Lean nox trap catalyst for diesel exhaust purification system and use thereof

Abstract

The present application belongs to the field of catalysis technology, and particularly relates to a lean NOx trap catalyst of a diesel engine exhaust purification system and application thereof. x The lean NOx trap catalyst of the diesel engine exhaust purification system comprises a substrate and a coating layer coated on the substrate, characterized in that the coating layer comprises a NO x storage component, a noble metal, a manganese-containing composite oxide and a cerium-aluminum composite oxide; the mass fraction of the manganese-containing composite oxide in the coating layer is 20-40%, and the mass fraction of the cerium-aluminum composite oxide is 50-70%. The lean NO x x trap catalyst of the present application uses a manganese-cerium-zirconium composite oxide and a cerium-aluminum composite oxide as a carrier, and the manganese-cerium-zirconium composite oxide works together with a platinum group noble metal to oxidize NO in a lean combustion stage, thereby improving the low-temperature NO x storage capacity, and further improving the low-temperature NO x conversion efficiency, and having the characteristics of high low-temperature NO x storage capacity and high low-temperature NO x conversion efficiency.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to a lean-burn NO in a diesel engine exhaust purification system. x The catalyst for trapping and its application: catalytic purification of nitrogen oxides in diesel vehicle exhaust through a process of first storing and then reducing. Background Technology

[0002] Lean-burn engines, especially diesel engines, offer advantages such as high fuel economy and low CO2 emissions, making diesel vehicles increasingly popular in most developed countries, particularly in Europe. However, compared to stoichiometric gasoline engines, diesel vehicles emit higher levels of exhaust pollutants, primarily due to soot and NOx. x It has been criticized for its emissions. The current Euro VI emission standards again mandate a significant reduction in NOx emissions. x Emissions. Diesel engines operate under oxygen-rich conditions, resulting in an air-fuel ratio in exhaust far greater than 14.7. Under these conditions, the purification effect of three-way catalytic converters is insufficient. Currently, the technology applied to NO emissions from diesel vehicle exhaust... x The mainstream technologies for catalytic purification include selective catalytic reduction (SCR) and lean-burn NO2. x Lean NO x Trap, LNT, etc.

[0003] For light-duty diesel engines, LNT is considered a promising NOx. x Catalytic purification and post-treatment technology. Compared with other technologies, the biggest advantage of LNT technology is that it does not require the addition of additional reducing agents. It effectively solves the problem of NO pollutants at low temperatures, especially during cold starts and idling. x And the issue of unburned HC emissions. LNT is a cyclical process; in actual systems, the lean-burn phase typically lasts 1–2 minutes, and the rich-burn phase lasts 3–5 seconds. During the longer lean-burn phase (λ>1), NO... x First, it adsorbs onto the catalyst surface, and then stores on the catalyst in the form of nitrite or nitrate. When the reaction atmosphere switches to a brief fuel-rich phase (λ<1), NO... x The catalyst is reduced to gases such as N2 by reducing gases such as H2, CO, and HC, which regenerates the catalyst, and then the next cycle begins.

[0004] To meet the National VI emission standards for light-duty diesel vehicles x Emission standards require the combined use of LNT and SCR denitrification technologies. LNT is mainly used to address NO2 before the exhaust gas temperature reaches the high activity temperature range of the SCR catalyst. x Emissions issues.

[0005] Existing lean NOx The catalyst for capturing NO exists at low temperatures x The problem of low conversion efficiency, while lean NO x NO trapping catalyst x Purification performance and its NO x Storage capacity is closely related. Manganese-cerium composite oxides have good NO oxidation performance. For example, CN102688691A discloses a manganese-based oxide-promoted LNT catalyst using MnO. x - Base metal oxide mixtures (e.g., MnO) x -CeO2) replaces platinum in the LNT system, and NO x Storage materials and NO x The raw materials are also used in combination. However, these catalysts are effective even at low space velocities (volume space velocity of 25,000 h⁻¹). -1 ), low temperature NO x The conversion rate is also not high. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a lean-burn NOx capture catalyst for diesel engine exhaust gas purification systems and its application. The catalyst of this invention exhibits excellent low-temperature NOx capture performance. x With its superior storage performance, this catalyst, used upstream of SCR catalysts, effectively purifies nitrogen oxides emitted from lean-burners in diesel engines. The catalyst oxidizes unburned hydrocarbons (HC) and carbon monoxide (CO), and captures and reduces nitrogen oxides (NOx). x ).

