Catalytic filtering membrane for methane sensor, preparation method of catalytic filtering membrane and methane sensor

Abstract

The invention relates to a catalytic filter membrane for a methane sensor, the catalytic filter membrane is prepared by high-temperature sintering of slurry formed by wet grinding and mixing, and the slurry comprises a nano platinum catalyst, a catalyst carrier, a dispersant and a binder, the catalyst carrier is one or more of aluminum oxide, gallium oxide, titanium oxide, cerium oxide and zirconium oxide, and the dispersing agent is one or more of glycerol, triethanolamine, a polyacrylic acid aqueous solution and ethanol. The binder is one or more of epoxy resin glue, polyurethane glue, nano silica sol, low-melting-point glass powder, a sodium silicate aqueous solution and a potassium silicate aqueous solution. The invention also relates to a corresponding preparation method and a methane sensor. And the interfering gas is subjected to catalytic combustion before reaching the surface of the sensing layer, so that the diffusion and reaction properties of methane molecules are effectively adjusted, the selectivity of the methane sensor is remarkably improved, the packaging volume is reduced, and the packaging cost is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of compound detection technology, and in particular to a catalytic filter membrane for a methane sensor, a method for preparing the same, and a methane sensor. Background Technology

[0002] Methane, a major component of natural gas, is widely used in homes and industry. With the increasing consumption of natural gas, detecting gas leaks in homes has become a growing problem, necessitating the selection of low-cost, reliable sensing devices for methane detection. The main interfering gases in the home environment are ethanol vapor or other volatile organic compounds, for example, from cleaning agents, cooking, or the storage of food and beverages. Therefore, to prevent false alarms, there is a strong demand for selective gas sensors that have no cross-sensitivity to ethanol.

[0003] Semiconductor gas sensors, also known as MOS gas sensors, typically use n-type oxides (such as SnO2, WO3, or In2O3) as gas-sensitive materials, enabling them to sensitively detect reducing gases such as CH4, H2, and CO, as well as oxidizing gases such as NO2 and O3. Tin dioxide (SnO2) is the most widely used semiconductor metal oxide in gas sensing, capable of detecting combustible gases like methane and toxic gases like carbon monoxide. Compared to other metal oxides, tin dioxide has a lower operating temperature range (200–400°C), thus requiring lower heating power to achieve good performance. However, although tin dioxide-based MOS sensors are widely accepted in the market, their selective response to methane under certain conditions remains unsatisfactory. For example, when SnO2 sensors are used as household methane detectors, they exhibit high cross-sensitivity to volatile organic compounds (VOCs), such as ethyl acetate, acetone, and ethanol.

[0004] For methane detection in kitchens, it is necessary to improve selectivity for methane and avoid false alarms caused by interfering gases such as ethanol and ethyl acetate. Currently, filters have been shown to have a significant moderating effect on gas diffusion and reaction. In methane detection, activated carbon is a classic and effective solution for improving selectivity. For example, a filter composed of carbon particles, using TO series encapsulation, can be installed on the metal cap of the sensor to effectively isolate VOC gases, such as ethanol and other common organic vapors in daily life (Patent Nos.: CN 113376222A, CN 211478138 U). However, activated carbon is a physical filter that prevents the interaction of interfering gases with the sensing material by accumulating them. The main drawback of this type of filter is that it saturates after a period of time, and a saturated filter cannot suppress the cross-sensitivity of interfering gases. As the number of interfering gases increases, the sensor's selectivity may decrease, leading to false alarms. Summary of the Invention

[0005] The main objective of this invention is to address the above-mentioned problems by providing a catalytic filtration membrane for a methane sensor, its preparation method, and a methane sensor.

[0006] To achieve the above objectives, a first aspect of the present invention provides a catalytic filter membrane for a methane sensor, characterized in that the catalytic filter membrane is prepared by wet grinding and mixing of a slurry followed by high-temperature sintering. The slurry comprises a nano-platinum catalyst, a catalyst support, a dispersant, and a binder. The catalyst support is one or more of alumina (Al2O3), gallium oxide (Ga2O3), titanium oxide (TiO2), cerium oxide (CeO2), and zirconium oxide (ZrO2). The dispersant is one or more of glycerol, triethanolamine, an aqueous solution of polyacrylic acid, and ethanol. The binder can be organic or inorganic. The organic binder is one or more of epoxy resin adhesive and polyurethane adhesive, and the inorganic binder can be one or more of nano-silica sol, low-melting-point glass powder, an aqueous solution of sodium silicate, and an aqueous solution of potassium silicate.

