CN111841622B - Catalyst for metal modified molecular sieve based diesel oxidation catalyst and preparation and use methods thereof - Google Patents
Catalyst for metal modified molecular sieve based diesel oxidation catalyst and preparation and use methods thereof Download PDFInfo
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- 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
- B01J29/48—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 arsenic, antimony, bismuth, vanadium, niobium tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
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- 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
- B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
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- B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
- B01J2229/10—After treatment, characterised by the effect to be obtained
- B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
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Abstract
The invention discloses a catalyst for a metal modified molecular sieve based diesel oxidation catalyst, which is prepared by modifying a ZSM-5 type molecular sieve and Ag by using a V/Mo/K ternary metal2O is a main catalytic active component, CeO2And ZrO2As a cocatalyst, gamma-Al2O3And SiO2Is a coating base material. The catalyst is coated on DOC, and can efficiently purify PM, HC and CO in exhaust gas of a diesel engine. The invention uses ternary metal to modify molecular sieve and Ag2The main catalytic active component formed by O replaces the noble metal in the traditional DOC catalyst, so that the raw material cost of the DOC catalyst is reduced, the sulfur resistance and the thermal stability of the DOC catalyst are improved, and the purification performance of the novel DOC catalyst on carbon components in PM is enhanced. The application of the ternary metal modified molecular sieve reduces the particle size of catalyst particles, increases the surface catalytic active sites of the catalyst per unit mass, and reduces the dosage of metal oxide.
Description
Technical Field
The invention belongs to the technology of diesel engine tail gas pollutant purification, and particularly relates to a catalyst which is used for a Diesel Oxidation Catalyst (DOC) and has good exhaust Particulate Matter (PM) purification performance, and a preparation method thereof.
Background
PM emissions from diesel engines have extremely stringent control requirements and a diesel particulate trap (DPF) is a mandatory exhaust aftertreatment device. However, when the amount of PM deposited in the DPF is large, the exhaust gas pressure becomes too high, and the combustion in the diesel cylinder deteriorates. Therefore, the DPF must be frequently subjected to "active regeneration" during use, i.e., the exhaust temperature of the diesel engine is increased by a method such as post-injection in a cylinder or an exhaust pipe to oxidize the deposited PM in the DPF. However, the active regeneration process not only occupies the normal running time of the diesel engine, increases the maintenance cost of the whole engine and generates additional fuel consumption, but also seriously damages the reliability and the service life of the DPF carrier due to frequent high-temperature regeneration. One effective way to reduce the frequency of DPF regeneration is to reduce the amount of PM input to the DPF, which requires that other aftertreatment devices upstream of the DPF be able to share a portion of the PM purification duties. The typical combination sequence of the diesel engine after-treatment system is DOC + DPF + Selective Catalytic Reduction (SCR), namely, only DOC is arranged in front of DPF, if technical measures are taken to improve the purification effect of DOC on PM, the aims of reducing PM input flow of DPF and prolonging the regeneration period of DPF can be achieved.
Disclosure of Invention
The invention aims to provide a ZSM-5 type molecular sieve modified by V/Mo/K ternary metal and Ag, which is suitable for oxidation purification of HC, CO and PM in DOC2O is used as main catalytic active component and CeO2And ZrO2A catalyst for a metal modified molecular sieve based diesel oxidation catalyst as a cocatalyst, a preparation method and a use method thereof.
The technical scheme adopted for realizing the purpose of the invention is as follows:
the catalyst for metal modified molecular sieve based diesel oxidation catalyst comprises a main catalytic active component, a cocatalyst, a coating base material and a carrier, and is characterized in that the main catalytic active component is a V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2O, and the V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2The mass fractions of O in the main catalytic active component are respectively as follows: 70-80%, 20-30%, V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2The sum of the mass fractions of O is 100 percent.
Specifically, the V, Mo and K elements are respectively expressed as V2O5、MoO3And K2O form is supported on the surface of a ZSM-5 type molecular sieve, and V2O5、MoO3、K2The O, ZSM-5 type molecular sieve accounts for the mass fractions of the V/Mo/K ternary metal modified ZSM-5 type molecular sieve respectively: 5-10%, 10-20%, 5-10%, 60-80%, V2O5、MoO3、K2The sum of the mass fractions of the O, ZSM-5 type molecular sieves is 100%.
