Precious metal-vanadium doped yttrium oxide composite catalyst as well as preparation method and application thereof

Abstract

The invention provides a noble metal-vanadium doped yttrium oxide composite catalyst as well as a preparation method and application thereof. The catalyst comprises a carrier, precious metal and vanadium, wherein the precious metal and the vanadium are loaded on the carrier, and the carrier is yttrium oxide with a lamellar structure. Ru and V nanoparticles are simultaneously loaded on the lamellar Y2O3 carrier, so that the cracking yield of the catalyst to polyethylene and the selectivity of the catalyst to liquid alkane can be remarkably improved under the combined action of carrier morphology, Ru and V. Wherein the cracking yield of polyethylene is greater than or equal to 45%; in the product of the cracked polyethylene, the liquid alkane accounts for more than or equal to 40%.

Description

Technical Field

[0001] The invention relates to the technical field of catalyst materials, in particular to a noble metal-vanadium doped yttrium oxide composite catalyst and a preparation method and application thereof. Background Art

[0002] With the rapid development of the global economy, plastic products have become an indispensable material in modern life. However, the mass production and use of plastic products, especially high molecular polymers such as polyethylene, have also caused serious environmental problems. Polyethylene is widely used in packaging, pipes, containers and daily necessities due to its excellent chemical stability, mechanical properties and low price. However, the degradation process of polyethylene is slow, and it often takes decades to hundreds of years to completely decompose, resulting in a large amount of waste plastics accumulating in the environment, destroying the ecosystem, endangering biological safety, and even affecting human health through the food chain.

[0003] At present, the main methods of dealing with waste plastics are landfill and incineration. However, landfill not only occupies a large amount of land resources, but also may cause soil and groundwater pollution; incineration will release harmful gases and pose a serious threat to the atmospheric environment. In this context, catalytic cracking technology has attracted widespread attention because of its ability to efficiently convert waste polyethylene into low-molecular hydrocarbon compounds. By introducing a catalyst, the polyethylene molecular chain can be broken at a lower temperature to generate small molecular hydrocarbon products. Catalytic cracking not only reduces energy consumption, but also improves the selectivity and yield of the product, thereby achieving a more economical and environmentally friendly resource utilization of polyethylene waste.

[0004] However, the existing catalytic cracking reaction of polyethylene is incomplete, especially the yield of light hydrocarbon products still needs to be improved. Therefore, it is necessary to develop a catalyst that can improve the cracking degree of polyethylene and the selectivity for light hydrocarbon products. Summary of the invention

[0005] The purpose of the present invention is to provide a noble metal-vanadium doped yttrium oxide composite catalyst to prepare Y 2 O 3 The carrier is loaded with Ru and V nanoparticles at the same time.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a noble metal-vanadium doped yttrium oxide composite catalyst, comprising a carrier, a noble metal and vanadium loaded on the carrier, wherein the carrier is yttrium oxide with a lamellar structure.

[0008] As an embodiment of the present invention, the precious metal includes at least one of ruthenium, rhodium, palladium, osmium, iridium and platinum.

[0009] As a preferred embodiment of the present invention, the noble metal is ruthenium.

[0010] As an embodiment of the present invention, the loading amount of the noble metal is 2 to 4 wt % based on the carrier.

[0011] As an embodiment of the present invention, the loading amount of vanadium is 1 to 10 wt % based on the carrier.

[0012] As an embodiment of the present invention, in the noble metal-vanadium doped yttrium oxide composite catalyst, the ratio of the loading amount of vanadium to the loading amount of the noble metal is (0.3-1):1.

[0013] The second aspect of the present invention provides a method for preparing the noble metal-vanadium doped yttrium oxide composite catalyst according to the first aspect of the present invention, comprising the following steps:

[0014] S1: dissolving a noble metal source into water to form a solution A; dissolving a yttrium source, a vanadium source and a dispersant into water to form a solution B;

[0015] S2: The solution A and the solution B prepared in step S1 are mixed to form a reaction solution, urea is added to make the pH of the reaction solution in the range of 7 to 8, the reaction is carried out at 70 to 100° C. for 8 to 12 hours, and the obtained precipitated product is washed and dried to obtain a catalyst precursor;

[0016] S3: calcining the catalyst precursor obtained in step S2 at 550-700° C. for 1.5-3 h in an atmosphere formed by hydrogen and argon to obtain the noble metal-vanadium doped yttrium oxide composite catalyst.

