Microscale noble metal modified Co / Al2O3 catalyst as well as preparation method and application thereof

Abstract

The invention discloses a trace noble metal modified Co / Al2O3 catalyst. The catalyst takes Al2O3 as a carrier, Co as an active component and noble metal X as a secondary active component for exerting a synergistic effect, the composition of the catalyst is represented as X-Co / Al2O3, the noble metal X is one or more of Pt, Ru, Rh, Pd and Ir, the content of Co in the catalyst is 10-15 wt.%, and the atomic ratio of the noble metal to Co is 1: (300-600). The invention also discloses a preparation method and application of the catalyst. According to the catalyst, Al2O3 serves as a carrier, Co serves as an active component, precious metal serves as a secondary active component, the loading capacity of the precious metal is effectively reduced, and the price is relatively low; when the catalyst is applied to polyolefin degradation, the conversion rate of polyolefin can reach 95% or above and the liquid product selectivity can reach 90% or above.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic cracking of waste plastics, and particularly relates to a Co / Al catalyst modified with trace noble metals 2 O 3 and its preparation method and application. Background Art

[0002] Polyolefin materials are also known as inert plastics due to their stable C-C bond structure and excellent physical properties, becoming the plastics with the largest demand and usage, accounting for more than half of the global plastic production. Improper post-treatment after use will bring serious "white" pollution problems and microplastics that pose a threat to health. Facing the global environmental problem of plastic pollution, there is an urgent need to develop effective and economical plastic recycling and upgrading processes to achieve circular economy through chemical recycling and reuse of waste plastics.

[0003] Hydrocracking of waste plastics to prepare liquid fuels is an under-explored route in chemical recycling processes. In recent years, metal-acid bifunctional catalysts with mild reaction conditions and fast reaction rates have attracted much attention for the hydrocracking of polyolefin waste plastics into liquid fuels. Noble metal catalysts such as Pt, Ru, Rh, Ir, and Pd show excellent activity for polyolefin cracking to obtain high-value liquid fuels, and are catalysts for hydrocracking that have been widely studied in recent years. Although the reaction conditions of noble metal catalysts are mild, the high noble metal loading leads to a high cost of chemical upgrading and recycling of waste plastics, which is not suitable for large-scale economic recycling of waste plastics.

[0004] Currently, there are two development directions for solutions that attempt to improve the economic competitiveness of plastic chemical recycling by reducing catalyst costs. One direction is to design catalysts with non-noble metals (such as Fe, Co, Ni, Mo) as the catalyst active center. For example, researchers such as Siddhesh S Borkar used a cobalt-based catalyst (Co / SiO 2 ) for the hydrogenolysis reaction of polyethylene. At 275 °C, 3 MPa H 2 and a reaction time of 8 h, the liquid (C 5 -C 30 ) yield reached 55% (ACS Sustainable Chem. Eng. 2023, 11, 10142 - 10157), proving that the single non-noble metal Co can indeed be used as the catalyst active center, but the yield needs to be further improved. The other direction is to modify noble metal active center catalysts with non-noble metals. For example, the research results of Chen Zezhou et al. showed that the non-noble metal Fe modified Pt / Al 2 O 3The catalytic performance of the catalyst can efficiently convert PE into hydrocarbon fuels (Chemical Engineering Journal 446 (2022) 136213). However, in this catalyst, the active center is noble metal Pt, and the noble metal content is as high as 0.82 wt.%, and the excessive loading of Fe (Fe / Pt = 1) will cause partial inactivation of Pt sites, resulting in a decrease in catalytic performance. In addition, since the noble metal still dominates, the improvement in cost is also very limited. Summary of the Invention

[0005] To solve the problem of the high cost of noble metal catalysts for plastic pyrolysis, the present invention aims to provide a Co / Al modified with trace noble metals 2 O 3 catalyst and its preparation method. This catalyst has a low noble metal content, provides metal sites with hydrogenation function and acidic sites with cracking function, has a high conversion rate and liquid product selectivity for the pyrolysis of different polyolefin waste plastics, and the preparation method is simple.

