CN111468114B - Diesel oxidation catalyst with high thermal stability and preparation method thereof - Google Patents

Diesel oxidation catalyst with high thermal stability and preparation method thereof Download PDF

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CN111468114B
CN111468114B CN202010386847.3A CN202010386847A CN111468114B CN 111468114 B CN111468114 B CN 111468114B CN 202010386847 A CN202010386847 A CN 202010386847A CN 111468114 B CN111468114 B CN 111468114B
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catalyst
noble metal
platinum
palladium
coating
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CN111468114A (en
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朱敬芳
常仕英
于飞
马江丽
殷雪梅
赖慧龙
汪朝强
杨冬霞
赵云昆
桓源峰
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Kunming Sino Platinum Metals Catalyst Co ltd
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Kunming Sino Platinum Metals Catalyst Co ltd
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    • 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
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    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/101—Three-way catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
    • F01N3/2825—Ceramics
    • F01N3/2828—Ceramic multi-channel monoliths, e.g. honeycombs
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    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/10—Carbon or carbon oxides
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    • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/14—Nitrogen oxides
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Abstract

The invention discloses a diesel oxidation catalyst with high thermal stability and a preparation method thereof. The catalyst consists of a carrier and a coating, wherein the coating consists of noble metals of platinum and palladium, modified alumina, an auxiliary agent and a binder; the loading capacity of the coating is 80-180 g/L; the loading capacity of the platinum is 1 to 100g/ft 3 The loading capacity of palladium is 1-100 g/ft 3 (ii) a The mass ratio of the modified oxide to the alumina in the modified alumina is 0-20: 80 to 100; the mass ratio of the auxiliary agent to the modified alumina is 0-10: 90 to 100; the mass ratio of the binder to the modified alumina is 2-10: 90 to 98. The preparation method comprises the steps of loading platinum and palladium on the modified aluminum oxide material, adding an auxiliary agent and a binder to prepare catalyst coating slurry, coating the coating slurry on the honeycomb ceramic carrier, drying and calcining. The catalyst has excellent oxidation performance on CO, hydrocarbon and NO in tail gas discharged by a diesel vehicle after being calcined for 100 hours in a muffle furnace at 650 ℃, and has excellent thermal stability.

Description

Diesel oxidation catalyst with high thermal stability and preparation method thereof
Technical Field
The invention belongs to the technical field of catalysts, and relates to a diesel oxidation catalyst with high thermal stability and a preparation method thereof.
Background
The release of the national six-code for heavy-duty diesel vehicles GB17691-2018 presents new requirements and challenges for both catalytic activity and durability of diesel vehicle aftertreatment system catalysts. When the particulate matter trapping catalyst (CDPF catalyst) in the diesel vehicle aftertreatment system is actively regenerated, fuel oil is sprayed in an engine cylinder, a diesel vehicle oxidation catalyst (DOC catalyst) positioned at the front end of the CDPF catalyst is needed to combust the fuel oil to rapidly raise the temperature to 600 ℃, so that the regeneration of the CDPF catalyst is assisted, the temperature of an inner bed of the DOC catalyst reaches above 650 ℃, the service life of the diesel vehicle national six-catalyst is prolonged to 70 kilometers from 10 kilometers of the national five, the active regeneration frequency of the CDPF catalyst is increased, and the requirement on the thermal stability of the DOC catalyst is higher.
The thermal stability of the catalyst is strongly related to the thermal stability of the catalyst coating material and the sintering resistance of the active noble metal. The high-temperature stability of the noble metal Pt is poor, and the noble metal Pt is easy to volatilize at high temperature, so that a Pt-Pd bimetallic system is adopted in the diesel engine national six DOC catalyst, and the thermal stability of the catalyst is improved by means of the mutual synergistic action of Pt-Pd. The type of the noble metal precursor and the dispersion degree of the noble metal on the carrier material have great influence on the sintering resistance of the noble metal serving as an active component.
The first generation precious metal precursors used in automotive exhaust catalysts were mainly chlorides, such as chloroplatinic acid, chloropalladite, etc., but the activity of the catalyst was affected by the residual chlorine. Therefore, simple nitrate-type precious metal precursors such as palladium nitrate, platinum nitrate, rhodium nitrate and the like become second-generation precious metal precursors used for catalysts, but the nitrate-type precious metal precursors have strong acidity, damage the structures on the surfaces of certain carrier materials, reduce the dispersion and adhesion of active metals on the carrier materials, and influence the activity and the thermal stability of the catalysts. Therefore, the precious metal precursor which does not contain elements such as sulfur, chlorine, phosphorus, nitrate radical and the like and has good water solubility and stability is synthesized to be used for preparing the automobile exhaust catalyst, the adverse effect caused by the first-generation precious metal precursor can be avoided, the introduced organic functional group, hydroxyl ions and the like can be combined with active sites on the carrier material, precious metal particles are anchored on the active sites of the carrier material better, the dispersion degree of the precious metal particles on the carrier material is improved, more precious metal active components are exposed outside, the contact surface with a reactant is increased, the activity of the catalyst is improved, and in the calcining process, the precious metal particles are not easy to volatilize and aggregate due to the enhancement of the anchoring effect, and the thermal stability of the catalyst is further improved.
The addition of the auxiliary agent has a great promotion effect on the dispersion of the noble metal on the carrier material, the noble metal particles are anchored with the active sites of the carrier material better by the addition of the auxiliary agent, the dispersion degree of the noble metal on the carrier material is improved, and the noble metal particles are prevented from volatilizing and agglomerating in the high-temperature calcination process, so that the aging performance of the catalyst is improved, and the catalyst has excellent thermal stability.
Therefore, the method has great practical application significance for improving the catalytic performance and the thermal stability of the diesel catalyst oxidation type catalyst by changing the types of the noble metal precursors and adding the auxiliary agent at the same time.
Disclosure of Invention
In view of the above, the present invention aims to provide a diesel oxidation catalyst with high thermal stability and a preparation method thereof, wherein the catalytic activity of the diesel oxidation catalyst after high temperature aging is improved by changing the type of a noble metal precursor and adding an auxiliary agent at the same time, so as to ensure the durability of the catalyst.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a diesel oxidation catalyst with high thermal stability comprises a catalyst carrier and a catalyst coating.
The carrier of the catalyst is a ceramic or metal carrier with a honeycomb structure.
The catalyst coating consists of noble metals of platinum and palladium, modified alumina, an auxiliary agent and a binder; the load capacity of the coating is 80-180 g/L; the loading capacity of the noble metal platinum is 1-100 g/ft 3 The loading capacity of the palladium is 1 to 100g/ft 3 (ii) a The mass ratio of the modified oxide to the alumina in the modified alumina is 0-20: 80 to 100 portions; the mass ratio of the auxiliary agent to the modified alumina is 0-10: 90 to 100; the mass ratio of the binder to the modified alumina is 2-10: 90 to 98.
Further, the precursor of the noble metal platinum is any one or more of tetramine platinum hydrogen carbonate (II), tetramine platinum dihydroxide (II) and tetramine dihydroxyplatinum dihydroxide (IV);
further, the precursor of the noble metal palladium is any one or more of tetraamminepalladium (II) hydrogen carbonate, tetraamminepalladium (II) dihydroxide and acetimidopalladam (II) tetramer;
further, the modified oxide of the modified alumina comprises one or more of praseodymium oxide, neodymium oxide, yttrium oxide and barium oxide;
further, the auxiliary agent is one or more of malic acid, lysine, tartaric acid and maleic acid;
further, the binder comprises one or more of alumina colloid, silica colloid and zirconia colloid.
