CN113600188A - Catalyst for purifying tail gas of gasoline vehicle and preparation method thereof - Google Patents
Catalyst for purifying tail gas of gasoline vehicle and preparation method thereof Download PDFInfo
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- CN113600188A CN113600188A CN202110914903.0A CN202110914903A CN113600188A CN 113600188 A CN113600188 A CN 113600188A CN 202110914903 A CN202110914903 A CN 202110914903A CN 113600188 A CN113600188 A CN 113600188A
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/56—Platinum group metals
- B01J23/63—Platinum group metals with rare earths or actinides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8643—Removing mixtures of carbon monoxide or hydrocarbons and nitrogen oxides
- B01D53/8646—Simultaneous elimination of the components
- B01D53/865—Simultaneous elimination of the components characterised by a specific catalyst
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Abstract
The invention relates to a gasoline vehicle tail gas purification catalyst and a preparation method thereof, wherein the catalyst comprises a honeycomb carrier, a lower Pt coating, a middle Pd coating and an upper Rh coating, and the lower Pt coating also comprises a first Pt-loaded cerium-zirconium composite oxide, CeO2‑Al2O3And an alkaline earth metal compound, the intermediate Pd coating further comprising Pd-supported La2O3‑Al2O3A second cerium-zirconium composite oxide and an alkaline earth metal compound, wherein the upper Rh coating layer also comprises a third cerium-zirconium composite oxide loaded with Rh and La2O3‑Al2O3. The Pt coating in the catalyst of the invention is at the lowest layer due to the heat conduction shieldHigh-temperature sintering caused by rapid contact with tail gas is relieved; at the same time, the first cerium-zirconium composite oxide and CeO2The synergistic effect of the preparation process of firstly alkalizing, loading and then acidifying the doped alumina and the Pt precursor promotes the interaction between Pt and the carrier, greatly improves the high-temperature stability of Pt, and the prepared tail gas purification catalyst still has high conversion capacity of hydrocarbon, carbon monoxide and nitrogen oxide after aging.
Description
Technical Field
The invention belongs to the technical field of motor vehicle tail gas purification catalysts, and particularly relates to a gasoline vehicle tail gas purification catalyst and a preparation method thereof.
Background
In 2019, the emission of carbon monoxide (CO) of motor vehicles nationwide is 771.6 ten thousand tons, the emission of Hydrocarbons (HC) is 189.2 ten thousand tons, and the emission of nitrogen oxides (NOx) is 635.6 ten thousand tonsAnd the amount of the Particulate Matters (PM) is 7.4 ten thousand tons, so that serious air pollution is caused, and the health of residents in large and medium-sized cities is greatly threatened. In order to control the pollutant emission of motor vehicles, the light automobile pollutant emission regulation (called country I for short) is continuously tightened from 2001 in China, and the light automobile pollutant emission regulation goes through five stages from country I to country V to implement the country V I. Three-way catalysts (TWCs) can simultaneously convert harmful CO, HC and NOx in automobile exhaust into nontoxic CO2And H2O, so the application is very wide.
In recent years, the price of Pt is stable and the price of Pd continues to rise with fluctuations in the supply and demand of the precious metal market. In 9 months of 2020, the monthly average price of Pd is about 2.5 times that of Pt. In the sixth stage of China, in order to meet the strict requirement of pollutant emission limit, the noble metal dosage of the three-way catalyst is generally higher, and a Pd-Rh formula is mainly adopted. The severe fluctuation of the price of the Pd noble metal leads the cost of an automobile exhaust after-treatment system to be greatly increased, and the economic acceleration is slowed down, so that the automobile industry faces unprecedented challenges, and numerous automobile enterprises aim at focusing on the Pt noble metal which has stable price and similar catalytic characteristics with the Pd noble metal. However, the high temperature thermal stability of Pt noble metals is inferior to Pd, and the catalytic activity after high temperature aging is usually very different from Pd. Accordingly, many researchers have focused on the industrial problem of how to improve the high-temperature aging resistance of Pt catalysts.
Related researchers in patent CN 109012665B, supported noble metal by uniform precipitation method, improved Pt dispersion, although the catalytic activity is improved, reduced noble metal particle size, easy aggregation and growth under high temperature, and certain risk in the practical application process.
