A high-stability palladium-based molecular sieve catalyst, a preparation method and application thereof

Abstract

The present application relates to a kind of high stability palladium-based molecular sieve catalyst and its preparation method and application, the high stability palladium-based molecular sieve catalyst includes SSZ-13 hydrophobic modification molecular sieve and active component supported on SSZ-13 hydrophobic modification molecular sieve;The active component includes palladium oxide particle;With the total mass of the high stability palladium-based molecular sieve catalyst as 100wt%, the content of active component in the high stability palladium-based molecular sieve catalyst is 0.5wt%-5wt%.The high stability palladium-based molecular sieve catalyst uses SSZ-13 hydrophobic modification molecular sieve as carrier, the adsorption capacity of catalyst to water is weakened, so as to achieve the purpose of reducing palladium oxide material water poisoning inactivation, avoid its inactivation under high temperature hydrothermal condition, its methane catalytic oxidation activity, hydrothermal aging performance and stability are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of methane catalytic combustion technology, and in particular to a highly stable palladium-based molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] Global warming and air pollution are increasingly serious problems, causing enormous harm to people's lives and production. Among traditional energy sources, natural gas consumption is second only to oil and coal, and it is widely used in industrial production and mobile energy applications. The main component of natural gas is methane, the second largest greenhouse gas globally after carbon dioxide. Therefore, while utilizing natural gas, it is also necessary to ensure the treatment of incompletely burned methane. Methane treatment can generally be divided into direct combustion and catalytic combustion. If the traditional direct combustion method is used, the combustion temperature will exceed 1500℃, producing carbon monoxide (CO) and other hydrocarbons (HC). x NO x This process, including other methods, leads to secondary pollution. In contrast, catalytic combustion can often achieve complete methane oxidation at lower temperatures (300℃~800℃), making it safer and more environmentally friendly. Therefore, designing and preparing efficient and stable methane oxidation catalysts is one of the effective methods to solve the problem of methane emissions in waste gas.

[0003] Methane oxidation catalysts can be broadly classified into two categories: non-precious metal-based catalysts and precious metal-based catalysts. Precious metal palladium-based catalysts have been widely studied and applied due to their good low-temperature activity. However, the exhaust gas temperature of natural gas vehicles typically reaches a maximum of 550℃, with a low methane concentration of approximately 500-1000 ppm, and also contains a large amount of water vapor, about 15%. Under these harsh conditions of high temperature and high humidity, the active component PdO is prone to sintering and reacts with water to form Pd(OH)₂, leading to severe sintering deactivation of the catalyst. Most research tends to focus on achieving the lowest possible ignition temperature under dry conditions, neglecting the problem of vapor-induced sintering deactivation.

[0004] Therefore, how to develop a palladium-based catalyst material that maintains high activity and stability under harsh conditions of high vapor concentration and its preparation method has become an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a highly stable palladium-based molecular sieve catalyst, its preparation method, and its application. The highly stable palladium-based molecular sieve catalyst uses SSZ-13 hydrophobically modified molecular sieve as a support, which weakens the catalyst's ability to adsorb water, thereby reducing the water poisoning deactivation of palladium oxide and avoiding its deactivation under high-temperature hydrothermal conditions. The hydrothermal stability of its methane oxidation catalyst is significantly improved.

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

[0007] In a first aspect, the present invention provides a highly stable palladium-based molecular sieve catalyst, the highly stable palladium-based molecular sieve catalyst comprising an SSZ-13 hydrophobically modified molecular sieve and an active component supported on the SSZ-13 hydrophobically modified molecular sieve; the active component comprises palladium oxide;

[0008] Based on a total mass of 100 wt% for the highly stable palladium-based molecular sieve catalyst, the content of the active component in the highly stable palladium-based molecular sieve catalyst is 0.5 wt% to 5 wt%, for example, it can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0009] SSZ-13 molecular sieve exhibits a trend of increasing hydrophobicity with increasing silicon-to-aluminum ratio. However, in actual synthesis, high silicon-to-aluminum ratio synthesis is difficult and costly. This invention modifies SSZ-13 molecular sieve hydrophobically, weakening its water adsorption capacity, thereby reducing water poisoning deactivation of palladium oxide. The palladium-based molecular sieve catalyst prepared using the hydrophobically modified molecular sieve as a support has reduced water adsorption capacity, avoiding deactivation under high-temperature hydrothermal conditions. This not only improves the hydrothermal aging stability of the palladium-based molecular sieve catalyst, but also demonstrates a high conversion rate of 96% after 36 hours of stability testing at 410℃, significantly enhancing the catalyst's stability.

[0010] The active component in the high-stability palladium-based molecular sieve catalyst provided by this invention is palladium oxide, which has higher stability.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0012] Preferably, the average particle size D of the palladium oxide particles is 0.5nm-5nm, for example, it can be 0.5nm, 1nm, 2nm, 3nm, 4nm or 5nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] This invention further controls the average particle size D of palladium oxide particles to be 0.5 nm-5 nm. The activity of palladium oxide exhibits a volcano-like relationship with its average particle size. Due to differences in the strength of the metal-support interaction, the molecular sieve support state affects the shape of the Pd particles. By controlling the size of the Pd particles, PdO crystal faces and active sites with different activities can be formed. If the average particle size of palladium oxide is too large, the catalyst's reactivity decreases; if the average particle size of palladium oxide particles is too small, its methane oxidation activity also decreases.

