High-stability palladium-based molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention relates to a high-stability palladium-based molecular sieve catalyst as well as a preparation method and application thereof. The high-stability palladium-based molecular sieve catalyst comprises an SSZ-13 hydrophobic modified molecular sieve and an active component loaded on the SSZ-13 hydrophobic modified molecular sieve, the active component comprises palladium oxide particles; based on 100 wt% of the total mass of the high-stability palladium-based molecular sieve catalyst, the content of the active component in the high-stability palladium-based molecular sieve catalyst is 0.5 wt%-5 wt%. According to the high-stability palladium-based molecular sieve catalyst, an SSZ-13 hydrophobic modified molecular sieve is used as a carrier, so that the adsorption capacity of the catalyst to water is weakened, the purpose of reducing water poisoning inactivation of palladium oxide substances is achieved, inactivation of the palladium oxide substances under the high-temperature hydrothermal condition is avoided, and the methane catalytic oxidation activity, the hydrothermal aging performance and the stability of the catalyst are obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of methane catalytic combustion, and in particular to a high-stability palladium-based molecular sieve catalyst and a preparation method and application thereof. Background Art

[0002] Global warming and air pollution are becoming increasingly serious problems, causing great harm to people's production and life. Among traditional energy sources, natural gas consumption is second only to oil and coal, and is widely used in industrial production and mobile energy fields. The main component of natural gas is methane, which is the world's second largest greenhouse gas after carbon dioxide. Therefore, when using natural gas, it is also necessary to ensure the treatment of incompletely burned methane. The treatment of methane can generally be divided into direct combustion and catalytic combustion. If the traditional direct combustion method is used, the combustion temperature will exceed 1500°C, producing carbon monoxide (CO) and other hydrocarbons (HC x ), NO x In contrast, the catalytic combustion method can often achieve complete oxidation of methane at a lower temperature (300℃~800℃), which is safer and more environmentally friendly. Therefore, designing and preparing efficient and stable methane oxidation catalysts is one of the effective ways to solve the methane emissions in exhaust gas.

[0003] Methane oxidation catalysts can be mainly divided 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 temperature of natural gas vehicles is usually up to 550°C, and the methane concentration is low, about 500-1000ppm, and it also contains a large amount of water vapor, about 15%. Under the 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 , resulting in severe sintering and deactivation of the catalyst. Most studies tend to focus on achieving the lowest possible ignition temperature under dry conditions, while ignoring the problem of steam-induced sintering and deactivation.

[0004] Therefore, how to develop a palladium-based catalyst material and a preparation method thereof that can maintain high activity and high stability under harsh conditions of high vapor concentration has become a problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a high-stability palladium-based molecular sieve catalyst and its preparation method and application. The high-stability palladium-based molecular sieve catalyst uses SSZ-13 hydrophobically modified molecular sieve as a carrier to weaken the catalyst's adsorption capacity for water, thereby achieving the purpose of reducing the water poisoning and deactivation of palladium oxide substances, avoiding its deactivation under high-temperature hydrothermal conditions, and significantly improving the hydrothermal stability of its methane oxidation catalyst.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a high-stability palladium-based molecular sieve catalyst, wherein the high-stability palladium-based molecular sieve catalyst comprises 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] Taking the total mass of the high stability palladium-based molecular sieve catalyst as 100wt%, the content of active components in the high stability palladium-based molecular sieve catalyst is 0.5wt%-5wt%, for example, it can be 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0009] SSZ-13 molecular sieve has a rule that its hydrophobicity increases with the increase of silicon-aluminum ratio, but in actual synthesis, high silicon-aluminum ratio synthesis is difficult and costly. The present invention reduces the water poisoning and inactivation of palladium oxide substances by hydrophobically modifying SSZ-13 molecular sieve. The palladium-based molecular sieve catalyst prepared with hydrophobically modified molecular sieve as carrier has a weakened adsorption capacity for water, which avoids its inactivation under high-temperature hydrothermal conditions, not only improves the hydrothermal aging stability of the palladium-based molecular sieve catalyst, but also the high-stability palladium-based molecular sieve catalyst has a conversion rate of up to 96% after a 36-hour stability test at 410°C, which greatly improves the stability of the catalyst.