[0006] The catalyst of the present invention is a Co / Al modified with trace noble metals 2 O 3 catalyst. This catalyst uses Al 2 O 3 as the carrier, Co as the active component, and noble metal X as the secondary active component to exert a synergistic effect; its composition is expressed as X-Co / Al 2 O 3 , and the noble metal X is one or more elements of Pt, Ru, Rh, Pd, and Ir; in the X-Co / Al 2 O 3 catalyst, the content of Co is 10-15 wt.%, and the atomic ratio of noble metal to Co is 1:(300-600).

[0007] The preparation method of the above-mentioned Co / Al modified with trace noble metals provided by the present invention 2 O 3 catalyst includes the following steps:

[0008] (1) Prepare an isopropanol solution of aluminum isopropoxide, add sulfuric acid solution to this solution, age at 260 °C, and then filter, wash, dry, and calcine in sequence to obtain a nano-γ-Al 2 O 3 carrier;

[0009] (2) Prepare an aqueous solution of noble metal X, then load noble metal X onto Co 3 O 4 nano-particles, and finally dry and calcine to obtain X-Co nano-particles;

[0010] (3) Mix the nano-γ-Al 2 O 3 support from step (1) and the X-Co nanoparticles from step (2), add ethanol, and mix evenly by ultrasonic assistance. Finally, obtain the described X-Co / Al 2 O 3 catalyst through drying.

[0011] In the above step (1):

[0012] Preferably, the mass percentage concentration of the sulfuric acid solution is 0.5 - 1 wt.%.

[0013] Preferably, the aging time is 20 - 45 h.

[0014] Preferably, the drying temperature is 30 - 70 °C under reduced pressure, and the drying time is 20 - 24 h. Or preferably, the vacuum drying temperature is 30 °C, and the drying time is 48 h.

[0015] Preferably, the calcination temperature is 500 - 800 °C, and the calcination time is 3 - 5 h. Further preferably, the calcination temperature is 600 - 700 °C, and the calcination time is 4 - 5 h.

[0016] In the above step (2):

[0017] Preferably, the noble metal is loaded by the impregnation method.

[0018] Preferably, the atomic ratio of the noble metal to Co is 1:(400 - 600).

[0019] Preferably, the drying temperature is 80 - 110 °C, and the drying time is 10 - 15 h.

[0020] Preferably, the calcination temperature is 100 - 300 °C, and the calcination time is 1 - 3 h. Further preferably, the calcination temperature is 200 - 300 °C, and the calcination time is 1 - 2 h.

[0021] In the above step (3):

[0022] Preferably, the ultrasonic time is 30 - 60 min. Further preferably, it is 30 - 40 min.

[0023] Preferably, the drying temperature is 150 - 200 °C, and the drying time is 6 - 8 h.

[0024] The present invention also provides the application of the above-mentioned Co / Al 2 O 3 catalyst modified with trace noble metals in the hydrocracking reaction of polyolefin plastics, including the following steps:

[0025] (1) The Co / Al2 O 3 The catalyst, polyolefin and solvent are mixed in a high-pressure reactor;

[0026] (2) After purging 3 times with the reaction gas, it is filled to the reaction pressure. After reaching the reaction temperature, timing starts and stirring is carried out. After reacting for a certain time, the temperature is decreased and the pressure is released. The gas product is collected with an air bag, and then the solid-liquid two phases are separated by suction filtration.

[0027] Preferably, the solvent is one of n-hexane, n-nonane, and ethanol. Further preferably, the solvent is n-nonane.

[0028] Preferably, X-Co / Al 2 O 3 The mass ratio of the catalyst to the polyolefin is 1:(6 - 8), and X-Co / Al 2 O 3 The mass ratio of the catalyst to the solvent is 1:(20 - 40).

[0029] Preferably, the reaction gas is one of hydrogen, air, and nitrogen. Further preferably, it is hydrogen.

[0030] Preferably, the reaction pressure is 0.5 - 2 MPa.

[0031] Preferably, the reaction temperature is 250 - 300 °C.

