Catalyst for purifying tail gas of explosion-proof diesel engine and preparation method of catalyst

Abstract

The invention discloses a catalyst for purifying tail gas of an explosion-proof diesel engine and a preparation method of the catalyst, and relates to the technical field of catalyst preparation. The catalyst comprises the following components: an active component: platinum, palladium or rhodium, wherein the loading capacity is 0.1-1.0%; a cerium oxide-lanthanum oxide compound, which accounts for 10 to 30%; and the ratio of the manganese oxide-cobaltosic oxide compound is 5-15%. Through innovative component design and a preparation process, the catalytic activity at a low temperature is remarkably improved, palladium is taken as a core noble metal component, and a manganese oxide-cobaltosic oxide composite oxide is combined as a bimetallic synergistic center, so that oxidation reduction sites for efficiently activating carbon monoxide and nitrogen oxide are formed, and the catalytic activity of the catalyst is improved. The nanometer fibrous mesoporous molecular sieve MCM-41 and gamma-type aluminum oxide greatly enhance the diffusion and adsorption capacity of waste gas molecules, oxygen-enriched active sites are introduced through pulse type nitrogen plasma treatment, and the waste gas adsorption capacity in the cold start stage is enhanced by utilizing Lewis acid sites, so that the instantaneous conversion efficiency of NOX and CO at low temperature is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and in particular relates to a catalyst for purifying exhaust gas of explosion-proof diesel engines and a preparation method thereof. Background Art

[0002] Explosion-proof diesel exhaust purification catalyst is a special catalytic material designed for flammable and explosive environments such as coal mines and oil fields. It is intended to efficiently process carbon monoxide, hydrocarbons, nitrogen oxides and particulate matter in diesel exhaust. Its core is composed of precious metals such as platinum, palladium, rhodium or transition metal oxides, and converts CO and HC into carbon dioxide and water through redox reactions. The catalyst adopts a honeycomb ceramic or metal carrier structure, combined with an explosion-proof design to ensure stable operation in high temperature, high humidity and severe vibration environments, and avoid safety hazards caused by static electricity accumulation. In addition, the technology needs to adapt to the low-temperature exhaust characteristics of diesel engines, optimize the ignition temperature and conversion efficiency, meet strict emission standards such as National VI, and have the characteristics of long life and low maintenance cost, providing dual protection of environmental protection and safety for high-risk operation scenarios.

[0003] Existing diesel exhaust purification catalysts (such as selective catalytic reduction catalysts, diesel oxidation catalysts / carbon monoxide oxidation catalysts) are insufficiently active at low temperatures (<200°C), have low conversion efficiencies for nitrogen oxides and carbon monoxide during the cold start phase, and have problems such as high usage of precious metals, sulfur poisoning, and hydrothermal aging. In traditional technologies, although rare earth doping and carrier structure optimization can partially improve performance, it is difficult to balance low-temperature activity and long-term stability. In addition, the special operating conditions of explosion-proof diesel engines (high humidity, frequent starts and stops) further increase the risk of catalyst failure.

[0004] To this end, we provide a catalyst for purification of explosion-proof diesel engine exhaust and a preparation method thereof to solve the above-mentioned problems. Summary of the invention

[0005] The purpose of the present invention is to provide a catalyst for purifying explosion-proof diesel engine exhaust and a preparation method thereof. The improved diesel engine exhaust purification catalyst has high low-temperature activity, controllable cost and can adapt to complex working conditions.

[0006] To solve the above technical problems, the present invention is implemented through the following technical solutions.

[0007] The present invention is a catalyst for purifying exhaust gas from explosion-proof diesel engines and a preparation method thereof, comprising the following components: Active ingredients: Platinum, palladium or rhodium: loading 0.1-1.0%; Cerium oxide-lanthanum oxide complex: 10-30%; Manganese oxide-cobalt tetraoxide complex: 5-15%; Hierarchical porous composite carrier: Nanofibrous mesoporous molecular sieve material MCM-41: 50-70%; Gamma alumina: 20-40%; Additives: Tungsten trioxide or molybdenum trioxide: 3-8%; Zirconium dioxide: 2-5%.

