Rare earth-alkaline earth composite modified porous ceramic ball catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of synthesis ammonia catalytic materials, and particularly relates to a rare earth-alkaline earth composite modified porous ceramic ball catalyst and a preparation method thereof. According to the catalyst, a porous alumina ceramic ball is used as a carrier, alkaline earth metal (Mg and Ca) and rare earth metal (La and Ce) are co-embedded into a carrier pore channel in sequence through a step-by-step ultrasonic-assisted ion exchange method, a gradient distribution structure with the embedded alkaline earth metal and the coated rare earth metal is formed, and finally trace precious metal is loaded as an active center. The method realizes deep and uniform loading of the composite metal, and effectively solves the problems of easy agglomeration of noble metal, insufficient carrier structure stability and low mass transfer efficiency in the traditional catalyst. The prepared catalyst shows a synergistic effect of deep deoxidation, high stability, high mechanical strength and excellent poisoning resistance in a synthesis ammonia raw material gas deoxidation process, and is suitable for complex industrial working conditions of high temperature, high humidity and high space velocity.

Description

Technical Field

[0001] This invention belongs to the field of synthetic ammonia catalytic materials technology, specifically relating to a rare earth-alkaline earth composite modified porous ceramic ball catalyst and its preparation method. Background Technology

[0002] Ammonia (NH3) is a promising green energy storage intermediate and carbon-free energy carrier due to its high energy density, high hydrogen content, and the fact that it does not produce harmful gases when decomposed. As one of the world's largest chemical products, it is a key substance for fertilizer production, new energy storage, and industrial raw materials.

[0003] In the ammonia synthesis industry, trace amounts of oxygen in the feed gas (a mixture of hydrogen and nitrogen) are a key impurity causing catalyst poisoning in ammonia synthesis. Ammonia synthesis catalysts use iron as the active component; if the oxygen content in the feed gas exceeds 1 ppm, it will rapidly oxidize the iron active sites to form Fe3O4, leading to a sharp drop in catalytic activity of 30%-50%. Data from an 800,000-ton-per-year ammonia synthesis plant shows that incomplete deoxygenation leads to increased catalyst replacement frequency, resulting in annual direct economic losses exceeding 30 million yuan, while system energy consumption increases by 15%-20%. Therefore, deeply removing oxygen from the feed gas to below 0.5 ppm is a core technological requirement for ensuring the efficient and stable operation of ammonia synthesis plants.

[0004] In existing deoxygenation technologies, noble metal catalysts (such as palladium and platinum) supported on porous ceramic spheres are widely used due to their excellent low-temperature activity, but they face insurmountable technical bottlenecks. Firstly, noble metal nanoparticles are prone to migration and aggregation in high-temperature (>300℃) and water-vapor environments, leading to a reduction in the active surface area from 50 m² / h⁻¹. 2 / g decreased to 20m 2 Below a certain value, the catalyst lifetime is usually less than 2000 hours. Secondly, the support structure is not stable enough: under high humidity (relative humidity > 80%) conditions, the porosity of traditional alumina ceramic balls will decrease by 10%-15% due to water vapor adsorption, the gas mass transfer resistance will increase, and the deoxygenation efficiency will fluctuate by ±0.3ppm.

[0005] To address these issues, the industry has attempted to optimize performance through carrier modification. For example, CN112823876B discloses a porous ceramic sphere catalyst embedded with alkaline earth metals (Mg, Ca), which utilizes the solid alkali properties of alkaline earth metals to promote oxygen adsorption and inhibits agglomeration through interaction with noble metals. However, this technology has limitations: the stabilizing effect of single alkaline earth metal modification on noble metals is limited, with a stabilizing effect of up to 25,000 h. -1 At high air velocity, the deoxygenation depth can only reach 1 ppm; and alkaline earth metal oxides (such as MgO) easily react with water vapor to generate Mg(OH)2, which leads to blockage of the carrier pores. After 1000 hours of continuous operation, the porosity decreases by 12%, which cannot meet the requirements of long-term operation.

