Coconut shell activated carbon supported metal oxide catalysts and their application in flue gas purification

Abstract

This invention relates to the field of flue gas purification catalyst technology, specifically to a coconut shell activated carbon-supported metal oxide catalyst and its application in flue gas purification. It uses hierarchical porous coconut shell activated carbon as a carrier, constructed sequentially through surface Al2O3 modification, inner cerium-lanthanum composite oxide loading, and a core manganese-copper active center. The key to its preparation lies in a three-step sequential impregnation-calcination process: first, the carrier surface is modified with aluminum sulfate solution; then, cerium and lanthanum nitrates are loaded to form a catalyst promoter layer; finally, the active components are loaded with an alcohol-water solution of manganese acetate and copper, and activated by calcination in a weakly reducing atmosphere. This method, by constructing a gradient structure of the modification layer, promoter layer, and active layer, significantly improves the dispersion of the active components, the low-temperature activity of the catalyst, and its anti-sintering ability. The resulting catalyst exhibits advantages such as high activity, long lifespan, and good stability in the field of volatile organic compound purification.

Description

Technical Field

[0001] This invention relates to the field of flue gas purification catalyst technology, and more specifically, to a coconut shell activated carbon supported metal oxide catalyst and its application in flue gas purification. Background Technology

[0002] The practical application of coconut shell activated carbon supported on transition metal oxides as a flue gas purification catalyst is severely limited by the key bottleneck of sulfur poisoning. In complex flue gas containing SO2, NOx, and VOCs simultaneously, existing catalysts face a dilemma: Firstly, highly active sites compete with sulfides for poisoning: The transition metal active centers such as Mn and Fe introduced to obtain high catalytic activity have a strong chemical affinity for SO2. SO2 will preemptively occupy and permanently occupy these active sites, forming a metal sulfate shell with extremely high thermal stability. This leads to the rapid and irreversible decay of the core function of the catalyst. Traditional anti-sulfur strategies (such as adding alkaline promoters) often come at the cost of sacrificing low-temperature activity or VOCs degradation efficiency.

[0003] Secondly, the sulfur blockage effect of the adsorption channels on the carrier: The rich microporous structure of coconut shell activated carbon is the basis for its adsorption and concentration of pollutants. However, SO2 and its oxidation products tend to accumulate at the pore inlets and inner surfaces, which not only directly poisons the active components loaded on it, but also physically blocks the mass transfer channels, causing the internal active sites to become ineffective due to lack of feed, resulting in the overall catalyst lifetime being far lower than the weighted expected lifetime of each component.

[0004] Currently, the industry generally views sulfur poisoning as a problem that needs to be tolerated or mitigated, lacking a fundamental solution that proactively manages the migration and transformation pathways of sulfur species from the initial catalyst design level. Summary of the Invention

[0005] The purpose of this invention is to provide a coconut shell activated carbon supported metal oxide catalyst and its application in flue gas purification. A sulfur species management and conversion zone is constructed inside the catalyst system to achieve the targeted capture and harmless conversion of SO2, thereby creating a local low-sulfur or even sulfur-free microenvironment for the core catalytic reaction zone, ensuring the long-term stable operation of the main catalytic function, and solving the problems mentioned in the background art.

[0006] To achieve the above objectives, firstly, the present invention provides a method for preparing a coconut shell activated carbon supported metal oxide catalyst, comprising the following steps: S1. Carrier pretreatment and surface modification: The hierarchical pore coconut shell activated carbon is immersed in a precursor solution containing aluminum source and organic carbon source. After drying, it is calcined at 400-500℃ under an inert atmosphere to form a surface composite modification layer on its outer surface and at the entrance of the macropores. S2, inner layer functional component loading: The carrier treated in S1 is immersed in an aqueous solution containing cerium salt and lanthanum salt of a specific viscosity, and dried using a gradient temperature program to position the precursor in the middle region of the carrier channels. Then it is calcined in an air atmosphere to form an inner layer Ce-La composite oxide. S3, Core Active Component Loading: The support treated in S2 is immersed in an alcohol-water mixed solution containing manganese and copper salts, dried at low temperature, and calcined in a weakly reducing atmosphere to form a core Mn-Cu-based catalytic active center inside the pores of the support. S4. Post-processing: Cool the product obtained in S3 and store it in an inert atmosphere to obtain the catalyst.

