STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] This invention was made with government support under Award Number DE-SC0019456 awarded by the Department of Energy. The Government has certain rights to the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63/175,241 filed April 15, 2021, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

[0003] Nitrous oxide is a potent greenhouse gas emitted in both agricultural and industrial chemistry and is approximately 300 times worse than carbon dioxide. Nitrous oxide is also generally present in N _x O _y which are general pollutants that are formed in several important industrial processes, as well as exhaust gases from internal combustion engines (e.g., automotive exhaust). Existing technologies reduce nitrous oxide to nitrogen as shown in equations (1)-(3):

4 ·NO + 4NH ₃ + 0 ₂ ®· 4N ₂ + 6H ₂ 0 (1)

2 N ₂ 0 ®· 2N ₂ + 0 ₂ (3).

These reactions were developed primarily to deal with effluent from combustion of ammonia to produce nitric acid in the Ostwald process, which is the current principle source of NxOy pollution. There is considerable recent interest in combustion of ammonia as a power source that does not emit carbon dioxide. By way of example, the testing of cargo ships utilizing NH ₃ as a fuel source in ongoing. However, a challenge that must be overcome is that the combustion of NH ₃ produces NO _x , including N ₂ 0, wherein the removal is done by reactions (1)-(3). Most schemes for abatement in these systems reduce gaseous ·NO, ·N0 ₂ and N ₂ 0 to gaseous N ₂ . This is done in an uneconomical method in terms of atom economy and energy consumption.

[0004] In view of the foregoing, there remains a need for processes for converting nitrogen oxides to less harmful and/or usable forms (e.g., nitrate for crop fertilization).

BRIEF DESCRIPTION OF THE FIGURES

[0005] Figure 1 A shows the FTIR spectroscopic data showing initial formation of c/s-Na ₂ N ₂ 0 ₂ and NaN0 ₃ in KBr.

[0006] Figure 1 B shows a comparison of FTIR data for ball milling results of Na ₂ 0/KBr under 3 atm ¹⁴ N ₂ 0 (red) and ¹⁵ N ₂ 0 (black). The spectra shown were obtained after ball milling (approximately 6 h).

[0007] Figure 2A shows the FTIR spectroscopic data showing formation of c/s-Na ₂ N ₂ 0 ₂ and NaN0 ₃ in KBr upon further milling. [0008] Figure 2B shows KBr pellet FTIR spectra as a function of time for ball milling of Na20 (0.5g) in KBr (1.5g) under 30 psi, 2.0 ATM N ₂ 0.

[0009] Figure 3 shows initial rates of production of nitrate as a function of time (h) for KF, KBr, KCI, and Kl. [0010] Figure 3B shows absorbance results under various milling times.

[0011 ] Figure 4 shows mole fraction in total Na distribution for the first 20.5 h of ball milling 0.5 g l\la ₂ 0 in 1.5 g KBr.

[0012] Figure 5A shows computed values AG ₂ 98 (kcal/mol) for reaction of Na ₂ 0 and N ₂ 0 in the gas phase.

[0013] Figure 5B shows a computed structure of intermediate adduct formed in reaction of Na ₂ 0 and N ₂ .

[0014] Figure 6A shows FTIR data of aquation product showing band due to nitrate near 1384 cm ^·1 .

[0015] Figure 6B shows FTIR data indicating presence of frans-Na ₂ N ₂ 0 ₂ .

[0016] Figure 7 shows peak position for N ₂ 0 absorbance in pellets of containing Na ₂ 0 (0.5 gram) in matrices of KF, KCI, KBr, and Kl (1.5 gram) made in KBr pellets. Also shown is a spectrum of N ₂ 0 in ball milled in only KBr.

[0017] Figure 8 shows time evolution showing the decrease in the band due to c/s Na ₂ N ₂ 0 ₂ and the increase in the band due to encapsulated N ₂ 0.

[0018] Figure 9 shows the FTIR spectroscopic data showing initial formation of c/s-Na ₂ N ₂ 0 ₂ and NaNCh in KBr in the first two spectra as these peaks grow in. The dashed line spectrum is an authentic spectrum in which 100 mg of KNO3 ball milled in KBr is overlaid to confirm assignment of this peak under these conditions.

[0019] Figure 10A shows a comparison of yield NaNCh under a variety of reaction conditions and demonstrates the production of approximately 50 % yield nitrate product utilizing Na ₂ 0 ₂ in KCI.

[0020] Figure 10B shows FTIR data for reaction of Na ₂ 0 ₂ rather than Na ₂ 0 show a higher initial product yield for Na ₂ 0 ₂ . In addition they show that a different intermediate complex is present with the peroxide rather than the oxide.

[0021] Figure 11A shows yield as a function of milling time for oxidation of N ₂ 0 in (a) Na ₂ 0 ₂ only (b) Na ₂ 0 ₂ (0.5 g) mixed with KCI (2 g), and (c) Na ₂ 0 (0.5 g) mixed with KCI (1.5 g) and milled first under N ₂ 0, then under 0 ₂ , and this sequence repeating under alternating gas atmospheres.

[0022] Figure 11 B shows the combined yield of about 70% conversion to nitrite and nitrate showing the roughly even distribution of the individual products in an expanded view.

[0023] Figure 12A shows the reaction of 'NO(g) and N ₂ 0(g) with K0 _2' (s) and Na ₂ N ₂ 0 ₂ (s) (left) after about 3 minutes reaction in the FTIR spectrometer. [0024] Figure 12B shows the reaction of 'NO(g) and I\l20(g) with KC^s) and Na2N202(s) (left) after about 10 minutes reaction in the FTIR spectrometer showing the complete bleaching of the gas phase and solid phase to a white powder containing only nitrate and nitrite products.

[0025] Figure 13 shows bands observed in reaction of a ball milled mixture of 1.5 g KCI, 0.5 g NaN02, 0.5 g Na20 for 4 hours which produced a mixture of NaNCh and Na202 in KCI as the dominant entries. This mixture was then place in an FTIR gas cell with CaF2 windows and filled with a 1.5% *NO(g) in balance N2(g). Reaction was initiated by injection of 5 mL O2 into the gas phase.

[0026] Figure 14 shows the absorbance versus time for the reaction shown in Figure 13.

[0027] Figure 15 shows a sequence of reactions in accordance with embodiments of the disclosed processes.

DETAILED DESCRIPTION

[0028] Provided herein are processes to convert NO/N2O exhaust gas (e.g., waste) to nitrate in a form that may be used directly (e.g., for crop fertilization). In contrast to conventional processes, the disclosed processes comprise further oxidation of N _x O _y rather than reduction. The Ostwald process itself can in principle be replaced by a much greener approach. The processes disclosed herein advantageously provide a new route to conversion at low temperatures and low pressures using mechanical chemical activation of salts to trap and oxidize NO _x and N2O to nitrate.

[0029] The harsh pollution arising from ·NO, ·N02 and their reaction products with air has been apparent for more than a century. The need to also remove waste N2O has increased after it became recognized as a significant atmospheric greenhouse gas three hundred times more harmful than carbon dioxide. The BASF DeNOx process (equation (3) above) destroys it by high temperature thermal decomposition of a ceria-based catalysts covered with platinum gauze. In addition to destruction of valuable NH ₃ in the DeNO _x process, it also wastes the chemical potential present of a set of reactive species {·NO, ·N02, IN O} which could be further oxidized rather than reduced.

[0030] Nearly a century ago Lewis and Randal used thermodynamic data to calculate that there is a nearly balanced equilibrium between dinitrogen and nitric acid as shown in eqn. (4):

[0031] In principle this would provide a lower energy "green" approach to the Ostwald process in which ammonia is burned to produce nitric acid and nitrates. Thermodynamic data show clearly that further oxidation of ·NO, ·N02 and N2O to nitrate is favorable at low temperatures if nitric acid is the product, and for production of alkali metal nitrates the window of opportunity is considerably higher. The most difficult gas to deal with in terms of production of nitrate is nitrous oxide. As part of a broader program aimed at converting the mixture ·NO, ·N02 and N2O to a useful product, we have looked at part at reaction of the individual components. Extensive kinetic studies in the gas phase are available since reduction of diesel exhaust emissions has also been widely studied. The road to further oxidation is less studied for the simple reason that nitric acid cannot be emitted from exhaust. However trapping the gases in designed metal oxides could lead to production of a solid material which could be used directly for agricultural fertilization.

[0032] As an initial goal towards investigating the feasibility of designing a catalyst for reaction (4) an easier but still challenging project is the conversion of waste N2O into nitrate as shown in eqn. (5):

(5).

[0033] Thermodynamic data for this reaction show that DH ⁰ = -95 kcal/mol, AS ⁰ = -70 cal/mol deg which is a large enough driving force to make it feasible over a range of temperature. The thermodynamic stability of expected intermediates for reaction (5) is less and it is well known that the "deeper" oxidation of nitrogen is more favorable than its "early" oxidation. For that reason the stability and reactivity of Na ₂ N ₂ 0 ₂ which in both its cis and trans forms may be pivotal to developing a catalytic system for eqn. (5), and ultimately finding conditions to catalyze equilibrium formation of nitrate by eqn (4).

