CN114588931A - Nitrogen oxide trapping catalyst based on noble metal modified molecular sieve, and preparation method and application thereof - Google Patents
Nitrogen oxide trapping catalyst based on noble metal modified molecular sieve, and preparation method and application thereof Download PDFInfo
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- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 title claims abstract description 189
- 239000003054 catalyst Substances 0.000 title claims abstract description 94
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical class [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 title claims abstract description 78
- 229910000510 noble metal Inorganic materials 0.000 title claims abstract description 30
- 238000002360 preparation method Methods 0.000 title claims description 29
- 230000003197 catalytic effect Effects 0.000 claims abstract description 71
- 239000011248 coating agent Substances 0.000 claims abstract description 60
- 238000000576 coating method Methods 0.000 claims abstract description 60
- 239000002808 molecular sieve Substances 0.000 claims abstract description 54
- 229910052726 zirconium Inorganic materials 0.000 claims abstract description 32
- 229910052763 palladium Inorganic materials 0.000 claims abstract description 31
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 23
- MCMNRKCIXSYSNV-UHFFFAOYSA-N ZrO2 Inorganic materials O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 claims abstract description 22
- 239000012752 auxiliary agent Substances 0.000 claims abstract description 21
- 229910052751 metal Inorganic materials 0.000 claims abstract description 21
- 239000002184 metal Substances 0.000 claims abstract description 21
- 229910003158 γ-Al2O3 Inorganic materials 0.000 claims abstract description 21
- 229910052681 coesite Inorganic materials 0.000 claims abstract description 17
- 229910052906 cristobalite Inorganic materials 0.000 claims abstract description 17
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum oxide Inorganic materials [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 claims abstract description 17
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 17
- 229910052682 stishovite Inorganic materials 0.000 claims abstract description 17
- 229910052905 tridymite Inorganic materials 0.000 claims abstract description 17
- 239000003463 adsorbent Substances 0.000 claims abstract description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 43
- 239000006255 coating slurry Substances 0.000 claims description 31
- 239000002002 slurry Substances 0.000 claims description 30
- 238000005303 weighing Methods 0.000 claims description 27
- 239000008367 deionised water Substances 0.000 claims description 23
- 229910021641 deionized water Inorganic materials 0.000 claims description 23
- 238000000746 purification Methods 0.000 claims description 22
- 238000001035 drying Methods 0.000 claims description 21
- 239000007787 solid Substances 0.000 claims description 21
- 238000003756 stirring Methods 0.000 claims description 21
- 239000000203 mixture Substances 0.000 claims description 20
- 239000000919 ceramic Substances 0.000 claims description 13
- 239000007789 gas Substances 0.000 claims description 13
- 229910052878 cordierite Inorganic materials 0.000 claims description 11
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 claims description 11
- 238000001704 evaporation Methods 0.000 claims description 11
- 239000002245 particle Substances 0.000 claims description 11
- 238000000034 method Methods 0.000 claims description 10
- 239000011148 porous material Substances 0.000 claims description 10
- 239000000741 silica gel Substances 0.000 claims description 10
- XLYOFNOQVPJJNP-ZSJDYOACSA-N heavy water Substances [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 claims description 9
- OERNJTNJEZOPIA-UHFFFAOYSA-N zirconium nitrate Inorganic materials [Zr+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O OERNJTNJEZOPIA-UHFFFAOYSA-N 0.000 claims description 9
- LBVWQMVSUSYKGQ-UHFFFAOYSA-J zirconium(4+) tetranitrite Chemical compound [Zr+4].[O-]N=O.[O-]N=O.[O-]N=O.[O-]N=O LBVWQMVSUSYKGQ-UHFFFAOYSA-J 0.000 claims description 9
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 8
- 239000002202 Polyethylene glycol Substances 0.000 claims description 8
- 229910017604 nitric acid Inorganic materials 0.000 claims description 8
- 229920001223 polyethylene glycol Polymers 0.000 claims description 8
- 229910002422 La(NO3)3·6H2O Inorganic materials 0.000 claims description 7
- 229910002027 silica gel Inorganic materials 0.000 claims description 7
- 230000008569 process Effects 0.000 claims description 6
- 239000002994 raw material Substances 0.000 claims description 6
- 238000007664 blowing Methods 0.000 claims description 5
- 238000013461 design Methods 0.000 claims description 5
- 238000007598 dipping method Methods 0.000 claims description 5
- 239000012530 fluid Substances 0.000 claims description 5
- 239000007788 liquid Substances 0.000 claims description 5
- 230000008020 evaporation Effects 0.000 claims description 3
- 238000004821 distillation Methods 0.000 claims 1
- 238000001179 sorption measurement Methods 0.000 abstract description 6
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 abstract description 5
- 238000006243 chemical reaction Methods 0.000 abstract description 5
- 229910052717 sulfur Inorganic materials 0.000 abstract description 5
- 239000011593 sulfur Substances 0.000 abstract description 5
- 230000007774 longterm Effects 0.000 abstract description 4
- 230000032683 aging Effects 0.000 abstract description 3
- 230000007246 mechanism Effects 0.000 abstract description 3
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 50
- QVQLCTNNEUAWMS-UHFFFAOYSA-N barium oxide Chemical compound [Ba]=O QVQLCTNNEUAWMS-UHFFFAOYSA-N 0.000 description 25
- 239000000243 solution Substances 0.000 description 18
- 238000002485 combustion reaction Methods 0.000 description 13
- 238000006722 reduction reaction Methods 0.000 description 13
- 238000005516 engineering process Methods 0.000 description 8
- 238000011156 evaluation Methods 0.000 description 7
- 239000000446 fuel Substances 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 5
- 238000005070 sampling Methods 0.000 description 5
- 238000002347 injection Methods 0.000 description 4
- 239000007924 injection Substances 0.000 description 4
- 238000005245 sintering Methods 0.000 description 4
- 239000004215 Carbon black (E152) Substances 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 238000000227 grinding Methods 0.000 description 3
- 229930195733 hydrocarbon Natural products 0.000 description 3