Disclosure of Invention
The invention aims to solve the problems that in the prior art of three-way catalysts, the high-temperature thermal stability of Pt noble metal is poor, and the ageing resistance of the catalyst is reduced after equivalent Pd is replaced, and provides a gasoline vehicle tail gas purification catalyst and a preparation method thereof.
In order to solve the defects of the prior art, the invention adopts the following technical scheme:
on one hand, the embodiment of the invention provides a gasoline vehicle tail gas purification catalyst, which comprises a carrier, and a lower coating, a middle coating and an upper coating which are sequentially coated on the carrier, wherein the lower coating is loaded with Pt, the middle coating is loaded with Pd, and the upper coating is loaded with Rh;
the lower coating layer also comprises a first cerium-zirconium composite oxide loaded with Pt, CeO2-Al2O3And an alkaline earth metal compound, the intermediate coating further comprising Pd-supported La2O3-Al2O3A second cerium-zirconium composite oxide and an alkaline earth metal compound, wherein the upper coating layer also comprises a third cerium-zirconium composite oxide loaded with Rh and La2O3-Al2O3。
Further, the first cerium-zirconium composite oxide in the lower coating layer comprises the following components: 5 to 45wt% of ZrO250 to 80 weight percent of CeO2And 5 to 15 weight percent of La2O3、Y2O3、Pr6O11、Nd2O3One or more of them.
Further, CeO is arranged in the lower coating layer2-Al2O3Comprises the following components: 5 to 40 weight percent of CeO2And 60 to 95 weight percent of Al2O3。
Further, La in the intermediate coating layer and the upper coating layer2O3-Al2O3Comprises the following components: 1 to 5 weight percent of La2O3And 95 to 99 weight percent of Al2O3。
Further, the second cerium-zirconium composite oxide in the intermediate coating comprises the following components: 35 to 75wt% of ZrO220 to 50 weight percent of CeO2And 5 to 15 weight percent of La2O3、Y2O3、Pr6O11、Nd2O3One ofOr several of them.
Further, the alkaline earth metal compound in the lower layer coating and the middle layer coating is one or more of strontium sulfate, strontium carbonate, strontium hydrogen phosphate, strontium nitrate, strontium acetate, strontium oxide, strontium hydroxide, barium sulfate, barium carbonate, barium hydrogen phosphate, barium nitrate, barium acetate, barium oxide and barium hydroxide.
Further, the third cerium-zirconium composite oxide in the upper coating comprises the following components: 60 to 90wt% of ZrO25 to 25 weight percent of CeO2And 5 to 15 weight percent of La2O3、Y2O3、Pr6O11And Nd2O3One or more of them.
On the other hand, the embodiment of the invention provides a preparation method of a catalyst for purifying tail gas of a gasoline vehicle, which comprises the following steps:
(1) coating of the lower coating: dropwise adding an alkaline solution into the Pt precursor solution until the pH value of the mixed solution is 10-12 to prepare a Pt solution; adding the first cerium-zirconium composite oxide into deionized water, stirring for 10-30min, slowly adding the prepared Pt solution, stirring for 30-60min, dropwise adding an acid solution until the pH value of the mixed solution is 3-5, and adding CeO after 60-90min2-Al2O3And an alkaline earth metal compound, continuously stirring for 60-90min, performing ball milling to obtain lower-layer coating slurry, coating the slurry on a honeycomb carrier, drying the coated carrier at 80-150 ℃ for 0.2-24 h, and roasting the dried catalyst at 350-650 ℃ for 1-5 h to obtain a first semi-finished catalyst;
(2) coating of the intermediate coating: mixing the second cerium-zirconium composite oxide and La2O3-Al2O3Mixing an alkaline earth metal compound and deionized water according to a required proportion, ball-milling to obtain slurry, adding a Pd noble metal solution with a corresponding calculated amount into the slurry to form intermediate coating slurry, coating the slurry on the first semi-finished product catalyst prepared in the step (1), drying the coated catalyst at 80-150 ℃ for 0.2-24 h, roasting the dried catalyst at 350-650 ℃ for 1-5 h to obtain a second semi-finished productA catalyst;
(3) coating of the upper coating: mixing the third cerium-zirconium composite oxide and La2O3-Al2O3Mixing the catalyst and deionized water according to a required ratio, preparing slurry after ball milling, adding Rh precious metal solution with a corresponding calculated amount into the slurry to prepare upper-layer coating slurry, coating the slurry on the second semi-finished catalyst prepared in the step (2), drying the coated catalyst at 80-150 ℃ for 0.2-24 h, and roasting the dried catalyst at 350-650 ℃ for 1-5 h.