[0007] The slurry is produced using a wet grinding process, effectively and uniformly dispersing the Pt catalyst and nano-binder materials within the alumina and other catalyst supports, thus effectively addressing the issue of powder particle agglomeration. Simultaneously, the slurry achieves good Pt dispersibility, resulting in higher catalytic activity. Furthermore, the flexible Pt / Al2O3 process ratio allows for effective optimization of catalytic filtration performance for different substrate structures.

[0008] Preferably, the components of the slurry, by weight percentage, include:

[0009]

[0010] Preferably, the components of the slurry, by weight percentage, include:

[0011]

[0012] The catalyst support is alumina, the dispersant is glycerol, and the binder is nano-silica sol.

[0013] A second aspect of the present invention provides a method for preparing the catalytic filter membrane for a methane sensor, characterized in that the preparation method comprises:

[0014] The nano-platinum catalyst is dispersed in a dispersant to form a Pt-containing dispersion solvent. A catalyst support is added to the Pt-containing dispersion solvent, and the mixture is wet-milled in a ball mill for 1–4 hours to form a dispersion solution. A binder is added to the dispersion solution, and the mixture is wet-milled in a ball mill for 3–7 hours. A magnetic heating and stirring device is used to heat and stir the mixture until the viscosity meets the preset requirements, such as 3000–8000 cP or 5000 cP, with 5000 cP being the optimal viscosity. This ensures that the Pt-catalyzed alumina slurry meets the requirements for dispensing process and film thickness, thus obtaining the slurry.

[0015] Preferably, the preparation method further includes: applying the slurry to the gas-sensitive material area of ​​the sensor using a dispensing process, uniformly dispersing the Pt / Al2O3 catalytic filter coating above the gas-sensitive material Pd-SnO2, and sintering it at 450℃~550℃ for 5~7 hours, for example, sintering it in air at 500℃ for 6 hours to form a catalytic filter membrane with a thickness of 20±2μm.

[0016] A third aspect of the present invention provides a methane sensor, the main feature of which is that the methane sensor includes a gas-sensitive material and the catalytic filter membrane, wherein the catalytic filter membrane is prepared on the gas-sensitive material by dispensing and sintering to achieve a high-efficiency filtration effect for interfering gases.

[0017] Preferably, the catalytic filter membrane is prepared on a semiconductor gas-sensitive heating substrate, such as a MEMS suspended film micro-hot plate, a cantilever beam micro-hot plate, a ceramic heating substrate, or a Pt heating wire. The slurry can be flexibly applied to substrate materials with different heating structures, and within a certain viscosity range, planar dispensing sintering or spherical impregnation sintering processes can be achieved.

[0018] Preferably, the preparation method of the gas-sensitive material is as follows: palladium nanoparticles and nano-conductive carbon powder are added and dissolved in a polyacrylic acid dispersion solution; nano-tin oxide powder is added to the dispersion solution and wet-milled using a ball mill; then silica sol is added to the dispersion solution, and wet-milling is continued; the viscosity of the dispersion solution is adjusted to above 10000 cp by stirring; the gas-sensitive paste is printed onto the window position of the gas-sensitive material using a thick film printing process; and finally, it is sintered in air, preferably at 500°C for 6 hours.

[0019] Preferably, the palladium nanopowder has a mass content of 2%, the nano-conductive carbon powder has a mass content of 5%, the polyacrylic acid has a mass content of 35%, the nano-tin oxide powder has a mass content of 48%, and the silica sol has a mass content of 10%.

[0020] This invention relates to a catalytic filter membrane for a methane sensor and its preparation method, as well as a methane sensor. The catalytic filter membrane, based on a platinum-supported catalyst, is applied to the top of the sensing layer using a spray dispensing method. This allows for catalytic combustion of interfering gases before they reach the sensing layer surface, effectively regulating the diffusion and reaction properties of methane molecules, significantly improving the selectivity of the methane sensor, and providing an improved solution for selective response to methane in the presence of interfering gases such as ethanol, carbon monoxide, and hydrogen. Simultaneously, it reduces the packaging volume and effectively lowers packaging costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the catalytic filtering MEMS methane sensor chip prepared in this invention, which is packaged using an SMD surface mount technology.