[0017] As an embodiment of the present invention, the noble metal source is a water-soluble salt containing a noble metal.

[0018] As an embodiment of the present invention, the yttrium source is a water-soluble salt containing yttrium.

[0019] As an embodiment of the present invention, the vanadium source is a water-soluble organic salt containing vanadium.

[0020] As an embodiment of the present invention, the dispersant includes but is not limited to hexadecyltrimethylammonium bromide.

[0021] As an embodiment of the present invention, in solution A, the concentration of the noble metal source is 0.1 to 0.5 g / mL.

[0022] As an embodiment of the present invention, in solution B, the concentration of the yttrium source is 0.1 to 0.5 g / mL.

[0023] As an embodiment of the present invention, the amount of the dispersant added is 15 to 50 wt % of the yttrium source.

[0024] As an implementation scheme of the present invention, in step S3, the volume ratio of hydrogen to argon is (0.05-0.1):1.

[0025] The third aspect of the present invention provides an application of the precious metal-vanadium doped yttrium oxide composite catalyst described in the first aspect of the present invention, wherein the precious metal-vanadium doped yttrium oxide composite catalyst is used for catalytic cracking of polyethylene, wherein the cracking yield of polyethylene is ≥45%; and the proportion of C5 to C21 alkanes in the product of cracking polyethylene is ≥40%.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention adopts the coprecipitation method to prepare the lamellar Y 2 O 3 The carrier is loaded with Ru and V nanoparticles at the same time to obtain a noble metal-vanadium doped yttrium oxide composite catalyst. Through the combined effects of the carrier morphology, Ru and V, the catalyst can significantly improve the cracking yield of polyethylene and the selectivity of C5-C21 alkanes. Among them, the cracking yield of polyethylene is ≥45%; in the products of cracked polyethylene, the proportion of C5-C21 alkanes is ≥40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 For Example 1 (3Ru-5V / Y 2 O 3 ) and Example 2 (3Ru-10V / Y 2 O 3 ) XRD test spectrum of the prepared catalyst;

[0029] Figure 2 For comparative example 1 ((3Ru+5V) / Y 2 O 3 ) and Comparative Example 2 ((3Ru+10V) / Y 2 O 3 ) XRD test spectrum of the prepared catalyst;

[0030] Figure 3 The SEM images of the catalysts prepared in Example 1 (a) and Example 2 (b);

[0031] Figure 4 These are SEM images of the catalysts prepared in Comparative Example 1 (Figure a) and Comparative Example 2 (Figure b). DETAILED DESCRIPTION

[0032] For better explanation of the purpose, technical scheme and advantage of the present invention, the present invention will be further described below in conjunction with specific embodiment and accompanying drawing, but embodiment does not limit the present invention in any form.Unless otherwise specified, the reagent, method and equipment adopted in the present invention are conventional reagents, methods and equipment in the art.Unless otherwise specified, the reagents and materials used in the present invention are commercially available.

[0033] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0034] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0035] The reagents or instruments used in the present invention without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0036] A first aspect of the present invention provides a noble metal-vanadium doped yttrium oxide composite catalyst, comprising a carrier, a noble metal and vanadium loaded on the carrier, wherein the carrier is yttrium oxide with a lamellar structure.

[0037] Yttrium oxide (Y 2 O 3 ) As a rare earth oxide with excellent thermal and chemical stability, it has become an ideal catalyst carrier. The layered structure of yttrium oxide can not only maintain structural stability at high temperatures, but also provide a good dispersion environment for active components, preventing the catalyst from sintering or deactivation during the reaction.

[0038] By loading noble metal active components on a vanadium (V) modified layered yttrium oxide support, V, Y 2 O 3 The interaction between the three elements regulates the electron density of the active center. 2 O 3 The introduction of V into the carrier can also adjust the pH of the catalyst, increase the number of acidic sites, and allow the catalytic cracking of polyethylene to react under milder conditions, thereby increasing the yield and selectivity of liquid alkanes; it can also further reduce the agglomeration of precious metals on the carrier and improve the catalytic efficiency.