A method for preparing a diesel oxidation catalyst with high thermal stability is characterized by comprising the following steps:
(1) Noble metal platinum and noble metal palladium supported modified alumina: calculating and measuring the volume of a noble metal precursor solution according to the loading amounts of noble metal platinum and noble metal palladium; dispersing modified alumina in deionized water, respectively or mixing precursor solutions of noble metal platinum and noble metal palladium, then dropwise adding the precursor solutions into the modified alumina solution at a certain flow rate, and fully stirring to obtain slurry loaded with noble metal platinum and noble metal palladium;
(2) Addition of an auxiliary agent: adding an auxiliary agent into the slurry containing the noble metals platinum and palladium prepared in the step (1), and fully stirring;
(3) Addition of a binder: adding a binder to the slurry containing the noble metal and the auxiliary agent prepared in the step (2);
(4) Grinding the particle size of the slurry: grinding the slurry containing the noble metal, the auxiliary agent and the binder prepared in the step (3) in a grinding machine;
(5) Coating of a coating: coating the ground slurry of the step (4) on a honeycomb carrier under vacuum suction pressure;
(6) Drying and calcining the catalyst: drying and calcining the catalyst coated in the step (5) to prepare the catalyst in a fresh state;
(7) Aging of the catalyst: and (4) calcining the fresh catalyst prepared in the step (6) in a muffle furnace to prepare the aged catalyst.
Further, the precursor solution of the noble metal platinum in the step (1) is any one or more of tetramine platinum hydrogen carbonate (II), tetramine platinum dihydroxide (II) and tetramine dihydroxy platinum dihydroxide (IV), and the precursor of the noble metal palladium is any one or more of tetramine palladium hydrogen carbonate (II), tetramine palladium dihydroxide (II) and tetramer of palladium acetate imine (II); the modified oxide of the modified alumina comprises one or more of praseodymium oxide, neodymium oxide, yttrium oxide and barium oxide; the dripping speed of the noble metal precursor is 0.1 ml/min-20 ml/min.
Further, the auxiliary agent in the step (2) is one or more of malic acid, lysine, tartaric acid and maleic acid.
Further, the binder in the step (3) comprises one or more of alumina colloid, silica colloid and zirconia colloid.
Further, the D90= 5-50 um of the ground slurry in the step (4);
further, in the step (6), the drying temperature of the catalyst is 120-180 ℃, the time is 2-5 h, the calcination temperature of the catalyst is 450-650 ℃, and the calcination time is 2-6 h.
Further, the calcination temperature of the catalyst in the step (7) is 650 ℃ and the calcination time is 100h.
Compared with the prior art, the invention provides a diesel oxidation catalyst with high thermal stability and a preparation method thereof.
The invention provides a diesel vehicle oxidation catalyst with high stability and a preparation method thereof. The invention improves the dispersion degree of noble metal on the oxide carrier and prevents the volatilization and aggregation of noble metal particles in the sintering process by changing the species of noble metal precursors and adding an auxiliary agent simultaneously, thereby improving the aging performance of the catalyst, ensuring that the catalyst has excellent thermal stability and improving the durability of the catalyst.
The precursor of the noble metal platinum used in the invention is any one or more of tetramine platinum hydrogen carbonate (II), tetramine platinum dihydroxide (II) and tetramine dihydroxyplatinum dihydroxide (IV); the precursor of the noble metal palladium is any one or more of tetraamminepalladium (II) hydrogen carbonate, tetrahydroxygen tetraamminepalladium (II) and acetimidipalladium (II) tetramer, compared with the common noble metals such as platinum chloride, palladium chloride, platinum nitrate, palladium nitrate and the like, the noble metal precursor used by the invention does not contain elements such as chlorine, nitrate and the like, does not corrode a modified alumina carrier material, does not have residual chlorine, introduces organic functional groups and hydroxyl ions, can be combined with active sites on the carrier material, better anchors the noble metal particles on the active sites of the carrier material to improve the dispersion degree of the noble metal particles on the carrier material, exposes more noble metal active components outside, increases the contact surface with reactants, improves the activity of the catalyst, and is not easy to volatilize and aggregate due to the enhancement of the anchoring effect in the calcining process, thereby improving the thermal stability of the catalyst. Meanwhile, the auxiliary agent is added to disperse the noble metal, so that noble metal particles are anchored with active sites of the carrier material better, the dispersion degree of the noble metal on the carrier material is improved, and the noble metal particles are prevented from volatilizing and agglomerating in the high-temperature calcination process, thereby improving the aging performance of the catalyst and ensuring that the catalyst has excellent thermal stability.
The catalyst disclosed by the invention has excellent oxidation performance on CO, hydrocarbon and NO in the tail gas emission of a diesel vehicle, still has excellent catalytic oxidation performance after being aged for a long time at a high temperature by a muffle furnace, and has excellent thermal stability and durability.