[0010] The active component of the high-stability palladium-based molecular sieve catalyst provided by the present invention is palladium oxide, and the active component of this composition 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. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

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

[0013] The present invention further controls the average particle size D of the palladium oxide particles to be 0.5nm-5nm, and the activity of the palladium oxide material and the average particle size are in a volcano-shaped pattern. Due to the difference in the metal-carrier interaction strength, the molecular sieve carrier state will affect the shape of the Pd particles. PdO crystal faces and active sites with different activities can be formed by controlling the size of the Pd particles. If the average particle size of the palladium oxide is too large, the reaction activity of the catalyst is reduced. If the average particle size of the 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 the high-stability palladium-based molecular sieve catalyst as described in the first aspect, the preparation method comprising the following steps:

[0015] (1) mixing SSZ-13 molecular sieve, water, ethanol and a first silane coupling agent, and obtaining a first product through a first reaction; mixing the first product, toluene and a second silane coupling agent, and then calcining to obtain a SSZ-13 hydrophobically modified molecular sieve after a second reaction;

[0016] (2) mixing a palladium source and an aqueous solution of a SSZ-13 hydrophobically modified molecular sieve, stirring to obtain a mixture, adding an alkali solution, adjusting the pH, standing, and obtaining the high-stability palladium-based molecular sieve catalyst through solid-liquid separation and calcination.

[0017] The invention firstly performs hydrophobic modification treatment on the SSZ-13 molecular sieve, firstly reacts 6 hydroxyl groups formed by hydrolysis of a first silane coupling agent with hydroxyl groups on the surface of the SSZ-13 molecular sieve, thereby forming a large number of hydroxyl groups on the surface of the SSZ-13 molecular sieve, and then reacts with hydroxyl groups formed by hydrolysis of a second silane coupling agent, thereby introducing organic hydrophobic chain groups on the surface of the SSZ-13 molecular sieve to the maximum extent. The synthesis method is simple and the conditions are easy to control. The surface hydroxyl content of the obtained modified SSZ-13 molecular sieve is low and the surface contains a large number of organic groups, thereby greatly improving the hydrophobicity of the modified SSZ-13 molecular sieve and weakening the water adsorption capacity of the modified SSZ-13 molecular sieve, thereby achieving the purpose of reducing the water poisoning and inactivation of palladium oxide substances.

[0018] Then, the palladium oxide is loaded on the molecular sieve by the deposition precipitation method (DP), and the palladium oxide material is dispersed more evenly. At the same time, the interaction between the palladium oxide and the SSZ-13 hydrophobically modified molecular sieve can be significantly enhanced, and the low-temperature catalytic performance and stability of the palladium-based molecular sieve catalyst can be effectively improved. The operation is simple and controllable, and no high-temperature activation treatment is required, which is more energy-saving. At the same time, compared with the catalyst prepared by the traditional impregnation method, the active palladium oxide material in the method of the present invention is easy to form and has a high content; the active palladium oxide material has a high dispersion; most of the active palladium oxide materials are in regular spherical shapes attached to the surface of the molecular sieve to expose more active sites.

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

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

[0021] Preferably, the mass ratio of the SSZ-13 molecular sieve and the 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, and other unlisted values ​​within the numerical range are also applicable, preferably 1:(0.02-0.05).

[0022] In the present invention, the mass ratio of the SSZ-13 molecular sieve and the first silane coupling agent is further optimized to be 1:(0.01-0.05) to ensure that the hydrothermal aging ability of the molecular sieve catalyst after subsequent palladium element loading is stronger. If the mass ratio of the SSZ-13 molecular sieve and the first silane coupling agent is too large, that is, the amount of the first silane coupling agent added is too small, and the hydroxyl groups on the surface of the molecular sieve carrier are too few, the hydrophobic performance of the molecular sieve is not obvious, the hydrothermal aging ability of the molecular sieve catalyst is poor, and the long-term stability of the catalyst is reduced; if the mass ratio of the SSZ-13 molecular sieve and the first silane coupling agent is too small, that is, the amount of the first silane coupling agent added is too large, the molecular sieve pores will be blocked, the material transmission in the reaction process will be affected, and the catalytic efficiency will be reduced.