[0008] The present invention is further configured such that the specific surface area of ​​the nanofibrous mesoporous molecular sieve material MCM-41 and gamma-type alumina is ≥500 square meters / gram, and the pore size distribution is 2-50 nanometers.

[0009] The present invention is further configured such that the platinum, palladium or rhodium is used as a main catalyst with a loading amount of 0.1%-1.0%, and activates NOx and CO molecules through surface adsorption to achieve efficient redox reaction at a low temperature <200°C, among which palladium is preferred due to its strong catalytic activity and low toxicity to CO and HC.

[0010] The present invention is further configured such that the active component and the auxiliary agent form Lewis acid sites, thereby enhancing the adsorption capacity of exhaust gas in the cold start phase and reducing the instantaneous emission load.

[0011] A method for preparing a catalyst for purifying exhaust gas from an explosion-proof diesel engine comprises the following steps: a. Weigh nanofibrous mesoporous molecular sieve MCM-41 and gamma-alumina in proportion, mix by ball milling for 2 hours, with a ball-to-material ratio of 10:1 and a rotation speed of 400 rpm to ensure uniform dispersion of the powder, prepare a 0.5 mol / L cerium nitrate-lanthanum nitrate mixed solution with a molar ratio of 1:1-2:1, optimize the pore structure of the carrier, and improve the uniformity of rare earth loading; b. The mixed carrier is immersed in a rare earth solution, ultrasonicated for 30 minutes at a power of 300W, and then centrifuged for washing to ensure that the rare earth ions are fully penetrated and the oxygen vacancy generation capacity is enhanced; c. Calcination at 500°C for 2 hours in a nitrogen atmosphere to generate a cerium oxide-lanthanum oxide composite layer, forming a stable oxide layer and improving the low-temperature oxygen activation efficiency; d. Centrifuge at 3000 rpm for 5 min to remove the unadsorbed solution, and repeat washing twice to purify the carrier surface; e. A pulsed nitrogen plasma reactor was used with a power of 300W and a treatment time of 30 minutes to increase the surface oxygen vacancy concentration, introduce oxygen-rich active sites, and accelerate the low-temperature catalytic reaction; f. impregnating with manganese nitrate-cobalt nitrate solution, with a molar ratio of 2:1-4:1, drying at 110°C and calcining at 400°C for 3 hours to construct a bimetallic synergistic oxidation center and reduce the dependence on precious metals; g. Use chloroplatinic acid and tungsten trioxide / molybdenum trioxide solution for impregnation, dry at 120℃, and then reduce with hydrogen at 500℃ for 1 hour, with a hydrogen flow rate of 50mL / min, to accurately control the dispersion of precious metals and enhance the tolerance to sulfur poisoning; h. Tetragonal zirconium dioxide with a particle size of 5-15 nm is loaded on the surface of gamma-alumina and ground with the catalyst to inhibit high-temperature water vapor erosion and extend the service life; i. Soak the catalyst in 0.1 mol / L dilute nitric acid at pH 2 for 15 minutes and dry at 110°C to enhance the surface acid sites and improve the pollutant adsorption capacity during the cold start phase; j. In a fixed bed reactor, simulated exhaust gas was introduced at 180°C, with nitrogen oxides NOx = 500ppm, carbon monoxide CO = 1000ppm, and oxygen O 2 =5%, nitrogen N 2 balance, detect NOx and CO conversion rate; conduct 200 hours sulfur aging test, SO 2 At a concentration of 50ppm, the catalytic efficiency attenuation rate was compared before and after aging to verify the low-temperature activity and long-term stability indicators; k. Crush the catalyst into 20-40 mesh particles and verify the exhaust gas purification efficiency of mining excavator, WK-35 type, to ensure that the sixth stage motor vehicle pollutant emission standards are met, NOx≤35mg / km, CO≤1.0g / km.

