Vanadium-substituted heteropoly acid SCR catalyst and preparation method thereof
阅读说明：本技术 钒取代型杂多酸scr催化剂及其制备方法 (Vanadium-substituted heteropoly acid SCR catalyst and preparation method thereof ) 是由 徐刚 刘琦 王世豪 于 2020-05-18 设计创作，主要内容包括：本发明公开了一种钒取代型磷钨杂多酸催化剂及其制备方法,属于大气污染控制技术领域。该复合氧化物催化剂采用乙醚萃取法与浸渍法制备,其特点是磷钨钒三组分间的协同效应使其具有良好的脱硝性能。本发明所制备的复合氧化物催化剂,在300～450℃的温度范围内,氮氧化物脱除效率能够达到90％以上且具有良好的氮气选择性和抗水抗硫性,可用于燃煤电厂、工业锅炉、建材炉窑等固定源及柴油车移动源排放氮氧化物的脱除,具有良好的应用前景。(The invention discloses a vanadium-substituted phosphotungstic heteropoly acid catalyst and a preparation method thereof, belonging to the technical field of atmospheric pollution control. The composite oxide catalyst is prepared by an ether extraction method and an impregnation method, and is characterized in that the synergistic effect among three components of phosphorus, tungsten and vanadium ensures that the composite oxide catalyst has good denitration performance. The composite oxide catalyst prepared by the invention has the nitrogen oxide removal efficiency of over 90 percent in the temperature range of 300-450 ℃, has good nitrogen selectivity and water and sulfur resistance, can be used for removing nitrogen oxide discharged from fixed sources such as coal-fired power plants, industrial boilers, building material furnaces and the like and mobile sources of diesel vehicles, and has good application prospect.)
1. Vanadium-substituted heteropoly acid SCR catalystCharacterized in that it has the chemical formula ER12-xVx/TiO2Wherein the non-metal element E is P or Si, the metal element R is W or Mo, and TiO2The mass fraction of the heteropoly acid in the catalyst is 10-30 wt.%, x represents the substitution number of vanadium atoms, the value of x is not more than 3, and the vanadium atoms are used for substituting heteroatoms in heteropoly acid molecules, so that the vanadium-substituted heteropoly acid compound has SCR activity.
2. The vanadium-substituted heteropoly acid SCR catalyst of claim 1, wherein: the heteropoly acid molecules substituted by vanadium atoms are phosphotungstic acid, phosphomolybdic acid, silicotungstic acid or silicomolybdic acid molecules.
3. The vanadium-substituted heteropoly acid SCR catalyst of claim 1, wherein: the mass fraction of heteropolyacid in the catalyst is 15-30 wt.%.
4. The vanadium-substituted heteropolyacid SCR catalyst according to any one of claims 1 to 3, characterized in that: the heteropoly acid is phosphotungstic heteropoly acid, and the compound molecule of the heteropoly acid is PW12-xVx/TiO2The mass fraction of the heteropoly acid in the catalyst is 10-30 wt.%, x represents the substitution number of vanadium atoms, and the value of x is (1-3).
5. A method for preparing the vanadium-substituted heteropoly acid SCR catalyst according to claim 1, comprising the steps of:
a. dissolving a metalate and a non-metalate which have a molar ratio of metal atoms to non-metal atoms of 10:1 as reactants in water, fully mixing, and reacting at 80-100 ℃ for at least 30 minutes, wherein the non-metal element in the non-metalate is P or Si, and the metal element in the metalate is W or Mo;
b. dissolving vanadate in water to obtain a vanadate solution, wherein the molar ratio of vanadium atoms to non-metal atoms in the step a is 2x:1, adding the vanadate solution into the product solution in the step a, and continuing to react for at least 30 minutes, wherein the value of x is (0.5-1.5);
c. adding a proper amount of dilute sulfuric acid with the mass percentage concentration not higher than 50 wt.% into the product solution in the step b, adjusting the pH of the solution to be 1.8-3.0, and continuing the reaction for at least 1 hour;
d. transferring the product solution reacted in the step c to a separating funnel, continuously dropwise adding 50 wt.% dilute sulfuric acid in the extraction process by adopting an ether extraction method, taking down the oily substance in the lower layer after extraction, removing ether, recrystallizing and drying to obtain vanadium-substituted heteropoly acid;
e. loading the vanadium-substituted heteropoly acid prepared in the step d in anatase TiO by adopting an impregnation method2Wherein the mass fraction of the heteropoly acid is heteropoly acid and anatase TiO210-30 wt.% of the total mass, stirring the heteropolyacid and anatase TiO at room temperature2For 2-5 hours to obtain a slurry-like mixture;
f. naturally drying the slurry mixture obtained in the step e, or drying the slurry mixture in a vacuum drying oven at 60-90 ℃ for 6-12 hours, and then roasting the slurry mixture at 400-500 ℃ for 2-4 hours to obtain the vanadium-substituted heteropoly acid SCR catalyst.