[0007] To achieve the above technical objectives, the technical solution adopted in the embodiments of the present invention is as follows:

[0008] In a first aspect, embodiments of the present invention provide a lean-burn NO emission system for diesel engine exhaust purification. x The trapping catalyst includes a matrix and a coating applied to the matrix, the coating containing NO. x The coating contains storage components, precious metals, manganese-containing composite oxides, and cerium-aluminum composite oxides; the manganese-containing composite oxides account for 20-40% by mass, and the cerium-aluminum composite oxides account for 50-70% by mass.

[0009] Furthermore, the NO x The storage component is an alkaline earth metal oxide.

[0010] Furthermore, the precious metal is a platinum group metal, and the loading of the precious metal is 3-5 g / L.

[0011] Furthermore, the manganese-containing composite oxide is a manganese-cerium-zirconium composite oxide, containing MnO.x Cerium dioxide and zirconium dioxide, of which MnO x The mass fraction of cerium dioxide is 10-20%, the mass fraction of cerium dioxide is 30-50%, and the mass fraction of zirconium dioxide is 40-60%.

[0012] Furthermore, the precious metals include platinum (Pt), palladium (Pd), and rhodium (Rh), with Pt / Rh = 10:1-20:1 and Pd / Rh = 1:1-3:1 by mass ratio.

[0013] Furthermore, the alkaline earth metal oxide is barium oxide, and the mass fraction of the alkaline earth metal oxide in the coating is 3-10%.

[0014] Furthermore, the cerium-aluminum composite oxide comprises cerium dioxide and aluminum oxide, wherein the mass fraction of cerium dioxide is 20-40% and the mass fraction of aluminum oxide is 60-80%.

[0015] Furthermore, the coating amount is 300-400 g / L.

[0016] Secondly, embodiments of the present invention provide the aforementioned lean NO x The lean-burn NOx capture catalyst is applied to a diesel engine exhaust purification system. When the engine operates under lean-burn conditions, the lean-burn NOx capture catalyst removes NO from the engine exhaust. x Stored on the catalyst coating, NO will be released when the engine switches to fuel-rich conditions. x Restored to N2.

[0017] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows:

[0018] The lean NO of the present invention x The catalyst for NO capture utilizes manganese-cerium-zirconium composite oxide and cerium-aluminum composite oxide as supports. The manganese-cerium-zirconium composite oxide, in the lean-burn stage, works in conjunction with platinum group metals to oxidize NO, thereby improving NO capture efficiency at low temperatures. x Storage capacity, thereby improving low-temperature NO x Conversion efficiency. The lean NO of this invention... x Catalysts for capturing NO in engine exhaust x When in contact, NO at 200-350℃ x Storage capacity is greater than 2.0 g / L. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Example 1

[0021] A lean-burn NO in a diesel engine exhaust purification system x The catalyst trapping includes a support and a coating applied to the support, wherein the catalyst support is a cordierite ceramic support with a volume of 0.73 L and a pore density of 400 mesh / square inch;

[0022] The total coating amount is 320 g / L, including a total loading of 3.2 g / L of precious metals, 80 g / L of manganese-cerium-zirconium composite oxide, 224.8 g / L of cerium-aluminum composite oxide, and 12 g / L of barium oxide. The precious metals include 2.6 g / L of Pt, 0.4 g / L of Pd, and 0.2 g / L of Rh.

[0023] The preparation method of the lean-burn NOx capture catalyst for the above-mentioned diesel engine exhaust gas purification system includes the following steps:

[0024] (1) Preparation of manganese-cerium-zirconium composite oxide: The co-precipitation method was adopted. Manganese nitrate, cerium nitrate and zirconium oxynitrate were prepared into a metal ion solution according to the mass ratio of manganese dioxide, cerium dioxide and zirconium dioxide of 1:3.5:5.5. Then, the solution was added dropwise to excess ammonia water. The pH was maintained between 9 and 10 throughout the process. Then, 5% of the mass of the composite oxide was added to the solution and stirred for 15 min. The resulting suspension was aged in a 70℃ water bath for 12 h. The solution was filtered and the filter cake was washed with distilled water 3 to 5 times. Then, it was spray dried at 260℃. The resulting precursor was calcined at 550℃ with air for 5 h and then allowed to stand for 10 h.

[0025] (2) Preparation of cerium-aluminum composite oxide: The cerium nitrate solution was impregnated onto the aluminum oxide by an equal volume impregnation method with a mass ratio of cerium oxide to aluminum oxide of 3:7. The mixture was then left to stand for 10 hours, dried at 120°C for 8 hours, and finally calcined at 550°C for 2 hours.

