CN115518676B - Catalyst product for lean-burn engine tail gas treatment and application thereof - Google Patents
Catalyst product for lean-burn engine tail gas treatment and application thereof Download PDFInfo
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- CN115518676B CN115518676B CN202211111489.0A CN202211111489A CN115518676B CN 115518676 B CN115518676 B CN 115518676B CN 202211111489 A CN202211111489 A CN 202211111489A CN 115518676 B CN115518676 B CN 115518676B
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- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D1/00—Processes for applying liquids or other fluent materials
- B05D1/36—Successively applying liquids or other fluent materials, e.g. without intermediate treatment
- B05D1/38—Successively applying liquids or other fluent materials, e.g. without intermediate treatment with intermediate treatment
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- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
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- B05D7/50—Multilayers
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- B05D7/584—No clear coat specified at least some layers being let to dry, at least partially, before applying the next layer
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- 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
- F01N3/18—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
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- B01J29/00—Catalysts comprising molecular sieves
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- B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
- B01J29/65—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38, as exemplified by patent documents US4046859, US4016245 and US4046859, respectively
- B01J29/66—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38, as exemplified by patent documents US4046859, US4016245 and US4046859, respectively containing iron group metals, noble metals or copper
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Abstract
The invention discloses a catalyst product for treating tail gas of a lean-burn engine and application thereof, wherein the catalyst product adopts a flow-through type monolithic substrate, a layered catalyst covering the whole substrate length is arranged on the wall of the substrate, and the layered catalyst comprises a first coating, a second coating and a third coating which are arranged from inside to outside; the first coating comprises a passive oxynitride adsorbing catalyst composition and the second coating comprises NO 2 Reduction catalyst composition, third coating comprising NO x Reducing the catalyst composition; the first coating absorbs NO in the tail gas at a temperature below 150 DEG C x And releasing NO above 250 DEG C x The method comprises the steps of carrying out a first treatment on the surface of the The second coating layer will NO x NO of a certain proportion of 2 Convert to NO, make NO 2 And the concentration ratio of NO is 0.8-1.2: 1, a step of; the third coating layer will NO x Conversion to N 2 . The catalyst preparation is prepared by PNA catalyst and NO 2 The reduction catalyst and the SCR catalyst are loaded in different areas of the same carrier to realize NO x Adsorption, release, NO 2 Reduction to NO, NO x Cycle of reduction, thereby increasing NO x Is used for reducing the treatment rate of the steel plate.
Description
Technical Field
The invention belongs to the field of catalysts for post-treatment of tail gas of fuel vehicles, and particularly relates to a catalyst product for treating tail gas of a lean-burn engine and application thereof.
Background
Based on the negative effect of nitrogen oxides on the climate, the U.S. Environmental Protection Agency (EPA) mandates that nitrogen dioxide (NO 2 ) Nitric Oxide (NO) and nitrous oxide (N) 2 O) is collectively referred to as NO x . The tail gas of diesel vehicle with high air-fuel ratio is NO x Discharged fromThe main source. As a typical lean-burn engine, diesel vehicles generally employ a combination of selective reduction catalytic SCR technology and cooled exhaust gas recirculation technology to meet stringent emissions regulations. However, the SCR catalyst can only exert good NO if the exhaust gas temperature reaches the ignition temperature (more than 200 ℃) x And the emission reduction effect is achieved. The tail gas temperature during cold start of diesel vehicle is below 180deg.C and lasts for about 3min, during which NO x The emissions are discharged into the air with little treatment. NO of cold start emission x Contributing to total NO x 80% of the emissions. In addition, in order to improve the fuel economy, technologies such as advanced combustion, engine miniaturization, turbocharging and the like are continuously updated and applied to diesel engines, so that the exhaust temperature is low, and the duration and the strength of the cold start effect are more remarkable.
To solve NO in tail gas of cold start stage x Emission problem, passive NO x Adsorbents (PNAs) have been developed to adsorb NO at low SCR activity x With the increase of the temperature of the tail gas, the SCR to be downstream can catalyze with high efficiency, and the PNA can convert NO x Rapidly release and recover NO x Adsorption function.
Kangmins proposes a PNA-carrying architecture, namely DOC+PNA+SCRF (i.e. SCR catalyst coated on a particle trap (DPF) +CC-SCR. The system has excellent NO x The emission reduction effect, but involves 5 post-processing units outside the machine, the system architecture is complex, the implementation cost is high, and great pressure is brought to packaging and arrangement. Zhuang Xinmo discloses a DOC and PNA coupling scheme called DCSC unit, and performs various patent layouts aiming at different framework structure molecular sieve components of DCSC. The disadvantage of this unit is that since DCSC contains a large amount of noble metal active components, which are unevenly distributed in the carrier multi-stage pore canal, agglomeration easily occurs at high temperature to form large particles, and these agglomerated particles have a large charge density, which easily gives out electrons, to NO in the original emission x Oxidation is far greater than adsorption, resulting in passive NO exhibited by DCSC x Low adsorption capacity and NO due to DCSC treatment 2 Far higher than NO, unfavorable for subsequent NH 3 SCR rapid reaction, reduced selective catalytic reduction treatmentRate.