[0023] Preferably, the mass ratio of the 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, and other values ​​not listed within the numerical range are also applicable.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0039] Preferably, the calcination time in step (1) is 1 h-5 h, for example, 1 h, 2 h, 3 h, 4 h or 5 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the palladium source in step (2) comprises any one of palladium nitrate, palladium sulfate or palladium acetate, or a combination of at least two thereof, 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, and a combination of palladium nitrate, palladium sulfate and palladium acetate.

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

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

[0043] Preferably, the pH adjustment in 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, and other values ​​not listed within the numerical range are also applicable.

[0044] In the present invention, the state of the active components on the molecular sieve carrier is controlled by adjusting the pH. When the pH value exceeds 9, the particle size of the palladium oxide generated by the reaction is too large, and the activity of the palladium oxide substance and the particle size show a volcano-shaped law, thereby reducing the reaction activity of the catalyst. When the pH value is lower than 7, the high dispersion of the Pd substance by the acidic sites leads to its excessive dispersion and too small particle size, and its methane oxidation activity also decreases accordingly.

[0045] Preferably, the standing time in step (2) is 4 h-10 h, for example, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

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

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

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

[0050] Preferably, the heating rate of the calcination in step (2) is 1°C / min-5°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min or 5°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

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

[0053] In a third aspect, the present invention provides a use of the high-stability palladium-based molecular sieve catalyst as described in the first aspect, wherein the high-stability palladium-based molecular sieve catalyst is used to catalyze methane combustion.

[0054] The high-stability palladium-based molecular sieve catalyst of the present invention is used for catalyzing methane combustion, and has not only excellent catalytic activity but also excellent hydrothermal stability. The high-stability palladium-based molecular sieve catalyst has a conversion rate of up to 96% after a 36-hour stability test at 410°C, and has good stability.

[0055] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0056] (1) mixing SSZ-13 molecular sieve, water and ethanol in a mass ratio of 1:(10-20):(2-5), adding 1,2-bis(triethoxysilyl)ethane, wherein the mass ratio of the SSZ-13 molecular sieve to the 1,2-bis(triethoxysilyl)ethane is 1:(0.01-0.15), stirring at 60° C.-70° C. for a first reaction for 5 h-20 h, performing a first washing with ethanol, and performing a first drying at 90° C.-110° C. for 1 h-12 h to obtain a first product;

[0057] The first product, toluene and dodecyltrimethoxysilane are mixed in a mass ratio of 1:(15-25):(0.004-0.008), a second reaction is carried out at 60°C-70°C for 5h-20h, a second washing is carried out with ethanol, a second drying is carried out at 90°C-110°C for 1h-12h, and then a calcination is carried out at 450°C-550°C for 1h-5h to obtain a SSZ-13 hydrophobically modified molecular sieve;

[0058] (2) Add SSZ-13 hydrophobically modified molecular sieve into water, and ultrasonically treat for 10 min-30 min to obtain an SSZ-13 hydrophobically modified molecular sieve aqueous solution, add a palladium source dropwise into the SSZ-13 hydrophobically modified molecular sieve aqueous solution, and stir for 1 h-3 h to obtain a mixture, add a sodium hydroxide solution with a concentration of 0.01 mol / L-0.05 mol / L to adjust the pH to 7-9, and let stand for 4 h-10 h. Centrifuge, perform a third washing, perform a third drying at 90°C-110°C for 1 h-5 h, and calcine at 550°C-650°C in an air atmosphere for 1 h-5 h to obtain the high stability palladium-based molecular sieve catalyst.

[0059] 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.

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

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

[0062] (2) The present invention firstly performs a hydrophobic modification on the SSZ-13 molecular sieve, and the obtained SSZ-13 hydrophobically modified molecular sieve has a low surface hydroxyl content and contains a large number of organic groups on the surface, thereby greatly improving its hydrophobicity. Then, the palladium element is loaded on the molecular sieve by the deposition precipitation method (DP), and the palladium oxide substance is dispersed more evenly. At the same time, the interaction between the palladium oxide and the molecular sieve can be significantly enhanced, and the low-temperature catalytic performance and stability of the SSZ-13 molecular sieve catalyst are effectively improved.