[0014] In a second aspect, the present invention provides a method for preparing a highly stable palladium-based molecular sieve catalyst as described in the first aspect, the method comprising the following steps:

[0015] (1) Mix SSZ-13 molecular sieve, water, ethanol and first silane coupling agent, and obtain the first product through the first reaction; mix the first product, toluene and second silane coupling agent, and then calcine after the second reaction to obtain SSZ-13 hydrophobic modified molecular sieve.

[0016] (2) Mix the palladium source with the aqueous solution of SSZ-13 hydrophobic modified molecular sieve, stir to obtain a mixture, add alkali solution, adjust the pH, let stand, and obtain the high-stability palladium-based molecular sieve catalyst by solid-liquid separation and calcination.

[0017] This invention first modifies SSZ-13 molecular sieve hydrophobically. Six hydroxyl groups formed by the hydrolysis of a first silane coupling agent react with hydroxyl groups on the surface of the SSZ-13 molecular sieve, resulting in a large number of hydroxyl groups on the surface. These hydroxyl groups then react with hydroxyl groups formed by the hydrolysis of a second silane coupling agent, maximizing the introduction of organic hydrophobic chain groups onto the surface of the SSZ-13 molecular sieve. This synthesis method is simple and the conditions are easy to control. The resulting modified SSZ-13 molecular sieve has a low hydroxyl content and contains a large number of organic groups, thus greatly improving its hydrophobicity and reducing its water adsorption capacity, thereby reducing the inactivation of palladium oxide by water poisoning.

[0018] Then, palladium oxide is loaded onto the molecular sieve using a deposition-precipitation (DP) method, resulting in a more uniform dispersion of the palladium oxide. This significantly enhances the interaction between palladium oxide and the hydrophobically modified SSZ-13 molecular sieve, effectively improving the low-temperature catalytic performance and stability of the palladium-based molecular sieve catalyst. The process is simple and controllable, requiring no high-temperature activation, thus saving energy. Furthermore, compared to catalysts prepared using traditional impregnation methods, the method of this invention facilitates the formation of active palladium oxide with high content; the active palladium oxide exhibits high dispersion; and most of the active palladium oxide adheres to the molecular sieve surface in regular spherical shapes, exposing more active sites.

[0019] Preferably, the first silane coupling agent in step (1) includes 1,2-bis(triethoxysilyl)ethane and / or 1,2-bis(trimethoxysilyl)ethane, more preferably 1,2-bis(triethoxysilyl)ethane.

[0020] Preferably, in step (1), the second silane coupling agent comprises any one or a combination of at least two of dodecyltrimethoxysilane, mercaptopropyltrimethoxysilane, or methylphenyldimethoxysilane. Typical but non-limiting combinations include combinations of dodecyltrimethoxysilane and mercaptopropyltrimethoxysilane, combinations of mercaptopropyltrimethoxysilane and methylphenyldimethoxysilane, combinations of dodecyltrimethoxysilane and methylphenyldimethoxysilane, and combinations of dodecyltrimethoxysilane, mercaptopropyltrimethoxysilane, and methylphenyldimethoxysilane. Preferred is dodecyltrimethoxysilane.

[0021] Preferably, the mass ratio of SSZ-13 molecular sieve and first silane coupling agent in step (1) is 1:(0.01-0.15), for example, it can be 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.09, 1:0.1, 1:0.12, 1:0.13, 1:0.14 or 1:0.15, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1:(0.02-0.05).

[0022] In this invention, the mass ratio of SSZ-13 molecular sieve to the first silane coupling agent is further optimized to 1:(0.01-0.05) to ensure stronger hydrothermal aging ability of the molecular sieve catalyst after palladium loading. If the mass ratio of SSZ-13 molecular sieve to the first silane coupling agent is too large, i.e., the amount of the first silane coupling agent added is too small, the removal of hydroxyl groups on the surface of the molecular sieve support is insufficient, which will lead to insignificant hydrophobicity of the molecular sieve, poor hydrothermal aging ability of the molecular sieve catalyst, and reduced long-term stability of the catalyst. If the mass ratio of SSZ-13 molecular sieve to the first silane coupling agent is too small, i.e., the amount of the first silane coupling agent added is too large, the molecular sieve channels will be blocked, affecting the mass transport during the reaction process and reducing its catalytic efficiency.

[0023] Preferably, the mass ratio of SSZ-13 molecular sieve, water, and ethanol in step (1) is 1:(10-20):(2-5), for example, it can be 1:10:2, 1:10:3, 1:10:4, 1:10:5, 1:15:2, 1:15:3, 1:15:4, 1:15:5, 1:20:2, 1:20:3, 1:20:4 or 1:20:5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the temperature of the first reaction in step (1) is 60℃-70℃, for example, it can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃ or 70℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the reaction time in step (1) is 5h-20h, for example, it can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, step (1) further includes a first washing and a first drying after the first reaction.

[0027] Preferably, the solvent used in the first washing step (1) includes ethanol.

[0028] Preferably, the temperature of the first drying step (1) is 90℃-110℃, for example, it can be 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃ or 110℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the drying time in step (1) is 1h-12h, for example, it can be 1h, 2h, 4h, 6h, 8h, 10h or 12h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, in step (1), the mass ratio of the first product, toluene, and the second silane coupling agent is 1:(15-25):(0.004-0.008), for example, it can be 1:15:0.004, 1:15:0.005, 1:15:0.006, 1:15:0.007, 1:15:0.008, 1:20:0.004, 1:20:0.005, 1:20:0.006, 1:20:0.007, 1:20:0.008, 1:25:0.004, 1:25:0.005, 1:25:0.006, 1:25:0.007, or 1:25:0.008, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the temperature of the second reaction in step (1) is 60℃-70℃, for example, it can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃ or 70℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the reaction time in step (1) is 5h-20h, for example, it can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the roasting in step (1) further includes a second washing and a second drying.

[0034] Preferably, the solvent used in the second washing step (1) includes ethanol.

[0035] Preferably, the temperature of the second drying step (1) is 90℃-110℃, for example, it can be 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃ or 110℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the drying time in step (1) is 1h-12h, for example, it can be 1h, 2h, 4h, 6h, 8h, 10h or 12h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the heating rate of the roasting in step (1) is 1℃ / min-5℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the roasting temperature in step (1) is 450℃-550℃, for example, it can be 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃ or 550℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the roasting time in step (1) is 1h-5h, for example, it can be 1h, 2h, 3h, 4h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the palladium source in step (2) includes any one or a combination of at least two of palladium nitrate, palladium sulfate, or palladium acetate, wherein typical but non-limiting combinations include a combination of palladium nitrate and palladium sulfate, a combination of palladium sulfate and palladium acetate, a combination of palladium nitrate and palladium acetate, or a combination of palladium nitrate, palladium sulfate, and palladium acetate.

[0041] Preferably, the alkaline solution in step (2) includes sodium hydroxide and / or potassium hydroxide.

[0042] Preferably, the concentration of the alkaline solution in step (2) is 0.01 mol / L to 0.05 mol / L, for example, it can be 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.035 mol / L, 0.04 mol / L, 0.045 mol / L or 0.05 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, step (2) refers to adjusting the pH of the solution to 7-9, for example, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8 or 9, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] In this invention, the state of the active components on the molecular sieve support is controlled by adjusting the pH. When the pH value exceeds 9, the palladium oxide particles generated by the reaction are too large. The activity of palladium oxide is related to the particle size in a volcano-like manner, which reduces the reaction activity of the catalyst. When the pH value is below 7, the high dispersion of Pd at the acidic sites leads to excessive dispersion and small particle size, which also reduces the methane oxidation activity.

[0045] Preferably, the settling time in step (2) is 4h-10h, for example, it can be 4h, 5h, 6h, 7h, 8h, 9h or 10h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, step (2) includes a third washing and a third drying process before calcination.

[0047] Preferably, the solvent used in the third washing step (2) includes ethanol.

[0048] Preferably, the temperature of the third drying step (2) is 90℃-110℃, for example, it can be 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃ or 110℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the third drying time in step (2) is 1h-12h, for example, it can be 1h, 2h, 4h, 6h, 8h, 10h or 12h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, the heating rate of the calcination in step (2) is 1℃ / min-5℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] Preferably, the calcination temperature in step (2) is 550℃-650℃, for example, it can be 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃ or 650℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, the calcination time in step (2) is 1h-5h, for example, it can be 1h, 2h, 3h, 4h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] Thirdly, the present invention provides an application of the highly stable palladium-based molecular sieve catalyst as described in the first aspect, wherein the highly stable palladium-based molecular sieve catalyst is used to catalyze the combustion of methane.

[0054] The high-stability palladium-based molecular sieve catalyst of this invention is used for catalytic methane combustion. It not only has excellent catalytic activity, but also excellent hydrothermal stability. After a stability test at 410°C for 36 hours, the conversion rate of this high-stability palladium-based molecular sieve catalyst is still as high as 96%, which shows good stability.

[0055] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0056] (1) Mix SSZ-13 molecular sieve, water and ethanol in a mass ratio of 1:(10-20):(2-5), and then add 1,2-bis(triethoxysilyl)ethane, wherein the mass ratio of SSZ-13 molecular sieve to 1,2-bis(triethoxysilyl)ethane is 1:(0.01-0.15). Stir at 60℃-70℃ for 5h-20h for the first reaction, wash with ethanol for the first time, and dry at 90℃-110℃ for 1h-12h to obtain the first product.

[0057] The first product, toluene, and dodecyltrimethoxysilane were mixed at a mass ratio of 1:(15-25):(0.004-0.008), and a second reaction was carried out at 60℃-70℃ for 5h-20h. The mixture was then washed with ethanol, dried at 90℃-110℃ for 1h-12h, and calcined at 450℃-550℃ for 1h-5h to obtain SSZ-13 hydrophobic modified molecular sieve.

[0058] (2) Add SSZ-13 hydrophobic modified molecular sieve to water and sonicate for 10 min-30 min to obtain SSZ-13 hydrophobic modified molecular sieve aqueous solution. Add palladium source dropwise to SSZ-13 hydrophobic modified molecular sieve aqueous solution and stir for 1 h-3 h to obtain a mixture. Add sodium hydroxide solution with a concentration of 0.01 mol / L-0.05 mol / L to adjust the pH to 7-9. Let stand for 4 h-10 h, centrifuge, third wash, and third drying at 90℃-110℃ for 1 h-5 h. Calcinate in air at 550℃-650℃ for 1 h-5 h to obtain the high-stability palladium-based molecular sieve catalyst.

