Oxidation catalyst based on composite metal citrate coating to form catalyst coating

Abstract

This invention discloses an oxidation catalyst with high efficiency in treating hydrocarbons (HC) and carbon monoxide (CO) based on a composite metal citrate coating. The catalyst consists of a DOC support and a catalyst coated on the DOC support. The catalyst is formed by coating and sintering a catalyst coating solution, which includes a solid intermediate and a metal ion solution. The solid intermediate is a cerium-manganese-potassium composite citrate, and the metal ion solution contains lanthanum-manganese-copper-nickel nitrates and citric acid. The invention also includes a coating method for the catalyst. This catalyst does not contain precious metals and can replace existing oxidation catalysts using precious metal catalysts, reducing user costs.

Description

Technical Field

[0001] This invention relates to an oxidation catalyst (DOC) used in diesel engine exhaust aftertreatment systems. Background Technology

[0002] Existing diesel engine exhaust aftertreatment oxidation catalysts (DOCs) on the market use a catalyst made by coating a co-catalyst such as alumina / cerium oxide with a precious metal catalyst. The amount of precious metal coating is generally 10-40 g / ft. 3 The greater the amount of precious metal coating, the better the catalytic effect. However, precious metals are expensive, making them unaffordable for most users.

[0003] CN101939097A relates to a catalyst system for reactions of nitrogen oxides, carbon monoxide, hydrocarbons, and sulfur that is free of or substantially free of platinum group metals, comprising a substrate and a repair substrate coating, the repair substrate coating comprising at least one oxide solid, said oxide solid comprising one or more materials selected from the group consisting of: support material oxides, catalysts, and mixtures thereof.

[0004] CN101767000A provides a direct oxidation catalyst for diesel vehicle exhaust soot and its preparation method. The catalyst material consists of an oxide support MO2 and a bimetallic oxide active component AxByOz, forming an AxByOz / MO2 structure. A and B are two metals selected from La, Ce, Fe, K, and Cu, and MO2 is an oxide support such as TiO2, γ-Al2O3, CeO2, or ZrO2. The preparation method involves forming a complex solution by reacting an ionic solution of A and B with complexing agents such as citric acid, urea, PVP, and oxalic acid, then adding one of the aforementioned oxides while mechanically stirring to ensure full adsorption. The solution is then placed in a muffle furnace at 500-700℃, where it rapidly decomposes and the active component is synthesized in situ on the oxide surface.

[0005] CN102000565A discloses a method for preparing a composite catalyst for eliminating carbon soot from diesel vehicles, using a Ce-Zr-based rare earth composite as a support and supporting La-Mn-based perovskite as the active component; the support contains cerium dioxide and zirconium dioxide, and alumina or rare earth oxides are added as crystal stabilizers. The preparation process includes: (1) dissolving nitrates or carbonates of cerium, zirconium and stabilizers respectively, adding a surfactant solution, adjusting the reaction pH to 7-11, and then obtaining a precipitate, which is then calcined to prepare a Ce-Zr-based rare earth composite support; (2) dissolving nitrates or citrates of lanthanum, manganese and additives respectively, preparing a sol impregnation solution, impregnating the Ce-Zr-based rare earth composite support in the sol, evaporating and drying it, and then calcining it to obtain the composite catalyst.

[0006] The above method produces catalyst particles. During the coating process on DOC or DPF supports, the particles need to be combined with binders and other additives to bind to the DOC or DPF supports. The addition of additives causes the coating solution to react chemically with the catalyst particles during the preparation and sintering process, resulting in a significant reduction in its catalytic performance after coating.

[0007] The patent application with application number 2020110169933, entitled "An Oxidation Catalyst for Diesel Engine Exhaust Aftertreatment and Its Manufacturing Method," proposes a catalyst coating with cerium-zirconium composite oxide as the inner coating and lanthanum-manganese-copper composite oxide as the outer coating. The process involves first preparing cerium-zirconium composite oxide powder, then coating the inner coating with cerium-zirconium composite oxide powder and alumina sol, and finally coating the outer coating with lanthanum-manganese-copper copper nitrate solution. After sintering, the resulting catalyst coating in DOC (Diesel Exhaust Catalyst) exhibits good treatment effects on particulate matter, HC, CO, and NOx. However, further research has revealed that the coating can be improved to enhance the treatment effect on HC and CO. Summary of the Invention

[0008] The purpose of this invention is to provide an oxidation catalyst based on a composite metal citrate coating to form a catalyst coating that can efficiently process hydrocarbons HC and carbon monoxide CO.