Drawings
FIG. 1 is a graph comparing the oxidation capacity of CO of catalysts prepared in example 1 of the present invention and comparative example 1, the abscissa represents temperature in units, and the ordinate represents CO conversion efficiency in units%.
Fig. 2 is a graph comparing the oxidation capacity of the catalysts prepared in example 1 of the present invention and comparative example 1 for hydrocarbon (THC) in terms of temperature on the abscissa and THC conversion efficiency on the ordinate in%.
FIG. 3 is a graph comparing the oxidation capacities of the catalysts NO prepared in example 1 of the present invention and comparative example 1, with the abscissa representing the temperature and the ordinate representing the NO 2 The ratio/NOx is given in%.
Detailed Description
In order to better illustrate the present invention and to facilitate understanding of the technical aspects of the present invention, the present invention will be described below based on examples and comparative examples.
Example 1
(1) Weighing 343g of praseodymium oxide modified alumina, dissolving in 1500ml of deionized water, and stirring for 30min;
(2) Weighing a tetraammine palladium (II) hydrogen carbonate solution to ensure that the mass of a noble metal Pd simple substance is 0.64g and a tetraammine platinum (II) hydrogen carbonate solution to ensure that the mass of a noble metal Pt simple substance is 3.19g, uniformly mixing the tetraammine palladium (II) hydrogen carbonate solution and the tetraammine platinum (II) hydrogen carbonate solution, dropwise adding the tetraammine palladium (II) hydrogen carbonate solution and the tetraammine platinum (II) hydrogen carbonate solution into the slurry in the step (1) at the speed of 5ml/min, and stirring for 30min;
(3) Weighing 5g of malic acid, adding into the noble metal slurry prepared in the step (2), and stirring for 30min;
(4) Weighing 10g of alumina colloid into the slurry prepared in the step (3), and stirring for 30min;
(5) Grinding the slurry prepared in (4) in a grinder until the D90=30um of the slurry;
(6) Coating the slurry prepared in the step (5) on a honeycomb ceramic carrier by vacuum suction, wherein the size of the carrier is 190.5X 101.6,400cpsi, and the coating dry weight of the catalyst is 180g/L;
(7) Drying the coated catalyst at 120-150 ℃ for 2h;
(8) Calcining the dried catalyst in a muffle furnace at 500 ℃ for 1h to prepare a fresh catalyst;
(9) And (3) calcining the fresh catalyst in a muffle furnace at 650 ℃ for 100h to prepare the aged catalyst.
Example 2
(1) Weighing 343g of neodymium oxide modified alumina, dissolving in 1500ml of deionized water, and stirring for 30min;
(2) Weighing a palladium (II) tetraammine dihydrogen hydroxide solution to ensure that the mass of a noble metal Pd simple substance is 0.64g and a platinum (II) tetraammine dihydrogen hydroxide solution to ensure that the mass of a noble metal Pt simple substance is 3.19g, firstly dripping the palladium (II) tetraammine dihydrogen hydroxide solution into the solution in the step (1) at the speed of 10ml/min, then dripping the platinum (II) tetraammine dihydrogen hydroxide solution into the slurry containing the palladium at the speed of 10ml/min, and stirring for 30min;
(3) Weighing 5g of lysine, adding into the precious metal slurry prepared in the step (2), and stirring for 30min;
(4) Weighing 10g of silica colloid into the slurry prepared in the step (3), and stirring for 30min;
(5) Grinding the slurry prepared in (4) in a grinder until the D90=10um of the slurry;
(6) Coating the slurry prepared in the step (5) on a honeycomb ceramic carrier by vacuum suction, wherein the size of the carrier is 190.5X 101.6,400cpsi, and the coating dry weight of the catalyst is 180g/L;
(7) Drying the coated catalyst at 120-150 ℃ for 2h;
(8) Calcining the dried catalyst in a muffle furnace at 500 ℃ for 1h to prepare a fresh catalyst;
(9) And (3) calcining the fresh catalyst in a muffle furnace at 650 ℃ for 100h to prepare the aged catalyst.