[0006] Other improvement schemes also have drawbacks: while simple modification with rare earth metals (La, Ce) can stabilize noble metals through strong interactions, it reduces the mechanical strength of the support (compressive strength drops from 180 MPa to below 140 MPa); increasing the density of the support to enhance strength will result in a decrease in specific surface area from 150 m² / m³. 2 / g decreased to 80m 2 / g limits catalytic activity. In addition, existing metal modification techniques mostly employ impregnation methods, resulting in metal enrichment on the support surface (the metal content inside the pores is only 30% of the surface content), and insufficient utilization of precious metals deep within the pores, further restricting deoxidation efficiency.

[0007] With the development of ammonia synthesis plants towards larger scale and lower carbon emissions, higher requirements are being placed on deoxygenation catalysts in industry: they need to operate at space velocities of 5000-25000 h⁻¹. -1 It stably achieves a deoxidation depth below 0.5 ppm within a certain range, while possessing a service life of over 3000 hours and resistance to sulfur and moisture interference. Existing single-metal modification or traditional carrier structures can no longer meet these requirements.

[0008] Therefore, there is an urgent need to develop a new type of feed gas deoxygenation catalyst with composite metal synergy as the core and synergistic optimization in terms of activity stability, mass transfer efficiency and structural strength, so as to break through the deoxygenation bottleneck in the ammonia synthesis process and improve the overall process sustainability. Summary of the Invention

[0009] The purpose of this invention is to provide a rare earth-alkaline earth composite modified porous ceramic ball catalyst and its preparation method, which aims to solve the problems of rapid activity decay, poor mechanical strength and low mass transfer efficiency of existing noble metal deoxygenation catalysts under high temperature and humidity, high space velocity and long cycle operation conditions, so as to achieve synergistic improvement of catalytic activity, structural strength and stability, and is suitable for deep deoxygenation and purification of synthetic ammonia feed gas.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] The first aspect of this invention provides a rare earth-alkaline earth composite modified porous ceramic ball catalyst, the catalyst comprising: a porous alumina ceramic ball support, a composite modified metal, and a noble metal active component; the composite modified metal is a combination of alkaline earth metal and rare earth metal, and the total loading of the composite modified metal is 3-8 wt% of the support mass; the noble metal active component is Pd or Pt, and the loading is 0.5-2% of the support mass.

[0012] Furthermore, the specific surface area of ​​the porous alumina ceramic spheres is 120-200 m². 2 / g, porosity 40-55%, pore size 2-10μm, surface roughness Ra 1.5-3.0μm.

[0013] Furthermore, the alkaline earth metal is Mg or Ca, and the rare earth metal is La or Ce; the mass ratio of alkaline earth metal to rare earth metal is 1:0.5-2.

[0014] Alkaline earth metal oxides are solid basics, and their surface oxygen sites have a strong adsorption and activation capacity for oxygen molecules in the feed gas, lowering the energy barrier for subsequent hydrodeoxygenation reactions. Rare earth metal oxides possess excellent oxygen storage and release capabilities and strong electronic interactions with noble metals. The redox cycle of CeO2 can effectively activate oxygen species, and its electronic modification of noble metals can change the d-electron density of noble metals, enhancing their dissociation and adsorption capacity for hydrogen. At the same time, this strong interaction acts like an anchor, fixing noble metal nanoparticles to the support surface, significantly inhibiting their Ostwald ripening and migration aggregation at high temperatures. When the two metal oxides coexist, a stable composite oxide or solid solution structure may also form at the interface with the alumina support, enhancing the overall thermal stability and anti-hydration capacity of the support, avoiding the problem of hydration expansion and pore collapse caused by a single alkaline earth metal component in a high-humidity environment.

[0015] The second aspect of this invention provides a method for preparing the above-mentioned rare earth-alkaline earth composite modified porous ceramic ball catalyst, comprising the following steps:

[0016] (1) The porous alumina ceramic ball carrier was immersed in nitric acid solution, washed, and dried to obtain a carrier with surface hydroxylation.

[0017] (2) Prepare an alkaline earth metal nitrate solution, immerse the surface-hydroxylated carrier in the alkaline earth metal nitrate solution, stir, and apply ultrasound during the stirring process;

[0018] (3) Prepare a rare earth metal nitrate solution. The carrier treated in step (2) is directly immersed in the rare earth metal nitrate solution without drying and calcination. Stir, apply ultrasound during stirring, and let stand after stirring.

