A cerium-based catalyst against poisoning and low by-products, and a preparation method and application thereof

Abstract

The application discloses an anti-poisoning low-byproduct cerium catalyst and a preparation method and application thereof. The catalyst is prepared by dissolving Cr(NO3)3, Ce(NO3)3 and ZrO(NO3)2 into H2O with NaOH as a precipitant to synthesize a uniformly dispersed composite metal oxide catalyst. The prepared catalyst has abundant oxygen vacancies and acid sites, exhibits long-time stability and excellent low-temperature catalytic performance in CVOCs catalytic oxidation, and has less byproducts in tail gas after catalysis. The raw materials used in the method are cheap and easy to obtain, the preparation method is simple and easy to popularize, and in addition, the catalyst exhibits excellent high-activity and high-selectivity CVOCs catalytic oxidation activity.

Description

Technical Field

[0001] This invention relates to the field of CVOCs catalysts, specifically to a cerium catalyst with low poisoning resistance and low byproducts, its preparation method, and its application. Background Technology

[0002] The continuous advancement of industrialization and urbanization in my country has brought about numerous ecological and environmental problems, with air pollution being particularly critical. Chlorinated volatile organic compounds (CVOCs) possess characteristics such as stronger biotoxicity, higher chemical stability, and extreme difficulty in biodegradation, causing environmental pollution and harming human health. Currently, the elimination of CVOCs pollutants from stationary source exhaust emissions mainly employs low-temperature catalytic oxidation technology. Due to its advantages such as high treatment efficiency, low reaction temperature, low energy consumption, and low risk of secondary pollution, it is a promising CVOCs control technology.

[0003] Cerium-based catalysts have Ce 4+ and Ce 3+ With two oxidation states, Cr can undergo redox cycles, thus exhibiting excellent oxygen storage and release capabilities, and is widely used in environmental catalysis. As an inexpensive transition metal element, Cr exhibits good activity in the Deacon reaction, which is beneficial for dechlorination. Cr formed by the interaction of cerium and chromium... 6+ Zr possesses strong oxidizing power, which is beneficial for the deep oxidation of CVOCs. Zr's large ionic radius allows it to partially replace Ce in the CeO2 lattice. 4+ This process forms a CeO2-ZrO2 solid solution, significantly increasing the number of active oxygen species, their mobility, and the number of acidic sites in the catalyst, which is beneficial for reducing toxic byproducts. Furthermore, for composite metal oxide catalysts, the balance between acidic and active sites is a key factor in promoting the catalytic oxidation of CVOCs. Therefore, designing and synthesizing Ce-based oxide catalysts with high selectivity and high stability for the low-temperature, harmless removal of CVOCs is of great significance for the efficient removal of CVOCs in industries such as coating, printing and dyeing, and pharmaceuticals. Summary of the Invention

[0004] This invention provides a cerium-based catalyst with low poisoning resistance and low byproducts, its preparation method, and its applications. The prepared catalyst possesses abundant oxygen vacancies and acidic sites, exhibiting long-term stability and excellent low-temperature catalytic performance in the catalytic oxidation of CVOCs (at a space velocity of 15000 mL·g⁻¹). -1 ·h -1 (At a chlorobenzene concentration of 500 ppm, a removal efficiency of 90% can be achieved at 240℃). This catalyst produces fewer toxic byproducts in the tail gas after catalytic oxidation. Furthermore, the raw materials used in this catalyst are inexpensive and readily available, the preparation method is simple and rapid, energy consumption is low, and the yield is high, making it a promising candidate for catalytic oxidation of CVOCs.

[0005] The purpose of this invention is to provide a method for preparing a cerium-based catalyst with low poisoning and low by-products for the low-temperature catalytic removal of CVOCs, as well as the application of the catalyst prepared by this method in the removal of CVOCs in industries such as coating, printing and dyeing, and pharmaceuticals.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a cerium catalyst resistant to poisoning and with low byproducts includes the following steps:

[0008] 1) Weigh out Cr(NO3)3 and Ce(NO3)3, dissolve them in water, and stir magnetically to form a mixed solution A;

[0009] Measure out ZrO(NO3)2 and dissolve it in water, and denote it as solution B. Add solution B to mixed solution A under magnetic stirring, and then add NaOH solution dropwise until the pH value rises to 9-11, and continue stirring.

[0010] 2) After stirring and aging, the precipitate is separated by centrifugation. After removing the supernatant, the collected precipitate is washed with water by centrifugation. The product obtained after washing is dried and placed in an air atmosphere in a muffle furnace to be heated to 425-575℃ and kept for 3-5 hours. After natural cooling, a cerium-based catalyst with resistance to poisoning and low by-products is obtained.

