Palladium-based molecular sieve catalyst and preparation method and application thereof

Abstract

The invention provides a palladium-based molecular sieve catalyst and a preparation method and application thereof. According to the palladium-based molecular sieve catalyst, an all-silicon molecular sieve is used as a carrier, and palladium oxide nanoparticles encapsulated in the all-silicon molecular sieve are used as active components; the outer surface of the all-silicon molecular sieve is coated with metal oxide nanoparticles for protecting the active components. According to the invention, the all-silicon molecular sieve is used as a carrier, and the active component is encapsulated in the all-silicon molecular sieve, so that the active component can be effectively anchored, contact between water in a reaction atmosphere and the active component can be inhibited, and migration, aggregation and inactivation of the active component under a high-temperature hydrothermal condition are prevented. More importantly, the metal oxide nano-particles can preferentially react with SO2 gas, so that active components are prevented from being poisoned, and generation of inactive PdSO4 species is avoided. In conclusion, the palladium-based molecular sieve catalyst has excellent stability and sulfur poisoning resistance, and can maintain high efficiency and stability in methane catalytic purification.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and specifically relates to a palladium-based molecular sieve catalyst and a preparation method and application thereof. Background Art

[0002] The main component of natural gas is methane, which is a clean and low-carbon energy source widely used in energy, transportation, industry and other fields. With the widespread use of natural gas, natural gas vehicles have also developed rapidly around the world. Natural gas vehicles use clean and low-carbon methane as fuel, which can reduce the emission of greenhouse gas carbon dioxide, but effective measures still need to be taken to control the emission of incompletely burned methane. Methane catalytic oxidation technology is one of the most promising methane emission control technologies for natural gas vehicles. Its core is a high-efficiency methane oxidation catalyst. At present, palladium (Pd)-based catalysts have good low-temperature activity in methane oxidation reactions and have been widely studied and applied, but they also have the problem of poor resistance to sulfur poisoning. There is an urgent need to develop efficient and stable methane oxidation catalysts.

[0003] CN113559916A discloses a molecular sieve encapsulated noble metal catalyst and a preparation method thereof, wherein the active component of the catalyst is one or more of the noble metals Pd, Pt, Ru and Rh, the carrier is H-ZSM-5, Silicalite-1 and Beta molecular sieve, wherein the loading amount of the noble metal nanoparticles is 0.2-5wt.%. The catalyst preparation process is cumbersome and time-consuming, and requires multiple noble metals as active components, and the production cost is high, which is not conducive to the industrial production of the catalyst. More importantly, the anti-sulfur performance of the catalyst has not been significantly improved, and it is difficult to be widely used in sulfur-containing atmospheres.

[0004] CN118976488A discloses a sulfur-resistant catalyst and its preparation method and application. The preparation method comprises: mixing a platinum source, a vanadium source, oxalic acid, aluminum oxide and a solvent under stirring conditions to obtain a suspension; and drying and sintering the suspension to obtain the sulfur-resistant catalyst. CN116139880A discloses a method for preparing a catalyst for catalytic combustion that is resistant to sulfur poisoning, which specifically includes the following steps: S1. Dissolving a noble metal salt and a second metal salt in water respectively to obtain a noble metal salt solution and a second metal salt solution; S2. Adding polyvinyl pyrrolidone to a polyol, and simultaneously adding the noble metal salt solution and the second metal salt solution to the polyol for reaction to obtain a sol or solution, wherein the molar ratio of the noble metal element in the noble metal salt solution to the second metal element in the second metal salt solution is (0.1-9):1; S3. Fully mixing the sol or solution obtained in step S2, a catalyst carrier powder and an organic solvent to load the noble metal and the second metal components onto the catalyst carrier, and calcining to obtain a catalyst that is resistant to sulfur poisoning. CN105107501A discloses a sulfur-resistant catalyst for treating automobile exhaust, which is composed of the following components in percentage by weight: nano aluminum oxide, 20-30%; aluminum gel, 3-7%; nano titanium dioxide, 3-7%; nano cerium oxide, 5-8%; nano zirconium oxide, 5-10%; nano lanthanum oxide, 2-5%; platinum nitrate, 0.5-1.5%; rhodium nitrate, 0.5-1%; palladium nitrate, 0.5-1.5%; liquorice extract, 2.5-5%; water, the balance. Although the catalyst prepared by the above prior art has improved the anti-sulfur poisoning performance, the improvement is not enough. After long-term use in a sulfur-containing atmosphere, poisoning and deactivation will still occur. Therefore, its anti-sulfur performance is poor.