[0034] Due to the fact that enzymatic reduction of nitric oxide often proceeds through a hyponitrite that eliminates nitrous oxide there have been numerous studies of nitrous oxide from hyponitrites. Studies of oxidation of binding of nitrous oxide and its further oxidation to nitrite or nitrate are rare. There are numerous studies of binding of nitrous oxide and its reduction as shown in eqn. (3). Yet, there are no reports of nitrous oxide binding and subsequent oxidation in a direct reaction. Studies on oxidation of trans metal hyponitrites have been done by Oza, Mendenhall, Addison and Gould. The binding of nitrous oxide to sodium oxide to produce cis- Na ₂ N20 ₂ at 360 °C (eqn 6) was reported by Jansen and Feldman as well as its later decomposition at 360 °C to orthonitrite.

This complex is reported to decompose to orthonitrite at a temperature of approximately 360 °C. Thus, there is a narrow window of stability to prepare this little studied complex.

[0035] This disclosure describes studies of binding of nitrous oxide to sodium oxide under ball milling conditions. There has been a surge of activity in the area of mechanical chemical activation and catalysis which offers several advantages when dealing with gases reacting and sticking to solids to produce a solid product.

The work of the Schuth group, in particular the oxidation reactions utilizing chlorination reactions at lower temperatures than typically needed prompted us to attempt this in nitrous oxide chemistry. At higher temperatures gas release rather than absorption becomes increasingly favorable for entropic reasons. This appears to provide an advantage in the disclosed processes compared to higher temperature reactions where gas release rather than binding becomes thermodynamically favored for entropic reasons. [0036] In some embodiments, the disclosure provides processes comprising mixing oxide/peroxide/superoxide catalysts with added transition metal catalyst and support by ball milling to prepare a matrix capable of trapping and converting both N2O and NO to nitrate.

[0037] The disclosure provides processes for preparing a nitrate comprising contacting a nitrogen oxide with a metal oxide under milling conditions to form a nitrate.

[0038] Initial investigation of ball milling of Na20 and N2O was done to find a lower temperature route to cis- Na2N2C>2 than the 360 °C reported by Jansen and Feldmen. In part the fact a pure crystalline form is produced implies that lattice energy contributions may play a significant role in the stability. The decomposition of amorphous c/s-Na2N202 has been reported to occur at temperatures above 100 °C. In initial ball milling studies, reactions of Na20 alone, or in the presence of silica gel, zeolites, fluorocarbon oil, and silicone oil were done by loaded the cell and heating it in an oven at 80 °C or 140 °C and then placing the cell in the RETSCH mm500 mixer mill and filling it with N2O and ball milling for as long as eight hours. Infrared studies did not indicate formation of c/s-Na2N202 or other products. The fluorocarbon oil under these conditions was found to react with the sodium oxide presumably forming sodium fluoride and a 0 cross linked polymer that was difficult to clean.

[0039] Solid Na20 by itself was ball milled at room temperature under N2O at 1-3 atm pressure. Initial spectra taken using a diamond ATR compression cell of the product showed definitive evidence for formation of small amounts of c/s-Na2N202. The very moisture sensitive nature of the mixture of primarily unreacted sodium oxide and smaller amounts of c/s-Na2N202 always led to slow hydration and decomposition releasing N2O gas. Pellet spectra taken in KBr left no doubt that c/s-Na2N202 was formed. It was then decided to do the ball milling in a mixture of KBr and Na20, typically 0.5 gram Na20 mixed with 1.5 to 2.5 grams anhydrous KBr. Exposure of the mixture resulted in an increase in formation of c/s-Na2N202 at room temperature and this was unequivocally proven by use of isotopically labelled ¹ %0 as shown in Figures 1A and 1B.

[0040] Production of nitrate was proven by direct addition methods to the KBr pellet spectra and quantified by dissolution of the samples in distilled water. Ball milling of the KBr/Na20 sample matrix under ¹⁵ N2<3 resulted in isotopic shifts in excellent agreement with literature values for Na2N2C>2 and NaNCh and is summarized in Table 1. Note that in all FTIR data in KBr it is not possible to assign the counterion. As such, this and other salts could be referred to as {Na, K}N2q2 but this is not done for simplicity.

Table 1. Tabulated peak assignments for balling milling reactions of Na20 and ¹ 0 or ¹⁵ N20. [0041] Continued milling of the solid led to approach of an approximately steady state peak level for cis- I\la ₂ l\l ₂ 0 ₂ but growth of peaks due to nitrate as shown in Figures 2A and 2B. The only source of oxygen in these reactions was nitrous oxide. The net stoichiometry of nitrate formation under these conditions corresponds to reaction (7).

Na ₂ 0 + 5N ₂ 0 2NaN0 _{3 +} 4N ₂ AG°298 = -210 kcal/mol (7)

The band at 2228 cnr ¹ is attributed to Na ₂ 0 trapped within the KBr pellet. Possible sources of this are either displacement under pressure of N2O a phenomenon that has been observed with CO2.

[0042] The KBr pellet data provides relative ratios of product and how they change with time, but more quantitative data were obtained by studies of hydrolysis reactions of weighed solid samples. The initial rate of nitrate production derived from aqueous ATR spectra of hydrolyzed samples as a function of time are shown for KF, KCI, KBr and Kl in Figure 3.

[0043] The rates of reaction appear to be roughly in the order KBr » KCI » Kl » KF. The spectra for the KF reaction also appear to show lower amounts of c/s-Na ₂ N ₂ 0 ₂ than the other alkali metal halides. Ball milling the reaction and then stopping it under gas pressure did not lead to continued product buildup.

[0044] Even in the absence of added Na ₂ 0, KBr alone under milling conditions was shown to lead to pellets with encapsulated nitrous oxide and these may be seen in Figure 1 for both ¹⁴ N ₂ 0 and ¹⁵ N ₂ 0. Infrared data have been reported that indicate surface bound N2O on higher valent oxides as have others. This has been studied in the present disclosed processes, but no evidence of detectable complex formation at room temperature on the surface of a pristine KBr pellet has been identified. Encapsulated carbon dioxide has also been detected in KBr pellets, presumably from trace contamination. At present, results on ball milling of only KBr and N2O and getting a small signal of encapsulated N2O are attributed to a minor trapping which may occur as part of the ball milling procedure. Moreover, long term study of pellets containing c/s-IN^INhC^ indicate that there is a parallel decrease in bands due to hyponitrite together with an increase in bands of encapsulated nitrous oxide. Without wishing to be bound to any particular theory, it is suggested that slow migration of trace water through the pellet matrix is responsible.

[0045] In basic solution it is known that the c/s-Na ₂ N ₂ 0 ₂ rapidly loses N2O but that the trans isomer does this only in acidic solution. Study of both basic and acidic hydrolysis and the volume of N2O evolved as detected by gas phase FTIR studies indicates a rough reaction profile showing the time evolution of products in this reaction. A first picture of these results is shown in Figure 4.

[0046] As shown in Figure 4 there is a slow production of NaN0 ₃ that occurs throughout the reaction. Surprisingly the N2O evolution studies showed that after an induction period of about two hours there is a fairly rapid rise in concentration of c/s-Na2N202 to nearly 0.6 mole fraction of all distributed sodium oxide starting material. This then decreases and remains roughly constant. The basic hydrolysis product showed consistent low levels of frans-IN^IN C^ < 0.1 mole fraction present in solution. An exact match was obtained by comparison of an authentic sample. There is no evidence in the pellet FTIR data for formation in the pellet itself of trans- Na ₂ N ₂ 0 ₂ . Without wishing to be bound to any particular theory, it is possible this arises from the cis isomer hydrolysis but it seems more likely to the authors that it may arise from hydrolysis of an unidentified intermediate material. It should also be added that iodometric titration for the presence of peroxide in the solution shows levels less than » 4% in these reactions. In most cases there are no signs of significant Fe concentration in the salt matrix or corrosion of the mixing chamber. In the presence of not sufficiently dry material, the presence of moisture has led to some corrosion and detection of Fe in the salt matrix. The role of trace Fe catalysis of the oxidation cannot be excluded, but provided all materials are rigorously dry there is no significant evidence for that.

[0047] The reaction at room temperature of pure Na ₂ 0 does not proceed at a significant rate. Without wishing to be bound to any particular theory, the reaction of CO2 under these conditions is virtually instantaneous in keeping with the generally faster rate of reaction of 0=C=0 where nucleophilic attack on the central carbon leads directly to product. In contrast, migration to the terminal N of N=N=0 appears to present a larger barrier. This occurs in the binding of NHC’s as discovered by Severin and in keeping with known computational studies.

[0048] The reaction does not occur in the absence of ball milling, there is no sign of extensive corrosion of the ball milling jar. The apparently beneficial effect of salt with respect to the chemistry and photochemistry of nitrogen oxides has been studied by Grassian, and other atmospheric scientists, and there are reports in organic and inorganic literature in this regard. Without wishing to be bound to any particular theory, with respect to ball milling, the apparent effect of salt addition to Na20 may be related to mechanical action favoring formation of a mixed lattice. There is literature precedent for this type of possibility. It is clear that Na ₂ 0 has a high lattice energy which needs to be overcome. Calorimetric studies of the enthalpy of displacement of nitrous oxide in c/s- Na2N202 by carbon dioxide to form Na2C03 will give insight into the experimental reaction energetics.

