CN115055206A - Acidic site protection modified Cu-SAPO-34 catalyst and preparation method and application thereof - Google Patents

Acidic site protection modified Cu-SAPO-34 catalyst and preparation method and application thereof Download PDF

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CN115055206A
CN115055206A CN202110991760.3A CN202110991760A CN115055206A CN 115055206 A CN115055206 A CN 115055206A CN 202110991760 A CN202110991760 A CN 202110991760A CN 115055206 A CN115055206 A CN 115055206A
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sapo
nitrate
catalyst
alkali metal
rare earth
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李涛
蒙莹
张守特
陈真
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Huazhong University of Science and Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • 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
    • B01J29/82—Phosphates
    • B01J29/84—Aluminophosphates containing other elements, e.g. metals, boron
    • B01J29/85—Silicoaluminophosphates (SAPO compounds)
    • 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
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8621—Removing nitrogen compounds
    • B01D53/8625—Nitrogen oxides
    • B01D53/8628—Processes characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/349—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of flames, plasmas or lasers

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to an acidic site protection modified Cu-SAPO-34 catalyst, and a preparation method and application thereof. The preparation method of the invention introduces rare earth metal or alkali metal into the Cu-SAPO-34 framework, reduces the attack of water molecules on the Cu-SAPO-34 framework, and inhibits the loss of acid sites. The invention is based on the inactivation mechanism of Cu-SAPO-34, carries out rare earth metal ion doping or alkali metal ion exchange on the Cu-SAPO-34, effectively improves the low-temperature hydrothermal stability of the Cu-SAPO-34, and enables the Cu-SAPO-34 to have wider application prospect.

Description

Acidic site protection modified Cu-SAPO-34 catalyst and preparation method and application thereof
Technical Field
The invention belongs to the technical field of catalysts, and particularly relates to an acidic site protection modified Cu-SAPO-34 catalyst, and a preparation method and application thereof.
Background
NO emitted from diesel vehicle x Is NO in city x Due to the positive engine of diesel vehiclesHigh internal temperature during normal operation, NO x Is difficult to avoid and seriously harms the ecological environment and human health, so that the post-treatment of the tail gas of diesel vehicles is required to reduce NO x And (4) discharging. NH is widely adopted in diesel vehicle tail gas aftertreatment device 3 SCR unit for NO in exhaust gases x The core of which is NH 3 -an SCR catalyst. Common NH 3 The SCR catalyst includes noble metal catalysts, metal oxides, molecular sieves, etc., wherein the small pore molecular sieve has excellent performance, low cost, and high NH content 3 And the catalyst is unique in SCR catalyst and has bright application prospect. The small-pore copper-based molecular sieve Cu-SAPO-34 belongs to chabazite type (CHA) molecular sieve, and has wide activity temperature window and high N 2 Selectivity, better low-temperature activity and higher high-temperature hydrothermal stability are of great interest, but due to the special composition of the silicoaluminophosphate molecular sieve, the molecular sieve is prepared under the low-temperature hydrothermal condition<At 100 ℃, under the condition of water content),
Figure BDA0003232581550000011
the acid sites are attacked by water molecules, resulting in irreversible silanol condensation and Si-O (H) -Al bond cleavage hydrolysis, which collapses the structure of Cu-SAPO-34, leading to deactivation (ACS Catalysis,2013,3:2083-2093, Journal of Catalysis,2015,322: 84-90, Nature Communications,2019,10: 101137). The poor low-temperature hydrothermal stability of Cu-SAPO-34 limits the development of the method in industrial application, and therefore, the improvement of the low-temperature hydrothermal stability of Cu-SAPO-34 is very necessary.
CN105749965A discloses a preparation method of a Cu-SAPO-34 catalyst doped with metal cerium, the technical scheme improves the activity of the Cu-SAPO-34 catalyst, but the obtained CeCu-SAPO-34 catalyst has poor high-temperature activity, the operation method is too complicated, the period for preparing the catalyst is longer, and the time cost is higher. CN110479358A discloses a dysprosium-modified Cu-SAPO-34 molecular sieve denitration catalyst and a preparation method thereof, and the obtained dysprosium-doped Cu-SAPO-34 catalyst has poor low-temperature hydrothermal resistance. Patent CN110193378A discloses a preparation method of a CuM/SAPO-34 molecular sieve, wherein M is an alkali metal element, and although the obtained catalyst has excellent low-temperature hydrothermal stability, the preparation method is a one-pot method, and the universality and difference of other preparation methods are not considered.
