CN110721701B - Cobalt-chromium modified catalyst and preparation method and application thereof - Google Patents
Cobalt-chromium modified catalyst and preparation method and application thereof Download PDFInfo
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- 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
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- B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/85—Chromium, molybdenum or tungsten
- B01J23/88—Molybdenum
- B01J23/887—Molybdenum containing in addition other metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
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- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
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- B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/889—Manganese, technetium or rhenium
- B01J23/8898—Manganese, technetium or rhenium containing also molybdenum
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- B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
Abstract
The invention discloses a cobalt-chromium modified catalyst and a preparation method and application thereof, wherein the cobalt-chromium modified catalyst comprises the following raw materials: (i) a catalyst support comprising titanium dioxide; (ii) the metal catalyst comprises a chromium source precursor, a cobalt source precursor, a vanadium source precursor and a molybdenum source precursor; wherein the vanadium content in the catalyst is not less than 2 wt%. The catalyst can realize the catalytic oxidation of sulfur-containing volatile organic compounds while efficiently removing nitrogen oxides, and finally realize the catalytic oxidation of sulfur-containing volatile organic compounds and NOxAnd (4) synergistic purification.
Description
Technical Field
The invention relates to the field of environmental protection, and particularly relates to a cobalt-chromium modified catalyst, and a preparation method and application thereof.
Background
The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.
Nitrogen Oxides (NO)x) And Volatile Organic Compounds (VOCs) are the main precursors of atmospheric haze. NOxThe environment-friendly type solid-state gas is one of main atmospheric pollution pollutants in the world, causes photochemical smog, acid rain, ozone layer damage and other environmental problems, seriously influences the living environment and the living quality of people, causes huge damage to the environment and the society, and sets increasingly strict emission standards for fixed source combustion emission in various countries. Sulfur-containing volatile organic compounds, such as methyl mercaptan, are a typical unpleasant odor that is emitted to varying degrees during natural gas industry, petroleum processing, and animal husbandry processes. After being discharged, the paint is easy to generate acidic aerosol in the atmosphere, thereby causing environmental problems such as photochemical smog pollution, acid rain and the like, and has toxic action on human bodies. In the industrial emission process, the removal of the acid is particularly important in industrial flue gas because the acid has strong acidity and is easy to cause corrosion to downstream equipment. The removal of sulfur-containing VOCs in industrial applications has been mainly achieved by adsorption, biological processes and catalytic combustion processes, which have received much attention due to their higher activity and fewer by-products.
At present, the Selective Catalytic Reduction (SCR) technology is the most widely applied denitration technology in coal-fired power plants, and the principle of the SCR technology is that NO is converted by a reducing agent under the action of a catalyst under the condition of proper temperaturexConversion to N only2And H2And O. The reducing agent can be hydrocarbon (such as methane, propylene, etc.), ammonia, urea, etc., and ammonia (NH) is mainly used in industrial application3) NH due to mature technology and higher denitration efficiency3SCR technology has become the mainstream technology for denitration of coal-fired thermal power plants in various countries.
The prior SCR catalyst of the traditional vanadium-tungsten-titanium system usually adopts TiO2As a carrier, V2O5As active ingredient (vanadium content generally not exceeding 1% by weight) and in WO3(tungsten trioxide) or MoO3(molybdenum trioxide) as cocatalyst, which has high activity and SO resistance2Characteristic, is used in power plants (such as V)2O5-WO3/TiO2Or V2O5-MoO3/TiO2Is a widely used commercial SCR catalyst), applicants have found that such catalysts have poor low temperature activity, a narrow operating temperature range, and an active component V2O5For example, the reaction operating temperature is 300-. When the flue gas temperature is close to the optimal reaction temperature of the catalyst, the reaction rate is high, otherwise, the amount of the catalyst required for realizing the same denitration efficiency needs to be increased, and the increase of the amount of the catalyst inevitably increases the SCR denitration cost. Meanwhile, the traditional SCR catalyst does not have the function of removing VOCs while denitrating.