[0049] It is interesting to note that a roughly steady state concentration of c/s-Na ₂ N ₂ 0 ₂ during the production of nitrate . This implies that following buildup of cis- the rate of its formation as well as the rate of its oxidation may be roughly equal. So far the reaction has not been studied in the presence of added oxygen, and the only source of oxygen is N2O itself. This may imply that a common activated intermediate may be formed under mixing conditions which may activate N2O towards reaction with either Na ₂ 0 or Na ₂ 0 ₂ . Without wishing to be bound to any particular theory, a possible explanation is the formation of a trapped salt complex. It is believed that it is unlikely that anything corresponding to NaONa(g) would be formed with a long enough lifetime to interact directly with N2O. Nevertheless we have computed what that reaction profile would look like. A simple computed mechanism is shown in Figures 5A and 5B.

[0050] Figure 5A shows the reaction proceeds by initial exothermic formation of an encounter complex (AG298 +1, DH -7.5) which passes through a low lying transition state ((AG298 +2.5, DH -6.5) to form a more stable isomer A (AG298 -22.5, AG -33) with a less stable isomer B (AG298 -20, DH -26) and the reaction would be expected to occur at a very fast rate in the gas phase. It should be pointed out that this is in contrast to the reaction of NHC ligands with N=N=0 where enthalpies of activation on the range of 15 kcal/mole and higher exist. Figure 5B shows a computed structure of an intermediate adduct formed in the reaction.

[0051 ] The computed mechanism does not take into account any type of lattice involvement. It does illustrate a remarkably low estimate for the multipoint attack of Na-O-Na on N=N=0. It implies that if the mixer mill action could rapidly generate these "naked fragments” they would rapidly react. This is in contrast to computational barrier for NHC addition and migration which is much higher. It provides some hope that adjustment of conditions may lead to improvement in rate and yield. At present, maximum yields of nitrate produced based on sodium oxide reactant go fairly smoothly to approximately 50% and then taper off. Without wishing to be bound to any particular theory, it is believed that that the presence of alkali metal halides may be linked to formation not of naked Na20 but of a salt solvated form which has some mobility and also affinity for nitrous oxide. In spite of a relatively slow rate of conversion and only moderate yields, this represents the first conversion of nitrous oxide to nitrate at low temperatures (35 to 42 °C on average) and 30 psi, 3 atm absolute pressure of N2O. It proceeds through formation of c/s-Na ₂ N ₂ 0 ₂ which may now be conveniently studied in a KBr matrix for its reactions and for additional oxidation methods.

[0052] In some embodiments, nitrous oxide is oxidized in the presence of sodium oxide to produce sodium nitrate. This is done in the presence of catalysts and also uses mechanical chemical activation (e.g., by ball milling) the solid reagents under gas pressure.

[0053] In some embodiments, the nitrogen oxide is selected from the group consisting nitric oxide (NO), nitrogen dioxide (NO ₂ ) nitrogen trioxide (NO ₃ ), nitrous oxide (N ₂ O), dinitrogen dioxide (N ₂ O ₂ ), dinitrogen trioxide (N ₂ O ₃ ), dinitrogen tetroxide (N ₂ O ₄ ), dinitrogen pentoxide (N ₂ O ₅ ), nitrosylazide (N ₄ O), oxatetrazole (N ₄ O), trinitramide (N4O6), and a combination thereof. In some embodiments, the nitrogen oxide comprises nitrous oxide.

[0054] In some embodiments, the nitrogen oxide is a mixture. By way of example, in some embodiments, the mixture is a mixture of nitrous oxide and other nitrogen oxides.

[0055] In some embodiments, the milling conditions further comprising milling in the presence of oxygen gas (O2). In these embodiments, the milling can be conducted in an atmosphere that is a mixture of the nitrogen oxide and oxygen (e.g., 1:2 parts N ₂ 0:0 ₂ by volume). Alternatively, the milling also can be conducted wherein the nitrogen dioxide and oxygen are each introduced into the system in alternating sequences. For example, the milling can be conducted for a time period in the presence of nitrogen oxide, then the nitrogen oxide is evacuated, and oxygen gas is introduced into the system. Without wishing to be bound to any particular theory, the binding of N2O to suitably prepared salt mixtures of metal oxides is faster than any subsequent oxidation.

High conversion of dispersed metal oxides to approximately 90% in 1 h ball milling may be achieved. During this time period oxidation by nitrous oxide of the c/s-hyponitrite salt to nitrite and nitrate salts is slow compared to the rapid rate of binding. [0056] The binding of suitably prepared salts in which Na ₂ 0 or K2O in a salt matrix that has been ball milled occurs rapidly upon gas contact, and within 1 to 2 hours ball milling time is nearly complete based on FTIR data. The rate of oxidation of this product by ball milling under N2O is much slower than the rate of binding. The rate of oxidation of this product by ball milling with Na ₂ 0 ₂ is also slower. The rate of oxidation by O2 gas occurs in 1-3 hours ball milling. A mixture of nitrite and nitrate product is formed in yields of approximately 90% in this time under suitable milling conditions at ambient temperature and pressures of 30 pounds per square inch pressure of pure O2.

[0057] It is known that KCI and Na ₂ 0 and K2O can form antiperovskite structures of formula IV Ox, wherein x X is Cl, Br, I , NO2 or other small anion. Under active conditions of ball milling these or a disordered form of them or other as yet unknown structure appear to play a role in the catalytic oxidation.

[0058] For simplicity of illustration "NaaOCI” is used but materials containing K instead of Na, and also containing various K and Na mixtures in different ratios may be used. Anions other than chloride have been tested but in actual usage, due to the need for agricultural compatibility, bromide, nitrite, and superoxide anions have also been tested.

[0059] For simplicity of illustration "NaaOCI” is used herein but materials containing K instead of Na, and also containing various K and Na mixtures in different ratios may be used. Chloride is contemplated, as well as other anions such as bromide, nitrite, and superoxide anions.

[0060] The initial step in oxidation of N2O starting with "NaaOCI” is binding of N2O to form the cis hyponitrite c/s-Na ₂ N ₂ 0 ₂ . This reaction is rapid and only small amounts of nitrite and nitrate are produced under the N2O atmosphere. It is sufficiently fast initially that a negative pressure in the reactor is formed and essentially all the N2O present is bound in less than thirty minutes and the reactor needs to be refilled with N2O. If Na ₂ 0 is present in excess, the rate of binding of over 95% of the N2O may be achieved within about a half hour. Without wishing to be bound by any particular theory it is possible that this involves rapid binding of initially exposed sites very rapidly followed by a slower exposure of buried sites due to the destructive impact that occurs during the ball milling process.

[0061 ] Once formed, c/s-Na ₂ N ₂ 0 ₂ contained within the salt matrix reacts slowly when ball milling is done under an atmosphere of N2O over a period of hours to form a mixture of sodium nitrite and sodium nitrate. The initial product formed is primarily nitrate with a smaller amount of nitrite being detected.

[0062] Once formed, c/s-Na ₂ N ₂ 0 ₂ contained within the salt matrix reacts more rapidly when ball milling is done under an atmosphere of O2, for example, within 1-3 hours forming a nearly equal mixture of sodium nitrite and sodium nitrate. A plausible scenario for this reaction is a two step process in which Na ₂ N ₂ 0 ₂ reacts with O2 to form 2 NaN02 in the first step. [0063] In a second step, which is also rapid, NaN0 ₂ is oxidized further to NaN03. A complex ratio exists with an initial large portion of the reaction channel producing nitrate and then later nitrite. Combined yields of nitrate and nitrite approaching 90% may be achieved in this method.

[0064] The further oxidation of nitrite obtained in the mixture described can be achieved; however, it requires the addition of more Na ₂ 0. This oxidation follows the net stoichiometry NaN0 _{2 +} Na ₂ 0 + O2 Na ₂ 0 _{2 +} NaN0 ₃ .

[0065] In an aspect, the disclosed processes provide oxidation of NaN0 ₂ to NaN03 under ball milling and as a function of the salt mixture used. The ability to oxidize in the solid state using O2 and ball milling at ambient temperatures has never been reported to our knowledge. Even in solution such nitrite to nitrate oxidations are typically performed at temperatures of 100 to 400 °C. The anti-perovskite structure formed in the reaction of Na ₂ 0 and NaN0 ₂ consists of an Na30(+) cage with an N0 ₂ (-) anion trapped in its interior. The oxidation of NaN0 ₂ in KCI alone is not rapid under identical conditions. The oxidation of NaN0 ₂ in a mixture of Na ₂ 0 and KCI is rapid under typical conditions. Surprisingly, the oxidation of Na ₂ 0 which has been ball milled together with NaN0 ₂ is also facile without the presence of added KCI. Without wishing to be bound by any one theory it is believed that the anti-perovskite structure presents an active reaction channel for O2 binding and activation.