Example 3
(1) Weighing 343g of yttria-modified alumina, dissolving in 1500ml of deionized water, and stirring for 30min;
(2) Weighing an iminium palladium (II) acetate tetramer solution to ensure that the mass of a noble metal Pd simple substance is 0.64g and a dihydroxide tetraammine dihydroxyplatinum (IV) solution to ensure that the mass of a noble metal Pt simple substance is 3.19g, firstly dropwise adding the dihydroxide tetraammine dihydroxyplatinum (IV) solution into the solution in the step (1) at a speed of 15ml/min, then dropwise adding the iminium palladium (II) acetate tetramer solution into the slurry containing platinum at a speed of 5ml/min, and stirring for 30min;
(3) Weighing 5g of tartaric acid, adding the tartaric acid into the noble metal slurry prepared in the step (2), and stirring for 30min;
(4) Weighing 10g of silica colloid into the slurry prepared in the step (3), and stirring for 30min;
(5) Grinding the slurry prepared in (4) in a grinder until the D90=20um of the slurry;
(6) Coating the slurry prepared in (5) on a honeycomb ceramic carrier by vacuum suction, wherein the size of the carrier is 190.5 x 101.6,400cpsi, and the coating dry weight of the catalyst is 180g/L;
(7) Drying the coated catalyst at 120-150 ℃ for 2h;
(8) Calcining the dried catalyst in a muffle furnace at 500 ℃ for 1h to prepare a fresh catalyst;
(9) And (3) calcining the fresh catalyst in a muffle furnace at 650 ℃ for 100h to prepare the aged catalyst.
Example 4
(1) Weighing 343g of barium oxide modified alumina, dissolving in 1500ml of deionized water, and stirring for 30min;
(2) Weighing a tetraammine palladium (II) hydrogen carbonate solution to ensure that the mass of a noble metal Pd simple substance is 0.64g and a tetraammine platinum (II) hydrogen carbonate solution to ensure that the mass of a noble metal Pt simple substance is 3.19g, uniformly mixing the tetraammine palladium (II) hydrogen carbonate solution and the tetraammine platinum (II) hydrogen carbonate solution, dropwise adding the tetraammine palladium (II) hydrogen carbonate solution and the tetraammine platinum (II) hydrogen carbonate solution into the slurry in the step (1) at the speed of 5ml/min, and stirring for 30min;
(3) Weighing 5g of maleic acid, adding the maleic acid into the noble metal slurry prepared in the step (2), and stirring for 30min;
(4) Weighing 10g of alumina colloid into the slurry prepared in the step (3), and stirring for 30min;
(5) Grinding the slurry prepared in (4) in a grinder until the D90=30um of the slurry;
(6) Coating the slurry prepared in the step (5) on a honeycomb ceramic carrier by vacuum suction, wherein the size of the carrier is 190.5X 101.6,400cpsi, and the coating dry weight of the catalyst is 180g/L;
(7) Drying the coated catalyst at 120-150 ℃ for 2h;
(8) Calcining the dried catalyst in a muffle furnace at 500 ℃ for 1h to prepare a fresh catalyst;
(9) And (3) calcining the fresh catalyst in a muffle furnace at 650 ℃ for 100h to prepare the aged catalyst.
Example 5
(1) Weighing 343g of praseodymium oxide modified alumina, dissolving in 1500ml of deionized water, and stirring for 30min;
(2) Measuring a tetraammine palladium (II) hydrogen carbonate solution to ensure that the mass of the simple substance of the noble metal Pd is 1.28g and a tetraammine platinum (II) hydrogen carbonate solution to ensure that the mass of the simple substance of the noble metal Pt is 2.55g, uniformly mixing the tetraammine palladium (II) hydrogen carbonate solution and the tetraammine platinum (II) hydrogen carbonate solution, dropwise adding the mixture into the slurry in the step (1) at the speed of 5ml/min, and stirring for 30min;
(3) Weighing 5g of malic acid, adding into the noble metal slurry prepared in the step (2), and stirring for 30min;
(4) Weighing 10g of alumina colloid into the slurry prepared in the step (3), and stirring for 30min;
(5) Milling the slurry prepared in (4) in a mill until the D90=30um of the slurry;
(6) Coating the slurry prepared in the step (5) on a honeycomb ceramic carrier by vacuum suction, wherein the size of the carrier is 190.5X 101.6,400cpsi, and the coating dry weight of the catalyst is 180g/L;
(7) Drying the coated catalyst at 120-150 ℃ for 2h;
(8) Calcining the dried catalyst in a muffle furnace at 500 ℃ for 1h to prepare a fresh catalyst;
(9) And (3) calcining the fresh catalyst in a muffle furnace at 650 ℃ for 100h to prepare the aged catalyst.