Further, the alkaline solution in the step (1) is one or more of ammonia water, tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetraethylammonium bromide.
Further, the acidic solution in the step (1) is one or more of nitric acid, formic acid, acetic acid, oxalic acid, citric acid, acrylic acid, glycolic acid, glycine and alanine.
Compared with the prior art, the invention has the following advantages:
the preparation method is simple and easy to operate, the prepared three-way catalyst Pt coating is positioned at the lowest layer, and high-temperature sintering caused by rapid contact with tail gas is relieved due to heat conduction shielding. The Pt precursor is firstly alkalized and adsorbed under the condition of pH value of 10-12 and then acidified and loaded under the condition of pH value of 3-5, so that the technical problem of poor Pt distribution uniformity is effectively solved, and simultaneously the initial particle size of Pt can be improved to a certain extent, which is favorable for reducing the aggregation and growth speed of Pt noble metal particles under the condition of continuous high temperature, the high cerium characteristic of the first cerium-zirconium composite oxide and the CeO of alumina2The doping is beneficial to the dispersion of the Pt noble metal, the synergistic effect of the designs promotes the interaction of Pt and the carrier, the prepared tail gas purifying catalyst greatly improves the high-temperature stability of Pt, and the catalyst still has high conversion capability of hydrocarbon, carbon monoxide and nitrogen oxide after aging.
Detailed Description
The technical solution of the present invention is further illustrated by the following specific examples.
Comparative example 1
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; the Pd coating is adhered on the carrier, the coating amount of the cured product is 100g/L, and the content of Pd is 50g/ft3(ii) a An Rh coating is adhered on the Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) coating process of Pd coating: 1000g of the first zirconium oxide composite oxide and 1000g of La were mixed2O3-Al2O3Mixing 200g of barium oxide and a proper amount of deionized water, performing ball milling to obtain coating slurry, adding a corresponding calculated amount of palladium nitrate solution into the slurry, coating the coating slurry on a honeycomb ceramic carrier according to the coating amount of a cured product of 100g/L, drying the coated catalyst at 120 ℃ for 5 hours, and then roasting the dried catalyst at 550 ℃ for 3 hours. Wherein the first zirconium oxide composite oxide comprises CeO240wt％、ZrO2 50wt％、La2O3 5wt％、Y2O3 5wt％，La2O3-Al2O3Has a composition of 5wt% of La2O3And 95wt% of Al2O3；
(2) Coating process of Rh coating: 1000g of the second zirconia composite oxide and 1000g of La were mixed2O3-Al2O3Mixing with a proper amount of deionized water, performing ball milling to obtain coating slurry, adding a rhodium nitrate solution with a corresponding calculated amount into the slurry, coating the coating slurry on a Pd coating-coated honeycomb ceramic carrier according to the coating amount of a cured product of 100g/L, drying the coated catalyst at 120 ℃ for 5 hours, and then roasting the dried catalyst at 550 ℃ for 3 hours. Wherein the second zirconium dioxide composite oxide comprises CeO230wt％、ZrO2 60wt％、La2O3 5wt％、Y2O3 5wt％，La2O3-Al2O3Has a composition of 5wt% of La2O3And 95wt% of Al2O3。
Comparative example 2
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; a Pd-Pt coating is attached on the carrier, the coating amount of a cured product is 100g/L, and the content of Pd is 25g/ft3Pt content of 25g/ft3(ii) a An Rh coating is adhered on the Pd-Pt coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) coating process of Pd-Pt coating: 1000g of the first zirconium oxide composite oxide and 1000g of La were mixed2O3-Al2O3Mixing 200g of barium oxide and a proper amount of deionized water, performing ball milling to obtain coating slurry, adding a palladium nitrate solution and a platinum nitrate solution with corresponding calculated amounts into the slurry, coating the coating slurry on a honeycomb ceramic carrier according to the coating amount of a cured product of 100g/L, drying the coated catalyst at 120 ℃ for 5 hours, and then roasting the dried catalyst at 550 ℃ for 3 hours. Wherein the first zirconium oxide composite oxide comprises CeO2 40wt％、ZrO2 50wt％、La2O3 5wt％、Y2O3 5wt％，La2O3-Al2O3Has a composition of 5wt% of La2O3And 95wt% of Al2O3。
(2) The Rh coating was applied using the same procedure and chemical composition as in comparative example 1.