[0009] This invention relates to an oxidation catalyst based on a composite metal citrate coating, used in diesel engine exhaust aftertreatment systems to primarily treat hydrocarbon and carbon monoxide pollutants. It comprises a DOC support and a catalyst coated on the DOC support. The catalyst is characterized by being formed by coating and sintering a catalyst coating solution, which includes a solid intermediate and a metal ion solution. The solid intermediate is a cerium-manganese-potassium composite citrate, wherein the molar ratio of cerium, manganese, and potassium is 1:(0.5-1). The catalyst coating method includes the following steps: (0.1-0.3), citric acid is (0.5-0.8) times the total molar amount of cerium, manganese, and potassium, the metal ion solution contains lanthanum, manganese, copper, and nickel nitrates and citric acid, wherein the molar ratio of lanthanum, manganese, copper, and nickel is 1:(2-4):(1-2):(1-3), citric acid is (0.7-1.0) times the total molar amount of lanthanum, manganese, copper, and nickel ions, and the ratio of solid intermediate to metal ion solution is 1:(0.5-0.8) based on the molar ratio of cerium to lanthanum.

[0010] A. Dissolve cerium nitrate, manganese nitrate, and potassium nitrate in water according to the molar ratio of cerium, manganese, and potassium to prepare a mixed solution. Add citric acid in the specified ratio, heat and stir at (78-85)℃ until it becomes a viscous fluid, and dry at (100-200)℃ for (4-10) hours to obtain a solid intermediate.

[0011] B. Dissolve lanthanum nitrate, manganese nitrate, copper nitrate and nickel nitrate in water according to the molar ratio of lanthanum, manganese, copper and nickel elements in the metal ion solution, add citric acid in the specified ratio, add solid intermediate after dissolution, ball mill for (5-20) hours, and prepare a catalyst coating solution with a solid intermediate content of (10-20) wt%.

[0012] C. Coat the catalyst coating solution onto the DOC support, dry it, and then sinter it at (550-650)℃.

[0013] D. Repeat step C until the catalyst coating amount in the DOC support is (50-100) g / L.

[0014] In this invention, the molar ratio of cerium, manganese, and potassium in the solid intermediate is 1:(0.7-0.9):(0.15-0.25).

[0015] Preferably, in step A, (5-20)% by weight of polyethylene glycol or polyethylene glycol-polypropylene glycol block copolymer of citric acid is added to the mixed solution.

[0016] In step A, the drying temperature is preferably (140-160)℃.

[0017] In step B, polyethylene glycol or polyethylene glycol-polypropylene glycol block copolymer, weighing (5-20)% of citric acid, is also added to the metal ion solution.

[0018] This invention involves heating and reacting metal nitrates with citric acid in solution to remove NO2, resulting in a metal composite citrate. The coating is applied using a mixture of citrate and metal ion solution. After sintering, the decomposition of citric acid creates fine pores, giving the catalyst a high specific surface area. The metal ion solution used in the catalyst composition acts as a binder with the DOC support, avoiding the negative effects of using binders such as alumina sol, which can lead to the coating of alumina catalyst. This allows the oxidation catalyst to efficiently treat HC and CO in diesel engine exhaust, without containing precious metals, and can replace existing oxidation catalysts with precious metal catalysts, reducing user costs. Detailed Implementation

[0019] The DOC carrier used in the following examples is a cylindrical DC cordierite carrier with a diameter of 143.8 mm, a length of 100 mm, a mesh size of 400, and a volume of 1.62 L. Example 1

[0020] According to the molar ratio of cerium, manganese and potassium elements of 1:0.9:0.2, 434 g of Ce(NO3)3·6H2O, 322 g of 50 wt% Mn(NO3)2 aqueous solution and 20 g of KNO3 were dissolved in 2.0 L of water to prepare a solution. 294 g of C6H8O7·H2O and 30 g of polyethylene glycol were added. The solution was stirred and heated in an 80 °C water bath to evaporate and concentrate it into a viscous fluid. The solution was dried in an oven at 150 °C for 6 hours and then cooled to obtain 495 g of solid intermediate.

