Oxidation catalyst based on composite rare earth citrate coating forming a catalyst coating

Abstract

The application discloses a kind of oxidation type catalytic converter with high-efficiency processing hydrocarbon HC and carbon monoxide CO based on composite rare earth citrate coating forming catalyst coating, which is composed of DOC carrier and catalyst coated in the DOC carrier, and the catalyst is formed by coating and sintering of catalyst coating liquid, the catalyst coating liquid includes solid intermediate and metal ion solution, the solid intermediate includes inner layer and outer layer, the inner layer is cerium-zirconium-potassium composite citrate-alumina composite, and the outer layer is lanthanum-manganese-copper-nickel composite citrate, the metal ion solution contains nitrate and citric acid of lanthanum-manganese-copper-nickel, and further includes the coating method of the catalytic converter, the catalytic converter does not contain noble metal, and can replace the oxidation type catalytic converter of existing noble metal catalyst used, to reduce the use cost of user.

Description

TECHNICAL FIELD

[0001] The present application relates to oxidation catalysts used in diesel exhaust aftertreatment systems. BACKGROUND

[0002] The catalyst used in the oxidation catalysts (DOC) for diesel exhaust aftertreatment available in the market is a noble metal catalyst coated on a coating layer of an auxiliary catalyst such as alumina / ceria, and the noble metal coating amount generally needs to be 10-40 g / ft 3 , and the greater the noble metal coating amount, the better the catalytic effect. However, the noble metal is expensive, and users cannot afford it.

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

[0004] CN101767000A provides a diesel vehicle exhaust soot direct oxidation catalyst and a preparation method thereof. The catalytic material is composed of an oxide carrier MO2 and a bimetallic oxide active component AxByOz, and the structure is AxByOz / MO2. A and B are two metals selected from La, Ce, Fe, K and Cu, and MO2 is an oxide carrier such as TiO2, γ-Al2O3, CeO2 and ZrO2. The preparation method is to form a complex solution by mixing ion solutions of A and B with complexing agents such as citric acid, urea, PVP and oxalic acid, then add one of the above oxides while mechanically stirring to make it fully adsorb, and then put the solution into a muffle furnace at 500-700°C, so that the solution rapidly reacts and decomposes to synthesize the active component in situ on the surface of the oxide.

[0005] CN102000565A discloses a preparation method of a composite catalyst for eliminating diesel vehicle soot, which takes a Ce-Zr-based rare earth composite as a carrier and a La-Mn-based perovskite as an active component. The carrier contains cerium dioxide and zirconium dioxide, and alumina or rare earth oxide is added as a crystal form stabilizer. The preparation process steps include: (1) dissolving nitrate or carbonate of cerium, zirconium and the stabilizer respectively, adding a surfactant solution, adjusting the reaction pH to 7-11, then obtaining a precipitation solution, and roasting to prepare the Ce-Zr-based rare earth composite carrier; (2) dissolving nitrate or citrate of lanthanum, manganese and the additive respectively, preparing a sol impregnation solution, impregnating the Ce-Zr-based rare earth composite carrier in the sol, evaporating and drying, and then roasting to obtain the composite catalyst.

[0006] The above scheme produces catalyst particles, and in the process of coating the DOC or DPF carrier, the particles need to be combined into the DOC or DPF carrier with the help of adhesives and other aids. The addition of the aids causes the coating liquid to chemically react with the catalyst particles during the preparation and sintering process, and the catalytic performance of the coated catalyst is greatly reduced.

[0007] The patent application with application number 2020110169933 and invention name of Oxidation Type Catalyst for Diesel Engine Exhaust Aftertreatment and Manufacturing Method Thereof proposes a catalyst coating with cerium-zirconium composite oxide as the inner coating and lanthanum-manganese-copper composite oxide as the outer coating. The cerium-zirconium composite oxide powder is first prepared, the inner coating is coated with cerium-zirconium composite oxide powder and alumina sol, the outer coating is coated with lanthanum-manganese-copper nitric acid solution, and the catalyst coating in the DOC is sintered to have good treatment effect on particulate matter, HC, CO and NOx. However, it is further found that the coating can still be improved to improve the treatment effect of HC and CO. SUMMARY

[0008] The purpose of the present application is to provide an oxidation type catalyst based on composite rare earth citrate coating to form a catalyst coating with high efficiency in treating hydrocarbons HC and carbon monoxide CO.