Comparative example 3
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; a lower layer of Pt coating is attached to the honeycomb carrier, the coating amount of a cured product is 50g/L, and the content of Pt is 25g/ft3(ii) a Attaching an intermediate Pd coating on the lower Pt coating, and coating a condensateThe covering amount is 50g/L, and the content of Pd is 25g/ft3(ii) a An upper Rh coating is adhered on the middle Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) coating process of the lower layer Pt coating: 1000g of a first cerium zirconium composite oxide and 1000g of CeO2-Al2O3Mixing 100g of barium oxide and a proper amount of deionized water, performing ball milling to obtain coating slurry, adding a platinum nitrate solution with a corresponding calculated amount into the slurry, coating the coating slurry on a honeycomb ceramic carrier according to the coating amount of a cured product of 50g/L, drying the coated catalyst at 120 ℃ for 5 hours, and then roasting the dried catalyst at 550 ℃ for 3 hours. Wherein the first cerium-zirconium composite oxide comprises CeO2 50wt％、ZrO2 40wt％、La2O3 5wt％、Y2O3 5wt％，CeO2-Al2O3Has a composition of 40wt% of CeO2And 60wt% of Al2O3。
(2) Coating process of the intermediate Pd coating: 1000g of a second cerium-zirconium composite oxide and 1000g of La2O3-Al2O3Mixing 100g of barium oxide and a proper amount of deionized water, performing ball milling to obtain coating slurry, adding a corresponding calculated amount of palladium nitrate solution into the slurry, coating the coating slurry on the semi-finished catalyst containing the lower Pt coating prepared in the step (1) according to the coating amount of a cured product of 50g/L, drying the coated catalyst at 120 ℃ for 5 hours, and then roasting the dried catalyst at 550 ℃ for 3 hours. Wherein the second cerium-zirconium composite oxide comprises CeO2 45wt％、ZrO2 45wt％、La2O3 5wt％、Y2O3 5wt％，La2O3-Al2O3Has a composition of 5wt% of La2O3And 95wt% of Al2O3。
(3) Coating process of upper Rh coating: 1000g of a third cerium-zirconium composite oxide and 1000g of La2O3-Al2O3Mixing with a proper amount of deionized water, performing ball milling to obtain coating slurry, adding a corresponding calculated amount of rhodium nitrate solution into the slurry, coating the coating slurry on the semi-finished catalyst containing the lower Pt coating and the middle Pd coating prepared in the step (2) according to the coating amount of a condensate of 100g/L, drying the coated catalyst at 120 ℃ for 5 hours, and then roasting the dried catalyst at 550 ℃ for 3 hours. Wherein the third cerium-zirconium composite oxide comprises CeO2 25wt％、ZrO2 65wt％、La2O3 5wt％、Y2O3 5wt％，La2O3-Al2O3Has a composition of 5wt% of La2O3And 95wt% of Al2O3。
Example 1
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; a lower layer of Pt coating is attached to the honeycomb carrier, the coating amount of a cured product is 50g/L, and the content of Pt is 25g/ft3(ii) a An intermediate Pd coating is adhered on the lower Pt coating, the coating amount of a cured product is 50g/L, and the content of Pd is 25g/ft3(ii) a An upper Rh coating is adhered on the middle Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) coating process of the lower layer Pt coating: dropwise adding ammonia water into the platinum nitrate solution with the corresponding calculated amount until the pH value is 11 to prepare a Pt solution; adding 1000g of first cerium-zirconium composite oxide into deionized water, stirring for 20min, slowly dropwise adding the prepared Pt solution, stirring for 45min, dropwise adding a nitric acid solution until the pH value is 4, and adding 1000g of La after 75min2O3-Al2O3And 100g of barium oxide, stirring for 75min, performing ball milling to obtain coating slurry, coating the coating slurry on a honeycomb ceramic carrier according to the coating amount of a cured substance of 50g/L, drying the coated catalyst at 120 ℃ for 5h, and roasting the dried catalyst at 550 ℃ for 3 h. Wherein the first cerium-zirconium composite oxideSeparation into CeO2 50wt％、ZrO2 40wt％、La2O35wt％、Y2O3 5wt％，CeO2-Al2O3Has a composition of 40wt% of CeO2And 60wt% of Al2O3。
(2) The middle Pd coating layer has the same coating process and chemical composition as that of comparative example 3.
