A novel catalyst for SCR flue gas denitration, a preparation method and application thereof

Abstract

The application belongs to the field of environmental catalytic materials and air pollution control technology, and discloses a novel catalyst for SCR flue gas denitration, a preparation method and application thereof. The simple sol-gel method + alkali etching method is used for synthesizing the iron molybdate catalyst, the method is simple and fast, the conditions are easy to control, and the repeatability is high. The low-crystallinity iron molybdate catalyst rich in vacancies prepared by the application can be used for nitrogen oxide treatment, and can achieve more than 90% conversion rate at a temperature of less than or equal to 250 DEG C, and has more than 80% denitration performance in a wide temperature window range, and has a good industrial application prospect. The catalyst preparation method of the application is simple and fast, the conditions are easy to control, and the repeatability is high, the catalyst material used in the application has a wide source and a relatively low price, the catalyst cost is low, and the application is environment-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, and it 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 indirectly leads to a series of environmental problems such as acid rain, photochemical smog, and haze. Therefore, the development of efficient NO removal x Purification materials and technologies are of great significance in controlling and reducing nitrogen oxide emissions.

[0003] Currently, flue gas denitrification technologies mainly include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), absorption, adsorption, and storage reduction (NSR). Among them, ammonia selective catalytic reduction (NH3-SCR) is the most commonly used technology worldwide, 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 suitable for temperatures between 300-450°C, the biological toxicity of V2O5 is detrimental to public health, and the cost is relatively high. Therefore, from an academic and industrial perspective, new SCR catalysts should have characteristics such as a wide temperature window, low cost, and high low-temperature activity (<300°C).

[0004] Iron molybdate (Fe2(MoO4)3) has been widely concerned in the fields of photoelectricity, 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). China has rich reserves of iron ore and molybdenum ore, so the raw materials are widely available and low in price. However, in the field of NH3-SCR, the related research is less, and the researchers mainly focus on the use of molybdenum element in the form of Mo single atom or MoO3, and its own potential as a catalyst is ignored, which limits the research and application of iron molybdate in the field of denitrification. SUMMARY

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

[0006] The technical scheme of the present application is as follows:

[0007] A new catalyst for SCR flue gas denitrification, which is a low-crystallinity iron molybdate catalyst with anion or cation vacancies, Fe2(MoO4)3.

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

[0009] (1) Fe2(MoO4)3 precursor is prepared by sol-gel method, and calcination treatment is carried out to obtain Fe2(MoO4)3 catalyst;

[0010] (2) Fe2(MoO4)3 catalyst is put into an alkaline solution and stirred to obtain a mixed solution;

[0011] (3) The mixed solution is water-washed and filtered to neutral filtrate, and the precipitate is dried to obtain a low-crystallinity iron molybdate catalyst rich in anion or cation vacancies.

[0012] The calcination treatment temperature is 400-700℃, the calcination treatment time is 3-12h, and the heating rate is 3-8℃ / min.

[0013] The specific base solution preferably used includes, but is 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 water (NH3·H2O) solution, urea (CO(NH2)2) solution.

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

[0015] The drying temperature of the precipitate is 80-120℃.

[0016] The application of the above novel catalyst in the field of denitration.

[0017] The beneficial effects of the present application are:

[0018] (1) The iron molybdate catalyst in the present application effectively improves the low-temperature activity of the denitration reaction, and widens the temperature window (the removal rate of nitrogen oxides is greater than or equal to 80%) from 350-400℃ to 225-400℃, which has a good industrial application prospect.

[0019] (2) The catalyst preparation method of the present application is simple and fast, the conditions are easy to control, and the repeatability is high. The catalyst material used in the present application has a wide source and a relatively low price, and the catalyst cost is low and environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The NO catalytic removal activity graph of the catalyst prepared in Example 1 is shown in Figure 1. x The NO catalytic removal activity graph of the catalyst prepared in Example 2 is shown in Figure 2.

[0021] Figure 2 The NO catalytic removal activity graph of the catalyst prepared in Example 2 is shown in Figure 2. x The NO catalytic removal activity graph of the catalyst prepared in Example 2 is shown in Figure 2.

[0022] Figure 3 The X-ray diffraction spectrum (XRD) of the catalyst prepared in Example 5 is shown in Figure 5.

[0023] Figure 4 The X-ray photoelectron spectrum (XPS) of the catalyst prepared in Example 5 is shown in Figure 6, in which (a) is the O1s spectrum, and (b) is the Mo3d spectrum.

[0024] Figure 5 The NO catalytic removal activity graph of the catalyst prepared in Example 3 is shown in Figure 3. x The NO catalytic removal activity graph of the catalyst prepared in Example 3 is shown in Figure 3. DETAILED DESCRIPTION

[0025] The specific embodiments of the present application are further described below in conjunction with the drawings and technical solutions.

[0026] A method for preparing a novel catalyst for SCR flue gas denitrification. 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 alkali-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, and urea (CO(NH2)2) solution.

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

[0033] In the present invention, in step (2), the amount of the alkaline solution used 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 drying treatment temperature is 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, comprising the following steps:

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

[0039] Step (2) 1 g of catalyst A was dispersed in 30 mL of 0.34 M NaOH solution and stirred 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 then pressing it into a 20-40 mesh granular sample.

[0042] Example 2

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

[0044] Example 3

[0045] Referring to Example 1, the amount of alkaline 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 subjected to alkaline etching.

[0048] Test Example 1

[0049] Using the catalyst of Example 1, 0.5 g of 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 spectrum is shown in Table 1. Figure 3 shown.

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

[0055] <![CDATA[碱液浓度 / mol·L -1 ]]> crystallinity 0(Catalyst A) 60.10415 0.085 52.29148 0.17 41.86664 0.34 /

[0056] Test Example 4

[0057] 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 ) accounts for O 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 solution concentrations α / (O α +O β ) and Fe / Mo element content

[0059] <![CDATA[碱液浓度 / 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 types x Conversion rate

[0066]

[0067] In summary, alkali etching of FeMoO3 samples can be achieved by constructing Mo 6+ Vacancies, increase the amount of surface active oxygen, reduce crystallinity to improve the denitrification activity of the catalyst, with a low crystallinity iron molybdate catalyst rich in metal vacancies, with a denitrification performance of more than 80% in a wide temperature window (225 ~ 400 ℃), and has good industrial application prospects.

[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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A catalyst for SCR flue gas denitrification, characterized in that: The catalyst is a low-crystallinity iron molybdate catalyst with molybdenum ion vacancies; The invention is characterized in that it adopts a two-step synthesis method, namely, a sol-gel method coupled with alkaline etching, and the steps are as follows: (1) Fe2(MoO4)3 precursor was prepared by sol-gel method and calcined to obtain 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 with molybdenum vacancies; The invention is characterized in that the stirring time of the alkaline solution is 5 to 10 minutes, and the concentration of the alkaline solution is 0.1 to 0.34 mol·L -1 .

2. The catalyst according to claim 1, characterized in that The calcination temperature is 400-700° C., the calcination time is 3-12 h, and the heating rate is 3-8° C. / min.

3. The catalyst according to claim 1, 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.

4. The catalyst according to claim 1, characterized in that The temperature for the precipitate drying treatment is 80-120°C.

5. Use of the catalyst according to claim 1 in the field of denitrification.

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