[0063] (3) The high-stability palladium-based molecular sieve catalyst provided by the present invention is used to catalyze methane combustion, and not only has excellent catalytic activity, but also has excellent hydrothermal stability. The high-stability palladium-based molecular sieve catalyst has a conversion rate of up to 96% after a 36-hour stability test at 410°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 Graph showing the methane combustion conversion rate of the catalysts of Examples 1-3 of the present invention and Comparative Examples 1-2;

[0065] Figure 2 It is a performance test diagram of catalytic methane combustion of the catalysts of Example 1 of the present invention and Comparative Example 1 after hydrothermal aging at 650° C. and 750° C.;

[0066] Figure 3 It is a test chart of the catalytic stability of methane combustion of the catalysts of Examples 1-3 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0067] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only 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 shall be subject to the claims.

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

[0069] Example 1

[0070] This embodiment provides a high-stability palladium-based molecular sieve catalyst, which includes a SSZ-13 hydrophobically modified molecular sieve carrier 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 the total mass of the high-stability palladium-based molecular sieve catalyst being 100wt%, the content of the active component is 1wt%.

[0072] The preparation method of the high stability palladium-based molecular sieve catalyst provided in this embodiment comprises the following steps:

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

[0074] The first product, toluene and dodecyltrimethoxysilane (Aldrich, 3069-21-4) were mixed in a mass ratio of 1:20:0.006, and the mixture was reacted for a second time at 60°C for 12 hours, washed with ethanol for a second time, dried for a second time at 100°C for 10 hours, and then calcined at 500°C for 2 hours to obtain a SSZ-13 hydrophobically modified molecular sieve;

[0075] (2) Add SSZ-13 hydrophobically modified molecular sieve into water, ultrasonically treat for 20 minutes to obtain an SSZ-13 hydrophobically modified molecular sieve aqueous solution, add palladium nitrate dropwise into the SSZ-13 hydrophobically modified molecular sieve aqueous solution, stir for 2 hours to obtain a mixture, add a sodium hydroxide solution with a concentration of 0.025 mol / L to adjust the pH to 8, let stand for 5.5 hours, centrifuge, perform a third washing, perform a third drying at 100° C. for 2 hours, and calcine at 600° C. in an air atmosphere for 3 hours 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 It can be seen that the conversion rate can reach 50% at 384°C, 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 It can be seen that the catalyst still has good catalytic activity after hydrothermal aging at 650℃ and 750℃ respectively.

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

[0079] Example 2

[0080] This embodiment provides a high-stability palladium-based molecular sieve catalyst, which includes a SSZ-13 hydrophobically modified molecular sieve carrier 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 the total mass of the high-stability palladium-based molecular sieve catalyst being 100 wt%, the content of the active component is 0.8 wt%.

[0082] The preparation method of the high stability palladium-based molecular sieve catalyst provided in this embodiment comprises the following steps:

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

[0084] The first product, toluene and dodecyltrimethoxysilane (Aldrich, 3069-21-4) were mixed in a mass ratio of 1:15:0.004, reacted for a second time at 65°C for 10 hours, washed with ethanol for a second time, dried for a second time at 90°C for 12 hours, and then calcined at 450°C for 5 hours to obtain SSZ-13 hydrophobically modified molecular sieve;

[0085] (2) Add SSZ-13 hydrophobically modified molecular sieve into water, ultrasonically treat for 30 minutes to obtain an SSZ-13 hydrophobically modified molecular sieve aqueous solution, add palladium sulfate dropwise into the SSZ-13 hydrophobically modified molecular sieve aqueous solution, stir for 2.5 hours to obtain a mixture, add a 0.03 mol / L sodium hydroxide solution to adjust the pH to 7, let stand for 6 hours, centrifuge, perform a third washing, perform a third drying at 90° C. for 5 hours, and calcine at 550° C. in an air atmosphere for 5 hours to obtain the high stability palladium-based molecular sieve catalyst.

[0086] Example 3

[0087] This embodiment provides a high-stability palladium-based molecular sieve catalyst, which includes a SSZ-13 hydrophobically modified molecular sieve carrier 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 the total mass of the high-stability palladium-based molecular sieve catalyst being 100 wt%, the content of the active component is 0.9 wt%.