[0022] Figure 2 A graph showing the anti-interference test data for a MEMS methane sensor without a catalytic filter membrane.

[0023] Figure 3 The graph shows the anti-interference test data of the MEMS methane sensor with the optimal composition and content of the added catalytic filter membrane according to the present invention.

[0024] Figure 4 Charts showing the anti-interference test data of the MEMS methane sensor with added catalytic filter membrane content adjustment according to the present invention.

[0025] Figure 5 Charts showing the anti-interference test data of the MEMS methane sensor with added catalytic filter membrane composition adjustment according to the present invention. Detailed Implementation

[0026] To provide a clearer understanding of the technical content of this invention, the following embodiments are provided in detail. However, it is important to note that these descriptions are merely for further illustrating the features and advantages of this invention, and not for limiting the scope of the claims.

[0027] The gas-sensitive structure of the MEMS methane gas sensor is a porous structure composed of tiny particles of n-type metal oxide. When in contact with oxygen in the air, at a certain temperature (typically 300–500°C), the active centers on the oxide surface chemically adsorb O2, and oxygen is adsorbed onto the particles in the form of anions to form O2. 2- O - This leads to a decrease in free electrons, increasing the surface resistance of the material. When the material surface comes into contact with the reducing gas methane, O... - The electrons captured return to the surface of the sensitive material, reducing the surface resistance. The reaction equation for methane in this process is as follows:

[0028] CH4+4O - →CO2 + 2H2O + 4e -

[0029] However, gases such as CO, ethanol, VOCs, and NO2 also exhibit redox properties when in contact with sensitive materials, making them common interfering gases for methane detection in everyday and industrial environments. Palladium can catalyze the oxidation of various reducing gases and has high catalytic efficiency for methane, while platinum can catalyze the oxidation of other reducing gases besides CH4, but its catalytic efficiency for methane is low. This invention utilizes the properties of these two catalytic elements to provide a methane semiconductor gas sensor that achieves high-efficiency filtration by simultaneously adding a catalytic filter coating to a MEMS semiconductor gas-sensitive material using a jet dispensing process.

[0030] The mechanism is as follows: before the interfering gas reacts with the gas-sensitive material, the interfering gas undergoes a catalytic combustion reaction with platinum-doped inorganic oxides to burn off the largest amount of interfering gas, thus acting as a methane filter. Furthermore, the platinum catalytic filter membrane does not catalyze the combustion of methane; any temperature rise in the sensor is primarily due to the combustion of the interfering gas. Based on the power-law response relationship of the sensor, the gas-sensitive response mechanism of the sensor structure is analyzed. When the catalytic filter membrane encounters the interfering gas and undergoes a catalytic combustion reaction, the interfering gas typically reacts with the more reactive O₂ on the surface. 2- The reaction, while oxygen adsorption on the surface of gas-sensitive metal oxides mainly takes the form of O. - Mainly, interfering gases do not participate and O - Therefore, adding a catalytic filter membrane has no effect on the type of oxygen adsorbed by the sensor, the basic sensing mechanism remains unchanged, and the oxidation products generated by catalytic combustion also have no effect on the gas-sensitive response mechanism.

[0031] The specific embodiments for fabricating the catalytic filtering MEMS methane sensor of the present invention are as follows:

[0032] like Figure 1 As shown, the MEMS methane sensor chip is fabricated by sequentially setting an insulating layer 2, a platinum heating layer 3, a dielectric layer 4, a gas-sensitive interdigitated electrode 5, a dielectric layer 6, a gas-sensitive material 7, and a catalytic filter membrane 8 on a substrate 1.

[0033] A 250nm±10nm SiO2 support film was formed by thermal oxidation on a 100 single-crystal silicon substrate. A 500nm±25nm SiO2 and a 250nm±10nm Si3N4 support film were grown by low-temperature plasma vapor deposition (PECVD). The support film was then annealed at 550℃ for 30 minutes to eliminate internal stress. A 10nm±5nm tantalum adhesion layer and a 420nm±20nm platinum heating layer were deposited using magnetron sputtering and patterned using a lift-off process. A 300nm±15nm Si3N4 dielectric film was then grown by PECVD. A 10nm±5nm tantalum adhesion layer and a 450nm±25nm platinum interdigitated electrode layer were deposited using magnetron sputtering and patterned using a lift-off process. The film was then annealed at 650℃ for 60 minutes to improve heating resistance and test electrode film stability. A 500nm±25nm SiO2 passivation layer was deposited using low-temperature plasma deposition, and a gas-sensitive material window was created using RIE plasma etching.