[0066] When prepared in advance by milling Na ₂ 0 and KCI together, N2O binds rapidly and in near quantitative yield in 2-4 hours producing c/s-IN^INbC^ in the salt matrix with very little oxidation. The reduction in pressure goes from 3 atm absolute pressure to approximately 0.3 atm absolute pressure, indicating roughly 90% binding of the first loading of nitrous oxide into the reactor. Addition of more nitrous oxide also results in rapid uptake provided sodium oxide is present in excess. Infrared spectral data show this to be almost exclusively c/s-Na2N202 with very little formation of nitrate.

[0067] The complete oxidation of c/s-IN^INbC^ to NaN03 by O2 can be achieved in the presence of excess Na ₂ 0 but it also produces an equivalent of Na ₂ 0 ₂ . The Na ₂ 0 ₂ so produced can be however further oxidized by addition of 2 ·N02 gas which quantitatively produces 2 NaN03.

[0068] This suggests that the final product of oxidation of N2O to NaN03 by O2 and excess Na ₂ 0 will contain significant amounts of Na ₂ 0 ₂ . This can be, however, readily converted by passing the initial gas stream input through the salt matrix. Even in the absence of special gas mixing this reaction appears to be rapid. The utilization of aerosol oxidation techniques, possibly augmented by photochemical or electrochemical methods, may be used to drive the reaction to completion.

[0069] The salt matrix so formed may also utilize compounds of S, P, Ca, Fe, Cu, Mo, Zn and other essential plant nutrients. This would most likely be in the form of IN^SC , NasPC , Fe(N03)2, Cu(N03)2,

Na2Mo04, ZnO, CaO or CaC>2. It is not expected that this will alter the established reaction pattern but may advantageously accelerate or catalyze some of the reactions. For example, anhydrous CaSC (gypsum, drierite) may be used to finish dehydration of the exhaust stream that contains the nitrogen oxides and then later combined with the final product in a single blended fertilizer. [0070] The metal oxide can be any suitable metal oxide. In some embodiments, the metal oxide comprises an alkali metal oxide. In some embodiments, in conjunction with other above or below embodiments, the alkali metal oxide is selected from the group consisting of sodium oxide (Na20), sodium peroxide (Na202), lithium peroxide (U2O2), potassium oxide (K2O), and a combination thereof. In some embodiments, the alkali metal oxide is selected from the group consisting of sodium oxide, sodium peroxide, and a combination thereof.

[0071] The disclosed processes comprise milling conditions. In some embodiments, the milling conditions comprise or is ball milling. An illustrative mill is the mixer mill MM500 nano commercially available from Retsch GmbH. In some embodiments, means other than ball milling can be used for mechanical or electrical activation (e.g., planetary ball mill, twin screw extruder, impact milling, sheering milling, as well as electric spark or photochemical activation during milling may be used).

[0072] In keeping with aspects of the disclosed processes, an alkali metal hyponitrite is formed upon contacting the nitrogen oxide with the alkali metal oxide. In some embodiments, the alkali metal hyponitrite is sodium hyponitrite (IN^INhCy. In some embodiments, in conjunction with other above or below embodiments, the sodium hyponitrite is c/s- sodium hyponitrite.

[0073] In various embodiments, the disclosed processes further comprise a catalyst. In some embodiments, in conjunction with other above or below embodiments, the nitrogen oxide with the metal oxide in the presence of a catalyst. In some embodiments, the catalyst comprises or is a metal halide salt (e.g., a potassium halide). Suitable potassium halides include, for example, potassium bromide, potassium chloride, potassium iodide, and a combination thereof. In some embodiments, the catalyst comprises iron. Without wishing to be bound to any particular theory, it is believed that iron from a steel reaction vessel can act as a catalyst.

[0074] In some embodiments, the disclosed processes are conducted in a suitable solvent. Illustrative suitable solvents include, for example, a liquid nitrate salt (e.g., alkali metal nitrate salt). In some embodiments the alkali metal nitrate salt is selected from the group consisting lithium nitrate, sodium nitrate, potassium nitrate, and a combination thereof.

[0075] In keeping with aspects of the disclosure, the disclosed processes are conducted at a suitable temperature. In some embodiments, the processes comprise contacting the nitrogen oxide with the metal oxide at a temperature of less than 360 °C (e.g., 355, 350, 340, 330, 320, 310, 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 35, 30, 25, 23, or 20 °C or less). In some embodiments, the temperature is 150 °C or less. In some embodiments, the temperature is 38 °C. In some embodiments, the temperature is 35 °C or less. In some embodiments, the temperature is 25 °C or less.

[0076] In keeping with aspects of the disclosure, the disclosed processes are conducted at a suitable pressure. In some embodiments, in conjunction with other above or below embodiments, the process comprises contacting the nitrogen oxide with the metal oxide at ambient pressure. [0077] The present disclosure provides a route that can be applied practically to the later stages of oxidation of NxOy. In some embodiments, the disclosed method utilizes N2 as a feedstock. In some embodiments, the complex c/s- may be prepared by ball milling Na20 in KBr under an atmosphere of N2O at ambient temperature. The complex is unequivocally proven by its FTIR spectrum as well as that of Na2 ¹⁵ N202 obtained by ball milling under ¹ %0 atmosphere which is in exact agreement with data from its synthesis at a temperature of 360 °C over 2 hours. The complex builds up to an approximate steady state concentration over time as it is converted slowly to Na(K)N0 ₃ . The reaction yields based on initial Na20 are on the order of 15% after 8 hours of ball milling, and approach approximately 50% conversion over longer periods. Slow hydrolysis of c/s-IN^INbC^ in a KBr pellet produces NaOH and spectral bands attributed to weakly bound N2O encapsulated in the KBr matrix. Computational data on the possible interaction of KBr and N2O support formation of a weak interaction which may be instrumental in activation of nitrous oxide.

[0078] As described herein, the processes disclosed herein advantageously provide a new route to conversion at low temperatures and low pressures using mechanical chemical activation of salts to trap and oxidize NOx and N2O to nitrate. This is achieved using a matrix containing compounds which are compatible with fertilizer use and which may be subsequently blended and used without purification. For example, in some embodiments the materials and components used in the disclosed processes are compatible with a fertilizer (e.g., NPK fertilizer) and can contain one or more of the following nutrients: ammonia, chitosan, clays (e.g., bentonite, gypsum, clinoptilolite), inorganic salts (e.g., calcium containing salts, phosphorous containing salts), and trace metals (e.g., Na, K, Cl, P, Ca, 0, S, Mo, Fe, Zn, Cu, Si, Br, Cs, Ba, or a combination thereof). The nature of the blended mixture can be advantageously tuned to match the desire application (e.g., to best suit the needs of the crop and soil).

[0079] The disclosed processes are advantageous in an agricultural setting wherein handling of liquid ammonia is often done. The use of liquid ammonia on a farm as a source of electricity to power farm equipment and also to transmit to local towns for use may be achieved using the processes disclosed herein. Further, the mechanical and electrical energy needed (e.g., for ball-milling or other grinding processes) may be obtained from windmill and solar energy sources. The direct use of wind or water energy to mill grain can eliminate conversion to electrical energy. There are a number of advantages to this system including that the fertilizer components are produced from waste gases in a low population density area where the product may be used with minimal transportation.

[0080] In some embodiments, a gas comprising N2O and ·NO and ·N02 can be obtained using a series of metal oxide mixtures to remove and oxidize first ·NO and ·N02 leaving essentially pure N2O which is treated in the reactions disclosed herein. The sequencing and components used in the combined treatment process also represent a new method of dealing with N2O and ·NO and ·N02 produced in a process wherein ammonia is burned or where nitrous oxide is produced. An illustrative embodiment is illustrated in the block diagram presented in Figure 15 showing a sequence of reactions wherein raw materials are activated, reacted and blended to yield product. EMBODIMENTS

1. A process for preparing a nitrate comprising contacting a nitrogen oxide with a metal oxide under milling conditions to form a nitrate.

2. The process of embodiment 1 , wherein the nitrogen oxide is selected from the group consisting nitric oxide (NO), nitrogen dioxide (NO ₂ ) nitrogen trioxide (NO ₃ ), nitrous oxide (N ₂ O), dinitrogen dioxide (N ₂ O ₂ ), dinitrogen trioxide (N ₂ O ₃ ), dinitrogen tetroxide (N ₂ O ₄ ), dinitrogen pentoxide (N ₂ O ₅ ), nitrosylazide (N ₄ O), oxatetrazole (N ₄ O), trinitramide (N ₄ O ₆ ), and a combination thereof.

3. The process of embodiment 1 , wherein the nitrogen oxide comprises nitrous oxide.

4. The process of any one of embodiments 1-3, wherein the metal oxide comprises an alkali metal oxide.

5. The process of embodiment 4, wherein the alkali metal oxide is selected from the group consisting of sodium oxide (Na20), sodium peroxide (Na202), lithium peroxide (U2O2), potassium oxide (K2O), and a combination thereof.

6. The process of embodiment 5, wherein the alkali metal oxide is selected from the group consisting of sodium oxide, sodium peroxide, and a combination thereof.

7. The process of any one of embodiments 1-6, wherein the milling conditions is ball milling.

8. The process of any one of embodiments 4-7, wherein an alkali metal hyponitrite is formed upon contacting the nitrogen oxide with the alkali metal oxide.