[0005] In summary, developing a methane oxidation catalyst with both excellent stability and resistance to sulfur poisoning has become an urgent problem to be solved. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a palladium-based molecular sieve catalyst and its preparation method and application. The palladium-based molecular sieve catalyst provided by the present invention has excellent stability and anti-sulfur poisoning performance, and can maintain high efficiency and stability in methane catalytic purification.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a palladium-based molecular sieve catalyst, which uses an all-silicon molecular sieve as a carrier and palladium oxide nanoparticles encapsulated inside the all-silicon molecular sieve as an active component; the outer surface of the all-silicon molecular sieve is coated with metal oxide nanoparticles for protecting the active component.

[0009] The present invention uses an all-silicon molecular sieve as a carrier, which has excellent hydrophobicity. Encapsulating the active components inside the all-silicon molecular sieve can not only effectively anchor palladium oxide nanoparticles, but also inhibit the water in the reaction atmosphere from contacting the active components, preventing them from migrating, aggregating and deactivating under high-temperature hydrothermal conditions. In addition, the metal oxide nanoparticles coated on the outer surface of the all-silicon molecular sieve act as a protective layer, which can preferentially react with SO2 in the reaction atmosphere, prevent it from poisoning the active components of palladium oxide, and avoid the generation of inactive PdSO4 species. In summary, the palladium-based molecular sieve catalyst has excellent long-term stability and anti-sulfur poisoning performance, and can maintain high efficiency and stability in methane catalytic purification.

[0010] Preferably, the all-silicon molecular sieve includes any one of an MFI configuration all-silicon molecular sieve, an MEL configuration all-silicon molecular sieve or a CHA configuration all-silicon molecular sieve, or a combination of at least two thereof.

[0011] In the present invention, the MFI-configured all-silicon molecular sieve, usually referring to the Silicalite-1 molecular sieve, is a silicon-based molecular sieve with unique properties and wide applications. It has a double ten-membered ring cross-channel structure and can form a two-dimensional channel system. It is composed of a chain structure composed of silicon-oxygen tetrahedrons, forming a hexagonal stacking topological structure, and does not contain aluminum in the skeleton, and has higher hydrothermal stability, lipophilicity and hydrophobicity.

[0012] Preferably, the particle size D50 of the palladium oxide nanoparticles is 2-5 nm, for example, 2 nm, 3 nm, 4 nm or 5 nm.

[0013] In the present invention, palladium oxide nanoparticles of suitable particle size are encapsulated inside the all-silicon molecular sieve, which is beneficial to improving the activity and long-term stability of the catalyst in the methane oxidation reaction.

[0014] Preferably, based on the mass of the palladium-based molecular sieve catalyst, the mass fraction of palladium is 0.5-1.5wt%, for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt% or 1.5wt%, etc.

[0015] Preferably, the metal oxide nanoparticles for protecting the active components include any one of CeO2 nanoparticles, MnO2 nanoparticles or MgO nanoparticles, or a combination of at least two thereof.

[0016] In the present invention, the above-mentioned types of metal oxide nanoparticles can preferentially react with SO2 in the atmosphere to prevent the catalyst from being deactivated by sulfur poisoning, and after a period of application, the nanoparticles such as CeO2 can be regenerated by changing the reaction atmosphere, thereby greatly improving the catalyst's resistance to sulfur poisoning.

[0017] Preferably, the particle size D50 of the nanoparticles is 10-60 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm or 60 nm.

[0018] In the present invention, nanoparticles with suitable particle sizes are conducive to being evenly distributed on the outer surface of the molecular sieve, thereby effectively exerting their protective effect.

[0019] In a second aspect, the present invention provides a method for preparing the palladium-based molecular sieve catalyst as described in the first aspect, the preparation method comprising the following steps:

[0020] The template, silicon source, palladium source and solvent are mixed, and then crystallized to obtain a crystallized product.

[0021] The crystallized product is post-treated to obtain an all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles.