- 150000002430 hydrocarbons Chemical class 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 229910052697 platinum Inorganic materials 0.000 description 3
- 238000006479 redox reaction Methods 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 239000003344 environmental pollutant Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 231100000719 pollutant Toxicity 0.000 description 2
- 230000001603 reducing effect Effects 0.000 description 2
- 238000003878 thermal aging Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 238000004378 air conditioning Methods 0.000 description 1
- 238000010531 catalytic reduction reaction Methods 0.000 description 1
- 239000003426 co-catalyst Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 125000004435 hydrogen atom Chemical class [H]* 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- KTUFCUMIWABKDW-UHFFFAOYSA-N oxo(oxolanthaniooxy)lanthanum Chemical compound O=[La]O[La]=O KTUFCUMIWABKDW-UHFFFAOYSA-N 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 230000004083 survival effect Effects 0.000 description 1
- 230000009044 synergistic interaction Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J29/00—Catalysts comprising molecular sieves
- B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
- B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
- B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
- B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
- B01J29/44—Noble metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9413—Processes characterised by a specific catalyst
- B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
- B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/0215—Coating
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
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- B01D2255/102—Platinum group metals
- B01D2255/1023—Palladium
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- B01D2258/00—Sources of waste gases
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Abstract
The invention discloses a nitrogen oxide trapping catalyst based on a noble metal modified molecular sieve. The catalyst takes Pd and Zr binary metal modified ZSM-5 type molecular sieve as a main catalytic active component, BaO as an adsorbent and La2O3And ZrO2As a cocatalyst, gamma-Al2O3And SiO2Is a coating auxiliary agent. The catalyst is coated in an LNT catalyst, and can efficiently purify NOx discharged by a diesel engine through an adsorption-reduction mechanism. The invention reduces the consumption of noble metal, improves the sulfur resistance and the heat aging resistance of the LNT catalystThe catalytic activity is also obviously improved. The Zr in the modified molecular sieve enhances the integral catalytic activity of the main catalytic active component. La2O3And ZrO2Composed of the catalyst promoter and SiO in the coating auxiliary agent2All effectively inhibit BaO and gamma-Al2O3The high-temperature reaction ensures the long-term and stable exertion of the BaO adsorption function and prolongs the service life of the catalytic coating.
Description
Technical Field
The invention belongs to the technology of purifying pollutants in the tail gas of an internal combustion engine for a vehicle, and particularly relates to a lean-burn nitrogen oxide trapping (LNT) catalyst for purifying nitrogen oxide (NOx) in the exhaust gas of a diesel engine and a preparation method thereof.
Background
The diesel engine has high thermal efficiency, large power output, firmness and durability, is popular among users in the field of road transportation, and becomes the main power source of medium and heavy load passenger and cargo transport vehicles in China. However, the emission amount of NOx in the exhaust gas of diesel engines is relatively high, and with the increasing strictness of the emission regulations of motor vehicles, the development of the technology for controlling the emission of NOx of diesel engines has become a decisive factor for the survival and death of the diesel engines for vehicles. At present, the most widely applied diesel engine NOx emission control technology is a Selective Catalytic Reduction (SCR) technology, but the purification system is large in size and weight and is not suitable for being applied to medium and small vehicle diesel engines; the SCR system has high production cost, so that the price of a diesel engine product is improved, and the market competitiveness is weakened; and even if a copper-based molecular sieve catalyst is applied, the SCR technology still cannot meet the requirement of high-efficiency purification of NOx under the working conditions of low exhaust temperature such as cold start and the like. Therefore, the technology for purifying NOx efficiently by using a diesel engine with miniaturization, low cost and multiple functions becomes a research focus in the fields of automobiles and internal combustion engines at present, and various new technologies and new products are produced.
NOx emitted from diesel engines is an acidic gaseous oxide that readily chemically reacts with and is thus chemisorbed on the surface of a basic solid oxide. However, since it is difficult for the chemisorbed NOx to spontaneously desorb from the basic oxide, it is necessary to adopt a method ofThe technical principle can be applied to the actual exhaust NOx purification process of the diesel engine only by realizing the controllable desorption of NOx by active measures. Therefore, experts and scholars in the field of internal combustion engine emission propose LNT technical schemes based on adsorption-reduction purification principle, and the working process is as follows: an LNT catalyst is arranged in an exhaust system of the diesel engine; firstly, controlling the running condition of the diesel engine under a normal lean-burn working condition, wherein NOx discharged by the diesel engine reacts with alkaline oxide components in an LNT catalyst and is adsorbed on the surface of the alkaline oxide; when the adsorption amount of basic oxides in the LNT catalyst is close to saturation, the operating condition of the diesel engine is adjusted to a rich combustion condition, and at the same time, not only is the NOx generated by in-cylinder combustion greatly reduced, but also a large amount of Hydrocarbon (HC) and hydrogen (H) are generated2) And gas components having reducing activity such as carbon monoxide (CO) which undergo oxidation-reduction reaction with NOx adsorbed on the surface of the basic oxide to produce H under the action of the main catalytic active component in the LNT catalyst2O、CO2、N2And the like, and realizes the high-efficiency purification of NOx.