Therefore, the prior art still lacks a modification method for improving the low-temperature hydrothermal stability of Cu-SAPO-34.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a method for improving the low-temperature hydrothermal stability of Cu-SAPO-34, and aims to stabilize a Cu-SAPO-34 framework, reduce the attack of water molecules on the Cu-SAPO-34 framework, inhibit the loss of acid sites, effectively improve the low-temperature hydrothermal stability of the Cu-SAPO-34 and enable the Cu-SAPO-34 to have wider application prospect based on the inactivation mechanism of the Cu-SAPO-34.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing an acid site protection modified Cu-SAPO-34 catalyst, wherein a rare earth metal or an alkali metal is introduced into a Cu-SAPO-34 framework, so as to reduce the attack of water molecules on the Cu-SAPO-34 framework and inhibit the loss of acid sites.
This application includes rare earth ion doping and alkali ion exchange.
Rare earth metal ions are doped into the Cu-SAPO-34, the rare earth metal ions occupy cation sites of the Cu-SAPO-34, the framework is stabilized, and the attack of water molecules on the Cu-SAPO-34 framework is reduced; furthermore, the rare earth metal ions not only promote isolated Cu 2+ The catalyst migrates to 6-MR sites, and Lewis acid sites can be provided, so that the activity of the catalyst is improved.
Alkali metal ion exchange: and (2) carrying out alkali metal ion exchange on the Cu-SAPO-34 by using a liquid ion exchange method, a solid ion exchange method and an impregnation method, wherein alkali metal ions exchange protons on Si-O (H) -Al in the Cu-SAPO-34 catalyst, so that the acid center strength of the catalyst is changed, but the attack of water molecules on the framework is weakened, and the framework is stabilized.
Preferably, rare earth metals are introduced into a Cu-SAPO-34 framework, and specifically comprise the following components: adding rare earth metal nitrate in the process of synthesizing Cu-SAPO-34 by a one-pot method, crystallizing, washing, drying and roasting to obtain the Cu-SAPO-34 doped with rare earth metal ions.
Preferably, the ratio of the amount of the rare earth metal substance to the amount of the copper substance is 0.2-1.8, the crystallization temperature is 180-220 ℃, the crystallization time is 2-4 days, the calcination temperature is 500-700 ℃, and the calcination time is 4-6 h.
Preferably, the rare earth metal nitrate is scandium nitrate, yttrium nitrate, lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, samarium nitrate, ytterbium nitrate, dysprosium nitrate, holmium nitrate or erbium nitrate.
Preferably, the alkali metal is introduced into the Cu-SAPO-34 framework by a liquid ion exchange method, a solid ion exchange method or an impregnation method;
preferably, the liquid ion exchange method is as follows: dispersing Cu-SAPO-34 powder in an alkali metal salt solution, uniformly stirring, drying, grinding, and roasting in an air atmosphere;
preferably, the solid-state ion exchange method is as follows: dispersing Cu-SAPO-34 powder in an alkali metal salt solution, and uniformly stirring to obtain a suspension; the suspension is subjected to vacuum rotary evaporation, drying and grinding, and then is roasted in the air atmosphere, and solid-state ion exchange occurs in the roasting process;
preferably, the impregnation method is specifically as follows: dispersing Cu-SAPO-34 powder in an alkali metal salt solution, performing ultrasonic treatment to obtain a suspension, standing, drying, grinding, and roasting in an air atmosphere.
Preferably, the alkali metal salt is an alkali metal nitrate comprising lithium nitrate, sodium nitrate, potassium nitrate or cesium nitrate, the alkali metal ion content of the alkali metal salt solution is 0.5-3 wt%, the roasting temperature for roasting in the air atmosphere is 450-600 ℃, and the roasting time is 4-6 h.
Preferably, the method further comprises alkaline gas treatment, namely, the Cu-SAPO-34 powder is stood in an alkaline gas atmosphere and treated at a certain temperature, and the alkaline gas is preferably NH 3 、PH 3 Or N 2 H 4 Preferably, the treatment temperature is 25-100 ℃, the treatment time is 4-36h, and the flow rate of the alkaline gas is 20-40 mL/min.
The invention also uses alkaline gas protection: treating Cu-SAPO-34 with an alkaline gas
Figure BDA0003232581550000041
Protons of acid sites and Cu on the backbone 2+ And the combination can also reduce the attack of water molecules on the framework, and effectively improve the low-temperature hydrothermal stability of the Cu-SAPO-34.
Preferably, the preparation method of the Cu-SAPO-34 comprises the following steps:
(1) uniformly mixing a copper sulfate pentahydrate solution and tetraethylenepentamine, adding phosphoric acid and pseudo-boehmite, uniformly stirring, adding silica sol, uniformly stirring, adding diethylamine and seed crystal, and continuously stirring to obtain a mixed product;
(2) crystallizing the mixed product at 180 ℃ and 200 ℃ for 2-4 days, washing, drying, and roasting at 500 ℃ and 700 ℃ for 4-6h to obtain the Cu-SAPO-34.
According to another aspect of the invention, the Cu-SAPO-34 catalyst prepared by the preparation method is provided.
According to another aspect of the invention, the Cu-SAPO-34 catalyst prepared by the preparation method is applied to automobile exhaust aftertreatment.
The invention has the following beneficial effects:
(1) based on the inactivation mechanism of Cu-SAPO-34, the invention carries out rare earth metal ion doping or alkali metal ion exchange on Cu-SAPO-34, stabilizes the Cu-SAPO-34 framework, reduces the attack of water molecules on the Cu-SAPO-34 framework, inhibits the loss of acid sites, effectively improves the low-temperature hydrothermal stability of Cu-SAPO-34, and enables the Cu-SAPO-34 to have wider application prospect.
(2) According to the invention, a one-pot method is used for preparing the rare earth metal ion doped Cu-SAPO-34, in the preparation process, the rare earth metal ions can be rapidly combined with tetraethylenepentamine, easily occupy cation sites in a CHA cage, promote the stability of a framework, weaken the attack of water molecules on the framework in the low-temperature hydrothermal treatment process, almost no change is caused to the crystal structure of the catalyst, and the crystallinity can still be maintained; and rare earth metal ionsThe presence of the seed can promote isolated Cu 2+ The catalyst migrates to 6-MR, and simultaneously, Lewis acid sites can be provided, so that the catalytic activity and the low-temperature hydrothermal resistance of Cu-SAPO-34 are improved. In addition, the one-pot method for preparing the rare earth metal ion doped Cu-SAPO-34 catalyst has the advantages of low time cost, simple and convenient process flow and simple operation, and is beneficial to industrialization.
(3) The invention uses liquid ion exchange method, solid ion exchange method and dipping method to prepare the Cu-SAPO-34 of alkali metal ion exchange, in the ion exchange process, alkali metal ions replace the protons in Si-O (H) -Al in the Cu-SAPO-34, the acid center strength of the Cu-SAPO-34 is adjusted, and the problem that the Cu-SAPO-34 catalyst is easy to be attacked by water molecules in the low-temperature hydrothermal process and the structure is collapsed due to the framework hydrolysis can be solved. The method adopts three different methods to carry out the ion exchange of the alkali metal, and reflects the universality and the difference of the application of different preparation methods. The liquid ion exchange process can ensure that the alkali metal ions are exchanged more thoroughly, and the catalyst obtained by the method has better low-temperature hydrothermal resistance; the solid ion exchange process saves a plurality of steps of washing, drying and the like, reduces the discharge of industrial wastewater and is simple and convenient to operate; the process of the dipping method can truly reflect the process of the action of the Cu-SAPO-34 catalyst and alkali metal ions in the diesel vehicle tail gas aftertreatment system.
(4) The Cu-SAPO-34 catalyst is treated by alkaline gas, and the surface of the catalyst is adsorbed by the alkaline gas, so that the protection effect can be achieved. The adsorbed alkaline gas is combined with the protons of Si-O (H) -Al in the Cu-SAPO-34 catalyst, and can be prevented from being combined in the low-temperature hydrothermal process
Figure BDA0003232581550000051
The acid sites are reduced, so that the acid sites are better reserved; meanwhile, alkaline gas can be combined with isolated Cu2+ on the framework, and the isolated Cu can be combined after low-temperature hydrothermal treatment 2+ The number of ions and their redox capabilities are still retained. Therefore, the Cu-SAPO-34 catalyst treated by the alkaline gas has excellent low-temperature hydrothermal resistance.
Drawings
Fig. 1 is an XRD pattern of the catalyst of example 1-2 and the comparative example, and (a) in fig. 1 and (b) in fig. 1 are XRD patterns of samples before and after the low-temperature hydrothermal treatment, respectively.
FIG. 2 is a graph of NO conversion for the catalysts of examples 1-2 versus the comparative example.
Fig. 3 is an XRD pattern of the catalyst of examples 3 to 5, and fig. 3 (a) and 3 (b) are XRD patterns of samples before and after the low-temperature hydrothermal treatment, respectively.
FIG. 4 is a graph of NO conversion for the catalysts of examples 3-5 versus a comparative example.
Fig. 5 is XRD charts of the catalyst of example 3 and the catalysts of examples 6 to 7, and fig. 5 (a) and 5 (b) are XRD charts of samples before and after the low-temperature hydrothermal treatment, respectively.
FIG. 6 is a graph of NO conversion for the catalyst of example 3, the catalysts of examples 6-7, and a comparative example.
Fig. 7 is an XRD pattern of the catalyst of example 8 and the comparative example, and (a) in fig. 7 and (b) in fig. 7 are XRD patterns of samples before and after the low-temperature hydrothermal treatment, respectively.
Fig. 8 is a graph of NO conversion for the catalyst of example 8 versus a comparative example.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1
This example is a one-pot method of preparing cerium ion doped Cu-SAPO-34 using cerium nitrate hexahydrate (Ce (NO) nitrate 3 ) 3 ·6H 2 O), the molar ratio of Ce/Cu is 0.8, and the specific process is as follows:
(1) dissolving 1.48g of blue vitriod in 35.5g of deionized water, then adding 1.136g of tetraethylenepentamine, and stirring for 2 hours to obtain a solution A; 2.056g of cerous nitrate hexahydrate is dissolved in 15g of deionized water, and the mixture is stirred for 30min to obtain a solution B;
(2) pouring the solution B into the solution A, and stirring for 1h to obtain a mixed solution;
(3) adding 6.23g of phosphoric acid into the mixed solution, stirring for 5min, then adding 4.36g of pseudo-boehmite, and stirring for 1 h;
(4) then 4.73g of silica sol is added and stirred for 1 hour;
(5) finally, 6.07g of diethylamine and 0.3g of seed crystal are added and stirred for 3 hours;
(6) and transferring the uniformly stirred mixed solution into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, crystallizing for 2 days at 200 ℃ to obtain a hydrothermal product, washing and drying the hydrothermal product, roasting for 5 hours in an air atmosphere at 600 ℃, wherein the heating rate in the roasting process is 2 ℃/min, and thus the Ce ion doped Cu-SAPO-34 catalyst is obtained, which is named as CuCe-SAPO-34.
Placing 2g of prepared CuCe-SAPO-34 catalyst powder into a 250mL round-bottom flask, adding 100mL of deionized water, carrying out low-temperature hydrothermal treatment at 80 ℃ for 96h, washing, and drying to obtain the CuCe-SAPO-34 catalyst subjected to low-temperature hydrothermal treatment, wherein the name is CuCe-SAPO-34-LTH.
Example 2
This example is a preparation method of samarium ion doped Cu-SAPO-34, which is a one-pot method, and the adopted rare earth metal nitrate is samarium nitrate hexahydrate (Sm (NO) 3 ) 3 ·6H 2 O), the molar ratio of Sm/Cu is 1.2, and the specific process is as follows:
(1) dissolving 1.48g of blue vitriod in 35.5g of deionized water, then adding 1.136g of tetraethylenepentamine, and stirring for 2 hours to obtain a solution A; 3.1575g of samarium nitrate hexahydrate is dissolved in 15g of deionized water, and the mixture is stirred for 30min to obtain a solution B;
(2) pouring the solution B into the solution A, and stirring for 1h to obtain a mixed solution;
(3) adding 6.23g of phosphoric acid into the mixed solution, stirring for 5min, then adding 4.36g of pseudo-boehmite, and stirring for 1 h;
(4) then 4.73g of silica sol is added and stirred for 1 hour;
(5) finally, 6.07g of diethylamine and 0.3g of seed crystal are added and stirred for 3 hours;
(6) and transferring the uniformly stirred mixed solution into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, crystallizing for 2 days at 200 ℃ to obtain a hydrothermal product, washing and drying the hydrothermal product, roasting for 6 hours in an air atmosphere at 550 ℃, wherein the heating rate in the roasting process is 2 ℃/min, and obtaining the Sm ion doped Cu-SAPO-34 catalyst which is named as CuSm-SAPO-34.