6. The method for preparing the vanadium-substituted heteropoly acid SCR catalyst according to claim 5, wherein: in the step a, the reaction temperature is 90-100 ℃.
7. The method for preparing the vanadium-substituted heteropoly acid SCR catalyst according to claim 5, wherein: in said step b, the vanadium to non-metal atomic ratio is 2:1, i.e. x ═ 1.
8. The method for preparing the vanadium-substituted heteropoly acid SCR catalyst according to claim 5, wherein: in the step c, the pH of the solution is adjusted to 2.0-3.0, and the reaction is continued.
9. The method for preparing the vanadium-substituted heteropoly acid SCR catalyst according to claim 5, wherein: in the step e, the mass fraction of the heteropoly acid is 15-30 wt.%, and the stirring time is 3-5 hours.
10. The method for preparing the vanadium-substituted heteropoly acid SCR catalyst according to claim 5, wherein: in the step f, drying for 8-12 hours at 70-90 ℃ in a vacuum drying oven, wherein the roasting temperature is 450-500 ℃ and the roasting time is 4 hours.
Technical Field
The invention relates to an SCR catalyst and a preparation method thereof, in particular to a heteropoly acid SCR catalyst and a preparation method thereof, belonging to the technical field of preparation of catalytic materials and the technical field of air pollution control.
Background
Atmospheric environmental protection is related to human survival and development, currently, the situation of atmospheric pollution in major industrially developed countries in the world is severe, regional atmospheric environmental problems are increasingly prominent, particularly, opportunities for industrial revolution are missed in the economic development process of third world countries, the situation of changing pollution into economic development is still difficult to get rid of in the current economic process, but most developing countries have realized that the traditional industrial development path is difficult to continue, and the atmospheric control strategy advocated by the countries is developed, so that remarkable effects are achieved. Wherein, in 6 months in 2013, the air pollution control action plan of China firstly mentions the new height of the air pollution control as one of the main air pollutants, namely Nitrogen Oxide (NO)x) Emission standards are also becoming more stringent. Most of the compounds have toxicity, can induce acid rain to cause ozone holes, have serious damage effect on the environment and cause great harm to human health. Emission control has become a research focus in the field of environmental catalysis and atmospheric control. Selective catalytic reduction of nitrogen oxides NH by ammonia gas3SCR is the most widely used technology for removing nitrogen oxides at present, and a high-efficiency and stable catalyst is the key of the SCR technology.
Currently, the industrial application of the mature NH is3The SCR catalyst is a V-based catalyst which, although having good SCR catalytic activity, has some unavoidable disadvantages, such as V2O5Has the advantages of biological toxicity, narrow active temperature window and N at high temperature2Poor selectivity, etc., which greatly limits their further industrial applications. Therefore, development of a compound having better N2The novel environment-friendly SCR catalyst with selectivity and wide temperature window becomes a technical problem to be solved urgently.
Disclosure of Invention
In order to solve the problems of the prior art, the invention aims to overcome the defects in the prior art and provide the vanadium-substituted heteropoly acid SCR catalyst and the preparation method thereof.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
a vanadium-substituted heteropoly acid SCR catalyst with chemical formula of ER12-xVx/TiO2Wherein the non-metal element E is P or Si, the metal element R is W or Mo, and TiO2The mass fraction of the heteropoly acid in the catalyst is 10-30 wt.%, x represents the substitution number of vanadium atoms, the value of x is not more than 3, and the vanadium atoms are used for substituting heteroatoms in heteropoly acid molecules, so that the vanadium-substituted heteropoly acid compound has SCR activity.
As a preferred technical scheme of the invention, the heteropoly acid molecules substituted by vanadium atoms are phosphotungstic acid, phosphomolybdic acid, silicotungstic acid or silicomolybdic acid molecules.
As a preferred technical scheme of the invention, the mass fraction of the heteropoly acid in the catalyst is 15-30 wt.%. More preferably, the mass fraction of heteropolyacid is 15 wt.%.
As a preferable technical scheme of the invention, the heteropoly acid is phosphotungstic heteropoly acid, and the compound molecule of the heteropoly acid is PW12-xVx/TiO2The mass fraction of the heteropoly acid in the catalyst is 10-30 wt.%, x represents the substitution number of vanadium atoms, and the value of x is (1-3). More preferably, the substitution number of the vanadium atom is 1, i.e., x is 1.
