CN112412588A - Diesel engine tail gas aftertreatment catalyst unit - Google Patents
Diesel engine tail gas aftertreatment catalyst unit Download PDFInfo
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- CN112412588A CN112412588A CN201910766464.6A CN201910766464A CN112412588A CN 112412588 A CN112412588 A CN 112412588A CN 201910766464 A CN201910766464 A CN 201910766464A CN 112412588 A CN112412588 A CN 112412588A
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Images
Classifications
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- 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
- F01N3/24—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
-
- 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
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
-
- 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
- F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
- F01N3/106—Auxiliary oxidation catalysts
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- 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
- F01N3/18—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 methods of operation; Control
- F01N3/20—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 methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
Abstract
The invention relates to the technical field of diesel engine emission control, and discloses a diesel engine tail gas aftertreatment catalyst unit which is arranged between the rear end of an engine and a diesel particulate filter (CSF) unit and comprises a catalyst carrier, wherein a selective reduction catalyst (SCR) and a diesel catalytic oxidation catalyst (DOC) are coupled to the catalyst carrier. By matching the catalyst and the rear-stage SCR, the urea injection window of the aftertreatment system is widened, the close-coupled catalyst of the DOC and the SCR is realized at the front stage, and the reduction of the activity of the catalyst in the use process is avoided.
Description
Technical Field
The invention relates to the technical field of emission control of diesel engines, in particular to a catalyst unit for aftertreatment of diesel engine tail gas.
Background
Current diesel exhaust emission regulations require carbon monoxide/hydrocarbons (CO/HC) from incomplete combustion, Particulate Matter (PM) and NO produced by the combustion processxIt is desirable to control their emissions using an aftertreatment system. The conventional approach is to use a Diesel Oxidation Catalyst (DOC) to control CO/HC emissions and to produce NO2To satisfy the subsequent passive regeneration of a diesel particulate trap (CSF) and the reaction of a selective reduction catalyst (SCR). Or combusting fuel to provide sufficient temperature for active regeneration of CSF. Wall flow catalyst coated CSF for particle treatment andSCR to carry out NOxThe emission control of (1). In the regeneration of PM trapped in CSF, the regeneration can be generally classified into NO2For passive regeneration of oxidant and with O2Is the active regeneration of the oxidant. As previously mentioned, DOC is used to generate NO2Either for passive regeneration of the CSF or for combustion of fuel to provide sufficient temperature for active regeneration. Ammonia Slip Catalyst (ASC) to prevent NH carry over during urea over spray3And (4) leakage.
Referring to fig. 1, in a conventional diesel exhaust aftertreatment system, a DOC unit, a CSF, an SCR unit and an ASC unit are sequentially connected from an outlet of an engine supercharger, a urea solution spraying unit is disposed between the CSF and the SCR unit, and the ASC unit is integrated on the SCR unit. Referring to fig. 2, the ASC unit may also be a separate catalyst unit.
With the tightening of emission legislation and the reduction of engine outlet temperatures, current systems have difficulty meeting emission requirements.
Disclosure of Invention
The invention aims to solve the problems and provides a catalyst unit for aftertreatment of diesel engine exhaust, which widens a urea injection window of a system and a catalyst unit formed by close coupling of DOC and SCR through the matching of the catalyst and a rear-stage SCR, and avoids the reduction of catalyst activity in the using process.
The technical scheme adopted by the invention is as follows:
a catalyst unit for the after-treatment of tail gas of a diesel engine is characterized in that the catalyst unit is arranged between the rear end of the engine and a CSF unit and comprises a catalyst carrier, and an SCR catalyst and a DOC catalyst are coupled to the catalyst carrier.
Further, the catalyst carrier is a whole, the inlet end is a first part, the outlet end is a second part, and the coupling relationship between the SCR catalyst and the DOC catalyst is as follows: the bottom layer of the inlet end of the catalyst carrier is provided with an SCR catalyst, the upper part of the SCR catalyst is coated with a DOC catalyst, and the bottom layer of the outlet end of the catalyst carrier is provided with the DOC catalyst.
