A gas sensor for ammonia nitrogen gas detection and a preparation method thereof

Abstract

The application provides a gas sensor for ammonia nitrogen gas detection and a preparation method thereof. The gas sensor for ammonia nitrogen gas detection comprises a gas sensitive reaction layer and a porous catalytic conversion layer outward from a substrate. The gas sensitive reaction layer comprises a reference electrode and a sensitive electrode which are symmetrically arranged on the upper surface of the substrate. The porous catalytic conversion layer comprises a porous catalytic film arranged above the gas sensitive reaction layer. A test electrode is further arranged between the sensitive electrode and the substrate. The gas sensor for ammonia nitrogen gas detection can catalyze the reaction of ammonia gas and nitrogen oxide, and simultaneously detect NH3 and NOx by using a single element. x All of the responses are used for detecting the composition and concentration of the residual gas, so as to realize the purpose of regulating the ammonia nitrogen gas content.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor manufacturing technology, specifically relating to a gas sensor for ammonia nitrogen gas detection and its preparation method. Background Technology

[0002] Given the current severe environmental protection situation and increasingly stringent requirements for engine exhaust emissions, the development of suitable gas sensors is urgently needed. SCR technology, as a common method for engine exhaust aftertreatment, uses a urea solution as a reducing agent. The urea solution undergoes hydrolysis upon preheating in the exhaust pipe, producing ammonia and water. The NH3 generated from the urea solution then reacts with NO. x The process reduces NO to harmless nitrogen and water, thus removing NO. x The purpose is to regulate engine combustion, control the injection quantity of urea solution, monitor the operating status of the SCR, and prevent excessive ammonia emissions due to excessive injection of urea solution. Therefore, NO2 needs to be monitored at the outlet of the SCR catalyst. x The concentration of NH3 is precisely controlled to regulate the injection volume of the urea solution. This demonstrates the effectiveness of efficient, environmentally friendly, and controllable exhaust gas aftertreatment methods and high-performance vehicle-mounted NOx systems. x NH3 sensors are an indispensable key technology for constructing engine exhaust aftertreatment systems.

[0003] Currently, internationally mature NH3 and NO x Hybridized sensors are primarily potential-type sensors based on zirconium oxide (ZrO2). Among them, potential-type NO... x Sensors can be mainly classified into the following types based on their electrochemical reaction mechanisms: equilibrium potential type, current type, and mixed potential type.

[0004] The equilibrium potential type uses sodium ion conductors and noble metal electrodes. Its reaction mechanism is due to the reaction of sodium ions with nitrogen oxides, thereby changing the chemical potential. The advantage of the equilibrium potential type is high testing accuracy, but the disadvantage is that the melting point of sodium ion conductors is around 500℃, making it unsuitable for engine exhaust conditions. Current-type nitrogen oxide sensors rely on two oxygen pumps for detection. This sensor has good response, but its manufacturing process is complex. The mixed potential type nitrogen oxide sensor uses a metal oxide as the sensitive electrode, ZrO2 as the oxygen ion conductor, and a noble metal electrode as the reference electrode. Nitrogen oxides undergo a catalytic reaction at the sensitive electrode, affecting oxygen ion transport and forming a response potential. This type of sensor combines the advantages of metal oxide semiconductors and traditional potential type sensors, featuring simple manufacturing and high sensitivity. Summary of the Invention

[0005] The purpose of this invention is to provide a gas sensor for ammonia nitrogen gas detection and its preparation method. In the gas sensor for ammonia nitrogen gas detection, a porous catalytic membrane catalyzes the reaction between ammonia and nitrogen oxides, and a unit-based design achieves simultaneous detection of NH3 and NO. x Both sensors respond to detect the composition and concentration of residual gas, thereby controlling the ammonia nitrogen gas content. The gas sensor for ammonia nitrogen gas detection described in this invention can be well applied to the treatment and detection of engine exhaust gases.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a gas sensor for detecting ammonia nitrogen gas, wherein the gas sensor includes a gas-sensitive reaction layer and a porous catalytic conversion layer from the substrate outwards;

[0008] The gas-sensitive reaction layer includes a reference electrode and a sensitive electrode that are disposed separately and symmetrically at both ends of the upper surface of the substrate;

[0009] The porous catalytic conversion layer includes a porous catalytic membrane disposed above the gas-sensitive reaction layer;

[0010] A test electrode is also provided between the sensitive electrode and the substrate.