Disclosure of Invention
To solve NO in tail gas in cold start stage in the prior art x The invention provides the following technical scheme:
in a first aspect, the present invention provides a catalyst article for lean burn engine exhaust treatment, the catalyst article comprising a flow-through monolith substrate having a layered catalyst disposed on the walls of the substrate walls covering the entire substrate length, the layered catalyst comprising a first coating, a second coating and a third coating disposed from the inside to the outside; the first coating comprises a passive oxynitride adsorbing catalyst composition and the second coating comprises NO 2 Reduction catalyst composition, third coating comprising NO x Reducing the catalyst composition; the first coating absorbs NO in the tail gas at a temperature below 150 DEG C x And releasing NO above 250 DEG C x The method comprises the steps of carrying out a first treatment on the surface of the The second coating layer will NO x NO of a certain proportion of 2 Convert to NO, make NO 2 And the concentration ratio of NO is 0.8-1.2: 1, a step of; the third coating layer will NO x Conversion to N 2 。
In some embodiments provided herein, a passive oxynitride adsorption catalyst composition, NO 2 Reduction catalyst composition, NO x The loading ratio of the reduction catalyst composition is 30-50: 10: 95-120.
In some embodiments provided herein, the passive nox adsorber catalyst composition in the first coating layer has an loading of 30 to 50g/L; NO in the second coating 2 The loading of the reduction catalyst composition was 10.+ -.2 g/L; NO in the third coating x The loading of the reduction catalyst composition is 95-120 g/L.
In some embodiments of the present invention, the substrate is one of cordierite, silicon carbide, and a metal material.
In some embodiments of the present invention, the metal material is one of Fe-Cr-Ni alloy, co-Cr-Ni alloy, and Ni-Cr-Mo alloy.
In some embodiments provided herein, a passive oxynitride adsorption catalyst composition includes a precious metal active ingredient that is at least one of Pd, ag, co, and a first adsorptive refractory carrier that is a first molecular sieve or metal oxide.
In some embodiments provided herein, the passive oxynitride adsorption catalyst composition further comprises a base metal or a rare earth metal, at least one of the base metals being Mn, co, zr, ni, the rare earth metal being Ce or La.
In some embodiments of the invention provided, NO 2 The reduction catalyst composition comprises NO 2 Reducing the active ingredient and a second adsorptive refractory carrier, NO 2 The reduction active component is one or more of ferric oxide, cobalt oxide, copper oxide, barium oxide, calcium oxide, magnesium oxide, strontium oxide, tin oxide and germanium oxide, and the second adsorptive refractory carrier is silicon oxide or gamma-alumina.
In some embodiments of the invention provided, NO x The reduction catalyst composition comprises NO x Reducing the active ingredient and a third adsorptive refractory carrier, NO x The reducing active ingredient is one or more of Cu, mn, V, fe, co, W, ni, zn, ti, cr, Y, zr, nb, mo, and the third adsorptive refractory carrier comprises one or a symbiotic mixture of analcite, chabazite, heulandite, stilbite, erionite, mordenite, calcium zeolite, and sodium zeolite.
In a second aspect, the present invention provides a lean burn engine exhaust treatment apparatus comprising a catalyst article for lean burn engine exhaust treatment.
Compared with the prior art, the invention uses PNA catalyst and NO 2 The reduction catalyst and the SCR catalyst are supported on the same substrate, and the PNA catalyst solves the problem of low-temperature cold start NO x Emissions problems, NO 2 The reduction catalyst improves oxidation side reaction of PNA catalyst, on one hand, ensures NO and NO in tail gas 2 The equilibrium of (2) is close to 1:1, promoting a rapid SCR reaction, on the other hand, avoiding low temperature NO x The adsorption reaction generates excessive NO 2 From the source control N 2 O is generated and reacted.
Drawings
FIG. 1 coating scheme one employed in examples 1-3 of the present invention.
FIG. 2A coating scheme II employed in comparative examples 3-5 of the present invention.
FIG. 3 coating scheme III employed in comparative examples 6-7 of the present invention.
Detailed Description
The invention is further described in connection with the following examples which are provided solely for the purpose of better illustrating the technical solution of the invention and are not intended to limit the claims. The invention is not limited to the specific examples and embodiments described herein. Further modifications and improvements may readily occur to those skilled in the art without departing from the spirit and scope of the invention.
Existing lean burn engine exhaust treatment systems include separate PNA units and SCR units, where the PNA units oxidize 40% -90% of the NO to NO 2 Thereby leading to NO and NO 2 The ratio is much less than 1:1, impeding the rapid SCR reaction. The invention supports PNA catalyst and SCR catalyst on the same monolithic substrate to form a catalyst with low temperature NO x SCR catalyst with adsorption function and NO addition between PNA catalyst coating and SCR catalyst coating 2 Reduction catalyst coating for oxidizing more than 90% of NO to NO 2 Re-reducing to NO, thereby regulating NO and NO 2 The ratio is close to 1:1, promoting rapid SCR reaction.
The catalyst product for treating the tail gas of the lean-burn engine adopts a monolithic substrate, wherein a layered catalyst is coated on the wall of the substrate, and the layered catalyst covers the whole length of the monolithic substrate and is sequentially provided with a first coating, a second coating and a third coating from inside to outside; the first coating comprises a passive oxynitride adsorbing catalyst composition and the second coating comprises NO 2 Reduction catalyst composition, third coating comprising NO x Reducing the catalyst composition; the first coating absorbs NO in the tail gas at a temperature below 150 DEG C x And releasing NO above 250 DEG C x The method comprises the steps of carrying out a first treatment on the surface of the The second coating layer will NO x NO of a certain proportion of 2 Convert to NO, make NO 2 And the concentration ratio of NO is 0.8 to 1.2:1, a step of; the third coating layer will NO x Conversion to N 2 。
In some embodiments provided herein, a passive oxynitride adsorption catalyst composition, NO 2 Reduction catalyst composition, NO x The loading ratio of the reduction catalyst composition is 30-50: 10: 95-120. Within this ratio range, it is ensured that the second coating will partially NO 2 Can reduce NO to NO and then convert NO 2 Is adjusted to approximately 1:1.