[0026] (3) Preparation of Pt / Pd / MnO2-CeO2-ZrO2: Platinum nitrate solution and palladium nitrate solution were co-impregnated onto the manganese-cerium-zirconium composite oxide by an equal volume impregnation method, then left to stand for 10 hours, dried at 120℃ for 8 hours, and finally calcined at 550℃ for 2 hours.

[0027] (4) Preparation of Rh / CeO2-Al2O3: Rhodium nitrate solution was impregnated onto the cerium-aluminum composite oxide by an equal volume impregnation method, then left to stand for 10 hours, dried at 120℃ for 8 hours, and finally calcined at 550℃ for 2 hours.

[0028] (5) Catalyst preparation: Pt / Pd / MnO2-CeO2-ZrO2, Rh / CeO2-Al2O3, and barium acetate were added to deionized water, with a solid content of 30%. The mixture was stirred evenly to form a slurry. The slurry was then processed using a ball milling process to control the particle size D. 90 The slurry is mixed thoroughly and then coated onto the carrier. It is then dried at 120°C for 8 hours and calcined at 550°C for 2 hours.

[0029] Example 2

[0030] A lean-burn NO in a diesel engine exhaust purification system x The catalyst trapping includes a support and a coating applied to the support, wherein the catalyst support is a cordierite ceramic support with a volume of 0.73 L and a pore density of 400 mesh / square inch;

[0031] The total coating amount is 380 g / L, including a total loading of 4.5 g / L of precious metals, 140 g / L of manganese-cerium-zirconium composite oxide, 215.5 g / L of cerium-aluminum composite oxide, and 20 g / L of barium oxide. The precious metals include 3.8 g / L of LPt, 0.5 g / L of LPd, and 0.2 g / L of LRh. The preparation method of the lean-burn NOx capture catalyst for the above-mentioned diesel engine exhaust gas purification system includes the following steps:

[0032] (1) Preparation of manganese-cerium-zirconium composite oxide: The co-precipitation method was adopted. Manganese nitrate, cerium nitrate and zirconium oxynitrate were prepared into a metal ion solution according to the mass ratio of manganese dioxide, cerium dioxide and zirconium dioxide of 1:2:2. Then, the solution was added dropwise to excess ammonia water. The pH was maintained between 9 and 10 throughout the process. Then, 5% of the mass of the composite oxide was added to the solution and stirred for 15 min. The resulting suspension was aged in a 70℃ water bath for 12 h. The solution was filtered and the filter cake was washed with distilled water 3 to 5 times. Then, it was spray-dried at 260℃. The resulting precursor was calcined at 550℃ with air for 5 h and then allowed to stand for 10 h.

[0033] (2) Preparation of cerium-aluminum composite oxide: The cerium nitrate solution was impregnated onto the aluminum oxide by an equal volume impregnation method with a mass ratio of cerium oxide to aluminum oxide of 2:3. The mixture was then left to stand for 10 hours, dried at 120°C for 8 hours, and finally calcined at 550°C for 2 hours.

[0034] (3) Preparation of Pt / Pd / MnO2-CeO2-ZrO2: Platinum nitrate solution and palladium nitrate solution were co-impregnated onto the manganese-cerium-zirconium composite oxide by an equal volume impregnation method, then left to stand for 10 hours, dried at 120℃ for 8 hours, and finally calcined at 550℃ for 2 hours.

[0035] (4) Preparation of Rh / CeO2-Al2O3: Rhodium nitrate solution was impregnated onto the cerium-aluminum composite oxide by an equal volume impregnation method, then left to stand for 10 hours, dried at 120℃ for 8 hours, and finally calcined at 550℃ for 2 hours.

[0036] (5) Catalyst preparation: Pt / Pd / MnO2-CeO2-ZrO2, Rh / CeO2-Al2O3, and barium acetate were added to deionized water, with a solid content of 32%. The mixture was stirred evenly to form a slurry. The slurry was then processed using a ball milling process to control the particle size D. 90 The slurry is mixed thoroughly and then coated onto the carrier. It is then dried at 120°C for 8 hours and calcined at 550°C for 2 hours.