There have been related studies to try to improve or enhance the high temperature stability of vanadium based catalysts, such as reported in WO 2005/046864 for TiO containing vanadium2/WO3/SiO2Improvement in thermal stability of "SCR catalyst". According to a preferred embodiment thereof, based on TiO2/WO3/(SiO2) In which vanadium is not represented by V2O5In the form of Rare Earth Vanadates (REVO)4) Exist in the form of (1). This embodiment introduces the rare earth vanadate in powder form into the support material TiO by simply mixing and calcining the support with the rare earth vanadate2/WO3/(SiO2) In (1). Alternatively, the rare earth metal vanadate may also be formed in situ during the calcination of the catalyst from the precursor. Thus, with doping V2O5Compared with the material of (2), TiO doped with rhenium vanadate2/WO3/(SiO2) Has better thermal stability, however, the inventors have found that operating temperatures below 300 ℃ are better for NOxThe conversion of (c) is still weak. Therefore, on the premise of not changing the traditional vanadium-tungsten-titanium system, the improvement degree of the catalyst is still limited by simply changing the existing form of vanadium in the catalyst, and although the improvement degree is improved to different degrees, the investigation on catalysis is still neededThe structure of the catalyst and the mechanism of SCR reaction seek that the catalyst can keep higher catalytic activity and thermal stability under the condition of reducing vanadium content.
Disclosure of Invention
Therefore, the invention aims to provide a cobalt-chromium modified catalyst and a preparation method and application thereof, the catalyst is a double-effect catalyst, the directional modulation of the oxidation reduction property and the acidity of the surface of the catalyst is realized by designing the components of the catalyst, the catalytic oxidation of volatile organic compounds, particularly sulfur-containing volatile organic compounds (such as methyl mercaptan, methyl sulfide and the like) is realized while the catalyst efficiently removes nitrogen oxides, and finally the catalytic oxidation of sulfur-containing VOCs and NO is realizedxThe activity of the catalyst in the medium and low temperature is improved, so that the catalyst has a wider working temperature and has stable catalyst activity at 250-550 ℃. The catalyst of the invention can remove VOCs and NO synergisticallyxThe rate is high, the dosage of the catalyst is effectively reduced, and the cost is greatly reduced; the catalyst of the invention is especially suitable for the smoke generated in the production processes of natural gas industry, petroleum processing and animal husbandry.
Specifically, the invention is realized by the following technical scheme:
in a first aspect of the present invention, there is provided a cobalt-chromium modified catalyst comprising or consisting of the following raw materials: (i) a catalyst support comprising or being titanium dioxide; (ii) a metal catalyst comprising or consisting of: a chromium source precursor, a cobalt source precursor, a vanadium source precursor and a molybdenum source precursor; wherein, the vanadium content (namely the content of vanadium element) in the catalyst is not less than 2wt percent. The balance of the catalyst is titanium dioxide.
In some embodiments, the catalyst contains vanadium in an amount of 2 to 3 wt%, and in still other embodiments, in an amount of 2 to 2.5 wt%, and more preferably 2.5 wt%.
In the catalyst, the content of molybdenum is 3-10 wt% calculated by element; in some embodiments, the molybdenum content is 2.5 to 5 wt%, more preferably 4.5 wt%.
In some embodiments of the invention, the cobalt is present in the catalyst in an amount of 1 to 3 wt% on an elemental basis, and in still other embodiments, the amount is preferably 2 to 2.5 wt%, more preferably 2.5 wt%.
In some embodiments of the invention, the catalyst contains chromium in an amount of from 2 to 5 wt% on an elemental basis, and in still other embodiments, the amount is preferably from 3.5 to 4.5 wt%, and more preferably 4.5 wt%.
In some embodiments of the invention, the cerium is present in the catalyst in an amount of 0.5 to 1.5 wt% calculated as the element, and in still other embodiments, the amount is preferably 0.8 to 1.2 wt%, more preferably 1 wt%.
In the catalyst of the present invention, the chromium source precursor, the cobalt source precursor, the vanadium source precursor and the molybdenum source precursor may be those conventionally used in the art.
However, the applicant found in the research that the catalysts prepared by selecting different precursors can realize the catalytic performance, but the performances of the catalysts are particularly obviously different. For example, taking a vanadium source precursor as an example, a commonly used vanadium source precursor is ammonium metavanadate or vanadyl oxalate, but when ammonium metavanadate or vanadyl oxalate is used, stable molding of the catalyst under high vanadium conditions (usually, the vanadium content is higher than 1 wt%) cannot be ensured, and under high vanadium conditions, for N, the catalyst is stable2The selectivity is reduced, and the reaction activity is reduced.
In some embodiments of the present invention, the applicant found that when the chromium source precursor is chromium nitrate, the cobalt source precursor is cobalt nitrate, the vanadium source precursor is vanadyl acetylacetonate, the molybdenum source precursor is ammonium molybdate tetrahydrate, and the cerium source precursor is cerium nitrate or cerium sulfate, the prepared catalyst has better catalytic stability, and more excellent oxidation performance and relatively higher denitration performance for sulfur-containing volatile organic compounds.
In earlier studies, the applicant found that NH in SCR reaction under high vanadium conditions can be avoided by using phosphotungstic acid as a tungsten source precursor and simultaneously using vanadyl acetylacetonate as a vanadium source precursor3The oxidation is severe, a problem that a large amount of side reactions occur is promoted to affect the reaction efficiency, and the catalyst can realize a high vanadium content of not less than 2 wt%Stable formation under the condition, and can effectively avoid N caused by the promotion of the oxidation-reduction property of the catalyst2The selectivity decreases. In the treatment, the combination of tungsten and molybdenum (such as phosphotungstic acid and molybdenum trioxide) can improve the stability of the catalyst, and particularly, when CVOCs are treated, the use of the phosphotungstic acid can promote the opening of C-Cl bonds in the CVOCs, so that the decomposition of the CVOCs is accelerated, and the oxidation efficiency of the CVOCs is greatly improved while the SCR reaction activity is ensured. And on the premise of using tungsten phosphate, the addition of molybdenum trioxide can enhance the acidity of the surface of the catalyst, further improve the oxidation efficiency of CVOCs and ensure the denitration efficiency. Thus, there is also a trend in the art to use both simultaneously to enhance the acidity of the catalyst surface. However, such a design is only suitable for the treatment of CVOCs, and the applicant does not have the above advantages in the treatment of sulfur-containing volatile organic compounds, but rather, unexpectedly, the oxidation efficiency and denitration efficiency of the catalyst using the same as the raw material are difficult to be improved or at least difficult to be maintained at a better level at the same time, and especially the advantages in the middle and low temperature section are not existed.
In addition, as for the molybdenum source precursor, sodium molybdate dihydrate or molybdenum pentachloride is also conventionally used in the field, but in the research of the invention, the applicant finds that the catalyst prepared by the two molybdenum source precursors has difficulty in achieving the beneficial effects of ammonium molybdate tetrahydrate, and supposes that the possible reason is that the existence of sodium and chlorine in the sodium molybdate dihydrate or the molybdenum pentachloride has great influence on the reaction.
