CN108579756B - Laminaria-shaped Mn-Fe bimetal oxide loaded CeO2Catalyst, preparation method and application - Google Patents
Laminaria-shaped Mn-Fe bimetal oxide loaded CeO2Catalyst, preparation method and application Download PDFInfo
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Abstract
The invention belongs to the field of flue gas denitration, and particularly relates to kelp-shaped Mn-Fe bimetal oxide loaded CeO2Low temperature flue gas denitration catalyst. Aiming at the problems that the existing supported denitration catalyst has low selectivity, poor specificity, non-uniformity, poor stability, low efficiency, difficult fixation of active components on a catalyst carrier, narrow catalyst activity window in the actual use of a flue gas pipeline and easy SO (sulfur oxide) absorption2Poisoning and the like, provides a kelp-like bimetal oxide Mn-Fe loaded CeO2A preparation method of a low-temperature flue gas denitration catalyst. The Mn-Fe bimetallic oxide with a folded sea belt shape is prepared by a hydrothermal-calcination method to be used as a carrier, and meanwhile, the Mn-Fe bimetallic oxide can also be used as a low-temperature active component to load CeO2The particles improve the sulfur resistance, and are the environment-friendly NH with wide application prospect3-an SCR denitration catalyst.
Description
Technical Field
The invention belongs to the field of flue gas denitration, and particularly relates to kelp-shaped Mn-Fe bimetal oxide loaded CeO2Low temperature flue gas denitration catalyst.
Background
With the explosive increase in the number of global vehicles and the burning of fossil energy, NOx(NO/N2O/NO2) Row of (2)The release amount increases year by year. Causes a plurality of environmental problems such as acid rain, chemical smog and the like, and causes great pollution to the living environment of people. Thus chemically treating NO emitted from the environmentx(NO/N2O/NO2) To make it nontoxic N2Becomes very important. Selective Catalytic Reduction (SCR) is the most widely used flue gas denitration technology in the world today. The method adopts NH3As a reducing agent, reducing NOx to N2. The denitration catalysts most applied to the power plant at present are V-W-Ti series of catalysts, and have the advantages of high activity and good sulfur resistance, but the denitration activity temperature window of the denitration catalysts is 400 ℃ of 300-.
Mn element has a plurality of valence states such as +2, +4, +6, +7 and the like, and activation energy required for conversion between valence states is low, so that the Mn element has excellent denitration performance at low temperature, and is a recognized active component of a low-temperature denitration catalyst, but MnO is used for preparing the Mn element2It also has a number of disadvantages, e.g. SO resistance2Poor performance, poor water resistance, easy agglomeration of the catalyst at high temperature and the like, thereby changing MnO2The defects become important research points in the denitration field in recent years, and MnO is mainly improved by doping or compounding metal oxides such as Fe, V, Cr and the like2Surface acidity or specific surface area of (2), reduction of SO2For MnO2The toxic action of the above-mentioned drugs. However, the active components are mainly granular, have small specific surface area, and are easy to agglomerate at high temperature or in the presence of water vapor, so that the activity is reduced.
The invention patent with Chinese patent application number CN201510407537.4 discloses an anti-SO2And H2An O-poisoned low-temperature denitration catalyst and a preparation method thereof. The preparation of the catalyst of this patent selects a honeycomb ceramic matrix, first impregnated with TiO2-molecular sieve composite sol coating TiO2Molecular sieve coating, and finally impregnation loading of active components Mn, Fe, Ce and Sn. The method obtains better denitration performance and sulfur resistance. However, the method still has the following disadvantages: (1) Mn-Fe-Ce-Sn active component is prepared by impregnation processA carrier is supported, severe agglomeration is easily caused, and distribution may be uneven, (2) a honeycomb ceramic substrate is used as a catalyst carrier, which has no catalytic activity per se and wastes materials.