Specifically, the cocatalyst is made of CeO2And ZrO2Is prepared from the CeO2And ZrO2Accounting for 60-80 percent and 20-40 percent of the mass fraction of the cocatalyst, and CeO2And ZrO2The sum of the mass fractions of (a) and (b) is 100%.
In particular, the coating base material consists of gamma-Al2O3And SiO2Is prepared from the gamma-Al2O3And SiO2The coating comprises 75-85% and 15-25% of gamma-Al in the base material of the coating respectively2O3And SiO2The sum of the mass fractions of (a) and (b) is 100%.
Specifically, the gamma-Al2O3From pure powdery gamma-Al2O3Said SiO2From the product of silica gel calcination.
Specifically, the main catalytic active component, the cocatalyst and the coating base material form a catalytic coating of the catalyst for the diesel oxidation catalyst, the mass fractions of the main catalytic active component, the cocatalyst and the coating base material in the catalytic coating are respectively 20-30%, 10-20% and 50-70%, and the sum of the mass fractions of the main catalytic active component, the cocatalyst and the coating base material is 100%.
Specifically, the carrier is 400-mesh cordierite honeycomb ceramic, the mass fractions of the catalytic coating and the carrier in the catalyst for the diesel oxidation catalyst are respectively 15-30% and 70-85%, and the sum of the mass fractions of the catalytic coating and the carrier is 100%.
The invention also provides a preparation method of the catalyst for the metal modified molecular sieve based diesel oxidation catalyst, which comprises the following operation steps:
(1) designing the composition of a catalyst;
according to the proportion, the following proportions are respectively designed: V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2Mass fraction of O, V2O5、MoO3、K2Mass fractions of O and ZSM-5 type molecular sieves, CeO2And ZrO2Mass fraction of (a), gamma-Al2O3And SiO2The mass fraction of the main catalytic active component, the mass fraction of the cocatalyst and the coating base material, the target mass fraction range of the catalytic coating and the carrier, and preparing coating slurry corresponding to the mass of the catalytic coating;
(2) preparing a V/Mo/K ternary metal modified ZSM-5 type molecular sieve;
calculating V required for preparing the V/Mo/K ternary metal modified ZSM-5 type molecular sieve according to the proportion of each component designed in the step (1) and the prepared coating slurry corresponding to the mass of the catalytic coating2O5、MoO3、K2The mass of the O and ZSM-5 type molecular sieves; further 234.0g NH4VO3Preparation 182.0g V2O5Each 1163.8g (NH)4)6Mo7O2Preparation 1008.0g of MoO3Each 202.2g KNO3Preparation 94.2g K2O, per 182.0g V2O5Adding 180.0-360.0 g of oxalic acid in a conversion ratio to calculate NH required for preparing the V/Mo/K ternary metal modified ZSM-5 type molecular sieve4VO3、(NH4)6Mo7O2、KNO3And the mass of oxalic acid; weighing NH of determined mass4VO3、(NH4)6Mo7O2、KNO3Adding the 4 raw materials into deionized water with the mass 5-10 times that of the V/Mo/K ternary metal modified ZSM-5 type molecular sieve together, and stirring to prepare a solution; adding a ZSM-5 type molecular sieve with determined mass into the solution, stirring to prepare a suspension, grinding the suspension on a grinding machine until the median particle size is 0.5-0.8 mu m, then stirring vigorously at 70-90 ℃ for 6-12 h, and after stirring, slowly evaporating the liquid to dryness at 70-90 ℃; drying the evaporated powder at 90-110 ℃ for 4-8 h, and roasting the dried powder at 550-650 ℃ for 2-3 h to obtain a V/Mo/K ternary metal modified ZSM-5 type molecular sieve;
(3) preparing coating slurry;