[0059] 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.

[0060] Compared with the prior art, the present invention has at least the following beneficial effects:

[0061] (1) This invention reduces the water adsorption capacity of SSZ-13 molecular sieve by hydrophobically modifying it, thereby reducing the water poisoning deactivation of palladium oxide. The high-stability palladium-based molecular sieve catalyst prepared using SSZ-13 hydrophobically modified molecular sieve as a carrier has a reduced water adsorption capacity, thus avoiding its deactivation under high-temperature hydrothermal conditions.

[0062] (2) The present invention first performs hydrophobic modification on SSZ-13 molecular sieve. The resulting SSZ-13 hydrophobic modified molecular sieve has a low hydroxyl content and contains a large number of organic groups on its surface, thereby greatly improving its hydrophobicity. Then, palladium is loaded onto the molecular sieve by deposition precipitation (DP), which makes the palladium oxide material more uniformly dispersed. At the same time, it can significantly enhance the interaction between palladium oxide and molecular sieve, effectively improving the low-temperature catalytic performance and stability of SSZ-13 molecular sieve catalyst.

[0063] (3) The high-stability palladium-based molecular sieve catalyst provided by the present invention is used to catalyze the combustion of methane. It not only has excellent catalytic activity, but also excellent hydrothermal stability. After a stability test at 410°C for 36 hours, the conversion rate of the high-stability palladium-based molecular sieve catalyst is still as high as 96%. Attached Figure Description

[0064] Figure 1 These are methane combustion conversion graphs of the catalysts in Examples 1-3 and Comparative Examples 1-2 of this invention;

[0065] Figure 2 These are performance test diagrams of the catalysts of Example 1 and Comparative Example 1 of the present invention after hydrothermal aging at 650°C and 750°C for catalytic methane combustion.

[0066] Figure 3 These are test graphs of the methane combustion catalytic stability of the catalysts in Examples 1-3 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0067] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0068] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used are conventional methods and techniques in the art.

[0069] Example 1

[0070] This embodiment provides a highly stable palladium-based molecular sieve catalyst, which includes an SSZ-13 hydrophobically modified molecular sieve support and an active component; the active component is palladium oxide particles. The average particle size D of the palladium oxide particles is 2.8 nm.

[0071] Based on a total mass of 100 wt% for the highly stable palladium-based molecular sieve catalyst, the content of the active component is 1 wt%.

[0072] The preparation method of the highly stable palladium-based molecular sieve catalyst provided in this embodiment includes the following steps:

[0073] (1) SSZ-13 molecular sieve, water and ethanol were mixed in a mass ratio of 1:16:4, and then 1,2-bis(triethoxysilyl)ethane (Aldrich, 16068-37-4) was added. The mass ratio of SSZ-13 molecular sieve to 1,2-bis(triethoxysilyl)ethane was 1:0.03. The reaction was carried out at 60°C for 12 h, followed by a first wash with ethanol and a first drying at 100°C for 10 h to obtain the first product.

[0074] The first product, toluene, and dodecyltrimethoxysilane (Aldrich, 3069-21-4) were mixed at a mass ratio of 1:20:0.006, and a second reaction was carried out at 60°C for 12 h. The mixture was then washed with ethanol, dried at 100°C for 10 h, and finally calcined at 500°C for 2 h to obtain SSZ-13 hydrophobic modified molecular sieve.

[0075] (2) Add SSZ-13 hydrophobic modified molecular sieve to water and sonicate for 20 min to obtain SSZ-13 hydrophobic modified molecular sieve aqueous solution. Add palladium nitrate dropwise to SSZ-13 hydrophobic modified molecular sieve aqueous solution and stir for 2 h to obtain a mixture. Add sodium hydroxide solution with a concentration of 0.025 mol / L to adjust the pH to 8, let stand for 5.5 h, centrifuge, wash for the third time, dry for the third time at 100℃ for 2 h, and calcine at 600℃ in air atmosphere for 3 h to obtain the high-stability palladium-based molecular sieve catalyst.

[0076] The conversion rate of the prepared high-stability palladium-based molecular sieve catalyst is as follows: Figure 1 As shown, from Figure 1 As can be seen, the conversion rate can reach 50% at 384℃, which is significantly better than other embodiments.

[0077] The conversion rate of the prepared high-stability palladium-based molecular sieve catalyst is as follows: Figure 2 As shown, from Figure 2 As can be seen, the catalyst still has good catalytic activity after hydrothermal aging at 650℃ and 750℃, respectively.

[0078] A schematic diagram of the methane combustion catalytic stability test of the prepared high-stability palladium-based molecular sieve catalyst is shown below. Figure 3 As shown, from Figure 3 As can be seen, after catalytic oxidation of methane at 410℃ for 36 hours, the methane conversion rate is still 96%.

[0079] Example 2

[0080] This embodiment provides a highly stable palladium-based molecular sieve catalyst, which includes an SSZ-13 hydrophobically modified molecular sieve support and an active component; the active component is palladium oxide particles. The average particle size D of the palladium oxide particles is 3.4 nm.

[0081] Based on a total mass of 100 wt% for the highly stable palladium-based molecular sieve catalyst, the content of the active component is 0.8 wt%.

