A MnO2 catalyst for efficient catalytic purification of acetonitrile x / SiO2@CeO2 catalyst and its preparation method

Abstract

A MnO2 catalyst for efficient catalytic purification of acetonitrile x This paper discusses SiO2@CeO2 catalysts and their preparation methods, belonging to the fields of catalysis chemistry and environmental chemistry. It involves using MnO... x MnO was prepared by loading it onto a SiO2@CeO2 core-shell structure support. x / SiO2@CeO2 catalyst. The preparation method is as follows: silica microspheres are prepared using a method similar to [preparation method], followed by SiO2@CeO2 preparation using a urea decomposition and precipitation method. The above steps are repeated to adjust the CeO2 loading. MnO is then impregnated using an impregnation method. x MnO was prepared by loading the sample onto the surface of a core-shell SiO2@CeO2 support and then calcining the sample in a muffle furnace at 450℃ for 3 hours. x / SiO2@CeO2 catalyst. This catalyst features a uniform dispersion of transition metal oxides on the support surface, exhibiting good catalytic purification performance for acetonitrile, and shows significant application potential in the treatment of nitrogen-containing organic pollutants.

Description

Technical Field

[0001] This invention relates to a core-shell structured supported MnO2 prepared by urea thermal decomposition precipitation and impregnation methods for the efficient catalytic purification of nitrogen-containing organic pollutants. x / SiO2@CeO2 catalyst and its preparation method belong to the field of nanomaterial preparation. Background Technology

[0002] Selective catalytic combustion (SCC) is a technology that converts nitriles into N2, CO2, and H2O. Due to its high purification efficiency and low secondary pollution, it has become one of the most promising technologies. The key to this method is the development of catalysts with good low-temperature oxidation activity, high-temperature stability, and low cost. Currently, common catalysts mainly include noble metal catalysts and non-noble metal catalysts. Noble metal catalysts have high catalytic oxidation capacity, but although they possess high catalytic oxidation activity, they are prone to causing the peroxidation product NO. x The emissions of nitrogen-containing organic pollutants cause secondary pollution, and their high price limits their application in catalytic purification. Compared with precious metal catalysts, transition metal oxide catalysts have become the preferred target catalysts for the catalytic purification of nitrogen-containing organic pollutants due to their low price and suitable redox capabilities.

[0003] Currently, some studies have been conducted both domestically and internationally on the catalytic purification of nitrogen-containing organic pollutants such as organic nitriles. Zhang et al. (Zhang Yaoyu, et al., Journal of Colloid and Interface Science, 2021, 584: 193-203) prepared yCuCeO using the sol-gel method. x -HZSM-5 catalyst was used for the catalytic purification of acetonitrile, and the results were obtained at 600 ppm CH3CN, 5% O2, N2 (balanced gas), GHSV = 48000 mL / g. -1 .h -1 The activity was evaluated under a gaseous environment. Among them, 1.5CuCeO... x -HZSM-5 and 2CuCeO x The HZSM-5 catalyst exhibited the best catalytic oxidation performance, with the complete conversion temperature of acetonitrile reaching T0. 100％ The temperature was 225℃. Zhang et al. (Zhang Runduo, et al., Applied Catalysis B: Environmental, 2014, 146: 79-93) prepared a series of SBA-15 supported transition metal and noble metal catalysts for the catalytic purification of acetonitrile using an impregnation method. The catalysts were prepared at 1000 ppm CH3CN, 5% O2, GHSV = 20000 mL. -1 .h-1 The catalytic purification performance of acetonitrile under various gaseous conditions was evaluated. Cu / SBA-15 exhibited the best catalytic activity, with T... 90％ It is 360℃.

[0004] However, to our knowledge, MnO is not currently being used. x MnO supported on a SiO2@CeO2 core-shell structure x Literature or reports on the use of / SiO2@CeO2 catalysts for the catalytic purification of acetonitrile. Summary of the Invention

[0005] The main objective of this invention is to use urea thermal decomposition precipitation and impregnation methods to process MnO x MnO was prepared by loading a SiO2@CeO2 core-shell structure carrier and then calcining it. x / SiO2@CeO2 catalyst. In this catalyst, cerium dioxide is uniformly coated on the surface of silica microspheres to form a core-shell structure, and MnO... x The catalyst is evenly distributed on the surface, which enables the resulting catalyst to achieve a high conversion rate of acetonitrile at low temperatures, so that the converted product is mainly N2 or contains a small amount of ammonia.

[0006] The catalyst structure of this invention: manganese oxide MnO x Loaded on a SiO2@CeO2 core-shell structure carrier, and MnO x The SiO2@CeO2 core-shell structure is formed by uniformly coating SiO2 microspheres with CeO2 on the surface of the core-shell structure carrier.

[0007] The loading of Ce element is 5-1 wt%, preferably 7 wt%, and the loading of Mn element is 7-25 wt%, preferably 14 wt%.