calculating Ag required for preparing the coating slurry according to the proportion of each component designed in the step (1) and the prepared coating slurry corresponding to the quality of the catalytic coating2O、CeO2、ZrO2、γ-Al2O3And SiO2The mass of (c); then according to each 339.8g AgNO3Preparation 231.7g Ag2O, Ce (NO) per 434.1g3)3·6H2O preparation of 172.1g CeO2Every 429.3g of Zr (NO)3)4·5H2O preparation 123.2g ZrO2And SiO in silica gel2Calculating the AgNO required by preparing the coating slurry by the mass fraction3、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O and the mass of silica gel; calculating the mass of the polyethylene glycol and the nitric acid consumed for preparing the catalytic coating 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; weighing AgNO with determined mass3、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O, pure powder gamma-Al2O3Adding 8 raw materials into deionized water with the mass 5-10 times of that of the catalytic coating prepared in the step (2) together, and uniformly stirring to form slurry; grinding the slurry on a grinding machine until the median particle size is 0.8-1.0 mu m, and stirring the ground slurry for 36-60 hours at 70-90 ℃ to obtain coating slurry;
(4) coating the coating slurry;
designing the mass of said support to be coated with a catalytic coating; weighing a carrier with determined mass, immersing the carrier in coating slurry at the temperature of 60-80 ℃, and ensuring that the upper end surface of the carrier is higher than the liquid level of the slurry; after the coating slurry is naturally lifted to fill all pore channels of the carrier, taking the carrier out of the coating slurry, blowing off residual fluid in the pore channels, drying at 90-110 ℃ for 6-12 h, and roasting at 500-600 ℃ for 2-4 h; and repeating the processes of dipping, drying and roasting for 2-3 times to obtain the catalyst for the metal modified molecular sieve based diesel oxidation catalyst.
The invention also provides a using method of the catalyst for the metal modified molecular sieve based diesel oxidation catalyst, the prepared catalyst for the metal modified molecular sieve based diesel oxidation catalyst is packaged, and the packaged catalyst is arranged in an exhaust passage close to an exhaust manifold assembly of a diesel engine.
The conventional DOC purifies gaseous pollutants such as HC and CO in diesel engine exhaust mainly by catalyzing oxidation reaction of the pollutants and SOF component in PM, and has almost no catalytic action on oxidation reaction of carbon component in PM. Therefore, upgrading and modification of the catalyst in the conventional DOC are necessary to add the function of purifying the carbonaceous component in PM to the DOC. The inventor proposes that a ternary metal modified ZSM-5 type molecular sieve obtained by jointly modifying a ZSM-5 type molecular sieve by using vanadium (V), molybdenum (Mo) and potassium (K) is used for replacing a precious metal main catalytic active component in the traditional DOC, so that the catalytic activity of the DOC on oxidation reaction of carbon components in PM is improved. The above 3 metal elements are respectively vanadium pentoxide (V)2O5) Molybdenum trioxide (MoO)3) Potassium oxide (K)2O) on the surface of a ZSM-5 type molecular sieve, wherein V2O5Providing a catalytic active center, and bearing main catalytic duties; MoO3On the one hand guarantee V2O5And the high temperature stability of ZSM-5 type molecular sieve, on the one hand, the secondary catalytic function is assumed; k2O on one hand and V2O5/MoO3Has synergistic catalysis effect, and the composite application of three oxides can further improve the oxidation reaction catalysis performance of the whole catalyst, and on the other hand, K2O has good fluidity at high temperature and can provide more active species in a runaway state for PM oxidation under loose contact conditions. Meanwhile, although the ternary metal modified ZSM-5 type molecular sieve catalyst has higher high-temperature (more than or equal to 400 ℃) catalytic activity, the low-temperature (less than 400 ℃) catalytic activity is relatively lower, and the silver (Ag)/silver oxide (Ag)2O) catalytic material has the catalytic performance of low-temperature oxidation reaction close to noble metal Pt, and the catalytic activity of the whole catalyst for low-temperature oxidation reaction can be obviously improved by adding a small amount of the O) catalytic material into the DOC catalyst. In addition, in order to improve the oxygen storage capacity of the DOC catalyst and further improve the oxidation reaction catalytic performance of the novel catalyst, an appropriate amount of cerium oxide (CeO) needs to be added into the catalyst formula2) And zirconium oxide (ZrO)2) As a cocatalyst.