[0039] In some embodiments of the present invention, the precious metal includes at least one of ruthenium (Ru), rhodium (Rh), palladium (Rd), osmium (Os), iridium (Ir), and platinum (Pt).

[0040] In some embodiments of the present invention, the noble metal is ruthenium (Ru). Ruthenium (Ru) as a noble metal catalyst has excellent cracking activity and selectivity. Loading ruthenium on the yttrium oxide carrier can effectively improve the efficiency of polyethylene cracking reaction.

[0041] In some embodiments of the present invention, the loading amount of the noble metal is 2-4 wt % based on the carrier.

[0042] In some embodiments of the present invention, based on the carrier, the loading amount of vanadium is 1 to 10 wt %, preferably 4 to 6 wt %, and more preferably 5 wt %.

[0043] In some embodiments of the present invention, in the noble metal-vanadium doped yttrium oxide composite catalyst, the ratio of the vanadium loading to the noble metal loading is (0.3-1): 1. When the ratio of the vanadium loading to the noble metal loading is within this range, the catalytic performance of the catalyst can be further improved, and the cracking efficiency and selectivity of polyethylene can be improved.

[0044] The second aspect of the present invention provides a method for preparing the noble metal-vanadium doped yttrium oxide composite catalyst according to the first aspect of the present invention, comprising the following steps:

[0045] S1: dissolving a noble metal source into water to form a solution A; dissolving a yttrium source, a vanadium source and a dispersant into water to form a solution B;

[0046] S2: The solution A and the solution B prepared in step S1 are mixed to form a reaction solution, urea is added to make the pH of the reaction solution in the range of 7 to 8, the reaction is carried out at 70 to 100° C. for 8 to 12 hours, and the obtained precipitated product is washed and dried to obtain a catalyst precursor;

[0047] S3: calcining the catalyst precursor obtained in step S2 at 550-700° C. for 1.5-3 h in an atmosphere formed by hydrogen and argon to obtain the noble metal-vanadium doped yttrium oxide composite catalyst.

[0048] The present invention utilizes urea precipitation method to prepare Y 2 O 3 Precursor, vanadium ions and noble metal ions are deposited on its surface, and then calcined to obtain the noble metal-vanadium doped yttrium oxide composite catalyst. In the preparation method of the present invention, urea is added, and urea will slowly decompose to generate NH 3 With CO 2Adjust the pH value of the solution. By adjusting the initial pH value of the reaction solution, Y 2 O 3 The carrier forms a lamellar structure after hydrothermal reaction and calcination.

[0049] The method of the present invention can make the vanadium element and the noble metal element uniformly loaded on the carrier, thereby improving the catalytic efficiency.

[0050] In some embodiments of the present invention, the noble metal source is a water-soluble salt containing a noble metal, and the water-soluble salt includes but is not limited to chlorides and nitrates of the noble metal element.

[0051] In some embodiments of the present invention, the yttrium source is a water-soluble salt containing yttrium, specifically including but not limited to yttrium nitrate hexahydrate (Y(NO 3 ) 3 6H 2 O).

[0052] In some embodiments of the present invention, the vanadium source is a water-soluble organic salt containing vanadium, specifically including but not limited to vanadyl oxalate (VOC 2 O 4 ).

[0053] In some embodiments of the present invention, the dispersant includes but is not limited to cetyltrimethylammonium bromide (CTAB).

[0054] In some embodiments of the present invention, in solution A, the concentration of the noble metal source is 0.1-0.5 g / mL.

[0055] In some embodiments of the present invention, in solution B, the concentration of the yttrium source is 0.1-0.5 g / mL, and the amount of the vanadium source added is determined according to the loading amount of vanadium.

[0056] In some embodiments of the present invention, in solution B, the amount of the dispersant added is 15 to 50 wt % of the yttrium source.

[0057] In some embodiments of the present invention, in step S3, the volume ratio of hydrogen to argon is (0.05-0.1):1.

[0058] In some embodiments of the present invention, the washing in step S2 is performed by alternately washing twice with deionized water and ethanol to remove excess urea and dispersant.

