CN113856746A - Hierarchical pore molecular sieve based denitration catalyst and preparation method and application thereof - Google Patents
Hierarchical pore molecular sieve based denitration catalyst and preparation method and application thereof Download PDFInfo
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- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 title claims abstract description 152
- 239000002808 molecular sieve Substances 0.000 title claims abstract description 151
- 239000003054 catalyst Substances 0.000 title claims abstract description 100
- 239000002149 hierarchical pore Substances 0.000 title claims abstract description 67
- 238000002360 preparation method Methods 0.000 title claims abstract description 38
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 95
- 238000000034 method Methods 0.000 claims abstract description 53
- 239000003513 alkali Substances 0.000 claims abstract description 32
- 229910052742 iron Inorganic materials 0.000 claims abstract description 31
- 238000010306 acid treatment Methods 0.000 claims abstract description 18
- 238000000197 pyrolysis Methods 0.000 claims abstract description 15
- 238000001035 drying Methods 0.000 claims abstract description 14
- 238000005406 washing Methods 0.000 claims abstract description 12
- 238000005342 ion exchange Methods 0.000 claims abstract description 10
- 238000011068 loading method Methods 0.000 claims abstract description 10
- 238000000967 suction filtration Methods 0.000 claims abstract description 5
- 239000011148 porous material Substances 0.000 claims description 26
- 239000003546 flue gas Substances 0.000 claims description 23
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 20
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 18
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 16
- 239000003638 chemical reducing agent Substances 0.000 claims description 12
- 239000007864 aqueous solution Substances 0.000 claims description 11
- 230000008569 process Effects 0.000 claims description 11
- 239000000243 solution Substances 0.000 claims description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 8
- KTWOOEGAPBSYNW-UHFFFAOYSA-N ferrocene Chemical compound [Fe+2].C=1C=C[CH-]C=1.C=1C=C[CH-]C=1 KTWOOEGAPBSYNW-UHFFFAOYSA-N 0.000 claims description 8
- 238000004519 manufacturing process Methods 0.000 claims description 7
- 239000003153 chemical reaction reagent Substances 0.000 claims description 6
- 239000007787 solid Substances 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 238000001354 calcination Methods 0.000 claims 1
- 239000003795 chemical substances by application Substances 0.000 claims 1
- 238000006243 chemical reaction Methods 0.000 description 31
- 239000002253 acid Substances 0.000 description 14
- 230000000694 effects Effects 0.000 description 14
- 241000894007 species Species 0.000 description 14
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 13
- 239000000203 mixture Substances 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- 239000002585 base Substances 0.000 description 7
- 230000003197 catalytic effect Effects 0.000 description 7
- 238000009792 diffusion process Methods 0.000 description 7
- 239000008367 deionised water Substances 0.000 description 6
- 229910021641 deionized water Inorganic materials 0.000 description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
- 239000002131 composite material Substances 0.000 description 5
- 238000002156 mixing Methods 0.000 description 5
- 230000004913 activation Effects 0.000 description 4
- 238000010531 catalytic reduction reaction Methods 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 238000001179 sorption measurement Methods 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical group [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 125000004429 atom Chemical group 0.000 description 3
- 238000006555 catalytic reaction Methods 0.000 description 3
- 238000012512 characterization method Methods 0.000 description 3
- 230000006378 damage Effects 0.000 description 3
- 239000013110 organic ligand Substances 0.000 description 3
- 239000000779 smoke Substances 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 229910021536 Zeolite Inorganic materials 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000010000 carbonizing Methods 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 239000003245 coal Substances 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052593 corundum Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 125000005842 heteroatom Chemical group 0.000 description 2
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 2
- 238000005470 impregnation Methods 0.000 description 2
- 239000002105 nanoparticle Substances 0.000 description 2
- 230000033116 oxidation-reduction process Effects 0.000 description 2
- 229910052573 porcelain Inorganic materials 0.000 description 2
- 239000000376 reactant Substances 0.000 description 2
- 230000002468 redox effect Effects 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 229910001845 yogo sapphire Inorganic materials 0.000 description 2
- 239000010457 zeolite Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 241000196324 Embryophyta Species 0.000 description 1
- 241000203475 Neopanax arboreus Species 0.000 description 1
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000003916 acid precipitation Methods 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
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- 230000008021 deposition Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000008676 import Effects 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 231100001143 noxa Toxicity 0.000 description 1
- 231100000719 pollutant Toxicity 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
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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
- B01J29/04—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
- B01J29/46—Iron group metals or copper
-
- 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
- B01D—SEPARATION
- B01D2251/00—Reactants
- B01D2251/20—Reductants
- B01D2251/206—Ammonium compounds
- B01D2251/2062—Ammonia
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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
- B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
- B01J2229/10—After treatment, characterised by the effect to be obtained
- B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
- B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
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- Biomedical Technology (AREA)
- Oil, Petroleum & Natural Gas (AREA)
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Abstract
The invention provides a hierarchical pore molecular sieve based denitration catalyst and a preparation method and application thereof, wherein the preparation method comprises the following steps: sequentially carrying out alkali treatment and acid treatment on the ZSM-5 molecular sieve, and then carrying out suction filtration, washing and drying to obtain the Na-type hierarchical pore ZSM-5 molecular sieve; ion exchange is carried out on the molecular sieve, and NH is obtained after washing and drying4A type multistage hole ZSM-5 molecular sieve; to NH4Roasting the type multistage hole ZSM-5 molecular sieve to obtain an H type multistage hole ZSM-5 molecular sieve; and loading Fe on the H-type hierarchical pore ZSM-5 molecular sieve by adopting an encapsulation-pyrolysis method to obtain an H-type hierarchical pore Fe/ZSM-5 molecular sieve, and roasting to obtain the hierarchical pore molecular sieve-based denitration catalyst, wherein in the hierarchical pore molecular sieve-based denitration catalyst, iron species are used as active centers and are highly dispersed in the hierarchical pore molecular sieveIn the duct.
