Herein, we demonstrate the synthesis of ammonia via atmospheric dielectric barrier discharge (DBD) plasma discharge over zeolite 5A. The presence of the zeolite in the DBD reactor promoted the ...formation of microdischarges and a change of the voltage–current characteristics of the reactor, leading to an enhanced catalytic performance. The perturbation of the zeolite surface electronic properties due to atmospheric plasma led to an enhanced reactive state at the zeolite surface which promoted the dissociation of nitrogen and the subsequent formation of ammonia. An energy yield of 15.5 g-NH3/kW h was observed at an equimolar N2 to H2 ratio in the presence of zeolite 5A, which is at least 50 times higher than that obtained in the absence of the zeolite.
Microporous crystals have emerged as highly appealing catalytic materials for the plasma catalytic synthesis of ammonia. Herein, we demonstrate that zeolitic imidazolate frameworks (ZIFs) can be ...employed as efficient catalysts for the cold plasma ammonia synthesis using an atmospheric dielectric barrier discharge reactor. We studied two prototypical ZIFs denoted as ZIF-8 and ZIF-67, with a uniform window pore aperture of 3.4 Å. The resultant ZIFs displayed ammonia synthesis rates as high as 42.16 μmol NH3/min gcat. ZIF-8 displayed remarkable stability upon recycling. The dipole–dipole interactions between the polar ammonia molecules and the polar walls of the studied ZIFs led to relatively low ammonia uptakes, low storage capacity, and high observed ammonia synthesis rates. Both ZIFs outperform other microporous crystals including zeolites and conventional oxides in terms of ammonia production. Furthermore, we demonstrate that the addition of argon to the reactor chamber can be an effective strategy to improve the plasma environment. Specifically, the presence of argon helped to improve the plasma uniformity, making the reaction system more energy efficient by operating at a low specific energy input range allowing abundant formation of nitrogen vibrational species.
Herein, we demonstrate a synergistic approach with radiofrequency plasma to synthesize ammonia in the presence of Ni-MOF-74 as catalyst. The Ni-MOF displayed higher ammonia yields as compared to the ...pure Ni metal. Specifically, ammonia yields as high as 0.23 g-NH3 (g-catalyst·kWh)−1 and energy cost of 265 MJ mol–1 over Ni-MOF were observed. The enhanced catalytic activity of the Ni-MOF in the presence of plasma was attributed to the presence of pores, which improved mass transfer of guest and product molecules during reaction, the presence of open Ni metal sites, and lower surface hydrogen recombination. Furthermore, the ammonia energy yield of our plasma-Ni MOF catalyst is superior to those of the state-of-the-art RF plasma catalytic systems.
Titanium alloys have become increasingly important for biomedical materials due to their high specific strength, good corrosion resistance, and excellent biocompatibility. In this research work, ...different heat treatments were performed for obtaining equiaxed and Widmanstätten microstructures of Ti-Al-4V extra low interstitials (ELI) alloy. To promote nucleation of <inline-formula> <tex-math notation="LaTeX">\alpha _{2} </tex-math></inline-formula> precipitates (Ti 3 Al), an aging process was carried out at 515 °C and 575 °C for 2, 288, and 576 h. The corrosion behavior was analyzed by double-cycle potentiodynamic corrosion tests. Hank's balanced salt solution (HBSS) was used as the electrolyte, and the tests were maintained at 37 °C. This study uses the eddy current (EC) nondestructive evaluation technique, based on the principle of electromagnetic induction, in an effort to monitor corrosion damage in the medical Ti-6Al-4V alloy. The experimental results show significative electrical conductivity variations in EC data of different Ti-6Al-4V ELI alloy microstructures mainly on equiaxed and Widmanstätten conditions before and after corrosion performance.
Nonthermal plasma is a promising alternative for ammonia synthesis at gentle conditions. Metal meshes of Fe, Cu, Pd, Ag, and Au were employed as catalysts in radio frequency plasma for ammonia ...synthesis. The energy yield for all these transition metal catalysts ranged between 0.12 and 0.19 g-NH3/kWh at 300 W and, thus, needs further improvement. In addition, a semimetal, pure gallium, was used for the first time as catalyst for ammonia synthesis, with energy yield of 0.22 g-NH3/kWh and with a maximum yield of ∼10% at 150 W. The emission spectra, as well as computer simulations, revealed hydrogen recombination as a primary governing parameter, which depends on the concentration or flux of H atoms in the plasma and on the catalyst surface. The simulations helped to elucidate the underlying mechanism, implicating the dominance of surface reactions and surface adsorbed species. The rate limiting step appears to be NH2 formation on the surface of the reactor wall and on the catalyst surface, which is different from classical catalysis.
The 2020 plasma catalysis roadmap Bogaerts, Annemie; Tu, Xin; Whitehead, J Christopher ...