[0009] The oxidation type catalyst based on composite rare earth citrate coating to form a catalyst coating of the present application is used in the diesel engine exhaust aftertreatment system to mainly treat hydrocarbon and carbon monoxide pollutants, and is composed of a DOC carrier and a catalyst coated in the DOC carrier. The catalyst is formed by coating and sintering of a catalyst coating liquid, and the catalyst coating liquid includes a solid intermediate and a metal ion solution. The solid intermediate includes an inner layer and an outer layer. The inner layer is a cerium-zirconium-potassium composite citrate-alumina composite, in which the molar ratio of cerium-zirconium-potassium elements is 1:(0.2-0.5):(0.2-0.5), and the ratio of cerium element to alumina is 1 mol:(100-300)g. The outer layer is a lanthanum-manganese-copper-nickel composite citrate, in which the molar ratio of lanthanum-manganese-copper-nickel elements 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-nickel ions. The ratio of the inner layer to the outer layer is 1:(0.2-0.5) according to the molar ratio of cerium to lanthanum. The metal ion solution contains nitrate and citric acid of lanthanum-manganese-copper-nickel, in which the molar ratio of lanthanum-manganese-copper-nickel elements 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-nickel ions. The ratio of the solid intermediate to the metal ion solution is 1:(0.2-0.4) according to the molar ratio of cerium to lanthanum. The coating method of the catalyst includes the following steps:

[0010] A. Dissolve cerium nitrate, zirconium nitrate and potassium nitrate in water according to the proportion of cerium, zirconium and potassium in the intermediate solid, and prepare a mixed solution. Add citric acid according to the proportion, and then add alumina powder according to the proportion. Stir and heat at 78-85 ℃ until a viscous fluid is formed. Dry at 120-200 ℃ for 4-10 hours, cool, and obtain a cerium-zirconium-potassium composite citrate-alumina composite;

[0011] B. Dissolve lanthanum nitrate, manganese nitrate, copper nitrate and nickel nitrate in water according to the proportion of lanthanum, manganese, copper and nickel in the outer layer of the intermediate solid. Add citric acid according to the proportion, and then add the cerium-zirconium-potassium composite citrate-alumina composite. Ball mill for 5-20 hours, stir and heat at 78-85 ℃ until a viscous fluid is formed. Dry at 120-200 ℃ for 4-10 hours, cool, and crush to obtain the intermediate solid.

[0012] C. Dissolve lanthanum nitrate, manganese nitrate, copper nitrate and nickel nitrate in water according to the proportion of metal ions. Add citric acid according to the proportion, and then add the intermediate solid. Ball mill for 5-20 hours to prepare a catalyst coating solution with an intermediate solid content of 10-25 wt%.

[0013] D. Apply the catalyst coating solution to the DOC carrier, dry, and sinter at 550-650 ℃.

[0014] E. Repeat step D until the catalyst coating amount in the DOC carrier is 50-100 g / L.

[0015] In the present application, the alumina can be selected from γ-Al2O3 or pseudoboehmite.

[0016] Preferably, in step A, 5-20 wt% of polyethylene glycol or polyethylene glycol-polypropylene glycol block copolymer is added to the mixed solution.

[0017] In step A, the drying temperature is preferably 140-160 ℃.

[0018] In step B, 5-20 wt% of polyethylene glycol or polyethylene glycol-polypropylene glycol block copolymer is added to the citric acid.

[0019] The application removes NO2 by heating and reacting metal nitrate and citric acid in solution to form metal composite citrate, and the coating is coated by mixing citrate and metal ion solution, and after sintering, fine pores are formed due to the decomposition of citric acid, so that the catalyst has a high specific surface area, and the metal ion solution of the catalyst composition can play the role of a binder for the DOC carrier, avoiding the negative effects of using alumina sol and other binders to coat the catalyst, so that the oxidation type catalyst can efficiently treat HC and CO in diesel engine exhaust, does not contain noble metals, and can replace the existing noble metal catalyst oxidation type catalyst to reduce the user's use cost. DETAILED DESCRIPTION

[0020] The DOC carrier used in the following examples has a diameter of 143.8 mm, a length of 100 mm, a mesh size of 400, and a cylindrical straight-flow cordierite carrier, and a volume of 1.62 L. Example 1

[0021] According to the molar ratio of cerium, zirconium and potassium elements 1:0.3:0.4, 434 grams of Ce(NO3)3·6H2O, 128 grams of Zr(NO3)4·5H2O and 40 grams of KNO3 are dissolved in 1.7 L of water to form a solution, 322 grams of C6H8O7·H2O and 30 grams of polyethylene glycol are added, and after dissolution, 150 grams of pseudoboehmite powder is added, and the mixture is stirred and heated in a water bath at 80°C, and then evaporated and concentrated into a viscous fluid, and dried in an oven at 150°C for 6 hours to obtain 630 grams of cerium-zirconium-potassium composite citrate-alumina composite.