[0032] Preferably, the reaction time is 2 - 6 h.

[0033] Preferably, the types of waste plastics are one or more of LDPE (low-density polyethylene), HDPE (high-density polyethylene), PP (polypropylene), and GPPS (polystyrene).

[0034] Compared with the prior art, the present invention has the following advantages and prominent effects: The present invention uses Al 2 O 3 as the carrier, Co as the active component, and the noble metal X as the sub-active component, effectively reducing the loading amount of the noble metal and solving the problem of high cost of the noble metal catalyst for plastic cracking in the prior art; mixing the prepared X-Co / Al 2 O 3 catalyst with the polyolefin and the solvent for reaction can effectively improve the mass transfer and heat transfer rates and promote the depolymerization of the polyolefin. The introduction of trace noble metals plays a synergistic catalytic role between the metal sites and the acidic sites, effectively improving the performance of the catalyst, and enabling the polyolefin to reach a conversion rate of over 95% and a liquid product selectivity of over 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 For Co / Al prepared in Examples 1 - 9 2 O3 Catalysts, X-Co / Al 2 O 3 and Pt-Co / C-Al 2 O 3 X-ray diffraction (XRD) patterns of the catalysts.

[0036] Figure 2 For the Pt-Co / Al 2 O 3 catalysts prepared in Examples 5-8, STEM images and EDS-Mapping images. Detailed implementation manners

[0037] For a better understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. For the purpose of elaborating the present invention in detail, many process details are described in the following examples, which are not intended to unduly limit the present invention.

[0038]

Example 1

[0039] Isopropanol and aluminum isopropoxide were mixed and stirred to dissolve the aluminum isopropoxide, and then a 1 wt.% sulfuric acid solution was added to the solution to obtain a suspension; then the suspension was aged at 260 °C for 30 h, and then filtered and washed to obtain a γ-Al 2 O 3 precursor; finally, it was dried in vacuo at 30 °C for 48 h and placed in a muffle furnace and calcined at 650 °C for 5 h to obtain nano-γ-Al 2 O 3 support.

[0040] Co 3 O 4 nanoparticles and γ-Al 2 O 3 support were mixed in ethanol at a mass ratio of 10.2:89.8 and mixed evenly by ultrasonic assistance (30 min), and the Co 3 O 4 nanoparticles were loaded onto the γ-Al 2 O 3 support, and finally dried at 150 °C for 8 h to obtain Co / Al 2 O 3 catalyst.

[0041] According to the mass ratio of Co / Al 2 O 3 catalyst to PP being 1:6 and the mass ratio to n-nonane being 1:20, the three were physically mixed and then encapsulated in a reaction kettle.

[0042] After purging with hydrogen three times, it was filled to the reaction pressure, the temperature increase program was set to raise the temperature to the reaction temperature and stirred, the timing was started, then the temperature decrease program was set. After reaching room temperature, the gas-phase product was collected through an air bag, and the remaining reaction product was separated by suction filtration to obtain a liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0043]

Example 2

[0044] Isopropanol and aluminum isopropoxide were mixed and stirred to dissolve the aluminum isopropoxide, and then 1 wt.% sulfuric acid solution was added to the solution to obtain a suspension; then the suspension was aged at 260 °C for 30 h, and then filtered and washed to obtain γ-Al 2 O 3 precursor; finally, it was vacuum dried at 30 °C for 48 h and placed in a muffle furnace and calcined at 650 °C for 5 h to obtain nano-γ-Al 2 O 3 support.

[0045] According to the atomic ratio of (Ru + Rh):Co being 1:400 (where Ru:Rh is 1:1), ruthenium nitrosyl nitrate, rhodium(III) chloride trihydrate and Co 3 O 4 were weighed. Ruthenium nitrosyl nitrate and rhodium(III) chloride trihydrate were prepared into an aqueous solution, and it was impregnated onto Co 3 O 4 nano-particles. The impregnation can be carried out by the equal-volume impregnation method or the excess impregnation method. In this example, the excess impregnation method was used, that is, under the rotary evaporation at 60 °C, the ruthenium nitrosyl nitrate solution and rhodium(III) chloride solution were impregnated onto Co 3 O 4 nano-particles by multiple impregnation methods. Finally, it was dried at 100 °C for 12 h and placed in a muffle furnace and calcined at 300 °C for 1 h to obtain RuRh-Co nano-particles.