[0019] (4) Take out the carrier after step (3) standing, wash it with deionized water, dry it, and then calcine it;

[0020] (5) Using the equal volume impregnation method, the precursor solution of noble metal Pd or Pt is loaded onto the support after calcination in step (4), dried, and then reduced in a hydrogen atmosphere to obtain rare earth-alkaline earth composite modified porous ceramic ball catalyst.

[0021] Further, the concentration of the nitric acid solution in step (1) is 1-3 wt%, the temperature of the nitric acid solution is 80-100℃, and the soaking time is 2-4 hours.

[0022] Furthermore, the concentration of the alkaline earth metal nitrate solution in step (2) is 0.05-0.5 mol / L, and the pH value is 4.0-5.0.

[0023] Further, the stirring temperature in step (2) is 50-70℃, and the stirring time is 2-4 hours; the ultrasonic power is 150-250W, and the ultrasonic time is 20-40 minutes.

[0024] Furthermore, the concentration of the rare earth metal nitrate solution in step (3) is 0.05-0.5 mol / L, and the pH value is 5.5-6.5.

[0025] Further, in step (3), the stirring temperature is 70-90℃ and the stirring time is 3-5 hours; the ultrasonic power is 200-300W and the ultrasonic time is 30-60 minutes; the settling time is 12-24 hours.

[0026] This invention employs a stepwise ion exchange process to precisely control the spatial distribution of metal species within the pores of a carrier. In step (2), under lower pH conditions, the hydroxyl groups on the carrier surface are highly protonated and positively charged, which facilitates the diffusion of small-sized alkaline earth metal ions and their preferential exchange into the depths of the pores and the interior of the carrier framework. Subsequently, the second exchange step (3) is performed directly without intermediate calcination. At this point, the carrier surface undergoes a change in charge due to the first exchange step, and after adjusting to a higher pH, the surface hydroxyl groups are deprotonated, increasing their negative charge, which is more conducive to the adsorption of larger rare earth metal ions, causing them to be mainly distributed in the middle section of the pores and the surface area of ​​the carrier. This operation avoids the pore blockage that may occur after the pre-loaded metal is fixed by high-temperature calcination, ensuring the available specific surface area and active sites for the second exchange step. Its direct benefit is the formation of a gradient distribution structure with alkaline earth metal embedded and rare earth metal coated, providing a hierarchical anchoring environment for subsequent noble metal active centers, allowing the alkaline sites inside the carrier and the oxygen storage / stabilizing sites on the surface to perform their respective functions, thus optimizing the mass transfer and reaction pathways of the reactants within the pores.

[0027] Ultrasonic assistance is employed during ion exchange, utilizing the intense physical effects of ultrasonic cavitation to enhance mass transfer. The high-speed microjets and shock waves generated when cavitation bubbles collapse in the solution and on the carrier surface effectively disrupt the liquid film boundary layer on the carrier particles, significantly reducing external diffusion resistance. Simultaneously, this intense disturbance expels trapped gas within the pores and forces the solution to carry metal ions into deeper, more tortuous pores, overcoming the slowness and inhomogeneity of diffusion relying solely on concentration gradients. This significantly improves the uniformity of metal ion distribution and exchange efficiency throughout the entire pore system of the carrier.

[0028] Furthermore, the roasting temperature in step (4) is 500-600℃, and the roasting time is 3-5 hours.

[0029] Further, the precursor in step (5) is chloropalladium acid, palladium nitrate, chloroplatinic acid or platinum nitrate; the reduction temperature is 300-400℃ and the time is 2-4 hours.

[0030] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0031] 1. Significantly Improved Deoxidation Performance and Stability: Through the synergistic effect of rare earth and alkaline earth metals and a unique gradient distribution structure, not only is deep deoxidation achieved, but more importantly, the long-term stability of the catalyst is greatly improved. The noble metal nanoparticles are strongly anchored by rare earth metals, inhibiting migration and aggregation at high temperatures. This results in an extremely low activity decay rate after 3000 hours of long-term operation, with a lifespan far exceeding that of traditional catalysts.