[0011] The porous catalytic conversion layer in the gas sensor for ammonia nitrogen gas detection described in this invention can convert NH3 and NO... x The gases undergo destructive reactions. The gas-sensitive reaction layer has a reference electrode and a sensitive electrode, which can detect the remaining NH3 or NO after catalysis in the porous catalytic conversion layer. x The remaining gas enters the gas-sensitive reaction layer through a designed porous structure. The composition and content of the remaining gas are determined by the response results, thereby adjusting the required urea injection rate.

[0012] Preferably, the substrate is made of any one of zirconium oxide, aluminum oxide, or silicon oxide, with zirconium oxide being the most preferred.

[0013] Preferably, the porous catalytic membrane has at least two pores, such as two, ten, thirty, fifty, seventy or one hundred, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] The porous catalytic membrane of the present invention covers the reference electrode and the sensitive electrode, and the surface area of ​​the porous catalytic membrane is not greater than the surface area of ​​the substrate.

[0015] The porous catalytic membrane of the present invention has at least two pores, and the porous catalytic membrane can react NH3 and NO. xThe gases undergo an extinct reaction, and the purpose of the pores is to simultaneously react NH3 and NO. x The response simultaneously achieves catalytic and gas-sensitive reactions, ensuring redundancy.

[0016] Preferably, the reference electrode is made of Pt or Au.

[0017] Preferably, the material of the test electrode includes any one of Pt, Ag, Au or Pd.

[0018] In a second aspect, the present invention provides a method for preparing a gas sensor for ammonia nitrogen gas detection as described in the first aspect, the method comprising the following steps:

[0019] (1) The reference electrode paste and the test electrode paste are printed on the substrate by screen printing, and then dried and baked to obtain the reference electrode and the test electrode.

[0020] (2) Mix the sensitive electrode material with the printing paste to obtain the sensitive electrode printing paste, and then print it on the test electrode obtained in step (1) by screen printing. Then dry and bake to obtain the sensitive electrode.

[0021] (3) The catalyst slurry is printed on the sensitive electrode and the reference electrode according to the design drawing by screen printing, and then dried and baked to obtain a sensor blank with a catalyst film.

[0022] (4) The sensor blank described in step (3) is sintered and cooled sequentially to obtain the gas sensor for ammonia nitrogen gas detection.

[0023] This invention uses screen printing to prepare the reference electrode, test electrode, sensitive electrode and catalytic membrane respectively. Screen printing technology has the advantages of strong adhesion, adjustable size and easy photosensitive reaction.

[0024] Preferably, the drying temperature in step (1) is 60 to 100°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the drying time in step (1) is 20 to 40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes or 40 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the drying temperature in step (2) is 60 to 100°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the drying time in step (2) is 20 to 40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes or 40 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the mass ratio of the sensitive electrode material to the printing paste in step (2) is (2-5):1, for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the sensitive electrode material in step (2) includes any one or a combination of at least two of Cr2WO6 / WO3 nanocomposite oxide powder, MnCr2O4 powder, CoWO4 powder, NiWO4 or ZnWO4 powder.

[0030] Preferably, the W / Cr ratio in the Cr2WO6 / WO3 nanocomposite oxide powder is 1:(0.5-6), for example, it can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1 or 6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the sensitive electrode material further includes a modified material.

[0032] Preferably, the modified material includes any one or a combination of at least two of Pt, Au, or Pd. Typical but non-limiting combinations include combinations of Pt and Au, Pt and Pd, Au and Pd, or Pt, Au, and Pd.

[0033] The sensitive electrode material described in this invention uses tungsten-based and chromium-based multi-component or composite oxides as the sensing material. This type of material can be prepared by various methods and is effective against NH3 and NO. x The gas exhibits good responsiveness, and the raw materials are inexpensive, readily available, and easy to prepare, making it suitable for mass production.