(3) The coating process and chemical composition of the upper Rh coating were the same as in comparative example 3.
Example 2
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; a lower layer of Pt coating is attached to the honeycomb carrier, the coating amount of a cured product is 50g/L, and the content of Pt is 25g/ft3(ii) a An intermediate Pd coating is adhered on the lower Pt coating, the coating amount of a cured product is 50g/L, and the content of Pd is 25g/ft3(ii) a An upper Rh coating is adhered on the middle Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) the lower Pt coating layer was applied by the same procedure and chemical composition as in example 1, except that the first cerium-zirconium composite oxide had CeO as the component2 80wt％、ZrO2 10wt％、La2O3 5wt％、Y2O3 5wt％，CeO2-Al2O3Is 10 wt% of CeO2And 90wt% of Al2O3。
(2) The middle Pd coating layer was applied using the same procedure and chemical composition as in example 1.
(3) The coating process and chemical composition of the upper Rh coating layer were the same as in example 1.
Example 3
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; a lower Pt coating is adhered on the honeycomb carrier, the coating amount of a cured substance is 50g/L, and the Pt content is 25 g-ft3(ii) a An intermediate Pd coating is adhered on the lower Pt coating, the coating amount of a cured product is 50g/L, and the content of Pd is 25g/ft3(ii) a An upper Rh coating is adhered on the middle Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) the coating process and chemical composition of the lower Pt coating layer were the same as example 1;
(2) the intermediate Pd coating layer was applied by the same procedure and chemical composition as in example 1, except that the second cerium-zirconium composite oxide had CeO as the component2 25wt％、ZrO2 65wt％、La2O3 5wt％、Y2O3 5wt％。
(3) The coating process and chemical composition of the upper Rh coating layer were the same as in example 1.
Example 4
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; a lower layer of Pt coating is attached to the honeycomb carrier, the coating amount of a cured product is 50g/L, and the content of Pt is 25g/ft3(ii) a An intermediate Pd coating is adhered on the lower Pt coating, the coating amount of a cured product is 50g/L, and the content of Pd is 25g/ft3(ii) a An upper Rh coating is adhered on the middle Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) the coating process and chemical composition of the lower Pt coating layer were the same as example 2;
(2) the intermediate Pd coating layer was applied by the same procedure and chemical composition as in example 2, except that the second cerium-zirconium composite oxide had CeO as the component2 25wt％、ZrO2 65wt％、La2O3 5wt％、Y2O3 5wt％。
(3) The coating process and chemical composition of the upper Rh coating layer were the same as in example 2.
Example 5
Gasoline vehicle tail gasThe purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore wall thickness is 2.5mil, and the volume is 1.101L; a lower layer of Pt coating is attached to the honeycomb carrier, the coating amount of a cured product is 50g/L, and the content of Pt is 25g/ft3(ii) a An intermediate Pd coating is adhered on the lower Pt coating, the coating amount of a cured product is 50g/L, and the content of Pd is 25g/ft3(ii) a An upper Rh coating is adhered on the middle Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) the coating process and chemical composition of the lower Pt coating layer were the same as example 1;
(2) the coating process and chemical composition of the intermediate Pd coating are the same as those of example 1;
(3) the upper Rh coating was applied in the same manner and chemical composition as in example 1, except that the third cerium-zirconium composite oxide had CeO as the component2 5wt％、ZrO2 85wt％、La2O3 5wt％、Y2O3 5wt％。
Example 6
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; a lower layer of Pt coating is attached to the honeycomb carrier, the coating amount of a cured product is 50g/L, and the content of Pt is 25g/ft3(ii) a An intermediate Pd coating is adhered on the lower Pt coating, the coating amount of a cured product is 50g/L, and the content of Pd is 25g/ft3(ii) a An upper Rh coating is adhered on the middle Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) the coating process and chemical composition of the lower Pt coating layer were the same as example 2;
(2) the coating process and chemical composition of the intermediate Pd coating are the same as those of example 2;
(3) the upper Rh coating was applied in the same manner and chemical composition as in example 2, except that the third cerium-zirconium composite oxide was composed ofIs CeO2 5wt％、ZrO2 85wt％、La2O3 5wt％、Y2O3 5wt％。
Example 7
A gasoline car tail gas purification catalyst comprises a honeycomb ceramic carrier, the specification is phi 118.4mm multiplied by 100mm, the pore density is 750cpsi, the pore channel wall thickness is 2.5mil, and the volume is 1.101L; a lower layer of Pt coating is attached to the honeycomb carrier, the coating amount of a cured product is 50g/L, and the content of Pt is 25g/ft3(ii) a An intermediate Pd coating is adhered on the lower Pt coating, the coating amount of a cured product is 50g/L, and the content of Pd is 25g/ft3(ii) a An upper Rh coating is adhered on the middle Pd coating, the coating amount is 100g/L, and the content of Rh is 5g/ft3。
The preparation method of the catalyst for purifying the tail gas of the gasoline vehicle adopts the following process steps:
(1) the coating process and chemical composition of the lower Pt coating layer were the same as example 1; in addition to replacing ammonia with tetramethylammonium hydroxide, nitric acid with formic acid;
(2) the coating process and chemical composition of the intermediate Pd coating are the same as those of example 1;
(3) the coating process and chemical composition of the upper Rh coating layer were the same as in example 1.