From the above analysis, it can be seen that the LNT catalyst firstly requires an alkaline oxide adsorbent, and barium oxide (BaO) is a cheap alkaline metal oxide, has a good adsorption performance for NOx in engine exhaust, and has been applied to a certain extent in the LNT technical field; meanwhile, a main catalytic active component for catalyzing the oxidation-reduction reaction of the adsorbed NOx is also needed in the LNT catalyst; further, as a practical commercial catalyst, a co-catalyst, a coating assistant, a carrier, and the like are required in the LNT catalyst. Because the early LNT catalyst adopts the noble metal platinum (Pt) and/or palladium (Pd) as the main catalytic active component, the overall sulfur resistance and thermal aging resistance of the LNT catalyst are poor (the noble metal active center particles in a high dispersion state can be gradually sintered and agglomerated at high temperature), especially when the LNT catalyst is used as a functional unit of an aftertreatment system closer to an exhaust outlet of a cylinder, the exhaust temperature in the LNT catalyst is relatively high, the service life of the noble metal catalytic component is more easily reduced, and the defects lead to the failure of the early LNT technology in large-scale popularization and application on a diesel engine. The reason for the high-temperature sintering of the noble metal component is that gamma-Al2O3The coating auxiliary agent can generate structural deformation at high temperature, so that the fluidity of the coating auxiliary agent and the noble metal active center is enhanced, if the noble metal component is dispersed on a solid material with a structure which is not easy to deform at high temperature, the high-temperature sintering of the noble metal component can be effectively inhibited, and meanwhile, the enhancement of the dispersion degree of the noble metal component is beneficial to the enhancement of the catalytic activity.
Disclosure of Invention
In view of the above-mentioned prior art, an object of the present invention is to provide a NOx trap catalyst based on a noble metal-modified molecular sieve, which is applied to an LNT catalyst and can efficiently purify NOx emitted from a diesel engine through an adsorption-reduction mechanism, and which is suitable for the purification of NOx in diesel engine exhaust. The invention reduces the consumption of noble metal, improves the sulfur resistance and thermal aging resistance of the LNT catalyst, and obviously improves the catalytic activity. The Zr in the modified molecular sieve enhances the integral catalytic activity of the main catalytic active component. La2O3And ZrO2Composed of the catalyst promoter and SiO in the coating auxiliary agent2All effectively inhibit BaO and gamma-Al2O3The high-temperature reaction ensures the long-term and stable exertion of the BaO adsorption function and prolongs the service life of the catalytic coating.
In order to solve the technical problems, the invention provides a nitrogen oxide trapping catalyst based on a noble metal modified molecular sieve, which comprises a main catalytic active component consisting of a Pd and Zr binary metal modified ZSM-5 type molecular sieve and an adsorbent consisting of BaO; from La2O3And ZrO2The cocatalyst is composed of gamma-Al2O3And SiO2The catalyst comprises a coating auxiliary agent, a catalytic coating, a noble metal modified molecular sieve-based nitrogen oxide trapping catalyst and a catalyst carrier, wherein the catalytic coating is formed by the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent, and the noble metal modified molecular sieve-based nitrogen oxide trapping catalyst is formed by the catalytic coating and 400-mesh cordierite honeycomb ceramics; wherein:
in the main catalytic active component, the mass percentages of the Pd, Zr and ZSM-5 type molecular sieves are as follows: 8-15%/2-8%/80-90%, and the sum of the mass percentages is 100%; among the cocatalysts, the La2O3And ZrO2The mass percentage of the components is as follows: 30-60%/40-70%, the sum of the mass percentages is 100%; among the coating additives, the gamma-Al2O3And SiO2The mass percentage of the components is as follows: 60-80%/20-40%, the sum of the mass percentages is 100%; in the catalytic coating, the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent are as follows by mass percent: 0.5-5%/15-25%/5-10%/60-79.5%, the sum of the mass percentages is 100%; the 400-mesh cordierite honeycomb ceramic is used as a carrier of a catalyst, and the mass percentage ranges of the catalytic coating and the carrier are as follows: 15-30%/85-70%, and the sum of the mass percentages is 100%.
The preparation method of the catalyst mainly comprises the following steps:
(1) designing the composition of a catalyst;
(2) preparing a Pd and Zr binary metal modified ZSM-5 type molecular sieve;
(3) preparing coating slurry;
(4) and (4) coating the coating slurry.
The nitrogen oxide trapping catalyst based on the noble metal modified molecular sieve is packaged and then installed in an exhaust passage of a diesel engine, so that the efficient adsorption-reduction purification of NOx in exhaust is realized.