Description
Technical Field
The invention relates to a hierarchical pore molecular sieve based denitration catalyst, a preparation method and application thereof, and belongs to the technical field of flue gas denitration.
Background
Nitrogen oxides (NOx) are the main pollutants in the atmosphere. The emission of NOx in large quantities can cause serious harm to human health, living activities and natural ecological environment, including toxicity to human body, damage to plants by acid rain or acid mist, and damage to ozone layer by photochemical smog with hydrocarbon. Therefore, the denitration of flue gas and the development of an efficient denitration catalyst are very important. The zeolite molecular sieve and the modified molecular sieve are a class of catalysts which are actively researched at present, have the advantages of wider active temperature window, higher catalytic activity, better thermal stability and the like, and are concerned by a lot of attention in recent years. At present, heteroatom modified ZSM-5 molecular sieves for denitration have a microporous structure, but the catalytic action of the molecular sieves with the microporous structure is not ideal, and the molecular sieves have small pore diameters and narrow pore channels, and the diffusion and adsorption of molecules are bound, so that the conditions of short reaction residence time and high reaction rate cannot occur. In addition, the microporous molecular sieve has poor inner pore canal connectivity, long diffusion path and large transmission resistance, and carbon deposition often occurs in the use process, so that an acid active center is embedded in the microporous pore canal, the service life of the catalyst is shortened, and the catalytic effect is influenced. If a certain method can be adopted to shorten the diffusion path of the molecular sieve and increase the size of the pore channel, new development of the molecular sieve in the catalysis direction can be promoted. In addition, the active components in the catalyst are often agglomerated into clusters or large nanoparticles, which may cause that the active components cannot be uniformly dispersed on the surface of the catalyst, and further cause the reduction of catalytic activity, and affect the denitration effect, so that it is particularly important to realize the high dispersion of the active components in the catalyst.
Therefore, providing a novel hierarchical pore molecular sieve based denitration catalyst, and a preparation method and application thereof have become technical problems to be solved in the field.
Disclosure of Invention
In order to solve the above disadvantages and shortcomings, it is an object of the present invention to provide a method for preparing a hierarchical pore molecular sieve based denitration catalyst.
The invention also aims to provide the hierarchical pore molecular sieve based denitration catalyst prepared by the preparation method of the hierarchical pore molecular sieve based denitration catalyst.
The invention also aims to provide application of the multistage pore molecular sieve based denitration catalyst in a flue gas denitration treatment process.
Still another object of the present invention is to provide a flue gas denitration treatment method, which uses the above hierarchical pore molecular sieve based denitration catalyst.
In order to achieve the above objects, in one aspect, the present invention provides a preparation method of a hierarchical pore molecular sieve based denitration catalyst, wherein the preparation method comprises:
sequentially carrying out alkali treatment and acid treatment on the ZSM-5 molecular sieve, and then carrying out suction filtration, washing and drying to obtain the Na-type hierarchical pore ZSM-5 molecular sieve;
carrying out ion exchange on the Na-type hierarchical pore ZSM-5 molecular sieve, and then washing and drying to obtain NH4A type multistage hole ZSM-5 molecular sieve;
to the NH4Roasting the type multistage hole ZSM-5 molecular sieve to obtain an H type multistage hole ZSM-5 molecular sieve;
and loading Fe on the H-type hierarchical pore ZSM-5 molecular sieve by adopting an encapsulation-pyrolysis method to obtain an H-type hierarchical pore Fe/ZSM-5 molecular sieve, and roasting to obtain the hierarchical pore molecular sieve based denitration catalyst.
