Investigation of New Ammonia Synthesis Process Utilizing Vanadium-Based Hydrogen Permeable Alloy Membrane

Morimoto, Shinichirou; Yukawa, Hiroshi; Nambu, T.; Murata, Yoshinori

doi:10.2320/matertrans.mbw201507

Cited by 4 publications

(4 citation statements)

References 14 publications

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“…Certain transition metals and their hydrides, such as V, V 2 H, Nb, and NbH are all based on bcc metal arrangements, and this is why vanadium metal is used for hydrogen separation membranes [10] . In fact, a vanadium membrane reactor has been used to demonstrate NH 3 synthesis, but with very small apparent yield [11] . On top of this, as we discuss later, V and Nb have relatively low M−N bond energies among the early transition metals, which should be beneficial for catalytic activity.…”

Section: Figurementioning

confidence: 99%

Vanadium Hydride as an Ammonia Synthesis Catalyst

et al. 2020

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Early 3d transition metals, such as Ti, V, or Nb are known to be inactive for the Haber‐Bosch process, due to their strong M−N bonds. However, recently some hydride compounds have been found to effectively counteract this effect, imparting catalytic activity on a wide range of elements. With these hydride catalysts, hydride (and nitride) bulk diffusion mechanisms have been proposed; if so, more open structures should enhance their activity. Here, we expand the study to hydrides of other early transition metals, V and Nb. These metals benefit from body‐centered cubic (bcc) related structures which enhance hydride diffusion, in addition to having relatively lower M−N bond strengths. The activity of vanadium hydride, most likely with an active composition of VH0.44N0.16, is superior to the previously reported BaTiO2.5H0.5, and comparable to TiH2 and Cs−Ru/MgO at 400 °C under 5 MPa. These results show that there is more potential for developing new single‐phase hydride catalysts of previously overlooked elements without sacrificing activity.

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Section: Figurementioning

confidence: 99%

Vanadium Hydride as an Ammonia Synthesis Catalyst

et al. 2020

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“…The negative impact of high atmospheric CO 2 concentrations (and the finiteness of fossil fuels) have spurred significant interest in developing new ammonia synthesis methods with the goal of more efficient energy use and/or utilization of renewable energy . Potential alternative synthesis methods include synthesis in electrochemical cells, , plasma reactors, − and membrane reactors . Intriguingly, some membrane reactor configurations could even allow coupling ammonia synthesis with CO 2 capture (Figure ).…”

Section: Introductionmentioning

confidence: 99%

“…7 Potential alternative synthesis methods include synthesis in electrochemical cells, 4,8 plasma reactors, 9−11 and membrane reactors. 12 Intriguingly, some membrane reactor configurations could even allow coupling ammonia synthesis with CO 2 capture (Figure 1). In such a scenario, the retentate side of the membrane would be exposed to flue gas (essentially a N 2 /CO 2 mixture) from which N 2 would be removed, concentrating the CO 2 and facilitating its capture in a subsequent separation step.…”

Section: Introductionmentioning

confidence: 99%

Dissociation, Dissolution, and Diffusion of Nitrogen on V_xFe_y and V_xCr_y Alloy Membranes Studied by First Principles

et al. 2019

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N2-selective metal membranes could be used to couple the extraction of N2 from flue gas and NH3 synthesis within a single membrane reactor. The larger interstitial spaces of BCC metals make them attractive for fast permeation of the large N atom. The caveat is that N permeabilities reported thus far for pure BCC metals (e.g., V, Cr, Fe, Mo, and W) are insufficient for practical application. However, practical permeabilities could be achieved by alloying these metals. Here, we use density functional theory (DFT) to study how alloying V, a metal with high N solubility but low N diffusivity, with Fe and Cr impacts the dissociation, dissolution, and diffusion of nitrogen. Although N binding at vacancies was studied, binding at these defects was not particularly strong compared to regular interstitial sites, and thus, vacancies may not significantly affect solubility. The alloys present two types of interstitial octahedral (o) sites: V-rich (o1) and V-depleted (o2). Nitrogen binding strength correlates with the number of V nearest-neighbors; hence, binding in o1 sites is on average 1 eV stronger than in o2 sites. Ab initio thermodynamics suggests that this combination of strong and weak binding sites mitigates the reduction in solubility expected from the alloying (at least at relevant operating conditions). However, the heterogeneity of the interstitial sites generally leads to higher energy barriers for N hopping than those encountered in pure V (1.24 eV). The exception to this observation was the V0.25Fe0.75 alloy (1.01 eV). Based on our calculations, at 673 K and 5 bar (N2 pressure), N solubility and diffusivity in V0.25Fe0.75 would be ∼3 times smaller and ∼53 times larger than pure V, respectively. According to the solution–diffusion model, these findings indicate that an ∼18-fold higher permeability would be expected for V0.25Fe0.75 relative to V. Permeability is expected to be controlled by bulk diffusion rather than by surface processes, as in all alloys, we find the energy barrier for N2 dissociation at the alloy surface to be lower than the barrier for bulk diffusion in the same alloy.