[0034] Preferably, the raw materials for preparing the printing paste in step (2) include, by mass percentage: 28-32 wt% butyl carbitol acetate, for example, 28 wt%, 29 wt%, 30 wt%, 31 wt%, or 32 wt%, but not limited to the listed values; other unlisted values ​​within the range are also applicable; 8-12 wt% dibutyl phthalate, for example, 8 wt%, 9 wt%, 10 wt%, 11 wt%, or 12 wt%, but not limited to the listed values; other unlisted values ​​within the range are also applicable; 5-7 wt% ethyl cellulose, for example, 5 wt%, 6 wt%, or 7 wt%, but not limited to the listed values; other unlisted values ​​within the range are also applicable; and the balance is terpineol.

[0035] Preferably, the preparation method of the printing paste in step (2) is as follows: the raw materials are mixed according to the formula and then dried to obtain the brushing paste.

[0036] Preferably, the drying temperature is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the drying time is 18 to 32 hours, for example, it can be 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours or 32 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the catalyst slurry in step (3) includes any one or a combination of at least two of ZSM-5 molecular sieve slurry, SSZ-13 molecular sieve slurry, or ASPO-34 molecular sieve slurry. Typical but non-limiting combinations include combinations of ZSM-5 molecular sieve slurry and SSZ-13 molecular sieve slurry, combinations of SSZ-13 molecular sieve slurry and ASPO-34 molecular sieve slurry, combinations of ZSM-5 molecular sieve slurry and ASPO-34 molecular sieve slurry, or combinations of ZSM-5 molecular sieve slurry, SSZ-13 molecular sieve slurry, and ASPO-34 molecular sieve slurry.

[0039] The catalyst slurry described in this invention exhibits good temperature activity after being loaded with metal, and has the advantages of a wide operating temperature range, high nitrogen selectivity and good hydrothermal stability, making it very suitable as an SCR catalyst.

[0040] Preferably, the catalyst slurry is doped with rare earth elements.

[0041] Preferably, the rare earth element includes La.

[0042] Preferably, the drying time in step (3) is 20 to 40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes or 40 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the drying temperature in step (3) is 60 to 100°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] Preferably, the sintering temperature in step (4) is 900 to 1100°C, for example, it can be 900°C, 950°C, 1000°C, 1050°C or 1100°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] The sintering temperature described in this invention is 900–1100°C. If the sintering temperature is too high, the plates will sinter, making it impossible to achieve the desired NH3 and NO concentration. x If the reaction is too uniform, poor adhesion will result in peeling and damage during actual use, rendering the product unusable.

[0046] Preferably, the sintering time in step (4) is 1.5 to 2.5 hours, for example, it can be 1.5 hours, 1.7 hours, 1.9 hours, 2.1 hours, 2.3 hours or 2.5 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the endpoint of cooling down in step (4) is when the temperature drops to 23-35°C, for example, it can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C or 35°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] As a preferred embodiment of the present invention, the method for preparing the gas sensor for ammonia nitrogen gas detection provided in the second aspect of the present invention includes the following steps:

[0049] (1) The reference electrode paste and the test electrode paste are printed on the substrate by screen printing, and then dried and baked to obtain the reference electrode and the test electrode.

[0050] (2) Mix the sensitive electrode material and printing paste in a mass ratio of (2-5):1 to obtain the sensitive electrode printing paste, and then print it on the test electrode obtained in step (1) by screen printing. Then dry it at 70-90°C for 18-32 hours to obtain the sensitive electrode.

[0051] The raw materials for preparing the printing paste include, by weight percentage: 28-32 wt% butyl carbitol acetate, 8-12 wt% dibutyl phthalate, 5-7 wt% ethyl cellulose, and the balance being terpineol.

[0052] (3) The catalyst slurry is printed on the sensitive electrode and the reference electrode according to the design drawing by screen printing, and then dried and baked to obtain a sensor blank with a catalyst film.

[0053] (4) After sintering the sensor blank obtained in step (3) at 900-1100℃ for 1.5-2.5h, cool it down to 23-35℃ to obtain the gas sensor for ammonia nitrogen gas detection.

[0054] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) The gas sensor for ammonia nitrogen gas detection provided by the present invention can be used to process engine exhaust gas and can simultaneously detect the content of ammonia and nitrogen oxides.