According to the technical scheme, the beneficial effects of the invention are as follows:
the invention uses V/Mo/K ternary metal to modify ZSM-5 type molecular sieve and Ag2The main catalytic active component formed by O replaces the noble metal in the traditional DOC catalyst, so that the raw material cost of the DOC catalyst is reduced, the sulfur resistance and the thermal stability of the DOC catalyst are improved, and the catalytic activity and the selectivity of the novel DOC catalyst on the oxidation reaction of the carbon component in PM are enhanced. The application of the ternary metal modified molecular sieve avoids the direct application of metal oxide to the main catalytic active component, thereby reducing the particle size of metal oxide particles in the coating, increasing the catalytic active sites on the surface of the catalyst per unit mass, and reducing the dosage of the metal oxide. Ag2The addition of O improves the catalytic activity of the catalyst for low-temperature oxidation reaction. From CeO2、ZrO2The formed cocatalyst increases the oxygen storage capacity of the DOC catalyst, promotes the further enhancement of the integral catalytic activity of the catalyst, and also improves the thermal stability of the main catalytic active component. The preferential preparation of the ternary metal modified molecular sieve ensures the close combination of all components in the modified molecular sieve catalytic material and promotes the exertion of the synergistic catalytic action among different components.
Drawings
Fig. 1 is a schematic diagram of an engine evaluation system for diesel engine exhaust gas pollutant purification performance, in which: 1-a dynamometer; 2-a coupler; 3-test diesel engine; 4-an intake air flow meter; 5-an air inlet processor; 6-oil injector; 7-a fuel injection control system; 8-exhaust sampling port A; 9-temperature sensor a; 10-DOC; 11-temperature sensor B; 12-exhaust sample port B; 13-two-channel temperature display instrument; 14-an exhaust sampling valve; 15-PM analyzer; 16-air pump.
FIG. 2 shows an engine evaluation system for evaluating the purification performance of exhaust pollutants of a diesel engine, in which the DOC has an average exhaust temperature of 350 ℃ and a space velocity of 60000h-1Under the steady-state working condition, the PM purification efficiency of the exhaust pollutant purification reaction in the DOC under the catalysis of the catalyst prepared in the embodiment 1-3 is improved.
FIG. 3 is an engine evaluation for exhaust gas pollutant purification performance using the diesel engineThe system has average exhaust temperature of 450 ℃ and space velocity of 100000h in DOC-1Under the steady-state working condition, the PM purification efficiency of the exhaust pollutant purification reaction in the DOC under the catalysis of the catalyst prepared in the embodiment 1-3 is improved.
Fig. 4 shows PM purification efficiency of an exhaust pollutant purification reaction in DOC by using the diesel engine exhaust pollutant purification performance engine evaluation system in a european steady state test cycle (ESC) test under catalysis of the catalysts prepared in examples 1 to 3.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer.
Example 1
A preparation method of a catalyst for a metal modified molecular sieve based diesel oxidation catalyst comprises the following operation steps:
(1) catalyst composition design
Respectively designing the following components in percentage by mass: V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2The mass fractions of O and V are respectively 80% and 20%2O5、MoO3、K2The mass fractions of the O and ZSM-5 type molecular sieves are respectively 5%, 10%, 5% and 80%, and the mass fraction of the CeO2And ZrO2Respectively 60% and 40%, gamma-Al2O3And SiO2Respectively account for 75% and 25%, the mass fractions of the main catalytic active component, the cocatalyst and the coating base material respectively account for 30%, 20% and 50%, and the target mass percentage ranges of the catalytic coating and the carrier are as follows: 22-24 percent of the catalytic coating, 76-78 percent of the catalytic coating and the carrier, wherein the sum of the mass fractions of the catalytic coating and the carrier is 100 percent, and 2000g of coating slurry capable of generating the catalytic coating is prepared.
(2) Preparation of V/Mo/K ternary metal modified ZSM-5 type molecular sieve
27.0gNH was weighed4VO3、48.5g(NH4)6Mo7O2、45.1g KNO3And 20.8g of oxalic acid, adding the 4 raw materials into 2100g of deionized water together, and stirring to prepare a solution; 336g of powdery ZSM-5 type molecular sieve is weighed and added into the solution, the solution is stirred to prepare suspension, and the suspension is ground on a grinding machine to reach the median particle size (D)50Particle size) is within the range of 0.5-0.8 microns, then the mixture is stirred vigorously at 70 ℃ for 12 hours, and after stirring is completed, the liquid is slowly evaporated to dryness at 70 ℃; and drying the powder after evaporation to dryness at 90 ℃ for 8h, and roasting the dried powder at 550 ℃ for 3h to obtain the V/Mo/K ternary metal modified ZSM-5 type molecular sieve.
(3) Preparation of coating slurries
Weighing 264.0g AgNO3、605.4g Ce(NO3)3·6H2O、557.5g Zr(NO3)4·5H2O, 750g pure powdery gamma-Al2O3、1000g SiO2Adding 8 raw materials into 10000g of deionized water together, and uniformly stirring to form a slurry, wherein the mass content of the raw materials is 25% of silica gel, 300g of polyethylene glycol with the molecular weight of 20000, 500g of nitric acid and the V/Mo/K ternary metal modified ZSM-5 type molecular sieve prepared in the step (2); grinding the slurry on a grinder to a median particle size (D)50Particle size) is within the range of 0.8-1.0 micron, and the ground slurry is stirred for 60 hours at 70 ℃ to obtain coating slurry.
(4) Application of coating slurries
Weighing 1000g of the carrier, immersing the carrier in the coating slurry at 60 ℃, and ensuring that the upper end surface of the carrier is higher than the slurry liquid level; and 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 2 times to obtain the catalyst for the metal modified molecular sieve based diesel oxidation catalyst.
Example 2
A preparation method of a catalyst for a metal modified molecular sieve based diesel oxidation catalyst comprises the following operation steps:
(1) catalyst composition design
Respectively designing the following components in percentage by mass: V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2The mass fractions of O and V are respectively 80% and 20%2O5、MoO3、K2The mass fractions of the O and ZSM-5 type molecular sieves are respectively 10%, 20%, 10% and 60%, and the mass fraction of the CeO2And ZrO2Respectively 80% and 20%, gamma-Al2O3And SiO2Respectively account for 85 percent and 15 percent, respectively account for 20 percent, 10 percent and 70 percent of the mass fractions of the main catalytic active component, the cocatalyst and the coating base material, respectively, and the target mass percentage ranges of the catalytic coating and the carrier are as follows: 28-30 percent of the catalytic coating, 72-70 percent of the catalytic coating, and the sum of the mass percentages of the catalytic coating and the coating slurry is 100 percent, and 2000g of the catalytic coating can be generated by planning to prepare the coating slurry.
(2) Preparation of V/Mo/K ternary metal modified ZSM-5 type molecular sieve
Weighing 41.1gNH4VO3、73.9g(NH4)6Mo7O2、68.7g KNO363.3g of oxalic acid, adding the 4 raw materials into 3200g of deionized water together, and stirring to prepare a solution; weighing 192g of powdery ZSM-5 type molecular sieve, adding the powdery ZSM-5 type molecular sieve into the solution, stirring to prepare a suspension, and grinding the suspension on a grinder to a median particle size (D)50Particle size) is within the range of 0.5-0.8 microns, then the mixture is stirred vigorously for 6 hours at 90 ℃, and after stirring is completed, the liquid is slowly evaporated to dryness at 90 ℃; and drying the powder after evaporation for 4h at 110 ℃, and roasting the dried powder for 2h at 650 ℃ to obtain the V/Mo/K ternary metal modified ZSM-5 type molecular sieve.
(3) Preparation of coating slurries
117.3g of AgNO are weighed3、403.6g Ce(NO3)3·6H2O、139.4g Zr(NO3)4·5H2O, 1190g pure powdery gamma-Al2O3、840g SiO2Silica gel with mass content of 25 percent, 100g of polyethylene glycol with molecular weight of 20000 and 1000g of nitric acid and the preparation in the step (2)Adding the 8 raw materials into 15000g of deionized water together to obtain the V/Mo/K ternary metal modified ZSM-5 molecular sieve, and uniformly stirring to form slurry; grinding the slurry on a grinder to a median particle size (D)50Particle size) is within the range of 0.8-1.0 micron, and the ground slurry is stirred for 36 hours at 90 ℃ to obtain coating slurry.
(4) Application of coating slurries
Weighing 1000g of the carrier, immersing the carrier in the coating slurry at 80 ℃, and ensuring that the upper end surface of the carrier is higher than the slurry liquid level; 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 3 times to obtain the catalyst for the metal modified molecular sieve based diesel oxidation catalyst.
Example 3
A preparation method of a catalyst for a metal modified molecular sieve based diesel oxidation catalyst comprises the following operation steps:
(1) catalyst composition design
Respectively designing the following components in percentage by mass: V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2The mass fractions of O and V are 70% and 30%, respectively2O5、MoO3、K2The mass fractions of the O and ZSM-5 type molecular sieves are respectively 10%, 10% and 70%, and the mass fraction of the CeO2And ZrO2Respectively 75% and 25%, gamma-Al2O3And SiO2The mass fractions of the main catalytic active component, the cocatalyst and the coating base material are respectively 85% and 15%, the mass fractions of the main catalytic active component, the cocatalyst and the coating base material are respectively 30%, 10% and 60%, and the target mass percentage ranges of the catalytic coating and the carrier are as follows: 23-25 percent of the total weight of the catalyst, 77-75 percent of the total weight of the catalyst and the catalyst, and 2000g of the catalyst coating can be generated by planning to prepare coating slurry.
(2) Preparation of V/Mo/K ternary metal modified ZSM-5 type molecular sieve
Weighing 54.0gNH4VO3、48.5g(NH4)6Mo7O2、90.2g KNO3And 46.2g of oxalic acid, adding the 4 raw materials into 4000g of deionized water together, and stirring to prepare a solution; 294g of powdered ZSM-5 molecular sieve is weighed and added into the solution, a suspension is prepared by stirring, and the suspension is ground on a grinding machine to a median particle size (D)50Particle size) is within the range of 0.5-0.8 microns, then the mixture is stirred vigorously for 9 hours at 80 ℃, and after stirring is completed, the liquid is slowly evaporated to dryness at 90 ℃; and drying the powder after evaporation for 6h at 100 ℃, and roasting the dried powder for 3h at 600 ℃ to obtain the V/Mo/K ternary metal modified ZSM-5 type molecular sieve.
(3) Preparation of coating slurries
Weighing 264.0g AgNO3、378.4g Ce(NO3)3·6H2O、174.2g Zr(NO3)4·5H2O, 1020g pure powdery gamma-Al2O3、720g SiO2Adding 8 raw materials into 20000g of deionized water together, and uniformly stirring to form a slurry, wherein the mass content of the raw materials is 25% of silica gel, 200g of polyethylene glycol with the molecular weight of 20000, 600g of nitric acid and the V/Mo/K ternary metal modified ZSM-5 type molecular sieve prepared in the step (2); grinding the slurry on a grinder to a median particle size (D)50Particle size) is within the range of 0.8-1.0 micron, and the ground slurry is stirred for 48 hours at 80 ℃ to obtain coating slurry.
(4) Application of coating slurries
Weighing 1000g of the carrier, immersing the carrier in the coating slurry at 80 ℃, and ensuring that the upper end surface of the carrier is higher than the slurry liquid level; 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 600 ℃ for 3 h; repeating the processes of dipping, drying and roasting for 3 times to obtain the catalyst for the metal modified molecular sieve based diesel oxidation catalyst.
The PM purification efficiency of the exhaust pollutant purification reaction in the DOC under the catalysis of the catalyst prepared in examples 1 to 3 was evaluated by using the diesel engine exhaust pollutant purification performance engine evaluation system shown in fig. 1. Before the test, the catalysts prepared in the embodiments 1 to 3 are respectively cut and respectively combined into an integral catalyst, and the cut and combined integral catalyst is 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 (3) are controlled by using a dynamometer (1) and a coupling (2), the oil supply speed of an oil injector (6) to a diesel engine is adjusted by a fuel injection control system (7), and the proportion of the exhaust flow of the engine to the volume of a catalyst is controlled to be 60000h respectively-1And 100000h-1And the average exhaust temperature in the DOC (10) is controlled to be 350 ℃ and 450 ℃ respectively, and PM purification performance evaluation is carried out. The intake air flow measurement value of the intake air flow meter (4) provides feedback parameters for a control strategy of the fuel injection control system; and the air inlet processor (5) provides clean air with specific temperature and humidity for the engine. The temperature sensor A (9) and the temperature sensor B (11) respectively measure the exhaust temperature at two ends of the DOC (10), the exhaust temperature is displayed by the dual-channel temperature display instrument (13), and the average value of the two temperatures is obtained to obtain the average exhaust temperature in the DOC (10). Exhaust samples before and after being processed by the DOC (10) respectively enter an exhaust sampling valve (14) and a PM analyzer (15) through an exhaust sampling port A (8) and an exhaust sampling port B (12) for PM emission analysis, and exhaust after the PM analysis is discharged out of a laboratory through an air pump (16). By utilizing the engine evaluation system for the purification performance of the diesel engine exhaust pollutants, the average exhaust temperature in DOC is 350 ℃, and the airspeed is 60000h-1The average exhaust temperature in time and DOC is 450 ℃ and the space velocity is 100000h-1The PM purification efficiency of the catalysts prepared in examples 1 to 3 is shown in fig. 2 and 3, respectively.