Disclosure of Invention
Aiming at the problems of low selectivity, poor specificity, non-uniformity, poor stability, low efficiency, difficult fixation of active components on a catalyst carrier, narrow catalyst activity window in the actual use of a flue gas pipeline, low-temperature activity and SO resistance of the traditional supported denitration catalyst2Poor performance and the like, and provides a hydrothermal-calcination method for preparing sea-belt-shaped Mn-Fe bimetallic oxide loaded CeO2A preparation method of a low-temperature flue gas denitration catalyst. The catalyst prepared by the invention has simple conditions, high activity, wide active temperature range and H resistance2O anti-SO2The performance is superior, and the blockage is not easy to happen in the actual use. In addition, the kelp-shaped bimetallic oxide prepared by the method has both the catalyst activity and the carrier characteristic, and the catalyst cost is saved.
The technical scheme adopted by the invention is as follows: laminaria-shaped Mn-Fe bimetal oxide loaded CeO2Catalyst, and Mn-Fe bimetal oxide loaded CeO with folded sea belt shape prepared by hydrothermal-calcination method2The catalyst comprises a carrier and a low-temperature active component, wherein a sea-belt-shaped Mn-Fe bimetallic oxide is used as the carrier and the low-temperature active component simultaneously and is loaded with CeO2The sulfur resistance of the particles is improved, the molar ratio of the manganese source to the iron source in the catalyst is 1:1, and the molar ratio of the Mn source to the Ce source is 2: 1.
The above-mentioned wrinkled sea-belt-shaped CeO2-MnFeOXThe preparation method of the catalyst comprises the following steps:
(1) respectively dissolving a certain amount of manganese acetate and ferric sulfate in deionized water, and performing ultrasonic dispersion to obtain a manganese acetate solution and a ferric sulfate solution;
(2) uniformly mixing the manganese acetate solution obtained in the step (1) with a ferric sulfate solution, adding urea, and magnetically stirring for 0.5h at room temperature to obtain a mixed solution;
the invention prepares the metal salt solution, and carries out ultrasonic dispersion, so that the metal salt mixed solution is fully dissolved firstly, and then the urea is added, which is beneficial to the uniformity of the formation of the sea-tangle catalyst in the later period.
(3) Adding an aqueous ammonia solution dropwise into the mixed solution prepared in the step (2) while stirring, adjusting the pH to 10, and continuing stirring for 3 hours.
(4) And (4) transferring the mixed solution obtained in the step (3) into a polytetrafluoroethylene hydrothermal kettle with the volume capacity of 100ml for reaction, performing suction filtration, washing and drying to obtain the folded sea-tangle-shaped Mn-Fe composite oxide catalyst precursor.
(5) Taking the catalyst precursor in the step (4), dissolving the catalyst precursor in 200ml of deionized water, and adding a certain amount of Ce (NO)3)3·6H2Adjusting pH to 10 with ammonia water, filtering, washing, oven drying, and calcining to obtain CeO2-MnFeOXA catalyst.
The generation principle of the corrugated catalyst of the invention is as follows: the method comprises the steps of generating granular precipitated crystal seeds from Mn-Fe metal salt mixed liquor under the condition that the pH value is about 10, transferring the crystal seeds into a hydrothermal kettle, enabling the crystal seeds to only extend into a sheet-shaped precursor in a one-way mode in a high-temperature high-pressure reaction system, filtering out the precursor after the reaction is finished, calcining, and enabling the sheet-shaped structure to start to break and collapse in the high-temperature calcining process, losing the complete morphology and becoming a wrinkle shape, and increasing surface defects and improving the reaction activity due to the wrinkle sea-belt shape.
Wherein the molar ratio of manganese acetate, ferric sulfate and urea in the step (2) is 1:1: 3.
In the step (4), the reaction temperature in the hydrothermal kettle is as follows: the reaction time is 3-6 h at 90 ℃.
In the step (5), the roasting is carried out in a muffle furnace at 500 ℃ for 3 h.
The sea-belt-shaped Mn-Fe bimetal oxide load CeO2The catalyst is used for low-temperature flue gas denitration.