Comparative example 1
(1) Weighing 343g of yttria-modified alumina, dispersing in 1500ml of deionized water, and stirring for 30min;
(2) Measuring a palladium nitrate solution to enable the mass of the Pd elementary substance of the noble metal to be 0.64g, measuring a platinum nitrate solution to enable the mass of the Pt elementary substance of the noble metal to be 3.19g, mixing two noble metal precursor solutions of platinum nitrate and palladium nitrate, dropwise adding the mixture into the slurry in the step (1) at the speed of 5ml/min, and stirring for 30min;
(3) Weighing 10g of alumina colloid into the slurry prepared in the step (2), and stirring for 30min;
(4) Milling the slurry prepared in (3) in a mill until the D90=15um of the slurry;
(5) Coating the slurry prepared in (4) on a honeycomb ceramic carrier by vacuum suction, wherein the size of the carrier is 190.5 x 101.6,400cpsi, and the coating dry weight of the catalyst is 180g/L;
(7) Drying the coated catalyst at 120-150 ℃ for 2h;
(8) Calcining the dried catalyst in a muffle furnace at 500 ℃ for 1h to prepare a fresh catalyst;
(9) And (3) calcining the fresh catalyst in a muffle furnace at 650 ℃ for 100h to prepare the aged catalyst.
Respectively carrying out continuous ignition performance tests on the fresh catalyst and the aged catalyst on an engine bench at an airspeed of 100000h -1 The oxidation ability data of CO, THC, NO in the test results are shown in table 1, fig. 2, fig. 3.
TABLE 1 Oxidation capacity of the example and comparative catalysts for CO, THC and NO in the fresh and aged states
Figure BDA0002484109360000091
Remarking: t50 is the temperature at which the gas conversion efficiency reaches 50%.
Example analysis;
the data in table 1 show the oxidation capacities of the catalysts of the different examples and comparative examples to CO, THC and NO in fresh state and aged state, and it can be seen from the data in table 1 that the oxidation capacities of the catalysts of the examples to CO, THC and NO after aging are better than those of the catalysts of the comparative example 1, indicating that the catalyst for diesel vehicle exhaust oxidation of the present invention has excellent thermal stability.
The graph of figure 1 shows that the catalysts of example 1 and comparative example 1 have substantially the same catalytic oxidation capacity for CO in the fresh state. The catalyst of example 1 shows less attenuation after aging and the CO conversion efficiency curve is closer to that in the fresh state, whereas the catalyst of comparative example 1 shows a shift in the CO conversion efficiency curve toward a high temperature after aging and a rise in the light-off temperature T50 (the temperature corresponding to 50% conversion efficiency of CO) of 30 ℃. It is shown that the catalyst of example 1 has good thermal stability and the CO conversion efficiency after aging is essentially identical to that of the fresh state.
The graph of figure 2 shows that the catalysts of example 1 and comparative example 1 have substantially the same THC conversion capacity in the fresh state at low temperature points and the catalytic oxidation performance of example 1 is slightly better at high temperatures. The catalyst of example 1, which is aged, although the conversion efficiency is lowered at a higher temperature than when it is fresh, has a much better oxidizing ability to THC than that of comparative example 1, indicating that the catalyst of example 1 is excellent in thermal stability.
FIG. 3 is a graph showing that the catalyst of example 1 converts NO to NO in the fresh state as compared to the catalyst of comparative example 1 2 Slightly better performance, NO in the fresh state of the catalyst of example 1 2 The maximum ratio of NOx was 70%, and the catalyst of example 1 was deteriorated in its ability to oxidize NO after aging at high temperature for a long period of time, but NO was deteriorated 2 The proportion of NOx can reach 60 percent at all, and the catalyst has better catalytic activity, but NO is aged in comparative example 1 2 the/NOx ratio is poor over the entire test temperature range. Illustrating the high stability of the catalyst of example 1.
