A bismuth-nickel-iron composite oxide catalyst, a preparation method and application thereof

Abstract

The application discloses a bismuth-nickel-iron composite oxide catalyst, a preparation method and application. A bismuth source, a nickel source and an iron source are dissolved in a mixed solvent of ethanol and ethylene glycol, and then are fully stirred to obtain a mixed solution; oil amine and urea are added into the mixed solution, and after ultrasonic mixing, the mixture is moved to a polytetrafluoroethylene reaction kettle for a solvothermal reaction; after the reaction solution is cooled, the product is washed, dried and calcined, and finally the bismuth-nickel-iron composite oxide catalyst is obtained. The application prepares a spinel nanometer catalyst with stable performance, the NO removal rate of which reaches 90% at 175 DEG C, the denitration efficiency of which is as high as 100% at 225 DEG C, the medium-low temperature denitration performance of which is excellent, and the catalyst has the characteristics of high CO-SCR denitration efficiency and magnetic recyclability. In addition, proper bismuth doping is beneficial to improving the sulfur resistance of the nickel-iron catalyst, and thus the catalyst has a wide application prospect.

Description

Technical Field

[0001] This invention relates to a bismuth-nickel-iron composite oxide catalyst, its preparation method, and its application. Background Technology

[0002] Nitrogen oxides (NOx), as one of the major air pollutants, cause significant damage to the environment, and air pollution caused by NOx deserves the utmost attention. The main sources of NOx emissions are stationary and mobile pollution sources. Currently, most industrial production in my country still relies heavily on coal combustion for energy, and mobile source emissions have become a significant source of air pollution in large and medium-sized cities in China, making the prevention and control of this pollution urgent.

[0003] Selective catalytic reduction (SCR) technology has attracted widespread attention due to its high denitrification efficiency. Under the action of a catalyst, nitrogen oxides undergo a reduction reaction to generate nitrogen gas. NH3-SCR technology has good NO reduction performance in practical applications. x Removal efficiency is currently a relatively mature and widely used denitrification method, but it suffers from problems such as high cost and serious secondary pollution. In CO-SCR technology, CO has strong reducing properties and can be used as a reducing agent to effectively remove NO. x The CO-SCR method reduces NO emissions in the regenerated flue gas by reducing NO to N2, while CO is also removed. This effectively reduces the cost of denitrification and improves air quality. Therefore, the CO-SCR method is one of the more ideal denitrification technologies.

[0004] Spinel oxide is a polymetallic oxide. Studies have shown that the catalytic performance of AB₂O₄ spinel oxide for NOx catalysis is significantly influenced by the metal cations constituting the spinel structure, and the synergistic effect of the spinel structure greatly enhances the selectivity of the reduction product nitrogen. Nickel-iron spinel catalysts (NiFe₂O₄) have an inverse spinel structure and have been reported in the H₂-SCR field. Their excellent water resistance makes them industrially applicable, but they still have drawbacks such as easy catalyst agglomeration and large size, poor sulfur resistance, and an unsatisfactory activity temperature window at medium and low temperatures. Currently, spinel-structured catalysts are generally mainly used for H₂-SCR, with B-site metals, including noble metals (such as Pd) and transition metals (Mn, Zn, Al), as the main doping modifiers. However, the use of the transition metal element bismuth (Bi) in thermocatalysis is relatively rare. Therefore, this is the first time that the proposed solution to the above problems has been made by using the transition metal element bismuth (Bi) for A-site doping. Summary of the Invention

[0005] The present invention provides a bismuth-nickel-iron composite oxide catalyst, its preparation method, and its application in order to solve the problems existing in the prior art.

[0006] The technical solutions adopted in this invention are as follows:

[0007] A method for preparing a bismuth-nickel-iron composite oxide catalyst, characterized by comprising the following steps:

[0008] 1) Dissolve the bismuth source, nickel source and iron source together in a mixed solvent of ethanol and ethylene glycol, and then stir thoroughly to obtain a mixed solution;

[0009] 2) Add oleylamine and urea to the mixed solution in step 1), and after ultrasonication and stirring, transfer it to a polytetrafluoroethylene reactor for solvothermal reaction.

