Systems, methods and materials for NOx decomposition with metal oxide materials

Abstract

Systems and methods use oxygen uncoupling metal oxide material for decomposition of NO.sub.x. A gaseous input stream comprising NO.sub.x is contacted with a metal oxide particle, generating nitrogen (N.sub.2) gas and an oxidized metal oxide particle. After contacting the first gaseous input stream with the metal oxide particle, a first gaseous product stream is collected. The first gaseous product stream includes substantially no NO.sub.x. A second gaseous input stream comprising at least one sweeping gas is also contacted with the oxidized metal oxide particle. After contacting the oxidized metal oxide particle, the sweeping gas includes oxygen (O.sub.2) and a reduced metal oxide particle is generated. Then a second gaseous product stream is collected, where the second gaseous product stream includes oxygen (O.sub.2) gas.

Claims

1. A method comprising: contacting a first gaseous input stream comprising NO.sub.x with a metal oxide particle, whereupon the NO.sub.x in the first gaseous input stream reacts with the metal oxide particle to generate nitrogen (N.sub.2) gas and an oxidized metal oxide particle, wherein contacting the first gaseous input stream with the metal oxide particle occurs at a first temperature of from 400 C. to 700 C.; collecting a first gaseous product stream comprising substantially no NO.sub.x; contacting a second gaseous input stream comprising at least one sweeping gas with the oxidized metal oxide particle, whereupon the sweeping gas comprises oxygen (O.sub.2) gas after contacting the oxidized metal oxide particle and a reduced metal oxide particle is generated, wherein the at least one sweeping gas is oxygen (O.sub.2) gas free; wherein contacting the second gaseous input stream with the oxidized metal oxide particle occurs at a second temperature of from 600 C. to 1000 C.; and collecting a second gaseous product stream comprising the oxygen (O.sub.2) gas.

2. The method according to claim 1, wherein contacting the first gaseous input stream with the metal oxide particle occurs in a first reactor operating at the first temperature; and wherein contacting the second gaseous input stream with the oxidized metal oxide particle occurs in the first reactor operating at the second temperature.

3. The method according to claim 2, further comprising: monitoring NO.sub.x content in the first gaseous input stream; upon the NO.sub.x content exceeding a predetermined threshold, stopping contacting the first gaseous input stream with the metal oxide particle; after stopping contacting the first gaseous input stream with the metal oxide particle, heating the first reactor to the second temperature; after heating the first reactor to the second temperature, contacting the second gaseous input stream with the oxidized metal oxide particle; after a predetermined time, stopping contacting the second gaseous input stream with the oxidized metal oxide particle; and lowering a first reactor temperature to the first temperature.

4. The method according to claim 3, further comprising using the reduced metal oxide particle as the metal oxide particle during contacting the first gaseous input stream with the metal oxide particle.

5. The method according to claim 1, further comprising: providing the metal oxide particle to the first reactor, wherein contacting the first gaseous input stream with the metal oxide particle occurs in the first reactor operating at the first temperature; and wherein collecting the first gaseous product stream includes providing a first reactor outlet stream substantially free of NO.sub.x gas; and providing the oxidized metal oxide particle to the second reactor, wherein contacting the second gaseous input stream with the oxidized metal oxide particle occurs in a second reactor operating at the second temperature; and wherein collecting the second gaseous product stream includes providing a second reactor outlet stream comprising the oxygen (O.sub.2) gas.

6. The method according to claim 5, further comprising using the reduced metal oxide particle as the metal oxide particle provided to the first reactor.

7. The method according to claim 1, wherein the first gaseous product stream includes less than 0.001% by volume NO.sub.x.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A, 1B, and 1C show changes of state for a single fixed bed reactor system cycling between different stages of a NO.sub.x decomposition process using SOUMO material particles.

(2) FIG. 2 shows an example of a process that has four fixed bed reactors operating in parallel and at different stages of the SOUMO NO.sub.x decomposition lifecycle.