Compared with the prior art, the invention has the beneficial effects that: the ZSM-5 type molecular sieve can keep the stability of the structure thereof in the range of normal exhaust temperature of the diesel engine, so that Pt and Zr loaded on the surface of the ZSM-5 type molecular sieve through modification have poor high-temperature fluidity and are not easy to sinter. Therefore, the Pd and Zr binary metal modified ZSM-5 type molecular sieve is used for replacing noble metals Pt and Pd in the early LNT catalyst to serve as main catalytic active components of the LNT catalyst, so that the sulfur resistance and the heat aging resistance of the LNT catalyst are improved while the noble metal consumption is reduced and the raw material cost is reduced; meanwhile, due to the fact that the dispersion degree of Pd species in the LNT catalyst is improved, the catalytic performance of the main catalytic active component on the oxidation-reduction reaction of the adsorbed NOx, HC and other reducing components is also obviously improved. Method for modifying Zr in molecular sieve by using Pd and Zr binary metalAnd when the Pd species are added, the high-temperature sintering of the Pd species is further inhibited, and simultaneously, the catalytic activity of the main catalytic active component for catalyzing the reduction reaction of the adsorbed NOx is further enhanced through the synergistic interaction of the Pd species and the Zr species on the surface of the ZSM-5 type molecular sieve. La2O3And ZrO2The catalyst promoter effectively inhibits BaO + gamma-Al2O3→BaAlO2The reaction ensures the long-term and stable exertion of the BaO adsorption function on one hand and prolongs the service life of the catalytic coating on the other hand. SiO in coating auxiliary agent2Is also beneficial to inhibiting BaO + gamma-Al2O3→BaAlO2The reaction takes place.
Drawings
Fig. 1 is a schematic diagram of an engine evaluation system for NOx purification performance of an LNT catalyst.
Wherein: 1-a dynamometer; 2-a coupler; 3-test diesel engine; 4-an inlet flow controller; 5-air intake air conditioning; 6-oil injector; 7-a fuel injection control system; 8-exhaust sampling port A; 9-temperature sensor a; 10-diesel oxidation catalyst; 11-temperature sensor B; 12-LNT catalyst; 13-temperature sensor C; 14-exhaust sample port B; 15-an exhaust sampling channel; 16-engine exhaust gas analyzer; 17-air pump.
FIG. 2 is a graph showing an engine evaluation system for NOx purification performance using the LNT catalyst shown in FIG. 1, wherein the exhaust temperature is 250 ℃ and the airspeed is 50000h under a lean-burn condition of the diesel engine-1When the exhaust oxygen content under the rich combustion working condition is 1.1-1.2% and the ratio of the lean combustion operation time to the rich combustion operation time is 5, the purification efficiency of NOx is improved in the adsorption-reduction reaction of the NOx exhausted by the diesel engine under the catalysis of the catalyst prepared in the embodiment 1-3.
FIG. 3 is a graph showing an engine evaluation system for NOx purification performance using the LNT catalyst shown in FIG. 1, wherein the exhaust temperature is 350 ℃ and the space velocity is 100000h under a lean-burn condition of the diesel engine-1When the exhaust oxygen content under the rich combustion working condition is 1.1-1.2% and the ratio of the lean combustion operation time to the rich combustion operation time is 5, the purification efficiency of NOx is improved in the adsorption-reduction reaction of the NOx exhausted by the diesel engine under the catalysis of the catalyst prepared in the embodiment 1-3.
FIG. 4 is a graph showing NOx purification efficiency in adsorption-reduction reaction of NOx in exhaust gas of a diesel engine catalyzed by catalysts prepared in examples 1 to 3, when tested in a European Steady State Cycle (ESC) using the LNT catalyst shown in FIG. 1.
Detailed Description
The invention will be further described with reference to the following figures and specific examples, which are not intended to limit the invention in any way.
The invention provides a nitrogen oxide trapping catalyst based on a noble metal modified molecular sieve, which comprises the following components in percentage by weight: pd and Zr binary metal modified ZSM-5 type molecular sieve, BaO and La2O3、ZrO2、γ-Al2O3、SiO2And 400 mesh cordierite honeycomb ceramic.
Pd and Zr binary metal modified ZSM-5 type molecular sieves are used as main catalytic active components, and the mass percentages of the Pd, Zr and ZSM-5 type molecular sieves are as follows: 8-15%/2-8%/80-90%, and the sum of the mass percentages is 100%.
BaO is used as an adsorbent.
With La2O3And ZrO2Is a cocatalyst, and the La2O3And ZrO2The mass percentage of the components is as follows: 30-60%/40-70%, and the sum of the mass percentages is 100%.
With gamma-Al2O3And SiO2Is a coating assistant, and the gamma-Al2O3And SiO2The mass percentage of the components is as follows: 60-80%/20-40%, and the sum of the mass percentages is 100%.
The catalytic coating of the catalyst comprises the main catalytic active component, an adsorbent, a cocatalyst and a coating auxiliary agent, and the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent are as follows by mass percent: 0.5-5%/15-25%/5-10%/60-79.5%, the sum of the mass percentages is 100%.
The catalyst of the invention is composed of the catalytic coating and 400-mesh cordierite honeycomb ceramic, the 400-mesh cordierite honeycomb ceramic is a carrier of the catalyst of the invention, the catalytic coating is required to be coated on the carrier, and the mass percentage ranges of the catalytic coating and the carrier are as follows: 15-30%/70-85%, and the sum of the mass percentages is 100%.
