CN109590016B - Catalyst for diesel engine based on modified hydrotalcite derived oxide and preparation method thereof - Google Patents

Catalyst for diesel engine based on modified hydrotalcite derived oxide and preparation method thereof Download PDF

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CN109590016B
CN109590016B CN201811651005.5A CN201811651005A CN109590016B CN 109590016 B CN109590016 B CN 109590016B CN 201811651005 A CN201811651005 A CN 201811651005A CN 109590016 B CN109590016 B CN 109590016B
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molecular sieve
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CN109590016A (en
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吕刚
朱越
宋崇林
李亚松
张荣鑫
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Tianjin University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
    • B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
    • B01J29/46—Iron group metals or copper
    • 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
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/04—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of alkali metals, alkaline earth metals or magnesium
    • B01J20/041—Oxides or hydroxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/012—Diesel engines and lean burn gasoline engines

Abstract

The invention discloses a diesel engine catalyst based on modified hydrotalcite derived oxide, which adopts a bimetallic modified ZSM-5 molecular sieve and noble metal as main catalysts; BaO is adsorbent; CeO (CeO)2‑ZrO2Is a cocatalyst; bimetallic modified hydrotalcite derived oxide and gamma-Al2O3Is a coating base material; cordierite honeycomb ceramic is used as a carrier. The preparation process comprises the following steps: determining the usage amount of raw materials; preparing modified ZSM-5 type molecular sieve and modified hydrotalcite derived composite oxide, and preparing and coating slurry. The catalyst can efficiently catalyze the adsorption-reduction reaction of NOx in exhaust gas through the cyclic change of the lean/rich working condition of the diesel engine. The modified molecular sieve partially replaces noble metals in the LNT catalyst, so that the raw material cost is reduced, and the sulfur and heat resistance is improved; replacement of gamma-Al in LNT catalysts by modified hydrotalcite derived oxides2O3The NOx adsorption capacity of the catalyst is improved.

Description

Catalyst for diesel engine based on modified hydrotalcite derived oxide and preparation method thereof
Technical Field
The invention belongs to the technology of purifying diesel vehicle tail gas pollutants, and particularly relates to a catalyst for adsorbing-reducing and purifying Nitrogen oxide (NOx) pollutants in diesel vehicle tail gas and a preparation method thereof.
Background
NOx is an atmospheric pollutant with great harm, has direct toxic action on organisms, and is one of important inducers of disasters such as photochemical smog, acid rain, greenhouse effect and the like. With the rapid increase of the motor vehicle output and the conservation quantity in China, the contribution rate of NOx emission in the transportation industry is increased year by year, and particularly in urban areas, in recent years, the contribution rate of NOx emission from motor vehicle exhaust gas exceeds 50%. In vehicles, the NOx emission of diesel vehicles is relatively high, and in 2017, 70% of the NOx in the total NOx emission of the vehicles is emitted by the diesel vehicles. In order to protect the atmospheric environment and guarantee the health of the public, China sets increasingly strict emission regulations for limiting the emission of pollutants in the tail gas of automobiles, in particular to the coming VI emission regulations, wherein the emission limits for NOx of diesel vehicles are extremely strict. In order to meet the national vi emission regulations, various diesel NOx emission control technologies have been intensively studied, wherein Lean NOx Trap (LNT) technology, also called NOx Storage Reduction (NSR) technology, has been recognized by industry as one of the most potential technical measures for solving NOx emissions of medium and small diesel vehicles.
The principle of the technology is as follows: firstly, the diesel engine is controlled to operate under the traditional lean-burn working condition, at the moment, under the action of a main catalyst in a special catalyst (LNT catalyst for short) for LNT technology, a part of Nitric Oxide (NO) in exhaust gas is catalyzed and oxidized into nitrogen dioxide (NO)2) These NO2And residual NO in the exhaust gas is adsorbed on the surface of the catalyst by an adsorbent in the LNT catalyst in the form of nitrate/nitrite type adsorbent species; when the adsorption amount of NOx adsorbed on the surface of the LNT catalyst is close to the saturated adsorption amount of the adsorbent, the engine is adjusted to operate under the rich combustion condition, and at the moment, the exhaust temperature of the engine is increased, and oxygen (O) is generated2) The content is nearly zero, and unburned Hydrocarbon (HC), carbon monoxide (CO) and hydrogen (H) in the exhaust gas2) The reducing components are greatly increased, and the reducing components reduce NOx adsorbed on the surface of the LNT catalyst into nitrogen (N) gas by the action of the main catalyst in the LNT catalyst2) And the like; and the LNT catalyst after reaction also recovers the NOx adsorption capacity, namely the LNT catalyst realizes regeneration. The diesel engine is controlled to repeatedly run the lean burn/rich burn operation cycle, and the high-efficiency purification of the NOx emission of the diesel engine can be realized.
The LNT technology principle was originally proposed in the 80's 20 th century, and there are commercial product markets, but the technology has not been widely popularized and applied due to some defects and shortcomings of the traditional LNT catalyst. The traditional LNT catalyst is platinum (Pt)/barium oxide (BaO)/gamma-aluminum oxide (gamma-Al)2O3) Catalyst system, in which the noble metal Pt is used as the main catalyst, in lean burnThe operating conditions catalyze the oxidation of NO and the reduction of adsorbed NOx in rich conditions. Although Pt is an oxidation reaction catalyst with excellent performance, the reduction reaction catalytic activity of Pt needs to be improved, and the deficiency of the reduction reaction catalytic activity needs to be made up by improving the dosage of Pt; on the other hand, however, the expensive cost of precious metals and the significant deficiencies in sulfur and heat resistance lead to undesirable high Pt usage in LNT catalysts. The BaO adsorbent is a good NOx adsorbing material, the unit saturated adsorption capacity of NOx is very high, but the stability of a catalyst coating is deteriorated due to too much BaO in the traditional LNT catalyst, and the mass ratio of the NOx adsorbing material is limited, so that the integral saturated adsorption capacity of the traditional LNT catalyst is limited, the lean-burn/rich-burn working condition of a diesel engine is switched too frequently, and the power and the economic performance of the diesel engine are adversely affected. And gamma-Al2O3Is a good coating base material, and the mass proportion of the catalyst coating in the traditional LNT catalyst is generally more than 50 percent. However, gamma-Al2O3LNT catalytic activity and NO of the material itselfXHas poor adsorption capacity and simultaneously has gamma-Al at high temperature2O3Is also easy to generate phase change or react with BaO to generate BaAl with a spinel structure2O4Result in NOXThe storage active sites are reduced, thereby deteriorating the NOx purification performance of the LNT catalyst.
To overcome the performance deficiencies of the conventional LNT catalysts, a great deal of systematic and intensive research work has been conducted in the industry around the most important means of noble metal material substitution and novel adsorbent/coating base material development for the performance optimization of these two novel LNT catalysts. Research has found that the Catalytic activity of the metal modified molecular sieve catalyst for Reduction reaction exceeds that of the noble metal catalyst, for example, the copper (Cu)/iron (Fe) modified ZSM-5 type molecular sieve catalyst has been applied to a Selective Catalytic Reduction (SCR) NOx purification system of a diesel engine. Meanwhile, the Cu modified ZSM-5 type molecular sieve catalyst has good low-temperature oxidation-reduction reaction catalytic performance, while the Fe modified ZSM-5 type molecular sieve catalyst has higher high-temperature oxidation-reduction reaction catalytic activity, so that the Cu-Fe bimetal modified molecular sieve catalyst can be expected to have wider oxidation-reductionThe reaction catalysis performance is high, and the activity temperature window is high. In addition, research shows that a small amount of precious metal components can generate synergistic action with the metal modified molecular sieve type catalyst, and the catalytic activity of the whole oxidation-reduction reaction of the catalyst is obviously improved. On the other hand, a magnesium (Mg) -aluminum (Al) carbonate type hydrotalcite-derived composite oxide (molecular formula: Al)2O36MgO) has higher specific surface area, stronger alkalinity and good coating stability, and meets the requirements of high-performance LNT catalyst coating base materials and NOx additional adsorbents. In addition, the modified hydrotalcite derived composite oxide material obtained by partially replacing Al element with lanthanum (La) element and partially replacing Mg element with zinc (Zn) element has more excellent coating property and NOx adsorption performance. La-Zn bimetal modified hydrotalcite derived composite oxide is used for replacing most of gamma-Al2O3The coated base material can significantly increase the content of the additional adsorbent in the LNT catalyst, thereby improving the overall NOx adsorption performance of the LNT catalyst or reducing the amount of BaO adsorbent used.