(3) FIG. 3 shows a process flow diagram for a continuous NO.sub.x decomposition chemical looping system. LT and HT steam refer to low temperature and high temperature steam that act as a thermal cycling aid and as a O.sub.2-free sweeping gas.

(4) FIG. 4 shows an example method for NO.sub.x decomposition.

(5) FIG. 5 is a schematic diagram for an experimental set-up for fixed bed trials.

(6) FIG. 6 shows breakthrough curves for W doped Mg.sub.6MnO.sub.8 in a fixed bed reactor for 0% and 3% O.sub.2 provided with 500 ppm of NO at 650 C.

(7) FIG. 7 shows a breakthrough curve for unsupported CuCo.sub.2O.sub.4 in a fixed bed reactor with 500 ppm of NO feed at 550 C.

(8) FIG. 8 shows a breakthrough curve for CuCo.sub.2O.sub.4/CeO.sub.2 in a fixed bed reactor with 500 ppm of NO feed at 550 C.

DETAILED DESCRIPTION

(9) Systems and methods disclosed and contemplated herein relate to decomposition of NO.sub.x. Disclosed systems and processes eliminate the use of a reducing gas and employ a regenerative solid phase reducing agent for NO decomposition. These regenerative solid phase reducing agents are termed as Specialized Oxygen Uncoupling Metal Oxides or SOUMO. SOUMO material uptakes oxygen from NO.sub.x at a lower temperature, releasing N.sub.2. Without the use of a reducing gas at a higher temperature, acquired oxygen acquired is then released because of the oxygen uncoupling tendency of the SOUMO. Exemplary systems can be implemented as, for instance, fixed bed, moving bed, and fluidized bed reactors. In various implementations, systems can be run in semi-batch or continuous modes.

(10) Due to the regenerative characteristic of SOUMO, the system requires no additional chemical input making disclosed systems self-sustaining. As described in greater detail below, SOUMO material reacts selectively with the NO.sub.x in the flue gas and separates the product gases, O.sub.2 and N.sub.2, into two separate streams. This separation of products helps drive the reactions in a different manner than the catalytic processes.

(11) Temperature ranges of operation for the NO decomposition reaction include 400-700 C. Temperature ranges of operation for O.sub.2 uncoupling reaction include 600-1000 C. The system under these conditions achieves about, or equal to, 100% NO decomposition efficiency for a wide range of residence times.

(12) Operating pressures for both reactors can individually range from latm to 30 atm based on the pressure of the NO containing feed stream. The separation of the product gases also helps in maximizing the driving force for individual reactions by changing the operating parameters independently for both the reactions. Example systems and methods exhibit almost, or equal to, 100% selectivity towards N.sub.2. In other words, undesired by-products such as NO.sub.2 and N.sub.2O are not formed.

(13) Example systems and methods do not utilize a reducing gas, which in turn eliminates several auxiliary units, which can result in economic benefits for the chemical looping system over a commercial SCR system. Relatively inexpensive SOUMO materials can be used in the chemical looping mode (cost of material is <$1000/ton), which may be at least two orders of magnitude cheaper than materials required for conventional SCR systems.

(14) The overall reaction of exemplary processes is similar to direct catalytic decomposition due to the regenerative nature of SOUMO materials. However, exemplary systems and methods utilize different reactors to perform different functions. Typically, example systems include an NO.sub.x decomposition reactor and an oxygen uncoupling reactor. The NO.sub.x decomposition reactor strips the oxygen atom from the NO molecule. The oxygen uncoupling reactor releases acquired oxygen into the gas phase. Both these functions are performed in the same reactor in conventional direct catalytic decomposition reaction systems.