In some embodiments provided herein, the passive nox adsorber catalyst composition in the first coating layer has an loading of 30 to 50g/L; NO in the second coating 2 The loading of the reduction catalyst composition was 10.+ -.2 g/L; NO in the third coating x The loading of the reduction catalyst composition is 95-120 g/L. The loading of the passive oxynitride adsorption catalyst composition in the first coating needs to balance the low-temperature adsorption performance and the system back pressure, so the loading is set to be 30-50 g/L, and when the loading is lower than 30g/L, the NO is discharged from the cold start tail of the engine x Can not be fully adsorbed, and the NO can be further reduced by increasing the loading capacity x Concentration, above 50g/L, of cold start NO x The conversion efficiency is not further improved, and the back pressure of the system is increased to influence the fuel economy of the engine. Second coating NO 2 The loading of the reduction catalyst composition was controlled to 10.+ -.2 g/L, which is the main concern for NO 2 Is not limited, and the reduction efficiency of the catalyst is improved. Because the second coating is on the upper surface of the first coating, the desired reduction efficiency of the catalyst article can be met at the loading setting. The coating amount of the third coating layer is designed to be 95-120 g/L, mainly considering the reduction efficiency of NOx, different active components are selected, and different loading requirements exist, for example, when the active component is Cu, the coating amount can be reduced because the low-temperature performance of the active component is better than that of Fe.
In some embodiments of the present invention, the substrate is one of cordierite, silicon carbide, and a metal material.
In some embodiments of the present invention, the metal material is one of Fe-Cr-Ni alloy, co-Cr-Ni alloy, and Ni-Cr-Mo alloy.
In some embodiments provided herein, a passive oxynitride adsorption catalyst composition includes a precious metal active ingredient that is at least one of Pd, ag, co, and a first adsorptive refractory carrier that is a first molecular sieve or metal oxide. The first molecular sieve refers to one of a small pore molecular sieve with an eight-membered ring structure, a medium pore molecular sieve with a ten-membered pore structure and a large pore molecular sieve with a twelve-membered ring structure, and the first molecular sieve can further refer to one of BEA, FAU, MFI, CHA, LTA, AEI, FER, MCM, in particular to one of Beta, HEBA, SSZ-13, ZSM-5, SSZ-39 and HZSM-11. The first molecular sieve has a grain size of 0.01-10 μm and Si/al=1-30. Further, the grain size of the first molecular sieve is 100-1000 nm. The metal oxide is one of gamma-alumina, cerium oxide, praseodymium oxide, zirconium oxide and tungsten oxide and its composite oxide.
In some embodiments provided herein, the passive oxynitride adsorption catalyst composition further comprises a base metal or a rare earth metal, at least one of the base metals being Mn, co, zr, ni, the rare earth metal being Ce or La.
Preferably, the noble metal content is from 0.1wt% to 5wt% of the passive nox adsorber catalyst composition and the base metal is from 0.1wt% to 1wt% of the passive nox adsorber catalyst composition.
In some embodiments of the invention provided, NO 2 The reduction catalyst composition comprises NO 2 Reducing the active ingredient and a second adsorptive refractory carrier, NO 2 The reduction active component is one or more of ferric oxide, cobalt oxide, copper oxide, barium oxide, calcium oxide, magnesium oxide, strontium oxide, tin oxide and germanium oxide, and the second adsorptive refractory carrier is silicon oxide or gamma-alumina. NO (NO) 2 The reduction catalyst composition is preferably a symbiotic mixture of at least one of iron oxide, cobalt oxide, copper oxide, barium oxide, calcium oxide, magnesium oxide and one or two of silicon oxide and gamma-alumina.
In some embodiments of the invention provided, NO x The reduction catalyst composition comprises NO x Reducing the active ingredient and a third adsorptive refractory carrier,NO x the reducing active ingredient is one or more of Cu, mn, V, fe, co, W, ni, zn, ti, cr, Y, zr, nb, mo, and the third adsorptive refractory carrier comprises one or a symbiotic mixture of analcite, chabazite, heulandite, stilbite, erionite, mordenite, calcium zeolite, and sodium zeolite. More preferably, the third adsorptive refractory carrier is one or a symbiotic mixture of BEA, FAU, MFI, CHA, LTA, AEI, MOR, KFI, ROH frameworks, NO x The reducing active ingredient is a symbiotic mixture of one or more of Cu, fe, W, ti, zr, mo.
In a second aspect, the present invention provides a lean burn engine exhaust treatment apparatus comprising a catalyst article for lean burn engine exhaust treatment. By utilizing the composite catalyst provided by the application, a PNA unit does not need to be additionally added, and preferably, a lean-burn engine tail gas treatment device comprising a catalyst product for lean-burn engine tail gas treatment is provided with a DOC unit, a DPF unit, a catalyst product unit for lean-burn engine tail gas treatment and an ASC unit according to the tail gas flow direction.