In the above-described preparation method, the ZSM-5 molecular sieve used may be a commercially available conventional commercial ZSM-5 molecular sieve.
The source of the commercial ZSM-5 molecular sieve used in the present invention is not particularly limited, and commercially available products well known to those skilled in the art may be used; in a specific embodiment of the invention, the commercial ZSM-5 molecular sieve is specifically purchased from Qilu Huaxin Gaokou Co.
In the above-described production method, preferably, the reagent for alkali treatment is an aqueous sodium hydroxide solution having a concentration of 0.2 to 0.6 mol/L; more preferably 0.5 mol/L.
In the preparation method, preferably, the liquid-solid ratio of the sodium hydroxide aqueous solution to the ZSM-5 molecular sieve is 10-40:1, and the units are mL and g respectively; more preferably 20: 1.
In the above preparation method, preferably, the temperature of the alkali treatment is 313-363K, and the time is 30-120 min; more preferably, the temperature of the alkali treatment is 353K and the time is 60 min.
Wherein, the silicon atoms of the molecular sieve framework can be selectively removed by an alkali treatment method, so that the intragranular mesopores can be conveniently generated in the molecular sieve. The concentration of an alkali reagent used in alkali treatment can influence the mesoporous pore structure of the molecular sieve, and when the concentration of the alkali used in alkali treatment is too high, the collapse of the framework structure of the molecular sieve is easily caused, fragments containing a zeolite secondary structure are generated, and the denitration performance of the molecular sieve catalyst is greatly influenced.
In the above-mentioned production method, preferably, the reagent for acid treatment is hydrochloric acid, and the concentration of the hydrochloric acid is 0.05 to 0.3 mol/L; more preferably 0.1 mol/L.
In the preparation method, preferably, the liquid-solid ratio of the hydrochloric acid to the alkali-treated ZSM-5 molecular sieve is 5-25:1, with units of mL and g respectively; more preferably 10: 1.
In the above preparation method, preferably, the temperature of the acid treatment is 313-363K, and the time is 30-120 min; more preferably, the temperature of the acid treatment is 353K and the time is 60 min.
For NH3Selective catalytic reduction of NOx (NH)3SCR) reaction, the acid property of the surface of the catalyst determines the high-temperature denitration reaction activity of the catalyst, and the acid property of the surface of the prepared catalyst is adjusted by sequentially carrying out alkali treatment and acid treatment on the ZSM-5 molecular sieve, so that NH is facilitated3-the performance of the SCR reaction.
In the above-mentioned production method, it is preferable that the reagent for ion exchange is NH4Aqueous Cl solution.
In the above-described production method, preferably, the NH is4The concentration of the Cl aqueous solution is 0.8-1.2 mol/L; more preferably 1 mol/L;
the NH4The liquid-solid ratio of the Cl aqueous solution to the ZSM-5 molecular sieve subjected to alkali treatment and acid treatment is 5-20:1, and the units are mL and g respectively; more preferably 10: 1.
In the above preparation method, preferably, the temperature of the ion exchange is 323-363K, and the time is 60-180 min; more preferably, the temperature of the ion exchange is 353K and the time is 120 min.
In the preparation method, preferably, the roasting is 500-600 ℃ roasting for 4-8 h; more preferably, the firing is 550 ℃ for 6 h.
In the above preparation method, the washing is washing with deionized water; in addition, the invention does not have special requirements on the drying temperature and time, and the technicians in the field can reasonably set the drying temperature and time according to the actual operation needs on site as long as the aim of drying the target product can be fulfilled.
In the above-described production method, preferably, the iron source used for loading Fe by the encapsulation-pyrolysis method is ferrocene.
In the above-described production method, preferably, the encapsulation-pyrolysis method includes:
under the condition that the nitrogen flow is 3-20mL/min, the temperature of the system is raised to 500 ℃ at the temperature rise rate of 2-5 ℃/min, and the iron source is gasified and packaged for 30-120min at 500 ℃ of 300-; then the temperature of the system is raised to 400-700 ℃ at the temperature raising rate of 2-5 ℃/min, and the iron source is carbonized for 1-3h at 400-700 ℃.
In one embodiment of the invention, the encapsulation-pyrolysis process comprises:
under the condition that the nitrogen flow is 3mL/min, the temperature of the system is increased to 400 ℃ at the temperature increase rate of 2 ℃/min, and the iron source is gasified and packaged for 60min at 400 ℃; and then raising the temperature of the system to 500 ℃ at the temperature raising rate of 5 ℃/min, and carbonizing the iron source for 2h at 500 ℃.
In the above-described preparation method, all the water used is deionized water.