[0010] 3) After the reaction solution is cooled, the product is washed, dried, and calcined to finally obtain the bismuth-nickel-iron composite oxide catalyst.

[0011] Furthermore, the bismuth source is one or more of bismuth sulfate, bismuth chloride, and bismuth nitrate.

[0012] Furthermore, the nickel source is one or more of nickel sulfate, nickel nitrate, and nickel carbonate.

[0013] Furthermore, the iron source is one or more of ferric nitrate, ferric sulfate, and ferric phosphate.

[0014] Furthermore, the molar ratio of the bismuth source, nickel source and iron source is (0-0.2):(0.8-1):2; the volume ratio of ethanol to ethylene glycol is (0-2):(4:0).

[0015] Furthermore, in step 2), the volume of oleylamine added is 0-5 mL, and the mass of urea is 0-1 g.

[0016] Furthermore, in step 2), the solvothermal reaction temperature is 120-240℃, and the reaction time is 6-48h.

[0017] Furthermore, in step 3), the washing process involves washing 2-6 times with anhydrous ethanol, and the drying temperature is 80-120℃ for 6-24 hours.

[0018] Furthermore, in step 3), the calcination temperature is 400-600℃, the holding time is 4-6h, and the heating rate is 1-10℃ / min.

[0019] The present invention also discloses a bismuth-nickel-iron composite oxide catalyst prepared by the above preparation method.

[0020] The present invention also discloses the application of the above-mentioned bismuth-nickel-iron composite oxide catalyst, specifically to achieve CO-SCR flue gas denitrification under medium and low temperature conditions of 175-225℃. The bismuth-nickel-iron composite oxide catalyst has obvious anti-sulfur performance.

[0021] The present invention has the following beneficial effects:

[0022] 1) The catalyst of this invention has excellent denitrification efficiency, with NO denitrification efficiency as high as 90% to 100% in the low-temperature activity window of 175-225℃, realizing effective low-temperature flue gas denitrification.

[0023] 2) The optimal catalytic performance of the present invention is achieved when the Bi:Ni:Fe molar ratio is 0.05:0.95:2. Excessive or insufficient ratios are not conducive to the CO-SCR reaction.

[0024] 3) The catalyst of this invention exhibits a nanostructure, providing more active sites for the reaction, thereby further improving the denitrification efficiency of the catalyst.

[0025] 4) The catalyst prepared by this invention has a stable spinel structure and is magnetic and recyclable. Attached Figure Description

[0026] Figure 1 This is a diagram of the evaluation device for the low-temperature CO-SCR denitrification process.

[0027] Figure 2 These are TEM images of the catalysts obtained in Example 3 and Comparative Example 1 of the present invention.

[0028] (a) The prepared NiFe2O4 catalyst; (b) The prepared Bi 0.05 Ni 0.95 Fe2O4 catalyst

[0029] Figure 3 The graphs show the CO-SCR denitrification performance of the catalysts obtained in Examples 1-4 and Comparative Example 1 of this invention.

[0030] Figure 4 This is a comparison graph showing the sulfur resistance performance of the catalysts in Example 3 and Comparative Example 1. Detailed Implementation

[0031] The invention will now be further described with reference to the accompanying drawings.

[0032] Example 1

[0033] Dissolve 0.015g bismuth nitrate, 0.86g nickel nitrate and 2.42g ferric nitrate in 20mL ethanol and 40mL ethylene glycol, and stir until completely dissolved.

[0034] Add 3 mL of oleylamine and 0.531 g of urea to the mixed solution, sonicate for 20 min, and stir for 1 h. Pour the mixed solution into a 100 mL polytetrafluoroethylene reactor, and place the reactor in a 200 °C oven to maintain the temperature for 24 h.

[0035] After the reaction vessel cooled, the resulting black solution was centrifuged, washed three times with anhydrous ethanol, then dried in an 80℃ drying oven for 12 hours, and finally calcined in a muffle furnace at 400℃ for 4 hours at a rate of 2℃ / min.