[0011] This invention involves dissolving Cr(NO3)3 and Ce(NO3)3 in deionized water, slowly adding ZrO(NO3)2 solution, and using NaOH as a precipitant to precipitate the metal ions and disperse them evenly, thereby obtaining a ternary cerium-based composite oxide catalyst.

[0012] In this invention, firstly, a mesoporous catalyst with abundant active centers and acidic centers with uniform element dispersion was prepared by co-precipitation using Cr(NO3)3, Ce(NO3)3, and ZrO(NO3)2 as raw materials; secondly, the cerium-based composite oxide catalyst significantly improved stability and reduced by-products compared with ordinary cerium dioxide; and thirdly, this method can be used to prepare a variety of cerium-based composite oxide catalysts.

[0013] In this invention, Ce provides abundant oxygen vacancies and reactive sites, Cr provides dechlorination sites, enhancing the catalyst's resistance to chlorine poisoning, and Zr strengthens deep oxidation capabilities and inhibits the formation of toxic byproducts. The interaction of these three metal elements synergistically promotes the efficient catalytic degradation of chlorobenzene, resulting in a cerium-based catalyst with resistance to poisoning and low byproduct production.

[0014] In step 1), the molar ratio of Cr(NO3)3 to Ce(NO3)3 is 1:1 to 4, more preferably 1:2; the molar ratio of Cr(NO3)3 to Ce(NO3)3 is fixed at 1:2, and the molar ratio of the mixture of ZrO(NO3)2 with Cr(NO3)3 and Ce(NO3)3 is 1 / 3, 1 / 6, 1 / 9, or 1 / 12, preferably 1 / 9.

[0015] The mixing should be carried out under continuous stirring for 20–40 min, more preferably 30 min. The preferred concentration of the added NaOH solution is 3–9 mol·L⁻¹. -1 Preferably 6 mol·L -1 .

[0016] In step 2), the room temperature aging time is 8 to 14 hours, with the optimal time being 12 hours.

[0017] The precipitate should be washed with water 5-7 times, with 6 times being optimal. Six washings are the preferred number; fewer washings will result in an alkaline precipitate.

[0018] Drying conditions: Dry at 70-90℃ for 8-14 hours, with the optimal condition being drying at 80℃ for 12 hours.

[0019] The optimal method is to calcine at 450–550°C for 3.5–4.5 hours in air, and preferably at 500°C for 4 hours in air.

[0020] In step 1), the chemical formula of the Ce-based composite oxide catalyst is Zr(CeCr). x 1 / x represents the molar ratio of ZrO(NO3)2 mixed with Cr(NO3)3 and Ce(NO3)3 in different samples.

[0021] The preferred molar ratio of Cr(NO3)3 to Ce(NO3)3 is 1:2;

[0022] The preferred molar ratio of ZrO(NO3)2 to Cr(NO3)3 and Ce(NO3)3 is 1:9.

[0023] Most preferably, a method for preparing a cerium catalyst resistant to poisoning and with low byproducts for low-temperature removal of CVOCs includes the following steps:

[0024] 1) Weigh out appropriate amounts of Cr(NO3)3 and Ce(NO3)3 and dissolve them in deionized water. Stir magnetically for 30 minutes to form a mixed solution A. Measure out an appropriate amount of ZrO(NO3)2 and dissolve it in deionized water, labeled as solution B. Slowly add solution B while stirring magnetically. Weigh out an appropriate amount of NaOH and dissolve it in deionized water. Slowly add the NaOH solution dropwise while stirring magnetically until the pH value slowly rises to around 10. Continue stirring for 30 minutes. Stop stirring.

[0025] 2) After aging at room temperature overnight, the precipitate was centrifuged at 8000 rpm for 5 min / cycle. After removing the supernatant, the collected precipitate was washed 6 times with distilled water by centrifugation. The product obtained after washing was placed in an oven and dried at 80℃ for 12 h. The dried product was then placed in a muffle furnace and dried at 5℃·min. -1 The temperature was increased to 500℃ and held for 4 hours, and then naturally cooled to obtain the catalyst.

[0026] A cerium catalyst with low byproduct resistance to poisoning and low byproducts prepared by the above preparation method is a low-temperature CVOCs removal catalyst.

[0027] The above-mentioned cerium catalyst with low poisoning resistance and low by-products is used for the removal of CVOCs from the exhaust gas of a pharmaceutical plant.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The raw materials used are inexpensive and readily available, the preparation method is simple, the equipment is simple, it is easy to promote, and it can be produced on a large scale;

[0030] 2. It is a universal method for preparing Ce-based composite oxides, and can also be used to prepare high-performance CeCr, Zr(CeCr) and other multi-element composite oxides, as well as multi-element Ce-based composite oxide catalysts composed of these elements.

[0031] 3. The cerium-based composite oxide catalyst prepared by this method has advantages such as abundant active and acidic centers and uniform dispersion of metal elements. It has good resistance to chlorine poisoning and low toxic byproducts, thus exhibiting excellent low-temperature and high-selectivity CVOCs catalytic oxidation ability. Attached Figure Description

[0032] Figure 1 The XRD results are for the cerium-based composite oxide catalysts in Examples 1, 2, 3, 4, and 5.

[0033] Figure 2The SEM results for the cerium-based composite oxide catalysts in Examples 3 and 5 are shown below. (a) is the SEM spectrum of the CeO2 catalyst, (b) is the SEM spectrum of the Ce2Cr1 catalyst, and (c) is the SEM spectrum of the Zr(CeCr)3 catalyst.

[0034] Figure 3 The N2- adsorption-desorption results are for the cerium-based composite oxide catalysts in Examples 1, 2, 3, 4, and 5.

[0035] Figure 4 The H2-TPR results are for the cerium-based composite oxide catalysts in Examples 1, 2, 3, 4, and 5.

[0036] Figure 5 The results are NH3-TPD of cerium-based composite oxide catalysts in Examples 1, 2, 3, 4, and 5.

[0037] Figure 6 The results are GC / MS of the tail gas byproducts of the cerium-based composite oxide catalysts in Examples 3 and 5.

[0038] Figure 7 Examples 1, 2, 3, 4, and 5 show the catalytic oxidation activity (removal efficiency) of the Zr(CeCr) series catalysts for CVOCs.

[0039] Figure 8 Examples 1, 2, 3, 4, and 5 show the catalytic oxidation activity (mineralization efficiency) of the Zr(CeCr) series catalysts for cerium-based composite oxides. Detailed Implementation

[0040] Example 1: Preparation of Zr(CeCr)1 cerium-based composite oxide catalyst

[0041] Accurately weigh appropriate amounts of Cr(NO3)3 and Ce(NO3)3 and dissolve them in 100 ml of deionized water to form 0.2 mol·L⁻¹ -1 A mixed solution of Ce(NO3)3 and 0.1 mol·L⁻¹ Cr(NO3)3 was stirred continuously for 30 min to form solution A; an appropriate amount of ZrO(NO3)2 was dissolved in 100 ml of deionized water to form 0.1 mol·L⁻¹ Cr(NO3)3 solution. -1 ZrO(NO3)2 solution, denoted as solution B. Weigh out an appropriate amount of NaOH and dissolve it in deionized water to form a 6 mol·L⁻¹ solution. -1NaOH solution. Under magnetic stirring, slowly add NaOH solution dropwise until the pH slowly rises to 10. Continue stirring for 30 min. Stop stirring. Age at room temperature (25℃) for 12 hours. Separate the precipitate by centrifugation at 8000 rpm for 5 min / time. After removing the supernatant, wash the collected precipitate 6 times with distilled water by centrifugation. Place the washed product in an oven and dry at 80℃ for 12 h. Place the dried product in a muffle furnace and heat to 500℃ at a rate of 5℃·min⁻¹ and maintain for 4 h. After natural cooling, the catalyst is obtained.

[0042] Example 2: Preparation of Zr(CeCr)₂ cerium-based composite oxide catalyst

[0043] The concentration of the ZrO(NO3)2 solution weighed in Example 1 was changed to 0.05 mol·L⁻¹. -1 With all other conditions unchanged, a Ce-based composite oxide catalyst Zr(CeCr)2 sample was obtained.

[0044] Example 3: Preparation of Zr(CeCr)3 cerium-based composite oxide catalyst.

[0045] The concentration of the ZrO(NO3)2 solution weighed in Example 1 was changed to 0.033 mol·L⁻¹. -1 With all other conditions unchanged, a Ce-based composite oxide catalyst Zr(CeCr)3 sample was obtained.

[0046] Example 4: Preparation of Zr(CeCr)4 cerium-based composite oxide catalyst

[0047] The concentration of the ZrO(NO3)2 solution weighed in Example 1 was changed to 0.025 mol·L⁻¹. -1 With all other conditions unchanged, a Ce-based composite oxide catalyst Zr(CeCr)4 sample was obtained.

[0048] Example 5: Preparation of Ce2Cr1 cerium-based composite oxide catalyst

[0049] The concentration of the ZrO(NO3)2 solution weighed in Example 1 was changed to 0 mol·L⁻¹. -1 With all other conditions unchanged, Ce-based composite oxide catalyst Ce2Cr1 sample was obtained.

[0050] The XRD results of the cerium-based composite oxide catalyst are as follows: Figure 1 As shown in the figure, the diffraction peaks of some samples are mainly consistent with the characteristic peaks of the cubic fluorite-type CeO2 structure. No CrOx or ZrO2 phases were observed. The decrease in peak intensity of these characteristic peaks is due to some Cr and Zr ions entering the CeO2 lattice, forming defect sites, which leads to the decrease in peak intensity.

[0051] SEM results of cerium-based composite oxide catalysts are as follows: Figure 2 As shown in the figure, the Zr(CeCr)3 catalyst has a large number of porous structures.

[0052] The N2- adsorption-desorption results of cerium-based composite oxide catalysts are as follows: Figure 3 As shown in the figure, the catalyst exhibits a rich mesoporous structure.

[0053] The H2-TPR results of cerium-based composite oxide catalysts are as follows: Figure 4 As shown in the figure, the Zr(CeCr)3 catalyst exhibits the lowest hydrogen reduction peak temperature, demonstrating its optimal low-temperature oxidation performance.

[0054] The NH3-TPD results of the cerium-based composite oxide catalyst are as follows: Figure 5 As shown in the figure, the Zr(CeCr)3 catalyst has the highest amount of medium-strong acid, indicating that it has more acidic sites, which is beneficial to the adsorption and activation of CVOCs.

[0055] GC / MS results of cerium-based composite oxide catalysts are as follows Figure 6 As shown, the Δ peak is negligible, originating from the loss of polysiloxane components in the stationary phase of the chromatographic column. The molecular formulas and names corresponding to its numbers are shown in Table 1. The figure shows that the Zr(CeCr)3 catalyst significantly reduces the amount of polychlorinated byproducts in its exhaust gas compared to the Ce2Cr1 catalyst.

[0056] Table 1

[0057]

[0058]

[0059] Example 6: Evaluation of the catalytic oxidation performance of different Ce-based composite oxide catalysts for CVOCs

[0060] The catalysts prepared in Examples 1, 2, 3, 4, and 5 were applied to the catalytic oxidation of CVOCs, and all exhibited good catalytic activity. The removal efficiencies of the catalysts prepared in Examples 1, 2, 3, 4, and 5 are as follows: Figure 7 As shown in Figure 8, the reaction was carried out on a CVOCs catalytic oxidation evaluation device, which mainly consists of four parts: a gas pipeline, a fixed-bed reactor, a flow control system, and a gas detection system. During the experiment, a mass flow meter was used to accurately control each gas stream. A quartz tube with an outer diameter of 10 mm and an inner diameter of 6 mm was used as the catalytic reactor. The reactor was heated by an electric resistance furnace, and the temperature inside the reactor was monitored by a K-type thermocouple. The total flow rate of the mixed gas was 50 mL / min. -1The volume fraction of O2 is 20%, and the chlorobenzene is controlled to be 1000 ml·m³ by adjusting the ratio of two standard air flows. -3 During the experiment, the catalyst loading was 200 mg, the particle size was 40–60 mesh, and the corresponding mass hourly space velocity (WHSV) was 15000 mL·(g·h). -1 .

Claims

1. A method for preparing a cerium-based catalyst with low poisoning resistance and low byproducts, characterized in that, Includes the following steps: 1) Weigh out Cr(NO3)3 and Ce(NO3)3, dissolve them in water, and stir magnetically to form a mixed solution A; Weigh out ZrO(NO3)2 and dissolve it in water, denoted as solution B. Add solution B to mixed solution A under magnetic stirring, then add NaOH aqueous solution dropwise until the pH value rises to 9-11, and continue stirring. The molar ratio of Cr(NO3)3 to Ce(NO3)3 is 1:2; The molar ratio of ZrO(NO3)2 to the sum of Cr(NO3)3 and Ce(NO3)3 is 1:9; The concentration of the NaOH aqueous solution is 3~9 mol·L⁻¹. -1 ; 2) After stirring and aging for 8-14 hours, the precipitate is separated by centrifugation. After removing the supernatant, the collected precipitate is washed with water by centrifugation. The product obtained after washing is dried under the following conditions: drying at 70-90℃ for 8-14 hours. The dried product is then placed in an air atmosphere and heated to 450-550℃ and maintained for 3.5-4.5 hours. After natural cooling, a cerium catalyst with low by-product resistance to poisoning is obtained.

2. The method for preparing the cerium-based catalyst with low by-product resistance to poisoning according to claim 1, characterized in that, In step 1), the mixture is magnetically stirred for 20-40 minutes to form a mixed solution A.

3. The method for preparing the cerium-based catalyst with low byproduct resistance to poisoning according to claim 1, characterized in that, In step 2), the collected precipitate is washed with water by centrifugation 5 to 7 times.

4. A cerium-based catalyst with low byproduct resistance to poisoning prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the cerium-based catalyst with low poisoning and low by-products as described in claim 4 in the removal of CVOCs from industrial exhaust gases.

Images