[0008] The specific steps for catalyst synthesis are as follows:

[0009] (1) Adopting traditional Preparation of SiO2 microspheres by method:

[0010] A certain amount of ethanol and 25%-28% ammonia solution were measured and mixed in a beaker by magnetic stirring at room temperature for 10 min. An appropriate amount of TEOS (tetraethyl orthosilicate) was added dropwise to the mixture, and the solution gradually changed from colorless and transparent to a white suspension. The suspension was stirred at room temperature for 1 h and filtered. The sample was washed three times with deionized water and twice with ethanol to remove any possible ionic residues on the sample surface. The sample was then dried in an oven at 80℃ for 12 h to obtain SiO2 microspheres.

[0011] (2) Preparation of SiO2@CeO2 core-shell structured carrier by urea thermal decomposition precipitation method:

[0012] First, SiO2 microspheres were ultrasonically dispersed in deionized water. Ce(NO3)3·6H2O was added and stirred for 5 minutes, then the temperature was raised to 90°C. An appropriate amount of CO(NH2)2 was dissolved in deionized water and added to the above solution in batches. CO(NH2)2 slowly decomposed at the above solution temperature to produce NH3, which served as a precipitant, allowing Ce(NO3)3·6H2O to be uniformly deposited on the surface of SiO2 microspheres to prepare a core-shell structured carrier. The CeO2 loading could be controlled by repeating the steps of adding Ce(NO3)3·6H2O and adding CO(NH2)2. Ce will be lost during loading, so theoretically, the loading should be in excess relative to the actual loading.

[0013] (3) Preparation of MnO by impregnation method x / SiO2@CeO2 catalyst: First, SiO2@CeO2 support is ultrasonically dispersed in deionized water. A certain amount of Mn(NO3)4·4H2O is added to the above solution, and the mixture is stirred continuously for 6 hours. Then, it is placed in an 80℃ oven to remove excess moisture. The solid is then ground in an agate mortar and calcined in a muffle furnace at a heating rate of 3℃ per minute to 450℃ for 3 hours to obtain MnO. x / SiO2@CeO2 catalyst.

[0014] The prepared catalyst was used for the catalytic purification of CH3CN to generate nitrogen, with a corresponding temperature of 140-200℃.

[0015] The obtained catalyst was subjected to a reaction of 500 ppm CH3CN, 10% O2, He (balanced gas), and GHSV = 40000 mL / g. -1 .h -1 Activity tests were conducted in gaseous environments at different temperatures.

[0016] The catalyst in this invention innovatively utilizes a core-shell structure to separate different functional sites and expose more reactive sites, achieving a high conversion rate of acetonitrile at low temperatures, and has high application prospects in the catalytic purification of nitrogen-containing organic pollutants.

[0017] The crystal structure and morphology of the prepared catalyst were characterized using a D8 ADVANCE X-ray diffractometer (XRD), a Supra 55 scanning electron microscope (SEM), and a JEOL-2010 transmission electron microscope (TEM). The catalytic purification performance and selectivity of the catalyst for acetonitrile were evaluated using a Shimadzu GC-2014C gas chromatograph (GC) and an infrared flue gas analyzer. The results showed that the catalyst exhibited a generally regular spherical shape. Elemental surface scans from SEM and TEM revealed a uniform distribution of elements on the catalyst surface, with silica and cerium oxide forming a distinct core-shell structure. MnO x / SiO2@CeO2 and MnO x -CeO2 catalysts all exhibited excellent low-temperature catalytic activity for the catalytic purification of acetonitrile, but MnO showed better selectivity in the tests. x The / SiO2@CeO2 catalyst exhibits higher N2 selectivity. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the catalyst. Curves (a), (b), (c), and (d) represent MnO₂, respectively. x -CeO2, MnO x / SiO2, SiO2@CeO2 and MnO x XRD pattern of / SiO2@CeO2.

[0019] Figure 2 MnO x Scanning electron microscope images of the / SiO2@CeO2 catalyst and surface scan images of O, Si, Ce, and Mn elements.

[0020] Figure 3 MnO x Transmission electron microscopy images of the / SiO2@CeO2 catalyst and its elemental surface scan images of O, Si, Ce, and Mn.

[0021] Figure 4 The graph shows the catalytic activity test results of the catalyst and its comparative sample.

[0022] Figure 5 The graph shows the N2 selectivity test results for the catalyst and its comparative sample. Detailed Implementation

[0023] To further illustrate the present invention, detailed descriptions are provided below with examples and accompanying drawings illustrating the catalyst materials obtained by the present invention. However, the present invention is not limited to the following examples.

[0024] Example 1

[0025] (1) Adopting traditional Preparation of SiO2 microspheres: 62 mL of ethanol and 12 mL of 25%-28% ammonia solution were measured and mixed in a beaker at room temperature for 10 min. 6 mL of TEOS (tetraethyl orthosilicate) was added dropwise to the mixture, causing the solution to gradually change from colorless and transparent to a white suspension. The suspension was stirred at room temperature for 1 h and filtered. The microspheres were washed three times with deionized water and twice with ethanol to remove any possible ionic residues on the sample surface. Finally, the microspheres were dried in an oven at 80 °C for 12 h to obtain the SiO2 microspheres.