[0007] Secondly, the present invention provides the components, proportions, and working principle of the catalyst, including: The surface composite modification layer is mainly composed of aluminum species (such as alumina and aluminum-carbon complexes) formed by pyrolysis in an inert atmosphere and pyrolytic carbon derived from organic carbon sources (rich in oxygen-containing functional groups such as quinones). Its function is to reversibly adsorb and pre-convert SO2 molecules that enter the pores, and regulate their inward penetration rate and morphology, rather than permanently fix them.

[0008] In the inner Ce-La composite oxide, the molar ratio of Ce to La is (3:1) to (5:1). This component is specifically designed for the catalytic conversion of sulfur-containing species that penetrate through the surface layer, transforming them into sulfates and causing surface migration, thus preventing their deposition at the core active sites.

[0009] In the core Mn-Cu-based catalytic active center, Mn is present in a non-stoichiometric ratio with MnO. x (x=1.8-1.9) Cu exists in a highly dispersed state and interacts strongly with Mn species. The molar ratio of Mn to Cu is (10:1)-(20:1). Under the protection of the local low-sulfur microenvironment created by the preceding components, this region is dedicated to the efficient catalysis of NOx reduction or oxidation and deep oxidation of VOCs.

[0010] Thirdly, this invention provides the functional synergy and action process of the catalyst: In sulfur-containing flue gas, SO2 is first buffered and pretreated by the surface modification layer; then it migrates inward to the inner functional zone and is specifically catalyzed into an easily manageable sulfate form and guided to accumulate in the non-critical zone; finally, the purified reaction gas diffuses to the core active zone to carry out the main catalytic reaction; through the adsorption, migration, transformation and site management pathway of sulfur species, the active diversion and isolation of poisons are achieved, thereby preserving the core catalytic function.

[0011] Furthermore, the present invention provides the application of the catalyst in purifying industrial flue gas containing SO2, NOx and VOCs.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: This coconut shell activated carbon-supported metal oxide catalyst, and its application in flue gas purification, utilizes a functional partitioning design within the catalyst to actively divert and isolate the destructive effects of sulfur poisoning. In continuous testing with simulated flue gas at 180°C and containing 100 ppm SO2, the catalyst of this invention maintained a NO conversion rate of over 90% after 500 hours of operation. In contrast, a comparative catalyst prepared using the same active components via conventional co-impregnation methods showed an activity decrease of over 50% within 100 hours. Electron microscopy and sulfur elemental analysis confirmed that sulfur in the catalyst of this invention is primarily enriched in the pre-designed inner Ce-La-O layer. x The core Mn active sites in the region remain clean.

[0013] Because the core active region is protected from direct sulfur attack, its intrinsic catalytic performance is fully utilized. For recalcitrant chlorobenzene, the ignition temperature (Tignition temperature) of the catalyst of this invention at 180°C is [not specified]. 50 The temperature was reduced by about 30°C compared to the control catalyst, and the selectivity for toxic byproducts was extremely low throughout the reaction, indicating that the catalytic pathway was more efficient and thorough.

[0014] Furthermore, the main cause of catalyst deactivation in this invention is the accumulation of sulfate in the preset region, rather than the permanent destruction of active sites. Therefore, it can be regenerated by gentle temperature-controlled purging (such as nitrogen purging at 300°C). After five reactions to the regeneration cycle, its initial activity can still be maintained at more than 85%, while traditional catalysts are basically non-regenerable, which significantly reduces the cost of use. Attached Figure Description

[0015] Figure 1 This is an overall flowchart of Embodiment 1 of the present invention. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: This embodiment of the invention provides a method for preparing a coconut shell activated carbon supported metal oxide catalyst, comprising the following steps: S1. Carrier pretreatment and surface modification layer construction: Take 20g of graded porous coconut shell activated carbon (specific surface area 1200 m²) 2The sample (with an average pore size of 2.5 nm) was immersed in a 50 mL aqueous solution containing 2 g aluminum sulfate and 2 g citric acid, and stirred at room temperature for 4 hours. It was then dried in an oven at 80 °C for 12 hours. The dried sample was placed in a tube furnace and heated to 450 °C at a rate of 5 °C / min under a N2 atmosphere, held for 1 hour, and then allowed to cool naturally. After cooling, the sample was removed and labeled AC-Al.