The invention relates to a preparation method of a vanadium-substituted heteropoly acid SCR catalyst, which comprises the following steps:
a. dissolving a metalate and a non-metalate which have a molar ratio of metal atoms to non-metal atoms of 10:1 as reactants in water, fully mixing, and reacting at 80-100 ℃ for at least 30 minutes, wherein the non-metal element in the non-metalate is P or Si, and the metal element in the metalate is W or Mo; preferably, tungstate and phosphate with the molar concentration ratio of tungsten atoms to phosphorus atoms of 10:1 are taken as reactants and dissolved in water for fully mixing;
b. dissolving vanadate in water to obtain a vanadate solution, wherein the molar ratio of vanadium atoms to non-metal atoms in the step a is 2x:1, adding the vanadate solution into the product solution in the step a, and continuing to react for at least 30 minutes, wherein the value of x is (0.5-1.5);
c. adding a proper amount of dilute sulfuric acid with the mass percentage concentration not higher than 50 wt.% into the product solution in the step b, adjusting the pH of the solution to be 1.8-3.0, and continuing the reaction for at least 1 hour;
d. transferring the product solution reacted in the step c to a separating funnel, continuously dropwise adding 50 wt.% dilute sulfuric acid in the extraction process by adopting an ether extraction method, taking down the oily substance in the lower layer after extraction, removing ether, recrystallizing and drying to obtain vanadium-substituted heteropoly acid;
e. loading the vanadium-substituted heteropoly acid prepared in the step d in anatase TiO by adopting an impregnation method2Wherein the mass fraction of the heteropoly acid is heteropoly acid and anatase TiO210-30 wt.% of the total mass, stirring the heteropolyacid and anatase TiO at room temperature2For 2-5 hours to obtain a slurry-like mixture;
f. naturally drying the slurry mixture obtained in the step e, or drying the slurry mixture in a vacuum drying oven at 60-90 ℃ for 6-12 hours, and then roasting the slurry mixture at 400-500 ℃ for 2-4 hours to obtain the vanadium-substituted heteropoly acid SCR catalyst.
As a preferred technical scheme of the invention, in the step a, the reaction temperature is 90-100 ℃. More preferably, the reaction temperature is 90 ℃.
As a preferred embodiment of the present invention, in step b, the atomic ratio of vanadium to nonmetal is 2:1, i.e., x is 1.
As a preferable embodiment of the present invention, in step c, the pH of the solution is adjusted to 2.0 to 3.0, and the reaction is continued. More preferably, the pH is 2.
As a preferred technical solution of the present invention, in step e, the mass fraction of the heteropoly acid is 15-30 wt.%, and the stirring time is at least 3 hours. More preferably, the mass fraction of heteropolyacid is 15 wt.%, and the stirring time is 3-5 hours.
As a preferred technical scheme of the invention, in the step f, drying is carried out for 8-12 hours in a vacuum drying oven at 70-90 ℃, the roasting temperature is 450-500 ℃, and the roasting time is 4 hours. More preferably, the mass fraction of heteropolyacid is 15 wt.%, and the stirring time is 3 hours.
Further, the method comprises the following steps: putting a proper amount of the obtained catalyst into a continuous flow fixed bed reactor, wherein the reaction gas in the fixed bed reactor comprises 0.05 percent of NO and 0.05 percent of NH in percentage by mass3And 5% of O2By using N2As balance gas, the flow rate of the reaction gas is 300mL/min, and the space velocity is 90000cm3/(g.h), about 45500h-1The activity evaluation temperature range was 200-450 ℃, and the catalysts were then tested for nitrogen oxide conversion and nitrogen selectivity ratio.
Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:
1. according to the invention, vanadium atoms are adopted to substitute heteroatoms in heteropoly acid molecules to endow the heteropoly acid molecules with good oxidation-reduction performance, so that the heteropoly acid molecules can be used for SCR reaction; the titanium dioxide mainly exists in the form of anatase titanium dioxide which is beneficial to denitration reaction; meanwhile, the transfer of electrons among active components is promoted by the synergistic catalytic action of vanadium, tungsten and titanium, the oxygen content on the surface of the catalyst is increased, the adsorption and activation of reactant molecules are promoted, the denitration performance of the catalyst is effectively improved, the active temperature window of the catalyst is widened, and the denitration efficiency is good;
2. the net conversion rate of the nitrogen oxide of the composite catalyst is more than 90% in the temperature range of 300-450 ℃, and compared with a comparison sample, the activity data is greatly improved;
3. the composite catalyst can be used for removing nitrogen oxides discharged by fixed sources such as coal-fired power plants, industrial boilers, building material furnaces and the like and mobile sources of diesel vehicles.
Drawings
FIG. 1 is a graph comparing the nitrogen oxide conversion of example one of the present invention with that of a comparative example.
FIG. 2 is a graph comparing nitrogen selectivity in example one of the present invention and comparative example.
FIG. 3 is a graph showing the results of the water-resistant and sulfur-resistant performance tests of the catalysts of the examples of the present invention.
Detailed Description
The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below: