Ruthenium catalyst supported on sodium titanate nanowires, preparation method and application thereof

Abstract

The present invention discloses a ruthenium-loaded titanate nanowire catalyst, a preparation method thereof and an application thereof, belonging to the technical field of ruthenium-loaded catalysts. The preparation method of the ruthenium-loaded titanate nanowire catalyst comprises Step 1: dispersing nano-titanium dioxide in a solvent to obtain a first mixture; reacting the first mixture obtained in Step 1 under a certain pressure, and obtaining titanate nanowires after the reaction ends; dispersing the titanate nanowires obtained in Step 2 in a solvent to obtain a second mixture; adding an aqueous solution of ruthenium chloride to the second mixture obtained in Step 3, and stirring to obtain a third mixture; adding an aqueous solution of sodium borohydride to the third mixture obtained in Step 4, and stirring to obtain a fourth mixture, and obtaining a first precursor, namely the ruthenium-loaded titanate nanowire catalyst, after post-treatment. The catalyst prepared by the present invention shows excellent catalytic stability for the hydrocracking reaction of polyolefins, can be extended to the hydrocracking of commercial waste plastics, and the catalyst can be recovered and reused after the reaction ends.

Description

Technical Field

[0001] The present invention belongs to the technical field of ruthenium-loaded catalysts, and particularly relates to a ruthenium catalyst supported on sodium titanate nanowires, a preparation method thereof, and an application thereof. Background Art

[0002] Polyolefins are the most widely used plastics, accounting for about 57% of the total global plastics. Stable polyethylene products can exist in the soil environment for more than 400 years. Even biodegradable plastics require 6 months to completely degrade under specific conditions. Therefore, in all aspects of "plastic control", the degradation of polyolefin plastics is undoubtedly the most important link (Sci. Adv. 2017, 3, e1700782) (Nat. Rev. Chem. 2022, 6, 635-652). Chemical recycling of waste plastics has the advantages of short cycle, high efficiency, high added value, etc. compared with landfilling, incineration, and biodegradation (ACS Sustain. Chem. Eng. 2021, 9, 623−628) (ACS Catal. 2012, 2, 1924−1941). Chemical degradation and recycling technologies mainly include pyrolysis and catalytic hydrogenolysis, which can convert polyolefins into smaller hydrocarbons, including gaseous alkanes, high-value fuels, and lubricants. However, pyrolysis usually requires high reaction temperatures (573~1174 K), has poor selectivity, and the catalyst is prone to deactivation due to coking at high temperatures (Science 2020, 370, 437-441) (J. Am. Chem. Soc. 2022, 144, 5323−5334) (EnergyConvers. Manage. 2016, 115, 308–326) (ChemSusChem 2020, 13, 5808−5836). In recent years, solvent-free metal-catalyzed hydrogenolysis has provided a green and environmentally friendly method for the degradation and recycling of waste polyolefin plastics due to its good reactivity and product selectivity at relatively low temperatures.

[0003] In this context, Ru and Pt catalysts supported on carbon or metal oxides have shown good catalytic performance for this process, and the catalytic activity of Ru is particularly good, such as Ru / C (ACS Sustain. Chem. Eng. 2021, 9, 11661−11666) (JACS Au 2021, 1, 8−12), Ru / CeO2 (ACS Catal. 2022, 12, 4618−4627), Ru / WZrO x(JACS Au 2021, 1, 1422−1434), Ru / TiO2 (ACS Catal. 2021, 11, 8104−8115), etc. However, there are problems with Ru-catalyzed polyolefin hydrogenolysis, such as harsh reaction conditions (generally > 250 °C, hydrogen pressure > 3 MPa) and low yields of long-chain alkanes (> C6). Therefore, the design and development of high-performance Ru catalysts to achieve selective hydrogenolysis of polyolefin plastics under mild reaction conditions is one of the research hotspots in current plastic chemical degradation.