Disclosure of Invention
On the basis of the previous research, the invention provides a method for replacing most of noble metal by Cu-Fe bimetal modified ZSM-5 type molecular sieve and replacing most of gamma-Al by La-Zn bimetal modified hydrotalcite derived composite oxide, which is suitable for diesel vehicles2O3Characterized by a diesel engine catalyst based on modified hydrotalcite derived oxide and a preparation method thereof.
In order to solve the technical problems, the invention provides a catalyst for a diesel engine based on a modified hydrotalcite derived oxide, which comprises a modified ZSM-5 type molecular sieve, Pt, Pd, BaO and CeO2-ZrO2Solid solution, modified hydrotalcite-derived composite oxide, and gamma-Al2O3And a 400 mesh cordierite honeycomb ceramic carrier; the modified ZSM-5 type molecular sieve is a Cu-Fe bimetal modified ZSM-5 type molecular sieve, wherein Cu element is uniformly dispersed on the surface and in micropores of the ZSM-5 type molecular sieve in a CuO form, and Fe element is Fe2O3Is uniformly dispersed on the surface and in micropores of the ZSM-5 type molecular sieve, and the CuO and the Fe2O3The mass percentage of the zeolite to the ZSM-5 type molecular sieve is as follows: 5E &15%/5-10%/90-75%, and the sum of the mass percentages is 100%; the modified hydrotalcite-derived composite oxide is La-Zn bimetal modified hydrotalcite-derived composite oxide, and La partially replaces Al2O3Al in 6MgO type hydrotalcite-like compound-derived composite oxide, Al being partially substituted by Zn2O36 MgO-type hydrotalcite-like compound-derived composite oxide containing Mg, wherein La, Al, Zn and Mg are La, respectively2O3、Al2O3And ZnO and MgO are dispersed in the La-Zn bimetal modified hydrotalcite derived composite oxide, and La2O3And Al2O3The mole percentage of (A) is as follows: 50-80%/50-20%, the sum of the mole percentages is 100%; the mol percentages of ZnO and MgO are as follows: 25-75%/75-25%, the sum of the mole percentages being 100%; meanwhile, the ratio of the sum of the molar numbers of La ions and Al ions to the sum of the molar numbers of Zn ions and Mg ions in the La-Zn bimetal modified hydrotalcite derived composite oxide is 1: 3; the Cu-Fe bimetal modified ZSM-5 type molecular sieve, Pt and Pd form a main catalyst of the catalyst, and the mass sum of the Pt and the Pd and the mass percentage of the Cu-Fe bimetal modified ZSM-5 type molecular sieve are as follows: 2-5%/98-95%, the sum of the mass percentages is 100%; the BaO constitutes an adsorbent for the catalyst; the CeO2-ZrO2The solid solution constitutes the catalyst promoter of the catalyst; the La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3A coating base material constituting a catalyst; the La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3The mass percentage of the components is as follows: 75-90%/25-10%, the sum of the mass percentages is 100%; the main catalyst, the adsorbent, the cocatalyst and the coating base material form a catalytic coating of the catalyst, and the mass percentages of the main catalyst, the adsorbent, the cocatalyst and the coating base material respectively correspond to: 5-10%/10%/5-10%/80-70%, the sum of the mass percentages is 100%; the catalyst is composed of the catalytic coating and 400-mesh cordierite honeycomb ceramic, wherein the 400-mesh cordieriteThe catalyst coating is coated on the 400-mesh cordierite honeycomb ceramic, and the mass percentages of the catalyst coating and the 400-mesh cordierite honeycomb ceramic are as follows: 10-30%/90-70%, and the sum of the mass percentages is 100%.
Furthermore, the catalyst for diesel engine based on modified hydrotalcite derived oxide of the invention, wherein, in the cocatalyst, CeO2And ZrO2The mass percentage of the components is as follows: 80-50%/20-50%, the sum of the mass percentages being 100%.
In the main catalyst, the mass percentage of Pt and Pd is as follows: 25-50%/75-50%, the sum of the mass percentages being 100%.
gamma-Al in the coating base material2O3Generated by conversion of aluminum sol as a coating binder.
The preparation method of the catalyst for the diesel engine based on the modified hydrotalcite derived oxide comprises the following steps:
step one, determining the use amount of raw materials for preparing the catalyst:
respectively designing the mass percentage of the sum of Pt and Pd in the main catalyst and the Cu-Fe bimetal modified ZSM-5 type molecular sieve; in the main catalyst, the mass percentage of Pt and Pd is as follows: 25-50%/75-50%, the sum of the mass percentages being 100%; CuO and Fe in Cu-Fe bimetal modified ZSM-5 type molecular sieve2O3The mass percentage of the zeolite to the ZSM-5 type molecular sieve; CeO in cocatalyst2And ZrO2The mass percentage of the components is as follows: 80-50%/20-50%, the sum of the mass percentages is 100%; gamma-Al in the coating base material2O3Generated by the conversion of aluminum sol as a coating binder; La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al in coating base material2O3The mass percentage of (A); in the La-Zn bimetal modified hydrotalcite derived composite oxide, La2O3And Al2O3And the mol percentages of ZnO and MgO; mass percentages of the main catalyst, the adsorbent, the cocatalyst and the coating base material; catalytic coating and 400-mesh cordierite honeycomb ceramicThe mass percentage range of the carrier; and planning to configure the quality of the coating slurry that can produce the catalytic coating;
respectively calculating Pt, Pd and Cu-Fe bimetal modified ZSM-5 type molecular sieve, BaO and CeO in the catalytic coating prepared according to the proportion of each component in the catalyst2、ZrO2、γ-Al2O3La-Zn bimetal modified hydrotalcite derived composite oxide and Cu-Fe bimetal modified ZSM-5 type molecular sieve containing CuO and Fe2O3La in composite oxide derived from ZSM-5 type molecular sieve and La-Zn bimetal modified hydrotalcite2O3、Al2O3ZnO and MgO;
combined with each 517.9g of [ H ]2PtCl6·6H2O]Preparation of 195.1g Pt per 266.4g [ Pd (NO)3)2·2H2O]Preparation of 106.4g Pd per 255.4g [ Ba (CH)3COO)2]153.3g of BaO per 434.1g of [ Ce (NO)3)3·6H2O]Preparation of 172.1g of CeO2Every 429.3g of [ Zr (NO)3)4·5H2O]Preparation of 123.2g ZrO2Every 187.6g [ Cu (NO) ]3)2]79.5g of CuO per 808.0g of [ Fe (NO)3)3·9H2O]Preparation of 159.7g Fe2O3Each 866.0g of [ La (NO)3)3·6H2O]Preparation of 325.8g La2O3Each 750.2g of [ Al (NO)3)3·9H2O]Preparation of 102.0g Al2O3Every 297.5g [ Zn (NO) ]3)2·6H2O]Preparation of 81.4g of ZnO per 256.4g of [ Mg (NO)3)2·6H2O]40.3g of MgO were prepared and the H consumed for the preparation of the catalyst was calculated2PtCl6·6H2O、Pd(NO3)2·2H2O、Ba(CH3COO)2、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O、Cu(NO3)2、Fe(NO3)3·9H2O、La(NO3)3·6H2O、Al(NO3)3·9H2O、Zn(NO3)2·6H2O、Mg(NO3)2·6H2The mass of O;
calculating the mass of the polyethylene glycol and the nitric acid consumed for preparing the coating slurry according to the proportion that every 100g of the catalytic coating needs 5-15 g of polyethylene glycol with the average molecular weight of 20000 and 25-50 g of nitric acid; according to Al in the alumina sol2O3Calculating the mass of the consumed aluminum sol required for preparing the coating slurry according to the actual mass percentage;
step two, preparing the Cu-Fe bimetallic modified ZSM-5 type molecular sieve:
weighing Cu (NO) according to the mass determined in the step one3)2And Fe (NO)3)3·9H2O, and per mole of Cu (NO)3)2And per mole Fe (NO)3)3·9H2O to 1-2L deionized water, adding Cu (NO)3)2And Fe (NO)3)3·9H2Adding O into deionized water, and stirring to prepare a mixed solution; adding a ZSM-5 type molecular sieve with determined mass into the mixed solution, stirring vigorously for 6-12 h at 70-80 ℃, and evaporating the liquid to dryness at 70-80 ℃; drying the evaporated powder at 90-110 ℃ for 4-8 h, and roasting at 550-600 ℃ for 2-3 h to obtain the Cu-Fe bimetal modified ZSM-5 molecular sieve;
step three, preparing the La-Zn bimetal modified hydrotalcite derived composite oxide:
weighing La (NO) according to the determined mass3)3·6H2O、Al(NO3)3·9H2O、Zn(NO3)2·6H2O and Mg (NO)3)2·6H2O, adding La (NO) according to the proportion of 0.5-1L of deionized water per mol of Zn ions and per mol of Mg ions3)3·6H2O、Al(NO3)3·9H2O、Zn(NO3)2·6H2O and Mg (NO)3)2·6H2Adding O into deionized water, and fully stirring to obtain a solution as a precursor solution;
weighing sufficient NaOH and Na2CO3And the mole number of NaOH is equal to that of Na2CO3The molar ratio of the NaOH to the Na is 2:1, and NaOH and Na are mixed according to the ratio that each mole of NaOH corresponds to 1L of deionized water2CO3Adding into deionized water, stirring thoroughly until NaOH and Na2CO3Completely dissolving to obtain a buffer solution;
adding a buffer solution into the precursor solution at a speed of 30-50 ml/min, stirring vigorously, and simultaneously, continuously measuring the pH value of the precursor solution in which the buffer solution is added by using a pH value analyzer; stopping adding the buffer solution when the pH value is between 9.5 and 10.5, continuing stirring for 2 to 4 hours, standing and aging for 24 to 48 hours, and filtering and separating an aged solid substance; washing the solid substance with deionized water for 3-5 times, drying at 90-110 ℃ for 8-16 h, roasting at 500-600 ℃ for 2-4 h, naturally cooling, and grinding on a ball mill for 1h to obtain La-Zn bimetal modified hydrotalcite derived composite oxide;
step four, preparing coating slurry:
weighing H of determined mass2PtCl6·6H2O、Pd(NO3)2·2H2O、Ba(CH3COO)2、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O, alumina sol, polyethylene glycol, nitric acid, the prepared Cu-Fe bimetal modified ZSM-5 type molecular sieve and La-Zn bimetal modified hydrotalcite derived composite oxide, adding all the raw materials into deionized water with the mass being 10-15 times of the total mass of the prepared catalytic coating, and fully stirring; adjusting the pH value of the mixed solution to 3-4 by using 1mol/L NaOH solution or pure glacial acetic acid, and continuously stirring the mixture to form uniform suspension; grinding the suspension on a wet grinding machine until the median particle size is within the range of 1.0-1.2 microns, and then stirring the ground suspension for 16-24 hours at the temperature of 60-80 ℃ to obtain coating slurry;
step five, coating the coating slurry
Designing the quality of a 400-mesh cordierite honeycomb ceramic carrier to be coated with a catalytic coating; the catalyst coating and the cordierite honeycomb ceramic carrier are as follows by mass percent: 10-30%/90-70% of the raw materials are mixed, and the raw materials are subjected to the following dipping, drying and calcining treatment:
immersing a cylindrical 400-mesh cordierite honeycomb ceramic carrier into the coating slurry at the temperature of 60-80 ℃, wherein the upper end face of the cordierite honeycomb ceramic carrier is higher than the liquid level of the coating slurry; after the coating slurry is naturally lifted to fill all pore channels of the cordierite honeycomb ceramic carrier, taking the cordierite honeycomb ceramic carrier out of the coating slurry, blowing off residual fluid in the pore channels, drying at 90-110 ℃ for 6-12 h, and calcining at 500-600 ℃ for 2-4 h;
and repeating the processes of dipping, drying and calcining for 2-3 times to obtain the catalyst for the diesel engine based on the modified hydrotalcite derived oxide.
The diesel engine catalyst based on the modified hydrotalcite derived oxide prepared by the preparation method is packaged, the packaged catalyst is installed in an exhaust passage of a diesel vehicle, and NOx pollutants in exhaust gas of the diesel vehicle are purified through NOx adsorption-reduction reaction.
Compared with the prior art, the invention has the beneficial effects that:
the Cu-Fe bimetallic modified ZSM-5 molecular sieve is adopted to replace most of noble metal materials in the LNT catalyst, so that the cost of raw materials for preparing the catalyst is reduced, and the sulfur resistance, heat resistance and catalytic activity of reduction reaction of the LNT catalyst are improved; meanwhile, the Cu-Fe bimetal modifies the ZSM-5 type molecular sieve, and the high catalytic activity temperature window of the LNT catalyst is expanded. La-Zn bimetal modified hydrotalcite derived composite oxide is adopted to replace most of gamma-Al in LNT catalyst2O3The coating base material provides an additional adsorbent except a BaO adsorbent for the LNT catalyst while keeping the stability of the coating not reduced, so that the NOx adsorption capacity of the LNT catalyst is greatly increased; and the La and Zn are respectively substituted for Al and Mg, so that the NOx adsorption performance of the hydrotalcite derived composite oxide material is further improved, and particularly the NOx saturated adsorption capacity at low temperature (less than 300 ℃) is obviously improved. In addition, La-Zn bimetal modified waterThe talc-derived composite oxide used as a coating base material can introduce La element into a catalyst coating, improve the high-temperature stability of the catalyst, and promote CeO2The catalyst and the main catalyst can play a synergistic catalysis role more efficiently.
Drawings
Fig. 1 is a schematic diagram of an engine evaluation system for NOx purification performance of an LNT catalyst.
Wherein: 1-a dynamometer; 2-a coupler; 3-test diesel engine; 4-an intake air flow meter; 5-air intake air conditioning; 6-oil injector; 7-a fuel injection control system; 8-exhaust sampling port A; 9-temperature sensor a; 10-exhaust manostat; 11-temperature sensor B; 12-LNT catalyst; 13-temperature sensor C; 14-exhaust sample port B; 15-exhaust sampling channel; 16-engine exhaust gas analyzer; 17-air pump.
FIG. 2 shows an engine evaluation system for NOx purification performance of the LNT catalyst under a lean-burn condition of a diesel engine with an exhaust temperature of 250 ℃ and an airspeed of 30000h-1Under the steady-state working condition, the purification efficiency of NOx in the adsorption-reduction reaction of the NOx exhausted by the diesel engine under the catalysis of the catalyst prepared in the embodiment 1-4 is improved.
FIG. 3 shows an engine evaluation system for NOx purification performance of the LNT catalyst under a lean-burn condition of a diesel engine with an exhaust temperature of 350 ℃ and an airspeed of 50000h-1Under the steady-state working condition, the purification efficiency of NOx in the adsorption-reduction reaction of the NOx exhausted by the diesel engine under the catalysis of the catalyst prepared in the embodiment 1-4 is improved.
Fig. 4 shows NOx purification efficiency of the NOx adsorption-reduction reaction of the diesel exhaust catalyzed by the catalysts prepared in examples 1 to 4 in the European steady state cycle (ESC) test using the LNT catalyst NOx purification performance engine evaluation system.
Detailed Description
The technical solution of the present invention is further described below by specific examples in conjunction with the accompanying drawings. It should be noted that the present embodiments are illustrative and not restrictive, and the present invention is not limited to the following embodiments.
The invention provides a modified hydrotalcite-based catalystThe catalyst for diesel engine to derive oxide includes Cu-Fe double metal modified ZSM-5 type molecular sieve, Pt, Pd, BaO and CeO2-ZrO2Solid solution, La-Zn bimetal modified hydrotalcite derived composite oxide, gamma-Al2O3And a 400 mesh cordierite honeycomb ceramic carrier.
(1) The main catalyst of the catalyst consists of a Cu-Fe bimetal modified ZSM-5 type molecular sieve, noble metals Pt and Pd, and the mass percentage of the sum of the noble metals Pt and Pd and the Cu-Fe bimetal modified ZSM-5 type molecular sieve is as follows: 2-5%/98-95%, and the sum of the mass percentages is 100%.
(2) Cu element in the Cu-Fe bimetal modified ZSM-5 type molecular sieve is uniformly dispersed on the surface and in micropores of the ZSM-5 type molecular sieve in a CuO form, and Fe element is Fe2O3Is uniformly dispersed on the surface and in micropores of the ZSM-5 type molecular sieve, and the CuO and the Fe2O3The mass percentage of the zeolite to the ZSM-5 type molecular sieve is as follows: 5-15%/5-10%/90-75%, and the sum of the mass percentages is 100%.
(3) The mass percentage of the noble metal Pt and Pd is as follows: 25-50%/75-50%, the sum of the mass percentages being 100%.
(4) The adsorbent of the catalyst of the invention is composed of BaO.
(5) From CeO2-ZrO2The catalyst of the present invention is composed of a solid solution, and CeO2And ZrO2The mass percentage of the components is as follows: 80-50%/20-50%, the sum of the mass percentages being 100%.
(6) La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3The coating base material of the catalyst of the invention is composed of the La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3The mass percentage of the components is as follows: 75-90%/25-10%, the sum of the mass percentages being 100%.