[0022] The all-silicon molecular sieve catalyst encapsulating palladium oxide nanoparticles is mixed with metal oxide nanoparticles, and then mechanically processed to obtain the palladium-based molecular sieve catalyst.

[0023] Preferably, the templating agent comprises tetrapropylammonium hydroxide.

[0024] Preferably, the silicon source comprises tetraethyl silicate.

[0025] Preferably, the palladium source comprises Pd(NH2CH2CH2NH2)2Cl2.

[0026] Preferably, the molar ratio of the template, silicon source, palladium source and solvent is (0.2-0.6):1:(0.003-0.009):(25-45), wherein the selection range of the template "0.2-0.6" can be, for example, 0.2, 0.3, 0.4, 0.5 or 0.6, etc., the selection range of the palladium source "0.003-0.009" can be, for example, 0.003, 0.005, 0.006, 0.007 or 0.009, etc., and the selection range of the solvent "25-45" can be, for example, 25, 30, 35, 40 or 45, etc.

[0027] Preferably, the crystallization temperature is 150-190°C, for example, 150°C, 160°C, 170°C, 180°C or 190°C.

[0028] Preferably, the crystallization time is 2-6 days, for example, 2 days, 3 days, 4 days, 5 days or 6 days.

[0029] Preferably, the post-treatment comprises centrifugation, washing, drying and calcination performed sequentially.

[0030] Preferably, the calcination temperature is 500-600°C, for example, 500°C, 550°C or 600°C.

[0031] Preferably, the calcination time is 6-10 h, for example, 6 h, 8 h or 10 h.

[0032] Preferably, the mass ratio of the all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles to the metal oxide nanoparticles is 1:(1-3), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5 or 1:3.

[0033] In the present invention, the all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and the metal oxide nanoparticles in a suitable mass ratio are helpful to improve the anti-sulfur poisoning performance of the catalyst.

[0034] Preferably, the mechanical processing method includes mechanical ball milling.

[0035] In the present invention, the process of mechanical ball milling is simple and has good repeatability. Compared with the chemical coating method, the processing time is short, the cost is low, and the utilization rate of raw materials is high. In addition, the coating layer obtained by mechanical ball milling has good uniformity.

[0036] Preferably, the ball milling speed of the mechanical ball milling is 300-500 rpm, for example, 300 rpm, 400 rpm or 500 rpm.

[0037] Preferably, the mechanical ball milling time is 0.5-1.5 h, for example, 0.5 h, 0.75 h, 1 h, 1.25 h or 1.5 h.

[0038] Preferably, the preparation method comprises the following steps:

[0039] (1) The template, silicon source, palladium source and solvent are stirred and mixed in a molar ratio of (0.2-0.6):1:(0.003-0.009):(25-45) for 2-10 hours (for example, 2 hours, 4 hours, 6 hours, 8 hours or 10 hours, etc.), and then the obtained mixture is crystallized at 150-190° C. for 2-6 days to obtain a crystallized product.

[0040] (2) The crystallized product is centrifuged, washed, dried and calcined in sequence to obtain an all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles; wherein the centrifugal speed is 4000-8000rpm (for example, it can be 4000rpm, 5000rpm, 6000rpm, 7000rpm or 8000rpm, etc.), the centrifugal time is 5-15min (for example, it can be 5min, 10min or 15min, etc.), the drying temperature is 60-100℃ (for example, it can be 60℃, 70℃, 80℃, 90℃ or 100℃, etc.), the calcination temperature is 500-600℃, and the calcination time is 6-10h.

[0041] (3) The all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and CeO2 powder are stirred and mixed in a mass ratio of 1:(1-3) for 10-30 minutes (for example, 10 minutes, 20 minutes or 30 minutes, etc.), and then mechanically milled by controlling the ball milling speed to 300-500 rpm and the ball milling time to 0.5-1.5 hours to obtain a palladium-based molecular sieve catalyst.

[0042] In a third aspect, the present invention provides an application of the palladium-based molecular sieve catalyst as described in the first aspect, wherein the palladium-based molecular sieve catalyst is applied to catalytic purification of methane in exhaust gas from natural gas vehicles and industrial waste gas.

[0043] Preferably, the temperature of the catalytic purification of methane is 200-700°C, for example, it can be 200°C, 300°C, 400°C, 500°C, 600°C or 700°C.