[0018] S2, Loading of the inner sulfur conversion functional zone: Prepare 50 mL of a mixed aqueous solution containing cerium nitrate (Ce(NO3)3·6H2O, 8.68 g) and lanthanum nitrate (La(NO3)3·6H2O, 1.73 g) (Ce / La molar ratio = 4:1), and add 1.5 g of sodium carboxymethyl cellulose to adjust the solution viscosity to 3.5 mPa·s. Take 20 g of the AC-Al sample obtained in S1 and immerse it in the above solution, stirring at room temperature for 6 hours; then use a gradient temperature drying method: first dry at 40℃ for 2 hours, then increase the temperature to 80℃ for 4 hours, and finally dry at 110℃ for 1 hour; after drying, calcine the sample in air at a rate of 3℃ / min to 500℃ for 2 hours, and then allow it to cool naturally; the resulting sample is labeled as AC-Al / CeLa.

[0019] S3, Core catalytic active region loading: Prepare 50 mL of alcohol-water mixed solution (ethanol volume fraction 40%), dissolve manganese acetate (Mn(CH3COO)2·4H2O, 3.68 g) and copper acetate (Cu(CH3COO)2·H2O, 0.20 g) (Mn / Cu molar ratio = 15:1); take 20 g of AC-Al / CeLa sample prepared by S2, immerse it in the above solution, stir at room temperature for 4 hours, and then gently dry at 50 °C for 12 hours; place the dried sample in a tube furnace, heat to 350 °C at 5 °C / min under a 5% H2 / N2 mixed atmosphere, hold for 2 hours, and then cool naturally to room temperature.

[0020] S4. Post-processing: The product obtained in S3 was removed under N2 protection and stored in a nitrogen-filled sample bottle to obtain the catalyst of this invention, labeled Catalyst-A. ICP-OES analysis showed that the final supported components were approximately: Al2O3 3.5%, CeO2 8.0%, La2O3 1.8%, MnO2 7.5%, and CuO 0.4%.

[0021] Example 2: Catalyst preparation with optimized core active components The difference from Example 1 lies in step S3: When preparing the alcohol-water mixed solution, the amount of manganese acetate was adjusted to 4.91 g and the amount of copper acetate to 0.10 g (Mn / Cu molar ratio = 40:1), and the remaining steps and parameters were exactly the same as in Example 1. The obtained catalyst was labeled Catalyst-B. Its lower Cu loading was intended to investigate the effect of different Mn / Cu ratios on activity.

[0022] Comparative Example 1: Catalyst preparation using the conventional co-impregnation method (without partitioning design) Take 20g of graded porous coconut shell activated carbon of the same specifications as in Example 1; prepare 100mL of aqueous solution containing all the metal salts in Example 1 (2g aluminum sulfate, 8.68g cerium nitrate, 1.73g lanthanum nitrate, 3.68g manganese acetate, 0.20g copper acetate) and 2g citric acid; immerse the activated carbon in the mixed solution, stir at room temperature for 8 hours, and dry at 80℃ for 12 hours; then divide the dried sample into two parts: One portion was heated to 450°C at a rate of 3°C / min and calcined for 2 hours in air atmosphere, and was labeled Comparative-C (oxidizing atmosphere).

[0023] Another portion was calcined for 2 hours at 350°C under a 5% H2 / N2 atmosphere, with the temperature increased at 5°C / min, and labeled Comparative-R (reducing atmosphere). This comparative example aims to simulate the method of loading all active components in a one-step process in the prior art.

[0024] Comparative Example 2: Preparation of catalysts without surface modification layer Using hierarchical porous coconut shell activated carbon as a carrier, skipping step S1 in Example 1, we started from step S2 (inner layer Ce-La loading) and then proceeded to step S3 (core Mn-Cu loading), with all parameters being the same as in Example 1; the resulting catalyst was labeled Comparative-D; the purpose of this comparative example was to verify the key role of the surface composite modification layer in buffering and guiding SO2.