[0034] Preparation of the gas-sensitive thin film: Palladium (Pd) nanoparticles and conductive carbon nanoparticles, at 2% and 5% by mass respectively, were dissolved in a dispersion solution containing 35% polyacrylic acid. The conductive carbon powder improved the conductivity of the gas-sensitive material. 48% by mass of nano-tin oxide (SnO2) powder was added to the Pd dispersion solution and wet-milled for 1 hour. 10% by mass of silica sol was added to the Pd-SnO2 nano-dispersion solution; the silica sol has a binding effect on the nanostructured materials and the dielectric layer. After another 5 hours of wet milling, the viscosity of the Pd-SnO2 dispersion solution was adjusted to above 10000 cp using a magnetic heating and stirring device. The gas-sensitive paste was then printed onto the window position of the gas-sensitive material using a thick-film printing process. Finally, the sensor chip containing the gas-sensitive material was sintered in air at 500℃ for 6 hours to form the gas-sensitive material thin film.

[0035] The MEMS methane sensor chip was finally etched with a front protective fixture to release the suspension membrane structure.

[0036] The preparation and transfer of a Pt-catalyst-containing Al2O3 support onto the surface of a chip gas-sensitive material were carried out as follows: 5% Pt nanoparticles were added and dissolved in 40% glycerol and dispersed. 45% alumina nanoparticles were added to the Pt-containing dispersion solvent, and the mixture was wet-milled for 3 hours using a ball mill. 10% silica sol was added to the Pt-Al3O2 nano-dispersion solution, and the mixture was wet-milled for 5 hours using a ball mill. The viscosity of the Pt-catalyst-containing alumina dispersion solution was adjusted to 5000 cP using a magnetic heating and stirring device. The prepared slurry was dispensed onto the gas-sensitive area of ​​the sensor using a dispensing process. The Pt / Al2O3 catalytic filter coating was uniformly dispersed above Pd-SnO2 and sintered in air at 500°C for 6 hours. The thickness of the catalytic filter membrane was 20 ± 2 μm. This catalytic filter membrane preparation process is simple and flexible, and also allows for mass production with good consistency.

[0037] The fabricated catalytic filtering MEMS methane sensor chip is packaged using SMD surface mount technology (SMD). Figure 1 As shown, the catalytic filter MEMS methane sensor was electrically aged for 7 days on an aging plate and passed the test, thus completing the fabrication process.

[0038] The fabricated catalytic filtration MEMS methane sensor was compared with a MEMS methane sensor without a catalytic filtration membrane in the test. Figure 2 As shown, in the traditional structure without a catalytic filter membrane, the sensitivity of the sensor varies in the methane concentration range of 1000ppm to 12500ppm when interfering gases such as ethanol, carbon monoxide, and hydrogen are present, and it is greatly affected by the interfering gases. In the structure of this invention with a catalytic filter membrane, different slurry components and contents are used, and the sensitivity of the sensor in the methane concentration range of 1000ppm to 12500ppm is improved by the influence of interfering gases. Different slurry components and contents have different filtering effects on interfering gases such as ethanol, carbon monoxide, and hydrogen.

[0039] Among them, the optimized slurry composition and content described above yielded the best results. For example... Figure 3 As shown, the sensor's sensitivity is unaffected by interfering gases in the methane concentration range of 1000ppm to 12500ppm, and it effectively filters interfering gases such as ethanol, carbon monoxide, and hydrogen.

[0040] This invention also provides a catalytic filtration membrane structure that can improve the effect of interfering gases. This catalytic filtration membrane structure is identical to the optimal combination except for the following mass percentage contents. The slurry corresponding to this catalytic filtration membrane is composed of the following components:

[0041]

[0042] like Figure 4 As shown, the sensor made from this catalytic filter membrane using the same method described above has improved sensitivity to interfering gases in the methane concentration range of 1000ppm to 12500ppm, and has a certain filtering effect on interfering gases such as ethanol, carbon monoxide, and hydrogen.