[0021] A solution was prepared by dissolving 217 g of La(NO3)3·6H2O, 537 g of 50 wt% Mn(NO3)2 aqueous solution, 121 g of Cu(NO3)2·3H2O, and 291 g of Ni(NO3)2·6H2O in 1.5 L of water according to the molar ratio of lanthanum, manganese, copper, and nickel being 1:3:1:2 and the molar ratio of cerium to lanthanum being 1:0.5. Then, 525 g of C6H8O7·H2O and 40 g of polyethylene glycol were added and dissolved. After dissolving, a ground and pulverized solid intermediate was added and stirred. The mixture was ball-milled for 10 hours to obtain the catalyst coating solution.

[0022] The catalyst coating solution was coated onto the DOC support, dried, and then placed in a kiln to be heated to 600°C at a heating rate of 100°C / hour and sintered for 2 hours. After cooling, the catalyst coating amount in the DOC support was 78 g / L after the coating and sintering were repeated 3 times. Example 2

[0023] 434 g of Ce(NO3)3·6H2O, 286 g of 50 wt% Mn(NO3)2 aqueous solution, and 20 g of KNO3 were prepared by dissolving them in 2.0 L of water according to the molar ratio of cerium, manganese, and potassium of 1:0.8:0.2. 294 g of C6H8O7·H2O and 30 g of polyethylene glycol were added, and the mixture was stirred and heated in an 80 °C water bath to evaporate and concentrate it into a viscous fluid. The fluid was then dried in an oven at 150 °C for 6 hours and cooled to obtain 490 g of solid intermediate.

[0024] A solution was prepared by dissolving 260 g of La(NO3)3·6H2O, 429 g of 50 wt% Mn(NO3)2 aqueous solution, 145 g of Cu(NO3)2·3H2O, and 349 g of Ni(NO3)2·6H2O in 1.5 L of water according to the molar ratio of lanthanum, manganese, copper, and nickel being 1:2:1:2 and the molar ratio of cerium to lanthanum being 1:0.6. Then, 670 g of C6H8O7·H2O and 50 g of polyethylene glycol were added and dissolved. After dissolving, a ground and pulverized solid intermediate was added and stirred. The mixture was then ball-milled for 10 hours to obtain the catalyst coating solution.

[0025] The catalyst coating solution was coated onto the DOC support, dried, and then placed in a kiln to be heated to 600°C at a heating rate of 100°C / hour and sintered for 2 hours. After cooling, the catalyst coating amount in the DOC support was 69 g / L after repeating the coating and sintering process 3 times. Example 3

[0026] 434 g of Ce(NO3)3·6H2O, 286 g of 50 wt% Mn(NO3)2 aqueous solution, and 20 g of KNO3 were prepared by dissolving them in 2.0 L of water according to the molar ratio of cerium, manganese, and potassium of 1:0.8:0.2. 294 g of C6H8O7·H2O and 30 g of polyethylene glycol were added, and the mixture was stirred and heated in an 80 °C water bath to evaporate and concentrate it into a viscous fluid. The fluid was then dried in an oven at 150 °C for 6 hours and cooled to obtain 492 g of solid intermediate.

[0027] A solution was prepared by dissolving 303 g of La(NO3)3·6H2O, 752 g of 50 wt% Mn(NO3)2 aqueous solution, 254 g of Cu(NO3)2·3H2O, and 305 g of Ni(NO3)2·6H2O in 1.5 L of water according to the molar ratio of lanthanum, manganese, copper, and nickel of 1:3:1.5:1.5 and the molar ratio of cerium to lanthanum of 1:0.7. Then, 670 g of C6H8O7·H2O and 40 g of polyethylene glycol were added and dissolved. After dissolving, a ground and pulverized solid intermediate was added and stirred. The mixture was ball-milled for 10 hours to obtain the catalyst coating solution.