The following table is a table of parameters for each of the coatings of examples 1-3 and comparative examples 1-7 of catalyst articles for lean burn engine exhaust treatment provided by the present invention.
TABLE 1
Table 1 (subsequent)
Example 1:
the embodiment provides a preparation method of a catalyst product for lean-burn engine exhaust treatment, which comprises the following steps:
s1: palladium nitrate is added into FER microporous molecular sieve slurry with Si/Al=25, grain size of 800nm and molecular sieve D50 of 5-8 mu m, after being stirred uniformly, 10% of alumina binder is added, and water is added to adjust the solid content to 30%, so as to obtain first slurry. The first slurry was uniformly applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2mil, a length of 5 inches, and a diameter of 12 inches by means of a 40Hz negative pressure suction at the upper feed and exit ends, dried at an upload dry weight of 35g/L, and calcined in air at 550 c to form a first coating having a precious metal content of 0.45wt%.
S2: mixing gamma-alumina with particle size of 1-3 μm with water to obtain alumina suspension, adding nano barium oxide colloid suspension according to the mass ratio of alumina to barium oxide of 7:3, and stirring uniformly to obtain second slurry with solid content of 30%. And uniformly coating the second slurry on the surface of the first coating in a mode of negative pressure suction at the upper feeding end and the air outlet end of 40Hz, wherein the uploading dry weight is 10g/L, and calcining in air at 550 ℃ after drying to form the second coating.
S3: adding water into a commercially available SSZ-39 molecular sieve with the D50 of 5-8 mu m and the Cu content of 3.5%, stirring and dispersing for 30min, then adding 5% of an alumina binder, and adding water to adjust the solid content to 30%, thus obtaining third slurry. Uniformly coating the third slurry on the surface of the second coating in a mode of negative pressure suction at the upper feeding end and the air outlet end of 40Hz, drying the second slurry at the dry weight of 95g/L, and calcining the second slurry in air at 550 ℃ to form a third coating, thus obtaining a catalyst product, and marking the catalyst product as catalyst No. 1.
Example 2:
the embodiment provides a preparation method of a catalyst product for lean-burn engine exhaust treatment, which comprises the following steps:
s1: silver nitrate is added into gamma-alumina suspension with the average particle size of 100nm, after being stirred uniformly, 10 percent of alumina binder is added, and water is added to adjust the solid content to 28 percent, so as to obtain first slurry. The first slurry was uniformly applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2mil, a length of 5 inches, and a diameter of 12 inches with an upload dry weight of 50g/L by means of a 40Hz negative pressure suction at the upper feed and outlet ends. After drying, the first coating is formed by calcination in air at 550 ℃.
S2: mixing gamma-alumina with particle size of 1-3 μm with water to obtain alumina suspension, adding nanometer barium oxide colloid suspension according to the mass ratio of alumina to barium oxide of 6:4, and stirring uniformly to obtain second slurry. And uniformly coating the second slurry on the surface of the first coating in a mode of negative pressure suction at the upper feeding end and the air outlet end of 40Hz, wherein the uploading dry weight is 10g/L, and calcining in air at 550 ℃ after drying to form the second coating.
S3: the BEA molecular sieve containing 5.2wt% fe was dispersed by adding water with stirring for 30 minutes, then 10% alumina binder was added, and water was added to adjust to 30% solids to obtain a third slurry. And uniformly coating the third slurry on the surface of the second coating in a mode of negative pressure suction at the upper feeding end and the air outlet end of 40Hz, drying the second slurry with the dry weight of 115g/L, and calcining the second slurry in air at 550 ℃ to form a third coating, thus obtaining the catalyst product.
Example 3:
the embodiment provides a preparation method of a catalyst product for lean-burn engine exhaust treatment, which comprises the following steps:
s1: adding cobalt oxide into SSZ-13 microporous molecular sieve slurry with Si/Al=14 and grain size of 200nm, stirring uniformly, and adding water to adjust the solid content of the slurry to 30% to obtain first slurry. The first slurry was uniformly applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2mil, a length of 5 inches, and a diameter of 12 inches by means of a 40Hz negative pressure suction at the upper feed and exit ends, dried at a dry weight of 50g/L, and calcined in air at 550 c to form a first coating.
S2: mixing gamma-alumina with particle size of 1-3 μm with water to obtain alumina suspension, adding nanometer barium oxide colloid suspension according to the mass ratio of alumina to barium oxide of 6:4, and stirring uniformly to obtain second slurry. And uniformly coating the second slurry on the surface of the first coating in a mode of negative pressure suction at the upper feeding end and the air outlet end of 40Hz, wherein the uploading dry weight is 10g/L, and calcining in air at 550 ℃ after drying to form the second coating.
S3: adding water into SSZ-39 molecular sieve containing Cu 3.5%, stirring and dispersing for 30min, then adding 5% of alumina binder, adding water and regulating the solid content to 30%, thus obtaining third slurry. And uniformly coating the third slurry on the surface of the second coating in a mode of negative pressure suction at the upper feeding end and the air outlet end of 40Hz, drying the second slurry with the dry weight of 95g/L, and calcining the second slurry in air at 550 ℃ to form a third coating, thus obtaining the catalyst product.