[0057] (2) The porous catalytic conversion layer in the gas sensor for ammonia nitrogen gas detection provided by the present invention can convert NH3 and NO... x The gases undergo destructive reactions. The gas-sensitive reaction layer has a reference electrode and a sensitive electrode, which can detect the remaining NH3 or NO after catalysis in the porous catalytic conversion layer. x The remaining gas enters the gas-sensitive reaction layer through a designed porous structure. The composition and content of the remaining gas are determined by the response results.

[0058] (3) The molecular sieve used in the porous catalytic conversion layer of the gas sensor for ammonia nitrogen gas detection provided by the present invention exhibits good temperature activity after being loaded with metal, and has the advantages of wide temperature application range, high nitrogen selectivity and good hydrothermal stability, making it very suitable as an SCR catalyst.

[0059] (4) The gas sensor for ammonia nitrogen gas detection provided by the present invention uses tungsten-based and chromium-based multi-component or composite oxides as the sensitive material in the gas-sensitive reaction layer. The sensitive material is sensitive to NH3 and NO. x The gas exhibits good responsiveness, and the raw materials are inexpensive, readily available, and easy to prepare, making it suitable for mass production. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the structure of the gas sensor for ammonia nitrogen gas detection provided in Embodiment 1 of the present invention;

[0061] Figure 2 This is a schematic diagram of the structure of the non-porous catalytic membrane and sensitive electrode material provided in Embodiment 1 of the present invention;

[0062] Figure 3 This is a schematic diagram of the structure of the non-porous catalytic membrane material provided in Embodiment 1 of the present invention.

[0063] In this diagram, 1 is the substrate, 2 is the reference electrode, 3 is the test electrode, 4 is the sensitive electrode, and 5 is the porous catalytic membrane. Detailed Implementation

[0064] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0065] Example 1

[0066] This invention provides a method such as Figure 1 The gas sensor shown is used for ammonia nitrogen gas detection. The gas sensor includes a gas-sensitive reaction layer and a porous catalytic conversion layer from the substrate 1 outwards.

[0067] The gas-sensitive reaction layer includes a reference electrode 2 and a sensitive electrode 4, which are disposed separately and symmetrically at both ends of the upper surface of the substrate 1.

[0068] The porous catalytic conversion layer includes a porous catalytic membrane 5 disposed above the gas-sensitive reaction layer;

[0069] A test electrode 3 is also provided between the sensitive electrode and the substrate.

[0070] The substrate 1 is a zirconium oxide substrate.

[0071] The method for preparing the gas sensor for ammonia nitrogen gas detection includes the following steps:

[0072] (1) The reference electrode paste and the test electrode paste are printed onto the substrate by screen printing, and then dried and baked to obtain the reference electrode and the test electrode, as shown below. Figure 2 As shown;

[0073] (2) The sensitive electrode material and printing paste are mixed at a mass ratio of 4:1 to obtain the sensitive electrode printing paste. This paste is then screen-printed onto the test electrode obtained in step (1), and subsequently dried at 80°C for 24 hours to obtain the sensitive electrode. Figure 3 As shown;

[0074] The raw materials for preparing the printing paste include, by weight percentage: 28 wt% butyl carbitol acetate, 12 wt% dibutyl phthalate, 7 wt% ethyl cellulose, and the balance being terpineol.

[0075] The sensitive electrode material is composed of Cr(NO3)3·9H2O and H... 40 N 10 O 41 W 12 The raw material is xH2O, and it is doped with Cr2WO6 / WO3 nanocomposite oxide powder with a doping ratio of W / Cr = 1:6.

[0076] (3) The catalyst slurry is printed on the sensitive electrode and the reference electrode according to the design drawing by screen printing, and then dried and baked to obtain a sensor blank with a catalyst film.

[0077] (4) After sintering the sensor blank described in step (3) at 1000℃ for 2 hours, cool it down to 25℃ to obtain the following... Figure 1 The gas sensor shown is used for ammonia nitrogen gas detection.

[0078] Example 2

[0079] This embodiment provides a gas sensor for detecting ammonia nitrogen gas, which is the same as that in Embodiment 1.

