Novel catalyst for SCR (selective catalytic reduction) flue gas denitration as well as preparation method and application of novel catalyst

Abstract

The invention belongs to the technical field of environmental catalytic materials and air pollution control, and discloses a novel catalyst for SCR flue gas denitration, and a preparation method and application thereof. A simple sol-gel method and an alkali etching method are adopted for synthesizing the iron molybdate catalyst, and the method is simple and rapid, conditions are easy to control, and repeatability is high. The prepared vacancy-rich low-crystallinity iron molybdate catalyst can be used for treating nitric oxide, the conversion rate can reach 90% or above at the temperature smaller than or equal to 250 DEG C, the denitration performance can reach 80% or above within the wide temperature window range, and the good industrial application prospect is achieved. The alkali treatment preparation method of the catalyst is simple and rapid, conditions are easy to control, repeatability is high, the catalyst material used in the method is wide in source and relatively low in price, and the catalyst is low in cost and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental catalytic materials and air pollution control, and relates to a novel vacancy-rich low-crystallinity iron molybdate catalyst, a synthesis method and application thereof in the field of denitration. Background Art

[0002] At present, people in most countries around the world still use chemical petroleum materials as basic fuels, and the nitrogen oxides produced after combustion are directly discharged into the atmosphere without treatment and protection, causing the concentration of nitrogen oxides in the atmospheric environment to exceed the standard sharply, which can no longer be controlled and eliminated by the ecological balance in the atmospheric environment. Nitrogen oxides have a pungent odor and are highly toxic. They can cause damage to the respiratory system, immune system, nervous system, etc., and pose a serious threat to life safety. Nitrogen oxides not only have a huge direct impact on human health, but also are fine particulate matter (PM 2.5 ) and ozone (O3), which will indirectly lead to a series of environmental problems such as acid rain, photochemical smog, and haze. Therefore, the development of efficient removal of NO x Purification materials and technologies are of great significance in controlling nitrogen oxide emissions.

[0003] At present, the flue gas denitrification technologies mainly include selective catalytic reduction technology (SCR), selective non-catalytic reduction technology (SNCR), absorption technology, adsorption technology and storage reduction technology (NSR). Among them, ammonia selective catalytic reduction (NH3-SCR) technology is the most commonly used technology in the world, and its core is the catalyst. The most widely used commercial catalyst for NH3-SCR is V2O5-WO3(MoO3) / TiO2. However, this type of catalyst is only applicable to the temperature range of 300-450℃, and the biological toxicity of V2O5 is not conducive to public health, and the cost is relatively high. Therefore, from an academic and industrial perspective, the new SCR catalyst should have the characteristics of a wide temperature window, low cost, high low-temperature activity (<300℃), etc.

[0004] Iron molybdate (Fe2(MoO4)3) has attracted extensive attention in the fields of optics, electrochemistry, sensing, etc. due to its chemical stability, rich acidity and environmental friendliness (ACS Appl. Mater. Interfaces, 2020, 12, 35152-35163; Journal of Materials Science: Materials in Electronics, 2019, 30, 14022–14029). my country has rich reserves of iron ore and molybdenum ore, so its raw materials are widely available and inexpensive. However, in the field of NH3-SCR, there are few related studies. Researchers mainly focus on the use of molybdenum in the form of single atoms or MoO3, and its potential as a catalyst itself is ignored, which limits the research and application of iron molybdate in the field of denitrification. Summary of the invention

[0005] In view of the above technical problems, the object of the present invention is to provide a new catalyst for SCR flue gas denitrification and a preparation method, namely, a vacancy-rich low-crystallinity iron molybdate and a preparation method.

[0006] The technical solution of the present invention:

[0007] A novel catalyst for SCR flue gas denitration is a low-crystallinity iron molybdate catalyst, Fe2(MoO4)3, having anion or cation vacancies.

[0008] A method for preparing a novel catalyst for SCR flue gas denitration is synthesized by a two-step method, namely, a sol-gel method coupled with alkaline etching, and the steps are as follows:

[0009] (1) preparing a Fe2(MoO4)3 precursor by a sol-gel method, and calcining the precursor to obtain a Fe2(MoO4)3 catalyst;

[0010] (2) adding Fe2(MoO4)3 catalyst into alkaline solution and stirring to obtain a mixed solution;

[0011] (3) washing the mixed solution with water and filtering it until the filtrate is neutral, and drying the precipitate to obtain a low-crystallinity iron molybdate catalyst rich in anion or cation vacancies.

[0012] The calcination temperature is 400-700° C., the calcination time is 3-12 hours, and the heating rate is 3-8° C. / min.