The preparation of the catalyst comprises the following steps
(1) Catalyst composition design
Respectively designing the mass percentages of Pd, Zr and ZSM-5 type molecular sieves in the main catalytic active component according to the mixture ratio of the components determined in claim 1; la in the cocatalyst2O3And ZrO2The mass percentage of (A); Gamma-Al in coating auxiliary agent2O3And SiO2The mass percentage of (A); the mass percentages of the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent are as follows; a mass percent range of the catalytic coating to the support; and planning to configure the quality of the coating slurry that can produce the catalytic coating;
respectively calculating the mass of the catalytic coating which can be generated according to the determined mixture ratio among the components and the planned preparation of the coating slurry, and respectively calculating the Pd, Zr, ZSM-5 type molecular sieve, BaO and La contained in the catalytic coating2O3、ZrO2SiO produced from silica gel2Pure gamma-Al2O3The mass of (c); combined with every 230.4g Pd (NO)3)2·2H2O preparation 106.4g Pd/429.3 g Zr (NO)3)4·5H2O preparation 91.2g Zr per 255.4g Ba (CH)3COO)2153.3g of BaO per 866g of La (NO) was prepared3)3·6H2O preparation 325.8g La2O3Every 429.3g of Zr (NO)3)4·5H2O preparation 123.2g ZrO2Calculating the Pd (NO) required for preparing the catalyst3)2·2H2O、Zr(NO3)4·5H2O(1)、Ba(CH3COO)2、La(NO3)3·6H2O、Zr(NO3)4·5H2The mass of O (2); according to SiO in silica gel2Calculating the mass of the silica gel required by the preparation of the coating slurry according to the mass percentage; per 100g of catalytic coatingCalculating the mass of the polyethylene glycol and the nitric acid which are required to be consumed for preparing the catalytic coating according to the ratio of 5-15 g of polyethylene glycol with the average molecular weight of 20000 to 25-50 g of nitric acid;
(2) preparation of Pd and Zr binary metal modified ZSM-5 type molecular sieve
Weighing determined mass of Pd (NO)3)2·2H2O, and per 100g Pd (NO)3)2·2H2Weighing deionized water according to the proportion of O to 0.5-2L of deionized water, and weighing the weighed Pd (NO)3)2·2H2Placing O into the weighed deionized water, and stirring to prepare a solution; weighing ZSM-5 type molecular sieve with determined mass, and adding the molecular sieve into the solution; violently stirring the mixture of the solution and the ZSM-5 type molecular sieve at the temperature of 50-80 ℃ for 8-16 h, and then evaporating water at the temperature of 70-90 ℃; drying the solid after water evaporation for 4-16 h at 80-110 ℃, and roasting the dried solid for 2-3 h at high temperature of 500-550 ℃ to obtain the Pd modified ZSM-5 type molecular sieve;
weighing Zr (NO) with determined mass3)4·5H2O (1) per 100g of Zr (NO)3)4·5H2Weighing deionized water according to the proportion of 1-2L of deionized water to O (1), and weighing the weighed Zr (NO)3)4·5H2O (1) is put into the weighed deionized water and is stirred to prepare a solution; adding the prepared Pd modified ZSM-5 type molecular sieve into the solution; violently stirring the mixture of the solution and the Pd modified ZSM-5 type molecular sieve at 50-80 ℃ for 8-16 h, and then evaporating water at 70-90 ℃; drying the solid after water evaporation for 4-16 h at 80-110 ℃, and roasting the dried solid for 2-3 h at high temperature of 500-550 ℃ to obtain the Pd and Zr binary metal modified ZSM-5 type molecular sieve;
(3) preparation of coating slurries
Weighing Ba (CH) with determined mass3COO)2、La(NO3)3·6H2O、Zr(NO3)4·5H2O (2), powdered gamma-Al2O3Silica gel, molecular weight20000 polyethylene glycol and nitric acid, and the Pd and Zr binary metal modified ZSM-5 molecular sieve prepared in step (2), adding the 8 raw materials into deionized water with the mass 5-15 times of that of the catalytic coating prepared in plan, and uniformly stirring to form slurry; the slurry was then ground on a grinder to a median particle size (D)50Particle size) is within the range of 0.8-1.0 micron, and then the ground slurry is stirred for 48-72 hours at the temperature of 50-70 ℃ to obtain coating slurry;
(4) application of coating slurries
Designing the quality of a 400-mesh cordierite honeycomb ceramic carrier to be coated with a catalytic coating; weighing 400-mesh cordierite honeycomb ceramic with determined mass, immersing a ceramic carrier in the coating slurry at 50-70 ℃, and ensuring that the upper end surface of the carrier is slightly 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 the temperature of 80-110 ℃ for 4-16 h, and roasting at the temperature of 500-600 ℃ for 2-4 h; and repeating the processes of dipping, drying and roasting for 2-3 times to obtain the nitrogen oxide trapping catalyst based on the noble metal modified molecular sieve.
The preparation of the catalyst of the present invention and the evaluation of the NOx purification efficiency in the adsorption-reduction reaction of NOx in diesel engine exhaust gas catalyzed by the catalyst will be described in detail below with reference to specific examples.
Example 1
(1) Catalyst composition design
The following proportions are respectively designed: the Pd and Zr in the Pd and Zr binary metal modified ZSM-5 type molecular sieve comprise the following components in percentage by mass: 8%/2%/90%, La2O3And ZrO2The mass percentage of the components is as follows: 60%/40%, gamma-Al2O3And SiO2The mass percentage of the components is as follows: 80%/20%, the mass percent of the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent is as follows: 5%/25%/10%/60%, and the proposed make-up coating slurry produced 2000g of catalytic coating.
(2) Preparation of modified molecular sieves
Weighing 17.3g Pd (NO)3)2·2H2O, putting the mixture into 0.09L of deionized water, and stirring to prepare a solution; adding 90g of ZSM-5 type molecular sieve into the solution, stirring vigorously at 50 ℃ for 16h, then evaporating the water to dryness at 70 ℃, drying the solid after the water is evaporated to dryness at 110 ℃ for 4h, and roasting the dried solid at 550 ℃ for 2h to obtain the Pd modified ZSM-5 type molecular sieve.