[0089] The preparation method of the high stability palladium-based molecular sieve catalyst provided in this embodiment comprises the following steps:

[0090] (1) SSZ-13 molecular sieve, water and ethanol were mixed in a mass ratio of 1:20:5, and 1,2-bis(trimethoxysilyl)ethane (Aldrich, 16068-37-4) was added, wherein the mass ratio of the SSZ-13 molecular sieve to 1,2-bis(triethoxysilyl)ethane was 1:0.05, and the mixture was stirred at 70° C. for a first reaction for 5 h, and ethanol was used for a first washing, and the mixture was first dried at 110° C. for 3 h to obtain a 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 the mixture was subjected to a second reaction at 70°C for 5 hours, followed by a second washing with ethanol, a second drying at 110°C for 3 hours, and then calcined at 450°C for 5 hours to obtain a SSZ-13 hydrophobically modified molecular sieve;

[0092] (2) Add SSZ-13 hydrophobically modified molecular sieve into water, ultrasonically treat for 30 minutes to obtain an SSZ-13 hydrophobically modified molecular sieve aqueous solution, add palladium acetate dropwise into the SSZ-13 hydrophobically modified molecular sieve aqueous solution, stir for 3 hours to obtain a mixture, add a sodium hydroxide solution with a concentration of 0.045 mol / L to adjust the pH to 8.8, let stand for 4 hours, centrifuge, perform a third washing, perform a third drying at 110° C. for 1 hour, and calcine at 550° C. in an air atmosphere for 5 hours to obtain the high stability palladium-based molecular sieve catalyst.

[0093] Example 4

[0094] This embodiment provides a high-stability palladium-based molecular sieve catalyst, which is different from Example 1 only in that when preparing the high-stability 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 high-stability palladium-based molecular sieve catalyst, which is different from Example 1 only in that when preparing the high-stability 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 high-stability palladium-based molecular sieve catalyst, which is different from Embodiment 1 only in that, when preparing the high-stability palladium-based molecular sieve catalyst, the end point of the pH adjustment in step (2) is 6.5.

[0099] Example 7

[0100] This embodiment provides a high-stability palladium-based molecular sieve catalyst, which is different from Embodiment 1 only in that, when preparing the high-stability palladium-based molecular sieve catalyst, the end point of the pH adjustment in step (2) is 9.4.

[0101] Comparative Example 1

[0102] This comparative example provides a palladium-based molecular sieve catalyst, which is different from Example 1 only in that when preparing the palladium-based molecular sieve catalyst, the hydrophobic modification of step (1) is not performed, but the unmodified SSZ-13 molecular sieve is directly used as a carrier for the deposition 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 It can be seen that the catalyst prepared by non-hydrophobic modified molecular sieve has little effect on 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 It can be seen that the catalytic activity of the catalyst is greatly reduced after hydrothermal aging at 650°C and 750°C, respectively. When the catalyst is prepared using a hydrophobic modified molecular sieve and subjected to hydrothermal aging, the activity is significantly better than that of the catalyst prepared using an unmodified molecular sieve, especially after hydrothermal aging at 750°C, there is still a 90% methane conversion rate at 522°C.

[0105] The schematic diagram of the methane combustion catalytic stability test of the prepared high-stability palladium-based molecular sieve catalyst is as follows Figure 3 As shown, from Figure 3 It can be seen that the activity of the catalyst prepared by unmodified molecular sieve is significantly reduced in the long-term stability test at 410°C.

[0106] Comparative Example 2

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

[0108] A palladium source is added dropwise to the SSZ-13 hydrophobically modified molecular sieve aqueous solution obtained in step (1) for impregnation, stirred at room temperature for 1 hour, dried by rotary evaporation at 60°C and then at 100°C, calcined at 600°C for 3 hours at a heating rate of 2°C / min, and then filtered, dried and calcined at high temperature in a hydrogen environment to obtain a palladium-based catalyst.

[0109] Comparative Example 3

[0110] This comparative example provides a palladium-based catalyst, which is different from Example 1 only in that, when preparing the palladium-based catalyst, the SSZ-13 molecular sieve is replaced by 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 is different 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] 1. Determination of methane conversion rate: 0.1 g of the catalyst prepared in Examples 1-7 and Comparative Examples 1-4 were used respectively, and dry methane gas was used as raw material, wherein the concentration of methane was 1000 ppm, the water content was 10%, the oxygen content was 3.5%, nitrogen was used as the balance gas, the total gas flow rate was 300 mL / min, and the mass space velocity was WHSV=180,000 mL / h / g, and the reaction was carried out on a continuous flow micro fixed bed, and the concentration change of methane in the tail gas was determined by gas chromatography. The temperature when the conversion rate was 10%, 50%, and 90% was recorded.