(2) ESC test: by adopting the evaluation system for the purification performance of the diesel engine exhaust pollutants, the PM purification efficiency of the purification reaction of the exhaust pollutants in the DOC under the catalysis of the catalyst prepared in the examples 1-3 is evaluated according to ESC test regulations specified in national standard GB 17691-2005 emission limits of compression ignition type and gas fuel ignition type engines for vehicles and automobile exhaust pollutants and a measurement method (China stages III, IV and V), and the result is shown in FIG. 4.
The embodiments described above are some, but not all embodiments of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Claims (9)
1. The catalyst for metal modified molecular sieve based diesel oxidation catalyst comprises a main catalytic active component, a cocatalyst, a coating base material and a carrier, and is characterized in that the main catalytic active component is a V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2O, and the V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2The mass fractions of O in the main catalytic active component are respectively as follows: 70-80%, 20-30%, V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2The sum of the mass fractions of O is 100 percent.
2. The catalyst of claim 1, wherein the V, Mo and K elements are V2O5、MoO3And K2O form is supported on the surface of a ZSM-5 type molecular sieve, and V2O5、MoO3、K2The O, ZSM-5 type molecular sieve accounts for the mass fractions of the V/Mo/K ternary metal modified ZSM-5 type molecular sieve respectively: 5-10%, 10-20%, 5-10%, 60-80%, V2O5、MoO3、K2The sum of the mass fractions of the O, ZSM-5 type molecular sieves is 100%.
3. The catalyst as claimed in claim 1, wherein the promoter is CeO2And ZrO2Is prepared from the CeO2And ZrO2Accounting for 60-80 percent and 20-40 percent of the mass fraction of the cocatalyst, and CeO2And ZrO2The sum of the mass fractions of (a) and (b) is 100%.
4. The catalyst for a metal-modified molecular sieve-based diesel oxidation catalyst as set forth in claim 1, wherein the coating base material is made of γ -Al2O3And SiO2Is prepared from the gamma-Al2O3And SiO2The coating comprises 75-85% and 15-25% of gamma-Al in the base material of the coating respectively2O3And SiO2The sum of the mass fractions of (a) and (b) is 100%.
5. The catalyst for a metal-modified molecular sieve-based diesel oxidation catalyst as set forth in claim 4, wherein the γ -Al is2O3From pure powdery gamma-Al2O3Said SiO2From the product of silica gel calcination.
6. The catalyst for the metal-modified molecular sieve-based diesel oxidation catalyst as set forth in any one of claims 1 to 5, wherein the main catalytic active component, the cocatalyst and the coating base material form a catalytic coating of the catalyst for the diesel oxidation catalyst, the mass fractions of the main catalytic active component, the cocatalyst and the coating base material in the catalytic coating are respectively 20-30%, 10-20% and 50-70%, and the sum of the mass fractions of the main catalytic active component, the cocatalyst and the coating base material is 100%.
7. The catalyst for the metal modified molecular sieve based diesel oxidation catalyst as claimed in claim 1, wherein the carrier is 400-mesh cordierite honeycomb ceramic, the mass fractions of the catalytic coating and the carrier in the catalyst for the diesel oxidation catalyst are respectively 15-30% and 70-85%, and the sum of the mass fractions of the catalytic coating and the carrier is 100%.