[0004] In recent years, researchers have found that the type of support has a great impact on the performance of Ru-catalyzed hydrogenolysis of polyolefins. For example, Tomishige et al. found that compared with Ru catalysts supported on other metal oxides, Ru / CeO2 has the best catalytic activity and selectivity, because the basic sites of CeO2 can obtain smaller Ru NPs (Appl. Catal. B 2021, 285, 119805). The Vlachos research group proposed a method to regulate the metal-support interaction in Ru / TiO2 using NH3 and demonstrated that stronger metal-support interaction can improve the ability of Ru NPs to adsorb and activate hydrogen, thereby promoting the hydrogenolysis of polypropylene (Nat. Commun. 2022, 13, 5186). These support effects can all be attributed to strong metal-support interaction (SMSI), which can regulate metal particle size, dispersion, electronic state, etc., and thus effectively enhance the performance of the catalyst. However, the above catalytic systems have relatively harsh conditions (240 °C, 6 MPa H2, 8 h) (250 °C, 3 MPa H2, 6 h), and there is no test on the recycling performance of the catalyst. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a ruthenium-loaded sodium titanate nanowire catalyst, its preparation method and application. The ruthenium-loaded sodium titanate nanowire catalyst can efficiently hydrogenolyze low-density polyethylene into liquid alkanes under milder reaction conditions, and at the same time, the catalyst has high stability and can be recycled.

[0006] To achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0007] The present invention provides a preparation method of a ruthenium-loaded sodium titanate nanowire catalyst, which includes the following steps:

[0008] Step 1: Disperse nano-titanium dioxide in a solvent to obtain a first mixture;

[0009] Step 2: React the first mixture obtained in Step 1 under a certain pressure, and obtain sodium titanate nanowires after the reaction ends;

[0010] Step 3: Disperse the sodium titanate nanowires obtained in Step 2 in a solvent to obtain a second mixture.

[0011] Step 4: Add an aqueous solution of ruthenium chloride to the second mixture obtained in Step 3 and stir to obtain a third mixture.

[0012] Step 5: Add an aqueous solution of sodium borohydride to the third mixture obtained in Step 4 and stir to obtain a fourth mixture. After post-treatment, a first precursor, i.e., ruthenium-loaded sodium titanate nanowire catalyst Ru / NTO, is obtained.

[0013] Furthermore, the method for preparing the ruthenium-loaded sodium titanate nanowire catalyst of the present invention further includes the following steps:

[0014] Step 6: Calcinate the first precursor obtained in Step 5 under an inert atmosphere to obtain a second precursor, i.e., ruthenium-loaded sodium titanate nanowire catalyst Ru / NTO-N.

[0015] Even further, the method for preparing the ruthenium-loaded sodium titanate nanowire catalyst of the present invention further includes the following steps:

[0016] Step 7: After post-treating the second precursor obtained in Step 6, perform reduction to obtain a ruthenium-loaded sodium titanate nanowire catalyst Ru / NTO-NH.

[0017] Furthermore, the method for preparing the ruthenium-loaded sodium titanate nanowire catalyst of the present invention further includes the following steps:

[0018] Step 6: Reduce the first precursor obtained in Step 5 under an Ar or H2 atmosphere to obtain a ruthenium-loaded sodium titanate nanowire catalyst Ru / NTO-H.

[0019] Furthermore, the mass ratio of ruthenium in the ruthenium chloride to the sodium titanate nanowires in terms of feed is 0.01 - 0.05:1, and the molar ratio of ruthenium chloride to sodium borohydride is 0.1:1; the solvent in Step 1 is an aqueous sodium hydroxide solution, and the solvents in Step 3 are water, methanol, or ethanol.

[0020] Even further, the molar concentration of the aqueous sodium hydroxide solution is 5 - 20 M, the molar concentration of the aqueous ruthenium chloride solution in Step 4 is 1.2 - 6.0 mmol / L, and the molar concentration of the aqueous sodium borohydride solution in Step 5 is 12 - 60 mmol / L.

[0021] The present invention also provides a ruthenium-loaded sodium titanate nanowire catalyst prepared by the method for preparing the ruthenium-loaded sodium titanate nanowire catalyst described above.

[0022] Furthermore, for the ruthenium-loaded sodium titanate nanowire catalyst of the present invention, in terms of weight percentage, the ruthenium loading amount in the ruthenium-loaded sodium titanate nanowire catalyst is 1 - 5 wt.%.

[0023] The present invention also provides the application of the ruthenium-loaded sodium titanate nanowire catalyst in the hydrocracking reaction of polyolefins.

[0024] Furthermore, the application of the ruthenium-loaded sodium titanate nanowire catalyst of the present invention in the hydrocracking reaction of polyolefins is specifically as follows: polyolefins are subjected to a hydrocracking reaction for 8 - 16 h under a hydrogen atmosphere of 1 - 3 MPa, at 180 - 200 °C, and under the catalysis of the ruthenium-loaded sodium titanate nanowire catalyst. After the reaction, the ruthenium-loaded sodium titanate nanowire catalyst is recovered and reused.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] Through the study of the preparation process conditions, the present invention determines the mechanism of the formation of SMSI between ruthenium nanoparticles and sodium titanate nanowires. The more significant metal-support interaction between ruthenium nanoparticles and sodium titanate nanowires effectively improves the charge state of ruthenium sites and the substrate adsorption ability, enabling the hydrocracking reaction of polyolefins to highly selectively produce liquid alkane products under relatively mild conditions. This catalyst exhibits excellent catalytic stability in the hydrocracking reaction of polyolefins and can be extended to the hydrocracking of commercial waste plastics. After the reaction, the catalyst can be recovered and reused.

[0027] In the present invention, through the redox reaction of Ru δ+ and Ti 3+ in an aqueous solution, sodium titanate nanowires can be coated on the surface of ruthenium nanoparticles, which is a wet chemical SMSI. Nitrogen calcination can improve the crystallinity of the catalyst and enhance the interaction between ruthenium and sodium titanate nanowires, ensuring the strength of SMSI during the hydrogen reduction process. Hydrogen reduction can make the Ru species more uniformly dispersed on the support and weaken the sodium titanate coating layer of ruthenium nanoparticles. Therefore, nitrogen calcination and hydrogen reduction of Ru / NTO can greatly improve the SMSI between ruthenium and the support.

[0028] The improved SMSI of the Ru / NTO-NH catalyst of the present invention is beneficial to the formation of smaller, positively charged ruthenium nanoparticles, resulting in a higher hydrogen coverage rate and a weaker alkane adsorption ability. Therefore, this catalyst is beneficial to the hydrocracking of internal C-C bonds in LDPE under mild conditions (180 °C, 1 MPa), obtaining a complete conversion rate (100%) and high-selectivity liquid alkanes (88%). Ru / NTO-NH can also be used in the hydrocracking reaction of other polyolefin plastics such as HDPE, PP, and LDPE plastic bags. It also exhibits good stability and recyclability, and no obvious decrease in activity is observed after 10 runs. Therefore, the present invention for the first time reveals the regulatory effect of SMSI on the selectivity of polyolefin hydrocracking, providing an effective approach for the selective hydrocracking of polyolefins. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 XRD pattern of the sodium titanate nanowires prepared in Example 1 of the present invention;

[0030] Figure 2 TEM image of the sodium titanate nanowires prepared in Example 1 of the present invention;

[0031] Figure 3 XRD pattern of the ruthenium - loaded catalyst on the sodium titanate nanowires prepared in Example 1 of the present invention;

[0032] Figure 4 TEM image of the ruthenium - loaded catalyst on the sodium titanate nanowires prepared in Example 1 of the present invention;

[0033] Figure 5 HRTEM image of the ruthenium - loaded catalyst on the sodium titanate nanowires prepared in Example 1 of the present invention;

[0034] Figure 6 HRTEM image of the ruthenium - loaded catalyst on the sodium titanate nanowires prepared in Example 2 of the present invention;

[0035] Figure 7 HRTEM image of the ruthenium - loaded catalyst on the sodium titanate nanowires prepared in Example 3 of the present invention;

[0036] Figure 8 HRTEM image of the ruthenium - loaded catalyst on the sodium titanate nanowires prepared in Example 4 of the present invention;

[0037] Figure 9 Gas - phase chromatogram of the product distribution of the hydrogenolysis of LDPE by the catalyst Ru / NTO - NH prepared in Example 5 of the present invention;

[0038] Figure 10 Gas - phase chromatogram of the product distribution of the hydrogenolysis of LDPE by the catalyst Ru / NTO in Comparative Example 1 of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be further described in detail below in conjunction with the embodiments.

[0040] Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those embodiments where specific techniques or conditions are not indicated, the techniques or conditions described in the literature in this field or according to the product specifications are followed. For reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained by purchase.

[0041] Example 1

[0042] This embodiment provides a method for preparing a ruthenium-loaded sodium titanate nanowire catalyst, which comprises the following steps:

[0043] Step 1: Disperse 1.2 g of nano-titanium dioxide powder in 60 mL of 10 M sodium hydroxide aqueous solution to obtain a first mixture;

[0044] Step 2: Transfer the first mixture to an autoclave, stir and react at a speed of 600 rpm in an oil bath for 24 h, wash with a large amount of deionized water until the solution pH = 7, and vacuum dry the precipitate at 80 °C to obtain sodium titanate nanowires;

[0045] Step 3: Disperse 300 mg of sodium titanate nanowires in 30 mL of deionized water to obtain a second mixture;

[0046] Step 4: Drop 25 mL of 6 mmol / L ruthenium chloride aqueous solution into the second mixture and stir at room temperature to obtain a third mixture;

[0047] Step 5: Drop 25 mL of 60 mmol / L sodium borohydride aqueous solution into the third mixture and stir at room temperature to obtain a fourth mixture, wash and dry to obtain a first precursor;

[0048] Step 6: Calcinate the first precursor in a nitrogen atmosphere at 400 °C for 2 h to obtain a second precursor;

[0049] Step 7: Wash and dry the second precursor, and reduce it in an Ar / H2 (5%) atmosphere at 450 °C for 3 h to obtain the ruthenium-loaded sodium titanate nanowire catalyst (Ru / NTO-NH).

[0050] The XRD and TEM diagrams of the sodium titanate nanowires, and the XRD diagram, TEM diagram and HRTEM diagram of the ruthenium-loaded sodium titanate nanowires are respectively as Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 and Figure 5 shown, where:

[0051] Figure 1 : According to the XRD pattern of the sodium titanate nanowires, the prepared sodium titanate nanowires have an amorphous lattice structure.

[0052] Figure 2 : According to the TEM pattern of the sodium titanate nanowires, the prepared support exhibits a nano-hollow wire structure.

[0053] Figure 3 : In the XRD pattern of the ruthenium-loaded sodium titanate nanowires, no diffraction peaks of Ru species (including Ru and RuO2) are detected, indicating that the Ru species have a high dispersion.

[0054] Figure 4 : In the TEM image of ruthenium-loaded sodium titanate nanowires, there are uniformly dispersed ruthenium nanoparticles with smaller particle sizes, and the average particle size is 1.4 nm.

[0055] Figure 5 : In the HRTEM image of ruthenium-loaded sodium titanate nanowires, ruthenium is covered by the sodium titanate carrier layer with a thickness of about 1.25 nm, and the lattice spacing of 0.21 nm is assigned to the (101) plane of Ru.

[0056] Example 2

[0057] This example provides a preparation method of ruthenium nanoparticles loaded on sodium titanate nanowires, and the method includes the following steps:

[0058] Step 1: Disperse 1.2 g of nano-titanium dioxide powder in 60 mL of 10 M sodium hydroxide aqueous solution to obtain a first mixture;

[0059] Step 2: Transfer the first mixture to an autoclave, stir and react in an oil bath at a speed of 600 rpm for 24 h, wash with a large amount of deionized water until the solution pH = 7, and vacuum dry the precipitate at 80 °C to obtain sodium titanate nanowires;

[0060] Step 3: Disperse 300 mg of sodium titanate nanowires in 30 mL of deionized water to obtain a second mixture;

[0061] Step 4: Drop 25 mL of 6 mmol / L ruthenium chloride aqueous solution into the second mixture and stir at room temperature to obtain a third mixture;

[0062] Step 5: Drop 25 mL of 60 mmol / L sodium borohydride aqueous solution into the third mixture and stir at room temperature to obtain a fourth mixture, wash and dry to obtain ruthenium-loaded sodium titanate catalyst Ru / NTO.

[0063] The HRTEM images of ruthenium-loaded sodium titanate are respectively as Figure 6 shown, where:

[0064] Figure 6 : It is observed that in the Ru / NTO sample, the carrier wraps around the ruthenium particles.

[0065] Example 3

[0066] This example provides a preparation method of ruthenium nanoparticles loaded on sodium titanate nanowires, and the method includes the following steps:

[0067] Step 1: Disperse 1.2 g of titanium dioxide nanoparticles in 60 mL of 10 M aqueous sodium hydroxide solution to obtain a first mixture;

[0068] Step 2: Transfer the first mixture to an autoclave, stir and react at a speed of 600 rpm in an oil bath for 24 h, wash with a large amount of deionized water until the solution pH = 7, and vacuum dry the precipitate at 80 °C to obtain sodium titanate nanowires;

[0069] Step 3: Disperse 300 mg of sodium titanate nanowires in 30 mL of deionized water to obtain a second mixture;

[0070] Step 4: Dropwise add 25 mL of 6 mmol / L ruthenium chloride aqueous solution to the second mixture, stir at room temperature to obtain a third mixture;

[0071] Step 5: Dropwise add 25 mL of 60 mmol / L sodium borohydride aqueous solution to the third mixture, stir at room temperature to obtain a fourth mixture, wash and dry to obtain a first precursor.