[0043] This invention also provides a catalytic filtration membrane structure that can improve the effect of interfering gases. This catalytic filtration membrane structure is identical to the optimal combination of components, except for the following: The slurry corresponding to this catalytic filtration membrane consists of the following components and their contents:

[0044]

[0045] like Figure 5 As shown, similarly, the sensor made from the catalytic filter membrane using the same method described above also shows improved sensitivity to interfering gases in the methane concentration range of 1000ppm to 12500ppm, and it also has a certain filtering effect on interfering gases such as ethanol, carbon monoxide, and hydrogen.

[0046] The catalytic filter membrane and high-selectivity MEMS methane sensor provided by this invention completely convert interfering gases into inert gases, such as CO2 and H2O, which are components of ambient air. The catalytic filter membrane neither saturates nor is consumed, ensuring long-term reliable operation of the sensor. Compared to filters made from activated carbon, the catalytic filter membrane is easier to manufacture and integrate into the sensor, resulting in a lower cost, smaller size, and easier mass production. The MEMS semiconductor methane sensor made from the catalytic filter membrane has advantages such as low power consumption, high selectivity, and good stability, making it particularly suitable for portable household gas sensor applications.

[0047] In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the invention. Therefore, this specification should be considered illustrative rather than restrictive.

Claims

1. A catalytic filter membrane for a methane sensor, characterized in that, The catalytic filtration membrane is prepared by wet grinding and mixing of a slurry and then sintering at high temperature. The slurry includes a nano-platinum catalyst, a catalyst support, a dispersant, and a binder. The catalyst support is one or more of alumina, gallium oxide, titanium oxide, cerium oxide, and zirconium oxide. The dispersant is one or more of glycerol, triethanolamine, polyacrylic acid aqueous solution, and ethanol. The binder is one or more of epoxy resin adhesive, polyurethane adhesive, nano-silica sol, low melting point glass powder, sodium silicate aqueous solution, and potassium silicate aqueous solution.

2. The catalytic filter membrane for a methane sensor according to claim 1, characterized in that, The components of the slurry, by weight percentage, include:

3. The catalytic filter membrane for a methane sensor according to claim 1, characterized in that, The components of the slurry, by weight percentage, include:

4. A method for preparing a catalytic filter membrane for a methane sensor according to any one of claims 1 to 3, characterized in that, The preparation method includes: The nano-platinum catalyst is dispersed in a dispersant to form a Pt-containing dispersion solvent. The catalyst support is added to the Pt-containing dispersion solvent, and the mixture is wet-milled in a ball mill for 1–4 hours to form a dispersion solution. A binder is added to the dispersion solution, and the mixture is wet-milled in a ball mill for 3–7 hours. A magnetic heating and stirring device is used to make the viscosity meet the preset requirements to obtain a slurry.

5. The preparation method according to claim 4, characterized in that, The preparation method further includes: The slurry is applied to the gas-sensitive material area of ​​the sensor using a dispensing process, and then sintered at 450℃~550℃ for 5~7 hours to form a catalytic filter membrane with a thickness of 20±2μm.

6. A methane sensor, characterized in that, The methane sensor comprises a gas-sensitive material and a catalytic filter membrane according to any one of claims 1 to 5, wherein the catalytic filter membrane is prepared on the gas-sensitive material by dispensing and sintering.

7. The methane sensor according to claim 6, characterized in that, The catalytic filtration membrane is prepared on a semiconductor gas-sensitive heating substrate, such as a MEMS suspended micro-hot plate, a cantilever beam micro-hot plate, a ceramic heating substrate, or a Pt heating wire.

8. The methane sensor according to claim 6, characterized in that, The preparation method of the gas-sensitive material is as follows: Palladium nanoparticles and nano-conductive carbon powder were added and dissolved in a polyacrylic acid dispersion solution. Nano-tin oxide powder was added to the dispersion solution and then wet-milled using a ball mill. Add silica sol to the dispersion solution, continue wet grinding in a ball mill, stir and adjust the viscosity of the dispersion solution to above 10000cp, use thick film printing process to print the gas-sensitive paste to the window position of the gas-sensitive material, and finally sinter in air to prepare the product.

9. The methane sensor according to claim 8, characterized in that, The palladium nanopowder has a mass content of 2%, the nano-conductive carbon powder has a mass content of 5%, the polyacrylic acid has a mass content of 35%, the nano-tin oxide powder has a mass content of 48%, and the silica sol has a mass content of 10%.

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