[0032] 2. Synergistic optimization of mechanical strength and catalytic activity: The composite metal oxide forms a stable solid solution structure with the support, which significantly enhances the compressive strength and wear resistance of the support while maintaining a high specific surface area and porosity. This successfully solves the industry problem of strength reduction caused by single rare earth modification or easy hydration and pore blockage by single alkaline earth modification, and achieves the unity of "high activity" and "high strength".

[0033] 3. The preparation process is efficient and reproducible: The method of combining stepwise ion exchange with ultrasound assistance overcomes the defects of uneven metal distribution in the traditional impregnation method, ensures the uniform distribution of active components in the carrier channels, improves the utilization rate of precious metals, and the process parameters are clear and easy to control, which is conducive to large-scale industrial production.

[0034] 4. Wide adaptability to operating conditions: This catalyst maintains excellent performance over a wide range of temperature, pressure and space velocity, and exhibits good resistance to water vapor and sulfur poisoning. It can meet the stringent requirements of ammonia synthesis units of different scales and complex feed gas conditions, and has broad application prospects. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Unless otherwise specified, all raw materials used in the examples are commercially available products.

[0037] Example 1

[0038] This embodiment provides a rare earth-alkaline earth composite modified porous ceramic ball catalyst, the catalyst comprising: a porous alumina ceramic ball support with a diameter of 5 mm and a specific surface area of ​​150 m². 2 / g, with a porosity of 48% and a surface roughness Ra of 2.0μm; the composite modified metal is composed of alkaline earth metal Mg and rare earth metal La, with a total loading of 5wt% of the carrier mass and a Mg to La mass ratio of 1:1; the noble metal active component Pd is loaded at 1wt% of the carrier mass.

[0039] The preparation method of the above catalyst includes the following steps:

[0040] (1) The porous alumina ceramic ball carrier was immersed in a 2wt% nitric acid solution at 80℃ for 3 hours, washed with deionized water until neutral, and dried at 120℃ for 6 hours to obtain a surface hydroxylated carrier.

[0041] (2) Prepare a magnesium nitrate solution with a concentration of 0.2 mol / L and adjust the pH of the solution to 4.5 with nitric acid; immerse the surface-hydroxylated carrier in the magnesium nitrate solution, stir at 60°C for 3 hours, and simultaneously apply 200W ultrasonic treatment for 30 minutes.

[0042] (3) Prepare a lanthanum nitrate solution with a concentration of 0.2 mol / L and adjust the pH of the solution to 5.8 with ammonia. The carrier treated in step (2) is directly immersed in the lanthanum nitrate solution without drying and calcination, stirred at 75°C for 4 hours, and subjected to ultrasonic treatment at 250W for 45 minutes. After stirring, let stand for 18 hours.

[0043] (4) Take out the carrier after step (3) standing, wash it with deionized water, dry it at 120°C for 5 hours, and then calcine it in air at 550°C for 4 hours.

[0044] (5) Using the equal-volume impregnation method, chloropalladium acid (H2PdCl4) solution was loaded onto the support after calcination in step (4), and the Pd loading was controlled to be 1 wt%. After impregnation, the solution was dried at 120 °C for 4 hours, and then reduced in a hydrogen atmosphere at 350 °C for 3 hours to obtain the catalyst.

[0045] Example 2

[0046] This embodiment provides a rare earth-alkaline earth composite modified porous ceramic ball catalyst, the catalyst comprising: a porous alumina ceramic ball support with a diameter of 8 mm and a specific surface area of ​​180 m². 2 / g, with a porosity of 42% and a surface roughness Ra of 2.5μm; the composite modified metal is composed of alkaline earth metal Ca and rare earth metal Ce, with a total loading of 6wt% of the carrier mass and a Ca to Ce mass ratio of 1:1.5; the noble metal active component Pt is loaded at 1.5wt% of the carrier mass.

[0047] The preparation method of the above catalyst includes the following steps:

[0048] (1) The porous alumina ceramic ball carrier was immersed in a 3wt% nitric acid solution at 90℃ for 2 hours, washed with deionized water until neutral, and dried at 120℃ for 7 hours to obtain a surface hydroxylated carrier.