(7) The La-Zn bimetal modified hydrotalcite derived composite oxide forms one of the coating base materials of the catalyst, and also plays a role of an additional adsorbent in the catalyst, wherein La, Al, Zn and Mg are respectively La2O3、Al2O3And ZnO and MgO are dispersed in the La-Zn bimetal modified hydrotalcite derived composite oxide, and La2O3And Al2O3The molar (mol) percentages of (A) are: 50-80%/50-20%, the sum of mol percentage is 100%; the mol percentages of ZnO and MgO are: 25-75%/75-25%, the sum of mol percentage is 100%; meanwhile, the ratio of the sum of the mol numbers of La ions and Al ions to the sum of the mol numbers of Zn ions and Mg ions in the La-Zn bimetal modified hydrotalcite derived composite oxide is as follows: 1:3.
(8) gamma-Al in the coating base material2O3Generated by conversion of aluminum sol as a coating binder.
(9) A main catalyst consisting of Cu-Fe bimetallic modified ZSM-5 type molecular sieve and noble metals Pt and Pd, an adsorbent consisting of BaO, and CeO2-ZrO2Cocatalyst composed of solid solution, La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3The formed coating base materials jointly form the catalytic coating of the catalyst, wherein the mass percentages of the main catalyst, the adsorbent, the cocatalyst and the coating base materials respectively correspond to that: 5-10%/10%/5-10%/80-70%, the sum of the mass percentages being 100%.
(10) The catalyst for the diesel engine based on the modified hydrotalcite derived oxide consists of the catalytic coating and 400-mesh cordierite honeycomb ceramic, wherein the 400-mesh cordierite honeycomb ceramic is a carrier of the catalyst, the catalytic coating needs to be coated on the 400-mesh cordierite honeycomb ceramic carrier, and the mass percentages of the catalytic coating and the 400-mesh cordierite honeycomb ceramic carrier are as follows: 10-30%/90-70%, and the sum of the mass percentages is 100%.
The preparation method of the catalyst for the diesel engine based on the modified hydrotalcite derived oxide comprises the following specific process steps: (1) determining the dosage of raw materials for preparing the catalyst; (2) preparing a Cu-Fe bimetal modified ZSM-5 type molecular sieve; (3) preparing La-Zn bimetal modified hydrotalcite derived composite oxide; (4) preparing coating slurry; (5) and coating the coating slurry.
The method for preparing the catalyst of the present invention is described in detail below with reference to specific examples.
Example 1
(1) Determination of the amount of raw materials for the preparation of the catalyst
The mass ratio of the sum of the noble metals Pt and Pd of the main catalyst and the Cu-Fe bimetallic modified ZSM-5 type molecular sieve in the catalyst prepared in the design example 1 is as follows: 98 percent in 2 percent; CuO and Fe in Cu-Fe bimetal modified ZSM-5 type molecular sieve2O3The mass ratio of the molecular sieve to the ZSM-5 type molecular sieve is as follows: 15%, 10%, 75%; the mass ratio of the noble metal Pt to Pd is as follows: 50 percent of 50 percent; CeO in cocatalyst2、ZrO2The mass ratio of (A) to (B) is as follows: 80 percent to 20 percent; La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al in coating base material2O3The mass ratio of (A) to (B) is as follows: 90 percent to 10 percent; La-Zn bimetal modified hydrotalcite derived composite oxide2O3And Al2O3The mol ratio of (A) is: 80 percent to 20 percent; the mol ratio of ZnO to MgO is: 50 percent of 50 percent; the mass ratio of the main catalyst, the adsorbent, the cocatalyst and the coating base material is as follows: 10%, 70%; 15g of polyethylene glycol having an average molecular weight of 20000 and 25g of nitric acid are required per 100g of catalytic coating. Calculating the raw material dosage required for preparing 2000g of catalytic coating according to the conversion ratio: h2PtCl6·6H2O 5.3g、Pd(NO3)2·2H2O 5.0g、Cu(NO3)269.4g、Fe(NO3)3·9H299.2g of O, 147.0g of ZSM-5 type molecular sieve and Ba (CH)3COO)2 333.2g、Ce(NO3)3·6H2O403.6g、Zr(NO3)4·5H2O 139.4g、La(NO3)3·6H2O 1351.0g、Al(NO3)3·9H2O 292.6g、Zn(NO3)2·6H2O 1740.4g、Mg(NO3)2·6H2O 1499.9g、γ-Al2O3140.0g, 500g nitric acid and 300g polyethylene glycol with the average molecular weight of 20000. Al in the alumina sol used in the present example2O3The content of (b) was 10.8%, from which 1296.3g of alumina sol was calculated.
(2) Preparation of Cu-Fe bimetal modified ZSM-5 type molecular sieve
Weighing Cu (NO) according to determined mass3)2And Fe (NO)3)3·9H2Adding the two raw materials into 0.7L of deionized water, and stirring to prepare a mixed solution; adding the ZSM-5 type molecular sieve with determined mass into the mixed solution, stirring vigorously for 12h at 70 ℃, and evaporating the liquid to dryness at 70 ℃ after the stirring is completed. And then drying the powder after evaporation at 90 ℃ for 8h, and roasting the dried powder at 550 ℃ for 3h to obtain the Cu-Fe bimetal modified ZSM-5 type molecular sieve.
(3) Preparation of La-Zn bimetal modified hydrotalcite derived composite oxide
Weighing La (NO) according to the determined mass3)3·6H2O、Al(NO3)3·9H2O、Zn(NO3)2·6H2O and Mg (NO)3)2·6H2And O, adding the 4 raw materials into 11L of deionized water, and fully stirring to prepare a solution, namely a precursor solution. 200g NaOH and 265g Na were weighed out2CO3The two substances are added into 5000g of deionized water and fully stirred until NaOH and Na2CO3Completely dissolved as buffer. Then adding the buffer solution into the precursor solution at the speed of 50ml/min, stirring vigorously, and simultaneously, continuously measuring the pH value of the precursor solution in which the buffer solution is being added by using a pH value analyzer; stopping adding the buffer solution when the pH value of the precursor solution is between 9.5 and 10.5, and continuously stirring the precursor solution for 2 hours; standing and aging the stirred precursor liquid for 24 hours, generating a large amount of solid substances in an aged precursor liquid container, separating the solid substances in the precursor liquid container through suction filtration, and then washing the solid substances with deionized water for 3 times; drying the washed solid substance at 90 ℃ for 16h, roasting the dried solid substance at 500 ℃ for 4h, naturally cooling the roasted solid substance, and grinding the solid substance on a ball mill for 1h to obtain the La-Zn bimetal modified hydrotalcite derivativeA composite oxide.
(4) Preparation of coating slurries
Weighing H of determined mass2PtCl6·6H2O、Pd(NO3)2·2H2O、Ba(CH3COO)2、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O, alumina sol, polyethylene glycol, nitric acid and prepared Cu-Fe bimetal modified ZSM-5 type molecular sieve and La-Zn bimetal modified hydrotalcite derived composite oxide, adding all the raw materials into 20000g of deionized water, and fully stirring; adjusting the pH value of the mixed solution to 3-4 by using 1mol/L NaOH solution or pure glacial acetic acid, and continuously stirring the mixture to form uniform suspension; and grinding the suspension on a wet grinding machine until the median particle size (D50 particle size) is within the range of 1.0-1.2 microns, and then stirring the ground suspension for 24 hours at 60 ℃ to obtain the coating slurry.
(5) Application of coating paste
Designing the quality of a 400-mesh cordierite honeycomb ceramic carrier to be coated with a catalytic coating; weighing a 400-mesh cordierite honeycomb ceramic carrier with determined mass, immersing the ceramic carrier in the coating slurry at 60 ℃, and ensuring that the upper end surface of the ceramic carrier is slightly higher than the liquid level of the slurry; after the slurry is naturally lifted to fill all pore channels of the carrier, taking the carrier out of the slurry, blowing off residual fluid in the pore channels, drying at 90 ℃ for 12h, and roasting at 500 ℃ for 4 h; repeating the processes of dipping, drying and roasting for 3 times to obtain the catalyst for the diesel engine based on the modified hydrotalcite derived oxide.
The catalyst for the diesel engine based on the modified hydrotalcite derived oxide, which is obtained by adopting the catalyst preparation loading method described in example 1, comprises the following catalytic coating and a 400-mesh cordierite honeycomb ceramic carrier in percentage by mass: 28-29%/72-71%, and the sum of the mass percentages is 100%.