In the above preparation method, preferably, the loading amount of Fe in the hierarchical pore molecular sieve based denitration catalyst is 3% to 10% based on 100% of the total weight of the hierarchical pore molecular sieve based denitration catalyst; more preferably 4%.
On the other hand, the invention also provides the hierarchical pore molecular sieve based denitration catalyst prepared by the preparation method of the hierarchical pore molecular sieve based denitration catalyst, wherein iron species are used as active centers and are highly dispersed in the pore channels of the hierarchical pore molecular sieve.
In another aspect, the invention also provides the application of the hierarchical pore molecular sieve based denitration catalyst in the flue gas denitration treatment process.
In another aspect, the present invention further provides a flue gas denitration treatment method, wherein the method includes:
and carrying out denitration treatment on the flue gas in the presence of a reducing agent and the hierarchical pore molecular sieve based denitration catalyst.
In the above-described method, preferably, the reducing agent includes NH3。
In the method, preferably, during the denitration treatment, the dosage of the denitration catalyst is calculated according to the following formula 1), and the space velocity is 30000--1The temperature is 100 ℃ and 600 ℃, NO and reducing agent NH in the flue gas3In a molar ratio of 0.5-2, flue gas and a reducing agent NH3The total volume flow of the flow rate is 500 mL/min;
in the formula 1), m is the dosage of the denitration catalyst and the unit is g;
vs is flue gas and reducing agent NH3The unit of the total volume flow of (1) is mL/min;
GHSV is space velocity in h-1；
Rho is the density of the denitration catalyst and is in g/cm3。
The source of the flue gas in the flue gas denitration treatment method is not particularly limited, and the flue gas (coal flue gas) needing denitration can be any flue gas.
In an embodiment of the present invention, specifically, NH3As reducing agent, NO is NO in coal flue gasxThe source is used for carrying out selective catalytic reduction on NO in a fixed bed in the presence of the hierarchical porous molecular sieve based denitration catalyst provided by the inventionxReaction, in which simulated smoke is composed of N2、NO、NH3、O2The composition and the reaction conditions are as follows: the dosage of the denitration catalyst is 0.3-0.6g, and the airspeed is 36000h-1The feed gas composition is: 1000ppm NO, 1000ppm NH3、3vol％O2、N2The reaction temperature is 100-: 500 ml/min;
in the experimental process, inlet and outlet gases are collected and analyzed on line through a testo350 portable smoke analyzer.
In the preparation method of the hierarchical pore molecular sieve based denitration catalyst provided by the invention, the ZSM-5 molecular sieve is subjected to alkali treatment to effectively remove framework silicon atoms and prepare mesoporous communicated with the outside, the introduced pore system can obviously reduce the diffusion limitation of reactants in pores, and the alkali treatment process is simple to operate and has low cost; the acid treatment can effectively wash off amorphous aluminum species remained in the pore channel structure after the alkali treatment, realize the process of dealumination again after desilication, and keep SiO2/Al2O3The method can keep the crystallinity of the ZSM-5 molecular sieve, and can further adjust the acid property and the pore structure of the sample after the alkali treatment to enhance the hierarchical pore moleculesThe accessibility of the active sites is screened, and the denitration reaction activity is effectively improved.
The preparation method of the hierarchical pore molecular sieve based denitration catalyst provided by the invention prepares the hierarchical pore molecular sieve based denitration catalyst with iron species as an active center highly dispersed in the pore canal of the hierarchical pore molecular sieve by an encapsulation-pyrolysis method; specifically, in the preparation process, firstly, the iron source (ferrocene) is gasified at the temperature of 300-500 ℃, the gasified iron source is packaged in the pore channel of the hierarchical pore molecular sieve in a molecular form, then the temperature is raised to the temperature of 400-700 ℃ to carbonize the gasified iron source, the iron source (ferrocene) is heated to decompose and remove the organic ligand in the iron source to release a single isolated Fe atom, and then after roasting, the Fe species are anchored in the pore channel of the molecular sieve to realize the uniform dispersion of the active component Fe species.
In the preparation method, on one hand, dense pores containing a large number of hydroxyl groups on the surface of the ZSM-5 molecular sieve stabilize uniformly dispersed active component Fe species to a great extent; on the other hand, the ZSM-5 molecular sieve is also an excellent host material, and can encapsulate an iron source in a cage in a molecular form, and then remove an organic ligand in the iron source to release a single isolated Fe atom through simple activation treatment (such as high-temperature roasting), and finally realize that an iron species as an active component is uniformly dispersed in the catalyst. The catalyst prepared by the method has good catalytic activity and product selectivity in catalytic reaction.