The coordination of Cr, Co, V, Mo and Ce in the catalyst of the invention provides a large amount of oxidation-reduction sites and acidic sites for the catalyst, increases the oxygen storage and release capacity of the surface of the catalyst, greatly improves the activity of medium-low temperature SCR, and improves the catalytic oxidation rate of VOCs (volatile organic compounds), especially sulfur-containing VOCs, and simultaneously improves the catalytic oxidation rate of NO (nitric oxide) in the catalystxThe removal efficiency of (2). On the premise that the catalyst contains no less than 2 wt% of vanadium, especially 2.5 wt% of vanadium, the introduction of Cr and Co is especially based on the specific contents (combination of contents of chromium content of 2-5 wt% and cobalt content of 1-3 wt%), especially 4.5 wt% and cobalt content2.5wt percent) greatly improves the oxidation-reduction property of the catalyst, thereby greatly improving the efficiency of the catalyst for catalyzing and oxidizing volatile organic compounds under the condition of medium and low temperature; the introduction of Cr, Ce and Mo especially greatly improves the oxidation-reduction sites and acid sites on the surface of the catalyst by using specific amounts (the content combination of 2-5 wt% of chromium, 0.5-1.5 wt% of cerium and 2.5-5 wt% of molybdenum, especially the content combination of 4.5 wt% of molybdenum, 4.5 wt% of chromium and 1.0 wt% of cerium) of Cr, Ce and Mo, increases the oxygen storage and release capacity of the surface of the catalyst, greatly improves the oxidation-reduction performance of the catalyst, and increases NH in SCR reaction3Due to the adsorption rate of NH in the SCR reaction3The adsorption of (A) is the first step of the SCR reaction and is also the rate-determining step for NH3The promotion of adsorption rate makes going on of denitration more high-efficient.
In the embodiments of the present invention, the combination of elements of Cr, Co, V, Mo, and Ce in the catalyst generates a synergistic effect, which can improve the performance of the catalyst, and especially, when the elements are combined in a specific content, the performance of the catalyst has an especially excellent improvement, and in some embodiments of the present invention, the preferable combination of elements is: the catalyst contains 2-3 wt% of vanadium, 2.5-5 wt% of molybdenum, 1-3 wt% of cobalt, 2-5 wt% of chromium and 0.5-1.5 wt% of cerium; in the content combination, the elements of the catalyst have better synergistic effect, so that the activity of the catalyst is better improved, and the sulfur-containing VOCs and NO are synergistically removedxThe catalyst has good effect, the efficiency is improved, the medium and low temperature activity of the catalyst is improved, and the efficiency at medium and low temperature is improved; in particular, in further embodiments, the combination of elements of the invention is: when the catalyst contains 2.5 wt% of vanadium, 4.5 wt% of molybdenum, 2.5 wt% of cobalt, 4.5 wt% of chromium and 1.0 wt% of cerium, the synergistic effect among the elements of the catalyst can be better played, and particularly the synergistic removal of sulfur-containing VOCs and NO is realizedxThe catalyst has the advantages of obvious improvement effect, obvious efficiency improvement, great improvement on the oxidation-reduction property and the denitration efficiency of the catalyst at medium and low temperatures, and obvious performance improvement of the catalyst at medium and low temperatures.
In a second aspect of the present invention, the present invention also provides a method for preparing the cobalt-chromium modified catalyst according to the first aspect of the present invention, which comprises mixing the raw materials, and performing ball milling and heat treatment processes.
In the catalyst preparation of the present invention, the balance is a carrier titanium dioxide.
In the preparation method, the ball milling comprises the steps of preliminarily mixing the raw materials, then adding the mixture into a ball milling tank for ball milling, wherein the ball milling lasts for 40-100min, and the rotating speed is 30-75 r/min. For example, the ball milling time can be 50-90min, and the rotating speed can be 50-65 r/min; alternatively, in a more preferred embodiment, the ball milling time is 70min and the rotational speed is 55 rpm.
In the preparation method of the present invention, the heat treatment process includes drying the ball-milled mixture and calcining in an air atmosphere; the drying temperature is 100-120 ℃, and the drying time is 5-9 h.
In the preparation method of the invention, the roasting comprises roasting for 2-6h at the temperature of 450-500 ℃.
In some embodiments of the invention, the firing is performed in a muffle furnace, comprising a 2-6h post-firing at a ramp rate of 2-10 ℃/min from room temperature to 450-500 ℃.
In some embodiments, the temperature rise in the roasting is performed in stages, including first raising the temperature from room temperature to 90-100 ℃, and recording as a low temperature stage; then the temperature is raised to 180 ℃ and 220 ℃ to represent the medium temperature; finally, the temperature is raised to 450-500 ℃, and the temperature is recorded as a high temperature section.
In some embodiments, the ramp rate at low temperature is 8-10 deg.C/min, preferably 8 deg.C/min, and the ramp to 90-100 deg.C is maintained for 5-10min, preferably 10 min.
In some embodiments, the temperature rise rate of the medium temperature section is 8-10 ℃/min, preferably 8 ℃/min, and the temperature rise to 180-220 ℃ is maintained for 8-12min, preferably 12 min.
In some embodiments, the temperature increase rate in the high temperature zone is 8-10 deg.C/min, preferably 8 deg.C/min, and the temperature is increased to 450-500 deg.C for 2-6 hours, preferably 3 hours.
Catalysis after calcinationThe metal elements in the agent are all in the form of metal oxides, and in the embodiment of the invention, the calcined vanadyl acetylacetonate is mainly V2O5Is the main active center, which is responsible for NOxThe removal of Co and Cr respectively generates Co-containing oxide (active form is Co)3O4) And Cr-containing oxide (active form is Cr)2O3) The medium-low temperature oxidizability of the catalyst can be synergistically improved, so that the oxidative decomposition rate and denitration efficiency of the sulfur-containing VOCs under medium-low temperature conditions are improved. Mo-containing oxides (active form is MoO) produced by roasting Mo and Ce respectively3) And oxides containing Ce (in active form CeO)2) With Cr-containing oxides (active form being Cr)2O3) Can greatly improve the oxidation-reduction sites and the acid sites on the surface of the catalyst, increase the oxygen storage and release capacity on the surface of the catalyst, greatly improve the oxidation-reduction performance of the catalyst, and increase NH in SCR reaction3Due to the adsorption rate of NH in the SCR reaction3The adsorption of (A) is the first step of the SCR reaction and is also the rate-determining step for NH3The promotion of adsorption rate makes going on of denitration more high-efficient to increase the redox nature of catalyst, promote SCR activity and VOCs catalytic oxidation rate, make the catalyst in coordination with the desorption contain sulphur VOCs and NOxThe catalyst has the advantages of obviously improved activity at medium and low temperature and improved catalytic efficiency. The above properties of the metal oxides are achieved under mutual synergy, and in particular the properties of the catalyst are optimal when the elements are present in the catalyst in the combination of the amounts of the embodiments described in the present invention.
For example, in some embodiments of the invention, the catalyst may be prepared to contain vanadium in an amount of 2 to 3 wt.%, molybdenum in an amount of 2.5 to 5 wt.%, cobalt in an amount of 1 to 3 wt.%, chromium in an amount of 2 to 5 wt.%, and Ce in an amount of 0.5 to 1.5 wt.%; in the content combination, the synergistic removal effect and the medium-low temperature activity of the catalyst are better, and especially, when the content of vanadium in the catalyst is 2.5 wt%, the content of molybdenum is 4.5 wt%, the content of cobalt is 2.5 wt%, the content of chromium is 4.5 wt%, and the content of cerium is 1.0 wt%, the synergistic removal effect and the medium-low temperature activity of the catalyst are optimal.
In a third aspect of the invention, the invention also provides the application of the cobalt-chromium modified catalyst in the first aspect as an SCR catalyst in removing nitrogen oxides and/or volatile organic compounds in fixed source flue gas; preferably, the volatile organic is a sulfur-containing volatile organic, such as methyl mercaptan. Preferably, the flue gas contains methyl mercaptan.
In some embodiments, the flue gas is produced in the processes of natural gas industry, petroleum processing and animal husbandry production, and is characterized in that the flue gas contains sulfur-containing volatile organic compounds; in some embodiments of the invention, the flue gas operating temperature is 250-.
Compared with the prior art, the invention has the following beneficial effects:
generally, an SCR catalyst often has better catalytic activity at high temperature, and the SCR catalyst needs to have good catalytic activity at medium and low temperature (for example, not higher than 400 ℃) so that the catalyst has stronger oxidation-reduction property and certain acidity, and the method for enhancing oxidation-reduction property and increasing acidity in the field is to add high-content vanadium and high-content tungsten, but the higher the oxidation-reduction property is, the more side reactions of the catalyst can occur in a high-temperature environment, for example, the ammoxidation reaction can increase, the added reducing agent ammonia can be oxidized into nitrogen oxide, so the activity of the catalyst can be obviously reduced after the catalyst is at a high temperature of, for example, 500 ℃, and the stable molding of the catalyst is not facilitated under the high-vanadium condition (more than 1 wt%), and the catalyst is not beneficial to the stable molding of the catalyst under the N condition2The selectivity of the catalyst is reduced, and the denitration efficiency is obviously reduced under certain conditions, such as 300 ℃, so that how to balance the problem and realize the directional modulation of the oxidation-reduction property and the acidity of the surface of the catalyst is particularly significant.
And the main technology of denitration is SCR method, and vanadium-based catalyst is mostly applied at present, but the operation temperature window is higher. In general, after the catalyst passes through the dust removal and desulfurization sections, the temperature is usually reduced to below 300-400 ℃, and the denitration is carried out at a medium-low temperature to easily generate sulfuric acidSalts cause problems such as clogging of catalyst channels, reduction of specific surface area and acid sites, and SO2The metal active ingredient is sulfated, resulting in irreversible deactivation, thereby seriously affecting the activity of the catalyst. When the flue gas contains sulfur-containing volatile organic compounds, C-S bonds of the flue gas are easy to open, and sulfate, sulfur dioxide, sulfur oxide and the like can be formed in the flue gas after the C-S bonds are opened, and the irreversible inactivation of the catalyst can be aggravated by the substances. Thus, the equilibrium catalyst is active against sulfur-containing volatile organics and NOxThe difficulty of the cooperative removal is high.
The catalyst of the invention solves the problems through special component design, realizes the directional modulation of the surface oxidation-reduction property and the acidity of the catalyst, balances the oxidation-reduction property and the acidity of the catalyst under the high vanadium condition (not less than 2wt percent), and solves the problem that the catalyst is difficult to stably form under the high vanadium condition; meanwhile, the catalyst can remove sulfur-containing volatile organic compounds and NO synergisticallyxAnd has wider working temperature and stable catalyst activity at 250-550 ℃.
The catalyst has a specific metal element composition, the metal elements take respective oxides as active forms to play a role under calcination, and the oxidation-reduction property of the catalyst is greatly improved by the specific composition and content, so that the efficiency of the catalyst in catalytic oxidation of volatile organic compounds under medium-low temperature conditions is greatly improved; meanwhile, the oxidation-reduction sites and the acid sites on the surface of the catalyst are greatly improved, the oxygen storage capacity on the surface of the catalyst is increased, the oxidation-reduction performance of the catalyst is greatly improved, and NH in SCR reaction is increased3The adsorption rate of (2) makes the denitration more efficient.
The catalyst disclosed by the invention has stable catalytic activity and high reaction rate in the working range of 250-550 ℃, effectively reduces the using amount of the catalyst, greatly reduces the cost, and has particularly excellent activity for removing sulfur-containing volatile organic compounds in a denitration synergistic manner.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only.
Preparation examples 1-10 preparation of cobalt-chromium modified catalysts
Unless otherwise specified, the metal elements in the catalyst are derived from the following raw materials: chromium nitrate, tungsten phosphate, vanadyl acetylacetonate, titanium dioxide, molybdenum trioxide, cobalt nitrate, cerium nitrate and manganese nitrate; the content of the raw materials is shown in table 1 below.
Taking raw materials according to the element composition shown in the table 1, preliminarily mixing the raw materials, adding the raw materials into a ball milling tank for ball milling for 70min at a rotating speed of 55 r/min, drying the ball-milled mixture (110 ℃, 6h), roasting the mixture in an air atmosphere, and roasting the mixture in a muffle furnace for 10min when the temperature is raised to 100 ℃ at a speed of 8 ℃/min; then heating to 200 ℃ at the speed of 8 ℃/min and keeping for 12 min; then heated to 500 ℃ at a rate of 8 ℃/min for 3 hours. After the baking and sintering, the catalyst is cooled along with the furnace to obtain powder with the granularity of 40-60 meshes.
TABLE 1 content of metal element in catalyst (wt%)
PREPARATION EXAMPLE 20 preparation of cobalt-chromium modified catalyst
The raw materials were used in the same amounts and compositions as in preparation example 1, using the following preparation method:
the raw materials are initially mixed and then added into a ball milling tank for ball milling for 70min at the rotating speed of 55 r/min, then the mixture after ball milling is dried (110 ℃, 6h) and roasted in air atmosphere, and the roasting is carried out in a muffle furnace, wherein the heating is carried out at the speed of 8 ℃/min until the temperature is raised to 500 ℃ and is kept for 3 h. After the baking and sintering, the cobalt-chromium modified catalyst is obtained by furnace cooling, and is powder with the granularity of 40-80 meshes.
Preparation example 21 preparation of cobalt-chromium modified catalyst
The raw materials were used in the same amounts and compositions as in preparation example 1, using the following preparation method:
taking raw materials, preliminarily mixing, adding into a ball milling tank, and carrying out ball milling for 70min at a rotating speed of 55 r/min; taking the ball-milled mixture out of the temperature of 110 ℃, drying for 6h, and directly roasting for 3h at 500 ℃ in the air atmosphere; finally, cooling along with the furnace to obtain the cobalt-chromium modified catalyst which is powder with the granularity of 20-90 meshes.
Example 22 Activity test for denitration and synergistic removal of Sulfur-containing VOCs from catalyst
And (3) testing conditions are as follows: the catalysts prepared in preparation examples 1 to 22 were used for evaluation of the activity of controlling the synergistic reaction of pollutants, 0.2g of catalyst, NO 500ppm, NH3500ppm, methyl mercaptan 50ppm, O25vol.％，N2The balance is realized, the total flow of the flue gas is 200mL/min, and the gas space velocity GHSV is 60,000h-1(Standard conditions), the NO to methyl mercaptan conversion was calculated as the outlet and inlet NO to methyl mercaptan content.
The results of the oxidation efficiency and the denitration efficiency are shown in tables 2 and 3, respectively.
TABLE 2
TABLE 3
Claims (30)
1. A cobalt-chromium modified catalyst comprises the following raw materials: (i) a catalyst support comprising titanium dioxide; (ii) the metal catalyst comprises a chromium source precursor, a cobalt source precursor, a vanadium source precursor and a molybdenum source precursor; wherein the vanadium content in the catalyst is not less than 2 wt%;
the chromium source precursor is chromium nitrate, the cobalt source precursor is cobalt nitrate, the vanadium source precursor is vanadyl acetylacetonate, and the molybdenum source precursor is ammonium molybdate tetrahydrate; the cerium source precursor is cerium nitrate or cerium sulfate;
the catalyst contains 2-3 wt% of vanadium, 3-10 wt% of molybdenum, 1-3 wt% of cobalt, 2-5 wt% of chromium and 0.5-1.5 wt% of cerium.
2. The cobalt-chromium modified catalyst according to claim 1 wherein the amount of vanadium contained in the catalyst is 2-2.5 wt%.
3. The cobalt-chromium modified catalyst according to claim 2 wherein the amount of vanadium contained in the catalyst is 2.5 wt%.
4. The cobalt-chromium modified catalyst according to claim 1, wherein the molybdenum content in the catalyst is from 2.5 to 5 wt%.