[0049] (2) Prepare a calcium nitrate solution with a concentration of 0.25 mol / L and adjust the pH of the solution to 4.8 with nitric acid; immerse the surface-hydroxylated carrier in the calcium nitrate solution and stir at 65°C for 2.5 hours, while simultaneously applying ultrasonic treatment at 220W for 35 minutes;

[0050] (3) Prepare a cerium nitrate solution with a concentration of 0.25 mol / L and adjust the pH of the solution to 5.5 with ammonia water; immerse the carrier treated in step (2) directly into the cerium nitrate solution without drying and calcination, stir at 80°C for 4.5 hours, and apply ultrasonic treatment of 280W for 50 minutes at the same time. After stirring, let it stand for 20 hours.

[0051] (4) Take out the carrier after step (3) and wash it with deionized water. Dry it at 120°C for 5.5 hours and then calcine it in air at 580°C for 3.5 hours.

[0052] (5) Using the equal-volume impregnation method, chloroplatinic acid (H2PtCl6) solution was loaded onto the support calcined in step (4), and the Pt loading was controlled to be 1.5 wt%. After impregnation, the solution was dried at 120 °C for 5 hours, and then reduced in a hydrogen atmosphere at 380 °C for 2.5 hours to obtain the catalyst.

[0053] Example 3

[0054] This embodiment provides a rare earth-alkaline earth composite modified porous ceramic ball catalyst, the catalyst comprising: a porous alumina ceramic ball support with a diameter of 6 mm and a specific surface area of ​​160 m². 2 / g, with a porosity of 50% and a surface roughness Ra of 2.2μm; the composite modified metal is composed of alkaline earth metal Mg and rare earth metal Ce, with a total loading of 4wt% of the carrier mass and a Mg to Ce mass ratio of 1:0.8; the noble metal active component is a composite of Pd and Pt, with a total loading of 1.2wt% of the carrier mass and a Pd to Pt mass ratio of 2:1.

[0055] The preparation method of the above catalyst includes the following steps:

[0056] (1) The porous alumina ceramic ball carrier was immersed in a 1.5wt% nitric acid solution at 85℃ for 3.5 hours, washed with deionized water until neutral, and dried at 120℃ for 6.5 hours to obtain a surface-hydroxylated carrier.

[0057] (2) Prepare a magnesium nitrate solution with a concentration of 0.15 mol / L and adjust the pH of the solution to 4.2 with nitric acid; immerse the surface-hydroxylated carrier in the magnesium nitrate solution and stir at 55°C for 3.5 hours, while simultaneously applying ultrasonic treatment at 180W for 25 minutes.

[0058] (3) Prepare a cerium nitrate solution with a concentration of 0.15 mol / L and adjust the pH of the solution to 5.9 with ammonia water; immerse the carrier treated in step (2) directly into the cerium nitrate solution without drying and calcination, stir at 70°C for 3 hours, and apply ultrasonic treatment of 240W for 40 minutes at the same time. After stirring, let it stand for 16 hours.

[0059] (4) Take out the carrier after step (3) and wash it with deionized water. Dry it at 120°C for 4.5 hours and then calcine it in air at 520°C for 4.5 hours.

[0060] (5) Using an equal-volume impregnation method, a mixed solution of chloropalladium acid (H2PdCl4) and chloroplatinic acid (H2PtCl6) was loaded onto the support calcined in step (4), controlling the total loading of Pd and Pt to be 1.2 wt% (of which Pd accounts for 0.8 wt% and Pt accounts for 0.4 wt%). After impregnation, the solution was dried at 120 °C for 4 hours, and then reduced in a hydrogen atmosphere at 320 °C for 3.5 hours to obtain the catalyst.

[0061] Example 4

[0062] This embodiment provides a rare earth-alkaline earth composite modified porous ceramic ball catalyst, the catalyst comprising: a porous alumina ceramic ball support with a diameter of 4 mm and a specific surface area of ​​190 m². 2 / g, with a porosity of 52% and a surface roughness Ra of 1.8μm; the composite modified metal is composed of alkaline earth metal Ca and rare earth metal La, with a total loading of 7wt% of the carrier mass and a Ca to La mass ratio of 1:2; the noble metal active component Pt is loaded at 0.8wt% of the carrier mass.