[0059] In some embodiments of the present invention, the drying temperature in step S2 is 40-60°C.

[0060] The third aspect of the present invention provides an application of the precious metal-vanadium doped yttrium oxide composite catalyst described in the first aspect of the present invention, wherein the precious metal-vanadium doped yttrium oxide composite catalyst is used for catalytic cracking of polyethylene, wherein the cracking yield of polyethylene is ≥45%; and the proportion of C5 to C21 alkanes in the product of cracking polyethylene is ≥40%.

[0061] The following are specific embodiments of the present invention.

[0062] Example 1

[0063] This embodiment provides a noble metal-vanadium doped yttrium oxide composite catalyst 3Ru-5V / Y 2 O 3 , the preparation method comprises the following steps:

[0064] S1: Preparation solution

[0065] 10 g of ruthenium trichloride (RuCl 3 ) was dissolved in 50 mL of water to form solution A;

[0066] 2 g of hexadecyltrimethylammonium bromide (CTAB) was added to 400 mL of deionized water to obtain a white turbid solution, followed by the addition of 6.2 g of yttrium nitrate hexahydrate (Y(NO 3 ) 3 6H 2 O, purity 99.999%) and 0.3 g vanadyl oxalate (VOC 2 O 4 , purity is 99%), and stirred thoroughly for 1 h until the solution becomes clear and transparent to form solution B;

[0067] S2: Add 800 μL of solution A and 54 g of urea to solution B, stir for 1 h to fully dissolve the urea, and obtain a reaction solution. The pH value of the reaction solution is 7.5. Stir and heat the reaction at 85°C for 8 h. Wash the obtained precipitated product twice with deionized water and ethanol respectively to remove urea and CTAB. Then, filter the obtained product and put it into a 60°C oven to dry for 6 h to obtain a catalyst precursor.

[0068] S3: The catalyst precursor obtained in step S2 is placed in a hydrogen and argon atmosphere (V 氢气 :V 氩气 =0.05:1), and then heated to 600°C at a rate of 2°C / min and calcined for 2h to obtain the noble metal-vanadium doped yttrium oxide composite catalyst, which is denoted as 3Ru-5V / Y 2 O 3 (Indicates that in Y 2 O 3 On the carrier, the loading amount of Ru is 3wt% and the loading amount of V is 5wt%).

[0069] Examples 2 to 13, Comparative Examples 3 to 5

[0070] A series of noble metal-vanadium doped yttrium oxide composite catalysts (the composition of the catalyst is shown in Table 1) are provided. Referring to the preparation method of Example 1, the catalysts of different compositions described in Table 1 are obtained by adjusting the type and amount of raw materials.

[0071] Table 1

[0072]

[0073]

[0074] Comparative Example 1

[0075] This comparative example provides a noble metal-vanadium doped yttrium oxide composite catalyst, the composition of which is the same as that of Example 1. For the purpose of distinction, the composition of the catalyst of Comparative Example 1 is marked as (3Ru+5V) / Y 2 O 3 , which also means that in Y 2 O 3 On the carrier, the loading amount of Ru is 3wt%, and the loading amount of V is 5wt%. The difference from Example 1 is that the preparation is carried out by impregnation method. The specific preparation method includes the following steps:

[0076] (1) 2 g of hexadecyltrimethylammonium bromide (CTAB) was added to 400 mL of deionized water to obtain a white turbid solution, followed by the addition of 6.2 g of yttrium nitrate hexahydrate (Y(NO 3 ) 3 6H 2 O, 99.999%) and 54g of urea, and stirred for 1h until the solution became clear and transparent; then the obtained solution was placed in a water bath and stirred and heated at 85°C for 8h, and the obtained precipitate was washed twice with deionized water and ethanol respectively to remove urea and CTAB, and then the obtained product was filtered and placed in a 60°C oven for drying for 6h, and the dried product was ground and calcined at 600°C in a hydrogen and argon atmosphere for 2h to prepare Y 2 O 3 Powder carrier;

[0077] (2) 10 g of ruthenium trichloride (RuCl 3 ) was dissolved in 50 mL of deionized water and stirred thoroughly until completely dissolved.