[0028] The catalyst coating solution was coated onto the DOC support, dried, and then placed in a kiln to be heated to 600°C at a heating rate of 100°C / hour and sintered for 2 hours. After cooling, the catalyst coating amount in the DOC support was 67 g / L after the coating and sintering were repeated 3 times.

[0029] Performance testing

[0030] Test method: The DOCs of Examples 1-3 were packaged separately and connected to the exhaust system of a 55KW diesel engine on a dynamometer test bench. At a fixed speed of 1500r / min, different exhaust temperatures were obtained by adjusting the output power. The concentrations of hydrocarbons (HC) and carbon monoxide (CO) at the front and rear ends of the DOC were measured at each temperature. The treatment efficiency % was calculated as (concentration after DOC - concentration before DOC) / concentration before DOC * 100%, and the treatment efficiency of the DOC for HC and CO was calculated.

[0031] The processing effect of Example 2 in the patent application specification with application number 2020110169933 is used as a comparative example.

[0032] The DOC-HC treatment efficiency at various engine exhaust temperatures is as follows:

[0033]

[0034] The CO removal efficiency of DOC at various engine exhaust temperatures is as follows:

[0035]

[0036] It is evident that Examples 1-3 significantly improved the processing efficiency of HC and CO.

Claims

1. An oxidation catalyst based on a composite metal citrate coating to form a catalyst coating, used in a diesel engine exhaust aftertreatment system primarily for treating hydrocarbon and carbon monoxide pollutants, comprising a DOC support and a catalyst coated on the DOC support, characterized in that, The catalyst is formed by coating and sintering a catalyst coating solution. The catalyst coating solution includes a solid intermediate and a metal ion solution. The solid intermediate is a cerium-manganese-potassium composite citrate, wherein the molar ratio of cerium, manganese, and potassium is 1:(0.5-1):(0.1-0.3). The metal ion solution contains lanthanum-manganese-copper-nickel nitrate and citric acid, wherein the molar ratio of lanthanum, manganese, copper, and nickel is 1:(2-4):(1-2):(1-3), and the citric acid is 0.7-1.0 times the total molar amount of lanthanum, manganese, copper, and nickel ions. The ratio of the solid intermediate to the metal ion solution is based on a cerium to lanthanum molar ratio of 1:(0.5-0.8). The coating method of this catalyst includes the following steps: A. Dissolve cerium nitrate, manganese nitrate, and potassium nitrate in water according to the molar ratio of cerium, manganese, and potassium to prepare a mixed solution. Add citric acid at 0.5-0.8 times the total molar amount of cerium, manganese, and potassium. Heat and stir at 78-85°C until it becomes a viscous fluid. Dry at 100-200°C for 4-10 hours to obtain a solid intermediate. B. Dissolve lanthanum nitrate, manganese nitrate, copper nitrate and nickel nitrate in water according to the molar ratio of lanthanum, manganese, copper and nickel elements in the metal ion solution, add citric acid in the specified proportion, add solid intermediate after dissolution, ball mill for 5-20 hours, and prepare a catalyst coating solution with a solid intermediate content of 10-20 wt%. C. Coat the catalyst coating solution onto the DOC support, dry it, and then sinter it at 550-650℃. D. Repeat step C until the catalyst coating amount in the DOC support is 50-100 g / L.

2. The catalyst according to claim 1, characterized in that, The molar ratio of cerium, manganese, and potassium in the solid intermediate is 1:(0.7-0.9):(0.15-0.25).

3. The catalyst according to claim 1, characterized in that, In step A, 5-20% by weight of polyethylene glycol or polyethylene glycol-polypropylene glycol block copolymer of citric acid is also added to the mixed solution.

4. The catalyst according to claim 1 or 2, characterized in that, In step A, the drying temperature is 140-160℃.

5. The catalyst according to claim 1 or 2, characterized in that, In step B, 5-20% by weight of polyethylene glycol or polyethylene glycol-polypropylene glycol block copolymer of citric acid is also added to the metal ion solution.

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