[0022] According to the molar ratio of lanthanum, manganese, copper and nickel elements 1:3:1:2, and the molar ratio of cerium and lanthanum 1:0.3, 130 grams of La(NO3)3·6H2O, 322 grams of 50wt% Mn(NO3)2 aqueous solution, 72 grams of Cu(NO3)2·3H2O and 174 grams of Ni(NO3)2·6H2O are dissolved in 2.0 L of water to form a solution, and then 353 grams of C6H8O7·H2O and 30 grams of polyethylene glycol are added, and after dissolution, the cerium-zirconium-potassium composite citrate-alumina composite is added, and ball milling is carried out for 10 hours, and then the mixture is stirred and heated in a water bath at 80°C, and then evaporated and concentrated into a viscous fluid, and dried in an oven at 150°C for 6 hours, and then cooled to obtain 1120 grams of solid intermediate.

[0023] 86 grams of La(NO3)3.6H2O, 215 grams of 50 wt% Mn(NO3)2aqueous solution, 48 grams of Cu(NO3)2.3H2O and 116 grams of Ni(NO3)2.6H2O are dissolved in 3.5 L of water to form a solution, then 235 grams of C6H8O7.H2O and 30 grams of polyethylene glycol are added, after dissolution, the ground and crushed solid intermediate is added, stirred and mixed, the mixed solution is ball milled for 10 hours to become a catalyst coating solution.

[0024] The catalyst coating solution is coated on the DOC carrier, after drying, it is put into a kiln and heated to 600°C at a heating rate of 100°C / hour, kept for 2 hours and cooled; after repeating the coating and sintering for 3 times, the catalyst coating amount in the DOC is 69 g / L. Example 2

[0025] 434 grams of Ce(NO3)3.6H2O, 172 grams of Zr(NO3)4.5H2O and 40 grams of KNO3 are taken in a proportion of 1:0.4:0.4 of the molar ratio of cerium, zirconium and potassium, dissolved in 1.8 L of water to form a solution, 340 grams of C6H8O7.H2O and 30 grams of polyethylene glycol are added, after dissolution, 250 grams of pseudo-boehmite powder is added, stirred and heated in a water bath at 80°C, evaporated and concentrated into a viscous fluid, dried in an oven at 150°C for 6 hours to obtain 750 grams of cerium-zirconium-potassium composite citrate-alumina composite.

[0026] 173 grams of La(NO3)3.6H2O, 429 grams of 50 wt% Mn(NO3)2aqueous solution, 145 grams of Cu(NO3)2.3H2O and 174 grams of Ni(NO3)2.6H2O are dissolved in 2.8 L of water to form a solution, then 471 grams of C6H8O7.H2O and 40 grams of polyethylene glycol are added, after dissolution, the ground and crushed cerium-zirconium-potassium-alumina composite oxide is added, ball milled for 10 hours, stirred and heated in a water bath at 80°C, evaporated and concentrated into a viscous fluid, dried in an oven at 150°C for 6 hours, cooled and 1395 grams of solid intermediate is obtained.

[0027] 86 grams of La(NO3)3.6H2O, 215 grams of 50 wt% Mn(NO3)2aqueous solution, 48 grams of Cu(NO3)2.3H2O and 116 grams of Ni(NO3)2.6H2O are dissolved in 3.5 L of water to form a solution, then 235 grams of C6H8O7.H2O and 30 grams of polyethylene glycol are added, after dissolution, the ground and crushed solid intermediate is added, stirred and mixed, the mixed solution is ball milled for 10 hours to become a catalyst coating solution.

[0028] The catalyst coating solution is coated in the DOC carrier, dried, and then placed in a kiln and heated to 600°C at a heating rate of 100°C / hour, held for 2 hours, and cooled. After repeating the coating and sintering 3 times, the catalyst coating amount in the DOC is 73 g / L. Example 3

[0029] According to the molar ratio of cerium, zirconium and potassium of 1:0.4:0.2, 434 g of Ce(NO3)3·6H2O, 172 g of Zr(NO3)4·5H2O and 20 g of KNO3 are dissolved in 1.8 L of water to form a solution, 303 g of C6H8O7·H2O and 30 g of polyethylene glycol are added, and after dissolution, 250 g of pseudoboehmite powder is added. Stirring and heating in a water bath at 80°C, evaporate and concentrate into a viscous fluid, dry in an oven at 150°C for 6 hours, and obtain 710 g of cerium-zirconium-potassium citrate-alumina composite.

