NOx sensor
First Claim
1. A NOx sensor comprising:
- a gas detection chamber composed of an internal space formed by a first zirconia solid electrolyte substrate having oxygen ion conductivity, an opposed second zirconia solid electrolyte having oxygen ion conductivity, and a spacer separating said zirconia solid electrolyte substrates;
a NOx sensing cell including a NOx sensing electrode fixed onto one side of said first zirconia solid electrolyte substrate in said gas detection chamber, said NOx sensing electrode being active to NOx and oxygen, and a reference electrode fixed onto the other side of said first zirconia solid electrolyte substrate, said reference electrode being active to at least oxygen;
a NOx conversion pumping cell including a NOx conversion electrode fixed onto said second zirconia solid electrolyte substrate in said gas detection chamber, said NOx conversion electrode being active to NOx and oxygen, and a counter electrode to be paired with said NOx conversion electrode, said counter electrode being fixed onto said second zirconia solid electrolyte substrate, being active to oxygen;
voltage applying means for applying a predetermined voltage to said NOx conversion pumping cell;
a first gas treatment chamber disposed between said gas detection chamber gas inlet leading to an atmosphere of a gas to be detected;
an inorganic porous member with a porosity of 5-40% by volume being loaded into only said first gas treatment chamber; and
means for measuring a potential difference between said NOx sensing electrode and said reference electrode while converting NOx in the gas to be detected into single component after a reducing gas in the gas to be detected is oxidized in said first gas treatment chamber, and thereby detecting a total NOx concentration in the gas to be detected.
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Abstract
The present invention discloses a NOx sensor for accurately detecting the total concentration of nitrogen oxides in a measured gas without being affected by interference gases. The sensor comprises a gas treatment chamber 5 arranged at the prior stage of the gas detection chamber 3, an inorganic porous member 25 loaded in the gas treatment chamber, and a NOx conversion pumping cell 14, 15 and/or an oxygen supplying pumping cell which supplies oxygen into the gas treatment chamber. When the measured gas is introduced in the gas treatment chamber, the interference gases contained in the measured gas are effectively oxidized by the supplied oxygen under the assistance of the catalytic activity of inorganic porous member. The total amount of the nitrogen oxides is measured in the gas detection chamber while NOx in the measured gas are converted into a single component (NO2 or NO) by the NOx conversion pumping cell after the interference gases are oxidized.
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Citations
25 Claims
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1. A NOx sensor comprising:
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a gas detection chamber composed of an internal space formed by a first zirconia solid electrolyte substrate having oxygen ion conductivity, an opposed second zirconia solid electrolyte having oxygen ion conductivity, and a spacer separating said zirconia solid electrolyte substrates;
a NOx sensing cell including a NOx sensing electrode fixed onto one side of said first zirconia solid electrolyte substrate in said gas detection chamber, said NOx sensing electrode being active to NOx and oxygen, and a reference electrode fixed onto the other side of said first zirconia solid electrolyte substrate, said reference electrode being active to at least oxygen;
a NOx conversion pumping cell including a NOx conversion electrode fixed onto said second zirconia solid electrolyte substrate in said gas detection chamber, said NOx conversion electrode being active to NOx and oxygen, and a counter electrode to be paired with said NOx conversion electrode, said counter electrode being fixed onto said second zirconia solid electrolyte substrate, being active to oxygen;
voltage applying means for applying a predetermined voltage to said NOx conversion pumping cell;
a first gas treatment chamber disposed between said gas detection chamber gas inlet leading to an atmosphere of a gas to be detected;
an inorganic porous member with a porosity of 5-40% by volume being loaded into only said first gas treatment chamber; and
means for measuring a potential difference between said NOx sensing electrode and said reference electrode while converting NOx in the gas to be detected into single component after a reducing gas in the gas to be detected is oxidized in said first gas treatment chamber, and thereby detecting a total NOx concentration in the gas to be detected. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
an oxidation catalyst pumping cell including an oxidation catalyst electrode composed of said inorganic porous member loaded into said first gas treatment chamber, said oxidation catalyst electrode comprising an oxygen-ion conductive solid electrolyte and serving as an anode electrode, and a cathode electrode to be paired with said oxidation catalyst electrode, said cathode electrode being arranged on a zirconia solid electrolyte substrate outside said gas detection chamber and being active to oxygen; and
voltage applying means for applying a predetermined voltage to said oxidation catalyst pumping cell.
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14. The NOx sensor according to claim 13, wherein said oxidation catalyst electrode comprises mainly an oxygen-ion-conductive solid electrolyte and a precious metal selected from the group consisting of Pt, Pd, Ir, Au, Rh, a mixture thereof, and an alloy thereof.
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15. The NOx sensor according to claim 14, wherein said oxygen-ion-conductive solid electrolyte to be added to said oxidation catalyst electrode falls within the range of 20 and 50% by volume with respect to the volume of said oxidation catalyst electrode.
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16. The NOx sensor according to claim 13, wherein said oxidation catalyst electrode comprises chiefly an oxygen-ion-conductive solid electrolyte and a metal oxide active to said reducing gas.
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17. The NOx sensor according to claim 13, wherein at least one gas inlet is formed in the top or bottom of said first gas treatment chamber.
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18. The NOx sensor according to claim 1, wherein said reference electrode of said NOx sensing cell is installed in said gas detection chamber.
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19. The NOx sensor according to claim 1, comprising:
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said reference electrode of said NOx sensing cell being installed across said first zirconia solid electrolyte substrate constituting said gas detection chamber, in a duct leading only to the air outside of said gas detection chamber;
an oxygen sensing electrode arranged in said detection chamber, said oxygen sensing electrode being active to oxygen alone; and
means for detecting the total NOx concentration while correcting the same for a potential difference between said reference electrode and said NOx sensing electrode and a potential difference between said reference electrode and said oxygen sensing electrode.