Comparative example 1:
the present comparative example provides a method of preparing a catalyst article for lean burn engine exhaust treatment comprising the steps of:
SSZ-39 molecular sieve with D50 of 5-8 μm and Cu content of 3.2wt.% is added with water, stirred and dispersed for 30min, then 5% alumina binder (hydrated alumina, TREO oxide content of 73.60%) is added, and water is added to adjust the solid content to 30%, thus obtaining slurry. And (3) coating the slurry on a through cordierite ceramic carrier with 600 meshes, a wall thickness of 3.2mil, a length of 5 inches and a diameter of 12 inches in a mode of negative pressure suction at a 40Hz upper feeding and air outlet end, drying, and calcining in air at 550 ℃ to obtain the catalyst product.
Comparative example 2:
the present comparative example provides a method of preparing a catalyst article for lean burn engine exhaust treatment comprising the steps of:
adding water into BEA molecular sieve containing 4.0% of Fe, stirring and dispersing for 30min, then adding 10% of alumina binder, adding water and regulating the solid content to be 32%, thus obtaining slurry. The slurry was applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2 mils, a length of 5 inches, and a diameter of 12 inches by means of a 40Hz negative pressure suction at the upper feed and exit ends. Drying and calcining in air at 550 ℃ to obtain the catalyst product.
Comparative example 3:
the present comparative example provides a method of preparing a catalyst article for lean burn engine exhaust treatment comprising the steps of:
s1: palladium nitrate is added into FER microporous molecular sieve slurry with Si/Al=25 and grain size of 800nm, after being stirred uniformly, 10% of alumina binder is added, and water is added to adjust the solid content of the slurry to 30%, so as to obtain first slurry. The first slurry was applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2 mils, a length of 5 inches, and a diameter of 12 inches, at a dry weight of 30g/L, a length of 1.5 inches, and calcined in air at 550 c from the inlet end in a top feed, 40Hz negative pressure suction mode to form a first coating.
S2: mixing gamma-alumina with particle size of 1-3 microns with water to obtain alumina suspension, adding nanometer barium oxide colloid suspension in the weight ratio of alumina to barium oxide of 6:4, and stirring to obtain the second slurry. And (3) coating the second slurry to the other end of the straight-through cordierite substrate from the air outlet end in a mode of feeding at the upper side and sucking at a negative pressure of 40Hz, wherein the coating length is 3.5 inches, the uploading dry weight is 10g/L, drying and calcining in air at 550 ℃ to form a second coating, and the sum of the lengths of the first coating and the second coating is the total length of the substrate, wherein the thickness of the first coating is larger than that of the second coating.
S3: adding water into SSZ-39 molecular sieve with Cu content of 3.5%, stirring and dispersing for 30min, then adding 5% of alumina binder, adding water and regulating to solid content to 30%, thus obtaining third slurry. And (3) coating third slurry on the surface of the second coating from the air outlet end in a mode of feeding at the upper part and sucking at a negative pressure of 40Hz, wherein the coating length is 3.5 inches, covering the whole second coating, drying the third slurry with the uploading dry weight of 100g/L, and calcining in air at 550 ℃ to form a third coating, thereby obtaining a catalyst product, and the catalyst product is marked as catalyst No. 2.
Comparative example 4:
the present comparative example provides a method of preparing a catalyst article for lean burn engine exhaust treatment comprising the steps of:
s1: silver nitrate is added into SSZ-13 microporous molecular sieve slurry with atomic ratio Si/Al=14 and grain size of 100nm, after being stirred uniformly, 10 percent of alumina binder is added, and water is added to adjust the solid content of the slurry to 30 percent, so as to obtain first slurry. The first slurry was applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2 mils, a length of 5 inches, and a diameter of 12 inches, with an upload dry weight of 40g/L, a length of 2 inches, and calcined in air at 550 c from the inlet end in a top feed, 40Hz negative pressure suction mode to form a first coating.
S2: mixing gamma-alumina with particle size of 1-3 μm with water to obtain alumina suspension, adding nano ferric oxide suspension according to the mass ratio of 3:7 of alumina to ferric oxide, and stirring uniformly to obtain second slurry. And (3) coating the second slurry to the other end of the straight-through cordierite substrate from the air outlet end in a mode of feeding at the upper side and sucking at a negative pressure of 40Hz, wherein the coating length is 3 inches, the uploading dry weight is 10g/L, drying and calcining in air at 550 ℃ to form a second coating, wherein the sum of the lengths of the first coating and the second coating is the total length of the substrate, and the thickness of the first coating is larger than that of the second coating, as shown in figure 2.
S3: adding water into BEA molecular sieve with D50 of 5-8 μm and Fe of 5.2%, stirring and dispersing for 30min, then adding 10% of alumina binder, adding water and regulating the solid content to 30%, thus obtaining third slurry. And (3) coating third slurry on the surface of the second coating from the air outlet end in a mode of feeding at the upper part and sucking at a negative pressure of 40Hz, wherein the coating length is 3.5 inches, covering the whole second coating, drying the third slurry with the uploading dry weight of 120g/L, and calcining in air at 550 ℃ to form a third coating, thus obtaining the catalyst product.