9. The process of embodiment 8, wherein the alkali metal hyponitrite is sodium hyponitrite (Na ₂ N ₂ 0 ₂ ).

10. The process of embodiment 9, wherein the sodium hyponitrite is c/s- sodium hyponitrite.

11. The process of any one of embodiments 1-10, further comprising contacting the nitrogen oxide with the metal oxide in the presence of a catalyst.

12. The process of embodiment 11 , wherein the catalyst comprises a metal halide salt.

13. The process of embodiment 12, wherein the metal halide salt comprises a potassium halide.

14. The process of embodiment 13, wherein the potassium halide comprises potassium bromide.

15. The process of any one of embodiments 1-14, further comprising contacting the nitrogen oxide with the metal oxide in the presence of a solvent.

16. The process of embodiment 15, wherein the solvent comprises a liquid nitrate salt.

17. The process of embodiment 16, wherein the liquid nitrate salt comprises an alkali metal nitrate salt. 18. The process of embodiment 17, wherein the alkali metal nitrate salt is selected from the group consisting lithium nitrate, sodium nitrate, potassium nitrate, and a combination thereof.

19. The process of any one of embodiments 1-18, further comprising contacting the nitrogen oxide with the metal oxide at a temperature of 300 °C or less.

20. The process of embodiment 19, wherein the temperature is 150 °C or less.

21. The process of embodiment 19, wherein the temperature is 35 °C or less.

22. The process of embodiment 19, wherein the temperature is 25 °C or less.

23. The process of any one of embodiments 1-22, further comprising contacting the nitrogen oxide with the metal oxide at ambient pressure.

24. The process of any one of embodiments 1-23, wherein the milling conditions comprise milling in the presence of oxygen gas.

25. The process of embodiment 24, wherein the nitrogen oxide is nitrous oxide.

26. The process of embodiment 25, wherein the ratio of nitrous oxide to oxygen is about 1 :2 by volume.

27. The process of embodiment 24, wherein the nitrogen oxide and oxygen gas are introduced in alternating sequences.

EXAMPLES

[0081 ] The following examples further illustrate the disclosed processes, but of course, should not be construed as in any way limiting their scope.

[0082] General: All manipulations were performed in a vacuum/atmospheres glove box equipped with a Braun gas purifier system. Open trays of indicating drierite were kept along the back of the glove box to reduce moisture content. Nitrous oxide, oxygen, and other gases used were obtained from Airgas, of research grade, and used as received. Isotopically labelled ¹⁵ N20 was obtained from Cambridge Isotopes and was 99% ¹⁵ N and used as received. KF, KBr, KOI, Kl salts were obtained from commercial vendor and were ACS certified purity. Salts were typically dried in an oven at 250 °C in an oven for several hours and then taken into the glove box and stored in sealed dry containers. Mixer mill experiments were performed in a RETSCH mm500 mixer mill in a 50 mL stainless steel grinding jar with a top with two ports for gas addition/evacuation. Infrared data were obtained on a Perkin Elmer Frontier FTIR spectrophotometer with MCT detector and ATR Diamond Cell Accessory. Gas Phase FTIR were obtained in a 10 cm International Crystal Laboratories glass cell with two stopcocks and equipped with either NaCI or CaF2 windows. Typical procedures are described below.

[0083] Example 1 A - Representative Ball Milling Experiment: The top and bottom and mixer cell pieces for the RETSCFI mm500 cell were heated in an oven to 145 °C or in some cases 220 °C for several hours. Rubber o-ring and gasket materials were heated in a lower temperature oven at 85 °C. These are all placed on trays in the oven, and the trays were taken quickly to the antechamber of the glove box and evacuated and filled with dry argon or nitrogen three times. Sufficient time was allowed for them to cool down to room temperature prior to their handling in the glove box. A 0.50 gram sample of Na ₂ 0 (which was not dried but used directly as received) was weighed quickly into the bottom half of the mixing jar. Following that a 1.50 gram sample of KCI (which had been dried at 250 °C in an oven and kept stored in the glove box) was weighed onto that. One 25 mm stainless steel ball was added to the 50 mL mixing jar, the jar was sealed and tightened in the glove box. It was then taken to the mixer mill and loaded into one of the two arms. The cell was evacuated and filled with N2O in three cycles, and then filled with 30 psi (about 2 atm pressure above atmospheric, 3 atm absolute pressure) N2O. The main tank valve to the N2O was then closed. This allowed the manifold and fitting and mixing jar to be under a near constant pressure since it could be replenished by a limited amount of gas on the high pressure side of the manifold and the main tank valve of the gas cylinder. A typical single cycle was to run for 5 minutes mixing at 30 Hz, then a rest period cycle of 2 minutes. A set of 12 of these cycles provides one hour of active mixing with 12 minutes of rest. This keeps the temperature of the mixing jar between ambient room temperature of 22 °C and a maximum mixing temperature of 38 ± 4 °C at the end of a 5 minute mixing cycle. The cooling down period is important. RETSCH recommends that a roughly even blend of empty space in the mixer mill, volume of mixing balls, and volume of material placed in the grinding jar. The short cycle time used with a rest period did not result in the authors view in any damage to the mixing jar. This ratio of solids and of active mixing to resting time was arrived at only after careful monitoring of test conditions. In view of the potentially hazardous conditions, appropriate safety measures were taken during these operations. Following one hour of milling the mill automatically stops. At that time the mixing jar is evacuated and taken from the mixer mill to the glove box for withdrawal of a sample for analysis. Inhalation of any powders is to be avoided and suitable protective equipment and procedures were followed. Samples were taken into the glove box and analyzed as described herein.

[0084] Example 1B - Ball milling of Na ₂ 0 in KBr under N2O pressure. A RETSCH mixing vessel, 50 mL volume and one 25 mm mixing ball were dried in an oven at 150 °C on a metal tray. In a separate oven the 0- rings were dried at 85 °C for several hours. These were taken while still hot to the vacuum ante-chamber. The mixing vessel was loaded with 1.5 grams KBr that had been pre-dried (250 °C) as well as 0.5 grams of Na ₂ 0 which was not dried, but was used as obtained from Alfa Inorganics from a fresh bottle avoiding the use of surface material. The cell was closed and taken out of the glove box and loaded into the mixer mill. A Schlenk manifold via butyl rubber tubing to allow evacuation and filling of the cell. The cell was evacuated twice and filled with a pressure of 35 psi pressure, yielding an absolute pressure of approximately 3 atm N2O in the cell. The cell was run on a programmed cycle of 90 seconds active mixing at 30 Hz followed by resting for 120 seconds to prevent over heating. The temperature of the cell was measured by both thermal scan and direct contact probes and found to be typically 30-32 °C during active operation. The temperature was never observed to exceed 35 °C. Typically a series of 10 to 20 intervals of a mixing cycle were used, and a sample withdrawn for analysis by FTIR at that time. The mixing cell was removed from the RETSCH sample holder, evacuated to remove nitrous oxide, and taken to the glove box antechamber. After three vacuum/argon cycles the cell was taken into the glove box. Samples were removed for analysis, the mixing vessel closed and taken out of the glove box for additional active mixing. On several occasions the mixing vessel was left overnight under an N O atmosphere to see if reaction would occur under static conditions, and negligible changes in spectra of the solid were observed.

[0085] FTIR Data Collection of Solid Samples. Three primary methods for sampling the solid were utilized.

[0086] A. ATR of the solid. In order to obtain quantitative data for the concentrations of nitrate and also trans hyponitrite in solution ATR studies were performed in which a weighed sample of about 150 mg was dissolved into 1 mL of distilled water. Considerable evolution of N O occurred during this time as indicated by the FTIR analysis.

[0087] Typically, the solid was taken in a special holder to the PE Diamond attenuated total reflectance (ATR) accessory and under dry conditions loaded and a spectrum taken. Due to the very hydroscopic nature of the sodium oxide/potassium bromide milled mixture deterioration of the product from atmospheric moisture or in some cases carbon dioxide was observed. Flowever initial spectra were found to give good qualitative results in agreement with pellet and solution studies.

[0088] B. Aqueous solution phase studies. In order to obtain reasonable quantitative data, particularly for nitrate and nitrite concentrations, a weighed sample of the mixer mill product was transferred to a 1 mL vial, and either H O or D O added to it and the FTIR spectrum run on the PE Diamond ATR. See Figure 6A. The band near 1384 cnr ¹ was assigned to nitrate. Calibration curves were shown to be linear in both nitrate and nitrite using standard techniques.

[0089] The presence of frans-IN^INhC^ was also observed. See Figure 6B. Weighed samples of authentic material were used to calibrate the technique in the same manner as was done for nitrate and reasonable accuracy was obtained.