9.4g of Zr (NO) were weighed3)4·5H2O, putting the mixture into 0.1L of deionized water, and stirring to prepare a solution; adding the prepared Pd modified ZSM-5 type molecular sieve into the solution, stirring vigorously at 80 ℃ for 8h, and then evaporating the water to dryness at 90 ℃. And drying the solid after water is evaporated to dryness at 100 ℃ for 8h, and roasting the dried solid at 550 ℃ for 2h to obtain the Pd and Zr binary metal modified ZSM-5 molecular sieve.
(3) Preparation of coating slurries
Weighing 833.0g Ba (CH)3COO)2、319.0g La(NO3)3·6H2O、278.8g Zr(NO3)4·5H2O, 960g powdery gamma-Al2O3、960g SiO2Adding 8 raw materials into 10kg of deionized water together, and uniformly stirring to form a slurry, wherein the mass content of the silica gel is 25%, 300g of polyethylene glycol with the molecular weight of 20000, 500g of nitric acid and the Pd and Zr binary metal modified ZSM-5 molecular sieve obtained 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 70 ℃ to obtain coating slurry.
(4) Application of coating slurries
Weighing 1kg of the carrier, immersing the carrier in the coating slurry at 70 ℃, and ensuring that the upper end surface of the carrier is slightly 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 110 ℃ for 4h, and roasting at 500 ℃ for 4 h. And repeating the processes of dipping, drying and roasting for 2 times to obtain the nitrogen oxide trapping catalyst based on the noble metal modified molecular sieve.
Example 2
(1) Catalyst composition design
The following proportions are respectively designed: the Pd and Zr in the Pd and Zr binary metal modified ZSM-5 type molecular sieve comprise the following components in percentage by mass: 15%/5%/80%, La2O3And ZrO2The mass percentage of the components is as follows: 30%/70%, gamma-Al2O3And SiO2The mass percentage of the components is as follows: 60%/40%, the mass percent of the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent is as follows: 0.5%/15%/5%/79.5%, and the coating slurry was formulated to produce 2000g of catalytic coating.
(2) Preparation of modified molecular sieves
Weighing 3.2g Pd (NO)3)2·2H2O, putting the mixture into 0.065L of deionized water, and stirring to prepare a solution; 8g of a ZSM-5 type molecular sieve was added to the solution and stirred vigorously at 80 ℃ for 8h, after which the water was evaporated to dryness at 90 ℃. And drying the solid after water is evaporated to dryness at 80 ℃ for 16h, and roasting the dried solid at a high temperature of 500 ℃ for 3h to obtain the Pd modified ZSM-5 type molecular sieve.
2.4g Zr (NO) are weighed3)4·5H2O, putting the mixture into 0.048L of deionized water, and stirring to prepare a solution; adding the prepared Pd modified ZSM-5 type molecular sieve into the solution, stirring vigorously for 16h at 50 ℃, and then evaporating water to dryness at 70 ℃. And drying the solid after water is evaporated to dryness at 80 ℃ for 16h, and roasting the dried solid at 550 ℃ for 2h to obtain the Pd and Zr binary metal modified ZSM-5 molecular sieve.
(3) Preparation of coating slurries
Weighing 499.8g Ba (CH)3COO)2、79.7g La(NO3)3·6H2O、243.9g Zr(NO3)4·5H2O, 954g of powdery gamma-Al2O3、2544g SiO225% by mass of silica gel, 100g of polyethylene glycol having a molecular weight of 20000, 250g of nitric acid andadding the 8 raw materials into 30kg of deionized water together, and uniformly stirring to form a 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 then the ground slurry is stirred for 72 hours at 50 ℃ to obtain coating slurry.
(4) Application of coating slurries
Weighing 1kg of the carrier, immersing the carrier in the coating slurry at 50 ℃, and ensuring that the upper end surface of the carrier is slightly 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 for 16h at 80 ℃, and roasting for 2h at 600 ℃. And repeating the processes of dipping, drying and roasting for 3 times to obtain the nitrogen oxide trapping catalyst based on the noble metal modified molecular sieve.
Example 3
(1) Catalyst composition design
The following proportions are respectively designed: the Pd and Zr binary metal modified ZSM-5 type molecular sieve comprises the following components in percentage by mass: 12%/8%/80%, La2O3And ZrO2The mass percentage of the components is as follows: 50%/50%, gamma-Al2O3And SiO2The mass percentage of the components is as follows: 75%/25%, the mass percent of the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent is as follows: 2%/20%/8%/70%, and the proposed make-up coating slurry produced 2000g of catalytic coating.
(2) Preparation of modified molecular sieves
Weighing 10.4g Pd (NO)3)2·2H2O, putting the mixture into 0.15L of deionized water, and stirring to prepare a solution; 32g of a ZSM-5 type molecular sieve was added to the solution and stirred vigorously at 70 ℃ for 12h, after which the water was evaporated to dryness at 80 ℃. And drying the solid after water is evaporated to dryness at 100 ℃ for 8h, and roasting the dried solid at 550 ℃ for 2h to obtain the Pd modified ZSM-5 type molecular sieve.
Weighing 15.1g Zr (NO)3)4·5H2O, putting the mixture into 0.2L of deionized water, and stirring to prepare a solution; adding the prepared Pd modified ZSM-5 type molecular sieve into the solution, stirring vigorously for 8h at 80 ℃, and then evaporating water to dryness at 90 ℃. And drying the solid after water is evaporated to dryness at 90 ℃ for 12 hours, and roasting the dried solid at a high temperature of 500 ℃ for 3 hours to obtain the Pd and Zr binary metal modified ZSM-5 type molecular sieve.