The low-temperature hydrothermal treatment conditions of the CuSm-SAPO-34 catalyst are also the same as those of the low-temperature hydrothermal treatment conditions in example 1, and the obtained catalyst is named CuSm-SAPO-34-LTH.
Example 3
This example is the preparation of a sodium ion exchanged Cu-SAPO-34 catalyst by liquid ion exchange using an alkali metal salt of sodium nitrate (NaNO) 3 ) The sodium content is 0.62 wt%, and the specific process is as follows:
0.017g of sodium nitrate is dissolved in 8mL of deionized water, and then 1g of Cu-SAPO-34 catalyst powder (the preparation process is shown in a comparative example) is added and stirred for 4 hours at room temperature. Washing, drying, and roasting for 5h in an air atmosphere at 550 ℃, wherein the heating rate in the roasting process is 2 ℃/min, and the obtained sample is a Cu-SAPO-34 catalyst for potassium ion exchange and is named as liquid Na/Cu-SAPO-34.
Putting 1g of prepared Cu-SAPO-34 catalyst powder into a 250mL round-bottom flask, adding 100mL of deionized water, carrying out low-temperature hydrothermal treatment at 80 ℃ for 96h, washing, and drying to obtain the Na/Cu-SAPO-34 catalyst subjected to low-temperature hydrothermal treatment, which is named as liquid Na/Cu-SAPO-34-LTH.
Example 4
This example illustrates the preparation of a potassium ion exchanged Cu-SAPO-34 catalyst by a liquid ion exchange process using an alkali metal salt of potassium nitrate (KNO) 3 ) The content of potassium is 1.24 wt%, and the specific process is as follows:
0.0404g of potassium nitrate was dissolved in 8mL of deionized water, and 1g of Cu-SAPO-34 catalyst powder (see comparative example for preparation) was added and stirred at room temperature for 3 hours. Washing, drying, roasting for 4h in an air atmosphere at 600 ℃, wherein the heating rate in the roasting process is 2 ℃/min, and the obtained sample is a Cu-SAPO-34 catalyst for potassium ion exchange and is named as liquid K/Cu-SAPO-34.
The low-temperature hydrothermal treatment conditions of the K/Cu-SAPO-34 catalyst are also the same as those of the low-temperature hydrothermal treatment conditions in example 3, and the obtained catalyst is named as liquid K/Cu-SAPO-34-LTH.
Example 5
This example is the preparation of a cesium ion-exchanged Cu-SAPO-34 catalyst by liquid ion-exchange using cesium nitrate (CsNO) as the alkali metal salt 3 ) The cesium content is 2 wt%, and the specific process is as follows:
0.1257g of cesium nitrate was dissolved in 8mL of deionized water, followed by addition of 1g of Cu-SAPO-34 catalyst powder (see comparative example for preparation) and stirring at room temperature for 5 h. Washing, drying, roasting for 5h in an air atmosphere at 550 ℃, wherein the heating rate in the roasting process is 2 ℃/min, and the obtained sample is a Cu-SAPO-34 catalyst for potassium ion exchange and is named as liquid Cs/Cu-SAPO-34.
The low-temperature hydrothermal treatment conditions of the Cs/Cu-SAPO-34 catalyst are also the same as those of the low-temperature hydrothermal treatment conditions in example 3, and the obtained catalyst is named as liquid Cs/Cu-SAPO-34-LTH.