8. A method for preparing a catalyst for a metal-modified molecular sieve-based diesel oxidation catalyst according to claim 7, comprising the steps of:
(1) designing the composition of a catalyst;
according to the proportion, the following proportions are respectively designed: V/Mo/K ternary metal modified ZSM-5 type molecular sieve and Ag2Mass fraction of O, V2O5、MoO3、K2Mass fractions of O and ZSM-5 type molecular sieves, CeO2And ZrO2Mass fraction of (a), gamma-Al2O3And SiO2The mass fraction of the main catalytic active component, the mass fraction of the cocatalyst and the coating base material, the target mass fraction range of the catalytic coating and the carrier, and preparing coating slurry corresponding to the mass of the catalytic coating;
(2) preparing a V/Mo/K ternary metal modified ZSM-5 type molecular sieve;
calculating V required for preparing the V/Mo/K ternary metal modified ZSM-5 type molecular sieve according to the proportion of each component designed in the step (1) and the prepared coating slurry corresponding to the mass of the catalytic coating2O5、MoO3、K2The mass of the O and ZSM-5 type molecular sieves; further 234.0g NH4VO3Preparation 182.0g V2O5Each 1163.8g (NH)4)6Mo7O2Preparation 1008.0g of MoO3Each 202.2g KNO3Preparation 94.2g K2O, per 182.0g V2O5Adding 180.0-360.0 g of oxalic acid in a conversion ratio to calculate NH required for preparing the V/Mo/K ternary metal modified ZSM-5 type molecular sieve4VO3、(NH4)6Mo7O2、KNO3And the mass of oxalic acid; weighing NH of determined mass4VO3、(NH4)6Mo7O2、KNO3Adding the 4 raw materials into deionized water with the mass 5-10 times that of the V/Mo/K ternary metal modified ZSM-5 type molecular sieve together, and stirring to prepare a solution; adding ZSM-5 type molecular sieve with determined mass into the solution, stirring to prepare suspensionGrinding the suspension on a grinding machine until the median particle size is 0.5-0.8 mu m, then stirring vigorously for 6-12 h at 70-90 ℃, and after stirring, slowly evaporating the liquid to dryness at 70-90 ℃; drying the evaporated powder at 90-110 ℃ for 4-8 h, and roasting the dried powder at 550-650 ℃ for 2-3 h to obtain a V/Mo/K ternary metal modified ZSM-5 type molecular sieve;
(3) preparing coating slurry;
calculating Ag required for preparing the coating slurry according to the proportion of each component designed in the step (1) and the prepared coating slurry corresponding to the quality of the catalytic coating2O、CeO2、ZrO2、γ-Al2O3And SiO2The mass of (c); then according to each 339.8g AgNO3Preparation of 231.7g Ag2O, Ce (NO) per 434.1g3)3·6H2O preparation of 172.1g CeO2Every 429.3g of Zr (NO)3)4·5H2O preparation 123.2g ZrO2And SiO in silica gel2Calculating the AgNO required by preparing the coating slurry by the mass fraction3、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O and the mass of silica gel; calculating the mass of the polyethylene glycol and the nitric acid consumed for preparing the catalytic coating 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; weighing AgNO with determined mass3、Ce(NO3)3·6H2O、Zr(NO3)4·5H2O, pure powder gamma-Al2O3Adding 8 raw materials into deionized water with the mass 5-10 times of that of the catalytic coating prepared in the step (2) together, and uniformly stirring to form slurry; grinding the slurry on a grinding machine until the median particle size is 0.8-1.0 mu m, and stirring the ground slurry for 36-60 hours at 70-90 ℃ to obtain coating slurry;
(4) coating the coating slurry;
designing the mass of said support to be coated with a catalytic coating; weighing a carrier with determined mass, immersing the carrier in coating slurry at the temperature of 60-80 ℃, and ensuring that the upper end surface of the carrier is higher than the liquid level of the slurry; after the coating slurry is naturally lifted to fill all pore channels of the carrier, taking the carrier out of the coating slurry, blowing off residual fluid in the pore channels, drying at 90-110 ℃ for 6-12 h, and roasting at 500-600 ℃ for 2-4 h; and repeating the processes of dipping, drying and roasting for 2-3 times to obtain the catalyst for the metal modified molecular sieve based diesel oxidation catalyst.
9. The method of using the catalyst for a metal-modified molecular sieve-based diesel oxidation catalyst of claim 1, wherein the obtained catalyst for a metal-modified molecular sieve-based diesel oxidation catalyst is packaged, and the packaged catalyst is installed in an exhaust passage adjacent to an exhaust manifold assembly of a diesel engine.
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