(3) Preparation of coating slurries
Weighing 666.4g Ba (CH)3COO)2、212.6g La(NO3)3·6H2O、278.8g Zr(NO3)4·5H2O, 1050g of powdery gamma-Al2O3、1400g SiO2Adding 8 raw materials into 20kg of deionized water together, and uniformly stirring to form a slurry, wherein the mass content of the silica gel is 25%, 200g of polyethylene glycol with the molecular weight of 20000, 300g of nitric acid and the Pd and Zr binary 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 the temperature of 60 ℃ to obtain coating slurry.
(4) Application of coating slurries
Weighing 1kg of the carrier, immersing the carrier in the coating slurry at 60 ℃, and ensuring that the upper end surface of the carrier is slightly 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 100 ℃ for 8h, and roasting at 550 ℃ for 3 h. And repeating the processes of dipping, drying and roasting for 2 times to obtain the nitrogen oxide trapping catalyst based on the noble metal modified molecular sieve.
Example 4
The NOx adsorption-reduction purification performance of diesel exhaust of the catalysts prepared in examples 1 to 3 was evaluated by using the LNT catalyst NOx 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) quasi-steady state working condition test: the torque and the rotating speed of the test diesel engine 3 are controlled by using the dynamometer 1 and the coupler 2, the fuel supply speed of the fuel injector 6 to the diesel engine is adjusted by the fuel injection control system 7, and the test diesel engine 3 is driven to circularly run according to the following setting conditions by combining the air intake flow controller 4 and the air intake air conditioner 5: lean-burn conditions: the ratio of the engine exhaust flow to the catalyst volume is 50000h-1Or 100000h-1And the temperature measured by the temperature sensor C13 is 250 ℃ or 350 ℃ respectively, and the operation is stable for 50s under the condition; second, rich combustion working condition: and increasing the fuel injection quantity of the engine to ensure that the oxygen content in the exhaust gas is between 1.1 and 1.2 percent, and stably operating for 10s under the condition. In addition, the intake air flow controller 4 can feed back the intake air flow to the fuel injection control system; the intake air conditioner 5 can provide the engine with clean air with specific temperature and humidity. Exhaust gas formed by combustion in a cylinder of the diesel engine is treated by a diesel oxidation catalyst 10 and then enters an LNT catalyst 12 for adsorption-reduction purification treatment.
Diesel exhaust before and after being treated by the LNT catalyst 12 is treated by an exhaust sampling port A8 and an exhaust sampling port B14 through an exhaust sampling passage 15, enters an engine exhaust analyzer 16 for NOx concentration analysis, and gas after NOx analysis is discharged out of a laboratory through an air pump 17. Temperature sensor a9 and temperature sensor B11 measure the exhaust gas temperature before and after the DOC, and temperature sensor C13 measures the temperature at the center of the LNT catalyst 12.
By utilizing the LNT catalyst NOx purification performance engine evaluation system, the exhaust temperature is 250 ℃ and the airspeed is 50000h under the lean-burn working condition of the diesel engine-1The time and exhaust temperature is 350 ℃, and the space velocity is 100000h-1In the diesel engine exhaust NOx adsorption-reduction reaction catalyzed by the catalysts prepared in examples 1 to 3, the purification efficiency of NOx is shown in fig. 2 and 3, respectively.
(2) ESC test: the NOx purification effect in the adsorption-reduction reaction of the exhaust NOx of the diesel engine catalyzed by the catalyst prepared in the examples 1-3 is evaluated by adopting the LNT catalyst NOx purification performance engine evaluation system according to ESC test regulations specified in national Standard GB 17691-2005 [ emission limits of vehicle compression ignition type and gas fuel ignition type engines and automobile exhaust pollutants ] and the measurement method (China stages III, IV and V) ], and is shown in FIG. 4.
In conclusion, the catalyst of the present invention is coated on the LNT catalyst, and can efficiently purify NOx emitted from the diesel engine through an adsorption-reduction mechanism. Pd and Zr binary metal modified ZSM-5 molecular sieve is used as a main catalytic active component, so that the consumption of noble metal is reduced, the sulfur resistance and the heat aging resistance of the LNT catalyst are improved, and the catalytic activity is also obviously improved. The addition of Zr in the modified molecular sieve inhibits Pd species from sintering at high temperature, and enhances the integral catalytic activity of the main catalytic active component. La2O3And ZrO2Composed of the catalyst promoter and SiO in the coating auxiliary agent2All the addition of the compound effectively inhibits BaO and gamma-Al2O3The high-temperature reaction ensures the long-term and stable exertion of the BaO adsorption function and prolongs the service life of the catalytic coating.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.
Claims (3)
1. A nitrogen oxide trapping catalyst based on a noble metal modified molecular sieve is characterized in that:
pd and Zr binary metal modified ZSM-5 type molecular sieves constitute main catalytic active components, and the mass percentages of the Pd, Zr and ZSM-5 type molecular sieves are as follows: 8-15%/2-8%/80-90%, and the sum of the mass percentages is 100%;
an adsorbent consisting of BaO;
from La2O3And ZrO2Constitute a cocatalyst, and the La2O3And ZrO2The weight percentage of the components is as follows: 30-60%/40-70%, the sum of the mass percentagesIs 100%;
from gamma-Al2O3And SiO2Make up a coating assistant, and the gamma-Al2O3And SiO2The mass percentage of the components is as follows: 60-80%/20-40%, the sum of the mass percentages is 100%;
the catalytic coating is composed of the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent, and the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent are as follows by mass percent: 0.5-5%/15-25%/5-10%/60-79.5%, the sum of the mass percentages is 100%;
the catalyst coating and 400-mesh cordierite honeycomb ceramic form a nitrogen oxide trapping catalyst based on a noble metal modified molecular sieve, the 400-mesh cordierite honeycomb ceramic is used as a carrier of the catalyst, and the mass percentage ranges of the catalyst coating and the carrier are as follows: 15-30%/85-70%, and the sum of the mass percentages is 100%.