[0072] Step 6: Calcinate the first precursor at 400 °C for 2 h under a nitrogen atmosphere to obtain a ruthenium-loaded sodium titanate nanowire catalyst Ru / NTO-N;

[0073] The HRTEM images of ruthenium-loaded sodium titanate nanowires are respectively as Figure 7 shown, where:

[0074] Figure 7 : It is observed that in the Ru / NTO-N sample, the contour of the outer coating layer is more obvious, and the crystallinity of the carrier is improved.

[0075] Example 4

[0076] This example provides a method for preparing ruthenium nanoparticles loaded on sodium titanate nanowires, which includes the following steps:

[0077] Step 1: Disperse 1.2 g of titanium dioxide nanoparticles in 60 mL of 10 M aqueous sodium hydroxide solution to obtain a first mixture;

[0078] Step 2: Transfer the first mixture to an autoclave, stir and react at a speed of 600 rpm in an oil bath for 24 h, wash with a large amount of deionized water until the solution pH = 7, and vacuum dry the precipitate at 80 °C to obtain sodium titanate nanowires;

[0079] Step 3: Disperse 300 mg of sodium titanate nanowires in 30 mL of deionized water to obtain a second mixture;

[0080] Step 4: 25 mL of 6 mmol / L ruthenium chloride aqueous solution was added dropwise to the second mixture, and stirred at room temperature to obtain a third mixture;

[0081] Step 5: 25 mL of 60 mmol / L sodium borohydride aqueous solution was added dropwise to the third mixture, and stirred at room temperature to obtain a fourth mixture, which was washed and dried to obtain the first precursor.

[0082] Step 6: The first precursor was reduced at 450 °C for 3 h under an Ar / H2 (5%) atmosphere to obtain the ruthenium-loaded sodium titanate nanowire catalyst (Ru / NTO-H).

[0083] The HRTEM images of ruthenium-loaded sodium titanate nanowires are shown as Figure 8 follows:

[0084] Figure 8 : It was observed that in the Ru / NTO-H sample, the carrier coating layer was partially reduced and the ruthenium dispersion was better.

[0085] Example 5

[0086] This example provides a preparation process for the hydrocracking reaction of low-density polyethylene. Specifically:

[0087] 500 mg of low-density polyethylene and 100 mg of Ru / NTO-NH prepared in Example 1 were placed in a stainless steel autoclave reactor. After sealing, the reactor was purged with H2 six times and pressurized with H2 to 1 MPa. The reaction kettle was placed in a preheated heating device and heated to 180 °C at a stirring speed of 600 rpm for 8 h. After the reaction, it was cooled and the components in the kettle were collected for analysis. The liquid-phase product was dissolved in dichloromethane, and the solid and liquid phases were separated by filtration. The solid was dried and weighed, and the liquid-phase product was weighed after rotary evaporation. The calculated conversion rate was 100%, the selectivity of the gas-phase product was 12%, and the selectivity of the liquid-phase product was 88%. The component selectivity of the liquid-phase product was analyzed by GC. The yields of C1-C5 components were 12%, the yields of C6-C21 components were 65%, and the yields of C22-C35 components were 23%.

[0088] The reaction process is shown as follows:

[0089]

[0090] The GC analysis of the liquid-phase component selectivity is shown as Figure 9 follows.

[0091] Comparative Example 1

[0092] The catalyst Ru / NTO prepared in Example 2 was used in the preparation process of the hydrocracking reaction of low-density polyethylene. Specifically:

[0093] 500 mg of low-density polyethylene and 100 mg of Ru / NTO were placed in a stainless-steel autoclave reactor. After sealing, the reactor was purged with H2 six times and pressurized with H2 to 1 MPa. The reaction kettle was placed in a preheated heating device and heated to 180 °C at a stirring speed of 600 rpm for 8 h. After the reaction, it was cooled and the components in the kettle were collected for analysis. The liquid-phase product was dissolved in dichloromethane, and the solid and liquid phases were separated by filtration. The solid phase was dried and weighed, and the liquid-phase product was weighed after rotary evaporation. The conversion rate was calculated to be 35%, the selectivity of the gas-phase product was 51%, and the selectivity of the liquid-phase product was 49%. The selectivity of the components of the liquid-phase product was analyzed by GC. The yields of C1-C5 components were 18%, the yields of C6-C21 components were 6%, and the yields of C22-C35 components were 11%.