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20. The NOx sensor according to claim 1, wherein said gas inlet arranged in said first gas treatment chamber is covered with a porous protective film.
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21. A NOx sensor comprising:
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a gas detection chamber composed of an internal space formed by a first zirconia solid electrolyte substrate having oxygen ion conductivity, an opposed second zirconia solid electrolyte having oxygen ion conductivity, and a spacer separating said zirconia solid electrolyte substrates;
a NOx detection cell including a NOx sensing electrode fixed onto one side of said first zirconia solid electrolyte substrate in said gas detection chamber, said NOx sensing electrode being active to NOX and oxygen, and a reference electrode fixed onto the other side of said first zirconia solid electrolyte substrate, said reference electrode being active to at least oxygen;
a NOx conversion pumping cell including a NOx conversion electrode fixed onto said second zirconia solid electrolyte substrate in said gas detection chamber, said NOx conversion electrode being active to NOx and oxygen, and a counter electrode to be paired with said NOx conversion electrode, said counter electrode being fixed onto said second zirconia solid electrolyte substrate, being active to oxygen;
voltage applying means for applying a predetermined voltage to said NOx conversion pumping cell;
a first gas treatment chamber communicating with said gas detect ion chamber and having a gas inlet leading to an atmosphere of a gas to be detected;
an oxidation catalyst pumping cell including an oxidation catalyst electrode arranged in said first gas treatment chamber, said oxidation catalyst electrode having a gas channel, being active to a reducing gas and oxygen, and serving as an anode electrode, and a cathode electrode to be paired with said oxidation catalyst electrode, said cathode electrode being arranged on a zirconia solid electrolyte substrate outside said gas detection chamber and being active to oxygen;
voltage applying means for applying a predetermined voltage to said oxidation catalyst pumping cell; and
means for measuring a potential difference between said NOx sensing electrode and said reference electrode NOx when NOx in the gas to be detected is converted into NO2 or NO by said NOx conversion pumping cell after the reducing gas in the gas to be detected is oxidized in said first gas treatment chamber, and thereby detecting the total NOx concentration in the gas to be detected. - View Dependent Claims (22, 23)
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24. A NOx sensor comprising:
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a gas detection chamber composed of an internal space formed by a first zirconia solid electrolyte substrate having oxygen ion conductivity, an opposed second zirconia solid electrolyte having oxygen ion conductivity, and a spacer separating said zirconia solid electrolyte substrates;
a NOx sensing cell including a NOx sensing electrode fixed onto one side of said first zirconia solid electrolyte in said gas detection chamber, said NOx sensing electrode being active to NOx and oxygen, and a reference electrode fixed onto the same side of said first zirconia solid electrolyte substrate, said reference electrode being active to oxygen and inactive to NOx;
a NOx conversion pumping cell including a NOx conversion electrode fixed onto said second zirconia solid electrolyte substrate in said gas detection chamber, said NOx conversion electrode being active to NOx and oxygen, and a counter electrode to be paired with said NOx conversion electrode, said counter electrode being fixed onto said second zirconia solid electrolyte substrate, being active to oxygen;
voltage applying means for applying a predetermined voltage to said NOx conversion pumping cell;
a first gas treatment chamber disposed between said gas detection chamber and a gas inlet leading to an atmosphere of a gas to be detected;
an inorganic porous member with a porosity of 5-40% by volume being loaded into only said first gas treatment chamber; and
means for measuring a potential difference between said NOx sensing electrode and said reference electrode while converting NOx in the gas to be detected into single component after a reducing gas in the gas to be detected is oxidized in said first gas treatment chamber, and thereby detecting a total NOx concentration in the gas to be detected.
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25. A NOx sensor comprising:
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a gas detection chamber composed of an internal space formed by a first zirconia solid electrolyte substrate having oxygen ion conductivity, an opposed second zirconia solid electrolyte having oxygen ion conductivity, and a spacer separating said zirconia solid electrolyte substrates;
a NOx detection cell including a NOx sensing electrode fixed onto one side of said first zirconia solid electrolyte substrate in said gas detection chamber, said NOx sensing electrode being active to NOx and oxygen, and a reference electrode fixed onto the same side of said first zirconia solid electrolyte substrate, said reference electrode being active oxygen and inactive to NOx;
a NOx conversion pumping cell including a NOx conversion electrode fixed onto said second zirconia solid electrolyte substrate in said gas detection chamber, said NOx conversion electrode being active to NOx and oxygen, and a counter electrode to be paired with said NOx conversion electrode, said counter electrode being fixed onto said second zirconia solid electrolyte substrate, being active to oxygen;
voltage applying means for applying a predetermined voltage to said NOx conversion pumping cell;
a first gas treatment chamber communicating with said gas detection chamber and having a gas inlet leading to an atmosphere of a gas to be detected;
an oxidation catalyst pumping cell including an oxidation catalyst electrode arranged in said first gas treatment chamber, said oxidation catalyst electrode having a gas channel, being active to a reducing gas and oxygen, and serving as an anode electrode, and a cathode electrode to be paired with said oxidation catalyst electrode, said cathode electrode being arranged on a zirconia solid electrolyte substrate outside said gas detection chamber and being active to oxygen;
voltage applying means for applying a predetermined voltage to said oxidation catalyst pumping cell; and
means for measuring a potential difference between said NOx sensing electrode and said reference electrode while converting NOx in the gas to be detected into NO2 or NO by said NOx conversion pumping cell after the reducing gas in the gas to be detected is oxidized in said first gas treatment chamber, and thereby detecting the total NOx concentration in the gas to be detected.
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Specification