2. The method of claim 1 for preparing a noble metal modified molecular sieve based nitrogen oxide capture catalyst, wherein the method comprises the steps of: the preparation method comprises the following steps:
(1) catalyst composition design
Respectively designing the mass percentages of Pd, Zr and ZSM-5 type molecular sieves in the main catalytic active component according to the mixture ratio of the components determined in claim 1; la in the cocatalyst2O3And ZrO2The mass percentage of (A); Gamma-Al in coating auxiliary agent2O3And SiO2The mass percentage of (A); the mass percentages of the main catalytic active component, the adsorbent, the cocatalyst and the coating auxiliary agent are as follows; (ii) a mass percent range of the catalytic coating to the support; and planning to configure the quality of the coating slurry that can produce the catalytic coating;
respectively calculating the Pd, Zr, ZSM-5 type molecular sieve, BaO and La contained in the catalytic coating according to the determined mixture ratio of the components and the quality of the catalytic coating which can be generated by planning and configuring the coating slurry2O3、ZrO2And silica gel stationFormed SiO2Pure gamma-Al2O3The mass of (c); combined with every 230.4g Pd (NO)3)2·2H2O preparation of 106.4g Pd/429.3 g Zr (NO)3)4·5H2O preparation 91.2g Zr per 255.4g Ba (CH)3COO)2153.3g of BaO per 866g of La (NO) were prepared3)3·6H2O preparation 325.8g La2O3Every 429.3g of Zr (NO)3)4·5H2O preparation 123.2g ZrO2Calculating the Pd (NO) required for preparing the catalyst3)2·2H2O、Zr(NO3)4·5H2O(1)、Ba(CH3COO)2、La(NO3)3·6H2O、Zr(NO3)4·5H2The mass of O (2); according to SiO in silica gel2Calculating the mass of the silica gel required by the preparation of the coating slurry according to the mass percentage; 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;
(2) preparation of Pd and Zr binary metal modified ZSM-5 type molecular sieve
Weighing determined mass of Pd (NO)3)2·2H2O, and per 100g Pd (NO)3)2·2H2Weighing deionized water according to the proportion of O corresponding to 0.5-2L of deionized water, and adding the weighed Pd (NO)3)2·2H2Adding O into the weighed deionized water, and stirring to prepare a solution; weighing ZSM-5 type molecular sieve with determined mass, and adding the molecular sieve into the solution; violently stirring the mixture of the solution and the ZSM-5 type molecular sieve at the temperature of 50-80 ℃ for 8-16 h, and then evaporating water at the temperature of 70-90 ℃; drying the solid after water evaporation for 4-16 h at 80-110 ℃, and roasting the dried solid for 2-3 h at high temperature of 500-550 ℃ to obtain the Pd modified ZSM-5 type molecular sieve;
weighing Zr (NO) with determined mass3)4·5H2O (1) per 100g of Zr (NO)3)4·5H2Weighing deionized water according to the proportion of 1-2L of deionized water to O (1), and weighing the weighed Zr (NO)3)4·5H2O (1) is put into the weighed deionized water and is stirred to prepare a solution; adding the prepared Pd modified ZSM-5 type molecular sieve into the solution; violently stirring the mixture of the solution and the Pd modified ZSM-5 type molecular sieve at 50-80 ℃ for 8-16 h, and then evaporating water at 70-90 ℃; drying the solid after drying the water by distillation at 80-110 ℃ for 4-16 h, and roasting the dried solid at 500-550 ℃ for 2-3 h to obtain the Pd and Zr binary metal modified ZSM-5 type molecular sieve;
(3) preparation of coating slurries
Weighing Ba (CH) with determined mass3COO)2、La(NO3)3·6H2O、Zr(NO3)4·5H2O (2), powdery gamma-Al2O3Adding the 8 raw materials into deionized water with the mass 5-15 times of that of the catalytic coating prepared in the step (2) together, and uniformly stirring to form slurry; the slurry was then ground on a mill to a median particle size (D)50Particle size) is within the range of 0.8-1.0 micron, and then the ground slurry is stirred for 48-72 hours at the temperature of 50-70 ℃ to obtain coating slurry;
(4) application of coating slurries
Designing the quality of a 400-mesh cordierite honeycomb ceramic carrier to be coated with a catalytic coating; weighing 400-mesh cordierite honeycomb ceramic with determined mass, immersing a ceramic carrier in the coating slurry at 50-70 ℃, and ensuring that the upper end surface of the carrier is slightly 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 the temperature of 80-110 ℃ for 4-16 h, and roasting at the temperature of 500-600 ℃ for 2-4 h; and repeating the processes of dipping, drying and roasting for 2-3 times to obtain the nitrogen oxide trapping catalyst based on the noble metal modified molecular sieve.
3. The application of the nitrogen oxide trapping catalyst based on the noble metal modified molecular sieve is to encapsulate the catalyst prepared by the preparation method of claim 2 and install the encapsulated catalyst in an exhaust passage of a diesel engine so as to realize the efficient adsorption-reduction purification of NOx in exhaust gas.
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