(15) The catalyst in the conventional direct decomposition process does not undergo any permanent reduction or oxidation under ideal operating conditions. In contrast, the active metal component(s) in the SOUMO material undergoes oxidation and reduction. For instance, in the NO.sub.x decomposition reactor, the oxidation state of the active metal component(s) in the SOUMO material increases due to the oxygen atoms being incorporated into the SOUMO material. In the oxygen uncoupling reactor, the oxidation state of the active metal component(s) in the SOUMO material reduces as the lattice oxygen is uncoupled into the gas phase. This change in oxidation state of the SOUMO material helps drive the NO.sub.x decomposition reaction at a lower temperature as compared to the direct catalytic NO.sub.x decomposition.

(16) The design of systems and methods disclosed herein also adds degrees of freedom to the overall process, allowing for different solid compositions that work for this process. As mentioned above, disclosed and contemplated systems employ a chemical looping approach that decomposes NO.sub.x into its constituents (N.sub.2 and O.sub.2) in two separate streams. Traditionally, direct decomposition of NO.sub.x is carried out over a catalyst where both N.sub.2 and O.sub.2 exit the reactor in one stream. Thus, the catalytic system is always under a dynamic equilibrium between NO.sub.x, the gas products and the catalyst surface. Hence, any additional O.sub.2 in the reactant stream disrupts the equilibrium, reducing the NO.sub.x decomposition efficiency.

(17) In the instantly disclosed systems and methods, because of the inherent separation of the two product streams, NO.sub.x decomposition efficiency is unaffected by the co-addition of O.sub.2 in the chemical looping mode. This structure helps achieve high selectivity towards N.sub.2 for NO.sub.x decomposition while maintaining high NO.sub.x decomposition activity. The separated O.sub.2 stream is a value-added product that can be utilized. The O.sub.2 stream in the instant systems and methods has the potential for reduction of parasitic power loads and boost in energy efficiency by reducing oxygen requirements from the air separation units. In contrast, in the catalytic direct decomposition system, an O.sub.2 stream is emitted into the atmosphere; in the SCR system the O.sub.2 stream is converted to H.sub.2O.

(18) The chemical looping mode reduces the decomposition temperature of NO.sub.x as compared to catalytic direct decomposition (typically 700-900 C.) due to the reaction being aided by the phase change of the reduced SOUMO phase to the oxidized SOUMO phase. Additionally, the SOUMO material does not oxidize NO into NO.sub.2, thus exemplifying the SOUMO material's selectivity towards NO.sub.x decomposition reaction. This structure illustrates a difference in reactivity and selectivity of the lattice oxygen available in the SOUMO particle as compared to molecular oxygen, either in gas phase or when adsorbed over a catalyst.

(19) In contrast, the catalyst used in direct NO.sub.x decomposition suffers from CO.sub.2 inhibition of the catalyst's active sites required for NO.sub.x decomposition. SOUMO materials used in exemplary systems and process are designed limit the loss of activity attributed to CO.sub.2 inhibition to 10%. This structure of the SOUMO materials displays an affinity towards NO.sub.x molecule more than the CO.sub.2 molecule for adsorption on the metal oxide surface.

(20) The direct catalytic decomposition process and the disclosed and contemplated systems and methods also differ in reaction pathways. Although both systems are driven by oxygen vacancies on the surface, the role and the nature of these vacancies are inherently different. In the direct catalytic decomposition process, the metal oxide surface maintains a constant amount of oxygen vacancies. The temperature of operation and the reactant composition are crucial for determining the concentration of these oxygen vacancies.

(21) In the instantly disclosed and contemplated systems, the reduced SOUMO material stores the oxygen from NO.sub.x in its oxygen vacancy, depleting the concentration of oxygen vacancies on the surface with time. In other words, the reduced SOUMO material acts as a reactant rather than a catalyst, forming a stable intermediate species. The lattice oxygen thus formed undergoes diffusion into the bulk metal oxide, creating additional oxygen vacancies on the surface. When all the oxygen vacancies are exhausted, the oxidized SOUMO metal oxide is heated to yield molecular O.sub.2 and generate new oxygen vacancies that are active towards NO.sub.x decomposition. Specifically, the oxidized SOUMO material that was the stable intermediate of the previous reaction, acts as a reactant, converting itself into the reduced SOUMO on reaction. Thus, the formation and depletion of oxygen vacancies occurs in two different reactors operating at two different conditions, leading to efficient removal of NO.sub.x. The solid phase also inherently interacts with the gas reactants in a different fashion than the traditional catalytic process.