[0080] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that the doping ratio of W / Cr in the sensitive electrode material described in step (2) is changed to 1:2.

[0081] Example 3

[0082] This embodiment provides a gas sensor for detecting ammonia nitrogen gas, which is the same as that in Embodiment 1.

[0083] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that the doping ratio of W / Cr in the sensitive electrode material described in step (2) is changed to 3:2.

[0084] Example 4

[0085] This embodiment provides a gas sensor for detecting ammonia nitrogen gas, which is the same as that in Embodiment 1.

[0086] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that the sensitive electrode material in step (2) is changed to MnCr2O4 powder in this example.

[0087] Furthermore, the raw materials for preparing the printing paste in step (2) are changed by mass percentage to include: 32wt% butyl carbitol acetate, 8wt% dibutyl phthalate, 5wt% ethyl cellulose, and the balance being terpineol.

[0088] Example 5

[0089] This embodiment provides a gas sensor for detecting ammonia nitrogen gas, which is the same as that in Embodiment 1.

[0090] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that the sensitive electrode material in step (2) is changed to CoWO4, NiWO4 and ZnWO4 powder.

[0091] Furthermore, the raw materials for preparing the printing paste in step (2) are changed by mass percentage to include: 30 wt% butyl carbitol acetate, 10 wt% dibutyl phthalate, 6 wt% ethyl cellulose, and the balance being terpineol.

[0092] Example 6

[0093] This embodiment provides a gas sensor for detecting ammonia nitrogen gas, which is the same as that in Embodiment 1.

[0094] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that the sintering temperature in step (4) is changed to 900°C in this example.

[0095] Example 7

[0096] This embodiment provides a gas sensor for detecting ammonia nitrogen gas, which is the same as that in Embodiment 1.

[0097] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that the sintering temperature in step (4) is changed to 1100℃ in this example.

[0098] Example 8

[0099] This embodiment provides a gas sensor for detecting ammonia nitrogen gas, which is the same as that in Embodiment 1.

[0100] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that the sintering temperature in step (4) is changed to 850°C in this example.

[0101] Example 9

[0102] This embodiment provides a gas sensor for detecting ammonia nitrogen gas, which is the same as that in Embodiment 1.

[0103] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that the sintering temperature in step (4) is changed to 1150℃ in this example.

[0104] Comparative Example 1

[0105] This comparative example provides a gas sensor for ammonia nitrogen gas detection. The only difference between this gas sensor and Example 1 is that the porous catalytic conversion layer is omitted in this comparative example.

[0106] The method for preparing the gas sensor for ammonia nitrogen gas detection differs from that in Example 1 only in that step (3) is omitted in this comparative example.

[0107] The gas sensors for ammonia nitrogen gas detection provided in Examples 1-7 of this invention can simultaneously detect NH3 and NO. x Both have a response and can be used to detect the composition and concentration of residual gas.

[0108] Compared to Example 1, the gas sensor for ammonia nitrogen detection provided in Example 8 has a lower sintering temperature, making it prone to peeling or damage of the electrodes and / or catalyst membrane during subsequent use, thus rendering it ineffective. The gas sensor for ammonia nitrogen detection provided in Example 9 has an excessively high sintering temperature, resulting in the formation of sintered blocks during sintering, which prevents it from detecting NH3 and NO. x The reaction is not uniform, therefore it is impossible to simultaneously react NH3 and NO. x Both responded.

[0109] Compared to Example 1, the gas sensor for ammonia nitrogen detection provided in Comparative Example 1 cannot detect NH3 and NO. x Catalytic reaction.

[0110] In summary, the porous catalytic membrane in the gas sensor for ammonia nitrogen detection provided by this invention catalyzes the reaction between ammonia and nitrogen oxides, and the use of a single-unit design achieves simultaneous detection of NH3 and NO. xBoth sensors respond to detect the composition and concentration of residual gas, thereby controlling the ammonia nitrogen gas content. The gas sensor for ammonia nitrogen gas detection described in this invention can be well applied to the treatment and detection of engine exhaust gases.