Example 2
(1) Determination of the amount of raw materials for the preparation of the catalyst
Design example 2 quality of noble metals Pt and Pd for main catalyst in the prepared catalystAnd the mass ratio of the Cu-Fe bimetallic modified ZSM-5 type molecular sieve to the Cu-Fe bimetallic modified ZSM-5 type molecular sieve is as follows: 5 percent to 95 percent; CuO and Fe in Cu-Fe bimetal modified ZSM-5 type molecular sieve2O3The mass ratio of the molecular sieve to the ZSM-5 type molecular sieve is as follows: 5%, 90%; the mass ratio of the noble metal Pt to Pd is as follows: 25 percent to 75 percent; CeO in cocatalyst2、ZrO2The mass ratio of (A) to (B) is as follows: 50 percent of 50 percent; La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al in coating base material2O3The mass ratio of (A) to (B) is as follows: 75 percent to 25 percent; La-Zn bimetal modified hydrotalcite derived composite oxide2O3And Al2O3The mol ratio of (A) is: 50 percent of 50 percent; the mol ratio of ZnO to MgO is: 75 percent to 25 percent; the mass ratio of the main catalyst, the adsorbent, the cocatalyst and the coating base material is as follows: 10%, 70%; per 100g of catalytic coating 15g of polyethylene glycol with an average molecular weight of 20000 and 50g of nitric acid are required. Calculating the raw material dosage required for preparing 2000g of catalytic coating according to the conversion ratio: h2PtCl6·6H2O 6.6g、Pd(NO3)2·2H2O 18.8g、Cu(NO3)222.4g、Fe(NO3)3·9H248.1g of O, 171.0g of ZSM-5 type molecular sieve and Ba (CH)3COO)2 333.2g、Ce(NO3)3·6H2O252.2g、Zr(NO3)4·5H2O 348.5g、La(NO3)3·6H2O 709.7g、Al(NO3)3·9H2O 614.8g、Zn(NO3)2·6H2O 2194.2g、Mg(NO3)2·6H2O 630.4g、γ-Al2O3350.0g, 1000g nitric acid and 300g polyethylene glycol with the average molecular weight of 20000. Al in the alumina sol used in the present example2O3The content of (b) was 10.8%, from which 3240.7g of alumina sol was calculated.
(2) Preparation of Cu-Fe bimetal modified ZSM-5 type molecular sieve
Weighing Cu (NO) according to determined mass3)2And Fe (NO)3)3·9H2O, adding the two raw materials into 0.46L of deionized water, and stirringMixing to prepare a mixed solution; adding the ZSM-5 type molecular sieve with determined mass into the mixed solution, stirring vigorously for 6h at 80 ℃, and evaporating the liquid to dryness at 80 ℃ after stirring. And then drying the powder after evaporation at 110 ℃ for 4h, and roasting the dried powder at 600 ℃ for 2h to obtain the Cu-Fe bimetal modified ZSM-5 type molecular sieve.
(3) Preparation of La-Zn bimetal modified hydrotalcite derived composite oxide
Weighing La (NO) according to the determined mass3)3·6H2O、Al(NO3)3·9H2O、Zn(NO3)2·6H2O and Mg (NO)3)2·6H2And O, adding the 4 raw materials into 5L of deionized water, and fully stirring to prepare a solution, namely a precursor solution. 200g NaOH and 265g Na were weighed out2CO3The two substances are added into 5000g of deionized water and fully stirred until NaOH and Na2CO3Completely dissolved as buffer. Then adding the buffer solution into the precursor solution at the speed of 30ml/min, stirring vigorously, and simultaneously, continuously measuring the pH value of the precursor solution in which the buffer solution is being added by using a pH value analyzer; stopping adding the buffer solution when the pH value of the precursor solution is between 9.5 and 10.5, and continuously stirring the precursor solution for 4 hours; standing and aging the stirred precursor liquid for 48 hours, generating a large amount of solid substances in an aged precursor liquid container, separating the solid substances in the precursor liquid container through suction filtration, and washing the solid substances with deionized water for 5 times; and drying the washed solid substance at 110 ℃ for 8h, roasting the dried solid substance at 600 ℃ for 2h, naturally cooling the roasted solid substance, and grinding the solid substance on a ball mill for 1h to obtain the La-Zn bimetal modified hydrotalcite derived composite oxide.
(4) Preparation of coating slurries
Weighing H of determined mass2PtCl6·6H2O、Pd(NO3)2·2H2O、Ba(CH3COO)2、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O, alumina sol, polyethylene glycol, nitric acid and prepared Cu-Fe bimetal modified ZSM-5 type molecular sieve and La-Zn bimetal modified hydrotalcite derived composite oxide, adding all the raw materials into 20000g of deionized water, and fully stirring; adjusting the pH value of the mixed solution to 3-4 by using 1mol/L NaOH solution or pure glacial acetic acid, and continuously stirring the mixture to form uniform suspension; and grinding the suspension on a wet grinding machine until the particle size of D50 is within the range of 1.0-1.2 microns, and then stirring the ground suspension for 16 hours at 80 ℃ to obtain the coating slurry.
(5) Application of coating paste
Designing the quality of a 400-mesh cordierite honeycomb ceramic carrier to be coated with a catalytic coating; weighing a 400-mesh cordierite honeycomb ceramic carrier with determined mass, immersing the ceramic carrier in the coating slurry at 80 ℃, and ensuring that the upper end surface of the ceramic carrier is slightly higher than the liquid level of the slurry; after the slurry is naturally lifted to fill all pore channels of the carrier, taking the carrier out of the slurry, blowing off residual fluid in the pore channels, drying at 110 ℃ for 6h, and roasting at 600 ℃ for 2 h; repeating the processes of dipping, drying and roasting for 2 times to obtain the catalyst for the diesel engine based on the modified hydrotalcite derived oxide.
The catalyst for the diesel engine based on the modified hydrotalcite derived oxide, which is obtained by adopting the catalyst preparation loading method described in example 2, comprises the following catalytic coating and a 400-mesh cordierite honeycomb ceramic carrier in percentage by mass: 20-21%/80-79%, and the sum of the mass percentages is 100%.
Example 3
(1) Determination of the amount of raw materials for the preparation of the catalyst
The mass ratio of the sum of the noble metals Pt and Pd of the main catalyst and the Cu-Fe bimetallic modified ZSM-5 molecular sieve in the catalyst prepared in the design example 3 is as follows: 5 percent to 95 percent; CuO and Fe in Cu-Fe bimetal modified ZSM-5 type molecular sieve2O3The mass ratio of the molecular sieve to the ZSM-5 type molecular sieve is as follows: 15%, 10%, 75%; the mass ratio of the noble metal Pt to Pd is as follows: 50 percent of 50 percent; CeO in cocatalyst2、ZrO2The mass ratio of (A) to (B) is as follows: 80 percent to 20 percent; La-Z in coating base materialn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3The mass ratio of (A) to (B) is as follows: 90 percent to 10 percent; La-Zn bimetal modified hydrotalcite derived composite oxide2O3And Al2O3The mol ratio of (A) is: 80 percent to 20 percent; the mol ratio of ZnO to MgO is: 75 percent to 25 percent; the mass ratio of the main catalyst, the adsorbent, the cocatalyst and the coating base material is as follows: 10%, 70%; 5g of polyethylene glycol having an average molecular weight of 20000 and 30g of nitric acid are required per 100g of catalytic coating. Calculating the raw material dosage required for preparing 2000g of catalytic coating according to the conversion ratio: h2PtCl6·6H2O 13.3g、Pd(NO3)2·2H2O 12.5g、Cu(NO3)267.3g、Fe(NO3)3·9H296.1g of O, 142.5g of ZSM-5 type molecular sieve and Ba (CH)3COO)2 333.2g、Ce(NO3)3·6H2O403.6g、Zr(NO3)4·5H2O 139.4g、La(NO3)3·6H2O 1233.2g、Al(NO3)3·9H2O 267.1g、Zn(NO3)2·6H2O 2383.0g、Mg(NO3)2·6H2O 684.6g、γ-Al2O3140.0g, 600g nitric acid and 100g polyethylene glycol with the average molecular weight of 20000. Al in the alumina sol used in the present example2O3The content of (b) was 10.8%, from which 1296.3g of alumina sol was calculated.
(2) Preparation of Cu-Fe bimetal modified ZSM-5 type molecular sieve
Weighing Cu (NO) according to determined mass3)2And Fe (NO)3)3·9H2Adding the two raw materials into 0.9L of deionized water, and stirring to prepare a mixed solution; adding the ZSM-5 type molecular sieve with determined mass into the mixed solution, stirring vigorously for 6h at 80 ℃, and evaporating the liquid to dryness at 80 ℃ after stirring. And then drying the powder after evaporation at 100 ℃ for 6h, and roasting the dried powder at 600 ℃ for 2h to obtain the Cu-Fe bimetal modified ZSM-5 type molecular sieve.