[0115] 2. 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°C for 16 h under the conditions of 10% water content, 3.5% oxygen content, nitrogen as balance gas, 500 mL / min total gas flow rate, and WHSV=100,000 mL / h / g. The catalyst was then used in the catalytic purification of methane. The raw material of methane was natural gas automobile exhaust gas, wherein the methane concentration was 1000 ppm, the water content was 10%, the oxygen content was 3.5%, nitrogen was balance gas, the total gas flow rate was 300 mL / min, and the mass space velocity was WHSV=180,000 mL / h / g. The reaction was carried out on a continuous flow micro fixed bed. The concentration change of methane in the exhaust gas was determined by gas chromatography. The temperature at which the conversion rate was 10%, 50%, and 90% was recorded.

[0116] (2) 0.3 g of the molecular sieve catalyst prepared in Example 1 and Comparative Example 1 was hydrothermally aged at 750°C for 16 h under the conditions of 10% water content, 3.5% oxygen content, nitrogen as balance gas, 500 mL / min total gas flow rate, and WHSV=100,000 mL / h / g. The catalyst was then used in the catalytic purification of methane. The raw material of methane was natural gas automobile exhaust gas, wherein the methane concentration was 1000 ppm, the water content was 10%, the oxygen content was 3.5%, nitrogen was balance gas, the total gas flow rate was 300 mL / min, and the mass space velocity was WHSV=180,000 mL / h / g. The reaction was carried out on a continuous flow micro fixed bed. The concentration change of methane in the exhaust gas was determined by gas chromatography. The temperature at which the conversion rate was 10%, 50%, and 90% was recorded.

[0117] 3. 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°C. The test conditions were: natural gas automobile exhaust gas was used as the methane raw material, wherein the methane concentration was 1000ppm, the water content was 10%, the oxygen content was 3.5%, nitrogen was used as the balance gas, the total gas flow rate was 300mL / min, and the mass space velocity was WHSV=180,000mL / h / g, to test the long-term catalytic stability of the catalyst.

[0118] Table 1

[0119]

[0120]

[0121] The test results show that:

[0122] (1) It can be seen from Examples 1 to 3 that the present invention reduces the adsorption capacity of the palladium-based molecular sieve catalyst to water by hydrophobically modifying the SSZ-13 molecular sieve and using it as a catalyst carrier to prepare the catalyst, thereby achieving the purpose of reducing the deactivation of the palladium oxide substance due to water poisoning, and avoiding its deactivation under high-temperature hydrothermal conditions. The prepared high-stability palladium-based molecular sieve catalyst still has a conversion rate of up to 96% after a stability test of 36 hours at 410°C. In a simulated natural gas automobile exhaust atmosphere, the high-stability palladium-based molecular sieve catalyst can still achieve a conversion rate of 90% at 522°C after hydrothermal aging at 750°C for 16 hours, while the catalyst prepared from the molecular sieve without hydrophobic modification has only a conversion rate of 50% at 596°C after hydrothermal aging at 750°C for 16 hours.

[0123] (2) By comparing Example 1 with Example 4-Example 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 subsequent palladium element loading is stronger. If the mass ratio of SSZ-13 molecular sieve and the first silane coupling agent is too large, too few hydroxyl groups on the surface of the molecular sieve carrier are removed, that is, the amount of the first silane coupling agent added is too small, which will lead to the hydrophobic performance of the molecular sieve being not obvious, and the hydrothermal aging ability of the molecular sieve catalyst is poor, thereby 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 is too large, the molecular sieve pores will be blocked, affecting the material transport during the reaction, and its catalytic efficiency will be reduced.