[0026] (2) Preparation of SiO2@CeO2 core-shell structured carrier by urea thermal decomposition precipitation: First, 1g of SiO2 microspheres were weighed and ultrasonically dispersed in deionized water for 30min. Then, 0.217g of Ce(NO3)3·6H2O was added and stirred for 5min, followed by heating to 90℃. 0.45g of CO(NH2)2 was dissolved in 20mL of deionized water and added rapidly in batches to the above solution. Ce(NO3)3·6H2O was uniformly deposited on the surface of SiO2 microspheres to prepare a core-shell structured carrier. The theoretical loading of a single precipitation was 7wt%. The above process was repeated to achieve the ideal loading.

[0027] (3) Preparation of MnO by impregnation method x / SiO2@CeO2 catalyst: First, 1g of SiO2@CeO2 support was ultrasonically dispersed in deionized water for 30min. Then, 0.346g of Mn(NO3)4·4H2O was added to the above solution, and the mixture was stirred continuously for 6h. The solution was then placed in an 80℃ oven to remove excess moisture. After the sample was removed, it was ground in an agate mortar and then calcined in a muffle furnace at a heating rate of 3℃ per minute to 450℃ for 3h to obtain MnO. x / SiO2@CeO2 catalyst.

[0028] MnO x The theoretical Ce loading in the / SiO2@CeO2 catalyst is 14 wt% (the actual loading is 7 wt% due to losses), and the theoretical Mn loading is 14 wt% (the actual loading is 14 wt%). The Mn and Ce loadings in the catalyst are consistent with the actual loadings of the catalysts mentioned above.

[0029] The prepared catalyst was tested in a solution of 500 ppm CH3CN, 10% O2, He (balanced gas), and GHSV = 40000 mL. - 1 .h -1 The activity test of this catalyst was conducted in a gaseous environment, and the T... 50％ and T 90％ The temperatures are 155℃ and 179℃, respectively.

Claims

1. A type of MnO x Applications of / SiO2@CeO2 catalyst: for the catalytic purification of CH3CN to produce nitrogen and MnO. x The SiO2@CeO2 catalyst is: manganese oxide MnO x Loaded on a SiO2@CeO2 core-shell structure carrier, and MnO x The SiO2@CeO2 core-shell structure is formed by uniformly coating SiO2 microspheres with CeO2 on the surface of the core-shell structure carrier.

2. The application according to claim 1, characterized in that, The loading of Ce is 5-14 wt%, and the loading of Mn is 7-25 wt%.

3. The application according to claim 1, characterized in that, The loading of Ce was 7 wt% and the loading of Mn was 14 wt%.

4. The application according to claim 1, characterized in that, The preparation method of the catalyst includes the following steps: (1) using (2) SiO2@CeO2 core-shell structured carrier was prepared by urea thermal decomposition precipitation method; (3) Preparation of MnO by impregnation method x / SiO2@CeO2 catalyst: First, SiO2@CeO2 support is ultrasonically dispersed in deionized water. A certain amount of Mn(NO3)4·4H2O is added to the above solution, and the mixture is stirred continuously for 6 hours before being placed at 80°C. o Remove excess moisture in an oven (C); after grinding the solid in an agate mortar, heat it in a muffle furnace to 450°C at a rate of 3°C per minute. o MnO was obtained by roasting C for 3 h. x / SiO2@CeO2 catalyst.

5. The application according to claim 4, characterized in that, Step (1) Preparation of SiO2 microspheres: Measure ethanol and 25%-28% ammonia water and stir and mix at room temperature; add an appropriate amount of TEOS (tetraethyl orthosilicate) dropwise to the above mixed solution, and the solution gradually changes from colorless and transparent to white suspension; stir the suspension at room temperature for 1 h and filter it, wash it three times with deionized water and twice with ethanol to remove possible ion residues on the sample surface, and then dry it to obtain SiO2 microspheres.

6. The application according to claim 4, characterized in that, Step (2) First, SiO2 microspheres are ultrasonically dispersed in deionized water. Ce(NO3)3·6H2O is added and stirred for 5 min, then the temperature is raised to 90 °C. CO(NH2)2 is dissolved in deionized water and added to the above solution in batches. CO(NH2)2 slowly decomposes at the above solution temperature to produce NH3 as a precipitant, so that Ce(NO3)3·6H2O is uniformly deposited on the surface of SiO2 microspheres to prepare a core-shell structure carrier. The CeO2 loading can be controlled by repeating the above steps of adding Ce(NO3)3·6H2O and adding CO(NH2)2.

7. In the application according to claim 1, the temperature corresponding to the catalyst catalytic purification is 140-200℃.

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