Further, the catalyst carrier is divided into two sections, the inlet end section is a first part, the outlet end section is a second part, and the coupling relationship between the SCR catalyst and the DOC catalyst is as follows: the first bottom layer is an SCR catalyst, the DOC catalyst is coated on the upper part of the SCR catalyst, and the DOC catalyst is arranged on the second bottom layer.
Further, the coupling relationship between the SCR catalyst and the DOC catalyst is as follows: and mixing the slurry of the DOC catalyst and the slurry of the SCR catalyst and coating the mixture on the catalyst carrier.
Further, the DOC catalyst of the second part is formed by coating of precious metal slurry, the content of the precious metal in each cubic foot of the carrier is 5-100g, and the precious metal is any one or both of Pt and Pd.
Further, the length ratio of the first portion to the second portion is 1:5 to 5: 1.
Further, the length ratio of the first portion to the second portion is 1:2 to 1: 1.
Further, the DOC catalyst coating length on the upper part of the SCR catalyst of the first part is 0.20-2 inches, the noble metal is Pt, Pd or the mixture of the Pt and the Pd, the proportion of the Pt and the Pd is 1:0-0:1, and the content of the noble metal is 2-40g/ft3。
Further, the DOC catalyst coating length of the upper part of the SCR catalyst of the first part is 0.5 inch-1 inch, the ratio of Pt and Pd is 2:1-1:2, and the content of the noble metal is 5-30g/ft3。
Further, the noble metal in the DOC catalyst slurry is Pt, Pd or the mixture of the Pt and the Pd, the proportion of the Pt and the Pd is 1:0-0:1, and the content of the noble metal is 5-40g/ft3The dry material weight ratio of DOC catalyst slurry to SCR catalyst slurry is 1:0.1-0.1:1, and the total coating amount is 0.5-4g/in3。
Further, the proportion of Pt and Pd is 2:1-1:2, and the content of noble metal is 10-30g/ft3。
Further, the SCR catalyst comprises Fe-based and Cu-based zeolite catalysts, and the zeolite is one or more of Beta, FAU, MFI, ZSM5, CHA, SAPO, AEI and AFX structures.
Further, the SCR catalyst also comprises V-group V-W-TiO2A catalyst.
The invention has the beneficial effects that:
(1) coating DOC on the upper part of the SCR or designing the DOC and the SCR in a mixing way can reduce the risk that organic soluble components (SOF) at the outlet of the engine cause the inlet of the SCR to be blocked; meanwhile, during active regeneration, the DOC on the upper part or in the SCR can partially combust HC, and the partially combusted HC can promote the desulfurization of the SCR. The SCR of the front stage and the whole system are protected.
(2) The SCR is placed at the turbine outlet of the engine so that urea can start to be injected at 180 degrees. And the start-up temperature of the traditional route is 240-260 degrees (at the outlet of the turbine), so that the temperature window of injection is effectively widened, and the NOx emission of the engine is well controlled.
Drawings
FIG. 1 is a schematic diagram of a prior art diesel exhaust treatment system in which an ASC unit is integrated with an SCR unit;
FIG. 2 is a schematic diagram of a prior art independent ASC unit treatment system in a diesel exhaust treatment system;
FIG. 3 is a schematic structural view of a first embodiment of a catalyst unit according to the present invention;
FIG. 4 is a schematic structural view of a second embodiment of the catalyst unit of the present invention;
FIG. 5 is a schematic structural view of a third embodiment of the catalyst unit of the present invention;
FIG. 6 is a schematic diagram of an embodiment of a diesel exhaust treatment system;
FIG. 7 is a schematic diagram of the second embodiment in a diesel exhaust gas treatment system;
FIG. 8 is a schematic diagram of an embodiment III applied to a diesel exhaust gas treatment system;
FIG. 9 is a table of atmospheric conditions in an SCR performance test;
FIG. 10 is a graph of temperature change in a test for SCR performance;
FIG. 11 is a graph of DOC/SCR NOx conversion efficiency in an SCR performance test;
FIG. 12 is a graph of HC injection test results before DOC/SCR in SCR performance testing;
FIG. 13 is a DOC/SCR NOx conversion efficiency table before and after HC injection.
