A mixed potential sensor device and methods for measuring total ammonia (NH3) concentration in a gas is provided. The gas is first partitioned into two streams directed into two sensing chambers. Each gas stream is conditioned by a specific catalyst system. In one chamber, in some instances at a te
A mixed potential sensor device and methods for measuring total ammonia (NH3) concentration in a gas is provided. The gas is first partitioned into two streams directed into two sensing chambers. Each gas stream is conditioned by a specific catalyst system. In one chamber, in some instances at a temperature of at least about 600�� C., the gas is treated such that almost all of the ammonia is converted to NOx, and a steady state equilibrium concentration of NO to NO2 is established. In the second chamber, the gas is treated with a catalyst at a lower temperature, preferably less than 450�� C. such that most of the ammonia is converted to nitrogen (N2) and steam (H2O). Each gas is passed over a sensing electrode in a mixed potential sensor system that is sensitive to NOx. The difference in the readings of the two gas sensors can provide a measurement of total NH3 concentration in the exhaust gas. The catalyst system also functions to oxidize any unburned hydrocarbons such as CH4, CO, etc., in the gas, and to remove partial contaminants such as SO2.
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The invention claimed is: 1. A method of detecting the concentration of ammonia in a gas comprising the steps of: receiving a source stream of gas; splitting the source stream of gas into first and second streams of gas; absorbing SO2 from at least one of said first and second streams of gas; expos
The invention claimed is: 1. A method of detecting the concentration of ammonia in a gas comprising the steps of: receiving a source stream of gas; splitting the source stream of gas into first and second streams of gas; absorbing SO2 from at least one of said first and second streams of gas; exposing one of said first and second streams of gas to a first catalyst system under conditions capable of converting NH3 present in the gas to N2; exposing the remaining one of said first and second streams of gas to a second catalyst system under conditions capable of converting NH3 present in the gas to NO; exposing each of said first and second streams of gas through a third catalyst system to establish a steady state equilibrium concentration ratio between NO and NO2; detecting the levels of NOx present in said first and second streams of gas; and calculating the difference in NOx concentrations between said first and second streams of gas. 2. The method of claim 1, wherein the first catalyst system comprises a low temperature catalyst selected from the group consisting of nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 3. The method of claim 1, wherein the second catalyst system comprises a high temperature catalyst selected from the group consisting of: nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 4. The method of claim 1, wherein the third catalyst system includes a catalyst selected from the group consisting of: RuO2, CuO, Ag, and Pt. 5. The method of claim 1, wherein the step of detecting the levels of NOx present in said first and second of gas is accomplished with mixed-potential-based sensing elements selective to NOx. 6. The method of claim 5, wherein the mixed-potential-based sensing elements comprise sensing electrodes deposited on oxygen-ion-conducting electrolytes and wherein a potential is measured between the sensing electrode and a reference electrode corresponding to a function of the NOx concentration in the gas. 7. The method of claim 5, wherein the mixed-potential-based sensing elements comprise NOx mixed-potential electrodes with WO3 as the NOx sensing electrode. 8. The method of claim 7, wherein the mixed-potential-based sensing elements comprise electrodes that contain from about 5 to about 40 vol % electrolyte. 9. The method of claim 1, wherein the step of detecting the levels of NOx present in said first and second streams of gas is accomplished with a sensing element comprising semiconductor metal oxide coatings, wherein adsorption of NOx on the sensing element results in a change in a physical parameter of the sensing element such as resistance or capacitance, that is measurable and may be correlated with NOx concentration in said first and second streams of gas. 10. A sensor for measuring total ammonia (NH3) concentration in a source stream of gas, comprising: a SO2-absorbing stage; first and second flow paths for dividing the source stream of gas into first and second streams of gas; a first catalyst system exposed to the first flow path for converting NH3 present in first stream of gas to N2; a second catalyst system exposed to the second flow path for converting NH3 present in the second stream of gas to NO; and a sensor element for detecting the levels of NOx present in the first and second streams of gas. 11. The sensor of claim 10, wherein the first catalyst system comprises a catalyst selected from the group consisting of nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 12. The sensor of claim 10, wherein the second catalyst system comprises a catalyst selected from the group consisting of: nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 13. The sensor of claim 10, wherein the sensor element comprises an amperometric sensor of a mixed-potential-based sensing element selective to NOx. 14. The sensor of claim 13, wherein the mixed-potential-based sensing elements comprise sensing electrodes deposited on oxygen-ion-conducting electrolytes and a potential is measured between the sensing electrode and a reference electrode corresponding to a function of the NOx concentration in the gas. 15. The sensor of claim 10, wherein at least one of the sensing elements comprise semiconductor metal oxide coatings, wherein adsorption of NOx on the sensing element results in a change in a physical parameter of the sensing element such as resistance or capacitance, that is measurable and may be correlated with NOx concentration in said first and second streams of gas. 16. The sensor of claim 10, wherein the SO2-absorbing stage comprises CaO, MgO, or a perovskite. 17. The sensor of claim 10, further comprising an equilibrating stage include RuO2, CuO, Ag, or mixtures thereof. 