5. The cobalt-chromium modified catalyst according to claim 4 wherein the molybdenum content in the catalyst is 4.5 wt%.
6. The cobalt-chromium modified catalyst according to claim 1, wherein the cobalt content in the catalyst is 2-2.5 wt%.
7. The cobalt-chromium modified catalyst according to claim 6 wherein the cobalt content in the catalyst is 2.5 wt%.
8. The cobalt-chromium modified catalyst according to claim 1, wherein the chromium content of the catalyst is from 3.5 to 4.5% by weight.
9. The cobalt-chromium modified catalyst according to claim 8 wherein the chromium content of the catalyst is 4.5 wt%.
10. The cobalt-chromium modified catalyst according to claim 1, wherein the cerium content in the catalyst is from 0.8 to 1.2 wt%.
11. The cobalt-chromium modified catalyst according to claim 10 wherein the cerium content in the catalyst is 1 wt%.
12. A method of preparing a cobalt-chromium modified catalyst as claimed in any one of claims 1 to 11 which comprises mixing the starting materials and then subjecting the mixture to a ball milling and heat treatment process.
13. The method of claim 12, wherein the ball milling comprises initially mixing the raw materials and then adding the mixture to a ball milling jar for ball milling at a speed of 30-75 rpm for 40-100 min.
14. A method according to claim 13, characterized in that the rotational speed is 50-65 revolutions/min,
the ball milling time is 50-90 min.
15. The method of claim 14, wherein the ball milling time is 70min and the rotation speed is 55 rpm.
16. The method of claim 12, wherein the heat treatment process comprises drying the ball-milled mixture and calcining in an air atmosphere.
17. The method as claimed in claim 16, wherein the drying temperature is 100-120 ℃ and the drying time is 5-9 h.
18. The method as claimed in claim 16, wherein the roasting comprises roasting for 2-6h at a temperature of 450-500 ℃.
19. The method as claimed in claim 18, wherein the baking is performed in a muffle furnace, and comprises baking for 2-6h after heating from room temperature to 450-500 ℃ at a heating rate of 2-10 ℃/min.
20. The method as claimed in claim 16, wherein the temperature rise in the roasting is performed in stages, including a temperature rise from room temperature to 90-100 ℃, expressed as a low temperature stage; then heating to 180 ℃ and 220 ℃, and recording as a medium temperature section; finally, the temperature is raised to 450-500 ℃, and the temperature is recorded as a high temperature section.
21. The method as claimed in claim 20, wherein the temperature rise rate of the low temperature stage is 8-10 ℃/min, and the temperature is maintained for 5-10min when the temperature is raised to 90-100 ℃.
22. The method as claimed in claim 21, wherein the heating rate of the low temperature stage is 8 ℃/min, and the heating time is 10min when the temperature is raised to 90-100 ℃.
23. The method as claimed in claim 20, wherein the temperature rise rate of the intermediate temperature stage is 8-10 ℃/min, and the temperature rise time is increased to 180-220 ℃ and kept for 8-12 min.
24. The method as claimed in claim 23, wherein the temperature rise rate in the middle temperature stage is 8 ℃/min, and the temperature rise time is up to 180 ℃ and 220 ℃ and is kept for 12 min.
25. The method as claimed in claim 20, wherein the temperature rise rate of the high temperature section is 8-10 ℃/min, and the temperature rise time is 500 ℃ and is maintained for 2-6 hours.
26. The method as claimed in claim 25, wherein the temperature rise rate of the high temperature section is 8 ℃/min, and the temperature rise time is up to 450 ℃ and 500 ℃ for 3 hours.
27. Use of a cobalt-chromium modified catalyst according to any one of claims 1 to 11 as an SCR catalyst for the removal of fixed source flue gas nitrogen oxides and/or volatile organic compounds.
28. The use of claim 27, wherein the volatile organic is sulfur-containing volatile organic.
29. The use according to claim 27, wherein the stationary source flue gas is flue gas generated during natural gas industry, petroleum processing, animal husbandry production.
30. The use of claim 27, wherein the flue gas temperature is 250-550 ℃.
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