Detailed Description
The following describes in detail an embodiment of the diesel exhaust aftertreatment catalyst unit of the invention with reference to the accompanying drawings.
The diesel engine exhaust aftertreatment catalyst unit is arranged between the rear end of the engine and the CSF unit, and comprises a catalyst carrier, and an SCR catalyst and a DOC catalyst are coupled on the catalyst carrier. The catalyst support is typically a honeycomb ceramic support.
The first embodiment is as follows:
referring to fig. 3, the catalyst carrier is a whole body, the inlet end is a first part, the outlet end is a second part, and the coupling relationship between the SCR catalyst and the DOC catalyst is as follows: the bottom layer of the inlet end of the catalyst carrier is provided with an SCR catalyst, the upper part of the SCR catalyst is coated with a DOC catalyst, and the bottom layer of the outlet end of the catalyst carrier is provided with the DOC catalyst.
Example two:
the difference between the second embodiment and the first embodiment is mainly that the catalyst carrier is segmented.
Referring to fig. 4, the catalyst carrier is divided into two sections, the inlet end section is a first portion, the outlet end section is a second portion, and the coupling relationship between the SCR catalyst and the DOC catalyst is as follows: the first bottom layer is an SCR catalyst, the DOC catalyst is coated on the upper part of the SCR catalyst, and the DOC catalyst is arranged on the second bottom layer.
In examples one and two, the DOC catalyst of the second section is formed by coating with a slurry of precious metal, the precious metal content is 5-100g per cubic foot of support, and the precious metal is any one or both of Pt and Pd. The ratio of the length of the first portion to the second portion is from 1:5 to 5:1, preferably from 1:2 to 1: 1. The DOC catalyst coating length on the upper portion of the SCR unit of the first section is 0.20 inches to 2 inches, preferably 0.5 inches to 1 inch. The noble metal is Pt, Pd or a mixture of the Pt and the Pd, the ratio of the Pt and the Pd is 1:0-0:1, preferably 2:1-1:2, the content of the noble metal is 2-40g/ft3Preferably 5 to 30g/ft3。
Example three:
referring to fig. 5, the coupling relationship between the SCR catalyst and the DOC catalyst is as follows: and mixing the slurry of the DOC catalyst and the slurry of the SCR catalyst and coating the mixture on a catalyst carrier.
In the third embodiment, the noble metal in DOC slurry is Pt, Pd or the mixture of the Pt and the Pd, and the proportion of the Pt and the Pd is 1:0-0:1, preferably 2:1-1: 2. The content of the noble metal is 5-40g/ft3Preferably 10 to 30g/ft3. The dry material weight ratio of DOC slurry to SCR slurry is 1:0.1-0.1:1, and the total coating amount is 0.5-4g/in3。
Referring to fig. 6, 7 and 8, when the embodiment of the invention is applied to an after-treatment system of diesel engine exhaust, the outlet of an engine supercharger is connected with a catalyst unit, a CSF unit, a rear-stage SCR unit and an ASC unit of the invention in sequence, so that the SOF of the engine outlet is reduced. In addition, urea injection can be realized at the front end of the catalyst unit, and a dual injection system can be realized. Nitrogen oxides are treated by a pre-injection at low temperatures (below 250 degrees) and by a post-injection at high temperatures (above 250 degrees).
In the three examples described above, the SCR catalyst of the catalyst unit and the catalyst of the later stage SCR unit comprise Fe-based and Cu-based zeolite catalysts, said zeolite being one or more of Beta, FAU, MFI, ZSM5, CHA, SAPO, AEI, AFX structures. The catalyst may also comprise V-group V-W-TiO2A catalyst.
The technical effects of the present invention will be explained below by experimental data.
Experimental samples:
SCR slurry: copper was loaded on zeolite of SSZ-13 using copper acetate. The copper content was 3.5%. Copper zeolite was made into a slurry with a solids content of 29%.