In practical application, in order to keep the air flow unobstructed, the contact area of the flue gas and the catalyst is increased, and the blockage of the catalyst by dust or particles is reduced. The catalyst can be made into a honeycomb type or a corrugated plate type and placed in an SCR denitration reactor, is arranged behind a dust remover and an FGD desulfurization device, and is applied to low-temperature flue gas denitration.
The catalyst is made into a honeycomb type or a corrugated plate type and is placed in the SCR denitration reactor and arranged behind the dust remover and the FGD desulfurization device, so that the full contact between gas and the kelp-shaped catalyst is facilitated, the advantage of large specific surface area of the kelp-shaped catalyst can be fully exerted, and the low-temperature flue gas denitration effect is better.
The invention has the beneficial effects that:
1. the invention prepares a sea-belt-shaped ferromanganese bimetal composite oxide with folds, the large-sheet-shaped composite has larger attachment surface, can be used as a carrier to fully load other active components, simultaneously consists of the ferromanganese composite and also serves as the active component, so that the active component is more fully exposed outside, and NH is improved3The adsorption of gas further improves the catalytic activity.
2. Compared with the traditional impregnation method, the method can be prepared in low-temperature hydrothermal, the conditions are simple, and then the active components are combined more firmly and distributed more uniformly through roasting, so that the active components are not easy to fall off in actual use.
3. The method uses Ce as an auxiliary element, the granular cerium oxide is dispersed on the kelp-shaped bimetallic oxide, and the Ce and Mn-Fe interact with each other to increase oxygen vacancy, improve catalytic activity and reduce SO2The sulfur resistance is increased on the surface of the generated ammonium sulfate deposited catalyst, and the service life and reversibility of the catalyst are improved.
Drawings
FIG. 1 shows a Laminaria-like MnFeO obtained in example 1XSEM pictures of (d).
FIG. 2 shows the Laminaria-like MnFeO obtained in example 1XLoaded with CeO2SEM pictures of the catalyst.
Detailed Description
The specific description of the sea-band-like supported CeO by the Mn-Fe bimetal oxide will be made with reference to the following examples and comparative examples2Low temperature flue gas denitration catalyst.
Example 1
(1) Respectively dissolving 1.5g of manganese acetate and 2.5g of ferric sulfate in deionized water, and performing ultrasonic dispersion to obtain a manganese acetate solution and a ferric sulfate solution;
(2) uniformly mixing the manganese acetate solution obtained in the step (1) with a ferric sulfate solution, adding 1.6g of urea, and magnetically stirring at room temperature for 0.5h to obtain a mixed solution;
(3) adding an aqueous ammonia solution dropwise into the mixed solution prepared in the step (2) while stirring, adjusting the pH to 10, and continuing stirring for 3 hours.
(4) Transferring the mixed solution obtained in the step (3) to a polytetrafluoroethylene hydrothermal kettle with the volume capacity of 100ml for reaction for 6 hours at the temperature of 90 ℃. And (4) carrying out suction filtration, washing and drying to obtain the folded sea-tangle-shaped Mn-Fe composite oxide catalyst precursor.
(5) Taking the catalyst in the step (4), dissolving the catalyst in 200ml of deionized water, and adding 1.9g of Ce (NO)3)3·6H2And O, adjusting the pH value to 10 by ammonia water, performing suction filtration, washing, drying, and roasting in a muffle furnace at 500 ℃ for 3 hours to obtain the large-fold sea-belt-shaped CeO2-MnFeOXA catalyst.
FIG. 1 shows a kelp-like MnFeOXSEM pictures of (d). As shown in the figure, the ferromanganese composite oxide is in a folded sheet shape, is similar to kelp, and has a large specific surface area.