[0044] Preferably, the water content in the natural gas vehicle exhaust and industrial waste gas is 2-10 vol.%, for example, 2 vol.%, 5 vol.%, 8 vol.% or 10 vol.%.

[0045] Preferably, the methane concentration in the natural gas vehicle exhaust and industrial waste gas is 500-2000 ppm, for example, it can be 500 ppm, 1000 ppm, 1500 ppm or 2000 ppm.

[0046] Preferably, the SO2 concentration in the natural gas vehicle exhaust and industrial waste gas is 5-20 ppm, for example, it can be 5 ppm, 10 ppm, 15 ppm or 20 ppm.

[0047] For example, in the catalytic purification process of methane, the total flow rate of natural gas vehicle exhaust or industrial waste gas can be 200-500 mL / min, such as 200 mL / min, 300 mL / min, 400 mL / min or 500 mL / min, and the mass space velocity is 50000-200000 mL·g -1 ·h -1 , for example 50000mL·g -1 ·h -1 、100000mL·g -1 ·h -1 、150000mL·g -1 ·h -1 or 200000mL·g -1 ·h -1 wait.

[0048] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The present invention uses an all-silicon molecular sieve as a carrier, which has excellent hydrophobicity. Encapsulating the active components inside the all-silicon molecular sieve can not only effectively anchor palladium oxide nanoparticles, but also inhibit the water in the reaction atmosphere from contacting the active components, preventing them from migrating, aggregating and deactivating under high-temperature hydrothermal conditions. In addition, the surface of the all-silicon molecular sieve is coated with metal oxide nanoparticles, which can preferentially react with SO2 in the atmosphere, preventing it from poisoning the active components of palladium oxide and avoiding the generation of inactive PdSO4 species. In summary, the palladium-based molecular sieve catalyst has excellent long-term stability and resistance to sulfur poisoning, and can maintain high efficiency and stability in methane catalytic purification.

[0051] (2) The palladium-based molecular sieve catalyst provided by the present invention can achieve a methane conversion rate of 90% at 380°C under a harsh simulated natural gas vehicle exhaust atmosphere, and has excellent low-temperature activity; it can maintain high stability (methane conversion rate > 90%) for at least 50 hours in a reaction atmosphere containing SO2; after a long period of reaction in an atmosphere containing SO2, the protective layer can be regenerated by changing the reaction atmosphere, which can greatly improve the catalyst's resistance to sulfur poisoning. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a graph showing the methane oxidation reaction activity of the palladium-based molecular sieve catalyst provided in Example 1, Examples 4-5 and Comparative Example 1 after pre-sulfidation treatment.

[0053] Figure 2 This is a stability test curve chart of the methane oxidation reaction performed on the palladium-based molecular sieve catalyst provided in Example 1, Examples 4-5 and Comparative Example 1.

[0054] Figure 3 The steady-state-regeneration test curve of the palladium-based molecular sieve catalyst against sulfur poisoning provided in Example 5 and Comparative Example 1. DETAILED DESCRIPTION

[0055] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0056] Example 1

[0057] The present embodiment provides a palladium-based molecular sieve catalyst, which uses an MFI-configuration all-silicon molecular sieve as a carrier and palladium oxide nanoparticles encapsulated inside the MFI-configuration all-silicon molecular sieve as an active component; the outer surface of the MFI-configuration all-silicon molecular sieve is coated with CeO2 nanoparticles.

[0058] The particle size D50 of the palladium oxide nanoparticles is 2.6 nm; based on the mass of the palladium-based molecular sieve catalyst, the mass fraction of palladium is 1 wt %.

[0059] The particle size D50 of the CeO2 nanoparticles is 20 nm.

[0060] This embodiment also provides a method for preparing the above-mentioned palladium-based molecular sieve catalyst, and the preparation method comprises the following steps:

[0061] (1) 13 mL of tetrapropylammonium hydroxide and 8.9 mL of tetraethyl silicate were added to 24.9 mL of deionized water in sequence, and the mixture was stirred at room temperature of 25°C for 6 h. Then, 1.4 mL of Pd(NH2CH2CH2NH2)2Cl2 was added, and the mixture was stirred at room temperature of 25°C for 30 min. After the mixture was added, the mixture was placed in a stainless steel reactor lined with polytetrafluoroethylene and crystallized at 170°C for 4 days to obtain a crystallized product.