[0013] Specific alkaline solutions preferably used include, but are not limited to, one or more of the following compounds: sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution, sodium carbonate (Na2CO3) solution, sodium bicarbonate (NaHCO3) solution, potassium bicarbonate (KHCO3) solution, ammonia (NH3·H2O) solution, urea (CO(NH2)2) solution.

[0014] The stirring time of the alkaline solution is 5 to 120 minutes, and the concentration of the alkaline solution is 0.1 to 1 mol·L -1 .

[0015] The precipitate drying treatment temperature is 80-120°C.

[0016] Application of the above-mentioned new catalyst in the field of denitrification.

[0017] Beneficial effects of the present invention:

[0018] (1) The iron molybdate catalyst of the present invention has an effectively improved low-temperature activity in the denitration reaction, and its temperature window (nitrogen oxide removal rate is greater than or equal to 80%) is widened from 350 to 400° C. to 225 to 400° C., which has a good industrial application prospect;

[0019] (2) The catalyst preparation method of the present invention is simple and quick, the conditions are easy to control, and the repeatability is high. The catalyst materials used in the present invention are widely available and relatively cheap, so the catalyst cost is low and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the NO of the catalyst prepared in Example 1 x Catalytic removal activity diagram;

[0021] Figure 2 is the NO of the catalyst prepared in Example 2 x Catalytic removal activity diagram;

[0022] Figure 3 is the X-ray diffraction pattern (XRD) of the catalyst prepared in Example 5;

[0023] Figure 4 1 and 1 , which are X-ray photoelectron spectra (XPS) of the catalyst prepared in Example 5, wherein (a) is an O1s spectrum and (b) is a Mo3d spectrum.

[0024] Figure 5 is the NO of the catalyst prepared in Example 3 x Catalytic removal activity diagram. DETAILED DESCRIPTION

[0025] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0026] A method for preparing a new catalyst for SCR flue gas denitration, the chemical formula of the iron molybdate catalyst is Fe2(MoO4)3. The specific synthesis method is as follows:

[0027] (1) using the existing sol-gel method to prepare Fe2(MoO4)3 precursor and calcining it;

[0028] (2) adding Fe2(MoO4)3 catalyst into alkaline solution and stirring;

[0029] (3) The mixed solution is washed with water and filtered until the filtrate is neutral, and the precipitate is dried to obtain an alkaline-etched iron molybdate catalyst.

[0030] In the present invention, the calcination temperature is 400-700° C., the calcination time is 3-12 hours, and the heating rate is 3-8° C. / min.

[0031] In the present invention, in step (2), the specific alkaline solution preferably used includes but is not limited to one or more of the following alkaline solutions: sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution, sodium carbonate (Na2CO3) solution, sodium bicarbonate (NaHCO3) solution, potassium bicarbonate (KHCO3) solution, ammonia (NH3·H2O) solution, urea (CO(NH2)2) solution.

[0032] In the present invention, in step (2), the stirring time is 5 to 120 min, preferably 10 to 30 min.

[0033] In the present invention, in step (2), the amount of the alkaline solution is 10 to 100 mL, preferably 10 to 30 mL.

[0034] In the present invention, in step (2), the concentration of the alkali solution is 0.1 to 1 mol·L -1 , preferably 0.17 to 0.34 mol·L -1 .

[0035] In the present invention, in step (3), the precipitate is dried at a temperature of 80 to 120°C, preferably 90 to 110°C.

[0036] Example 1

[0037] A method for preparing a novel catalyst for SCR flue gas denitrification, the steps are as follows:

[0038] Step (1), preparing Fe2(MoO4)3 catalyst by sol-gel method, calcining at 400°C for 5h, heating rate of 5°C / min, and pressing into 20-40 mesh granular sample, recorded as catalyst A;

[0039] Step (2) Disperse 1 g of catalyst A in 30 mL of 0.34 M NaOH solution and stir at room temperature for 10 and 30 min, respectively.

[0040] Step (3), filtering the sample obtained in step (2) with ultrapure water until the filtrate is neutral.

[0041] Step (4), drying the precipitate obtained in step (3) and pressing it into a 20-40 mesh granular sample.

[0042] Example 2

[0043] Catalyst A was prepared according to the steps of Example 1, and the concentrations of the alkali solution were 0.085, 0.177, and 0.34 M. Other conditions were fixed as follows: 30 mL of NaOH solution, stirring time of 10 min, alkali etching of catalyst A, and XRD and XPS tests of the above catalysts.

[0044] Example 3

[0045] Referring to Example 1, the amount of alkali solution was changed to 20, 30, and 40 mL, and the other conditions were fixed as follows: 0.17 M NaOH solution, stirring time of 10 min, and catalyst A was alkali etched.