[0063] The preparation method of the above catalyst includes the following steps:

[0064] (1) The porous alumina ceramic ball carrier was immersed in a 2.5wt% nitric acid solution at 95℃ for 2.5 hours, washed with deionized water until neutral, and dried at 120℃ for 8 hours to obtain a surface hydroxylated carrier.

[0065] (2) Prepare a calcium nitrate solution with a concentration of 0.3 mol / L and adjust the pH of the solution to 5.0 with nitric acid; immerse the surface-hydroxylated carrier in the calcium nitrate solution, stir at 70°C for 4 hours, and simultaneously apply ultrasonic treatment at 250W for 30 minutes.

[0066] (3) Prepare a lanthanum nitrate solution with a concentration of 0.3 mol / L and adjust the pH of the solution to 6.2 with ammonia. The carrier treated in step (2) is directly immersed in the lanthanum nitrate solution without drying and calcination, stirred at 85°C for 5 hours, and subjected to ultrasonic treatment of 300W for 60 minutes. After stirring, let stand for 24 hours.

[0067] (4) Take out the carrier after step (3) and wash it with deionized water. Dry it at 120°C for 6 hours and then calcine it in air at 600°C for 3 hours.

[0068] (5) Using the equal-volume impregnation method, platinum nitrate (Pt(NO3)4) solution was loaded onto the support after calcination in step (4), and the Pt loading was controlled to be 0.8 wt%. After impregnation, the solution was dried at 120 °C for 4 hours, and then reduced in a hydrogen atmosphere at 400 °C for 2 hours to obtain the catalyst.

[0069] Example 5

[0070] This embodiment provides a rare earth-alkaline earth composite modified porous ceramic ball catalyst, the catalyst comprising: a porous alumina ceramic ball support with a diameter of 7 mm and a specific surface area of ​​140 m². 2 / g, with a porosity of 45% and a surface roughness Ra of 2.8μm; the composite modified metal is a quaternary composite of Mg, Ca, La and Ce, with a total loading of 6wt% of the carrier mass and a mass ratio of the four metals of 1:1:1:1; the noble metal active component Pd is loaded at 1.5wt% of the carrier mass.

[0071] The preparation method of the above catalyst includes the following steps:

[0072] (1) The porous alumina ceramic ball carrier was immersed in a 2wt% nitric acid solution at 80℃ for 4 hours, washed with deionized water until neutral, and dried at 120℃ for 6 hours to obtain a surface hydroxylated carrier.

[0073] (2) Prepare a mixed solution containing magnesium nitrate and calcium nitrate, with a molar ratio of 1:1 and a total metal concentration of 0.2 mol / L. Adjust the pH of the solution to 4.6 with nitric acid to obtain a binary composite metal solution. Immerse the surface-hydroxylated carrier into the binary composite metal solution and stir at 60°C for 4 hours, while simultaneously applying 230W of ultrasonic treatment for 50 minutes.

[0074] (3) Prepare a mixed solution containing lanthanum nitrate and cerium nitrate, with a molar ratio of 1:1 and a total metal concentration of 0.2 mol / L. Adjust the pH of the solution to 5.8 with ammonia. Immerse the carrier treated in step (2) directly into the mixed solution of lanthanum nitrate and cerium nitrate without drying or calcining. Stir at 75°C for 4 hours and apply ultrasonic treatment at 260W for 55 minutes. After stirring, let stand for 22 hours.

[0075] (4) Take out the carrier after step (3) standing, wash it with deionized water, dry it at 120°C for 5 hours, and then calcine it in air at 560°C for 4 hours.

[0076] (5) Using an equal-volume impregnation method, palladium nitrate (Pd(NO3)2) solution was loaded onto the support calcined in step (4), with the Pd loading controlled at 1.5 wt%. After impregnation, the solution was dried at 120 °C for 5 hours, and then reduced in a hydrogen atmosphere at 360 °C for 3 hours to obtain the catalyst.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that the composite modified metal is replaced with only Mg metal for modification, step (3) is omitted in the preparation method, and the concentration of magnesium nitrate solution in step (2) is 0.4 mol / L.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 1 is that the composite modified metal is replaced with only metal La for modification, step (2) is omitted in the preparation method, and the concentration of lanthanum nitrate solution in step (3) is 0.4 mol / L.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 1 is that steps (2) and (3) are replaced with:

[0083] (2) Prepare a mixed solution containing magnesium nitrate and lanthanum nitrate, wherein the molar ratio of Mg to La is 1:1 and the total metal concentration is 0.4 mol / L. Adjust the pH of the solution to 5.0 with nitric acid.