[0062] Wherein, the molar ratio of tetrapropylammonium hydroxide, tetraethyl silicate, Pd(NH2CH2CH2NH2)2Cl2 and deionized water is 0.4:1:0.006:35.

[0063] (2) The crystallized product is centrifuged to collect the precipitate, which is then washed with deionized water for 6 times, dried at 80° C. for 10 h, and finally calcined in an air atmosphere at 550° C. for 8 h to obtain an MFI-configured all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles.

[0064] Wherein, the centrifugal speed is 6000 rpm and the centrifugal time is 10 min.

[0065] (3) 500 mg of the MFI-configured all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and 500 mg of CeO2 powder were stirred and mixed at a mass ratio of 1:1 at room temperature (25°C) for 10 minutes, and then the obtained mixture was added to a large ball mill. The ball milling speed was controlled to 400 rpm and the ball milling time was 0.5 h by mechanical ball milling to obtain a palladium-based molecular sieve catalyst, which was recorded as Ce1 / Pd@S-1.

[0066] Example 2

[0067] This embodiment provides a palladium-based molecular sieve catalyst, which uses an MFI-configuration all-silicon molecular sieve as a carrier and palladium oxide nanoparticles encapsulated inside the MFI-configuration all-silicon molecular sieve as an active component; the outer surface of the MFI-configuration all-silicon molecular sieve is coated with MnO2 nanoparticles.

[0068] The particle size D50 of the palladium oxide nanoparticles is 2 nm; based on the mass of the palladium-based molecular sieve catalyst, the mass fraction of palladium is 0.5 wt %.

[0069] The particle size D50 of the MnO2 nanoparticles is 20 nm.

[0070] This embodiment also provides a method for preparing the above-mentioned palladium-based molecular sieve catalyst, and the preparation method comprises the following steps:

[0071] (1) 13 mL of tetrapropylammonium hydroxide and 8.9 mL of tetraethyl silicate were added to 24.9 mL of deionized water in sequence, and the mixture was stirred at room temperature of 25°C for 6 h. Then, 0.7 mL of Pd(NH2CH2CH2NH2)2Cl2 was added, and the mixture was stirred at room temperature of 25°C for 30 min. After the mixture was completed, the mixture was placed in a stainless steel reactor lined with polytetrafluoroethylene and crystallized at 150°C for 6 days to obtain a crystallized product.

[0072] Among them, the molar ratio of tetrapropylammonium hydroxide, tetraethyl silicate, Pd(NH2CH2CH2NH2)2Cl2 and deionized water is 0.4:1:0.003:35.

[0073] (2) The crystallized product is centrifuged to collect the precipitate, which is then washed with deionized water for 6 times, dried at 60° C. for 10 h, and finally calcined in an air atmosphere at 500° C. for 10 h to obtain an MFI-configured all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles.

[0074] Wherein, the centrifugal speed is 4000 rpm and the centrifugal time is 15 min.

[0075] (3) 500 mg of the MFI-configured all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and 500 mg of MnO2 powder were stirred and mixed at a mass ratio of 1:2 at room temperature (25°C) for 20 minutes, and then the obtained mixture was added to a large ball mill. The ball mill speed was controlled to 300 rpm and the ball milling time was 1.5 h by mechanical ball milling to obtain a palladium-based molecular sieve catalyst.

[0076] Example 3

[0077] This embodiment provides a palladium-based molecular sieve catalyst, which uses an MFI-configuration all-silicon molecular sieve as a carrier and palladium oxide nanoparticles encapsulated inside the MFI-configuration all-silicon molecular sieve as an active component; the outer surface of the MFI-configuration all-silicon molecular sieve is coated with MgO nanoparticles.

[0078] The particle size D50 of the palladium oxide nanoparticles is 5 nm; based on the mass of the palladium-based molecular sieve catalyst, the mass fraction of palladium is 1.5 wt %.

[0079] The particle size D50 of the MgO nanoparticles is 20 nm.