[0090] The aquation products were analyzed using FTIR. In order to estimate the amount of total N O bound in the sample hydration studies using distilled water were performed. Samples were weighed on a glass weighing boat in the glove box. The weighing boat was then loaded into the 10 cm gas cell fitted with CaF windows. The gas cell was sealed and taken from the glove box, evacuated and a background spectrum obtained. One of the stopcock valves which had its glass stem sealed with a rubber septum had the external region evacuated utilizing the second valve. The stopcock was then closed, 1.0 mL water added by syringe through the rubber septum. Slow opening of the stopcock allowed the water to flow into the gas cell and into the weighing boat which was positioned underneath it. Evolution of gas was immediate and, in some cases, splattering of solid occurred. In blank experiments using a Hamilton gas tight syringe and valve, a known volume of gas was added to the gas cell to allow determination of the amount of N O liberated from the sample. As discussed above, in basic solution some frans-Na2N202 is formed. This does not release N2O but upon careful acidification of the solution it is steadily evolved.

[0091] C. Pellet press samples. IR spectra in KBr pellets provides information on the ratio of bands attributed to nitrate, hyponitrite, encapsulated nitrous oxide, and also of contaminant growth of sodium hydroxide or sodium carbonate. Due to the highly moisture sensitive nature of the pellets, above that of KBr alone, a "sandwich approach” was used in which into the pellet press a layer of pure KBr (100 mg) was placed on the bottom of the pellet press assembly, a layer containing a weighed amount of sample, 2 mg of sample diluted with KBr to a total mass of 100 mg. An additional 100 mg KBr was then placed on top of this, and the pellet pressed top assembly put on. This was then compressed in the cell and an FTIR spectrum run as quickly as possible.

[0092] A representative procedure is as follows. A sample of the mixer mill product, typically KBr/Na20 matrix was weighed onto an agate mortar in the glove box. A weighed additional amount of KBr was added and the sample ground for five minutes. In order to prevent surface contamination, to the pellet press assembly was added a layer of KBr of about 100 mg, then the sample of about 100 mg, and then an additional 100 mg on top of that of KBr to make a "sandwich" pellet. This was taken quickly to the FTIR and run immediately. Over long periods of time deterioration of the pellet made this was observed, first surface water appearing on the KBr, and then slower decrease in the signals due to c/s-Na2N202and appearance of peaks assigned to N2O trapped in the KBr matrix.

[0093] D. Attempt to detect a surface bound N2O on KBr pellet. The spectroscopic data from the pellet press samples gave evidence of N2O trapped in the KBr pellet. In order to test if N2O could enter the KBr or binding to the surface could be detected a blank pellet of KBr was placed in a holder in a 10 cm gas cell equipped with CaF2 windows. The cell was evacuated and filled with N2O at atmospheric pressure. The cell was left for approximately five hours and then it was evacuated and a series of spectra run. The initial spectrum did not show any deviation from the gas phase spectrum, and no evidence for a shift in absorbance was observed. Without wishing to be bound to any particular theory, it is believed that the outgassing most likely occurred from the rubber o-ring seals on the FTIR gas cell and are not ascribed to any detectable bands of N2O bound to KBr.

[0094] E. Quantitative determination of peroxide content of sample. Samples were analyzed for the presence of Na202 using standard iodometric titration procedures employing sodium thiosulfate. In all samples measured, peroxide was detected, however the total amount of peroxide never surpassed 2% of the sodium mole fraction.

[0095] F. Study of Nitrous Oxide Stretch Position in Alkali Halide Salts. In order to gain more information regarding the nature of the encapsulated FTIR the position of the band near 2228 cnr ¹ was compared as shown in Figure 7. As can be seen, there are only minor shifts in position as the halide is changed. In addition, the spectrum taken in pure KBr with no added Na20 is also present in a similar position. Without wishing to be bound to any particular theory, it is believed that this would tend to support encapsulation rather than coordination to the matrix. [0096] Further studies were done of the stability of the pellets under vacuum or O2 atmosphere. In a typical experiment a reaction pellet was loaded into a special holder and held in the 10 cm gas cell. The holder was either evacuated or evacuated and filled with O2. Data are shown in Figure 8.

[0097] Example 2. A series of reactions of Na ₂ 0 and N2O only, and in the presence of additives were studied at 140 °C in the mixer mill. This somewhat elevated temperature was chosen because the direct synthesis of c/s-Na ₂ N ₂ 0 ₂ by Feldman and Jansen occurred at 360 °C. Reactions were performed by placing the sealed mixer mill in the oven at 140 °C and then transferring it to the mixer mill and milling at 35 Hz for 20 cycles of 30 seconds mixing followed by 90 seconds rest. Reactions were also performed in which dried molecular sieves or clinoptilolite (a naturally occurring zeolite) were added as well as potential metal catalysts. A variety of results were obtained and low yields of nitrite and nitrate formation when performed under both N2O and O2, were obtained in some conditions.

[0098] Therefore, the reaction was performed at ambient temperature of 21 °C and which under active milling conditions rises to 36 °C using the current standard program of mixing. FTIR data indicated conversion to c/s-Na ₂ N ₂ 0 ₂ . This was repeated using ¹ %0 labeled nitrous oxide and the bands observed were found to compare well with that of Feldman and Jensen.

[0099] Example 3 - Further Oxidation of Na ₂ N ₂ 0 ₂ (cis and trans) to Na2N203, NaN0 and NaN03.

Without being bound to any particular theory, it is believed that presence of nitric oxide can be used to promote further oxidation. A number of reactions were performed starting from trans IN^INhC^ which even in its dehydrated form contains water. Moreover, it is believed that the reaction to oxidize nitrous oxide must go through an initial hyponitrite. Further, it is believed that the hyponitrites are sensitive complexes and can decompose in three common pathways which we illustrate with IN^INhC^:

Protonation:

Elimination of N2:

Elimination of 2-NO

[0100] Reaction of ^« N0/N20 and ground mixture of frans-NaN0 ₂ and KO2. In an exploratory reaction partially dehydrated commercial samples of trans- Na ₂ N ₂ 0 ₂ and KO2· were ground in an agate mortar and pestle in the glove box. The mixture was loaded placed inside the 10 cm gas cell on the bottom glass cylinder. The NaCI windows of the glass barrel closed and the cell taken to a Schlenk line where it was evacuated and then filled with a mixture of approximately 60 % ·NO and 40 % N2O. There was an immediate appearance of red brown color and the temperature of the cell rose to 50 °C from the exothermic reaction. After approximately three minutes the cell was taken to the FTIR and a series of FTIR spectra collected.

[0101] The FTIR data showed that ·N0 ₂ appeared and disappeared in the gas phase, and on a slower time scale NOCI was clearly detected and then vanished. The level of N2O did not appear to change significantly. In addition, the NaCI windows were coated with a thin film of NaN0 ₂ which could also be determined by its FTIR. After there were no further changes in the gas phase FTIR spectra, the cell was evacuated and filled with argon. A subsequent spectrum taken of the white solid product which could be seen on the wall of the glass cylinder showed that all hyponitrite had reacted and that a mixture of nitrate and nitrite were the products. Without wishing to be bound to any particular theory, it is believed that 1) ·NO gas enters the cell and rapidly reacts with KO2· (s) in the ground mixture to form KOONO(s) as in the first step; 2) The KOONO(s) dissociates to KO (s) and ·Nq2; the KO(s) then combines with ·NO to form KNO2 and/or combine with ·N0 ₂ to form KNO3. In addition, at higher ·NO levels the cleavage of surface KOONO(s) could react to form KNO2 and ·N0 ₂ in what would be a net second order process in ·NO; and 3) An unanticipated reaction was the rapid formation of NOCI, the disappearance of which is assigned to its attach on trans- Na ₂ N ₂ 0 ₂ (s) as well as KO2· leading to the formation of Cl·, NO2-, and NO3- salts formed in the white solid with Na+ and K+ cations.

[0102] Several additional experiments were performed in slightly different conditions. In addition to reaction (19) where K02· reacts with ·NO, pure O2 (g) was added by syringe to solid frans-IN^IN C^ under 1.5 % ·NO in N2. This was done using a vortex mixer and glass beads that were coated with cobalt. While this reaction did produce solid nitrite and nitrate products, examination of an aliquot of the gas mixture showed that N2O was released as well.

[0103] These results demonstrate that the disclosure provides the in situ preparation of c/s-Na ₂ N ₂ 0 ₂ (s) by balling milling at ambient temperatures 22-35 °C under a pressure of 3 atmospheres N ₂ 0(g), and its further slow oxidation to NaN03. Mechanical mixing of Na ₂ 0 and N2O at ambient temperature and pressure led to appearance of c/s-Na ₂ N ₂ 0 ₂ in both neat Na ₂ 0 as well as in Na ₂ 0 diluted in KBr. Spectroscopic study of the reaction diluted in KBr allowed spectroscopic characterization of pressed pellets as well as aqueous solution and surface ATR showed that c/s-Na ₂ N ₂ 0 ₂ was formed and slowly converted to NaN03 overtime.

[0104] It has been surprisingly discovered that, even in the absence of added O2 conversion of the c/s hyponitrite to nitrate was observed. Conversion of up to 50% based on starting Na ₂ 0 converted to nitrate have been achieved.

[0105] The addition of O2 under static conditions with no milling to c/s-Na ₂ N ₂ 0 ₂ that had been formed by milling of Na ₂ 0 to produce c/s-Na ₂ N ₂ 0 ₂ did not result in significant acceleration of nitrate production. At this point, the rate determining step appears to be formation of c/s-Na2N202 and this appears to occur under active milling conditions. Without wishing to be bound to any particular theory, it is believed that the rate of oxidation appears to also be linked to active mixing/milling.