[0094] The selectivity of the liquid-phase components analyzed by GC is as Figure 10 shown.

[0095] Comparative Example 2

[0096] The catalyst Ru / NTO-N prepared in Example 3 was used in the preparation process of the hydrocracking reaction of low-density polyethylene. Specifically:

[0097] 500 mg of low-density polyethylene and 100 mg of Ru / NTO-N were placed in a stainless-steel autoclave reactor. After sealing, the reactor was purged with H2 six times and pressurized with H2 to 1 MPa. The reaction kettle was placed in a preheated heating device and heated to 180 °C at a stirring speed of 600 rpm for 8 h. After the reaction, it was cooled and the components in the kettle were collected for analysis. The liquid-phase product was dissolved in dichloromethane, and the solid and liquid phases were separated by filtration. The solid phase was dried and weighed, and the liquid-phase product was weighed after rotary evaporation. The conversion rate was calculated to be 11%, the selectivity of the gas-phase product was 45%, and the selectivity of the liquid-phase product was 55%. The selectivity of the components of the liquid-phase product was analyzed by GC. The yields of C1-C5 components were 5%, the yields of C6-C21 components were 2%, and the yields of C22-C35 components were 4%.

[0098] Comparative Example 3

[0099] The catalyst Ru / NTO-H prepared in Example 4 was used in the preparation process of the hydrocracking reaction of low-density polyethylene. Specifically:

[0100] 500 mg of low-density polyethylene and 100 mg of Ru / NTO-H were placed in a stainless-steel autoclave reactor. After sealing, the reactor was purged with H2 six times and pressurized with H2 to 1 MPa. The reaction kettle was placed in a preheated heating device and heated to 180 °C at a stirring speed of 600 rpm for 8 h. After the reaction, it was cooled and the components in the kettle were collected for analysis. The liquid-phase product was dissolved in dichloromethane, and the solid and liquid phases were separated by filtration. The solid phase was dried and weighed, and the liquid-phase product was weighed after rotary evaporation. The calculated conversion rate was 50%, the selectivity of the gas-phase product was 60%, and the selectivity of the liquid-phase product was 40%. The component selectivity of the liquid-phase product was analyzed by GC. The yields of C1-C5 components were 30%, the yields of C6-C21 components were 6%, and the yields of C22-C35 components were 14%.

[0101] Examples 6-8

[0102] Examples 6-8 provide the preparation process of polyolefin hydrocracking reaction. The difference from Example 5 is that only one or two of the raw material polyolefin, reaction time, and temperature are changed, as specifically shown in Table 1.

[0103] Table 1 Polyolefin hydrocracking reaction conditions in Examples 6-8

[0104]

[0105] Example 9: Catalyst reuse activity test

[0106]

[0107] 500 mg of low-density polyethylene and 100 mg of Ru / NTO-NH were placed in a stainless-steel autoclave reactor. After sealing, the reactor was purged with H2 six times and pressurized with H2 to 1 MPa. The reaction kettle was placed in a preheated heating device and heated to 180 °C at a stirring speed of 600 rpm for 8 h. After the reaction, it was cooled and the components in the kettle were collected for analysis. The liquid-phase product was dissolved in dichloromethane, and the solid and liquid phases were separated by filtration. The catalyst was washed with a small amount of dichloromethane, dried, and then transferred to a stainless-steel autoclave reactor. 500 mg of low-density polyethylene was added. After the reactor was sealed, the reactor was purged with H2 six times and pressurized with H2 to 1 MPa. The reaction kettle was placed in a preheated heating device and heated to 180 °C at a stirring speed of 600 rpm for 8 h. After the reaction, it was cooled and the components in the kettle were collected for analysis. The liquid-phase product was dissolved in dichloromethane, and the solid and liquid phases were separated by filtration. The solid phase was dried and weighed, and the liquid-phase product was weighed after rotary evaporation. The conversion rate and the selectivity of each phase were calculated. The component selectivity of the liquid-phase product was analyzed by GC. The conversion rates in the reactions of the newly used catalyst and the catalyst reused 1-9 times were as follows: 100%, 100%, 100%, 100%, 100%, 99%, 98%, 98%, 95%, 95%. The yields of the target gaseous alkane products (C1~C5) in the reactions of the newly used catalyst and the catalyst reused 1-9 times were: 12%, 11%, 14%, 12%, 13%, 14%, 13%, 12%, 11%, 10%. The yields of the target liquid fuel alkane products (C6~C21) in the reactions of the newly used catalyst and the catalyst reused 1-9 times were: 65%, 64%, 65%, 63%, 64%, 62%, 63%, 61%, 62%, 62%. The yields of the target paraffin alkane products (C22~C35) in the reactions of the newly used catalyst and the catalyst reused 1-9 times were: 23%, 25%, 21%, 25%, 23%, 24%, 22%, 25%, 22%, 23%. The activity of the catalyst did not decrease significantly.