[0080] This embodiment also provides a method for preparing the above-mentioned palladium-based molecular sieve catalyst, and the preparation method comprises the following steps:

[0081] (1) 13 mL of tetrapropylammonium hydroxide and 8.9 mL of tetraethyl silicate were added to 24.9 mL of deionized water in sequence, and the mixture was stirred at room temperature of 25°C for 6 h. Then, 2.1 mL of Pd(NH2CH2CH2NH2)2Cl2 was added, and the mixture was stirred at room temperature of 25°C for 30 min. After the mixture was added, the mixture was placed in a stainless steel reactor lined with polytetrafluoroethylene and crystallized at 190°C for 2 days to obtain a crystallized product.

[0082] Among them, the molar ratio of tetrapropylammonium hydroxide, tetraethyl silicate, Pd(NH2CH2CH2NH2)2Cl2 and deionized water is 0.4:1:0.009:35.

[0083] (2) The crystallized product is centrifuged to collect the precipitate, which is then washed with deionized water for 6 times, dried at 100° C. for 10 h, and finally calcined in an air atmosphere at 600° C. for 6 h to obtain an MFI-configured all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles.

[0084] Wherein, the centrifugal speed is 8000 rpm and the centrifugal time is 5 min.

[0085] (3) 500 mg of the MFI-configured all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and 500 mg of MgO powder were stirred and mixed at a mass ratio of 1:1 at room temperature (25°C) for 30 minutes, and then the obtained mixture was added to a large ball mill. The ball milling speed was controlled to 500 rpm and the ball milling time was 1 hour by mechanical ball milling to obtain a palladium-based molecular sieve catalyst.

[0086] Example 4

[0087] The difference between this embodiment and embodiment 1 is that the amount of CeO2 powder added in step (3) is 1000 mg, so that the mass ratio of the MFI-configured all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and the CeO2 powder is 1:2.

[0088] The palladium-based molecular sieve catalyst obtained in this example is recorded as Ce2 / Pd@S-1.

[0089] The rest of the preparation methods and parameters were the same as those in Example 1.

[0090] Example 5

[0091] The difference between this embodiment and embodiment 1 is that the amount of CeO2 powder added in step (3) is 1500 mg, so that the mass ratio of the MFI-configured all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and the CeO2 powder is 1:3.

[0092] The palladium-based molecular sieve catalyst obtained in this example is recorded as Ce3 / Pd@S-1.

[0093] The rest of the preparation methods and parameters were the same as those in Example 1.

[0094] Example 6

[0095] The difference between this embodiment and embodiment 1 is that the MFI-configuration all-silicon molecular sieve is replaced by the MEL-configuration all-silicon molecular sieve.

[0096] The rest of the preparation methods and parameters were the same as those in Example 1.

[0097] Example 7

[0098] The difference between this embodiment and embodiment 1 is that the MFI-configuration all-silicon molecular sieve is replaced by a CHA-configuration all-silicon molecular sieve.

[0099] The rest of the preparation methods and parameters were the same as those in Example 1.

[0100] Example 8

[0101] The difference between this embodiment and embodiment 1 is that the mass ratio of the MFI-configuration all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and the CeO2 powder is 1:0.5.

[0102] The rest of the preparation methods and parameters were the same as those in Example 1.

[0103] Example 9

[0104] The difference between this embodiment and embodiment 1 is that the mass ratio of the MFI-configuration all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and the CeO2 powder is 1:4.

[0105] The rest of the preparation methods and parameters were the same as those in Example 1.

[0106] Example 10

[0107] The difference between this embodiment and embodiment 1 is that the ball milling speed of the mechanical ball mill is 200 rpm.

[0108] The rest of the preparation methods and parameters were the same as those in Example 1.

[0109] Embodiment 11

[0110] The difference between this embodiment and embodiment 1 is that the ball milling speed of the mechanical ball mill is 600 rpm.

[0111] The rest of the preparation methods and parameters were the same as those in Example 1.

[0112] Comparative Example 1

[0113] The difference between this comparative example and Example 1 is that no CeO2 layer is provided, that is, step (3) is not performed.

[0114] The rest of the preparation methods and parameters were the same as those in Example 1.