[0082] The preparation method of the highly stable palladium-based molecular sieve catalyst provided in this embodiment includes the following steps:

[0083] (1) SSZ-13 molecular sieve, water and ethanol were mixed in a mass ratio of 1:16:4, and then 1,2-bis(triethoxysilyl)ethane (Aldrich, 16068-37-4) was added. The mass ratio of SSZ-13 molecular sieve to 1,2-bis(triethoxysilyl)ethane was 1:0.02. The mixture was stirred at 65°C for 10 h for the first reaction, washed with ethanol for the first time, and dried at 90°C for 12 h to obtain the first product.

[0084] The first product, toluene, and dodecyltrimethoxysilane (Aldrich, 3069-21-4) were mixed at a mass ratio of 1:15:0.004. The mixture was subjected to a second reaction at 65°C for 10 h, followed by a second washing with ethanol, a second drying at 90°C for 12 h, and then calcined at 450°C for 5 h to obtain SSZ-13 hydrophobic modified molecular sieve.

[0085] (2) Add SSZ-13 hydrophobic modified molecular sieve to water and sonicate for 30 min to obtain SSZ-13 hydrophobic modified molecular sieve aqueous solution. Add palladium sulfate dropwise to SSZ-13 hydrophobic modified molecular sieve aqueous solution and stir for 2.5 h to obtain a mixture. Add sodium hydroxide solution with a concentration of 0.03 mol / L to adjust the pH to 7, let stand for 6 h, centrifuge, wash for the third time, dry for the third time at 90℃ for 5 h, and calcine at 550℃ in air atmosphere for 5 h to obtain the high-stability palladium-based molecular sieve catalyst.

[0086] Example 3

[0087] This embodiment provides a highly stable palladium-based molecular sieve catalyst, which includes an SSZ-13 hydrophobically modified molecular sieve support and an active component; the active component is palladium oxide particles. The average particle size D of the palladium oxide particles is 1.5 nm.

[0088] Based on a total mass of 100 wt% for the highly stable palladium-based molecular sieve catalyst, the content of the active component is 0.9 wt%.

[0089] The preparation method of the highly stable palladium-based molecular sieve catalyst provided in this embodiment includes the following steps:

[0090] (1) SSZ-13 molecular sieve, water and ethanol were mixed in a mass ratio of 1:20:5, and then 1,2-bis(trimethoxysilyl)ethane (Aldrich, 16068-37-4) was added. The mass ratio of SSZ-13 molecular sieve to 1,2-bis(triethoxysilyl)ethane was 1:0.05. The mixture was stirred at 70°C for 5 hours for the first reaction, washed with ethanol for the first time, and dried at 110°C for 3 hours to obtain the first product.

[0091] The first product, toluene, and dodecyltrimethoxysilane (Aldrich, 3069-21-4) were mixed in a mass ratio of 1:25:0.008, and a second reaction was carried out at 70°C for 5 h. The mixture was then washed with ethanol, dried at 110°C for 3 h, and calcined at 450°C for 5 h to obtain SSZ-13 hydrophobic modified molecular sieve.

[0092] (2) Add SSZ-13 hydrophobic modified molecular sieve to water and sonicate for 30 min to obtain SSZ-13 hydrophobic modified molecular sieve aqueous solution. Add palladium acetate dropwise to SSZ-13 hydrophobic modified molecular sieve aqueous solution and stir for 3 h to obtain a mixture. Add sodium hydroxide solution with a concentration of 0.045 mol / L to adjust the pH to 8.8, let stand for 4 h, centrifuge, wash for the third time, dry for the third time at 110℃ for 1 h, and calcine at 550℃ in air atmosphere for 5 h to obtain the high-stability palladium-based molecular sieve catalyst.

[0093] Example 4

[0094] This embodiment provides a highly stable palladium-based molecular sieve catalyst. The only difference from Example 1 is that, in preparing this highly stable palladium-based molecular sieve catalyst, the mass ratio of the SSZ-13 molecular sieve and 1,2-bis(triethoxysilyl)ethane in step (1) is 1:0.005.

[0095] Example 5

[0096] This embodiment provides a highly stable palladium-based molecular sieve catalyst. The only difference from Example 1 is that, in preparing this highly stable palladium-based molecular sieve catalyst, the mass ratio of the SSZ-13 molecular sieve and 1,2-bis(triethoxysilyl)ethane in step (1) is 1:0.2.

[0097] Example 6

[0098] This embodiment provides a highly stable palladium-based molecular sieve catalyst. The only difference from Example 1 is that, when preparing this highly stable palladium-based molecular sieve catalyst, the pH adjustment endpoint in step (2) is 6.5.

[0099] Example 7

[0100] This embodiment provides a highly stable palladium-based molecular sieve catalyst. The only difference from Example 1 is that, when preparing the highly stable palladium-based molecular sieve catalyst, the pH adjustment endpoint in step (2) is 9.4.

[0101] Comparative Example 1

[0102] This comparative example provides a palladium-based molecular sieve catalyst. The only difference from Example 1 is that, in preparing this palladium-based molecular sieve catalyst, the hydrophobic modification in step (1) is not performed. Instead, unmodified SSZ-13 molecular sieve is directly used as a support for deposition and precipitation reaction.

[0103] The conversion rate of the prepared high-stability palladium-based molecular sieve catalyst is as follows: Figure 1 As shown, from Figure 1 As can be seen from the above, the catalyst prepared by the unhydrophobically modified molecular sieve has little effect on the methane oxidation activity.