The applicant states that the present invention is illustrated in detail by the examples given above, but the present invention is not limited to the specific methods given above, which means that the present invention does not have to be implemented by means of the specific methods given above. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitution of each raw material and addition of auxiliary components, etc., of the product of the present invention, falls within the scope of protection and disclosure of the present invention.

Claims (5)

1. A diesel oxidation catalyst with high thermal stability comprises a catalyst carrier and a catalyst coating, wherein the catalyst carrier is a ceramic or metal carrier with a honeycomb structure; the method is characterized in that:
the catalyst coating consists of noble metals of platinum and palladium, modified alumina, an auxiliary agent and a binder;
the loading capacity of the coating is 80-180 g/L;
the loading capacity of the noble metal platinum is 1-100 g/ft 3 ；
The loading capacity of the noble metal palladium is 1-100 g/ft 3 ；
The mass ratio of the modified oxide to the alumina in the modified alumina is 0-20: 80 to 100;
the mass ratio of the auxiliary agent to the modified alumina is 0-10: 90 to 100;
the mass ratio of the binder to the modified alumina is 2-10: 90 to 98 portions of;
the modified oxide of the modified alumina comprises one or more of praseodymium oxide, neodymium oxide, yttrium oxide and barium oxide;
the precursor of the noble metal platinum is any one or more of tetramine platinum bicarbonate (II), tetramine platinum dihydroxide (II) and tetramine dihydroxyplatinum dihydroxide (IV); the precursor of the noble metal palladium is any one or more of tetraamminepalladium (II) hydrogen carbonate, tetrahydroxygen tetraamminepalladium (II) and acetimidylpralladium (II) tetramer;
the auxiliary agent is one or more of malic acid, lysine, tartaric acid and maleic acid;
the preparation method of the diesel oxidation catalyst comprises the following steps:
(1) Noble metal platinum and noble metal palladium supported modified alumina: calculating and measuring the volume of a noble metal precursor solution according to the loading amounts of noble metal platinum and noble metal palladium; dispersing modified alumina powder in deionized water, and fully stirring to obtain modified alumina slurry; respectively or after mixing, dropwise adding the precursor solutions of the noble metal platinum and the noble metal palladium into the modified alumina slurry at a certain flow rate, and fully stirring to obtain slurry loaded with the noble metal platinum and the noble metal palladium;
(2) Addition of an auxiliary agent: adding an auxiliary agent into the slurry containing the noble metals platinum and palladium prepared in the step (1), and fully stirring;
(3) Addition of a binder: adding a binder to the slurry containing the noble metal and the auxiliary agent prepared in the step (2);
(4) Grinding the particle size of the slurry: grinding the slurry containing the noble metal, the auxiliary agent and the binder prepared in the step (3) in a grinding machine;
(5) Coating of a coating: coating the ground slurry of the step (4) on a honeycomb carrier under vacuum suction pressure;
(6) Drying and calcining the catalyst: drying and calcining the catalyst coated in the step (5) to prepare the catalyst in a fresh state;
(7) Aging of the catalyst: and (4) calcining the fresh catalyst prepared in the step (6) in a muffle furnace to prepare the aged catalyst.
2. The diesel oxidation catalyst with high thermal stability of claim 1, wherein:
the binder comprises one or more of alumina colloid, silica colloid and zirconia colloid.
3. The diesel oxidation catalyst with high thermal stability of claim 1, wherein:
and (3) D90= 5-50 um of the ground slurry in the step (4).
4. The diesel oxidation catalyst with high thermal stability of claim 1, wherein:
in the step (6), the drying temperature of the catalyst is 100-180 ℃, the time is 2-10 h, the calcination temperature of the catalyst is 400-600 ℃, and the calcination time is 1-10 h.
5. The diesel oxidation catalyst with high thermal stability according to any one of claims 1 to 4, wherein:
and (4) in the step (7), the calcination temperature is 650 ℃ during the catalyst aging, and the calcination time is 100h.
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