[0025] Experimental Example 1: Catalytic performance and sulfur resistance test in simulated sulfur-containing flue gas Catalyst-A, Catalyst-B, Comparative-C, Comparative-R, and Comparative-D prepared above were respectively packed into a fixed-bed quartz tube reactor (inner diameter 8 mm), with a packing amount of 0.5 g (40-60 mesh). The reaction gas composition was: 500 ppm NO, 300 ppm toluene (representing VOCs), 100 ppm SO2, 5% O2, with N2 in equilibrium. The total flow rate was 500 mL / min, and the space velocity (GHSV) was 60,000 h⁻¹. -1The reaction temperature was set at 180℃, and the concentrations of NO and toluene in the reactor outlet gas were continuously monitored using an online Fourier transform infrared gas analyzer (FTIR). The test results are shown in Table 1.

[0026] Table 1: Test Results As shown in Table 1, Catalyst-A and Catalyst-B of the present invention exhibit excellent long-term stability in sulfur-containing flue gas, with an activity retention rate of over 89% after 500 hours of operation. In contrast, the conventional co-impregnated catalyst (Comparative-C / R) suffers severe deactivation within 100 hours, with an activity retention rate of less than 65%, and severe deactivation after 500 hours. Although Comparative-D, lacking a surface modification layer, exhibits better sulfur resistance than the conventional co-impregnation method, it is still significantly worse than the Catalyst-A with a fully partitioned design, demonstrating the importance of synergy among the functional layers.

[0027] Experimental Example 2: Characterization of Catalysts and Analysis of Sulfur Species Distribution The Catalyst-A and Comparative-C catalysts were characterized after 500 hours of operation as follows: XRD analysis: In the Catalyst-A spectrum, only weak characteristic diffraction peaks of CeO2 and MnO2 are visible, indicating that the active component is highly dispersed; while in the Comparative-C spectrum, strong characteristic diffraction peaks of MnSO4 and Ce2(SO4)3 appear.

[0028] TEM-EDS elemental surface scan: Elemental distribution analysis was performed on the cross-section of Catalyst-A catalyst particles. The results showed that the spatial distribution of S, Ce, and La elements highly overlapped, mainly concentrated in the central annular region (corresponding to the inner sulfur conversion zone), while the S signal was extremely weak at the Mn signal point in the core region of the particle. Conversely, in Comparative-C, the distribution of S, Mn, and Ce elements completely overlapped and was uniformly distributed throughout the entire particle.

[0029] XPS analysis: Analysis of the Mn 2p orbitals in Catalyst-A showed only slight changes in binding energy compared to the fresh catalyst, indicating that the chemical valence state and environment of Mn have not fundamentally changed; while in Comparative-C, the Mn 2p peak shifted significantly towards higher binding energies, confirming the formation of MnSO4.

[0030] The characterization results directly verified the effectiveness of the sulfur species site management mechanism of this invention. In Catalyst-A, sulfur was successfully guided and fixed in the inner Ce-La-O layer. xThe region protects the core Mn-Cu active sites, whereas in traditional catalysts, sulfur reacts indiscriminately with all active components, leading to overall poisoning.

[0031] Experimental Example 3: Catalyst Regeneration Performance Test The deactivated Catalyst-A and Comparative-C catalysts were removed from the reactor after 500 hours of operation.

[0032] Regeneration steps: Under N2 atmosphere, heat to 300℃ at 10℃ / min, then switch to pure N2 (100mL / min), purge at this temperature for 1 hour, and then cool to the reaction temperature of 180℃.

[0033] Test results: The regenerated Catalyst-A catalyst recovered 92% of its initial NO conversion rate. After repeating this regeneration-reaction cycle five times, Catalyst-A still achieved 86% of its initial activity after the fifth regeneration. In contrast, the Comparative-C catalyst, after the same regeneration procedure, only recovered about 10% of its deactivated level, and was almost completely deactivated after the second cycle, indicating that its deactivation was irreversible and permanent poisoning.