Example 6
This example is the preparation of a sodium ion exchanged Cu-SAPO-34 catalyst by a solid state ion exchange process using an alkali metal salt of sodium nitrate (NaNO) 3 ) The sodium content is 0.62 wt%, and the specific process is as follows:
dissolving 0.017g of sodium nitrate in 10mL of deionized water, then adding 1g of Cu-SAPO-34 catalyst powder (see a comparative example in the preparation process), stirring for 1min at room temperature, then quickly and thoroughly transferring to a rotary evaporator to perform vacuum rotary evaporation at 70 ℃ for 15min, drying the obtained powder at 110 ℃, uniformly grinding, and then roasting for 5h at 600 ℃ in an air atmosphere, wherein the obtained catalyst is named as solid Na/Cu-SAPO-34.
The low-temperature hydrothermal treatment conditions of the solid Na/Cu-SAPO-34 catalyst are also the same as those of the low-temperature hydrothermal treatment conditions in example 3, and the obtained catalyst is named as solid Na/Cu-SAPO-34-LTH.
Example 7
This example is the preparation of a sodium ion exchanged Cu-SAPO-34 catalyst by an impregnation method using an alkali metal salt of sodium nitrate (Na)NO 3 ) The sodium content is 0.62 wt%, and the specific process is as follows:
dissolving 0.017g of sodium nitrate in 3mL of deionized water, then adding 1g of Cu-SAPO-34 catalyst powder (the preparation process is shown in a comparative example), carrying out ultrasonic treatment for 30min, standing for 24h, then placing in an oven at 110 ℃ for drying, uniformly grinding, and then roasting for 5h in an air atmosphere at 550 ℃, wherein the obtained catalyst is named as impregnated Na/Cu-SAPO-34.
The low-temperature hydrothermal treatment conditions of the impregnated Na/Cu-SAPO-34 catalyst are also the same as those of the low-temperature hydrothermal treatment conditions in example 3, and the obtained catalyst is named as impregnated Na/Cu-SAPO-34-LTH.
Example 8
This example is NH 3 The Cu-SAPO-34 catalyst is treated by the following specific steps:
taking 1g of Cu-SAPO-34 catalyst powder and placing the powder in NH 3 In the atmosphere of (2), NH 3 The flow rate of (2) is 30mL/min, the treatment temperature is 40 ℃, the treatment time is 6h, and the obtained catalyst is named as NH 3 /Cu-SAPO-34。
NH 3 The low-temperature hydrothermal treatment conditions of the/Cu-SAPO-34 catalyst are also the same as those of the low-temperature hydrothermal treatment conditions in example 3, and the obtained catalyst is named as NH 3 /Cu-SAPO-34-LTH。
Comparative example
Cu-SAPO-34-LTH was used as a comparative example.
The Cu-SAPO-34 molecular sieve catalyst is prepared by the following method:
(1) 1.48g of blue vitriod is dissolved in 50.5g of deionized water, and then 1.136g of tetraethylenepentamine is added and stirred for 2 hours; adding 6.23g of phosphoric acid into the mixed solution, stirring for 5min, then adding 4.36g of pseudo-boehmite, and stirring for 1 h; then 4.73g of silica sol is added and stirred for 1 hour; finally, 6.07g of diethylamine and 0.3g of seed crystal are added and stirred for 3 hours to obtain a uniform mixed solution;
(2) and transferring the mixed solution into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, crystallizing for 2 days at 200 ℃ to obtain a hydrothermal product, washing and drying the hydrothermal product, roasting for 5 hours in an air atmosphere at 600 ℃, wherein the heating rate in the roasting process is 2 ℃/min, and obtaining the Cu-SAPO-34 catalyst which is named as Cu-SAPO-34.
Placing 2g of prepared Cu-SAPO-34 catalyst powder in a 250mL round-bottom flask, adding 100mL of deionized water, carrying out low-temperature hydrothermal treatment at 80 ℃ for 96h, washing, and drying to obtain the Cu-SAPO-34 catalyst subjected to low-temperature hydrothermal treatment, which is named as Cu-SAPO-34-LTH.
The examples 1 to 8 and the comparative example were subjected to catalyst performance test and XRD test, and the test results are shown in fig. 1 to 8.