(22) Example systems and methods can also be implemented as a series of fixed bed reactors. In those embodiments, the fixed bed reactors begin filled with a fully reduced SOUMO, MO. MO takes up oxygen from NO.sub.x from sources such as flue gas, converting it to N.sub.2. This conversion of MO to MO.sub.2 happens at a moderate temperature, where MO.sub.2 does not undergo thermal oxygen uncoupling.

(23) The outlet NO.sub.x concentration is continuously measured and when NO.sub.x begins to appear in the outlet stream, a three-way valve controlling the NO.sub.x source is switched such that the NO.sub.x flows to a fresh bed of MO, thus making this a continuous process. The oxidized bed, now filled with MO.sub.2, is heated to the uncoupling temperature and an O.sub.2-free sweeping gas, such as steam, is flowed over the bed to remove the oxygen as the SOUMO uncouples. Once the bed has completely uncoupled its oxygen, the reactor is cooled to the NO.sub.x uptake temperature and the sweeping gas is switched off. The bed is ready for another cycle of oxidation from NO.sub.x.

(24) Example Systems and Configurations

(25) FIGS. 1A, 1B, and 1C show changes of state for a single fixed bed reactor system cycling between different stages of a NO.sub.x decomposition process using SOUMO material particles. More specifically, FIGS. 1A, 1B and 1C show the reduced metal oxide phase and the oxidized metal oxide phase with the corresponding changes in temperature, feed gas, and outlet gas. In practice, multiple fixed bed reactors could be used wherein one reactor is being fed flue gas while the other reactors are in various stages of regeneration.

(26) The system can be optimized such that as soon as the breakthrough point of the reactor decomposing NO.sub.x is reached, another reactor is ready to begin decomposing NO.sub.x. This system can be expanded to n number of reactors of variable volume, such that there is SOUMO material ready to decompose NO.sub.x.

(27) In the stage shown in FIG. 1A, the bed is filled with reduced metal oxide particles and at lower temperatures, e.g., 400-700 C. Then NO.sub.x containing flue gas is injected into the bed. Thereafter, NO.sub.x in flue gas reacts in bed to produce a NO.sub.x free outlet gas and partially oxidized metal oxides (NO.sub.x+Reduced Metal Oxide.fwdarw.N.sub.2+Oxidized Metal oxide).

(28) In the stage shown in FIG. 1B, based on the breakthrough times, injection of flue gas is stopped when NO.sub.x concentration in the outlet gas increases. As mentioned above, in certain configurations, there are multiple reactors in parallel so when one reactor stops flue gas injection, another starts. Then the bed of partially oxidized metal oxides is heated to an uncoupling temperature, which can be between 600-1000 C. Next, a sweeping gas, which is O.sub.2-free, is injected over the bed.

(29) In the stage shown in FIG. 1C, in the presence of elevated temperature and sweeping gas, SOUMO particles will release their oxygen into sweeping gas (Oxidized Metal Oxide.fwdarw.Reduced Metal Oxide+O.sub.2). A separation step can separate the oxygen gas from the sweeping gas for a pure oxygen product. After the uncoupling process has completed (based on the time of reaction), injection of sweeping gas is stopped. Then, the reduced metal oxide particles are cooled to a lower temperature. The process can then return to the stage shown in FIG. 1A.

(30) FIG. 2 shows an example of a process that has four fixed bed reactors operating in parallel and at different stages of the SOUMO NO.sub.x decomposition lifecycle. The temperature range of operation for the NO.sub.x decomposition reaction is 400-700 C. and for O.sub.2 uncoupling reaction is 600-1000 C. The operating pressure for both reactors can individually range from latm to 30 atm based on the pressure of the NO.sub.x containing feed stream.