Comparative example 5:
the present comparative example provides a method of preparing a catalyst article for lean burn engine exhaust treatment comprising the steps of:
s1: palladium nitrate is added into FER microporous molecular sieve slurry with Si/Al=25 and grain size of 800nm, after being stirred uniformly, 10% of alumina binder is added, and water is added to adjust the solid content of the slurry to 30%, so as to obtain first slurry. From the air inlet end, the slurry was applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2mil, a length of 5 inches, and a diameter of 12 inches, with a dry weight of 35g/L, a length of 2 inches, and calcined in air at 550 ℃ after drying, in a 40Hz negative pressure suction mode, to form a first coating.
S2: mixing gamma-alumina with particle size of 1-3 μm with water to obtain alumina suspension, adding nano barium oxide colloid suspension according to the mass ratio of alumina to barium oxide of 6:4, and stirring uniformly to obtain the second slurry. And (2) coating the second slurry to the other end of the straight-through cordierite substrate from the air outlet end in a mode of feeding at the upper part and sucking at a negative pressure of 40Hz, wherein the coating length is 2 inches, the uploading dry weight is 10g/L, drying and calcining in air at 550 ℃ to form a second coating, wherein the sum of the lengths of the first coating and the second coating is the total length of the substrate, and the thickness of the first coating is larger than that of the second coating.
S3: adding water into SSZ-39 molecular sieve containing Cu 3.5%, stirring and dispersing for 30min, then adding 5% of alumina binder, adding water and regulating the solid content to be 28%, thus obtaining slurry. And (3) coating third slurry on the surface of the second coating from the air outlet end in a mode of feeding at the upper part and sucking at a negative pressure of 40Hz, wherein the coating length is 3.5 inches, covering the whole second coating, drying the third slurry with the uploading dry weight of 95g/L, and calcining in air at 550 ℃ to form a third coating, thus obtaining the catalyst product.
Comparative example 6:
the present comparative example provides a method of preparing a catalyst article for lean burn engine exhaust treatment comprising the steps of:
s1: silver nitrate is added into SSZ-13 microporous molecular sieve slurry with Si/Al=14 and grain size of 200nm, after being stirred uniformly, 10 percent of alumina binder is added, and water is added to adjust the solid content of the slurry to 30 percent. From the air inlet end, the slurry was applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2mil, a length of 5 inches, and a diameter of 12 inches, with a dry weight of 45g/L and a length of 2.5 inches, in a top feed, 40Hz negative pressure suction, and calcined in air at 550℃after drying to form a first coating.
S2: mixing gamma-alumina with particle size of 1-3 μm with water to obtain alumina suspension, adding nano ferric oxide suspension according to the mass ratio of 3:7 of alumina to ferric oxide, and stirring uniformly to obtain a second slurry. And (3) coating the second slurry to the other end of the straight-through cordierite substrate from the air outlet end in a mode of feeding at the upper part and sucking at the negative pressure of 40Hz, wherein the coating length is 2.5 inches, the uploading dry weight is 10g/L, drying and calcining in air at 550 ℃ to form a second coating, and the sum of the lengths of the first coating and the second coating is the total length of the substrate, and the thicknesses of the first coating and the second coating are the same.
S3: adding water into BEA molecular sieve containing 5.2% of Fe, stirring and dispersing for 30min, then adding 10% of alumina binder, adding water and regulating the solid content to be 30%, thus obtaining third slurry. And (3) coating the third slurry on the surfaces of the first coating layer and the second coating layer from the air inlet end in a mode of feeding at the upper part and sucking at the negative pressure of 40Hz, wherein the coating length is 5 inches, the uploading dry weight is 115g/L, and calcining in air at 550 ℃ after drying to form a third coating layer, thus obtaining the catalyst product.
Comparative example 7:
the present comparative example provides a method of preparing a catalyst article for lean burn engine exhaust treatment comprising the steps of:
s1: palladium nitrate is added into FER microporous molecular sieve slurry with Si/Al=25 and grain size of 800nm, after being stirred evenly, 10 percent of alumina binder is added, and water is added to adjust the solid content of the slurry to 30 percent. From the air inlet end, the slurry was applied to a through-type cordierite substrate having a mesh size of 600, a wall thickness of 3.2mil, a length of 5 inches, and a diameter of 12 inches, with a dry weight of 30/L, a length of 3.5 inches, and calcined in air at 550 ℃ after drying, in a 40Hz negative pressure suction mode, to form a first coating.
S2: mixing gamma-alumina with particle size of 1-3 μm with water to obtain alumina suspension, adding nano ferric oxide suspension according to the mass ratio of 3:7 of alumina to ferric oxide, and stirring uniformly to obtain second slurry. And (3) coating the second slurry to the other end of the straight-through cordierite substrate from the air outlet end in a mode of feeding at the upper part and sucking at the negative pressure of 40Hz, wherein the coating length is 2 inches, the uploading dry weight is 10g/L, drying and calcining in air at 550 ℃ to form a second coating, wherein the sum of the lengths of the first coating and the second coating is the total length of the substrate, and the thicknesses of the first coating and the second coating are the same.
S3: adding water into SSZ-39 molecular sieve containing Cu 3.5%, stirring and dispersing for 30min, then adding 5% of alumina binder, adding water and regulating the solid content to be 28%, thus obtaining third slurry. And (3) coating the third slurry on the surfaces of the first coating layer and the second coating layer from the air inlet end in a mode of feeding at the upper part and sucking at the negative pressure of 40Hz, wherein the coating length is 5 inches, the uploading dry weight is 95g/L, and calcining in air at 550 ℃ after drying to form a third coating layer, thus obtaining the catalyst product, and the catalyst product is marked as catalyst No. 3.