[0104] The conversion rate of the prepared high-stability palladium-based molecular sieve catalyst is as follows: Figure 2 As shown, from Figure 2 As can be seen, the catalytic activity of the catalyst decreased significantly after hydrothermal aging at 650℃ and 750℃, respectively. When the catalyst prepared by hydrophobically modified molecular sieve was hydrothermally aged, its activity was significantly better than that of the catalyst prepared by unmodified molecular sieve. In particular, after hydrothermal aging at 750℃, the methane conversion rate was still 90% at 522℃.

[0105] A schematic diagram of the methane combustion catalytic stability test of the prepared high-stability palladium-based molecular sieve catalyst is shown below. Figure 3 As shown, from Figure 3 As can be seen, the activity of the catalyst prepared by the unmodified molecular sieve decreased significantly in the long-term stability test at 410℃.

[0106] Comparative Example 2

[0107] This comparative example provides a palladium-based molecular sieve catalyst, which differs from Example 1 only in that, in preparing this palladium-based molecular sieve catalyst, step (2) uses an impregnation method to load the active component. The specific operation method is as follows:

[0108] The SSZ-13 hydrophobic modified molecular sieve obtained in step (1) was impregnated with palladium source dropwise, stirred at room temperature for 1 h, dried at 60°C by rotary evaporation at 100°C, calcined at 600°C for 3 h with a heating rate of 2°C / min, and then filtered, dried and calcined at high temperature in a hydrogen environment to obtain palladium-based catalyst.

[0109] Comparative Example 3

[0110] This comparative example provides a palladium-based catalyst, which differs from Example 1 only in that, in the preparation of this palladium-based catalyst, the SSZ-13 molecular sieve is replaced with an equal amount of natural zeolite in step (1).

[0111] Comparative Example 4

[0112] This comparative example provides a palladium-based molecular sieve catalyst, which differs from Example 1 only in that the content of the active component is 0.1 wt% when preparing the palladium-based molecular sieve catalyst.

[0113] Test method:

[0114] I. Determination of Methane Conversion: 0.1 g of the catalysts prepared in Examples 1-7 and Comparative Examples 1-4 were used as raw materials, with dry methane gas containing 1000 ppm methane, 10% water, 3.5% oxygen, and nitrogen as the balance gas. The total gas flow rate was 300 mL / min, and the mass hourly space velocity (WHSV) was 180,000 mL / h / g. The reaction was carried out in a continuous flow micro-fixed bed reactor. The change in methane concentration in the tail gas was determined by gas chromatography. The temperatures at conversion rates of 10%, 50%, and 90% were recorded.

[0115] II. Hydrothermal Aging Test: (1) 0.3 g of the molecular sieve catalyst prepared in Example 1 and Comparative Example 1 was hydrothermally aged at 650℃ for 16 h under the following conditions: water content 10%, oxygen content 3.5%, nitrogen as the balance gas, total gas flow rate 500 mL / min, and mass hourly space velocity (WHSV) = 100,000 mL / h / g. The catalyst was then used in the catalytic purification process of methane, using natural gas vehicle exhaust gas as the methane feedstock. The methane concentration was 1000 ppm, water content 10%, oxygen content 3.5%, nitrogen as the balance gas, total gas flow rate 300 mL / min, and WHSV = 180,000 mL / h / g. The reaction was carried out in a continuous flow micro-fixed bed. The change in methane concentration in the exhaust gas was determined by gas chromatography. The temperatures at conversion rates of 10%, 50%, and 90% were recorded.

[0116] (2) 0.3 g of the molecular sieve catalyst prepared in Example 1 and Comparative Example 1 was subjected to hydrothermal aging at 750 °C for 16 h under the following conditions: water content 10%, oxygen content 3.5%, nitrogen as the balance gas, total gas flow rate 500 mL / min, and mass hourly space velocity (WHSV) = 100,000 mL / h / g. This catalyst was then used in the catalytic purification process of methane, using natural gas vehicle exhaust gas as the methane feedstock. The methane concentration was 1000 ppm, the water content was 10%, the oxygen content was 3.5%, nitrogen was the balance gas, the total gas flow rate was 300 mL / min, and the WHSV was 180,000 mL / h / g. The reaction was carried out in a continuous flow micro-fixed bed reactor. The methane concentration change in the exhaust gas was determined by gas chromatography. The temperatures at conversion rates of 10%, 50%, and 90% were recorded.

[0117] III. Stability Test: The molecular sieve catalysts prepared in Examples 1-7 and Comparative Examples 1-4 were subjected to long-term methane catalytic oxidation at 410℃. The test conditions were as follows: natural gas vehicle exhaust gas was used as the raw material for methane, with a methane concentration of 1000 ppm, a water content of 10%, an oxygen content of 3.5%, nitrogen as the balance gas, a total gas flow rate of 300 mL / min, and a mass hourly space velocity (WHSV) of 180,000 mL / h / g. The long-term catalytic stability of the catalysts was tested.