[0106] Halides can play a role in nitrogen oxide chemistry. The observation of bands in the FTIR of the mixer mill product that are slightly blue shifted with respect to N2O gas, and the fact that these were not seen in other matrices suggested that an adduct between KBr and N2O might be stable. The more facile reaction in KBr under mixer mill conditions may serve to accelerate formation of c/s- under mixer mill conditions. The work of Ferdi Schueth on mixer mill oxidation has shown that decreases in temperature as well as radical formation may account for faster oxidation rates. There is a history of halide replacement in KBr pellets; indeed that technique is seldom used for that reason in organometallic chemistry since ligands may be displaced under pressure. It is known that "frustrated Lewis pairs" can be formed with N2O as shown in the elegant work of Stephan and others. During the active mixing conditions, the KBr matrix may in effect create momentary "frustrated Lewis pairs" capable of being trapped by N2O. In addition high speed ball milling can produce nano particle size materials of large surface area and higher energy.

[0107] The history of advances in catalytic chemistry has shown that initial discovery of low yield reactions may require step by step improvements to achieve a viable competitive industrial process. This work has demonstrated for the first time a one-step conversion of nitrous oxide to nitrate. The conversion is based on Na20 is on the order of 50%. However a path has been shown to exist, and the ultimate goal of nitrate conversion in a truly green process from air and water, as suggested by Lewis and Randall a century ago is feasible.

Example 4

[0108] KBr (1.5 g) that had been dried in an oven at 250 °C and Na20 (0.5 g) was loaded into the RETSCH cell with one 25 mm diameter ball. It was processed at 30 Hz for about 10 cycles, wherein each cycle involved 5 minutes mixing and 2 minutes rest. This was repeated twice, and spectra were taken which showed the slow growth of bands assigned to c/s-IN^INhC^. This was repeated and FTIR indicated qualitatively that this continued and the appearance of bands that might be assigned to nitrate formation. After approximately a net mixing time of six hours, another cycle was run and the FTIR spectrum run in KBr pellets. The samples consisted of about 20 mg of the actual sample that was diluted with an additional 50 mg of KBr and ground with a mortar and pestle in the glove box. It was loaded into the pellet press which had already been loaded with about 100 mg of KBr on the bottom, then the 70 mg sample, then another 100 mg on top. This "sandwich” approach was taken to slow the attack of atmospheric moisture on the reactive sodium oxide sample. Following the sample removal, to the RETSCH was added 100 mg of KNO ₃ that had also been dried in the oven. The RETSCH cell was closed, this sample was taken out and filled with 30 psi (all reactions were done with an initial loading of 30 psi N ₂ O). It was run through the 30 Hz mixing for 10 repetitions as were the other reactions.

[0109] An FTIR spectrum was run, and is shown in Figure 9 together with a previous sample that was run had had 5% KNO3 in KBr. The relative intensities at 1453.72 cnr ¹ were assigned to the nitrate absorbance were found to be 0.75 blue ( — ) spectrum. 0.39 red spectrum (-solid--), 0.62 black spectrum (solid line). The blue spectrum contained in two grams 0.1 gram KNO3. The black spectrum contained 0.1 (.75762) = 0.083 grams KNO3, however it was diluted by a factor of 20/70, so multiplication by 70/20 provides a value of 289 mg in the original spectrum. Subtracting the 100 mg added means approximately 189 mg was present in the original sample. The red spectrum had a value of 0.39 so it would be predicted (0.39/0.75)x 100 = 52 mg present in the sample, multiplying by 70/20 = 3.5 provides approximately 182 mg in the original sample. Now the original amount of Na20 was 500 mg. In the reaction Na20 + N2O + 2O2- > 2 NaN03, the weight increases by a factor of 2.74 and the Na20 of 0.5 g is equivalent to 0.5 x 2.74 = 1.37 gram. The estimated yield is 189 mg/1,370 mg or approximately 14 % conversion of N2O to nitrate. The data are in good agreement with literature spectra from NIST.

Example 5

[0110] Additional metal oxides have been investigated. Notably, the results show that Na2C>2 in KCI produces nitrate at a fast rate and in high yields (approximately 50%). See Figures 10A and 10B.

[0111] The long term reaction is also faster for Na2C>2 than for Na20 as depicted in Figure 10A, which shows the percent yield nitrate as a function of time in hours for reaction of Na2C>2 compared to other salts. The fact that it was competitive with the more basic and generally more reactive Na20 was surprising. It is an important advantage because Na2C>2 is both cheaper but also much less hazardous to handle than is Na20.

[0112] These reactions prompted investigation of a wider range of oxides, peroxides, and superoxides. The focus of this work is on trapping nitrate in a matrix that will be compatible with direct use as fertilizer, focused on Na, K, Ca, P, Mo, Fe, Cu oxygen complexes. The potential role of transition metal catalysts on the oxidation reaction have been investigated utilizing, Cu, Co, Fe. Some beneficial enhancement of rate has been detected. [0113] A second area that has been investigated is the investigation of injection of gases already present in the NOx gas exhaust with the metal oxides and their intermediates. This includes primarily the set of gases ·NO, •Nq2, and O2, wherein it has been demonstrated that the addition of ·NO (nitric oxide) to KO2· (potassium superoxide) yields unique oxidation conditions in the presence of chloride ions, wherein these promoters are added at timed intervals during the milling process.

Example 6

[0114] Sodium Peroxide Reactions with N2O in the Mixer Mill - This example demonstrates progress in achieving higher yields and faster rates of reaction using sodium peroxide rather than sodium oxide for reaction with nitrous oxide. Sodium peroxide is much easier to handle, and also much less expensive to produce than sodium oxide. Comparable or even better oxidation results via different intermediates have been observed using peroxide rather than oxide. In some preliminary survey reactions Na202 was added as a "closer” to some test Na20 reactions. No dramatic changes were seen in the later stages of reactions. Milling N2O with Na202 without added KCI showed low production of NaN03 which slowed and stopped at under 3 % yield, as shown in Figure 11A and 11B.

[0115] As shown in the middle curve of Figure 11 A, addition of KCI to the Na202 led to steady production of NaN03 under N2O atmosphere (30 psi) and ambient temperature 35 ± 5 °C. No nitrite production was observed. No sign of c/s-Na2N202 production was observed. The logical intermediate complex would have been Angeli's salt as shown in the following equation (8): Na202 + N2O ® Na2N203 (8).

[0116] Infrared data did not show any sign of reaction (18). Aside from nitrate production, a number of small bands which did not match any known compound were observed but did not accumulate in significant amounts. The unknown bands observed did not match those of an authentic sample of Na2N203. The possibility that Na2N2C>3 is produced but rapidly transformed to a different unknown complex or to product cannot be excluded. Reactions of various mixed ratios of Na ₂ 0 and Na ₂ 0 ₂ give approximately additive behavior initially and then appear to converge to a common rate. It should be remembered that commercial Na ₂ 0 often contains 10-20% Na202 and as discussed later interconversion between oxide and peroxide may also occur during the catalytic cycle.

[0117] Reaction of Na ₂ 0 with Alternation of Atmosphere from N2O to O2 in Sequence - An exciting aspect of the data in Figure 11 A was that obtained in the alternating gas reaction sequence shown at the top of the figure. In this experiment, a mixture of Na ₂ 0 and KCI was milled under N2O atmosphere for 5 hours. The N2O (30 psi) was then evacuated and replaced by O2 (30 psi) and milling continued for 3 hours.

[0118] The results shown in Figure 11 A demonstrate that Na ₂ 0 ₂ alone in the absence of added salt does not react significantly with nitrous oxide. Moreover, the FTIR spectral data showed that conversion of formed c/s- Na ₂ N ₂ 0 ₂ to NaN0 ₂ and NaNCh was near quantitative based on the N2O that was bound and then converted to nitrite and nitrate. In some embodiments, the yield over 24 hours is approximately 70-90%, based on Na ₂ 0 as the limiting reagent. The estimated yield estimates are typically lower based on Na ₂ 0 as the limiting reagent since commercially available Na20 contains impurities including Na202 and also sodium hydroxide and sodium carbonate which are less reactive than Na ₂ 0. The amount of impurities can differ on the age of the Na ₂ 0 sample and the extent of its exposure to atmospheric moisture. This typically lowers the actual observed yield from the spectroscopic rate of conversion. The combined product yield during the first eight hours was approximately 30%. The combined product yield over 24 hours was approximately 70% assuming the Na ₂ 0 was 100 % pure. The spectroscopic data show near quantitative binding of N2O when an excess of Na ₂ 0 is present, and near quantitative oxidation of the formed c/s- that is so formed when excess Na ₂ 0 is present. During the reaction process some of the Na ₂ 0 is also converted to Na ₂ 0 ₂ . In some embodiments, a 70% conversion of "Na ₂ 0" to nitrate and nitrite is achieved in 24 hours reproducibly. The lower apparent yield so calculated is not based on N2O which is converted but on Na ₂ 0 which is converted. The Na ₂ 0 ₂ that is so formed however may be reacted with ·NO, ·Nq2, and O2 to form nitrate. That is done, as described herein, and serves to more fully utilize the activity of the added "Na20".