[0078] (3) Take 1.85 g of Y prepared in step (1) 2 O 3 The powder carrier and 0.3g of vanadyl oxalate (VOC 2 O 4, 99%), added to 400 mL of deionized water and ultrasonicated for 2 h to uniformly disperse it to obtain a dispersion; 800 μL of the RuCl prepared in step (2) was added to the mixed solution. 3 The aqueous solution was added with 54 g of urea, and stirred for 3 h to fully mix the solution to obtain a reaction solution;

[0079] (4) placing the reaction solution obtained in step (3) in a water bath and stirring and heating at 85° C. for 8 h, washing the obtained precipitate twice with deionized water and ethanol respectively to remove urea, then filtering the obtained product and placing it in a 60° C. oven to dry for 6 h to obtain a catalyst precursor;

[0080] (5) placing the catalyst precursor dried in step (4) in a hydrogen-argon mixed atmosphere (V 氢气 :V 氩气 =0.05:1) and then heated to 600℃ at 2℃ / min for 2h to obtain 3Ru-5V / Y 2 O 3 catalyst.

[0081] Comparative Example 2

[0082] This comparative example provides a noble metal-vanadium doped yttrium oxide composite catalyst, the composition of which is the same as that of Example 2. For the purpose of distinction, the composition of the catalyst of Comparative Example 2 is marked as (3Ru+10V) / Y 2 O 3 , which also means that in Y 2 O 3 On the carrier, the loading amount of Ru is 3wt%, and the loading amount of V is 10wt%. The difference from Example 2 is that the preparation is carried out by impregnation method. The specific preparation method refers to Comparative Example 1, and only the added amount of vanadium oxalate is changed to 0.6g.

[0083] Performance Testing

[0084] The performance of the catalysts obtained in the above examples and comparative examples was characterized, and the specific test items, test methods and results are as follows:

[0085] 1. XRD test: XRD test was performed on the catalysts prepared in the above examples and comparative examples. Figure 1 and Figure 2 The peaks shown in the XRD diagram of the catalyst of Example 1 are all Y 2 O 3 The carrier does not show diffraction peaks of V and its compounds as well as Ru, which indicates that the particle sizes of V and Ru in Example 1 are relatively small. In the XRD diagram of the catalyst in Example 2, the peak near 2θ=32° is V generated by excess V. 2 O 5 ;

[0086] 2. Scanning electron microscope (SEM) characterization: XRD test was performed on the catalysts prepared in the above examples and comparative examples. Figure 3 and Figure 4 ;

[0087] Figure 3 (a) with Figure 4 (a) comparison, Figure 3 (b) with Figure 4 The comparison of (b) shows that the catalyst with a lamellar structure can be prepared by the urea precipitation method, while the lamellar structure of the catalyst prepared by the impregnation method has collapsed and the layers are bonded into blocks.

[0088] Combined with XRD and SEM characterization, it can be shown that the catalyst prepared by the present invention has a layered structure, and the noble metal and V are in the Y 2 O 3 Evenly dispersed on the carrier.

[0089] 3. Application performance

[0090] The catalysts prepared in the above examples and comparative examples are used to catalytically crack polyethylene, and the catalytic cracking of polyethylene includes the following steps:

[0091] 50 mg of polyethylene (melt index 6-9 g / 10 min under 190° C., 2.16 kg, particle size of about 1000 mesh) and 50 mg of the catalyst prepared in the above embodiment or comparative example are placed in a 50 mL quartz-lined autoclave and stirred evenly; after sealing, hydrogen is purged for 30 min to remove impurity gases and replace the atmosphere, and finally 2 MPa of hydrogen is introduced and heated at 250° C. with stirring for 10 hours; after cooling, the gas product is collected with a gas sampling bag and introduced into a gas chromatograph to analyze the gas composition (C1 to C4 alkanes); 40 mL of chloroform is added to the quartz liner, the liner is heated to 80° C. and stirred for 10 min, and then an appropriate amount of liquid is taken out for liquid chromatography analysis (C5 to C21 alkanes), and the mass of the liquid product is recorded as m1 (in mg); finally, the solid (hydrocarbons with carbon atoms>15+catalyst) is filtered, dried and weighed, recorded as m2 (in mg).