FIG. 2 shows a kelp-like MnFeOXLoaded with CeO2SEM pictures of the catalyst. As shown, the manganese iron sea-belt-like oxide surface contained particulate ceria, indicating that ceria was successfully supported on the surface of this large bimetallic composite oxide.
a. The catalyst is made into a honeycomb type, placed in an SCR denitration reactor, arranged behind a dust remover and an FGD desulfurization device, and applied to low-temperature flue gas denitration.
b. The catalyst is made into a corrugated plate type, placed in an SCR denitration reactor, arranged behind a dust remover and an FGD desulfurization device, and applied to low-temperature flue gas denitration.
c. The catalyst is made into a flat plate type, placed in an SCR denitration reactor, arranged behind a dust remover and an FGD desulfurization device, and applied to low-temperature flue gas denitration.
Comparative example 1
(1) Respectively dissolving 1.5g of manganese acetate and 2.5g of ferric sulfate in deionized water, and performing ultrasonic dispersion to obtain a manganese acetate solution and a ferric sulfate solution;
(2) uniformly mixing the manganese acetate solution obtained in the step (1) with a ferric sulfate solution, adding 1.6g of urea, and magnetically stirring at room temperature for 0.5h to obtain a mixed solution;
(3) adding an aqueous ammonia solution dropwise into the mixed solution prepared in the step (2) while stirring, adjusting the pH to 10, and continuing stirring for 3 hours.
(4) Transferring the mixed solution obtained in the step (3) to a polytetrafluoroethylene hydrothermal kettle with the volume capacity of 100ml to react for 3 hours at the temperature of 90 ℃. And (4) carrying out suction filtration, washing and drying to obtain the folded sea-tangle-shaped Mn-Fe composite oxide catalyst precursor.
(5) Taking the catalyst in the step (4), dissolving the catalyst in 200ml of deionized water, and adding 1.9g of Ce (NO)3)3·6H2And O, adjusting the pH value to 10 by ammonia water, performing suction filtration, washing, drying, and roasting in a muffle furnace at 500 ℃ for 3 hours to obtain the small-fold sea-belt-shaped CeO2-MnFeOXA catalyst.
The catalyst is made into a honeycomb type, placed in an SCR denitration reactor, arranged behind a dust remover and an FGD desulfurization device, and applied to low-temperature flue gas denitration.
Comparative example 2
(1) Respectively dissolving 1.5g of manganese acetate and 2.5g of ferric sulfate in deionized water, and performing ultrasonic dispersion to obtain a manganese acetate solution and a ferric sulfate solution;
(2) uniformly mixing the manganese acetate solution obtained in the step (1) with a ferric sulfate solution, adding 1.6g of urea, and magnetically stirring at room temperature for 0.5h to obtain a mixed solution;
(3) adding an aqueous ammonia solution dropwise into the mixed solution prepared in the step (2) while stirring, adjusting the pH to 10, and continuing stirring for 3 hours.
(4) Transferring the mixed solution obtained in the step (3) to a polytetrafluoroethylene hydrothermal kettle with the volume capacity of 100ml to react for 1h at the temperature of 90 ℃. And (4) carrying out suction filtration, washing and drying to obtain the folded sea-tangle-shaped Mn-Fe composite oxide catalyst precursor.
(5) Taking the catalyst in the step (4), dissolving the catalyst in 200ml of deionized water, and adding 1.9g of Ce (NO)3)3·6H2Regulating pH to 10 with ammonia water, filtering, washing and stoving to obtain lump CeO2-MnFeOXA catalyst.
The catalyst is made into a honeycomb type, placed in an SCR denitration reactor, arranged behind a dust remover and an FGD desulfurization device, and applied to low-temperature flue gas denitration.
Comparative example 3
(1) Respectively dissolving 1.5g of manganese acetate and 2.5g of ferric sulfate in deionized water, and performing ultrasonic dispersion to obtain a manganese acetate solution and a ferric sulfate solution;
(2) uniformly mixing the manganese acetate solution obtained in the step (1) with a ferric sulfate solution, adding 1.6g of urea, and magnetically stirring at room temperature for 0.5h to obtain a mixed solution;
(3) continuing to add 1.9g of Ce (NO) into the mixed solution prepared in step (2)3)3·6H2And O, dropwise adding an ammonia water solution while stirring, adjusting the pH to 10, and continuing stirring for 3 hours.