[0119] An additional surprise was the initial formation of predominantly NaNC^ after the first cycle of reaction with O2. Small amounts of NaN0 ₂ have been observed in several reactions but never in the amount seen in the alternating sequence reactions. A significant loss of c/s-Na ₂ N ₂ 0 ₂ in the direct reaction with O2 also was observed. We conclude that oxidation of c/s-Na ₂ N ₂ 0 ₂ by 3O2 (gas) is significantly faster than oxidation by N2O (gas). That was not expected. As an oxidant, N2O delivers a single O atom and has no barriers with respect to spin change.

In contrast 3O2 delivers two O atoms but spin conservation rules must be overcome.

[0120] Reaction of Na ₂ 0 with Fixed Gas Mixture 67 % O2 and 33 % N2O - In further experiments a fixed tank with a two to one ratio of 67 % O2 and 33 % N2O was used as the oxidizing gas. In contrast to the alternating gas sequence described above which was successful, the use of this fixed gas mixture did not show significant improvement and was found to be inferior to use of N2O alone. A plausible explanation is shown in reaction (9) where conversion of sodium oxide to sodium peroxide occurs: Na ₂ 0 + I/2O2 Na ₂ 0 ₂ DH° = -24 kcal/mol (9)

[0121 ] In effect this converted the reaction over to that of Na ₂ 0 ₂ alone but at a partial pressure of N2O that was 1/3 that used in other experiments. Moreover, as shown in the following equation (10), sodium peroxide is competent to convert nitrite to nitrate and regenerate Na ₂ 0: NaN0 _{2 +} Na ₂ 0 ₂ NaN0 _{3 +} Na ₂ 0 DH° = -2 kcal/mol (10).

[0122] In addition, N2O may also convert Na ₂ 0 to Na ₂ 0 ₂ with elimination of dinitrogen as shown in reaction (11): N3 ₂ 0 + N ₂ 0 N3 ₂ 0 _{2 +} N ₂ DH ^o = -4 kcal/mol (11)

[0123] This adds a complexity, but also a versatility to the catalytic system. Without wishing to be bound to any particular theory, it suggests that addition of transition metals known to activate peroxide catalytically may be possible.

[0124] Catalytic Oxidation of NaN0 ₂ to NaN03 in the Mixer Mill - The alternating gas feed milling approach provides an improved yield. As shown in the data in Figures 11 A and 11 B that NaN0 ₂ may be produced initially when c/s-Na ₂ N ₂ 0 ₂ is produced in the alternating gas sequence described in the previous section. This prompted an investigation of the relative rates of oxidation of NaN0 ₂ to NaN0 ₃ : NaN0 ₂ (KCI/Na ₂ 0 matrix) + Y20 ₂ (gas) - NaN0 ₃ (KCI/Na ₂ 0 matrix) (12) and NaN0 ₂ (KCI matrix) +Y ₂ 0 ₂ (gas) - NaN0 ₃ (KCI matrix) (13)

[0125] It was surprisingly discovered that the oxidation of nitrite to nitrate occurs as shown in eqn. (12) and at a speed comparable to the rate of reaction starting from Na ₂ 0 and N2O in the salt matrix. The salt mixture changes during the reaction as Na ₂ 0 is converted to NaN0 ₂ and NaN0 ₃ . At some point an in situ production of a composition approaching a eutectic mixture may occur and in effect lower the melting point. Work in liquid nitrate salt mixtures which melt in the 100 to 150 °C (e.g., 100, 110, 120, 130, 140 or 150 °C) range but keeping the mixer mill at temperatures below this may result in formation of a temporary molten state during an active collision in a localized area. Without wishing to be bound to any particular theory, it is possible that low melting eutectic mixtures could undergo local melting during an active collision and then solidify and also entrap nitrous oxide in the process.

Example 7

[0126] Gas-Solid State and Gas-Gas Reactions (Radical) - There are potential reactions in which the mixture of N2O, ·NO and ·N0 ₂ may allow utilization of the members of this "toxic trio” to accelerate their own destructive oxidation to nitrate. We have investigated this reaction in an FTIR gas cell in which we have combined ground powders of irans-N a ₂ l\l ₂ 0 ₂ (s) and K02*(s) and exposed it to ·NO gas.

[0127] A typical reaction setup is shown in Figure 12A in which a ground solid containing KO2· and trans- Na ₂ l\l ₂ 0 ₂ (s) initially forms ·N0 ₂ (brown/orange gas) in the infrared cell as well as other compounds. The nitrogen dioxide reacts over a 10 minute time period to completely remove nitrogen dioxide and convert the solid to a white powder containing nitrite and nitrate. In this reaction the infrared cell had NaCI windows and these were attacked by *N0 ₂ (g) to form NaNC^and + *CI(g) which rapidly reacted with + *NO(g) to form NOCI(g). Within 10 minutes the cell was clean and the solid was bleached white and shown to contain nitrite and nitrate. This sequence of reactions occurred much more rapidly than the reactions in the mixer mill. The solid product contained nitrite and nitrate and no other detectable products. However during the reaction nitrous oxide was eliminated from the trans hyponitrite in part which meant that this oxidation was not compatible with nitrate formation from the trans-hyponitrite. This implies that in general the c/s-hyponitrite is more prone to oxidation as opposed to decomposition and nitrous oxide elimination.

[0128] A complex series of reactions occurred and this was continuously monitored by gas phase FTIR in a cell with NaCI windows. There was a bright flash of orange color which occurred immediately and NOCI appeared and then disappeared within minutes in the gas phase infrared spectrum. The spectrum of solid NaN0 ₂ appeared on the NaCI gas windows of the cell. At the end of the experiment the powder at the bottom of the FTIR cell as shown in was white (Figure 12B) and contained only a mixture of NaN0 ₂ and NaN03.

[0129] A plausible explanation of the reaction in Figures 12A and 12B which occurred in minutes is based on an initial reaction of potassium superoxide with nitric oxide to form potassium peroxynitrite as shown in the first step (13i).

[0130] This compound is meta-stable and slowly decomposes to the nitrate isomer. The step in eqn. (13 ii) involves reversible cleavage of the KO-ONO bond to form radical products with *N0 ₂ (g) escaping to the gas phase. The step in reaction (13 iii) involves rotation of the escaped radical and its recombination to form an N-0 linkage and stable nitrate product.

[0131] The ·N0 ₂ radical is a much more reactive species than is .NO. Whereas .NO does not attack NaCI, .NO2 reacts rapidly as shown in eqn. (14):

[0132] The NOCI(gas) is formed in the gas phase and is a highly reactive oxidant which is subsequently neutralized by either KO2· or trans- Na ₂ N ₂ 0 ₂ . It was observed that some N2O was present at the end of the reaction. That indicates that the NOCI may have eliminated this by a complex mechanism. This may be dependent upon a number of factors including surface area of the solid.

[0133] The radical reaction mechanisms suggested that it might be possible to "neutralize" the Na ₂ 0 ₂ that is expected to be present in reactor 2 after oxidation of nitrite to nitrate by oxygen as described above. Under standard conditions, a mixture of 1.5 grams KOI, 0.5 grams Na ₂ 0, and 0.5 grams NaN0 ₂ were ball milled under ambient conditions and 3 atm O2 for a total of 4 hours. This produced the expected mixture of NaN0 ₃ and Na2(>2 produced as shown in eqn. (2). This mixture was loaded into an FTIR gas cell fitted with CaF2 windows and loaded into the cell on a stainless steel trough in the bottom of the cell. The cell was removed from the glove box, placed in the FTIR spectrometer and filled with *NO(g) 1.5 % in N2 at a total pressure of 1.5 atm. No reaction occurred. At that time 5 mL of O2 was added to the cell through a rubber septum fitted to the stopcock to initiate the reaction.

[0134] FTIR data at ambient temperature were obtained and are shown in Figure 13. In this reaction the peaks assigned to ·NO decrease continuously. The bands due to ·N02 grow and then decrease as does the peak due to a small equilibrium amount of the nitrogen dioxide dimer N ₂ O ₄ . Bands assigned to NOCI, as shown in figure 4, grow rapidly and then decrease over about 6 hours.

[0135] Figure 14 shows the absorbance versus time for the reaction shown in Figure 13. The rapid increase in ·N02 concentration following addition of O2 also decreases over time as shown. The concentration of NOCI grows relatively rapidly but decays more slowly and is not complete until about 6 hours.

[0136] The reaction mixture was left over the weekend and an FTIR spectrum of both gas and solid run on Monday. The gas spectrum showed that ·NO, ·N02, and NOCI had all gone to zero. A small amount of N2O which was present in the ·NO from the beginning was left unchanged. This is in keeping with the relatively inert character of N2O which was not oxidized under these conditions. An FTIR spectrum of the solid material showed it to contain only NaN03 and a low level of peroxide. Though not yet proven, the reaction sequence shown in eqns (15)-(17) are considered probable in accounting for the observed products.

[0137] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0138] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range and each endpoint, unless otherwise indicated herein, and each separate value and endpoint is incorporated into the specification as if it were individually recited herein.

[0139] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (for example, “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

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