[0034] Therefore, the catalyst of the present invention exhibits excellent renewability because its deactivation mechanism is the accumulation of sulfate in a preset buffer zone. It can be effectively desorbed or decomposed by gentle purging, greatly improving its economic efficiency and practical value.

[0035] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A coconut shell activated carbon supported metal oxide catalyst, characterized in that, The catalyst adopts a functional partition structure, including: Using graded porous coconut shell activated carbon as a carrier; A surface composite modification layer is formed on the outer surface of the carrier and at the large pore inlet, the surface composite modification layer being composed of aluminum-containing species and pyrolytic carbon; The inner Ce-La composite oxide is loaded in the middle region of the support channel; the core Mn-Cu-based catalytic active center is loaded inside the support channel.

2. The coconut shell activated carbon supported metal oxide catalyst according to claim 1, characterized in that, In the inner Ce-La composite oxide, the molar ratio of Ce to La is 3:1 to 5:

1.

3. The coconut shell activated carbon supported metal oxide catalyst according to claim 1, characterized in that, In the core Mn-Cu-based catalytic active center, Mn is present in a non-stoichiometric ratio with MnO. x It exists in the form where x = 1.8-1.9, Cu exists in a highly dispersed state, and the molar ratio of Mn to Cu is 10:1-20:

1.

4. The coconut shell activated carbon supported metal oxide catalyst according to claim 1, characterized in that, The surface composite modification layer is formed by impregnating and drying a precursor solution containing aluminum source and organic carbon source, and then calcining it at 400-500℃ in an inert atmosphere; The inner Ce-La composite oxide is formed by impregnation with a viscous aqueous solution containing cerium salt and lanthanum salt, followed by gradient heating and drying, and then calcination in an air atmosphere. The core Mn-Cu-based catalytic active center is formed by impregnation with a mixed alcohol-water solution containing manganese and copper salts, followed by low-temperature drying and calcination in a weakly reducing atmosphere.

5. A method for preparing a coconut shell activated carbon supported metal oxide catalyst as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Construction of surface composite modification layer: Hierarchical porous coconut shell activated carbon is impregnated in a precursor solution containing aluminum source and organic carbon source, dried, and then calcined at 400-500℃ under an inert atmosphere to obtain a surface-modified carrier. S2, Loading of inner cerium-lanthanum composite oxide: The support obtained in S1 was impregnated in an aqueous solution containing cerium salt and lanthanum salt with adjusted viscosity, dried using a gradient temperature program, and then calcined in an air atmosphere. S3, the support of the core manganese-copper based catalytic active center: the support after S2 treatment is immersed in an alcohol-water mixed solution containing manganese salt and copper salt, dried at low temperature, and then calcined in a weak reducing atmosphere. S4. Post-processing: Cool the product obtained in S3 and store it in an inert atmosphere.

6. The method for preparing the coconut shell activated carbon supported metal oxide catalyst according to claim 5, characterized in that, In step S1, the aluminum source is aluminum sulfate, the organic carbon source is citric acid, and the inert atmosphere is N2 atmosphere.

7. The method for preparing the coconut shell activated carbon supported metal oxide catalyst according to claim 5, characterized in that, In step S2, sodium carboxymethyl cellulose is used to adjust the solution viscosity; the gradient temperature drying is carried out in stages at 40°C, 80°C and 110°C.

8. The method for preparing the coconut shell activated carbon supported metal oxide catalyst according to claim 5, characterized in that, In step S3, the volume fraction of ethanol in the alcohol-water mixed solution is 40%; the weakly reducing atmosphere is a 5% volume fraction H2 / N2 mixed gas, and the calcination temperature is 350℃.

9. The application of a coconut shell activated carbon supported metal oxide catalyst as described in any one of claims 1-4 in the purification of industrial flue gas containing SO2, NOx and VOCs.

10. The application according to claim 9, characterized in that, After the catalyst was continuously operated for 500 hours in simulated flue gas containing 100ppm SO2 at 180℃, the NO conversion rate was maintained at >90%; after the catalyst was deactivated, it was regenerated by temperature-controlled purging at 300℃ under an inert atmosphere.

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