Here we leverage “minimal plasma” microkinetic models and select experiments in a dielectric-barrier discharge (DBD) plasma reactor to look for missing mechanistic insights. Relatively robust to model assumptions, our modeling supports the thesis that plasma N and H radicals are the kinetics-controlling plasma species for reactions involving the catalyst. This support stems from the realization that only the inclusion of N and H radicals in our models can readily explain key experimental observations for plasma-assisted NH3 synthesis such as the (i) similar catalytic activity for Fe and Ag (two metals at the opposite ends of N2 dissociation capabilities), (ii) activity increase in Fe (a metal that readily dissociates N2) relative to thermal catalysis, and (iii) detection of catalyst-bound N2HY species. We also find the N radicals (a source of surface-bound N*) to be more important in nitrophobic metals and H radicals (a hydrogenating agent via Eley–Rideal reactions) to be more important in nitrophilic metals. On the other hand, other mechanistic aspects such as the kinetic relevance of N2HY-forming pathways and dissolution reactions are discussed as a function of model assumptions. Our modeling suggests that some of these assumptions could be potentially clarified through in situ compositional analysis of catalyst adlayers (e.g., the fraction of radicals from the plasma bulk that reach the catalyst surface), as the adlayer composition seems to be rather sensitive to the plasma environment assumed to be “seen” by the catalyst.

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Plasma-catalytic ammonia synthesis: Packed catalysts act as plasma modifiers

Cited by 22 publications

References 59 publications

Plasma Catalysis Modeling: How Ideal Is Atomic Hydrogen for Eley–Rideal?

Plasma Catalysis Modeling: How Ideal Is Atomic Hydrogen for Eley–Rideal?

Ammonia synthesis by nonthermal plasma catalysis: a review on recent research progress

Plasma Radicals as Kinetics-Controlling Species during Plasma-Assisted Catalytic NH₃ Formation: Support from Microkinetic Modeling

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Plasma-catalytic ammonia synthesis: Packed catalysts act as plasma modifiers

Cited by 22 publications

References 59 publications

Plasma Catalysis Modeling: How Ideal Is Atomic Hydrogen for Eley–Rideal?

Plasma Catalysis Modeling: How Ideal Is Atomic Hydrogen for Eley–Rideal?

Ammonia synthesis by nonthermal plasma catalysis: a review on recent research progress

Plasma Radicals as Kinetics-Controlling Species during Plasma-Assisted Catalytic NH3 Formation: Support from Microkinetic Modeling

Contact Info

Product

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Plasma Radicals as Kinetics-Controlling Species during Plasma-Assisted Catalytic NH₃ Formation: Support from Microkinetic Modeling