The method utilizes a method for loading Fe to modify the ZSM-5 molecular sieve, the Fe is low in price and easy to obtain, and the d orbit of the Fe is not full, so that the Fe has strong oxidation-reduction capability; at the same time, for NH3The low-temperature denitration reaction activity of the SCR catalyst is determined by the redox property of the SCR catalyst, and the active component Fe is highly dispersed on the surface of the catalyst in an encapsulation-pyrolysis mode, so that the denitration reaction activity can be effectively improved.
In conclusion, the preparation method of the hierarchical pore molecular sieve based denitration catalyst provided by the invention has the advantages of low cost and simple operation, the prepared hierarchical pore molecular sieve based denitration catalyst has the characteristic of hierarchical pores (rich in mesopores and micropores), the mass transfer diffusion performance of the reaction can be improved by the hierarchical pore structure, more active sites can be exposed on the outer surface of the material, and the denitration catalyst has higher denitration reaction activity.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is an XRD pattern of the hierarchical pore molecular sieve-based denitration catalyst prepared in comparative example 1 of the present invention.
Fig. 2 is an XRD pattern of the hierarchical pore molecular sieve-based denitration catalyst prepared in example 1 of the present invention.
Fig. 3 is a graph showing denitration conversion rates of the hierarchical pore molecular sieve based denitration catalyst prepared in comparative example 1 and a commercial ZSM-5 molecular sieve at different temperatures according to the present invention.
Detailed Description
In order to clearly understand the technical features, objects and advantages of the present invention, the following detailed description of the technical solutions of the present invention will be made with reference to the following specific examples, which should not be construed as limiting the implementable scope of the present invention.
Comparative example 1
The comparative example provides a preparation method of a hierarchical pore molecular sieve based denitration catalyst, wherein the preparation method comprises the following specific steps:
mixing 30g of commercial ZSM-5 molecular sieve with 600mL of 0.5mol/L aqueous solution of sodium hydroxide, and placing the mixture in a 1000mL beaker at 353K for stirring for 60min to obtain an alkali-treated ZSM-5 molecular sieve;
mixing 15g of the base-treated ZSM-5 molecular sieve with 150mL of hydrochloric acid solution with the concentration of 0.1mol/L, and placing the mixture in a 250mL beaker at 353K for stirring for 60min to obtain the acid-base composite-treated ZSM-5 molecular sieve;
washing the reaction product with deionized water, and drying in an oven for 12h to obtain the Na-type hierarchical pore ZSM-5 molecular sieve;
respectively adding 10mL of NH to the ZSM-5 molecular sieve subjected to acid-base composite treatment under 353K4Ratio of Cl aqueous solution/g molecular sieve to 1mol/L NH4Carrying out ion exchange on Cl aqueous solution for three times, carrying out suction filtration, washing, and drying in an oven overnight to obtain NH4A type multistage hole ZSM-5 molecular sieve;
first, NH is measured4The water absorption capacity of the type multistage hole ZSM-5 molecular sieve is calculated to be 5g of NH4The deionized water amount required by dipping the type multi-stage hole ZSM-5 molecular sieve is calculated, and the corresponding Fe (NO) when the load amount of Fe in the multi-stage hole molecular sieve-based denitration catalyst is 4 percent (calculated by taking the total weight of the multi-stage hole molecular sieve-based denitration catalyst as 100 percent) is calculated3)3·9H2O mass, 5g of NH added to the beaker4Type multi-stage hole ZSM-5 molecular sieve, deionized water and Fe (NO)3)3·9H2O, standing for 24 hours at normal temperature, and drying in an oven overnight to obtain NH4A type hierarchical pore Fe/ZSM-5 molecular sieve;
reacting the NH with4Roasting the type hierarchical porous Fe/ZSM-5 molecular sieve in a muffle furnace at 550 ℃ for 6 hours to remove NH by roasting3And obtaining the H-shaped hierarchical pore Fe/ZSM-5 molecular sieve, namely the hierarchical pore molecular sieve based denitration catalyst which is marked as a sample A.