[0118] Table 1

[0119]

[0120]

[0121] The test results show that:

[0122] (1) As can be seen from Examples 1-3, the present invention uses hydrophobic modification of SSZ-13 molecular sieve as a catalyst support to prepare a catalyst, thereby reducing the water adsorption capacity of the palladium-based molecular sieve catalyst, thus reducing the water poisoning deactivation of palladium oxide and avoiding its deactivation under high-temperature hydrothermal conditions. The high-stability palladium-based molecular sieve catalyst prepared still has a conversion rate of up to 96% after a stability test at 410℃ for 36 hours. Under the simulated natural gas vehicle exhaust atmosphere, the high-stability palladium-based molecular sieve catalyst can still achieve a conversion rate of 90% at 522℃ after hydrothermal aging at 750℃ for 16 hours, while the catalyst prepared by the unmodified molecular sieve only has a conversion rate of 50% at 596℃ after hydrothermal aging at 750℃ for 16 hours.

[0123] (2) By comparing Example 1 with Examples 4-5, it can be seen that the present invention further controls the mass ratio of SSZ-13 molecular sieve and the first silane coupling agent to 1:(0.01-0.15) to ensure that the hydrothermal aging ability of the molecular sieve catalyst after palladium loading is stronger. If the mass ratio of SSZ-13 molecular sieve and the first silane coupling agent is too large, the removal of hydroxyl groups on the surface of the molecular sieve support will be too small, that is, the amount of the first silane coupling agent added will be too small, which will lead to the insignificant hydrophobicity of the molecular sieve and the poor hydrothermal aging ability of the molecular sieve catalyst, thus reducing the long-term stability of the catalyst. If the mass ratio of SSZ-13 molecular sieve and the first silane coupling agent is too small, that is, the amount of the first silane coupling agent added will be too large, which will lead to the blockage of the molecular sieve pores, affecting the mass transport in the reaction process and reducing its catalytic efficiency.

[0124] (3) By comparing Example 1 with Example 6-7, it can be seen that the present invention controls the state of the active components on the molecular sieve support by further adjusting the pH. When the pH value exceeds 9, the palladium oxide particles generated by the reaction are too large. The activity of palladium oxide and the particle size follow a volcano-like pattern, thus reducing the reaction activity of the catalyst. When the pH value is below 7, the high dispersion of Pd at the acidic sites leads to excessive dispersion and small particle size, and its methane oxidation activity decreases accordingly.

[0125] (4) As can be seen from Example 1 and Comparative Example 1, if the molecular sieve support is not hydrophobically modified, the hydrothermal stability of its methane oxidation catalyst is significantly reduced.

[0126] (5) As can be seen from Example 1 and Comparative Example 2, the present invention uses the deposition precipitation method (DP) to load palladium onto the molecular sieve, resulting in a more uniform dispersion of palladium oxide. At the same time, it can significantly enhance the interaction between palladium oxide and the molecular sieve, effectively improving the low-temperature catalytic performance of the SSZ-13 molecular sieve catalyst. However, when the palladium source is loaded onto the molecular sieve support using the traditional impregnation method instead of the deposition precipitation method, its catalytic activity is far inferior to that of the present invention. Furthermore, the catalyst prepared by the impregnation method contains Pd, which has no catalytic effect in the methane oxidation process. Secondly, it is impossible to achieve a high degree of dispersion of palladium oxide, resulting in a significant reduction in active sites. Finally, the interaction between palladium oxide and the molecular sieve is weakened, making it prone to agglomeration and deactivation in high-temperature and high-humidity environments.

[0127] (6) As can be seen from Example 1 and Comparative Example 3, the palladium-based molecular sieve catalyst prepared by the present invention by selecting a specific ZZS-13 molecular sieve support and combining hydrophobic modification treatment has higher activity in catalytic oxidation of methane. However, if only traditional natural zeolite is used for the same hydrophobic modification, its catalytic activity is far lower than that of the present invention when used as a catalyst support, and its stability is also not as good as that of the present invention.

[0128] (7) As can be seen from Example 1 and Comparative Example 4, when the content of active component is too low, the activity of the catalyst is greatly reduced.

[0129] In summary, this invention reduces the water adsorption capacity of SSZ-13 molecular sieve by hydrophobically modifying it, thereby minimizing the water poisoning deactivation of palladium oxide. The palladium-based molecular sieve catalyst prepared using SSZ-13 hydrophobically modified molecular sieve as a carrier exhibits reduced water adsorption capacity, preventing deactivation under high-temperature hydrothermal conditions. This highly stable palladium-based molecular sieve catalyst maintains a conversion rate of 96% after a 36-hour stability test at 410℃.

[0130] 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 highly stable palladium-based molecular sieve catalyst, characterized in that, The highly stable palladium-based molecular sieve catalyst comprises SSZ-13 hydrophobically modified molecular sieve and an active component supported on SSZ-13 hydrophobically modified molecular sieve. The active component includes palladium oxide particles; Based on a total mass of 100 wt% for the highly stable palladium-based molecular sieve catalyst, the content of the active component in the highly stable palladium-based molecular sieve catalyst is 0.5 wt%-5 wt%. The preparation method includes the following steps: (1) Mix SSZ-13 molecular sieve, water, ethanol and first silane coupling agent, and obtain the first product through the first reaction; mix the first product, toluene and second silane coupling agent, and then calcine after the second reaction to obtain SSZ-13 hydrophobic modified molecular sieve; (2) Mix the palladium source with the aqueous solution of SSZ-13 hydrophobic modified molecular sieve, stir to obtain a mixture, add alkaline solution, adjust the pH, let stand, and obtain the high-stability palladium-based molecular sieve catalyst by solid-liquid separation and calcination; The roasting temperature in step (1) is 450℃-550℃; The mass ratio of the SSZ-13 molecular sieve and the first silane coupling agent in step (1) is 1:(0.02-0.03); The alkaline solution in step (2) is a sodium hydroxide solution and / or a potassium hydroxide solution, with the pH adjusted to 7-9; The calcination temperature in step (2) is 550℃-650℃; Step (1) The first silane coupling agent comprises 1,2-bis(triethoxysilyl)ethane and / or 1,2-bis(trimethoxysilyl)ethane; Step (1) The second silane coupling agent includes any one or a combination of at least two of dodecyltrimethoxysilane, mercaptopropyltrimethoxysilane or methylphenyldimethoxysilane.