The catalyst samples obtained in examples 1 to 7 and comparative examples 1 to 3 were aged in a high temperature muffle furnace at 1050 ℃ for 20 hours under the same conditions, then packaged into a purifier, and subjected to a whole vehicle emission test according to a WLTC cycle, with the engine emission of the test vehicle being 1.4L, and the emission test results being shown in table 1.
TABLE 1 comparison of vehicle emissions test data
| THC(mg/km) | CO(mg/km) | NOX(mg/km) | |
| Comparative example 1 | 42.9 | 398.2 | 26.3 |
| Comparative example 2 | 47.4 | 436.6 | 26.5 |
| Comparative example 3 | 45.5 | 425.8 | 26.4 |
| Example 1 | 42.6 | 396.1 | 25.5 |
| Example 2 | 41.7 | 390.4 | 25.3 |
| Example 3 | 42.8 | 397.0 | 25.7 |
| Example 4 | 42.0 | 391.8 | 25.4 |
| Example 5 | 43.2 | 399.5 | 26.1 |
| Example 6 | 43.0 | 398.4 | 26.0 |
| Example 7 | 42.3 | 394.3 | 25.4 |
As can be seen from Table 1, compared with comparative example 1, the content of palladium in comparative example 2 is reduced by 50%, equivalent platinum is replaced, and pollutant emission of the whole vehicle is increased, which shows that the catalytic performance is reduced by simply replacing palladium with platinum under the traditional technical condition.
Comparative example 3 has the same precious metal content as comparative example 2, but with a three-layer coating technique, it can be seen from the table that each pollutant emission is reduced relative to comparative example 2, but still higher than in comparative example 1.
The noble metal content of examples 1-6 was the same as comparative example 2, using not only the three-layer coating technique but also a special platinum coating preparation process: according to the invention, the Pt precursor is firstly subjected to alkalization adsorption under the condition that the pH value is 10-12 and then subjected to acidification loading under the condition that the pH value is 3-5, and the table shows that the pollutant emission of the whole preparation method can be reduced to the same emission level as that of the comparative example 1.
Compared with the embodiment 1, the noble metal content of the embodiment 7 is the same, because the alkaline solution and the acid solution containing the organic group are adopted, the catalytic performance is further improved, and the pollutant discharge is further reduced.
In summary, from the results of the vehicle emission test of the catalyst in table 1, it can be known that the emission of pollutants in the entire vehicle is increased by simply replacing palladium with platinum or simply adopting a three-layer coating technology, but in embodiments 1 to 7 of the present invention, due to the adoption of a special platinum coating preparation process, the emission of pollutants in the prepared three-way catalyst can reach the same level as that of the palladium-rhodium catalyst before replacement, even better, and thus the technical problem of poor distribution uniformity of Pt is effectively solved.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to examples, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (10)
1. The catalyst for purifying the tail gas of the gasoline vehicle is characterized by comprising a carrier, and a lower coating, a middle coating and an upper coating which are sequentially coated on the carrier, wherein the lower coating is loaded with Pt, the middle coating is loaded with Pd, and the upper coating is loaded with Rh;
the lower coating layer also comprises a first cerium-zirconium composite oxide loaded with Pt, CeO2-Al2O3And an alkaline earth metal compound, the intermediate coating further comprising Pd-supported La2O3-Al2O3A second cerium-zirconium composite oxide and an alkaline earth metal compound, wherein the upper coating layer also comprises a third cerium-zirconium composite oxide loaded with Rh and La2O3-Al2O3。
2. The gasoline car exhaust gas purifying catalyst according to claim 1, wherein the first cerium-zirconium composite oxide in the lower coating layer comprises the following components: 5wt% -45 wt% of ZrO250 to 80 weight percent of CeO2And 5-15 wt% of La2O3、Y2O3、Pr6O11、Nd2O3One or more of them.