[0012] The present invention is further configured that after the raw material is ball-milled in step a, the particle size distribution D50 is measured by a laser particle size analyzer to be 12 μm, and the specific surface area is increased to 210 m² / g after pretreatment.

[0013] The present invention is further configured as follows: in step b, the centrifugal washing is performed using a 5000 rpm centrifuge for 5 minutes, and the mixture is washed three times with deionized water and ethanol in sequence, dried in an oven at 80° C. for 6 hours, and then ground and sieved to control the particle size to be less than 100 μm.

[0014] The present invention is further configured such that after 200 hours of sulfur aging in the step, the NOx conversion rate decreases by 8.7%, the CO conversion rate only decreases by 3.2%, and the sulfur resistance is better than that of commercial catalysts.

[0015] The present invention has the following beneficial effects.

[0016] 1. The present invention The present invention significantly improves the catalytic activity at low temperatures through innovative component design and preparation process. With palladium as the core precious metal component and combined with manganese oxide-cobalt tetroxide composite oxide as a bimetallic synergistic center, redox sites for efficient activation of carbon monoxide and nitrogen oxides are formed. The graded porous carrier constructed of nanofibrous mesoporous molecular sieve MCM-41 and gamma-type alumina greatly enhances the diffusion and adsorption capacity of exhaust gas molecules. Oxygen-rich active sites are introduced through pulsed nitrogen plasma treatment, and Lewis acid sites are used to enhance the exhaust gas adsorption capacity in the cold start phase, so that the instantaneous conversion efficiency of NOx and CO at low temperatures is significantly improved. Experiments show that under simulated exhaust gas conditions at 180°C, the NOx conversion rate is over 92%, the CO conversion rate exceeds 85%, and the activity decay rate after sulfur aging is only 1 / 3 of that of commercial catalysts, breaking through the technical bottleneck of insufficient low-temperature activity of traditional catalysts.

[0017] 2. The present invention The present invention significantly improves the ability to resist sulfur poisoning, hydrothermal aging and high-temperature sintering through the synergistic effect of multi-level structural design and functional components. The cerium oxide-lanthanum oxide complex effectively alleviates the poisoning effect of sulfur species on precious metals through the generation and migration of oxygen vacancies; zirconium dioxide is loaded on the surface of gamma-type alumina in the form of nanoparticles to form a physical barrier to inhibit the erosion of high-temperature water vapor on the carrier; the graded porous carrier structure significantly reduces the risk of structural collapse at high temperatures through pore size regulation and fibrous morphology design; in addition, the bimetallic synergistic oxidation center replaces part of the precious metal function, further reducing the dependence on platinum group metals. The 200-hour sulfur aging experiment shows that the NOx conversion rate only decreases by 8.7%, and the CO conversion rate remains at 96.8%. The anti-sulfur performance far exceeds that of traditional commercial catalysts. In actual vehicle verification, after the catalyst has been running continuously for 500 hours under complex working conditions of a mining excavator, the nitrogen oxide and carbon monoxide emissions still stably meet the National VI standards, proving its reliability in long-term use.

[0018] 3. The improved catalyst of the present invention significantly reduces the production cost and process complexity while ensuring high performance through component optimization and preparation process innovation. The rare earth elements are introduced in the form of a loaded complex, and the amount used is only 1 / 2 of that of the traditional rare earth doping technology. The uniform loading is achieved through the nitrate co-impregnation-ultrasonic dispersion process, avoiding the loss of active sites due to sintering. The ball milling mixing process of nanofibrous mesoporous molecular sieve MCM-41 and gamma-type alumina ensures the mechanical strength and formability of the carrier, which is suitable for large-scale production. The synergistic effect of the additives tungsten trioxide / molybdenum and zirconium dioxide inhibits high-temperature hydrothermal corrosion while improving the surface acidity. Fixed bed simulation and actual vehicle verification show that the catalyst can still maintain the emission control level of NOx≤35mg / km and CO≤1.0g / km under the conditions of high humidity and frequent start-stop of explosion-proof diesel engines, and the full life cycle cost is reduced by more than 40% compared with traditional catalysts. It is both environmentally friendly and economical, providing a cost-effective solution for diesel engine exhaust purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the drawings required for describing the embodiment are briefly introduced below.

[0020] Figure 1 It is a schematic diagram of the internal structure of the present invention.

[0021] Figure 2 It is a schematic diagram of the process of the present invention.

[0022] Figure 3 This is a comparison chart of the cold start performance of the present invention.

[0023] Figure 4 It is a comparison chart of the anti-sulfur performance of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] Example 1 See also Figure 1-Figure 4 , the present invention is a catalyst for purification of explosion-proof diesel engine exhaust and a preparation method thereof: Preparation and performance verification of explosion-proof diesel engine exhaust purification catalyst: Raw material ratio: Main catalyst: palladium (Pd) loading 0.5%; Cerium oxide-lanthanum oxide complex: 20% (molar ratio 1:1); Manganese oxide-cobalt tetroxide complex: 10% (molar ratio 2:1); Carrier: nanofibrous mesoporous molecular sieve MCM-41 (accounting for 60%, specific surface area 210m² / g, D50=12μm) and gamma-type alumina (accounting for 40%); Additives: tungsten trioxide (5%) and zirconium dioxide (3%).

[0026] Preparation method: Carrier pretreatment: MCM-41 and gamma-alumina were ball-milled in proportion for 2 hours (ball-to-material ratio 10:1, rotation speed 400 rpm) to obtain a mixed powder with a particle size D50 = 12 μm.

[0027] A 0.5 mol / L cerium nitrate-lanthanum nitrate mixed solution (molar ratio 1:1) was prepared, the carrier mixture was impregnated, ultrasonicated for 30 minutes (power 300 W), centrifuged and washed (5000 rpm, 5 min), repeated 3 times, and dried at 80°C for 6 h.

[0028] Rare earth composite layer deposition: The cerium oxide-lanthanum oxide composite layer was formed by calcining at 500°C for 2 hours in a nitrogen atmosphere to improve the low-temperature oxygen activation efficiency.

[0029] Surface modification: Pulsed nitrogen plasma treatment (power 300 W, 30 min) introduced oxygen-rich sites and enhanced the surface oxygen vacancy concentration.

[0030] It was impregnated with manganese nitrate-cobalt nitrate solution (molar ratio 2:1), dried at 110°C and calcined at 400°C for 3 hours to construct a bimetallic cooperative oxidation center.

[0031] Precious metal loading and additive integration: The samples were impregnated with chloroplatinic acid and tungsten trioxide / molybdenum trioxide solution, dried at 120°C, and reduced with hydrogen at 500°C (flow rate 50mL / min) to accurately disperse the Pd particles.

[0032] The surface of gamma-alumina is loaded with tetragonal zirconium dioxide with a particle size of 10 nm, and mixed grinding is performed to inhibit high-temperature water vapor erosion.

[0033] Post-processing and aging test: Soak in dilute nitric acid (pH=2) for 15 minutes and dry at 110℃ to enhance the surface acid sites.

[0034] The simulated tail gas (NOx=500ppm, CO=1000ppm, O 2 =5%) test: At 180°C, the initial conversion rates of NOx and CO were 92% and 98%, respectively.

[0035] 200 hours sulfur aging test (SO 2=50ppm), the NOx conversion rate decreased by 8.7%, while CO only decreased by 3.2%, and its anti-sulfur performance was better than that of commercial catalysts.

[0036] Real vehicle verification: Crushed into 30 mesh particles and loaded into the exhaust system of WK-35 mining excavator.

[0037] After 200 hours of continuous operation, NOx emissions are ≤35mg / km and CO emissions are ≤1.0g / km, meeting the National VI standard.

[0038] Table 1: Technical solution feature comparison table Example 2 See also Figure 1-4 , based on Example 1: Optimized preparation of low temperature and high stability catalysts: Raw material ratio adjustment: Main catalyst: palladium (Pd) loading 0.8%; Cerium oxide-lanthanum oxide complex: 25% (molar ratio 2:1); Manganese oxide-cobalt oxide complex: 12% (molar ratio 3:1); Carrier: MCM-41 (55%, surface area 230m² / g) and gamma alumina (45%); Additives: molybdenum trioxide (6%) and zirconium dioxide (4%); Key process improvements: Enhanced carrier structure: During ball milling, 1wt.% polyvinylpyrrolidone (PVP) was added as a dispersant to further reduce the particle size to D50 = 8μm and increase the specific surface area to 230m² / g; Bimetallic synergistic optimization: A gradient calcination method was used: pre-calcination at 350°C for 1 hour to remove organic matter, and then calcination at 450°C for 2 hours to promote uniform dispersion of Mn-Co oxides; Anti-sulfur strengthening treatment: Pre-oxidation treatment was performed before sulfur aging: air was introduced at 300°C for 1 hour to generate stable sulfate species and reduce the coverage of active sites; Performance characterization: Low temperature activity: At 150°C, the NOx conversion rate reaches 85%, and the CO conversion rate reaches 91%, which is 10% higher than that of Example 1.

[0039] Durability: After 200 hours of sulfur aging, the NOx conversion rate decreased by 7.2%, the CO conversion rate decreased by 2.8%, and the sulfur resistance performance was further improved.

[0040] After the high-temperature steam (800°C, 10% HO) shock test, the CO conversion rate retention rate increased to 92%.

[0041] Real car adaptability: Under -10℃ cold start conditions, the exhaust gas purification efficiency still meets the National VI standard, and the cold start time is shortened by 40%.

[0042] By adjusting the carrier structure, bimetallic ratio and anti-sulfur pretreatment process, Example 2 significantly improves low-temperature adaptability and long-term stability while maintaining high activity, and is suitable for diesel engine exhaust purification scenarios in cold regions.

[0043] Table 2: Technical solution feature comparison table The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that technicians in the relevant technical field can better understand and utilize the present invention.

Claims

1. A catalyst for purification of explosion-proof diesel engine exhaust, characterized in that: Includes the following ingredients: Active ingredients: Platinum, palladium or rhodium: loading 0.1-1.0%; Cerium oxide-lanthanum oxide complex: 10-30%; Manganese oxide-cobalt tetraoxide complex: 5-15%; Hierarchical porous composite carrier: Nanofibrous mesoporous molecular sieve material MCM-41: 50-70%; Gamma alumina: 20-40%; Additives: Tungsten trioxide or molybdenum trioxide: 3-8%; Zirconium dioxide: 2-5%.

2. A catalyst for purification of explosion-proof diesel engine exhaust according to claim 1, characterized in that: The specific surface area of ​​the nano-fibrous mesoporous molecular sieve material MCM-41 and gamma-type alumina is ≥500 square meters / gram, and the pore size distribution is 2-50 nanometers.

3. The catalyst for purification of explosion-proof diesel engine exhaust according to claim 1, characterized in that: The platinum, palladium or rhodium is used as the main catalyst with a loading amount of 0.1%-1.0%, and activates NOx and CO molecules through surface adsorption, achieving efficient redox reaction at a low temperature <200°C. Among them, palladium is preferred due to its strong catalytic activity and low toxicity to CO and HC.

4. The catalyst for purification of explosion-proof diesel engine exhaust according to claim 1, characterized in that: The active component and the auxiliary agent form Lewis acid sites, thereby increasing the adsorption capacity of exhaust gas in the cold start phase and reducing the instantaneous emission load.

5. A method for preparing a catalyst for purification of explosion-proof diesel engine exhaust, characterized in that: The following steps are involved: a. Weigh nanofibrous mesoporous molecular sieve MCM-41 and gamma-alumina in proportion, mix by ball milling for 2 hours, with a ball-to-material ratio of 10:1 and a rotation speed of 400 rpm to ensure uniform dispersion of the powder, prepare a 0.5 mol / L cerium nitrate-lanthanum nitrate mixed solution with a molar ratio of 1:1-2:1, optimize the pore structure of the carrier, and improve the uniformity of rare earth loading; b. The mixed carrier is immersed in a rare earth solution, ultrasonicated for 30 minutes at a power of 300W, and then centrifuged for washing to ensure that the rare earth ions are fully penetrated and the oxygen vacancy generation capacity is enhanced; c. Calcination at 500°C for 2 hours in a nitrogen atmosphere to generate a cerium oxide-lanthanum oxide composite layer, forming a stable oxide layer and improving the low-temperature oxygen activation efficiency; d. Centrifuge at 3000 rpm for 5 min to remove the unadsorbed solution, and repeat washing twice to purify the carrier surface; e. A pulsed nitrogen plasma reactor was used with a power of 300W and a treatment time of 30 minutes to increase the surface oxygen vacancy concentration, introduce oxygen-rich active sites, and accelerate the low-temperature catalytic reaction; f. impregnating with manganese nitrate-cobalt nitrate solution, with a molar ratio of 2:1-4:1, drying at 110°C and calcining at 400°C for 3 hours to construct a bimetallic synergistic oxidation center and reduce the dependence on precious metals; g. Use chloroplatinic acid and tungsten trioxide / molybdenum trioxide solution for impregnation, dry at 120℃, and then reduce with hydrogen at 500℃ for 1 hour, with a hydrogen flow rate of 50mL / min, to accurately control the dispersion of precious metals and enhance the tolerance to sulfur poisoning; h. Tetragonal zirconium dioxide with a particle size of 5-15 nm is loaded on the surface of gamma-alumina and ground with the catalyst to inhibit high-temperature water vapor erosion and extend the service life; i. Soak the catalyst in 0.1 mol / L dilute nitric acid at pH 2 for 15 minutes and dry at 110°C to enhance the surface acid sites and improve the pollutant adsorption capacity during the cold start phase; j. In a fixed bed reactor, simulated exhaust gas was introduced at 180°C, with nitrogen oxides NOx = 500ppm, carbon monoxide CO = 1000ppm, oxygen O2 = 5%, and nitrogen N2 as balance, and the NOx and CO conversion rates were tested; a 200-hour sulfur aging experiment was conducted with a SO2 concentration of 50ppm, and the catalytic efficiency attenuation rates before and after aging were compared to verify the low-temperature activity and long-term stability indicators; k. Crush the catalyst into 20-40 mesh particles and verify the exhaust gas purification efficiency of mining excavator, WK-35 type, to ensure that the sixth stage motor vehicle pollutant emission standards are met, NOx≤35mg / km, CO≤1.0g / km.

6. The method for preparing a catalyst for purification of explosion-proof diesel engine exhaust according to claim 5, characterized in that: After ball milling of the raw material in step a, the particle size distribution D50 is measured by a laser particle size analyzer to be 12 μm, and the specific surface area is increased to 210 m² / g after pretreatment.

7. The method for preparing a catalyst for purification of explosion-proof diesel engine exhaust according to claim 5, characterized in that: In the step b, the centrifugal washing is performed using a 5000 rpm centrifuge for 5 minutes, and the mixture is washed three times with deionized water and ethanol in sequence. After drying in an oven at 80° C. for 6 hours, the mixture is ground and sieved to control the particle size to be less than 100 μm.

8. The method for preparing a catalyst for purification of exhaust gas from explosion-proof diesel engines according to claim 5, characterized in that: After 200 hours of sulfur aging, the NOx conversion rate decreased by 8.7%, and the CO conversion rate decreased by only 3.2%, and the sulfur resistance was better than that of commercial catalysts.

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