[0092] Wherein, the yield of liquid alkane (%) = m1 / 50×100%;

[0093] Selectivity of liquid alkane (%) = m1 / (100-m2)×100%.

[0094] The results of the yield and selectivity of liquid alkanes in the catalytic cracking of polyethylene using various catalysts are shown in Table 2.

[0095] Table 2

[0096]

[0097] From the above results we can see that:

[0098] The comparison results of the above embodiments and comparative examples show that by 2 O 3 The carrier is loaded with Ru and V nanoparticles at the same time. Under the combined effect of the carrier morphology, Ru and V, the catalyst can significantly improve the cracking yield of polyethylene and the selectivity of liquid alkanes. Among them, the cracking yield of polyethylene is ≥45%; among the products of cracking polyethylene, the proportion of liquid alkanes is ≥40%.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A noble metal-vanadium doped yttrium oxide composite catalyst, characterized in that: The invention comprises a carrier, a noble metal and vanadium loaded on the carrier, wherein the carrier is yttrium oxide with a lamella structure.

2. The noble metal-vanadium doped yttrium oxide composite catalyst according to claim 1, characterized in that: The noble metal includes at least one of ruthenium, rhodium, palladium, osmium, iridium and platinum.

3. The noble metal-vanadium doped yttrium oxide composite catalyst according to claim 2, characterized in that: The noble metal is ruthenium.

4. The noble metal-vanadium doped yttrium oxide composite catalyst according to claim 1, characterized in that: The loading amount of the noble metal is 2 to 4 wt % based on the carrier.

5. The noble metal-vanadium doped yttrium oxide composite catalyst according to claim 1, characterized in that: The vanadium loading is 1 to 10 wt % based on the carrier.

6. The noble metal-vanadium doped yttrium oxide composite catalyst according to claim 1, characterized in that: In the noble metal-vanadium doped yttrium oxide composite catalyst, the ratio of the loading amount of vanadium to the loading amount of the noble metal is (0.3-1):

1.

7. The method for preparing the noble metal-vanadium doped yttrium oxide composite catalyst according to any one of claims 1 to 6, characterized in that: The steps include: S1: dissolving a noble metal source into water to form a solution A; dissolving a yttrium source, a vanadium source and a dispersant into water to form a solution B; S2: The solution A and the solution B prepared in step S1 are mixed to form a reaction solution, urea is added to make the pH of the reaction solution in the range of 7 to 8, the reaction is carried out at 70 to 100° C. for 8 to 12 hours, and the obtained precipitated product is washed and dried to obtain a catalyst precursor; S3: calcining the catalyst precursor obtained in step S2 at 550-700° C. for 1.5-3 h in an atmosphere formed by hydrogen and argon to obtain the noble metal-vanadium doped yttrium oxide composite catalyst.

8. The method for preparing the noble metal-vanadium doped yttrium oxide composite catalyst according to claim 7, characterized in that: Satisfies at least one of the following characteristics: (1) The noble metal source is a water-soluble salt containing a noble metal; (2) The yttrium source is a water-soluble salt containing yttrium; (3) The vanadium source is a water-soluble organic salt containing vanadium; (4) The dispersant includes hexadecyltrimethylammonium bromide.

9. The method for preparing the noble metal-vanadium doped yttrium oxide composite catalyst according to claim 7, characterized in that: Satisfies at least one of the following characteristics: (1) In solution A, the concentration of the noble metal source is 0.1 to 0.5 g / mL; (2) In solution B, the concentration of the yttrium source is 0.1 to 0.5 g / mL; (3) The amount of the dispersant added is 15 to 50 wt % of the yttrium source; (4) In step S3, the volume ratio of hydrogen to argon is (0.05-0.1):

1.

10. Use of the noble metal-vanadium doped yttrium oxide composite catalyst according to any one of claims 1 to 6, characterized in that: The noble metal-vanadium doped yttrium oxide composite catalyst is used for catalytic cracking of polyethylene, wherein the cracking yield of polyethylene is ≥45%; and in the product of the cracked polyethylene, the proportion of C5-C21 alkanes is ≥40%.

Images