18. A method of detecting the concentration of ammonia in a gas comprising the steps of: receiving a source stream of gas; splitting the source stream of gas into first and second streams of gas; absorbing SO2 from at least one of said first and second streams of gas; exposing one of said and first and second streams of gas to a first catalyst system under conditions capable of converting NH3 present in the gas to N2; exposing the remaining one of said first and second streams of gas to a second catalyst system under conditions capable of converting NH3 present in the gas to NO; exposing said first and second streams of gas through a third catalyst comprising a catalyst selected from the group consisting of: RuO2, CuO, Ag, and Pt; detecting the levels of NOx present in said first and second streams of gas; and calculating the difference in NOx concentrations between said first and second streams of gas. 19. The method of claim 18, wherein the first catalyst system comprises a low temperature catalyst selected from the group consisting of nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 20. The method of claim 18, wherein the second catalyst system comprises a high temperature catalyst selected from the group consisting of: nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 21. The method of claim 18, further comprising establishing a steady state equilibrium concentration ratio between NO and NO2. 22. The method of claim 18, wherein the step of detecting the levels of NOx present in said first and second of gas is accomplished with mixed-potential-based sensing elements selective to NOx. 23. The method of claim 22, wherein the mixed-potential-based sensing elements comprise sensing electrodes deposited on oxygen-ion-conducting electrolytes and wherein a potential is measured between the sensing electrode and a reference electrode corresponding to a function of the NOx concentration in the gas. 24. The method of claim 22, wherein the mixed-potential-based sensing elements comprise NOx mixed-potential electrodes with WO3 as the NOx sensing electrode. 25. The method of claim 18, wherein the step of detecting the levels of NOx present in said first and second streams of gas is accomplished with a sensing element comprising semiconductor metal oxide coatings, wherein adsorption of NOx on the sensing element results in a change in a physical parameter of the sensing element such as resistance or capacitance, that is measurable and may be correlated with NOx concentration in said first and second streams of gas. 26. The method of claim 24, wherein the mixed-potential-based sensing elements comprise electrodes that contain from about 5 to about 40 vol % electrolyte. 27. A method of detecting the concentration of ammonia in a gas comprising the steps of: receiving a source stream of gas; absorbing SO2 from the source stream of gas; splitting the source stream of gas into first and second streams of gas; exposing one of said first and second streams of gas to a first catalyst system under conditions capable of converting NH3 present in the gas to N2; exposing the remaining one of said first and second streams of gas to a second catalyst system under conditions capable of converting NH3 present in the gas to NO; detecting the levels of NOx present in said first and second streams of gas; and calculating the difference in NOx concentrations between said first and second streams of gas. 28. The method of claim 27, wherein the first catalyst system comprises a low temperature catalyst selected from the group consisting of nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 29. The method of claim 27, wherein the second catalyst system comprises a high temperature catalyst selected from the group consisting of: nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 30. The method of claim 27, further comprising the step of exposing said first and second streams of gas through a third catalyst system to establish a steady state equilibrium concentration ratio between NO and NO2. 31. The method of claim 27, wherein the third catalyst system includes a catalyst selected from the group consisting of: RuO2, CuO, Ag, and Pt. 32. The method of claim 27, wherein the step of detecting the levels of NOx present in said first and second of gas is accomplished with mixed-potential-based sensing elements selective to NOx. 33. The method of claim 32, wherein the mixed-potential-based sensing elements comprise sensing electrodes deposited on oxygen-ion-conducting electrolytes and wherein a potential is measured between the sensing electrode and a reference electrode corresponding to a function of the NOx concentration in the gas. 34. The method of claim 32, wherein the mixed-potential-based sensing elements comprise NOx mixed-potential electrodes with WO3 as the NOx sensing electrode. 35. The method of claim 34, wherein the mixed-potential-based sensing elements comprise electrodes that contain from about 5 to about 40 vol % electrolyte. 36. The method of claim 27, wherein the step of detecting the levels of NOx present in said first and second streams of gas is accomplished with a sensing element comprising semiconductor metal oxide coatings, wherein adsorption of NOx on the sensing element results in a change in a physical parameter of the sensing element such as resistance or capacitance, that is measurable and may be correlated with NOx concentration in said first and second streams of gas. 37. A sensor for measuring total ammonia (NH3) concentration in a source stream of gas comprising: first and second flow paths for dividing the source stream of gas into first and second streams of gas; a first catalyst system exposed to the first flow path for converting NH3 present in the first stream of gas to N2; a second catalyst system exposed to the second flow path for converting NH3 present in the second stream of gas to NO; a sensor element for detecting the levels of NOx present in the first and second streams of gas; a SO2-absorbing stage; and an equilibrating stage including RuO2, CuO, Ag, or mixtures thereof. 38. The sensor of claim 37, wherein the first catalyst system comprises a catalyst selected from the group consisting of nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 39. The sensor of claim 37, wherein the second catalyst system comprises a catalyst selected from the group consisting of: nickel aluminate (NiAl2O4), vanadium pentoxide (V2O5), Molybdenum Oxide (MoO3), tungsten oxide (WO3), iron oxide (FeO, Fe2O3, Fe3O4), cerium oxide (CeO2), copper oxide (CuO), manganese oxide (MnO2), ruthenium oxide (RuO2), silver (Ag), platinum (Pt) and copper (Cu), and any mixture or composites thereof. 40. The sensor of claim 37, wherein the sensor element comprises an amperometric sensor or a mixed-potential-based sensing element selective to NOx. 41. The sensor of claim 40, wherein the mixed-potential-based sensing elements comprise sensing electrodes deposited on oxygen-ion-conducting electrolytes and a potential is measured between the sensing electrode and a reference electrode corresponding to a function of the NOx concentration in the gas. 42. The sensor of claim 37, wherein at least one of the sensing elements comprise semiconductor metal oxide coatings, wherein adsorption of NOx on the sensing element results in a change in a physical parameter of the sensing element such as resistance or capacitance, that is measurable and may be correlated with NOx concentration in said first and second streams of gas. 43. The sensor of claim 37, wherein the SO2-absorbing stage comprises CaO, MgO, or a perovskite.
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