(3) Preparation of La-Zn bimetal modified hydrotalcite derived composite oxide
Weighing La (NO) according to the determined mass3)3·6H2O、Al(NO3)3·9H2O、Zn(NO3)2·6H2O and Mg (NO)3)2·6H2And O, adding the 4 raw materials into 6.5L of deionized water, and fully stirring to prepare a solution, namely a precursor solution. 200g NaOH and 265g Na were weighed out2CO3The two substances are added into 5000g of deionized water and fully stirred until NaOH and Na2CO3Completely dissolved as buffer. Then adding the buffer solution into the precursor solution at the speed of 40ml/min, stirring vigorously, and simultaneously, continuously measuring the pH value of the precursor solution in which the buffer solution is being added by using a pH value analyzer; stopping adding the buffer solution when the pH value of the precursor solution is between 9.5 and 10.5, and continuously stirring the precursor solution for 3 hours; standing and aging the stirred precursor liquid for 36h, generating a large amount of solid substances in an aged precursor liquid container, separating the solid substances in the precursor liquid container through suction filtration, and washing the solid substances with deionized water for 4 times; and drying the washed solid substance at 100 ℃ for 12h, roasting the dried solid substance at 600 ℃ for 2h, naturally cooling the roasted solid substance, and grinding the solid substance on a ball mill for 1h to obtain the La-Zn bimetal modified hydrotalcite derived composite oxide.
(4) Preparation of coating slurries
Weighing H of determined mass2PtCl6·6H2O、Pd(NO3)2·2H2O、Ba(CH3COO)2、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O, alumina sol, polyethylene glycol, nitric acid and prepared Cu-Fe bimetal modified ZSM-5 type molecular sieve and La-Zn bimetal modified hydrotalcite derived composite oxide, adding all the raw materials into 30000g of deionized water, and fully stirring; adjusting the pH value of the mixed solution to 3-4 by using 1mol/L NaOH solution or pure glacial acetic acid, and continuously stirring the mixture to form uniform suspension; will be describedGrinding the suspension on a wet grinding machine until the particle size of D50 is within the range of 1.0-1.2 microns, and then stirring the ground suspension for 20 hours at 70 ℃ to obtain coating slurry.
(5) Application of coating paste
Designing the quality of a 400-mesh cordierite honeycomb ceramic carrier to be coated with a catalytic coating; weighing a 400-mesh cordierite honeycomb ceramic carrier with determined mass, immersing the ceramic carrier in the coating slurry at 70 ℃, and ensuring that the upper end surface of the ceramic carrier is slightly higher than the liquid level of the slurry; after the slurry is naturally lifted to fill all pore channels of the carrier, taking the carrier out of the slurry, blowing off residual fluid in the pore channels, drying at 100 ℃ for 9h, and roasting at 500 ℃ for 4 h; repeating the processes of dipping, drying and roasting for 2 times to obtain the catalyst for the diesel engine based on the modified hydrotalcite derived oxide.
The catalyst for diesel engine based on modified hydrotalcite derived oxide, which is obtained by the catalyst preparation loading method described in example 3, has the following mass percentages of the catalytic coating and the 400-mesh cordierite honeycomb ceramic carrier: 10-11%/90-89%, and the sum of the mass percentages is 100%.
Example 4
(1) Determination of the amount of raw materials for the preparation of the catalyst
The mass ratio of the sum of the noble metals Pt and Pd of the main catalyst and the Cu-Fe bimetallic modified ZSM-5 molecular sieve in the catalyst prepared in the design example 4 is as follows: 5 percent to 95 percent; CuO and Fe in Cu-Fe bimetal modified ZSM-5 type molecular sieve2O3The mass ratio of the molecular sieve to the ZSM-5 type molecular sieve is as follows: 10%, 80%; the mass ratio of the noble metal Pt to Pd is as follows: 50 percent of 50 percent; CeO in cocatalyst2、ZrO2The mass ratio of (A) to (B) is as follows: 80 percent to 20 percent; La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al in coating base material2O3The mass ratio of (A) to (B) is as follows: 80 percent to 20 percent; La-Zn bimetal modified hydrotalcite derived composite oxide2O3And Al2O3The mol ratio of (A) is: 50 percent of 50 percent; the mol ratio of ZnO to MgO is: 50 percent of 50 percent; main catalyst, adsorbent, cocatalyst and coating base materialThe quantity proportion is as follows: 5%, 10%, 75%; 10g of polyethylene glycol having an average molecular weight of 20000 and 40g of nitric acid are required per 100g of catalytic coating. Calculating the raw material dosage required for preparing 2000g of catalytic coating according to the conversion ratio: h2PtCl6·6H2O 6.6g、Pd(NO3)2·2H2O 6.3g、Cu(NO3)222.4g、Fe(NO3)3·9H248.1g of O, 76g of ZSM-5 type molecular sieve and Ba (CH)3COO)2 333.2g、Ce(NO3)3·6H2O403.6g、Zr(NO3)4·5H2O 139.4g、La(NO3)3·6H2O 897.6g、Al(NO3)3·9H2O 777.6g、Zn(NO3)2·6H2O 1850.2g、Mg(NO3)2·6H2O 1594.6g、γ-Al2O3300.0g, 800g nitric acid and 200g polyethylene glycol with the average molecular weight of 20000. Al in the alumina sol used in the present example2O3The content of (b) was 10.8%, from which 2777.8g of alumina sol was calculated.
(2) Preparation of Cu-Fe bimetal modified ZSM-5 type molecular sieve
Weighing Cu (NO) according to determined mass3)2And Fe (NO)3)3·9H2Adding the two raw materials into 0.4L of deionized water, and stirring to prepare a mixed solution; adding the ZSM-5 type molecular sieve with determined mass into the mixed solution, stirring vigorously for 12h at 70 ℃, and evaporating the liquid to dryness at 70 ℃ after the stirring is completed. And then drying the powder after evaporation at 90 ℃ for 8h, and roasting the dried powder at 550 ℃ for 3h to obtain the Cu-Fe bimetal modified ZSM-5 type molecular sieve.
(3) Preparation of La-Zn bimetal modified hydrotalcite derived composite oxide
Weighing La (NO) according to the determined mass3)3·6H2O、Al(NO3)3·9H2O、Zn(NO3)2·6H2O and Mg (NO)3)2·6H2O, adding the 4 raw materials into 7L of deionized water,the mixture was thoroughly stirred to prepare a solution, which was a precursor solution. 200g NaOH and 265g Na were weighed out2CO3The two substances are added into 5000g of deionized water and fully stirred until NaOH and Na2CO3Completely dissolved as buffer. Then adding the buffer solution into the precursor solution at the speed of 40ml/min, stirring vigorously, and simultaneously, continuously measuring the pH value of the precursor solution in which the buffer solution is being added by using a pH value analyzer; stopping adding the buffer solution when the pH value of the precursor solution is between 9.5 and 10.5, and continuously stirring the precursor solution for 3 hours; standing and aging the stirred precursor liquid for 24 hours, generating a large amount of solid substances in an aged precursor liquid container, separating the solid substances in the precursor liquid container through suction filtration, and washing the solid substances with deionized water for 4 times; and drying the washed solid substance at 100 ℃ for 12h, roasting the dried solid substance at 500 ℃ for 4h, naturally cooling the roasted solid substance, and grinding the solid substance on a ball mill for 1h to obtain the La-Zn bimetal modified hydrotalcite derived composite oxide.
(4) Preparation of coating slurries
Weighing H of determined mass2PtCl6·6H2O、Pd(NO3)2·2H2O、Ba(CH3COO)2、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O, alumina sol, polyethylene glycol, nitric acid, and the prepared Cu-Fe bimetal modified ZSM-5 type molecular sieve and La-Zn bimetal modified hydrotalcite derived composite oxide, and adding all the raw materials into 25000g of deionized water, and fully stirring; adjusting the pH value of the mixed solution to 3-4 by using 1mol/L NaOH solution or pure glacial acetic acid, and continuously stirring the mixture to form uniform suspension; and grinding the suspension on a wet grinding machine until the particle size of D50 is within the range of 1.0-1.2 microns, and then stirring the ground suspension at 70 ℃ for 20 hours to obtain coating slurry.
(5) Application of coating paste
Designing the quality of a 400-mesh cordierite honeycomb ceramic carrier to be coated with a catalytic coating; weighing a 400-mesh cordierite honeycomb ceramic carrier with determined mass, immersing the ceramic carrier in the coating slurry at 70 ℃, and ensuring that the upper end surface of the ceramic carrier is slightly higher than the liquid level of the slurry; after the slurry is naturally lifted to fill all pore channels of the carrier, taking the carrier out of the slurry, blowing off residual fluid in the pore channels, drying at 90 ℃ for 12h, and roasting at 500 ℃ for 4 h; repeating the processes of dipping, drying and roasting for 3 times to obtain the catalyst for the diesel engine based on the modified hydrotalcite derived oxide.