Example 1
The embodiment provides a preparation method of a hierarchical pore molecular sieve based denitration catalyst, wherein the preparation method comprises the following specific steps:
mixing 30g of commercial ZSM-5 molecular sieve with 600mL of 0.5mol/L aqueous solution of sodium hydroxide, and placing the mixture in a 1000mL beaker at 353K for stirring for 60min to obtain an alkali-treated ZSM-5 molecular sieve;
mixing 15g of the base-treated ZSM-5 molecular sieve with 150mL of hydrochloric acid solution with the concentration of 0.1mol/L, and placing the mixture in a 250mL beaker at 353K for stirring for 60min to obtain the acid-base composite-treated ZSM-5 molecular sieve;
washing the reaction product with deionized water, and drying in an oven for 12h to obtain the Na-type hierarchical pore ZSM-5 molecular sieve;
respectively adding 10mL of NH to the ZSM-5 molecular sieve subjected to acid-base composite treatment under 353K4Ratio of Cl aqueous solution/g molecular sieve to 1mol/L NH4Carrying out ion exchange on Cl aqueous solution for three times, carrying out suction filtration, washing, and drying in an oven overnight to obtain NH4A type multistage hole ZSM-5 molecular sieve;
reacting NH4Roasting the type multistage hole ZSM-5 molecular sieve in a muffle furnace at 550 ℃ for 4 hours to remove NH by roasting3Obtaining the H-type hierarchical pore ZSM-5 molecular sieve;
exhausting air with nitrogen for half an hour;
mixing a 0.5g H type multistage hole ZSM-5 molecular sieve and 2g of ferrocene, and putting the mixture into a square porcelain boat;
inserting the square porcelain boat into the middle of the quartz tube, and controlling the temperature and pressure (unable to suppress pressure) in the tube to be about 3mL/min N2Setting the heating rate to be 2 ℃/min and heating to 400 ℃ under the flow (the flow rate can be adjusted to be small);
carrying out gasification encapsulation on ferrocene at the constant temperature of 400 ℃ for 1 hour;
heating to 500 ℃ at the heating rate of 5 ℃/min;
carbonizing ferrocene for 2 hours at the constant temperature of 500 ℃;
cooling, placing into a muffle furnace, and roasting at 550 deg.C for 4 hr to remove NH3And obtaining the H-shaped hierarchical pore Fe/ZSM-5 molecular sieve, namely the hierarchical pore molecular sieve based denitration catalyst which is marked as a sample B.
Characterization and Performance testing
The hierarchical pore molecular sieve based denitration catalysts prepared in comparative example 1 and example 1 were characterized and tested for performance and compared to a commercial ZSM-5 molecular sieve (designated sample C, which contains iron comparable to sample a) available from zilwitsin gakko, inc as follows:
1. the metal hetero atoms being present in the catalyst
Characterization of XRD
XRD characterization was performed on sample A and sample B, and the results are shown in FIGS. 1-2, respectively. As can be seen from FIG. 1, the characteristic diffraction peak of the ZSM-5 molecular sieve appears at the position where 2 theta is equal to 7.9-8.8 degrees and 23.2-24.4 degrees, and the baseline is stable without other mixed crystal peaks, which indicates that the synthesized sample A is the pure-phase ZSM-5 molecular sieve and the crystal phase structure of the molecular sieve is not damaged in the process of loading Fe; as can be seen from fig. 2, the XRD spectrum of sample B also shows five-finger characteristic peaks, and the sample has a high degree of crystallinity, which indicates that the synthesized sample B is also a pure-phase ZSM-5 molecular sieve, and the crystalline phase structure of the molecular sieve is not damaged during loading Fe by the encapsulation-pyrolysis method.
2. Evaluation of denitration Performance of catalyst
By NH3Is a reducing agent, NO is NOxA source for carrying out selective catalytic reduction NOx reaction in a fixed bed in the presence of a sample A, a sample B and a sample C respectively, wherein the simulated flue gas consists of N2、NO、NH3、O2The composition and the reaction conditions are as follows: the dosage of the denitration catalyst is 0.3-0.6g, and the airspeed is 36000h-1The feed gas composition is: 1000ppm NO, 1000ppm NH3、3vol％O2、N2The reaction temperature is 100-; import and export gas was collected and analyzed on-line by the testo350 portable smoke analyzer. The specific results are shown in FIG. 3.
As can be seen from FIG. 3, the NO of each sample increased with increasing temperaturexThe conversion rate of (A) has a remarkable rising trend. When the temperature of the catalyst of the sample C is 400 ℃, the denitration conversion rate has a peak value which reaches more than 90 percent, and the denitration conversion rate is obviously reduced by continuously increasing the temperature;
when the temperature of the catalysts of the sample A and the sample B is 300-500 ℃, the denitration conversion rate is always kept above 90%, and the conversion rate is always higher than that of the catalyst of the sample C. This indicates that samples a, B have a lower activation temperature and a wider temperature window than sample C. More specifically, the catalyst of sample B has the lowest activation temperature and the highest temperature window, and the denitration conversion rate is higher than that of the catalysts of sample a and sample C in all temperature ranges; compared with other types of denitration catalysts, the Fe-based molecular sieve catalyst has higher catalytic activity in a medium-high temperature section.