[0108] The above embodiments have described the implementation manners of the present invention in detail. However, the present invention is not limited to the above implementation manners. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the purpose of the present invention. The above are only the preferred and feasible embodiments of the present invention, and thus do not limit the scope of the rights of the present invention. Any equivalent structural changes made by using the content of the specification of the present invention are included within the scope of the rights of the present invention.

Claims

1. Preparation method of ruthenium catalyst supported on sodium titanate nanowires, characterized in that, It includes the following steps: Step 1: Disperse nano-titanium dioxide in a solvent to obtain a first mixture; Step 2: React the first mixture obtained in Step 1 under a certain pressure. After the reaction, sodium titanate nanowires are obtained; Step 3: Disperse the sodium titanate nanowires obtained in Step 2 in a solvent to obtain a second mixture; Step 4: Add an aqueous solution of ruthenium chloride to the second mixture obtained in Step 3 and stir to obtain a third mixture; Step 5: Add an aqueous solution of sodium borohydride to the third mixture obtained in Step 4 and stir to obtain a fourth mixture. After post-treatment, a first precursor, i.e., ruthenium-loaded sodium titanate nanowire catalyst Ru / NTO, is obtained; Step 6: Calcinate the first precursor obtained in Step 5 under a nitrogen atmosphere to obtain a second precursor, i.e., ruthenium-loaded sodium titanate nanowire catalyst Ru / NTO-N; Step 7: After post-treating the second precursor obtained in Step 6, reduce it under an Ar / H2 mixed atmosphere to obtain a ruthenium-loaded sodium titanate nanowire catalyst Ru / NTO-NH.

2. The preparation method of the ruthenium catalyst supported on sodium titanate nanowires according to claim 1, wherein, The mass ratio of ruthenium in the ruthenium chloride to the sodium titanate nanowires is 0.01 - 0.05:1, and the molar ratio of the ruthenium chloride to the sodium borohydride is 0.1:

1. The solvent in Step 1 is an aqueous sodium hydroxide solution, and the solvents in Step 3 are water, methanol or ethanol.

3. The preparation method of the ruthenium catalyst supported on sodium titanate nanowires according to claim 2, characterized in that, The molar concentration of the aqueous sodium hydroxide solution is 5 - 20 M, the molar concentration of the aqueous ruthenium chloride solution in Step 4 is 1.2 - 6.0 mmol / L, and the molar concentration of the aqueous sodium borohydride solution in Step 5 is 12 - 60 mmol / L.

4. A ruthenium-loaded sodium titanate nanowire catalyst prepared by the preparation method of the ruthenium-loaded sodium titanate nanowire catalyst according to any one of Claims 1 to 3.

5. The sodium titanate nanowire-supported ruthenium catalyst according to claim 4, characterized in that, By weight percentage, the ruthenium loading amount in the ruthenium-loaded sodium titanate nanowire catalyst is 1 - 5 wt.%.

6. Application of the ruthenium-loaded sodium titanate nanowire catalyst according to Claim 4 in the hydrocracking reaction of polyolefins.

7. Use of the ruthenium catalyst supported on sodium titanate nanowires according to claim 6 in the hydrocracking reaction of polyolefins, characterized in that, Under a hydrogen atmosphere of 1 - 3 MPa, at 180 - 200 °C, and under the catalytic action of the ruthenium-loaded sodium titanate nanowire catalyst, polyolefins undergo a hydrocracking reaction for 8 - 16 h. After the reaction, the ruthenium-loaded sodium titanate nanowire catalyst is recovered and reused.

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