After the catalyst products obtained in 3 examples and 7 comparative examples of the present invention were subjected to a hydrothermal aging test at 650℃for 100 hours, test samples having a diameter of 1 inch and a length of 5 inches were drilled, respectively, to conduct a steady-state performance test. The experimental conditions are shown in table 2. The temperature rising rate is set to be 6 ℃/min in the test process, the temperature is raised to 500 ℃, and second acquisition data of the concentration of each gas phase component at the inlet and the outlet are continuously recorded.
Table 2 steady state performance test atmosphere conditions
The ratio of the inlet NO concentration to the outlet NO concentration is the NOx conversion by subtracting the outlet NO concentration from the sum of the inlet NO concentration, the outlet NO2 concentration and the outlet N2O concentration by 2 times. The following table shows the NOx conversion performance of the catalyst articles obtained in the examples and comparative examples. Cold start NOx adsorption efficiency is defined as the first time 200 ℃ is reached from the start to the inlet temperature.
TABLE 3 steady state performance test results
| 100℃ | 150℃ | 175℃ | 200℃ | 300℃ | |
| Example 1 | 66.20％ | 82.40％ | 92.70％ | 96.80％ | 98.90％ |
| Example 2 | 46.60％ | 70.70％ | 83.80％ | 92.50％ | 99.6 |
| Example 3 | 68.50％ | 83.20％ | 92.90％ | 97.20％ | 99.20％ |
| Comparative example 1 | 20.30％ | 70.10％ | 82.80％ | 90.20％ | 98.30％ |
| Comparative example 2 | 9.70％ | 44.30％ | 56.30％ | 70.30％ | 94.20％ |
| Comparative example 3 | 64.40％ | 80.60％ | 89.90％ | 94.40％ | 98.60％ |
| Comparative example 4 | 43.40％ | 68.70％ | 80.20％ | 92.40％ | 98.90％ |
| Comparative example 5 | 64.90％ | 81.50％ | 90.30％ | 95.50％ | 98.90％ |
| Comparative example 6 | 43.80％ | 68.60％ | 81.30％ | 92.10％ | 99.20％ |
| Comparative example 7 | 62.50％ | 81.30％ | 89.70％ | 94.80％ | 98.90％ |
Results: comparative example 1 is a full length Cu-SSZ-39 catalyst and comparative example 2 is a full length Fe-BEA catalyst, the advantage of comparative example 1 over comparative example 2 is mainly better low temperature zone efficiency, but if under more stringent regulatory restrictions, at cold start (below 200 ℃ C.), there is still some NO x And the emission is easy to exceed the standard. It is therefore desirable to further increase the conversion efficiency in the low temperature zone. The advantages of comparative example 2 are mainly that the efficiency in the high temperature zone (. Gtoreq.300 ℃) is better than that of the copper-based catalyst, and are not elaborated on in the present invention.
The third coating of example 1, example 3, comparative example 5, comparative example 7 is all Cu-SSZ-39, which has the main effect of converting NO released after adsorption of the first coating x And partially reduced NO of the second coating. The first and second coatings of examples 1 and 3 were of full coating height, while the second and third coatings of comparative examples 3, 5, 7 were 30% -70% and 70% -30% respectively, and different catalytic materials, since the second coatings of examples 1, 3 completely cover the first coating, assuring NO desorption of the first coating x Is fully absorbed and catalytically reduced by the second coating to ensure NO 2 And NO, thus allowing the conversion efficiency of example 1, example 3 to be relatively improved. Whereas the first and second coatings of comparative examples 3, 5, and 7 are in "flow-through" relationship, partially desorbed NO x NO adsorbed by the first coating without reduction by the second coating x During the release process, not completely reduced by the second coating, but directly into the third coating for NH 3 SCR catalytic reaction, conversion efficiency is slightly lower.
In example 2, comparative example 4, comparative example 6, consistent with the examples described above, the first and second coatings of comparative example 4, comparative example 6 are in "flow-through" relationship, partially desorbed NO x NO adsorbed by the first coating without reduction by the second coating x During the release process, not completely reduced by the second coating, but directly into the third coating for NH 3 SCR catalystThe conversion efficiency is therefore somewhat lower.
Both sulfur poisoning tests and regeneration tests of the samples were performed in a fixed bed quartz reactor. N at 600 DEG C 2 Pretreating under atmosphere for 30min, then cooling the catalyst to 250deg.C, and introducing 50ppm SO 2 、5％O 2 、10％H 2 O、N 2 As equilibrium gas, hold for 40min, space velocity (GHSV) of 76000mL g cat -1 ·h -1 Finally, the sulfated SCR catalyst is obtained. Catalyst regeneration desulfurization is carried out at 550℃at 500ppm NH 3 、500ppmNO、10％O 2 、8％CO 2 、7％H 2 O and N 2 And regenerating the catalyst in the SCR atmosphere serving as the balance gas for 30min, wherein the airspeed is the same as that of the catalyst. After completion of sulfur poisoning and regeneration tests, steady state performance tests were performed using the simulated gases of table 2. The test procedure is as above, and the NO of the catalyst is calculated x Conversion efficiency. Table 4 shows NO of the catalyst article x Conversion properties. Cold start NO x Adsorption efficiency was defined as the first time the inlet temperature reached 200 ℃ from the beginning.