[0046] Example 4

[0047] Referring to Example 1, the composition of the alkali solution was changed to a mixed solution of NaOH and KOH and a mixed solution of NaOH and Na2CO3, respectively. The other conditions were fixed as an alkali solution concentration of 0.17 M, an alkali solution amount of 40 mL, and a stirring time of 10 min, and catalyst A was alkali-etched.

[0048] Test Example 1

[0049] Using the catalyst of Example 1, 0.5 g of the sample was subjected to a self-made catalyst micro-fixed bed continuous flow differential reactor, and NO was detected by a nitrogen oxide analyzer. x The test conditions are: 500ppm NH3, 500ppm NO, oxygen volume concentration of 3%, argon as balance gas, reaction gas flow rate of 250-300mL / min, reaction gas space velocity of 36000mL / g·h. The reaction activity of each catalyst is as follows Figure 1 shown.

[0050] Test Example 2

[0051] The catalyst of Example 2 was used, and the test conditions were the same as those of Test Example 1. The NO x The conversion rate results are as follows Figure 2 shown.

[0052] Test Example 3

[0053] The catalyst of Example 2 was used. The crystallinity of the samples of catalyst A under different alkali solution concentration treatment conditions is shown in Table 1, and the XRD spectra are shown in Figure 3 shown.

[0054] Table 1 Crystallinity of catalyst A at different alkali concentrations

[0055] <![CDATA[Alkali concentration / mol·L -1 > Crystallinity 0(Catalyst A) 60.10415 0.085 52.29148 0.17 41.86664 0.34 /

[0056] Test Example 4

[0057] Using the catalyst of Example 2, the XPS spectra of O1s and Mo3d of catalyst A under different alkali solution concentration treatment conditions are as follows: Figure 4 As shown, surface active oxygen (O α ) α / (O α +O β ) and Fe / Mo element contents are shown in Table 2.

[0058] Table 2 O of catalyst A at different alkali concentrations α / (O α +O β ) and Fe / Mo element content

[0059] <![CDATA[Alkali concentration / mol·L -1 > <![CDATA[O α / (O α +O β )]]> Fe / Mo 0(Catalyst A) 10.35％ 0.62548 0.085 10.85％ 0.91201 0.17 12.43％ 1.2294 0.34 46.56％ 13.1338

[0060] From Table 2 and Figure 4 It can be seen that the Mo in the catalyst can be etched away by alkali solution. 6+ , forming metal Mo 6+ vacancies, and with the increase of alkali etching concentration, the Mo 6+ The more metal vacancies there are, the higher the surface active oxygen content is, which is beneficial to improving the low-temperature denitrification activity of the catalyst.

[0061] Test Example 5

[0062] The catalyst of Example 3 was used to determine the NO x The conversion rate results are as follows Figure 5 shown.

[0063] Test Example 6

[0064] The catalyst of Example 4 was used to determine the NO x The conversion results are shown in Table 3.

[0065] Table 3 NO under different alkali solutions x Conversion rate

[0066]

[0067] In summary, alkali etching of FeMoO4 samples can be performed by constructing Mo 6+ Vacancies increase the amount of surface active oxygen and reduce the crystallinity to improve the denitrification activity of the catalyst. The low-crystallinity iron molybdate catalyst rich in metal vacancies has a denitrification performance of more than 80% in a wide temperature window (225-400°C) and has a good prospect for industrial application.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A novel catalyst for SCR flue gas denitrification, characterized in that: The novel catalyst is a low-crystallinity iron molybdate catalyst with anion or cation vacancies.

2. A method for preparing a novel catalyst for SCR flue gas denitration, characterized in that: The synthesis is carried out by a two-step method, namely, sol-gel method coupled with alkaline etching, the steps are as follows: (1) preparing a Fe2(MoO4)3 precursor by a sol-gel method, and calcining the precursor to obtain a Fe2(MoO4)3 catalyst; (2) adding Fe2(MoO4)3 catalyst into alkaline solution and stirring to obtain a mixed solution; (3) washing the mixed solution with water and filtering it until the filtrate is neutral, and drying the precipitate to obtain a low-crystallinity iron molybdate catalyst rich in anion or cation vacancies.

3. The preparation method according to claim 2, characterized in that: The calcination temperature is 400-700° C., the calcination time is 3-12 hours, and the heating rate is 3-8° C. / min.

4. The preparation method according to claim 2, characterized in that: The alkaline solution is one or a mixture of two or more of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution, potassium bicarbonate solution, ammonia solution, and urea solution.

5. The preparation method according to claim 2, characterized in that: The stirring time of the alkaline solution is 5 to 120 minutes, and the concentration of the alkaline solution is 0.1 to 1 mol·L -1 .

6. The preparation method according to claim 2, characterized in that: The temperature for the precipitate drying treatment is 80-120°C.

7. Application of the novel catalyst according to claim 1 in the field of denitration.

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