[0037] NO x Storage capacity test

[0038] The catalysts in embodiments 1 and 2 were subjected to NO treatment at 150℃, 200℃, 250℃, 300℃, 350℃ and 400℃, respectively. x Storage capacity test: The atmosphere contained 250 ppm NO, 10% O2, 5% H2O, and 5% CO2, with N2 as the balance gas, for a duration of 600 s and a volume hourly space velocity (VHSV) of 80,000 h⁻¹. -1 The concentration of the outlet product was detected using Fourier transform infrared spectroscopy (FTIR), and NO was calculated by integrating the adsorption curve. x Storage capacity, NO x The storage capacity results are shown in Table 1.

[0039] NO x Conversion efficiency evaluation

[0040] Twenty lean / rich fuel switching cycles were performed at 150℃, 200℃, 250℃, 300℃, 350℃ and 400℃ respectively. xConversion efficiency was evaluated using a lean-burn atmosphere containing 250 ppm NO, 10% O2, 1000 ppm CO, 300 ppm C3H6, 5% H2O, and 5% CO2, with N2 as the balance gas for 100 s. A rich-burn atmosphere containing 250 ppm NO, 0.5% O2, 2% CO, 0.5% H2, 900 ppm C3H6, 5% H2O, and 5% CO2, with N2 as the balance gas for 10 s. The volumetric hourly space velocity (VHSV) was 80,000 h⁻¹. -1 The concentration of the effluent product was determined using Fourier transform infrared spectroscopy (FTIR), and the average NO concentration over 20 cycles was calculated. x Conversion efficiency.

[0041] Table 1. NO content of catalysts in Examples 1 and 2 at different temperatures. x Storage capacity

[0042]

[0043] As can be seen from Table 1, within the temperature range of 200-350℃, the NO content of the catalysts in Examples 1 and 2... x The storage capacity is all above 2.0 g / L.

[0044] Table 2 shows the average NO content of the catalysts in Examples 1-2 under lean / rich combustion switching cycle conditions. x Conversion efficiency.

[0045]

[0046] Table 2 shows that, within a temperature range of 150-400℃, the NO content in Example 2... x The conversion efficiency was significantly higher than that of Example 1, wherein the catalyst in Example 2 was used in NO at 250-400℃. x Conversion rates were all above 94%.

[0047] The lean-burn NOx capture catalyst in this embodiment of the invention is applied to a diesel engine exhaust purification system. When the engine is running under lean-burn conditions, the lean-burn NOx capture catalyst removes NO from the engine exhaust. x Stored on the catalyst coating, NO will be released when the engine switches to fuel-rich conditions. x Reduced to N2. Lean NO x Catalysts for capturing NO in engine exhaust x When in contact, NO at 200-350℃ x Storage capacity is greater than 2.0 g / L.

[0048] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. The application of a lean-burn NOx capture catalyst in a diesel engine exhaust gas purification system, the lean-burn NOx capture catalyst comprising a matrix and a coating applied to the matrix, characterized in that, The coating is composed of NOx storage components, noble metals, manganese-containing composite oxides and cerium-aluminum composite oxides, wherein the NOx storage components are alkaline earth metal oxides. The coating contains 20-40% manganese composite oxide and 50-70% cerium-aluminum composite oxide by mass. The manganese-containing composite oxide is a manganese-cerium-zirconium composite oxide, composed of MnOx, cerium dioxide, and zirconium dioxide, wherein the mass fraction of MnOx is 10-20%, the mass fraction of cerium dioxide is 30-50%, and the mass fraction of zirconium dioxide is 40-60%. The cerium-aluminum composite oxide is composed of cerium dioxide and aluminum oxide, wherein the mass fraction of cerium dioxide is 20-40% and the mass fraction of aluminum oxide is 60-80%. The precious metals include platinum (Pt), palladium (Pd), and rhodium (Rh), with Pt / Rh = 10:1-20:1 and Pd / Rh = 1:1-3:1 by mass ratio. When the lean-burn NOx capture catalyst comes into contact with NOx in engine exhaust gas, the NOx storage capacity is greater than 2.0 g / L at 200-350°C. The lean-burn NOx capture catalyst is applied to the diesel engine exhaust purification system. When the engine is running under lean-burn conditions, the lean-burn NOx capture catalyst stores NOx in the engine exhaust gas on the catalyst coating. When the engine switches to running under rich-burn conditions, the NOx is reduced to N2.

2. The application of the lean-burn NOx capture catalyst in the diesel engine exhaust gas purification system according to claim 1, characterized in that, The alkaline earth metal oxide is barium oxide, and the mass fraction of the alkaline earth metal oxide in the coating is 3-10%.

Images