[0030] According to the molar ratio of lanthanum, manganese, copper and nickel of 1:2:1:2, and the molar ratio of cerium and lanthanum of 1:0.4, 173 g of La(NO3)3·6H2O, 286 g of 50wt% Mn(NO3)2 aqueous solution, 97 g of Cu(NO3)2·3H2O and 233 g of Ni(NO3)2·6H2O are dissolved in 2.4 L of water to form a solution, and then 403 g of C6H8O7·H2O and 30 g of polyethylene glycol are added. After dissolution, the cerium-zirconium-potassium citrate-alumina composite is added, ball milled for 10 hours, stirred and heated in a water bath at 80°C, evaporated and concentrated into a viscous fluid, dried in an oven at 150°C for 6 hours, and cooled to obtain 1280 g of solid intermediate.

[0031] According to the molar ratio of lanthanum, manganese, copper and nickel of 1:2:1:2, and the molar ratio of cerium and lanthanum of 1:0.4, 173 g of La(NO3)3·6H2O, 286 g of 50wt% Mn(NO3)2 aqueous solution, 97 g of Cu(NO3)2·3H2O and 232 g of Ni(NO3)2·6H2O are dissolved in 3.6 L of water to form a solution, and then 403 g of C6H8O7·H2O and 40 g of polyethylene glycol are added. After dissolution, the ground and crushed solid intermediate is added, stirred and mixed, and the mixed solution is ball milled for 10 hours to become a catalyst coating solution.

[0032] The catalyst coating solution is coated in the DOC carrier, dried, and then placed in a kiln and heated to 600°C at a heating rate of 100°C / hour, held for 2 hours, and cooled. After repeating the coating and sintering 3 times, the catalyst coating amount in the DOC is 70 g / L.

[0033] Performance test

[0034] Test method: The DOCs of Examples 1-3 were respectively packaged and connected to the exhaust system of a diesel engine with a rated power of 55 KW on an engine dynamometer test bench, at a fixed speed of 1500 r / 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, and the treatment efficiency of the DOC on HC and CO was calculated by taking the treatment efficiency%= (DOC rear concentration-DOC front concentration) / DOC front concentration*100%.

[0035] The treatment effect of Example 2 in the patent application specification with application number 2020110169933 was used as a comparative example.

[0036] The HC treatment efficiency of the DOC at each exhaust temperature of the engine was as follows:

[0037]

[0038] The CO treatment efficiency of the DOC at each exhaust temperature of the engine was as follows:

[0039]

[0040] It can be seen that the treatment efficiency of Examples 1-3 on HC and CO is obviously improved.

Claims

1. An oxidation catalyst based on a composite rare earth citrate coating to form a catalyst coating, used in a diesel engine exhaust aftertreatment system to treat 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 includes an inner layer and an outer layer. The inner layer is a cerium-zirconium-potassium composite citrate-alumina composite, wherein the molar ratio of cerium, zirconium, and potassium is 1:(0.2-0.5):(0.2-0.5), and the ratio of cerium to alumina is 1 mol:(100-300) g. The outer layer is a lanthanum-manganese-copper-nickel composite citrate, 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. The ratio of the inner layer to the outer layer is 1:(0.2-0.5) molar ratio of cerium to lanthanum. 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), and 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 1:(0.2-0.4) molar ratio of cerium to lanthanum. The coating method of this catalyst includes the following steps: A. Dissolve cerium nitrate, zirconium nitrate, and potassium nitrate in water according to the ratio of cerium, zirconium, and potassium elements in the inner layer of the solid intermediate to prepare a mixed solution. Add citric acid in the ratio mentioned above, and after dissolving, add alumina powder in the ratio mentioned above. Heat and stir at (78-85)℃ until it becomes a viscous fluid. Dry at (120-200)℃ for (4-10) hours and cool to obtain a cerium-zirconium-potassium composite citrate-alumina composite. B. Dissolve lanthanum nitrate, manganese nitrate, copper nitrate and nickel nitrate in water according to the lanthanum, manganese, copper and nickel ratio of the outer layer of the solid intermediate. Add citric acid according to the ratio. After dissolution, add cerium zirconium potassium composite citrate-alumina composite. Ball mill for (5-20) hours, heat and stir at (78-85)℃ until it becomes a viscous fluid. Dry at (120-200)℃ for (4-10) hours, cool, and pulverize to obtain the solid intermediate. C. Dissolve lanthanum nitrate, manganese nitrate, copper nitrate and nickel nitrate in water according to the metal ion solution ratio, add citric acid according to the ratio, add solid intermediate after dissolution, ball mill for (5-20) hours, and prepare a catalyst coating solution with a solid intermediate content of (10-25) wt%. D. The catalyst coating solution is coated onto the DOC support, dried, and then sintered at (550-650)℃. E. Repeat step D 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 alumina is γ-Al2O3.

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

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, characterized in that, In step B, polyethylene glycol or polyethylene glycol-polypropylene glycol block copolymer is also added at (5-20)% of the weight of citric acid.

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