[0036] After the reaction, the viscous black solution obtained was washed, dried, and calcined to obtain Bi. 0.01 Ni 0.09 Fe2O4 catalyst.

[0037] Example 2

[0038] Dissolve 0.044g bismuth nitrate, 0.85g nickel nitrate and 2.42g ferric nitrate in 20mL ethanol and 40mL ethylene glycol, and stir until completely dissolved.

[0039] Add 3 mL of oleylamine and 0.536 g of urea to the mixed solution, sonicate for 15 min, and stir for 1.5 h. Pour the mixed solution into a 100 mL polytetrafluoroethylene reactor, and place the reactor in a 200 °C oven to maintain the temperature for 24 h.

[0040] After the reaction vessel cooled, the resulting black solution was centrifuged, washed three times with anhydrous ethanol, then dried in a 90℃ drying oven for 12 hours, and finally calcined in a muffle furnace at 420℃ for 4 hours at a rate of 2℃ / min.

[0041] After the reaction, the viscous black solution obtained was washed, dried, and calcined to obtain Bi. 0.03 Ni 0.97 Fe2O4 catalyst.

[0042] Example 3

[0043] Dissolve 0.073g bismuth nitrate, 0.83g nickel nitrate and 2.42g ferric nitrate in 20mL ethanol and 40mL ethylene glycol, and stir until completely dissolved.

[0044] Add 3 mL of oleylamine and 0.53 g of urea to the mixed solution, sonicate for 20 min, and stir for 1.5 h. Pour the mixed solution into a 100 mL polytetrafluoroethylene reactor, and place the reactor in a 200 °C oven to maintain the temperature for 24 h.

[0045] After the reaction vessel cooled, the resulting black solution was centrifuged, washed three times with anhydrous ethanol, then dried in an 80℃ drying oven for 10 hours, and finally calcined in a muffle furnace at 450℃ for 4.5 hours at a rate of 2℃ / min.

[0046] After the reaction, the viscous black solution obtained was washed, dried, and calcined to obtain Bi. 0.05 Ni 0.95 Fe2O4 catalyst.

[0047] Example 4

[0048] Dissolve 0.146g bismuth nitrate, 0.785g nickel nitrate and 2.42g ferric nitrate in 20mL ethanol and 40mL ethylene glycol, and stir until completely dissolved.

[0049] Add 3 mL of oleylamine and 0.538 g of urea to the mixed solution, sonicate for 25 min and stir for 1.5 h. Pour the mixed solution into a 100 mL polytetrafluoroethylene reactor and place the reactor in a 200 °C oven to maintain the temperature for 24 h.

[0050] After the reaction vessel cooled, the resulting black solution was centrifuged, washed three times with anhydrous ethanol, then dried in a 100°C drying oven for 10 hours, and finally calcined in a muffle furnace at 500°C for 4 hours at a rate of 2°C / min.

[0051] After the reaction, the viscous black solution obtained was washed, dried, and calcined to obtain Bi. 0.1 Ni 0.9 Fe2O4 catalyst.

[0052] Comparative Example 1

[0053] Dissolve 0.746g of nickel nitrate and 2.39g of ferric nitrate in 20mL of ethanol and 40mL of ethylene glycol, and stir until completely dissolved.

[0054] Add 3 mL of oleylamine and 0.535 g of urea to the mixed solution, sonicate for 30 min, and stir for 2 h. Pour the mixed solution into a 100 mL polytetrafluoroethylene reactor, and place the reactor in a 200 °C oven to maintain the temperature for 24 h.

[0055] After the reaction vessel cooled, the resulting black solution was centrifuged, washed three times with anhydrous ethanol, then dried in an 80℃ drying oven for 12 hours, and finally calcined in a muffle furnace at 500℃ for 5 hours at a rate of 2℃ / min.

[0056] After the reaction was completed, the viscous black solution was washed, dried, and calcined to obtain the NiFe2O4 catalyst.

[0057] Using a fixed-bed evaluation device (such as...) Figure 1 To evaluate the performance of the prepared catalyst, the CO-SCR test conditions are as follows:

[0058] Total gas flow rate: 100 mL / min;

[0059] The NO concentration is 500 ppm;

[0060] The CO concentration is 5000 ppm;

[0061] N2 is used as the balance gas, the catalyst dosage is 0.1 g, and the mass hourly space velocity is 60000 mg·h⁻¹. -1 ·g -1 Performance tests were conducted under normal pressure, starting from room temperature and gradually increasing the temperature.

[0062] Figure 2 The morphology and structure of the catalysts in Example 3 and Comparative Example 1 were studied for TEM characterization.

[0063] Figure 2 Figure (a) shows the prepared NiFe2O4 catalyst (i.e., Comparative Example 1), with a size of approximately 10 nm, regular morphology, and obvious aggregation. Figure (b) shows the prepared Bi... 0.05 Ni 0.95 The Fe2O4 catalyst has smaller nanoparticles, with a size of about 5 to 10 nm, and is more uniformly dispersed (i.e., Example 3). The reduced catalyst particle size means that it will have a larger specific surface area to provide more active sites, thereby improving catalytic performance.

[0064] Figure 3 The CO-SCR denitrification performance of the catalysts obtained in Examples 1-4 and Comparative Example 1 is shown in the figure.

[0065] Within the activity testing temperature range, Bi 0.05 Ni 0.95 The NO conversion rate of the Fe2O4 catalyst was significantly higher than that of other catalysts, reaching 90% at 175℃. At 225℃, its denitrification efficiency reached 100%, demonstrating excellent low- and medium-temperature denitrification performance. These results indicate that the addition of a certain amount of Bi source significantly improved the NO removal efficiency of the catalyst. In contrast, the control NiFe2O4 catalyst showed a NO conversion rate of only about 60% at 175℃, while the optimized Bi source... 0.05 Ni 0.95 The denitrification performance of Fe2O4 catalyst can be improved by 30%. It is worth noting that when the Bi content is too high, the NO conversion rate of the catalyst decreases, indicating that excessive Bi doping is detrimental to NO conversion.

[0066] Figure 4 This is a comparison graph showing the sulfur resistance performance of the catalysts in Example 3 and Comparative Example 1.

[0067] The test temperature was 225℃. After stabilizing at 100% denitrification efficiency for 20 minutes, 100 ppm SO2 was introduced into the reaction gas to examine the difference in sulfur resistance between the catalysts of Example 3 and Comparative Example 1. After continuously introducing SO2 gas for 120 minutes and then cutting off the SO2 gas, it was found that the CO-SCR denitrification performance of the NiFe2O4 catalyst continuously decreased. This may be because sulfites occupied some of the active sites of the catalyst, and SO2 gas caused irreversible sulfur poisoning of the NiFe2O4 catalyst; while Bi...0.05 Ni 0.95 The Fe2O4 catalyst exhibits significant sulfur resistance; even with the SO2 gas cut off, its denitrification performance can still gradually improve, indicating that Bi doping can enhance the sulfur resistance of nickel-iron catalysts. This result is the first of its kind.

[0068] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. The application of a bismuth-nickel-iron composite oxide catalyst, characterized in that... : CO-SCR flue gas denitrification was achieved under medium-low temperature conditions of 175-225°C; the catalyst preparation method includes the following steps: Dissolve 0.073 g bismuth nitrate, 0.83 g nickel nitrate, and 2.42 g ferric nitrate in 20 mL ethanol and 40 mL ethylene glycol, stirring until completely dissolved; Add 3 mL of oleylamine and 0.53 g of urea to the mixed solution, sonicate for 20 min, and then stir for 1.5 h. The mixed solution was poured into a 100 mL polytetrafluoroethylene (PTFE) reactor, and the reactor was placed in a 200°C oven and kept at a constant temperature for 24 h. After the reactor cooled, the resulting black solution was centrifuged, washed three times with anhydrous ethanol, and then dried in an 80°C oven for 10 h. Finally, it was calcined in a muffle furnace at 450°C for 4.5 h at a rate of 2°C / min. After the reaction, the viscous black solution obtained was washed, dried, and calcined to obtain Bi. 0.05 Ni 0.95 Fe2O4 catalyst.

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