(31) FIG. 3 shows a process flow diagram for a continuous NO.sub.x decomposition chemical looping system. MO and MO.sub.2 are the reduced and the oxidized SOUMO particles respectively. The system shown in FIG. 3 includes moving/fluidized beds, where different reactors are operated under different gas compositions. In the circulating system shown in FIG. 3, typical operation begins by filling a bed with reduced metal oxide particles and at lower temperatures, e.g., 400-700 C. Then solids circulation is established with desired hourly space velocities. Next, NO.sub.x containing flue gas is injected into the NOx decomposition reactor.

(32) NO.sub.x in the flue gas reacts in the NOx decomposition reactor to produce a NO.sub.x free outlet gas and partially oxidized metal oxides (NO.sub.x+Reduced Metal Oxide.fwdarw.N.sub.2+Oxidized Metal oxide). The partially oxidized metal-oxide is sent to the O.sub.2 uncoupling reactor, where in the temperature of the second reactor is maintained at between 600-1000 C. A sweeping gas (such as, for example, H.sub.2O or N.sub.2) is continuously injected into the uncoupling reactor.

(33) In the presence of elevated temperature and sweeping gas, metal oxides will release their oxygen into the sweeping gas (Oxidized Metal Oxide.fwdarw.Reduced Metal Oxide+O.sub.2). A separation step can separate the oxygen gas from the sweeping gas for a pure oxygen product. After the uncoupling process has completed (based on the residence times), the metal-oxide is entrained to the NOx decomposition reactor wherein the particles are cooled to a lower temperature and the process can repeat.

(34) Example SOUMO Material

(35) The SOUMO particles can be synthesized by methods including but not limited to wet milling, extrusion, pelletizing, freeze granulation, co-precipitation, wet-impregnation, sol-gel and mechanical compression. Techniques, like sintering the synthesized SOUMO or adding a binder or a sacrificial agent with synthesis methods such as sol-gel combustion, can be used to increase the strength or the reactivity of the metal-oxide.

(36) The SOUMO particles have an active metal oxide component with one or more reducible metal combined with or without, one or more dopant(s) to induce active sites and aid the formation of oxygen vacancies and with or without a support metal oxide component to enhance surface area and the distribution of the active sites. The reducible oxygen uncoupling metal oxides can be a combination of Co, Cu, Mn, Sr etc. which can be combined with other oxides of metals such as Ti, V, Cr, Fe, Ni, Zn, Ru, Rh, Ce, La, W etc. in the form of dopants, promoters or substituents. Dopants and promoters are in a smaller quantity (0-20 wt %) that do not change the original crystal structure. Substituents refer to components which can form one or several mixed metal oxide phase(s) with the active metal oxide, for example CuCo.sub.2O.sub.4 etc.

(37) Quantities can range from stoichiometric ratios to make the mixed metal oxide, or in excess or lean quantities to get a mixture of the mixed metal oxide and the initial constituent(s). These reducible metals can be combined with oxides of group I and II metals such as Mg, Li, Na, Ca etc. to generate active sites when used as dopants or produce mixed metal oxides such as Mg.sub.6MnO.sub.8 or CaMnO.sub.3. The support metal oxide includes but is not limited to metal oxides such as SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, CeO.sub.2, WO.sub.3 or mixed metal oxides such as MgAl.sub.2O.sub.4. The support material quantity can range from 10-90 wt % with the balance being the active SOUMO material. Typical surface areas of these metal oxide materials can range from 0.05-100 m.sup.2/g and can be manipulated by but not limited to changing the composition of the metal oxide itself, changing the operational conditions, changing the sintering conditions

(38) Example Methods of Operation

(39) FIG. 4 shows example method 400 for NO.sub.x decomposition. Method 400 can be implemented, for instance, in single fixed bed systems, multiple fixed bed systems, and continuous chemical looping systems. SOUMO material disclosed and contemplated herein can be used as metal oxide particles during implementation of method 400.

(40) Example method 400 begins by contacting a first gaseous input stream comprising NO.sub.x with a metal oxide particle (operation 402). Upon contact, the NO.sub.x in the first gaseous input stream reacts with the metal oxide particle to generate nitrogen (N.sub.2) gas and an oxidized metal oxide particle. Typically, contacting the first gaseous input stream with the metal oxide particle occurs at a first temperature of from 400 C. to 700 C.

(41) After contacting the first gaseous input stream with the metal oxide particle (operation 402), a first gaseous product stream is collected (operation 404). The first gaseous product stream includes substantially no NO.sub.x. In some instances, the first gaseous product stream includes less than 0.001% by volume NO.sub.x.

(42) A second gaseous input stream comprising at least one sweeping gas is also contacted with the oxidized metal oxide particle (operation 406). After contacting the oxidized metal oxide particle, the sweeping gas includes oxygen (O.sub.2) and a reduced metal oxide particle is generated. Sweeping gas provided to the system is oxygen (O.sub.2) gas free. Operation 406 typically occurs at a second temperature of from 600 C. to 1000 C. Then a second gaseous product stream is collected (operation 408), where the second gaseous product stream includes oxygen (O.sub.2) gas.

(43) In some instances, operation 402 occurs in a first reactor operating at the first temperature and operation 406 occurs in the first reactor operating at the second temperature. As one alternative, operation 402 can occurs in a first reactor operating at the first temperature and operation 406 occurs in a second reactor operating at the second temperature.

(44) Method 400 can also include additional operations. For instance, method 400 can include monitoring NO.sub.x content in the first gaseous input stream and upon the NO.sub.x content exceeding a predetermined threshold, stopping contacting the first gaseous input stream with the metal oxide particle. Then, after stopping contacting the first gaseous input stream with the metal oxide particle, the reactor is heated to the second temperature. After heating the reactor to the second temperature, the second gaseous input stream is contacted with the oxidized metal oxide particle. After a predetermined time, contacting the second gaseous input stream with the oxidized metal oxide particle is stopped and the reactor temperature is lowered to the first temperature. In some instances, the reduced metal oxide particle is used as the metal oxide particle of operation 402.

(45) Method 400 can also include providing the metal oxide particle to a first reactor, where contacting the first gaseous input stream with the metal oxide particle occurs in the first reactor operating at the first temperature. Collecting the first gaseous product stream includes providing a first reactor outlet stream substantially free of NO.sub.x gas. Then the oxidized metal oxide particle is provided to the second reactor. Contacting the second gaseous input stream with the oxidized metal oxide particle occurs in a second reactor operating at the second temperature. Collecting the second gaseous product stream includes providing a second reactor outlet stream comprising the oxygen (O.sub.2) gas. Then, in some instances, the reduced metal oxide particle is used as the metal oxide particle provided to the first reactor.

EXPERIMENTAL EXAMPLES

(46) SOUMO Screening for NOx Activity

(47) Numerous composite metal oxides were initially considered based largely on their ability to thermally uncouple from oxygen. Metal oxides were initially tested in a Setsys Evolution thermo-gravimetric analyzer (TGA). The thermal uncoupling requirement led to most composites consisting at least partially of one of the typical chemical looping with oxidative uncoupling (CLOU) materials, including Mn, Cu and Co. Several showed the ability to uptake [O] from NO as demonstrated by a mass increase when the 5000 ppm NO reacted with the metal oxide. These metal oxides were screened for NO.sub.x decomposition reaction in the temperature range of 500 C. to 850 C. Correspondingly, the oxygen uncoupling reactions were carried out in the range of 800 C. to 1000 C.

(48) This uptake-uncoupling cycle was carried out with a thermal swing, where the [O] uptake from NO was at the specified temperature and the O.sub.2 uncoupling was done at 850 C. Ten such cycles were run for each of these variants to verify the recyclable nature of this process. The uptake is defined as moles of [O] taken up by the SOUMO per hour.

(49) Two high performing classes of metal oxides were found, an Mn based particle and a Co based particle. The Mn based particle is Mg.sub.6MnO.sub.8 and the Co based particle is CuCo.sub.2O.sub.4. Both of these particles showed slightly different preferred temperatures, where the Mg.sub.6MnO.sub.8 particle achieved its best performance at 650 C. and the CuCo.sub.2O.sub.4 particle achieved its best performance at 550 C. The NO uptake versus temperature is shown in Table 1.

(50) TABLE-US-00001 TABLE 1 NO uptake versus temperature between 500 C. and 700 C. for the Mn and Co based particles. Oxygen Uptake (mol O/hr) Temperature Mg.sub.6MnO.sub.8 CuCo.sub.2O.sub.4 500 C. N/A 14.192 550 C. 5.279 16.522 600 C. 6.959 14.247 650 C. 6.562 9.539 700 C. N/A 7.148

(51) Further attempts were made to enhance the particle performance including using dopants/promotors and supports to increase the surface area. The comparison of dopants/promotors and supports was done at the operating temperature that achieved the best performance for each class of metal oxide (550 C. for Co based particles and 650 C. for Mn based particles). For the Mn based particle, a lithium dopant and tungsten promoter were studied, along with an MnCu mixed particle. The lithium dopant showed a slight decrease in performance while the tungsten promoter showed a slight increase. The MnCu mixed oxide showed the best performance, about on par with that of the Co based material. These results are shown in Table 2.

(52) TABLE-US-00002 TABLE 2 Effect of dopants and promotors on Mn based particles Particle Oxygen Uptake (mol O/hr) Undoped Mg.sub.6MnO.sub.8 6.939 Li doped Mg.sub.6MnO.sub.8 5.164 W promoted Mg.sub.6MnO.sub.8 6.985 CuOW promoted Mg.sub.6MnO.sub.8 17.961

(53) For the Co-based materials, three different supports were used to increase the surface area; tungsten oxide, zirconium oxide, and cerium oxide. Each support showed an increase in the oxygen uptake over the unsupported material. The cerium support showed the best performance and was able to increase the oxygen uptake by 75%. These results are shown in Table 3.

(54) TABLE-US-00003 TABLE 3 Effect of supports on Co based particles Particle Oxygen Uptake (mol O/hr) CuCo.sub.2O.sub.4 9.135 CuCo.sub.2O.sub.4/WO.sub.3 support 9.476 CuCo.sub.2O.sub.4/ZrO.sub.2 support 13.773 CuCo.sub.2O.sub.4/CeO.sub.2 support 15.962
II. Resistance of SOUMO from Acid Gases:

(55) CO.sub.2 inhibition or poisoning is a problem in catalytic direct decomposition of NO.sub.x, where the addition of CO.sub.2 causes a reduction in the NO.sub.x conversion. SOUMO material can be tailored in such a way that the material shows a resistance to such an inhibition. The following is an example where CO.sub.2 inhibition was tested for both the Co and Mn based SOUMO particles.

(56) A ten cycle TGA test was run with 5000 ppm NO and 15% CO.sub.2 and compared to the results with only 5000 ppm NO. The results of the test are shown in Table 4. The presence of 15% CO.sub.2 does not show a significant reduction of oxygen uptake in either particle, for both particles there was less than a 10% reduction in oxygen uptake. Such a resistance towards CO.sub.2 has not been observed in the literature for the catalysts that have been investigated.

(57) TABLE-US-00004 TABLE 4 Effect of 15% CO.sub.2 on NO uptake. Oxygen Uptake Oxygen Uptake (mol O/hr) (mol O/hr) Particle 0% CO.sub.2 15% CO.sub.2 CuCo.sub.2O.sub.4 @ 550 C. 16.522 14.889 W promoted Mg.sub.6MnO.sub.8 6.986 6.452 @ 650 C.
II. Fixed Bed Test of SOUMO Materials

(58) Scaled-up fixed bed trials were run for further proof of concept. The residence time of the reactor was empirically estimated by running a blank run. The experimental set-up can be seen in FIG. 5. The NOx decomposition reaction and the oxygen uncoupling reaction was carried out in the same reactor by thermal cycling the bed. The following sections discuss the effect of oxygen co-addition, changing the gas hourly space velocity, and the effect of support on breakthrough times.

(59) A. Effect of Oxygen Co-Addition

(60) W promoted Mg.sub.6MnO.sub.8 was run in the fixed bed reactor at a GHSV of 1200 hr.sup.1 and a metal oxide to gas loading of 1.75 gs/cm.sup.3. A trial with 500 ppm of NO with balance N.sub.2 was run and compared to a trial with 500 ppm NO, 3% O.sub.2 and balance N.sub.2, both at a temperature of 650 C. The breakthrough time was compared against each other, to understand the effect of O.sub.2 towards NO conversion.

(61) FIG. 6 shows the NO conversion with time for both the trials after accounting for the residence time. As illustrated, the breakthrough time for both these trials approximately is the same, suggesting a preferential reaction favoring the decomposition of NO. Thus, SOUMO material can be customized to exhibit a high selectivity towards oxygen uptake from NO as compared to oxygen uptake from O.sub.2. In this example, the breakthrough time for both the trials was 40 seconds, during which the NO conversion was 99%. Also, during the [O] uptake from NO, N.sub.2O and NO.sub.2 were not detected, highlighting the absence of secondary undesired reactions in this system.

(62) B. Changing the Gas Hourly Space Velocity

(63) Unsupported CuCo.sub.2O.sub.4 was run at 4 gs/cm.sup.3 to probe the change in the breakthrough curve of NO.sub.x coming out of the reactor. The reactor was operated at 550 C., with oxygen uncoupling carried out at 850 C. Similar to the previous fixed bed experiment, the NO.sub.x concentration was 500 ppm with balance as N.sub.2. FIG. 7 shows data for NO.sub.x decomposition with time. The lower surface area of this SOUMO material encourages curve gas bypassing thus elongating the breakthrough curve to up to 120 s.

(64) C. Effect of Support on Breakthrough Times

(65) CuCo.sub.2O.sub.4 SOUMO material depicts higher oxygen uptake when CeO.sub.2 was used as a support, as seen in Table 3, above. The CeO.sub.2 supported CuCo.sub.2O.sub.4 SOUMO material was tested in the fixed bed reactor at 550 C., with oxygen uncoupling carried out at 850 C. The CeO.sub.2 supported CuCo.sub.2O.sub.4 SOUMO material was run at 1.85 gs/cm.sup.3, with 500 ppm NO.sub.x as the reactant feed. FIG. 8 shows the breakthrough curve for both these configurations. The plateau region is similar to the W promoted Mg.sub.6MnO.sub.8 breakthrough curve in FIG. 6 lasting for 35 s. The difference in behavior from FIG. 7 results from the increase in surface area due to the addition of the support.

(66) Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Example methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

(67) The terms comprise(s), include(s), having, has, can, contain(s), and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms a, an and the include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments comprising, consisting of and consisting essentially of, the embodiments or elements presented herein, whether explicitly set forth or not.

(68) The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). The modifier about should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression from about 2 to about 4 also discloses the range from 2 to 4. The term about may refer to plus or minus 10% of the indicated number. For example, about 10% may indicate a range of 9% to 11%, and about 1 may mean from 0.9-1.1. Other meanings of about may be apparent from the context, such as rounding off, so, for example about 1 may also mean from 0.5 to 1.4.

(69) Definitions of specific functional groups and chemical terms are described in more detail below. For purposes of this disclosure, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 75.sup.th Ed., inside cover, and specific functional groups are generally defined as described therein. For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated. For example, when a pressure range is described as being between ambient pressure and another pressure, a pressure that is ambient pressure is expressly contemplated.