[0046] The RuRh-Co nano-particles and γ-Al 2 O 3 support were mixed in ethanol at a mass ratio of 10.2:89.8 and uniformly mixed by ultrasonic assistance (30 min). The RuRh-Co nano-particles were loaded onto γ-Al 2 O 3 support. Finally, it was dried at 150 °C for 8 h to obtain RuRh-Co / Al 2 O 3 catalyst.

[0047] According to RuRh-Co / Al 2 O 3The catalyst, PP, and n-nonane were physically mixed in a ratio of 1:6, 1:20 respectively, and then encapsulated in a reaction kettle.

[0048] After purging with hydrogen three times, it was filled to the reaction pressure. The temperature increase program was set to rise to the reaction temperature and stirred. Timing was started, and then the temperature decrease program was set. After reaching room temperature, the gas-phase product was collected through an air bag, and the remaining reaction product was separated by suction filtration to obtain the liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0049]

Example 3

[0050] Isopropanol and aluminum isopropoxide were mixed and stirred to dissolve the aluminum isopropoxide. Then, a 1 wt.% sulfuric acid solution was added to the solution to obtain a suspension; the suspension was aged at 260 °C for 30 h, and then filtered and washed to obtain a γ-Al 2 O 3 precursor; finally, it was vacuum dried at 30 °C for 48 h and placed in a muffle furnace and calcined at 650 °C for 5 h to obtain a nano-γ-Al 2 O 3 support.

[0051] Chloroplatinic acid, iridium trichloride, and Co 3 O 4 were weighed according to the atomic ratio of (Pt + Ir):Co of 1:400 (where Pt:Ir is 2:1). Chloroplatinic acid and iridium trichloride were configured into an aqueous solution, and it was impregnated onto Co 3 O 4 nanoparticles. The chloroplatinic acid solution and iridium trichloride solution were impregnated onto Co 3 O 4 nanoparticles by the excess impregnation method under the rotary evaporation at 60 °C through multiple impregnation methods. Finally, it was dried at 100 °C for 12 h and placed in a muffle furnace and calcined at 300 °C for 1 h to obtain PtIr-Co nanoparticles.

[0052] The PtIr-Co nanoparticles and γ-Al 2 O 3 support were mixed in ethanol at a mass ratio of 10.2:89.8 and uniformly impregnated by ultrasonic (30 min) assistance. The PtIr-Co nanoparticles were loaded onto the γ-Al 2 O 3 support. Finally, it was dried at 150 °C for 8 h to obtain the PtIr-Co / Al 2 O 3 catalyst.

[0053] According to PtIr-Co / Al 2 O 3The catalyst, PP, and n-nonane were physically mixed in a ratio of 1:6, 1:20 respectively, and then encapsulated in a reaction kettle.

[0054] After purging with hydrogen three times, it was filled to the reaction pressure. The temperature was raised to the reaction temperature according to the set heating program and stirred, and the timing was started. Subsequently, the cooling program was set. After reaching room temperature, the gas-phase product was collected through an air bag, and the remaining reaction product was separated by suction filtration to obtain the liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0055]

Example 4

[0056] Isopropanol and aluminum isopropoxide were mixed and stirred to dissolve aluminum isopropoxide, and then 1 wt.% sulfuric acid solution was added to the solution to obtain a suspension; then the suspension was aged at 260 °C for 30 h, and then filtered and washed to obtain γ-Al 2 O 3 precursor; finally, it was vacuum dried at 30 °C for 48 h and placed in a muffle furnace and calcined at 650 °C for 5 h to obtain the nano-γ-Al 2 O 3 support.