The catalyst for diesel engine based on modified hydrotalcite derived oxide, which is obtained by the catalyst preparation loading method described in example 4, comprises the following catalytic coating and 400 mesh cordierite honeycomb ceramic carrier in percentage by mass: 25-26%/75-74%, the sum of the mass percentages being 100%.
The NOx adsorption-reduction purification performance of diesel exhaust of the catalysts prepared in examples 1 to 4 was evaluated by using the LNT catalyst NOx purification performance engine evaluation system shown in fig. 1. Before the test, the catalysts prepared in examples 1 to 4 were cut and combined into 4L monolithic catalysts, respectively, and the cut and combined monolithic catalysts were packaged. The test method comprises the following steps:
(1) and (3) steady-state working condition test: the torque and the rotating speed of a test engine (CY4102 type diesel engine) 3 are controlled by using a dynamometer 1 and a coupling 2, the temperature and the humidity of the inlet air of the engine are regulated to reach a stable state by using an inlet air conditioner 5, and the proportion of the exhaust flow of the engine to the volume of a catalyst is adjusted to be 30000h respectively in sequence-1And 50000h-1And sequentially controlling the temperature of the central point of the LNT catalyst 12 to be 250 ℃ and 350 ℃ respectively, and carrying out catalytic activity evaluation on the catalyst NOx adsorption-reduction reaction. In the test, the fuel supply speed of the fuel injector 6 to the diesel engine is adjusted through the fuel injection control system 7, so that the lean burn/rich burn working condition switching is realized in the running process of the diesel engine. Exhaust gas formed by combustion in a cylinder of the diesel engine passes through an exhaust stabilizer 10 and then enters an LNT (Low-Density fuel) catalyst for adsorption-reduction purification treatment. Diesel exhaust before and after LNT catalyst treatment enters an engine exhaust analyzer 16 from an exhaust sampling port A8 and an exhaust sampling port B14 through an exhaust sampling passage 15 for NOx concentration analysis, and gas after NOx analysisThe body is discharged out of the laboratory by the air pump 17. Temperature sensor a9 and temperature sensor B11 measure the exhaust gas temperature before and after the exhaust gas regulator 10, and temperature sensor C13 measures the temperature of the center of the LNT catalyst. The temperature measurements of the 3 temperature sensors and the intake air flow measurements of the intake air flow meter 4 provide feedback parameters for the control strategy of the fuel injection control system and the dynamometer. By utilizing the LNT catalyst NOx purification performance engine evaluation system, the exhaust temperature of the diesel engine is 250 ℃, and the airspeed is 30000h-1The time and exhaust temperature is 350 ℃, and the space velocity is 50000h-1In the diesel engine exhaust NOx adsorption-reduction reaction catalyzed by the catalysts prepared in examples 1 to 4, the purification efficiency of NOx is shown in fig. 2 and 3, respectively.
(2) ESC test: the NOx purification effect in the adsorption-reduction reaction of the exhaust NOx of the diesel engine catalyzed by the catalyst prepared in the examples 1-4 is evaluated by adopting the LNT catalyst NOx purification performance engine evaluation system according to ESC test regulations specified in national Standard GB 17691-2005 [ emission limits of vehicle compression ignition type and gas fuel ignition type engines and automobile exhaust pollutants ] and the measurement method (China stages III, IV and V) ], and is shown in FIG. 4.
In conclusion, the catalyst adopts a Cu-Fe bimetallic modified ZSM-5 type molecular sieve and noble metals Pt and Pd to form a main catalyst; BaO constitutes the adsorbent; CeO (CeO)2-ZrO2Solid solution constitutes a cocatalyst; La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3Forming a coating base material; 400-mesh cordierite honeycomb ceramic is used as a catalyst carrier. The preparation process comprises the following steps: determining the dosage of the catalyst raw material; preparing a Cu-Fe bimetal modified ZSM-5 type molecular sieve and a La-Zn bimetal modified hydrotalcite derived composite oxide, and preparing and coating slurry. Through the cyclic change of the lean/rich combustion working condition of the diesel engine, the catalyst can efficiently catalyze the adsorption-reduction purification reaction of NOx in exhaust. According to the invention, the Cu-Fe bimetallic modified ZSM-5 type molecular sieve is adopted to replace most of noble metal materials in the LNT catalyst, so that the cost of raw materials for preparing the catalyst is reduced, and the sulfur resistance, heat resistance and catalytic activity of reduction reaction of the LNT catalyst are improved; meanwhile, La + is adoptedZn bimetal modified hydrotalcite derived composite oxide replaces most of gamma-Al in LNT catalyst2O3The coating base material provides an additional adsorbent for the LNT catalyst while keeping the stability of the coating from being reduced, and greatly increases the NOx adsorption capacity of the LNT catalyst.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.

Claims (6)

1. A catalyst based on modified hydrotalcite derived oxide for diesel engine contains modified ZSM-5 molecular sieve, Pt, Pd, BaO and CeO2-ZrO2Solid solution, modified hydrotalcite-derived composite oxide, and gamma-Al2O3And a 400 mesh cordierite honeycomb ceramic carrier; the method is characterized in that:
the modified ZSM-5 type molecular sieve is a Cu-Fe bimetal modified ZSM-5 type molecular sieve, wherein Cu element is uniformly dispersed on the surface and in micropores of the ZSM-5 type molecular sieve in a CuO form, and Fe element is Fe2O3Is uniformly dispersed on the surface and in micropores of the ZSM-5 type molecular sieve, and the CuO and the Fe2O3The mass percentage of the zeolite to the ZSM-5 type molecular sieve is as follows: 5-15%/5-10%/90-75%, and the sum of the mass percentages is 100%;
the modified hydrotalcite-derived composite oxide is La-Zn bimetal modified hydrotalcite-derived composite oxide, and La partially replaces Al2O3Al in 6MgO type hydrotalcite-like compound-derived composite oxide, Al being partially substituted by Zn2O36 MgO-type hydrotalcite-like compound-derived composite oxide containing Mg, wherein La, Al, Zn and Mg are La, respectively2O3、Al2O3And ZnO and MgO are dispersed in the La-Zn bimetal modified hydrotalciteIn a derived composite oxide, and La2O3And Al2O3The mole percentage of (A) is as follows: 50-80%/50-20%, the sum of the mole percentages is 100%; the mol percentages of ZnO and MgO are as follows: 25-75%/75-25%, the sum of the mole percentages being 100%; meanwhile, the ratio of the sum of the molar numbers of La ions and Al ions to the sum of the molar numbers of Zn ions and Mg ions in the La-Zn bimetal modified hydrotalcite derived composite oxide is 1: 3;
the Cu-Fe bimetal modified ZSM-5 type molecular sieve, Pt and Pd form a main catalyst of the catalyst, and the mass sum of the Pt and the Pd and the mass percentage of the Cu-Fe bimetal modified ZSM-5 type molecular sieve are as follows: 2-5%/98-95%, the sum of the mass percentages is 100%; the BaO constitutes an adsorbent for the catalyst; the CeO2-ZrO2The solid solution constitutes the catalyst promoter of the catalyst; the La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3A coating base material constituting a catalyst; the La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al2O3The mass percentage of the components is as follows: 75-90%/25-10%, the sum of the mass percentages is 100%;
the main catalyst, the adsorbent, the cocatalyst and the coating base material form a catalytic coating of the catalyst, and the mass percentages of the main catalyst, the adsorbent, the cocatalyst and the coating base material respectively correspond to: 5-10%/10%/5-10%/80-70%, the sum of the mass percentages is 100%;
the catalyst consists of the catalytic coating and 400-mesh cordierite honeycomb ceramic, wherein the 400-mesh cordierite honeycomb ceramic is a carrier of the catalyst, the catalytic coating is coated on the 400-mesh cordierite honeycomb ceramic, and the catalytic coating and the 400-mesh cordierite honeycomb ceramic are as follows by mass percent: 10-30%/90-70%, and the sum of the mass percentages is 100%.
2. The catalyst for diesel engines based on modified hydrotalcite derived oxides according to claim 1, characterized in that: in the cocatalyst, CeO2And ZrO2The mass percentage of the components is as follows:80-50%/20-50%, the sum of the mass percentages being 100%.
3. The catalyst for diesel engines based on modified hydrotalcite derived oxides according to claim 1, characterized in that: in the main catalyst, the mass percentage of Pt and Pd is as follows: 25-50%/75-50%, the sum of the mass percentages being 100%.
4. The catalyst for diesel engines based on modified hydrotalcite derived oxides according to claim 1, characterized in that: gamma-Al in the coating base material2O3Generated by conversion of aluminum sol as a coating binder.