Journal of physics. D, Applied physics,
10/2020, Letnik:
53, Številka:
44
Journal Article
Recenzirano
Odprti dostop
Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chemicals and fuels, CH4 activation into hydrogen, higher hydrocarbons ...or oxygenates, and NH3 synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile organic compound remediation, particulate matter and NOx removal. In addition, plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over 'conventional' catalysis, as outlined in the Introduction. However, a better insight into the underlying physical and chemical processes is crucial. This can be obtained by experiments applying diagnostics, studying both the chemical processes at the catalyst surface and the physicochemical mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technology needed to meet these challenges.
AlPO-18 membranes for CO2/CH4 separation Carreon, Maria L; Li, Shiguang; Carreon, Moises A
Chemical communications (Cambridge, England),
2012-Feb-25, Letnik:
48, Številka:
17
Journal Article
Recenzirano
The synthesis of reproducible and continuous AlPO-18 membranes is demonstrated. The separation performance of these membranes for equimolar CO(2)/CH(4) gas mixtures is presented. The AlPO-18 ...membranes displayed CO(2) permeances as high as ~6.6 × 10(-8) mol m(-2) s Pa with CO(2)/CH(4) separation selectivities in the ~52-60 range at 295 K and 138 kPa.
Herein, we demonstrate that the performance of mesoporous silica SBA-15 and SBA-15-Ag during plasma ammonia synthesis depends on the plasma conditions. At high power, the mesoporous silica SBA-15 ...without Ag produces the largest amount of ammonia, but the addition of Ag provides a minor benefit at lower powers. Plasma conditions were analyzed through optical emission spectroscopy using N
2
, N
2
+
, and NH molecular bands and H
α
line. Stark broadening of H
α
line was used to find electron density, and N
2
molecular bands were used to assess N
2
vibrational excitation, important for plasma nitrogen decomposition. At similar input conditions, reactors with SBA-15 have higher electron density and higher N
2
vibrational temperature. Consistent with higher electron density, SBA-15 reactors have stronger N
2
+
emission intensity relative to the neutral N
2
. The addition of Ag results in higher N
2
rotational temperature, possibly due to localized heating. From the materials point of view, SBA-15 is a more robust catalyst with good surface area retention after plasma exposure due to the lack of local heating generated when a metal is in the structure. We identify two possible regimes during ammonia synthesis, a metal and a surface-plasma driven. At lower plasma densities, the addition of metal is beneficial, while at higher power and plasma density, the best performance is achieved without the aid of a metal catalyst.
Graphical Abstract
Mesoporous materials for Plasma Catalytic Ammonia Synthesis, at certain plasma conditions lead to different regimes, a plasma/surface and a metal dominated regimes of ammonia production.
Plasma-assisted catalysis is emerging as an alternative to several thermocatalytic processes. For ammonia synthesis, it could make the process milder, which would help production, decentralization, ...and compatibility with renewable energy. However, one major obstacle preventing optimization of the plasma-assisted process is the incipient mechanistic understanding of ammonia formation on plasma-exposed catalysts. Here, optical emission spectroscopy is consistent with only a weak effect of the metal on plasma composition and with the presence of small concentrations of plasma radicals in N2/H2 mixtures in dielectric barrier discharge (DBD) reactors, which are bound to enable new catalyst-involved pathways not considered in previous kinetic models for NH3 synthesis. Thus, we comprehensively examined, via density functional theory calculations, the energetics (favorability) of 51 reactions on Fe, Ni, Co, Pd, Ga, Sn, Cu, Au, and Ag. Enthalpic barriers for Eley–Rideal (ER) reactions involving N• and H• radicals were found to be negligible and hence supportive of the following: (i) plausible NNH formation and consequent prominent role of the associative pathway to form NH3 (consistent with some experimental reports detecting surface-bound N X H Y species), (ii) likelihood of N• adsorption taking over N2 * dissociation as the primary source of surface bound N*, and (iii) probable dominance of ER hydrogenation reactions over Langmuir–Hinshelwood ones. The energetics herein presented will allow thoroughly studying the pathway competition in future kinetic models, but numbers calculated here already suggest that the dominant pathway may change with the metal identity. For instance, N2H Y dissociation favorability is more likely to become competitive with ER hydrogenation earlier in the hydrogenation sequence the more nitrophilic the metals. Yet, the calculated favorability of ER reactions is also already consistent with the weaker dependence of initial NH3 turnover frequencies (TOFs) on metal identity compared to the thermocatalytic scenario. With practical implications for computational catalyst screening, TOFs experimentally measured herein for an atmospheric DBD reactor linearly correlate with ΔE rxn for the ER hydrogenation reaction H• + HNNH2 * → HNNH3 *. This descriptor may be robust to exact synthesis conditions, as its correlation with TOFs was maintained for earlier TOF data in a sub-atmospheric radio frequency reactor.
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