The catalyst was evaluated by the following method: adding 2g of catalyst into 6mL of deionized water, fully stirring to prepare slurry, immersing a cordierite carrier into the slurry to fill each pore channel with the slurry, then placing the cordierite carrier in a 100 ℃ drying oven for drying for 2h, drying the moisture in the cordierite carrier to obtain the prepared monolithic catalyst, placing the monolithic catalyst in a fixed bed catalyst activity evaluation device, and simulating the flue gas composition of 1000ppm NO and 1100ppm NH 3 ,5％O 2 And 10% of H 2 O, the reaction space velocity is 30000h -1 。
Fig. 1 is an XRD pattern of the catalyst of example 1-2 and the comparative example, and (a) in fig. 1 and (b) in fig. 1 are XRD patterns of samples before and after the low-temperature hydrothermal treatment, respectively.
FIG. 2 is a graph of NO conversion for the catalysts of examples 1-2 versus a comparative example.
As can be seen from the XRD chart of fig. 1 and the NO conversion chart of fig. 2, after the Cu-SAPO-34 molecular sieve catalyst containing NO rare earth metal ions is subjected to low-temperature hydrothermal treatment at 80 ℃ for 96 hours, the structure is collapsed, the crystallinity is significantly reduced, and the activity of the catalyst is greatly reduced, especially the low-temperature activity; the CuCe-SAPO-34-LTH catalyst can still keep a certain degree of crystallinity after being subjected to low-temperature hydrothermal treatment, and due to the introduction of Ce, a part of proton H on Si-OH-Al can be replaced + And the existence of Ce ions can change the angles of Si-O-Si bonds and Si-O-Al bonds of the molecular sieve, can stabilize the framework and weaken the attack of water molecules on the CHA molecular sieve framework, and secondly, the Ce ions are often used as Ce 3+ And Ce 4+ The catalyst has the form of easily generating oxidation-reduction reaction, and improves the oxidation-reduction capability of the molecular sieve catalyst, so that better catalytic activity can be maintained; the crystallinity of CuSm-SAPO-34-LTH is also significantly reduced, but its doping is such thatThe Sm ion provides a portion of the Lewis acid sites and thus maintains some NO conversion.
Fig. 3 is an XRD pattern of the catalysts of examples 3 to 5 and comparative example, and (a) in fig. 3 and (b) in fig. 3 are XRD patterns of the samples before and after the low-temperature hydrothermal treatment, respectively.
FIG. 4 is a graph of NO conversion for the catalysts of examples 3-5 versus a comparative example.
Fig. 5 is XRD patterns of the catalyst of example 3, examples 6 to 7 and the catalyst of comparative example, and fig. 5 (a) and 5 (b) are XRD patterns of samples before and after the low-temperature hydrothermal treatment, respectively.
FIG. 6 is a graph of NO conversion for the catalyst of example 3, the catalysts of examples 6-7, and the comparative example.
From the XRD patterns and NO conversion rate patterns of fig. 3-6, it can be seen that alkali metal ions change the catalyst acid center strength by exchanging protons on Si-o (h) -Al, the probability of catalyst framework being attacked by water molecules during low-temperature hydrothermal treatment is reduced, and the crystallinity and NO conversion rate of the modified catalyst are not significantly reduced. Meanwhile, as can be seen from FIG. 4, in contrast to other alkali metal ions (K) + Ions and Cs + Ion), Na + The introduction of ions can better improve the low-temperature hydrothermal stability of the Cu-SAPO-34 because of Na + Has a minimum radius of not stopping Cu 2+ Migration to favored sites, and large size of K + And Cs + The ions will block Cu by blocking the pore openings of the catalyst 2+ The migration of active centers, which in turn may be due to intragranular mass transfer limitations. Furthermore, as can be seen from FIG. 6, Na ion exchanged Cu-SAPO-34 catalyst prepared by different methods, wherein the liquid Na/Cu-SAPO-34 catalyst prepared by liquid ion exchange method has better hydrothermal stability against low temperature, probably because Na ion exchange is more thorough during the liquid ion exchange process, and the acid center strength of Cu-SAPO-34 can be changed more optimally.
Fig. 7 is an XRD pattern of the catalyst of example 8 and the comparative example, and (a) in fig. 7 and (b) in fig. 7 are XRD patterns of samples before and after the low-temperature hydrothermal treatment, respectively.
Fig. 8 is a graph of NO conversion for the catalyst of example 8 versus a comparative example.