5. A process for the preparation of a catalyst for diesel engines based on modified hydrotalcite derived oxides according to claim 1, characterized in that: the method comprises the following steps:
step one, determining the use amount of raw materials for preparing the catalyst:
respectively designing the mass percentage of the sum of Pt and Pd in the main catalyst and the Cu-Fe bimetal modified ZSM-5 type molecular sieve; in the main catalyst, the mass percentage of Pt and Pd is as follows: 25-50%/75-50%, the sum of the mass percentages being 100%; CuO and Fe in Cu-Fe bimetal modified ZSM-5 type molecular sieve2O3The mass percentage of the zeolite to the ZSM-5 type molecular sieve; CeO in cocatalyst2And ZrO2The mass percentage of the components is as follows: 80-50%/20-50%, the sum of the mass percentages is 100%; gamma-Al in the coating base material2O3Generated by the conversion of aluminum sol as a coating binder; La-Zn bimetal modified hydrotalcite derived composite oxide and gamma-Al in coating base material2O3The mass percentage of (A); in the La-Zn bimetal modified hydrotalcite derived composite oxide, La2O3And Al2O3And the mol percentages of ZnO and MgO; mass percentages of the main catalyst, the adsorbent, the cocatalyst and the coating base material; the mass percentage range of the catalytic coating and the 400-mesh cordierite honeycomb ceramic carrier; and planning the preparation of the coating slurryThe quality of the liquid that can form the catalytic coating;
respectively calculating Pt, Pd and Cu-Fe bimetal modified ZSM-5 type molecular sieve, BaO and CeO in the catalytic coating prepared according to the proportion of each component in the catalyst2、ZrO2、γ-Al2O3La-Zn bimetal modified hydrotalcite derived composite oxide and Cu-Fe bimetal modified ZSM-5 type molecular sieve containing CuO and Fe2O3La in composite oxide derived from ZSM-5 type molecular sieve and La-Zn bimetal modified hydrotalcite2O3、Al2O3ZnO and MgO;
combined every 517.9g H2PtCl6▪6H2O preparation of 195.1g Pt per 266.4g Pd (NO)3)2▪2H2O preparation of 106.4g Pd per 255.4g Ba (CH)3COO)2153.3g of BaO per 434.1g of Ce (NO) are prepared3)3▪6H2O preparation of 172.1g CeO2Every 429.3g of Zr (NO)3)4▪5H2O preparation 123.2g ZrO2Every 187.6g of Cu (NO)3)279.5g of CuO per 808.0g of Fe (NO) were prepared3)3▪9H2O preparation 159.7g Fe2O3Every 866.0g La (NO)3)3▪6H2O preparation 325.8g La2O3Every 750.2g of Al (NO)3)3▪9H2O preparation 102.0g Al2O3Every 297.5g Zn (NO)3)2▪6H2O preparation of 81.4g ZnO, per 256.4g Mg (NO)3)2▪6H2O40.3 g MgO and the H consumed for the preparation of the catalyst was calculated2PtCl6▪6H2O、Pd(NO3)2▪2H2O、Ba(CH3COO)2、Ce(NO3)3▪6H2O、Zr(NO3)4▪5H2O、Cu(NO3)2、Fe(NO3)3▪9H2O、La(NO3)3▪6H2O、Al(NO3)3▪9H2O、Zn(NO3)2▪6H2O、Mg(NO3)2▪6H2The mass of O;
calculating the mass of the polyethylene glycol and the nitric acid consumed for preparing the coating slurry according to the proportion that every 100g of the catalytic coating needs 5-15 g of polyethylene glycol with the average molecular weight of 20000 and 25-50 g of nitric acid; according to Al in the alumina sol2O3Calculating the mass of the consumed aluminum sol required for preparing the coating slurry according to the actual mass percentage;
step two, preparing the Cu-Fe bimetallic modified ZSM-5 type molecular sieve:
weighing Cu (NO) according to the mass determined in the step one3)2And Fe (NO)3)3▪9H2O, and per mole of Cu (NO)3)2And per mole Fe (NO)3)3▪9H2O to 1-2L deionized water, adding Cu (NO)3)2And Fe (NO)3)3▪9H2Adding O into deionized water, and stirring to prepare a mixed solution; adding a ZSM-5 type molecular sieve with determined mass into the mixed solution, stirring vigorously for 6-12 h at 70-80 ℃, and evaporating the liquid to dryness at 70-80 ℃; drying the evaporated powder at 90-110 ℃ for 4-8 h, and roasting at 550-600 ℃ for 2-3 h to obtain the Cu-Fe bimetal modified ZSM-5 molecular sieve;
step three, preparing the La-Zn bimetal modified hydrotalcite derived composite oxide:
weighing La (NO) according to the determined mass3)3▪6H2O、Al(NO3)3▪9H2O、Zn(NO3)2▪6H2O and Mg (NO)3)2▪6H2O, adding La (NO) into the mixture according to the proportion of 0.5-1L of deionized water per mol of Zn ions and per mol of Mg ions3)3▪6H2O、Al(NO3)3▪9H2O、Zn(NO3)2▪6H2O and Mg (NO)3)2▪6H2Adding O into deionized water, and fully stirring to obtain a solution as a precursor solution;
weighing sufficient NaOH and Na2CO3And the mole number of NaOH is equal to that of Na2CO3The molar ratio of the NaOH to the Na is 2:1, and NaOH and Na are mixed according to the ratio that each mole of NaOH corresponds to 1L of deionized water2CO3Adding into deionized water, stirring thoroughly until NaOH and Na2CO3Completely dissolving to obtain a buffer solution;
adding a buffer solution into the precursor solution at the speed of 30-50 mL/min, stirring vigorously, and simultaneously continuously measuring the pH value of the precursor solution added with the buffer solution by using a pH value analyzer; stopping adding the buffer solution when the pH value is between 9.5 and 10.5, continuing stirring for 2 to 4 hours, standing and aging for 24 to 48 hours, and filtering and separating an aged solid substance; washing the solid substance with deionized water for 3-5 times, drying at 90-110 ℃ for 8-16 h, roasting at 500-600 ℃ for 2-4 h, naturally cooling, and grinding on a ball mill for 1h to obtain La-Zn bimetal modified hydrotalcite derived composite oxide;
step four, preparing coating slurry:
weighing H of determined mass2PtCl6▪6H2O、Pd(NO3)2▪2H2O、Ba(CH3COO)2、Ce(NO3)3▪6H2O、Zr(NO3)4▪5H2O, alumina sol, polyethylene glycol, nitric acid, the prepared Cu-Fe bimetal modified ZSM-5 type molecular sieve and La-Zn bimetal modified hydrotalcite derived composite oxide, adding all the raw materials into deionized water with the mass being 10-15 times of the total mass of the prepared catalytic coating, and fully stirring; adjusting the pH value of the mixed solution to 3-4 by using 1mol/L NaOH solution or pure glacial acetic acid, and continuously stirring the mixture to form uniform suspension; grinding the suspension on a wet grinding machine until the median particle size is within the range of 1.0-1.2 microns, and then stirring the ground suspension for 16-24 hours at the temperature of 60-80 ℃ to obtain coating slurry;
step five, coating the coating slurry
Designing the quality of a 400-mesh cordierite honeycomb ceramic carrier to be coated with a catalytic coating; the catalyst coating and the cordierite honeycomb ceramic carrier are as follows by mass percent: 10-30%/90-70% of the raw materials are mixed, and the raw materials are subjected to the following dipping, drying and calcining treatment:
immersing a cylindrical 400-mesh cordierite honeycomb ceramic carrier into the coating slurry at the temperature of 60-80 ℃, wherein the upper end face of the cordierite honeycomb ceramic carrier is higher than the liquid level of the coating slurry; after the coating slurry is naturally lifted to fill all pore channels of the cordierite honeycomb ceramic carrier, taking the cordierite honeycomb ceramic carrier out of the coating slurry, blowing off residual fluid in the pore channels, drying at 90-110 ℃ for 6-12 h, and calcining at 500-600 ℃ for 2-4 h;
and repeating the processes of dipping, drying and calcining for 2-3 times to obtain the catalyst for the diesel engine based on the modified hydrotalcite derived oxide.
6. The application of the catalyst for the diesel engine based on the modified hydrotalcite derived oxide is characterized in that: the modified hydrotalcite-derived oxide-based catalyst for diesel engines prepared by the method of claim 5 is encapsulated and the encapsulated catalyst is installed in the exhaust gas duct of a diesel vehicle to purify the NOx pollutants in the exhaust gas of the diesel vehicle by NOx adsorption-reduction reaction.
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