(4) Filtering the mixed solution, washing, drying, and roasting in a muffle furnace at 500 ℃ for 3h to obtain granular Ce-MnFeOXA composite oxide catalyst.
The catalyst is made into a honeycomb type, placed in an SCR denitration reactor, arranged behind a dust remover and an FGD desulfurization device, and applied to low-temperature flue gas denitration.
Comparative example 4
(1) Respectively dissolving 1.5g of manganese acetate and 2.5g of ferric sulfate in deionized water, and performing ultrasonic dispersion to obtain a manganese acetate solution and a ferric sulfate solution;
(2) uniformly mixing the manganese acetate solution obtained in the step (1) with a ferric sulfate solution, adding 1.6g of urea, and magnetically stirring at room temperature for 0.5h to obtain a mixed solution;
(3) adding an aqueous ammonia solution dropwise into the mixed solution prepared in the step (2) while stirring, adjusting the pH to 10, and continuing stirring for 3 hours.
(4) Transferring the mixed solution obtained in the step (3) to a polytetrafluoroethylene hydrothermal kettle with the volume capacity of 100ml for reaction for 6 hours at the temperature of 90 ℃. And (4) carrying out suction filtration, washing and drying to obtain the Mn-Fe composite oxide catalyst precursor.
(5) Taking the catalyst in the step (4), dissolving the catalyst in 200ml of deionized water, and adding 1.9g of Ce (NO)3)3·6H2Regulating pH to 10 with ammonia water, filtering, washing, drying, and calcining at 500 deg.C in muffle furnace for 1 hr to obtain smooth sheet-shaped CeO2-MnFeOXA catalyst.
The catalyst is made into a honeycomb type, placed in an SCR denitration reactor, arranged behind a dust remover and an FGD desulfurization device, and applied to low-temperature flue gas denitration.
Comparative example 5
The cerium nitrate hexahydrate in the catalyst in the example 1 is removed, and the specific operation steps are as follows:
(1) respectively dissolving 1.5g of manganese acetate and 2.5g of ferric sulfate in deionized water, and performing ultrasonic dispersion to obtain a manganese acetate solution and a ferric sulfate solution;
(2) uniformly mixing the manganese acetate solution obtained in the step (1) with a ferric sulfate solution, adding 1.6g of urea, and magnetically stirring at room temperature for 0.5h to obtain a mixed solution;
(3) adding an aqueous ammonia solution dropwise into the mixed solution prepared in the step (2) while stirring, adjusting the pH to 10, and continuing stirring for 3 hours.
(4) Transferring the mixed solution obtained in the step (3) to a polytetrafluoroethylene hydrothermal kettle with the volume capacity of 100ml for reaction for 6 hours at the temperature of 90 ℃. Filtering, washing, drying, and roasting in a muffle furnace at 500 ℃ for 3h to obtain folded sea-belt-shaped MnFeOXA composite oxide catalyst.
The catalyst is made into a honeycomb type, placed in an SCR denitration reactor, arranged behind a dust remover and an FGD desulfurization device, and applied to low-temperature flue gas denitration.
Performance test of catalyst for low-temperature flue gas denitration
The invention carries out activity test on an SCR-photocatalysis dual-purpose fixed bed, measures about 3mL of catalyst and places the catalyst in a fixed bed quartz tube reactor, adopts a high-precision mass flowmeter (seven-star Huachuang, D07-19B type) to accurately control the flow of inlet gas, and uses N2As carrier gas, the gas composition is: [ NO ]]＝1000ppm、[NH3]＝1000ppm、 SO2＝300ppm、O23 vol% and reaction space velocity of 45000h-1Continuously ventilating for 30min before testing to make the catalyst adsorb and saturate so as to eliminate NOxThe concentration is reduced by the adsorption. Simultaneously, a KM9106 flue gas analyzer produced by Germany Kane company is used for detecting the import concentration to obtain accurate import NOxConcentration, [ NO ]x]in. Then gradually increasing the temperature and detecting NO at the outletxConcentration, [ NO ]x]out. According to the requirement of the reaction temperature, gradually raising the reaction temperature, and reading NO at the outlet at the temperature after stabilizing every 20 DEG CxThe concentrations and measurement data are shown in Table 1.