2. The preparation method according to claim 1, characterized in that, The average particle size D of the palladium oxide particles is 0.5 nm to 5 nm.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of SSZ-13 molecular sieve, water, and ethanol is 1:(10-20):(2-5).

4. The preparation method according to claim 1, characterized in that, Step (1) The temperature of the first reaction is 60℃-70℃.

5. The preparation method according to claim 1, characterized in that, Step (1) The time for the first reaction is 5h-20h.

6. The preparation method according to claim 1, characterized in that, Step (1) includes a first washing and a first drying after the first reaction.

7. The preparation method according to claim 6, characterized in that, Step (1) The solvent used in the first washing includes ethanol.

8. The preparation method according to claim 6, characterized in that, Step (1) The temperature of the first drying is 90℃-110℃.

9. The preparation method according to claim 6, characterized in that, Step (1) The first drying time is 1h-12h.

10. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the first product, toluene, and the second silane coupling agent is 1:(15-25):(0.004-0.008).

11. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the second reaction is 60℃-70℃.

12. The preparation method according to claim 1, characterized in that, In step (1), the second reaction takes 1-5 hours.

13. The preparation method according to claim 1, characterized in that, Step (1) includes a second washing and a second drying before roasting.

14. The preparation method according to claim 13, characterized in that, Step (1) The solvent used in the second washing includes ethanol.

15. The preparation method according to claim 14, characterized in that, Step (1) The second drying temperature is 90℃-110℃.

16. The preparation method according to claim 14, characterized in that, Step (1) The second drying time is 1h-12h.

17. The preparation method according to claim 1, characterized in that, The heating rate of the roasting in step (1) is 1℃ / min-5℃ / min.

18. The preparation method according to claim 1, characterized in that, The roasting time in step (1) is 1-5 hours.

19. The preparation method according to claim 1, characterized in that, The palladium source in step (2) includes any one or a combination of at least two of palladium nitrate, palladium sulfate, or palladium acetate.

20. The preparation method according to claim 1, characterized in that, The concentration of the alkaline solution in step (2) is 0.01 mol / L-0.05 mol / L.

21. The preparation method according to claim 1, characterized in that, The settling time in step (2) is 4h-10h.

22. The preparation method according to claim 1, characterized in that, Step (2) includes a third washing and a third drying process before calcination.

23. The preparation method according to claim 22, characterized in that, The solvent used in the third wash in step (2) includes ethanol.

24. The preparation method according to claim 22, characterized in that, The temperature for the third drying step (2) is 90℃-110℃.

25. The preparation method according to claim 22, characterized in that, The third drying time in step (2) is 1-12 hours.

26. The preparation method according to claim 1, characterized in that, The heating rate of calcination in step (2) is 1℃ / min-5℃ / min.

27. The preparation method according to claim 1, characterized in that, The calcination time in step (2) is 1-5 hours.

28. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix SSZ-13 molecular sieve, water and ethanol in a mass ratio of 1:(10-20):(2-5), and then add 1,2-bis(triethoxysilyl)ethane, wherein the mass ratio of SSZ-13 molecular sieve to 1,2-bis(triethoxysilyl)ethane is 1:(0.02-0.03). Stir at 60℃-70℃ for 5h-20h for the first reaction, wash with ethanol for the first time, and dry at 90℃-110℃ for 1h-12h to obtain the first product; The first product, toluene, and dodecyltrimethoxysilane were mixed at a mass ratio of 1:(15-25):(0.004-0.008), and a second reaction was carried out at 60℃-70℃ for 5h-20h. The mixture was then washed with ethanol, dried at 90℃-110℃ for 1h-12h, and calcined at 450℃-550℃ for 1h-5h to obtain SSZ-13 hydrophobic modified molecular sieve. (2) Add SSZ-13 hydrophobic modified molecular sieve to water and sonicate for 10 min-30 min to obtain SSZ-13 hydrophobic modified molecular sieve aqueous solution. Add palladium source dropwise to SSZ-13 hydrophobic modified molecular sieve aqueous solution and stir for 1 h-3 h to obtain a mixture. Add sodium hydroxide solution with a concentration of 0.01 mol / L-0.05 mol / L to adjust pH to 7-9, let stand for 4 h-10 h, centrifuge, third wash, third drying at 90℃-110℃ for 1 h-5 h, and calcine at 550℃-650℃ in air atmosphere for 1 h-5 h to obtain the high-stability palladium-based molecular sieve catalyst.

29. The application of a highly stable palladium-based molecular sieve catalyst prepared by the preparation method according to any one of claims 1-28, characterized in that, The highly stable palladium-based molecular sieve catalyst is used to catalyze the combustion of methane.

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