Front-end DOC slurry: DOC slurries (D50 =4-6 um) were prepared using ball mill milled alumina slurries. Palladium nitrate and platinum nitrate solutions were added to the alumina slurry, controlling the noble metal ratio at 2:1, the noble metal concentrations at 0.2wt%, 0.5wt% and 0.8 wt%.
Rear end DOC slurry: DOC slurries (D50 =4-6 um) were prepared using ball mill milled alumina slurries. Adding a palladium nitrate solution and a platinum nitrate solution into the alumina slurry, and controlling the ratio of the noble metal to be 1:1 and the concentration of the noble metal to be 0.5 wt%.
Experimental sample 1: coating of a Cu-SCR (CHA, Cu content 3.5%) catalyst slurry was carried out on Corning 5.66X 6 (diameter X length in inches), 400/4 (mesh/wall thickness) bare honeycomb ceramic support to a coating depth of 3 inches. The coating amount was 125 g/L. After coating, calcining for 500-1 h.
After calcination, the SCR end was coated with a front DOC slurry to a depth of 1 inch and at a loading of 125 g/L.
After coating was complete, the tail DOC slurry was applied from the other end to a depth of 3 inches and an application rate of 125 g/L. After the coating is finished, the catalyst is calcined for 500-1 h to finish the preparation of the catalyst.
Experimental sample 2: coating of a Cu-SCR (CHA, Cu content 3.5%) catalyst slurry was carried out on Corning 5.66X 3 (diameter. times. length, in.: inches), 400/4 (mesh/wall thickness) bare honeycomb ceramic support to a coating depth of 3 inches. The coating amount was 125 g/L. After coating, calcining for 500-1 h.
After calcination, the DOC tip was coated from either end face to a depth of 1 inch and in an amount of 125 g/L. The DOC coated end is the inlet end. And after the coating is finished, calcining for 500-1 h to finish the preparation of the DOC/SCR.
Another corning, 5.66 x 3 (diameter x length, unit: inch), 400/4 (mesh/wall thickness) blank honeycomb ceramic support was prepared. On which the coating of the back end DOC is performed. The coating amount was 125 g/L. After the coating is finished, the catalyst is calcined for 500-1 h to finish the preparation of the catalyst.
Experiment sample 3, mixing the slurry of front end DOC and SCR slurry in a weight ratio of 1: 1. The coating was performed on corning, 5.66 x 3 (diameter x length, unit: inch), 400/4 (mesh/wall thickness) blank honeycomb ceramic support. The coating depth was 3 inches and the coating amount was 250 g/L. After the coating is finished, the catalyst is calcined at 500 ℃ for 1 hour, and the preparation of the catalyst is finished.
Another corning, 5.66 x 3 (diameter x length, unit: inch), 400/4 (mesh/wall thickness) blank honeycomb ceramic support was prepared. On which the coating of the back end DOC is performed. The coating amount was 125 g/L. After the coating is finished, the catalyst is calcined for 500-1 h to finish the preparation of the catalyst.
Comparative sample 1: coating of a Cu-SCR (CHA, Cu content 3.5%) catalyst slurry was carried out on Corning 5.66X 3 (diameter. times. length, in.: inches), 400/4 (mesh/wall thickness) bare honeycomb ceramic support to a coating depth of 3 inches. The coating amount was 125 g/L. After coating, calcining for 500-1 h. The Cu-SCR catalyst is prepared.
And (3) testing a sample: a 3 inch long, 1 inch diameter swatch was taken from the inlet end of test sample 1 and a 3 inch long, 1 inch diameter swatch was taken from the preceding stage of test samples 2, 3 and control sample 1.
The experimental conditions are as follows: the SCR performance test was performed according to the atmosphere conditions in the table in fig. 9 and the temperature conditions in fig. 10. The SCR conversion efficiency results obtained refer to the DOC/SCR NOx conversion efficiency of FIG. 11.
Since the test sample contained the DOC function as compared with the comparative sample 1, the NOx conversion efficiency at high temperature was lowered and the high temperature window was reduced. But the low temperature window (< 250 ℃) is not affected, thus ensuring the ability of the close-coupled system to the low temperature NOx conversion efficiency of the DOC/SCR.