[0084] (3) Immerse the surface-hydroxylated carrier in the above mixed solution, stir at 70°C for 5 hours, and simultaneously apply ultrasonic treatment at 250W for 60 minutes. After stirring, let stand for 18 hours.

[0085] Comparative Example 4

[0086] The difference between this comparative example and Example 1 is that step (3) is replaced with:

[0087] (3) Take out the carrier after step (2), wash it with deionized water, dry it at 120°C for 5 hours, and then calcine it in air at 550°C for 4 hours; prepare a lanthanum nitrate solution with a concentration of 0.2 mol / L, and adjust the pH of the solution to 5.8 with ammonia; immerse the calcined carrier in the lanthanum nitrate solution, stir it at 75°C for 4 hours, and simultaneously apply ultrasonic treatment at 250W for 45 minutes. After stirring, let it stand for 18 hours.

[0088] Comparative Example 5

[0089] The difference between this comparative example and Example 1 is that ultrasound is not applied during the stirring process in steps (2) and (3), and the stirring time in step (2) is extended to 6 hours and the stirring time in step (3) is extended to 8 hours.

[0090] Comparative Example 6

[0091] The difference between this comparative example and Example 1 is that the rare earth metal La is replaced with the rare earth metal Sm.

[0092] Performance testing

[0093] Test samples: porous ceramic ball catalysts prepared in Examples 1-5 and Comparative Examples 1-6.

[0094] Test method:

[0095] 1. Deoxygenation performance test: conducted in a fixed-bed reactor. The catalyst was loaded into the reaction tube, and a mixture of H2 / N2 gas containing 0.8% O2 (simulating ammonia synthesis feed gas) was introduced. The test was conducted at 300℃, 2.0 MPa, and a space velocity of 20000 h⁻¹. -1 The reaction was carried out, and the oxygen content in the outlet gas was detected using a trace oxygen analyzer. The initial deoxygenation depth was the average value after the catalyst had been running stably for 100 hours; the long-term stability was the deoxygenation depth and activity decay rate after 3000 hours of continuous operation ((initial value - value after 3000 hours) / initial value × 100%).

[0096] 2. Mechanical strength test: 50 catalyst ceramic balls were randomly selected and their compressive strength was measured using a universal testing machine. The average value was taken.

[0097] 3. Wear resistance test: The drum method was used. A 50g catalyst sample was taken and continuously rolled in the drum at a speed of 30 rpm for 30 minutes. The mass loss rate (weight loss %) was then measured.

[0098] 4. Anti-poisoning performance test: 20ppm H2S was introduced into the raw gas and the system was run continuously for 1000 hours. The deoxygenation efficiency retention rate was examined (deoxygenation depth under sulfur-containing conditions / deoxygenation depth under sulfur-free conditions × 100%).

[0099] The test results are shown in Table 1.

[0100] Table 1 Performance Test Results

[0101]

[0102]

[0103] Note: Comparative Example 2 did not complete the 3000h test due to its low mechanical strength; the data is from the 2500h test.

[0104] As can be seen from the above performance test results, the catalysts prepared in Examples 1-5 of this invention all exhibit a synergistic optimization effect of deep deoxygenation, ultra-high stability, high mechanical strength and excellent wear resistance, which meets the stringent requirements of modern synthetic ammonia industry for catalysts for deep purification of raw gas.

[0105] Comparative Examples 1 and 2 exhibited severe high-temperature instability and insufficient support structural strength due to the lack of synergistic effects between rare earth and alkaline earth metals, proving that single metal modification cannot resolve the inherent contradiction between activity and stability.

[0106] Comparative Example 3, due to its inability to form a gradient distribution structure, exhibited poor stability of the noble metal. Its deoxygenation depth and long-term stability were significantly inferior to those of the Example, indicating that stepwise ion exchange is crucial for constructing synergistic active centers.