Its original sourceThis can be interpreted as: it is generally believed that in the SCR reaction, NH3The acid is adsorbed on the acid site of the catalyst and then reacts with NO, so that the acidity is opposite to NH3Adsorption is extremely important. The acid B and the acid L in the molecular sieve can adsorb gaseous NH3And B acid may be reacted with NH3Strong chemical adsorption is formed, and compared with a sample obtained by only carrying out alkali treatment, the sample obtained by the alkali treatment and the acid treatment of the invention has more B acid and can adsorb more NH3. The ZSM-5 molecular sieve is treated in an acid-base composite treatment mode to generate a plurality of mesopores, so that the molecular transmission path is greatly diffused, and the acid site of the molecular sieve catalyst is improved to NH3The adsorption capacity of (1).
The reason why the sample B catalyst prepared by the encapsulation-pyrolysis method has better SCR denitration activity than the sample a catalyst prepared by the impregnation method may be that: in the catalysts prepared by impregnation, the iron species are predominantly in the form of aggregated Fe2O3The form of the Fe-based catalyst exists outside the framework, the Fe species has an agglomeration phenomenon, and the denitration performance of the catalyst is influenced to a certain extent; in the catalyst prepared by the packaging-pyrolysis method, the active component iron species are uniformly dispersed in the molecular sieve pore canal, so that the active component can be prevented from agglomerating into clusters and even agglomerating into large nano particles, and the denitration activity of the obtained catalyst can be further enhanced.
From the above embodiments, it can be seen that the method for pretreating a ZSM-5 molecular sieve by alkali treatment and acid treatment synthesizes a hierarchical pore molecular sieve based denitration catalyst, the preparation method of the hierarchical pore molecular sieve based denitration catalyst is simple to operate, and has the dual advantages of a microporous structure and a mesoporous structure, so that not only can the mass transfer diffusion performance of the reaction be improved, but also more active sites can be exposed on the outer surface of the material, and the catalyst has excellent medium-high temperature denitration activity and a wider temperature window, specifically:
(1) the ZSM-5 molecular sieve is sequentially subjected to alkali treatment and acid treatment, wherein the alkali treatment can effectively remove framework silicon atoms to prepare mesoporous communicated with the outside, an introduced pore channel system can obviously reduce the diffusion limit of reactants in a pore channel, and the alkali treatment process is simple to operate and low in cost;
(2) the acid treatment can effectively wash off amorphous aluminum species remained in the pore channel structure after the alkali treatment, realize the process of dealumination again after desilication, and keep SiO2/Al2O3Thereby preserving the crystallinity of the ZSM-5 molecular sieve; meanwhile, the accessibility of the active sites of the prepared catalyst can be further enhanced during acid treatment, and the denitration reaction activity is effectively improved;
(3) for NH3Selective catalytic reduction of NOx (NH)3SCR) reaction, the acid property of the surface of the catalyst determines the high-temperature denitration reaction activity of the catalyst, and the acid property of the surface of the prepared catalyst is adjusted by sequentially carrying out alkali treatment and acid treatment on the ZSM-5 molecular sieve, so that NH is facilitated3-the performance of an SCR reaction;
(4) the method utilizes a method for loading Fe to modify the ZSM-5 molecular sieve, the Fe is low in price and easy to obtain, and the d orbit of the Fe is not full, so that the Fe has strong oxidation-reduction capability; at the same time, for NH3The low-temperature denitration reaction activity of the SCR catalyst is determined by the redox property of the SCR catalyst, and the active component Fe is highly dispersed on the surface of the SCR catalyst in a packaging-pyrolysis manner, so that the denitration reaction activity can be effectively improved;
(5) the preparation method of the hierarchical pore molecular sieve based denitration catalyst provided by the invention prepares the hierarchical pore molecular sieve based denitration catalyst with iron species as an active center highly dispersed in the pore canal of the hierarchical pore molecular sieve by an encapsulation-pyrolysis method; specifically, in the preparation process, firstly, an iron source (ferrocene) is gasified at the temperature of 300-;
in the preparation method, on one hand, dense pores containing a large number of hydroxyl groups on the surface of the ZSM-5 molecular sieve stabilize uniformly dispersed active component Fe species to a great extent; on the other hand, the ZSM-5 molecular sieve is also an excellent host material, and can encapsulate an iron source in a cage in a molecular form, and then remove an organic ligand in the iron source to release a single isolated Fe atom through simple activation treatment (such as high-temperature roasting), and finally realize that an iron species as an active component is uniformly dispersed in the catalyst. The catalyst prepared by the method has good catalytic activity and product selectivity in catalytic reaction.
The above description is only exemplary of the invention and should not be taken as limiting the scope of the invention, so that the invention is intended to cover all modifications and equivalents of the embodiments described herein. In addition, the technical features and the technical inventions of the present invention, the technical features and the technical inventions, and the technical inventions can be freely combined and used.