TABLE 4 test results of catalyst articles provided by the invention before and after sulfur poisoning
As shown in table 4, coating scheme one (example 1, example 2, example 3) employed a layered design with the first coating having a greater reactive interface with the second coating than coating scheme two and coating scheme three. And, since the second coating separates the first coating layer having oxidizing ability containing noble metal from the third coating layer, NO generated by the first coating layer 2 Is effectively reduced, thereby avoiding NO 2 Escape direct with NH 3 Contact is made to reduce N 2 And (3) generating O. From the steady state performance test results, it can be seen that the outlet of the catalyst involved in coating scheme one is at the highest N 2 The O concentration was much lower than coating scheme two (comparative example 3, comparative example 4, comparative example 5), coating scheme three (comparative example 6, comparative example 7).
Coating formulaCase two (comparative example 3, comparative example 4, comparative example 5) has the first coating layer disposed at the air inlet end and directly contacted with the exhaust gas, thus having better low temperature adsorptivity. At test temperatures below 175℃the NO x The conversion efficiency is high. After the temperature is higher than 200 ℃, the contact surface of the catalyst reduction layer limited by the scheme 2 is smaller, and NO is contained in the catalyst reduction layer at the same temperature x The conversion efficiency is slightly lower.
Coating protocol III (comparative example 6, comparative example 7) the first coating is applied to the substrate, avoiding SO 2 Oxidized with NH 3 Or the active center in the catalyst forms stable sulfur species to cover the catalyst surface to reduce the catalytic reduction activity, thereby the catalyst product has better sulfur resistance than the coating scheme II, and NO after the light-off temperature of the surface catalyst is reached X The conversion efficiency is slightly higher.
While the invention has been described with respect to the preferred embodiments, it will be understood that the invention is not limited thereto, but is capable of modification and variation without departing from the spirit of the invention, as will be apparent to those skilled in the art.
Claims (9)
1. A catalyst article for lean burn engine exhaust treatment employing a flow-through monolith substrate, characterized in that: the pore wall of the substrate is provided with a layered catalyst covering the whole length of the substrate, and the layered catalyst comprises a first coating, a second coating and a third coating which are arranged from inside to outside; the first coating comprises a passive oxynitride adsorption catalyst composition and the second coating comprises NO 2 A reduction catalyst composition, the third coating layer comprising NO x Reducing the catalyst composition; the first coating absorbs NO in the tail gas at a temperature lower than 150 DEG C x And releasing NO above 250 DEG C x The method comprises the steps of carrying out a first treatment on the surface of the The second coating layer will NO x NO of a certain proportion of 2 Convert to NO, make NO 2 And the concentration ratio of NO is 0.8-1.2: 1, a step of; the third coating layer is NO x Conversion to N 2 ；
The NO 2 Reduction catalysisThe agent composition comprises NO 2 Reducing the active ingredient and a second adsorptive refractory carrier, said NO 2 The reduction active component is one or more of ferric oxide, cobalt oxide, copper oxide, barium oxide, calcium oxide, magnesium oxide, strontium oxide, tin oxide and germanium oxide, and the second adsorptive refractory carrier is silicon oxide or gamma-alumina;
the second coating separates the first coating from the third coating.
2. The catalyst article for lean burn engine exhaust treatment of claim 1, wherein: passive oxynitride adsorption catalyst composition and NO 2 Reduction catalyst composition, NO x The loading ratio of the reduction catalyst composition is 30-50: 10: 95-120.
3. The catalyst article for lean burn engine exhaust treatment of claim 1, wherein: the loading capacity of the passive oxynitride adsorption catalyst composition in the first coating is 30-50 g/L; NO in the second coating 2 The loading of the reduction catalyst composition was 10.+ -.2 g/L; NO in the third coating x The loading of the reduction catalyst composition is 95-120 g/L.
4. The catalyst article for lean burn engine exhaust treatment of claim 1, wherein: the base material is one of cordierite, silicon carbide and metal materials.
5. The catalyst article for lean burn engine exhaust treatment of claim 4, wherein: the metal material is one of Fe-Cr-Ni alloy, co-Cr-Ni alloy and Ni-Cr-Mo alloy.
6. The catalyst article for lean burn engine exhaust treatment of claim 1, wherein: the passive oxynitride adsorption catalyst composition comprises a noble metal active ingredient and a first adsorptive refractory carrier, wherein the noble metal active ingredient is at least one of Pd, ag and Co, and the first adsorptive refractory carrier is a first molecular sieve or metal oxide.
7. The catalyst article for lean burn engine exhaust treatment of claim 6, wherein: the passive oxynitride adsorption catalyst composition further comprises a base metal or a rare earth metal, wherein the base metal is at least one of Mn, co, zr, ni, and the rare earth metal is Ce or La.
8. The catalyst article for lean burn engine exhaust treatment of claim 1, wherein: the NO x The reduction catalyst composition comprises NO x Reducing the active ingredient and a third adsorptive refractory carrier, said NO x The reducing active ingredient is one or more of Cu, mn, V, fe, co, W, ni, zn, ti, cr, Y, zr, nb, mo, and the third adsorptive refractory carrier comprises one or a symbiotic mixture of analcite, chabazite, heulandite, stilbite, erionite, mordenite, calcium zeolite, and sodium zeolite.
9. A lean burn engine exhaust gas treatment device comprising a catalyst article according to any one of claims 1 to 8 for lean burn engine exhaust gas treatment.
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