[0115] Performance Testing

[0116] In a simulated natural gas vehicle exhaust atmosphere, the catalytic purification effect of the palladium-based molecular sieve catalysts prepared in the above embodiments and comparative examples on methane in natural gas vehicle exhaust was investigated; wherein the simulated natural gas vehicle exhaust gas composition is: 0.2 vol.% CH4, 5 vol.% O2, 5 vol.% H2O, (5 ppm SO2) N2 as the balance gas; the mass space velocity is 100000 mL·g -1 ·h -1 , the total flow rate of natural gas vehicle exhaust is 200mL / min.

[0117] The above investigation results are as follows Figure 1 , Figure 2 , Figure 3 And as shown in Table 1.

[0118] The palladium-based molecular sieve catalysts provided in Example 1, Examples 4-5 and Comparative Example 1 were presulfurized for 1 hour in a simulated natural gas vehicle exhaust atmosphere containing 100 ppm SO2, and then the methane oxidation reaction performance was evaluated. Figure 1 The methane oxidation reaction activity curve shown in the figure shows that the palladium-based molecular sieve catalyst provided by the present invention can still completely catalyze and oxidize methane into carbon dioxide and water at 425°C after presulfurization, and can maintain a 100% methane conversion rate in the temperature range of 425-600°C, and its sulfur poisoning resistance and catalytic activity are good. However, the palladium-based molecular sieve catalyst provided in Comparative Example 1 can only completely catalyze and convert methane at 560°C after presulfurization, and obvious deactivation occurs.

[0119] Figure 2 The stability test curves of the palladium-based molecular sieve catalysts provided in Example 1, Examples 4-5 and Comparative Example 1 for methane oxidation reaction in a simulated natural gas vehicle exhaust atmosphere in the presence of 5 ppm SO2 are shown. It can be seen from the figure that in the presence of SO2, the palladium-based molecular sieve catalyst provided in Comparative Example 1 is completely deactivated in just 2 hours, while the palladium-based molecular sieve catalyst provided in Example 5 can maintain a methane conversion rate of more than 90% in a 50-hour stability test, showing excellent stability.

[0120] Figure 3 The steady-state-regeneration test curves of the anti-sulfur poisoning of the palladium-based molecular sieve catalysts provided in Example 5 and Comparative Example 1 are shown. It can be seen from the figure that in the presence of SO2, the palladium-based molecular sieve catalyst provided in Comparative Example 1 is completely deactivated in only 2 hours, and can restore the initial activity after atmosphere change regeneration, but still rapidly deactivates in a reaction atmosphere containing SO2. In contrast, since the palladium-based molecular sieve catalyst provided in Example 5 has the protective effect of CeO2, it still maintains a high activity within 60 hours, can restore the initial activity after atmosphere change regeneration, and can still maintain high stability in a reaction atmosphere containing SO2, indicating that CeO2 can not only protect the palladium-based molecular sieve catalyst from sulfur poisoning deactivation, but also can achieve CeO2 regeneration after reaction atmosphere change treatment, thereby maintaining longer anti-sulfur poisoning stability.

[0121] Table 1

[0122]

[0123] analyze:

[0124] It can be seen from the above table and the accompanying drawings that the palladium-based molecular sieve catalyst provided by the present invention can achieve a methane conversion rate of 80% at 380°C after pre-sulfurization with 100 ppm SO2 in a simulated harsh natural gas vehicle exhaust atmosphere, and can maintain high stability (methane conversion rate > 90%) within 50 hours in a reaction atmosphere containing SO2, showing excellent anti-sulfur performance.

[0125] By comparing Example 1 with Examples 8-9, it can be seen that if the mass ratio of the MFI-configured all-silicon molecular sieve encapsulated with palladium oxide nanoparticles and the CeO2 powder is too large, the CeO2 layer will be sparsely covered and the protective effect will be insufficient, resulting in poor anti-sulfur poisoning performance; if the mass ratio of the MFI-configured all-silicon molecular sieve encapsulated with palladium oxide nanoparticles and the CeO2 powder is too small, the CeO2 layer will be too densely covered, blocking the molecular sieve pores, resulting in poor methane catalytic oxidation performance.

[0126] By comparing Example 1 with Examples 10-11, it can be seen that if the milling speed of the mechanical ball mill is too small, the CeO2 layer will be poorly dispersed on the surface of the molecular sieve, resulting in poor resistance to sulfur poisoning; if the milling speed of the mechanical ball mill is too large, the CeO2 layer and the molecular sieve structure will be partially destroyed, resulting in poor methane oxidation activity.