As can be seen from FIGS. 7-8, NH is used 3 The treated Cu-SAPO-34 catalyst also has improved resistance to low temperature hydrothermal conditions, probably due to adsorbed NH 3 With Cu on the skeleton 2+ Combined with protons on Si-O (H) -Al, can stabilize the framework in the low-temperature hydrothermal treatment process and retain Cu 2+ And
Figure BDA0003232581550000121
content of acid sites.
It will be understood by those skilled in the art that the foregoing is only an exemplary embodiment of the present invention, and is not intended to limit the invention to the particular forms disclosed, since various modifications, substitutions and improvements within the spirit and scope of the invention are possible and within the scope of the appended claims.

Claims (10)

1. A preparation method of an acid site protection modified Cu-SAPO-34 catalyst is characterized in that rare earth metal or alkali metal is introduced into a Cu-SAPO-34 framework, so that the attack of water molecules on the Cu-SAPO-34 framework is reduced, and the loss of acid sites is inhibited.
2. The preparation method according to claim 1, characterized in that rare earth metals are introduced into the Cu-SAPO-34 framework, specifically: adding rare earth metal nitrate in the process of synthesizing Cu-SAPO-34 by a one-pot method, crystallizing, washing, drying and roasting to obtain the Cu-SAPO-34 doped with rare earth metal ions.
3. The method as claimed in claim 2, wherein the ratio of the amount of the rare earth metal to the amount of the copper is 0.2-1.8, the crystallization temperature is 180-220 ℃, the crystallization time is 2-4 days, the calcination temperature is 500-700 ℃, and the calcination time is 4-6 hours.
4. The method according to claim 2, wherein the rare earth metal nitrate is scandium nitrate, yttrium nitrate, lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, samarium nitrate, ytterbium nitrate, dysprosium nitrate, holmium nitrate, or erbium nitrate.
5. The production method according to claim 1, wherein the introduction of the alkali metal into the Cu-SAPO-34 framework is carried out by a liquid ion exchange method, a solid ion exchange method or an impregnation method;
preferably, the liquid ion exchange method is as follows: dispersing Cu-SAPO-34 powder in an alkali metal salt solution, uniformly stirring, drying, grinding, and roasting in an air atmosphere;
preferably, the solid-state ion exchange method is as follows: dispersing Cu-SAPO-34 powder in an alkali metal salt solution, and uniformly stirring to obtain a suspension; the suspension is subjected to vacuum rotary evaporation, drying and grinding, and then is roasted in the air atmosphere, and solid-state ion exchange occurs in the roasting process;
preferably, the impregnation method is specifically as follows: dispersing Cu-SAPO-34 powder in an alkali metal salt solution, performing ultrasonic treatment to obtain a suspension, standing, drying, grinding, and roasting in an air atmosphere.
6. The method as claimed in claim 5, wherein the alkali metal salt is an alkali metal nitrate comprising lithium nitrate, sodium nitrate, potassium nitrate or cesium nitrate, the alkali metal ion content of the alkali metal salt solution is 0.5-3 wt%, the calcination temperature for calcination in an air atmosphere is 450-600 ℃, and the calcination time is 4-6 h.
7. The preparation method of claim 1, further comprising an alkaline gas treatment, wherein the Cu-SAPO-34 powder is treated by standing in an alkaline gas atmosphere, preferably, the alkaline gas is NH 3 、PH 3 Or N 2 H 4 Preferably, the treatment temperature is 25-100 ℃, the treatment time is 4-36h, and the flow rate of the alkaline gas is 20-40 mL/min.
8. The method of claim 1, wherein the Cu-SAPO-34 is prepared by a method comprising the steps of:
(1) uniformly mixing a copper sulfate pentahydrate solution and tetraethylenepentamine, adding phosphoric acid and pseudo-boehmite, uniformly stirring, adding silica sol, uniformly stirring, adding diethylamine and seed crystal, and continuously stirring to obtain a mixed product;
(2) crystallizing the mixed product at 180 ℃ and 200 ℃ for 2-4 days, washing, drying, and roasting at 500 ℃ and 700 ℃ for 4-6h to obtain the Cu-SAPO-34.
9. A Cu-SAPO-34 catalyst prepared by the method according to any one of claims 1 to 8.
10. Use of the Cu-SAPO-34 catalyst prepared by the method according to any one of claims 1 to 8 in the aftertreatment of automobile exhaust gases.
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