3. The gasoline car exhaust gas purification catalyst according to claim 1, wherein the lower layer coating layer contains CeO2-Al2O3Comprises the following components: 5wt% -40 wt% of CeO2And 60-95 wt% of Al2O3。
4. The gasoline car exhaust gas purifying catalyst according to claim 1, wherein the intermediate coating layer and the upper coating layer have La therein2O3-Al2O3Comprises the following components: 1-5 wt% of La2O3And 95-99 wt% of Al2O3。
5. The gasoline car exhaust gas purifying catalyst according to claim 1, wherein the second cerium-zirconium composite oxide in the intermediate coating layer comprises the following components: 35wt% to 75wt% ZrO220 to 50 weight percent of CeO2And 5-15 wt% of La2O3、Y2O3、Pr6O11、Nd2O3One or more of them.
6. The gasoline car exhaust gas purification catalyst according to claim 1, wherein the alkaline earth metal compound in the lower layer coating and the intermediate coating is one or more of strontium sulfate, strontium carbonate, strontium hydrogen phosphate, strontium nitrate, strontium acetate, strontium oxide, strontium hydroxide, barium sulfate, barium carbonate, barium hydrogen phosphate, barium nitrate, barium acetate, barium oxide, and barium hydroxide.
7. The gasoline car exhaust gas purifying catalyst according to claim 1, wherein the third cerium-zirconium composite oxide in the upper coating layer comprises the following components: 60wt% -90 wt% of ZrO25 to 25 weight percent of CeO2And 5-15 wt% of La2O3、Y2O3、Pr6O11And Nd2O3One or more of them.
8. The method for preparing a catalyst for purifying the tail gas of a gasoline vehicle as set forth in claim 1, comprising the steps of:
(1) coating of the lower coating: dropwise adding an alkaline solution into the Pt precursor solution until the pH value of the mixed solution is 10-12 to prepare a Pt solution; adding the first cerium-zirconium composite oxide into deionized water, stirring for 10-30min, slowly adding the prepared Pt solution, stirring for 30-60min, dropwise adding an acid solution until the pH value of the mixed solution is 3-5, and adding CeO after 60-90min2-Al2O3And an alkaline earth metal compound, continuously stirring for 60-90min, performing ball milling to obtain lower-layer coating slurry, coating the slurry on a honeycomb carrier, drying the coated carrier at 80-150 ℃ for 0.2-24 h, and roasting the dried catalyst at 350-650 ℃ for 1-5 h to obtain a first semi-finished catalyst;
(2) coating of the intermediate coating: mixing the second cerium-zirconium composite oxide and La2O3-Al2O3Mixing an alkaline earth metal compound and deionized water according to a required proportion, preparing slurry after ball milling, adding a Pd precious metal solution with a corresponding calculated amount into the slurry to form intermediate coating slurry, coating the slurry on the first semi-finished catalyst prepared in the step (1), drying the coated catalyst at 80-150 ℃ for 0.2-24 h, and roasting the dried catalyst at 350-650 ℃ for 1-5 h to prepare a second semi-finished catalyst;
(3) coating of the upper coating: mixing the third cerium-zirconium composite oxide and La2O3-Al2O3Mixing the catalyst and deionized water according to a required ratio, preparing slurry after ball milling, adding Rh precious metal solution with a corresponding calculated amount into the slurry to prepare upper-layer coating slurry, coating the slurry on the second semi-finished catalyst prepared in the step (2), drying the coated catalyst at 80-150 ℃ for 0.2-24 h, and roasting the dried catalyst at 350-650 ℃ for 1-5 h.
9. The method for preparing the catalyst for purifying gasoline vehicle exhaust according to claim 8, wherein the alkaline solution in step (1) is one or more of ammonia water, tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetraethylammonium bromide.
10. The method for preparing a catalyst for purifying gasoline vehicle exhaust according to claim 8, wherein the acidic solution in step (1) is one or more of nitric acid, formic acid, acetic acid, oxalic acid, citric acid, acrylic acid, glycolic acid, glycine and alanine.
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