[0127] By comparing Example 1 with Comparative Example 1, it can be seen that if the CeO2 layer is not provided, there is no protection of CeO2, resulting in extremely poor anti-sulfur poisoning performance of the palladium-based molecular sieve catalyst.

[0128] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A palladium-based molecular sieve catalyst, characterized in that: The palladium-based molecular sieve catalyst uses an all-silicon molecular sieve as a carrier and palladium oxide nanoparticles encapsulated inside the all-silicon molecular sieve as an active component; the outer surface of the all-silicon molecular sieve is coated with metal oxide nanoparticles for protecting the active component.

2. The palladium-based molecular sieve catalyst according to claim 1, characterized in that The all-silicon molecular sieve includes any one of an MFI configuration all-silicon molecular sieve, an MEL configuration all-silicon molecular sieve or a CHA configuration all-silicon molecular sieve, or a combination of at least two thereof; Preferably, the particle size D50 of the palladium oxide nanoparticles is 2-5 nm; Preferably, based on the mass of the palladium-based molecular sieve catalyst, the mass fraction of palladium is 0.5-1.5 wt %.

3. The palladium-based molecular sieve catalyst according to claim 1 or 2, characterized in that The metal oxide nanoparticles used to protect the active components include any one of CeO2 nanoparticles, MnO2 nanoparticles or MgO nanoparticles, or a combination of at least two of them.

4. A method for preparing a palladium-based molecular sieve catalyst as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: The template, silicon source, palladium source and solvent are mixed, and then crystallized to obtain a crystallized product; Post-treating the crystallized product to obtain an all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles; The all-silicon molecular sieve catalyst encapsulating palladium oxide nanoparticles is mixed with metal oxide nanoparticles, and then mechanically processed to obtain the palladium-based molecular sieve catalyst.

5. The preparation method according to claim 4, characterized in that: The template agent includes tetrapropylammonium hydroxide; Preferably, the silicon source comprises tetraethyl silicate; Preferably, the palladium source comprises Pd(NH2CH2CH2NH2)2Cl2; Preferably, the molar ratio of the template, silicon source, palladium source and solvent is (0.2-0.6):1:(0.003-0.009):(25-45); Preferably, the crystallization temperature is 150-190°C; Preferably, the crystallization time is 2-6 days.

6. The preparation method according to claim 4 or 5, characterized in that: The post-treatment includes centrifugation, washing, drying and calcination performed in sequence; Preferably, the calcination temperature is 500-600°C; Preferably, the calcination time is 6-10 hours.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The mass ratio of the all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles to the metal oxide nanoparticles is 1:(1-3); Preferably, the mechanical processing method includes mechanical ball milling; Preferably, the ball milling speed of the mechanical ball milling is 300-500 rpm; Preferably, the mechanical ball milling time is 0.5-1.5 h.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The preparation method comprises the following steps: (1) stirring and mixing a template, a silicon source, a palladium source and a solvent in a molar ratio of (0.2-0.6):1:(0.003-0.009):(25-45) for 2-10 hours, and then crystallizing the obtained mixture at 150-190° C. for 2-6 days to obtain a crystallized product; (2) centrifuging, washing, drying and calcining the crystallized product in sequence to obtain an all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles; wherein the centrifugal speed is 4000-8000 rpm, the centrifugal time is 5-15 min, the drying temperature is 60-100° C., the calcination temperature is 500-600° C., and the calcination time is 6-10 h; (3) The all-silicon molecular sieve catalyst encapsulated with palladium oxide nanoparticles and CeO2 powder are stirred and mixed at a mass ratio of 1:(1-3) for 10-30 minutes, and then the palladium-based molecular sieve catalyst is obtained by mechanical ball milling with the ball milling speed controlled at 300-500 rpm and the ball milling time at 0.5-1.5 h.

9. An application of the palladium-based molecular sieve catalyst according to any one of claims 1 to 3, characterized in that: The palladium-based molecular sieve catalyst is used for catalytic purification of methane in natural gas vehicle exhaust and industrial waste gas.

10. The use according to claim 9, characterized in that: The temperature of the catalytic purification of methane is 200-700°C.

Images