Claims (19)
1. A preparation method of a hierarchical pore molecular sieve based denitration catalyst is characterized by comprising the following steps:
sequentially carrying out alkali treatment and acid treatment on the ZSM-5 molecular sieve, and then carrying out suction filtration, washing and drying to obtain the Na-type hierarchical pore ZSM-5 molecular sieve;
carrying out ion exchange on the Na-type hierarchical pore ZSM-5 molecular sieve, and then washing and drying to obtain NH4A type multistage hole ZSM-5 molecular sieve;
to the NH4Roasting the type multistage hole ZSM-5 molecular sieve to obtain an H type multistage hole ZSM-5 molecular sieve;
and loading Fe on the H-type hierarchical pore ZSM-5 molecular sieve by adopting an encapsulation-pyrolysis method to obtain an H-type hierarchical pore Fe/ZSM-5 molecular sieve, and roasting to obtain the hierarchical pore molecular sieve based denitration catalyst.
2. The method according to claim 1, wherein the agent for alkali treatment is an aqueous sodium hydroxide solution having a concentration of 0.2 to 0.6 mol/L.
3. The preparation method of claim 2, wherein the liquid-solid ratio of the aqueous sodium hydroxide solution to the ZSM-5 molecular sieve is 10-40:1, and the units are mL and g respectively.
4. The method as claimed in claim 1 or 2, wherein the temperature of the alkali treatment is 313-363K, and the time is 30-120 min.
5. The method according to claim 1, wherein the acid treatment is carried out using hydrochloric acid as a reagent, and the concentration of the hydrochloric acid is 0.05 to 0.3 mol/L.
6. The preparation method of claim 5, wherein the liquid-solid ratio of the hydrochloric acid to the alkali-treated ZSM-5 molecular sieve is 5-25:1, and the units are mL and g respectively.
7. The method as claimed in claim 1 or 5, wherein the temperature of the acid treatment is 313-363K and the time is 30-120 min.
8. The method according to claim 1, wherein the reagent for ion exchange is NH4Aqueous Cl solution.
9. The method of claim 8, wherein the NH is4The concentration of the Cl aqueous solution is 0.8-1.2 mol/L;
the NH4The liquid-solid ratio of the Cl aqueous solution to the ZSM-5 molecular sieve subjected to alkali treatment and acid treatment is 5-20:1, and the units are mL and g respectively.
10. The method as claimed in any one of claims 1 and 8 to 9, wherein the temperature of the ion exchange is 323-363K, and the time is 60 to 180 min.
11. The method as claimed in claim 1, wherein the calcination is carried out at 500-600 ℃ for 4-8 h.
12. The preparation method according to claim 1, wherein the iron source for loading Fe by the encapsulation-pyrolysis method is ferrocene.
13. The method of manufacturing according to claim 1 or 12, wherein the encapsulation-pyrolysis method comprises:
under the condition that the nitrogen flow is 3-20mL/min, the temperature of the system is raised to 500 ℃ at the temperature rise rate of 2-5 ℃/min, and the iron source is gasified and packaged for 30-120min at 500 ℃ of 300-; then the temperature of the system is raised to 400-700 ℃ at the temperature raising rate of 2-5 ℃/min, and the iron source is carbonized for 1-3h at 400-700 ℃.
14. The preparation method according to claim 1, wherein the supported amount of Fe in the hierarchical pore molecular sieve based denitration catalyst is 3 to 10% based on 100% by weight of the total hierarchical pore molecular sieve based denitration catalyst.
15. The multi-stage pore molecular sieve-based denitration catalyst obtained by the method for preparing a multi-stage pore molecular sieve-based denitration catalyst according to any one of claims 1 to 14, wherein iron species are highly dispersed as active centers in the pores of the multi-stage pore molecular sieve.
16. The use of the hierarchical pore molecular sieve based denitration catalyst of claim 15 in a flue gas denitration treatment process.
17. A flue gas denitration treatment method is characterized by comprising the following steps:
denitrating flue gas in the presence of a reducing agent and the hierarchical pore molecular sieve based denitration catalyst of claim 15.
18. The method of claim 17, wherein the reductant comprises NH3。
19. The method as claimed in claim 17 or 18, wherein the denitration catalyst is calculated according to the following formula 1) and has a space velocity of 30000-48000h-1The temperature is 100 ℃ and 600 ℃, NO and reducing agent NH in the flue gas3In a molar ratio of 0.5-2, flue gas and a reducing agent NH3The total volume flow of the flow rate is 500 mL/min;
in the formula 1), m is the dosage of the denitration catalyst and the unit is g;
vs is flue gas and reducing agent NH3The unit of the total volume flow of (1) is mL/min;
GHSV is space velocity in h-1；
Rho is the density of the denitration catalyst and is in g/cm3。
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