The calculation formula of the denitration efficiency is as follows:
table 1 denitration performance evaluation test data
As can be seen from Table 1, the Laminaria-like Mn-Fe bimetal oxide load CeO prepared by the invention2The low-temperature flue gas denitration catalyst has lower activity temperature, wider activity temperature range and excellent SO resistance2And (4) performance.
For comparative examples 1 to 3, the reaction time decreased from the wrinkled kelp shape to smaller wrinkled kelp shape, lump shape and granular shape, and the activity gradually decreased. It is shown that the reaction time becomes short, the reaction of Mn and Fe is not completely molded, the adhesion surface is lowered, and oxygen vacancies generated in the Mn-Fe double metal oxide are reduced, resulting in non-uniform dispersion of the particulate cerium oxide, and impaired sulfur resistance and activity. Compared with a wrinkled kelp-shaped structure, the specific surface area is small, the structure is unstable and easy to agglomerate, so that the reducing gas cannot be fully combined with the catalyst, and the activity of the catalyst is reduced. In comparative example 4, the firing time was shortened, and the surface of the resulting metal oxide was relatively smooth, and compared to example 1, the surface was not rough enough, the active sites were reduced, and the properties were deteriorated. Comparative example 5, in which cerium oxide was not added, decreased the acid sites provided by cerium, resulting in decreased sulfur resistance.
Claims (3)
1. Laminaria-shaped Mn-Fe bimetal oxide loaded CeO2The preparation method of the catalyst is characterized by comprising the following steps: the preparation method comprises the following steps:
(1) respectively dissolving manganese acetate and ferric sulfate in deionized water, and performing ultrasonic dispersion to obtain a manganese acetate solution and a ferric sulfate solution;
(2) uniformly mixing the manganese acetate solution obtained in the step (1) with a ferric sulfate solution, adding urea, and magnetically stirring for 0.5h at room temperature to obtain a mixed solution;
(3) dropwise adding an ammonia water solution into the mixed solution prepared in the step (2) while stirring, adjusting the pH to =10, and continuously stirring for 3 hours;
(4) transferring the mixed solution obtained in the step (3) into a polytetrafluoroethylene hydrothermal kettle with the volume capacity of 100ml for reaction, performing suction filtration, washing and drying to obtain a folded sea-belt-shaped Mn-Fe composite oxide catalyst precursor;
the hydrothermal reaction temperature is as follows: the reaction time is 3-6 h at 90 ℃;
(5) dissolving the catalyst precursor obtained in the step (4) in 200ml of deionized water, and adding Ce (NO)3)3·6H2O, adjusting the pH value to be =10 by ammonia water, filtering, washing, drying and roasting to obtain CeO2-MnFeOXA catalyst;
the roasting is carried out for 3 hours in a muffle furnace at 500 ℃;
the catalyst takes a sea-belt-shaped ferromanganese composite oxide as a carrier, and simultaneously as a main catalyst and a loaded cocatalyst CeO2Wherein the molar ratio of the Mn source to the Fe source in the catalyst is 1:1, and the molar ratio of the Mn source to the Ce source is 2: 1.
2. The Laminaria-like Mn-Fe bimetal oxide-loaded CeO according to claim 12The preparation method of the catalyst is characterized by comprising the following steps: in the step (2), the molar ratio of manganese acetate, ferric sulfate and urea is 1:1: 3.
3. The Laminaria-like Mn-Fe bimetal oxide-loaded CeO as claimed in claim 12Application of catalystThe method is characterized in that: the catalyst is made into a honeycomb type, a corrugated plate type or a flat plate type, is placed in an SCR denitration reactor, is arranged behind a dust remover and an FGD desulfurization device, and is applied to low-temperature flue gas denitration.
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