[0124] (3) By comparing Example 1 with Example 6-Example 7, it can be seen that the present invention controls the state of the active components on the molecular sieve carrier by further adjusting the pH. When the pH value exceeds 9, the particle size of the palladium oxide generated by the reaction is too large, and the activity of the palladium oxide substance and the particle size show a volcano-shaped law, thereby reducing the reaction activity of the catalyst. When the pH value is lower than 7, the high dispersion of the Pd substance due to the acidic sites leads to its excessive dispersion and too small particle size, and its methane oxidation activity decreases accordingly.

[0125] (4) It can be seen from Example 1 and Comparative Example 1 that if the molecular sieve carrier is not subjected to hydrophobic modification, the hydrothermal stability of the methane oxidation catalyst is significantly reduced.

[0126] (5) It can be seen from Example 1 and Comparative Example 2 that the present invention uses the deposition precipitation method (DP) to load the palladium element on the molecular sieve, and the palladium oxide substance is dispersed more evenly. At the same time, the interaction between the palladium oxide and the molecular sieve can be significantly enhanced, and the low-temperature catalytic performance of the SSZ-13 molecular sieve catalyst is effectively improved. When the palladium source is loaded on the molecular sieve carrier by the traditional impregnation method instead of the deposition precipitation method, its catalytic activity is far less excellent than the method of the present invention. At the same time, the catalyst prepared by the impregnation method contains Pd substance, which has no catalytic effect in the methane oxidation process; secondly, it is impossible to achieve a high dispersion of the palladium oxide substance, and the active sites are significantly reduced; finally, the interaction between the palladium oxide substance and the molecular sieve is weakened, and agglomeration and deactivation are prone to occur in a high temperature and high humidity environment.

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

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

[0129] In summary, the present invention reduces the water poisoning and deactivation of palladium oxide by hydrophobically modifying SSZ-13 molecular sieves and weakening their water adsorption capacity. The palladium-based molecular sieve catalyst prepared with the SSZ-13 hydrophobically modified molecular sieve as a carrier has a weakened water adsorption capacity, thereby avoiding its deactivation under high-temperature hydrothermal conditions. The high-stability palladium-based molecular sieve catalyst has a conversion rate of up to 96% after a 36-hour stability test at 410°C.

[0130] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A high stability palladium-based molecular sieve catalyst, characterized in that: The high-stability palladium-based molecular sieve catalyst comprises a SSZ-13 hydrophobically modified molecular sieve and an active component supported on the SSZ-13 hydrophobically modified molecular sieve; The active component includes palladium oxide particles; Based on the total mass of the high-stability palladium-based molecular sieve catalyst being 100wt%, the content of the active component in the high-stability palladium-based molecular sieve catalyst is 0.5wt%-5wt%.

2. The high stability palladium-based molecular sieve catalyst according to claim 1, characterized in that The average particle size D of the palladium oxide particles is 0.5 nm-5 nm.

3. A method for preparing a high-stability palladium-based molecular sieve catalyst as claimed in claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) mixing SSZ-13 molecular sieve, water, ethanol and a first silane coupling agent, and obtaining a first product through a first reaction; mixing the first product, toluene and a second silane coupling agent, and then calcining to obtain a SSZ-13 hydrophobically modified molecular sieve after a second reaction; (2) mixing a palladium source and an aqueous solution of a SSZ-13 hydrophobically modified molecular sieve, stirring to obtain a mixture, adding an alkali solution, adjusting the pH, standing, and obtaining the high-stability palladium-based molecular sieve catalyst through solid-liquid separation and calcination.

4. The preparation method according to claim 3, characterized in that: Step (1) The first silane coupling agent includes 1,2-bis(triethoxysilyl)ethane and / or 1,2-bis(trimethoxysilyl)ethane; Preferably, the second silane coupling agent in step (1) comprises any one of dodecyltrimethoxysilane, mercaptopropyltrimethoxysilane or methylphenyldimethoxysilane, or a combination of at least two thereof; Preferably, the mass ratio of the SSZ-13 molecular sieve, water and ethanol in step (1) is 1:(10-20):(2-5); Preferably, the mass ratio of the SSZ-13 molecular sieve to the first silane coupling agent in step (1) is 1:(0.01-0.15), preferably 1:(0.02-0.05).