[0107] In Comparative Example 4, the intermediate roasting step caused partial blockage of the carrier pores, resulting in insufficient rare earth metal exchange in the second step and a significant decrease in performance.

[0108] Comparative Example 5 showed that relying solely on mechanical stirring resulted in insufficient uniformity of metal ion dispersion, low utilization of precious metals, and poor initial activity and stability, highlighting the irreplaceable role of ultrasound assistance in achieving deep and uniform metal dispersion.

[0109] In Comparative Example 6, replacing La with Sm resulted in a significant decrease in performance, indicating that a specific Mg / Ca-La / Ce combination can produce the best synergistic effect, which cannot be achieved by a simple combination of all alkaline earth or rare earth metals.

[0110] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A rare earth-alkaline earth composite modified porous ceramic ball catalyst, the catalyst comprising: Porous alumina ceramic ball carrier, composite modified metal and noble metal active components; The composite modified metal is a combination of alkaline earth metals and rare earth metals, and the total loading of the composite modified metal is 3-8 wt% of the carrier mass; the noble metal active component is Pd or Pt, and the loading is 0.5-2% of the carrier mass.

2. The rare earth-alkaline earth composite modified porous ceramic ball catalyst according to claim 1, characterized in that, The specific surface area of ​​the porous alumina ceramic spheres is 120-200 m². 2 / g, porosity 40-55%, pore size 2-10μm, surface roughness Ra 1.5-3.0μm.

3. The rare earth-alkaline earth composite modified porous ceramic ball catalyst according to claim 1, characterized in that, The alkaline earth metal is Mg or Ca, and the rare earth metal is La or Ce; the mass ratio of alkaline earth metal to rare earth metal is 1:0.5-2.

4. The preparation method of the rare earth-alkaline earth composite modified porous ceramic ball catalyst according to any one of claims 1-3, comprising the following steps: (1) The porous alumina ceramic ball carrier was immersed in nitric acid solution, washed, and dried to obtain a carrier with surface hydroxylation. (2) Prepare an alkaline earth metal nitrate solution, immerse the surface-hydroxylated carrier in the alkaline earth metal nitrate solution, stir, and apply ultrasound during the stirring process; (3) Prepare a rare earth metal nitrate solution. The carrier treated in step (2) is directly immersed in the rare earth metal nitrate solution without drying and calcination. Stir, apply ultrasound during stirring, and let stand after stirring. (4) Take out the carrier after step (3) standing, wash it with deionized water, dry it, and then calcine it; (5) Using the equal volume impregnation method, the precursor solution of noble metal Pd or Pt is loaded onto the support after calcination in step (4), dried, and then reduced in a hydrogen atmosphere to obtain rare earth-alkaline earth composite modified porous ceramic ball catalyst.

5. The preparation method according to claim 4, characterized in that, The concentration of the nitric acid solution in step (1) is 1-3 wt%, the temperature of the nitric acid solution is 80-100℃, and the soaking time is 2-4 hours.

6. The preparation method according to claim 4, characterized in that, The concentration of the alkaline earth metal nitrate solution in step (2) is 0.05-0.5 mol / L, and the pH value is 4.0-5.

0.

7. The preparation method according to claim 4, characterized in that, The stirring temperature in step (2) is 50-70℃, and the stirring time is 2-4 hours; the ultrasonic power is 150-250W, and the ultrasonic time is 20-40 minutes.

8. The preparation method according to claim 4, characterized in that, The concentration of the rare earth metal nitrate solution in step (3) is 0.05-0.5 mol / L, and the pH value is 5.5-6.5; the stirring temperature in step (3) is 70-90℃, and the stirring time is 3-5 hours; the ultrasonic power is 200-300W, and the ultrasonic time is 30-60 minutes; the standing time is 12-24 hours.

9. The preparation method according to claim 4, characterized in that, The roasting temperature in step (4) is 500-600℃, and the roasting time is 3-5 hours.

10. The preparation method according to claim 4, characterized in that, The precursor in step (5) is chloropalladium acid, palladium nitrate, chloroplatinic acid, or platinum nitrate; the reduction temperature is 300-400℃ and the time is 2-4 hours.

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