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“…[16,54,55] Recently, new interest in this scientific question was triggered by the discovery of novel ammonia synthesis catalysts based on bcc metal hydrides. [54,56] The hydrides of titanium and vanadium are active but not the corresponding metals; and consequently vanadium membrane reactors, in which hydrogen is brought to the reaction center through the bulk, have been developed, [57] for an overview on membrane reactors see refs. [37,58].…”

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confidence: 99%

Bulk Thermodynamics Determines Surface Hydrogen Concentration in Membranes

Billeter

Kazaz

Borgschulte

2022

Adv Materials Inter

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nonconverted reactants. In this step, hydrogen may be separated from the mixture, and reused in the reaction. In a future scenario with hydrogen as a main energy carrier, the separation and/or purification of the energetically costly hydrogen will become even more important. [1][2][3] A promising way is the use of hydrogen selective membranes made of hydrogen absorbing metals, such as Pd and its alloys. [4,5] The permeability of such membranes is determined by the surface properties of both sides (dissociation/recombination) and by the bulk permeability (diffusion and solubility). [4] There has been substantial research effort in finding cheaper materials with a higher permeability than that of Pd (e.g., V, Nb, Ta, and their alloys [6][7][8][9][10] ), however, expensive Pd and Pd based alloys remain the superior membrane materials owing to their favorable surface properties. [5,11] Cheap materials such as V-based alloys will revolutionize the technology, if their surface properties can be modified to match those of Pd. Despite this rather straightforward goal, there is a knowledge gap of what these desirable surface properties are. Most works refer to concepts from surface science which describe the physisorption, dissociation (barrier), and chemisorption of hydrogen. [12] However, additional steps-the hopping to subsurface sites and adjacent bulk sites-are needed to model the permeation process adequately. Nevertheless, due to the complex interaction of steps, the predictive power of modeling is limited [4,6,13] and-more importantly-experimental verification only possible by comparison with very basic experiments (permeation kinetics, e.g. ref.[14]) due to the lack of operando hydrogen analysis.Baldi et al. have demonstrated electron energy loss spectroscopy as an analysis method for bulk hydrogen in nano-particles. [15] In this paper, we further developed the method to be able to probe the surface hydrogen content of hydride thin films in situ by reflecting electron energy loss spectroscopy (REELS). The method is applied in an experimental approach, in which the surface properties of membranes can be intentionally modified and their hydrogen content determined under operating conditions. We demonstrate the existence of a rate-limiting step by direct observation of the dependence of the permeation on the hydrogen content in a Pd/V composite membrane. The modeling yields the relevance of the individual layers, making it possible to link the results to the ones obtained from hydrogen uptakeThe functioning of hydrogen selective metal membranes relies on the finetuned interaction of their surfaces with the inner bulk. The link between hydrogen permeation and surface concentration is unveiled using a novel combination of thin film preparation and surface science analysis to probe and intentionally modify the surface properties of palladium vanadium composite membranes. The in situ preparation allows for observation of ultraclean hydrogenation and the quantification of the permeation as a function of temperature and p...

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Investigation of New Ammonia Synthesis Process Utilizing Vanadium-Based Hydrogen Permeable Alloy Membrane

Cited by 4 publications

References 14 publications

Vanadium Hydride as an Ammonia Synthesis Catalyst

Vanadium Hydride as an Ammonia Synthesis Catalyst

Dissociation, Dissolution, and Diffusion of Nitrogen on V_xFe_y and V_xCr_y Alloy Membranes Studied by First Principles

Bulk Thermodynamics Determines Surface Hydrogen Concentration in Membranes

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Investigation of New Ammonia Synthesis Process Utilizing Vanadium-Based Hydrogen Permeable Alloy Membrane

Cited by 4 publications

References 14 publications

Vanadium Hydride as an Ammonia Synthesis Catalyst

Vanadium Hydride as an Ammonia Synthesis Catalyst

Dissociation, Dissolution, and Diffusion of Nitrogen on VxFey and VxCry Alloy Membranes Studied by First Principles

Bulk Thermodynamics Determines Surface Hydrogen Concentration in Membranes

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Dissociation, Dissolution, and Diffusion of Nitrogen on V_xFe_y and V_xCr_y Alloy Membranes Studied by First Principles