[0111] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a gas sensor for detecting ammonia nitrogen gas, characterized in that, The gas sensor includes a gas-sensitive reaction layer and a porous catalytic conversion layer from the substrate outwards. The gas-sensitive reaction layer includes a reference electrode and a sensitive electrode that are disposed separately and symmetrically at both ends of the upper surface of the substrate; The porous catalytic conversion layer includes a porous catalytic membrane disposed above the gas-sensitive reaction layer; A test electrode is also disposed between the sensitive electrode and the substrate; The preparation method includes the following steps: (1) The reference electrode paste and the test electrode paste are printed on the substrate by screen printing, and then dried and baked to obtain the reference electrode and the test electrode. (2) Mix the sensitive electrode material with the printing paste to obtain the sensitive electrode printing paste, and then print it on the test electrode obtained in step (1) by screen printing. Then dry and bake to obtain the sensitive electrode. The sensitive electrode material includes any one or a combination of at least two of Cr2WO6 / WO3 nanocomposite oxide powder, MnCr2O4 powder, CoWO4 powder, NiWO4 or ZnWO4 powder; the W / Cr ratio in the Cr2WO6 / WO3 nanocomposite oxide powder is 1:(0.5~6); (3) The catalyst slurry is printed on the sensitive electrode and the reference electrode according to the design drawing by screen printing, and then dried and baked to obtain a sensor blank with a catalyst film; the catalyst slurry is doped with rare earth elements; (4) The sensor blank described in step (3) is sintered and cooled sequentially to obtain the gas sensor for ammonia nitrogen gas detection; The sintering temperature is 900~1100℃.

2. The preparation method according to claim 1, characterized in that, The substrate is made of any one of zirconium oxide, aluminum oxide, or silicon oxide.

3. The preparation method according to claim 2, characterized in that, The substrate is made of zirconium oxide.

4. The preparation method according to claim 1, characterized in that, The porous catalytic membrane has at least two pores.

5. The preparation method according to claim 1, characterized in that, The reference electrode is made of Pt or Au.

6. The preparation method according to claim 1, characterized in that, The test electrode is made of any one of Pt, Ag, Au, or Pd.

7. The preparation method according to claim 1, characterized in that, The drying temperature in step (1) is 60~100℃.

8. The preparation method according to claim 1, characterized in that, The drying time in step (1) is 20~40 min.

9. The preparation method according to claim 1, characterized in that, The drying temperature in step (2) is 60~100℃.

10. The preparation method according to claim 1, characterized in that, The drying time in step (2) is 20~40 min.

11. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the sensitive electrode material to the printing paste is (2~5):

1.

12. The preparation method according to claim 1, characterized in that, The sensitive electrode material also includes modified materials.

13. The preparation method according to claim 12, characterized in that, The modified material includes any one or a combination of at least two of Pt, Au, or Pd.

14. The preparation method according to claim 1, characterized in that, The raw materials for preparing the printing paste in step (2) include, by mass percentage: 28-32 wt% butyl carbitol acetate, 8-12 wt% dibutyl phthalate, 5-7 wt% ethyl cellulose, and the balance being terpineol.

15. The preparation method according to claim 14, characterized in that, The preparation method of the printing paste in step (2) is as follows: the raw materials are mixed according to the formula and then dried to obtain the printing paste.

16. The preparation method according to claim 15, characterized in that, The drying temperature is 70~90℃.

17. The preparation method according to claim 15, characterized in that, The drying time is 18-32 hours.

18. The preparation method according to claim 1, characterized in that, The catalyst slurry in step (3) includes any one or a combination of at least two of ZSM-5 molecular sieve slurry, SSZ-13 molecular sieve slurry or ASPO-34 molecular sieve slurry.

19. The preparation method according to claim 1, characterized in that, The rare earth element includes La.

20. The preparation method according to claim 1, characterized in that, The drying time in step (3) is 20~40 min.

21. The preparation method according to claim 1, characterized in that, The drying temperature in step (3) is 60~100℃.

22. The preparation method according to claim 1, characterized in that, The sintering time in step (4) is 1.5~2.5h.

23. The preparation method according to claim 1, characterized in that, The endpoint of cooling down in step (4) is when the temperature drops to 23~35℃.

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