The same test samples, after being subjected to hydrocarbon poisoning (bench test), were sampled and subjected to a bench test, and the results were shown in FIG. 12 for HC injection before DOC/SCR and in FIG. 13 for Table HC before and after DOC/SCR NOx conversion.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (13)
1. A diesel exhaust aftertreatment catalyst unit, characterized by: the catalyst unit is disposed between the rear end of the engine and the CSF unit, and includes a catalyst carrier on which an SCR catalyst and a DOC catalyst are coupled.
2. The diesel exhaust aftertreatment catalyst unit of claim 1, wherein: the catalyst carrier is a whole, the inlet end is a first part, the outlet end is a second part, and the coupling relation of the SCR catalyst and the DOC catalyst is as follows: the bottom layer of the inlet end of the catalyst carrier is provided with an SCR catalyst, the upper part of the SCR catalyst is coated with a DOC catalyst, and the bottom layer of the outlet end of the catalyst carrier is provided with the DOC catalyst.
3. The diesel exhaust aftertreatment catalyst unit of claim 1, wherein: the catalyst carrier is divided into two sections, the inlet end section is a first part, the outlet end section is a second part, and the coupling relation of the SCR catalyst and the DOC catalyst is as follows: the first bottom layer is an SCR catalyst, the DOC catalyst is coated on the upper part of the SCR catalyst, and the DOC catalyst is arranged on the second bottom layer.
4. The diesel exhaust aftertreatment catalyst unit of claim 1, wherein: the coupling relation of the SCR catalyst and the DOC catalyst is as follows: and mixing the slurry of the DOC catalyst and the slurry of the SCR catalyst and coating the mixture on the catalyst carrier.
5. A diesel exhaust aftertreatment catalyst unit according to claim 2 or 3, wherein: the DOC catalyst of the second part is formed by coating a precious metal slurry, wherein the content of the precious metal in the carrier per cubic foot is 5-100g, and the precious metal is any one or both of Pt and Pd.
6. A diesel exhaust aftertreatment catalyst unit according to claim 2 or 3, wherein: the length ratio of the first part to the second part is 1:5-5: 1.
7. The diesel exhaust aftertreatment catalyst unit of claim 6, wherein: the length ratio of the first part to the second part is 1:2-1: 1.
8. A diesel exhaust aftertreatment catalyst unit according to claim 2 or 3, wherein: the DOC catalyst coating length on the upper part of the SCR catalyst of the first part is 0.20-2 inches, the noble metal is Pt, Pd or the mixture of the Pt and the Pd, the proportion range of the Pt and the Pd is 1:0-0:1, and the content of the noble metal is 2-40g/ft3。
9. The diesel exhaust aftertreatment catalyst unit of claim 8, wherein: the DOC catalyst coating length of the upper part of the SCR catalyst of the first part is 0.5-1 inch, the ratio of Pt and Pd is 2:1-1:2, and the content of noble metal is 5-30g/ft3。
10. The diesel exhaust aftertreatment catalyst unit of claim 4, wherein: the noble metal in the DOC catalyst slurry is Pt, Pd or the mixture of the Pt and the Pd, the proportion of the Pt and the Pd is 1:0-0:1, and the content of the noble metal is 5-40g/ft3The dry material weight ratio of DOC catalyst slurry to SCR catalyst slurry is 1:0.1-0.1:1, and the total coating amount is 0.5-4g/in3。
11. The diesel exhaust aftertreatment catalyst unit of claim 10, wherein: the ratio of Pt and Pd is 2:1-1:2, and the content of noble metal is 10-30g/ft3。
12. The diesel exhaust aftertreatment catalyst unit according to any one of claims 1 to 4, wherein: the SCR catalyst comprises Fe-based and Cu-based zeolite catalysts, and the zeolite is one or more of Beta, FAU, MFI, ZSM5, CHA, SAPO, AEI and AFX structures.
13. The diesel exhaust aftertreatment catalyst unit of claim 12, wherein: the SCR catalyst also comprises V-group V-W-TiO2A catalyst.
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