[0057] Chloroplatinic acid, ruthenium nitrosyl nitrate and Co 3 O 4 were weighed according to the atomic ratio of (Pt + Ru):Co of 1:400 (where Pt:Ru is 1:2). Chloroplatinic acid and ruthenium nitrosyl nitrate were configured into an aqueous solution, and it was impregnated onto Co 3 O 4 nanoparticles. The chloroplatinic acid solution and ruthenium nitrosyl nitrate solution were impregnated onto Co 3 O 4 nanoparticles by the method of excess impregnation under the rotary evaporation at 60 °C through multiple impregnations. Finally, it was dried at 100 °C for 12 h and placed in a muffle furnace and calcined at 300 °C for 1 h to obtain PtRu-Co nanoparticles.

[0058] The PtRu-Co nanoparticles and γ-Al 2 O 3 support were mixed in ethanol in a mass ratio of 10.2:89.8 and uniformly impregnated by ultrasonic (30 min) assistance. The PtRu-Co nanoparticles were loaded onto γ-Al 2 O 3 support. Finally, it was dried at 150 °C for 8 h to obtain PtRu-Co / Al 2 O 3 catalyst.

[0059] According to PtRu-Co / Al 2 O3 The catalyst, PP, and n-nonane were physically mixed at a mass ratio of the catalyst to PP of 1:6 and a mass ratio of the catalyst to n-nonane of 1:20, and then encapsulated in a reaction kettle.

[0060] After purging with hydrogen three times, it was filled to the reaction pressure. The temperature increase program was set to raise the temperature to the reaction temperature and stirred. Timing was started. Subsequently, the temperature decrease program was set. After reaching room temperature, the gas-phase product was collected through an air bag, and the remaining reaction product was separated by suction filtration to obtain a liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0061]

Example 5

[0062] Isopropanol and aluminum isopropoxide were mixed and stirred to dissolve the aluminum isopropoxide. Then, a 1 wt.% sulfuric acid solution was added to the solution to obtain a suspension; the suspension was aged at 260 °C for 30 h, and then filtered and washed to obtain a γ-Al 2 O 3 precursor; finally, it was vacuum dried at 30 °C for 48 h and placed in a muffle furnace and calcined at 650 °C for 5 h to obtain a nano-γ-Al 2 O 3 support.

[0063] Chloroplatinic acid and Co 3 O 4 were weighed according to an atomic ratio of Pt:Co of 1:400. The chloroplatinic acid was prepared into an aqueous solution and impregnated onto the Co 3 O 4 nanoparticles. The chloroplatinic acid solution was impregnated onto the Co 3 O 4 nanoparticles by the excess impregnation method under the rotary evaporation at 60 °C through multiple impregnation methods. Finally, it was dried at 100 °C for 12 h and placed in a muffle furnace and calcined at 300 °C for 1 h to obtain Pt-Co nanoparticles.

[0064] The Pt-Co nanoparticles and the γ-Al 2 O 3 support were mixed in ethanol at a mass ratio of 10.2:89.8 and uniformly impregnated by ultrasonic (30 min) assistance. The Pt-Co nanoparticles were loaded onto the γ-Al 2 O 3 support. Finally, it was dried at 150 °C for 8 h to obtain the Pt-Co / Al 2 O 3 catalyst.

[0065] According to Pt-Co / Al 2 O 3The catalyst, PP, and n-nonane were physically mixed at a mass ratio of the catalyst to PP of 1:6 and a mass ratio of the catalyst to n-nonane of 1:20, and then encapsulated in a reaction kettle.

[0066] After purging with hydrogen three times, it was filled to the reaction pressure. The temperature increase program was set to raise the temperature to the reaction temperature and stirred. Timing was started. Subsequently, the temperature decrease program was set. After reaching room temperature, the gas-phase product was collected through an air bag, and the remaining reaction product was separated by suction filtration to obtain a liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0067]

Example 6

[0068] According to Pt-Co / Al 2 O 3 The catalyst (prepared in Example 5), LDPE, and HDPE mixture were physically mixed at a mass ratio of the catalyst to the LDPE and HDPE mixture of 1:6 and a mass ratio of the catalyst to n-nonane of 1:20, and then encapsulated in a reaction kettle.