5. The preparation method according to claim 3 or 4, characterized in that: Step (1) The temperature of the first reaction is 60°C-70°C; Preferably, the first reaction time in step (1) is 5h-20h; Preferably, step (1) further comprises a first washing and a first drying after the first reaction; Preferably, the solvent used in the first washing in step (1) comprises ethanol; Preferably, the temperature of the first drying in step (1) is 90°C-110°C; Preferably, the first drying time in step (1) is 1 h to 12 h.

6. The preparation method according to any one of claims 3 to 5, characterized in that: Step (1) The mass ratio of the first product, toluene and the second silane coupling agent is 1:(15-25):(0.004-0.008); Preferably, the temperature of the second reaction in step (1) is 60°C-70°C; Preferably, the time of the second reaction in step (1) is 1h-5h; Preferably, step (1) further comprises a second washing and a second drying before the calcination; Preferably, the solvent used in the second washing in step (1) comprises ethanol; Preferably, the temperature of the second drying in step (1) is 90°C-110°C; Preferably, the second drying time in step (1) is 1h-12h; Preferably, the heating rate of the calcination in step (1) is 1°C / min-5°C / min; Preferably, the calcination temperature in step (1) is 450°C-550°C; Preferably, the calcination time in step (1) is 1 h to 5 h.

7. The preparation method according to any one of claims 3 to 6, characterized in that: The palladium source in step (2) comprises any one of palladium nitrate, palladium sulfate or palladium acetate, or a combination of at least two thereof; Preferably, the alkali solution in step (2) comprises sodium hydroxide solution and / or potassium hydroxide solution; Preferably, the concentration of the alkali solution in step (2) is 0.01mol / L-0.05mol / L; Preferably, the pH adjustment in step (2) refers to adjusting the pH of the solution to 7-9; Preferably, the standing time in step (2) is 4h-10h.

8. The preparation method according to any one of claims 3 to 7, characterized in that: Step (2) also includes a third washing and a third drying before the calcination; Preferably, the solvent used in the third washing in step (2) comprises ethanol; Preferably, the temperature of the third drying in step (2) is 90°C-110°C; Preferably, the third drying time in step (2) is 1h-12h; Preferably, the heating rate of the calcination in step (2) is 1°C / min-5°C / min; Preferably, the calcination temperature in step (2) is 550°C-650°C; Preferably, the calcination time in step (2) is 1 h to 5 h.

9. The preparation method according to any one of claims 3 to 8, characterized in that: The preparation method comprises the following steps: (1) mixing SSZ-13 molecular sieve, water and ethanol in a mass ratio of 1:(10-20):(2-5), adding 1,2-bis(triethoxysilyl)ethane, wherein the mass ratio of the SSZ-13 molecular sieve to the 1,2-bis(triethoxysilyl)ethane is 1:(0.01-0.15), stirring at 60° C.-70° C. for a first reaction for 5 h-20 h, performing a first washing with ethanol, and performing a first drying at 90° C.-110° C. for 1 h-12 h to obtain a first product; The first product, toluene and dodecyltrimethoxysilane are mixed in a mass ratio of 1:(15-25):(0.004-0.008), a second reaction is carried out at 60°C-70°C for 5h-20h, a second washing is carried out with ethanol, a second drying is carried out at 90°C-110°C for 1h-12h, and then a calcination is carried out at 450°C-550°C for 1h-5h to obtain a SSZ-13 hydrophobically modified molecular sieve; (2) Add SSZ-13 hydrophobically modified molecular sieve into water, and ultrasonically treat for 10 min-30 min to obtain an SSZ-13 hydrophobically modified molecular sieve aqueous solution, add a palladium source dropwise into the SSZ-13 hydrophobically modified molecular sieve aqueous solution, and stir for 1 h-3 h to obtain a mixture, add a sodium hydroxide solution with a concentration of 0.01 mol / L-0.05 mol / L to adjust the pH to 7-9, and let stand for 4 h-10 h. Centrifuge, perform a third washing, perform a third drying at 90°C-110°C for 1 h-5 h, and calcine at 550°C-650°C in an air atmosphere for 1 h-5 h to obtain the high stability palladium-based molecular sieve catalyst.

10. An application of the high-stability palladium-based molecular sieve catalyst as claimed in claim 1 or 2, characterized in that: The high-stability palladium-based molecular sieve catalyst is used for catalyzing methane combustion.

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