[0069] After purging with hydrogen three times, it was filled to the reaction pressure. The temperature increase program was set to raise the temperature to the reaction temperature and stirred. Timing was started. Subsequently, the temperature decrease program was set. After reaching room temperature, the gas-phase product was collected through an air bag, and the remaining reaction product was separated by suction filtration to obtain a liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0070]

Example 7

[0071] According to Pt-Co / Al 2 O 3 The catalyst (prepared in Example 5), PP, and GPPS mixture were physically mixed at a mass ratio of the catalyst to the PP and GPPS mixture of 1:6 and a mass ratio of the catalyst to n-nonane of 1:20, and then encapsulated in a reaction kettle.

[0072] After purging with hydrogen three times, it was filled to the reaction pressure. The temperature increase program was set to raise the temperature to the reaction temperature and stirred. Timing was started. Subsequently, the temperature decrease program was set. After reaching room temperature, the gas-phase product was collected through an air bag, and the remaining reaction product was separated by suction filtration to obtain a liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0073]

Example 8

[0074] According to Pt-Co / Al 2 O 3 The catalyst (prepared in Example 5), LDPE, and GPPS mixture were physically mixed at a mass ratio of the catalyst to the LDPE and GPPS mixture of 1:6 and a mass ratio of the catalyst to n-nonane of 1:20, and then encapsulated in a reaction kettle.

[0075] After purging with hydrogen three times, it was filled to the reaction pressure. The temperature increase program was set to raise the temperature to the reaction temperature and stirred. Timing was started, and then the temperature decrease program was set. After reaching room temperature, the gas-phase product was collected through a gas bag, and the remaining reaction product was separated by suction filtration to obtain the liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0076]

Example 9

[0077] Chloroplatinic acid and Co were weighed according to the atomic ratio of Pt:Co of 1:400 3 O 4 , and chloroplatinic acid was configured into an aqueous solution and impregnated onto Co 3 O 4 nanoparticles. The chloroplatinic acid solution was impregnated onto Co 3 O 4 nanoparticles by the method of excess impregnation under the rotary evaporation at 60 °C through multiple impregnations. Finally, it was dried at 100 °C for 12 h and placed in a muffle furnace for calcination at 300 °C for 1 h to obtain Pt-Co nanoparticles.

[0078] The Pt-Co nanoparticles and commercial γ-Al 2 O 3 (C-Al 2 O 3 ) carriers were mixed in ethanol at a mass ratio of 10.2:89.8 and uniformly mixed by ultrasonic (30 min) assisted impregnation. The Pt-Co nanoparticles were loaded onto the C-Al 2 O 3 carriers. Finally, it was dried at 150 °C for 8 h to obtain the Pt-Co / C-Al 2 O 3 catalyst.

[0079] According to the ratio that the mass ratio of Pt-Co / C-Al 2 O 3 catalyst to PP was 1:6 and the mass ratio to n-nonane was 1:20, the three were physically mixed and then encapsulated in a reaction kettle.

[0080] After purging with hydrogen three times, it was filled to the reaction pressure. The temperature increase program was set to raise the temperature to the reaction temperature and stirred. Timing was started, and then the temperature decrease program was set. After reaching room temperature, the gas-phase product was collected through a gas bag, and the remaining reaction product was separated by suction filtration to obtain the liquid phase and solid residue. Among them, the reaction pressure was 1 MPa, the reaction temperature was 280 °C, the stirring speed was 300 rpm, and the reaction time was 4 h.

[0081] Product characterization:

[0082] The XRD patterns obtained in Examples 1-9 are as follows Figure 1 shown. It can be seen from Figure 1 that for the X-Co / Al 2 O 3 catalysts in Examples 2-8 and the Pt-Co / C-Al 2 O 3 catalyst in Example 9, characteristic diffraction peaks of Al 2 O 3 and Co 3 O 4 are all shown. Due to the low content of noble metals, characteristic diffraction peaks of noble metals cannot be observed.

[0083] The STEM images ( 2 O 3 a) and EDS-Mapping images ( Figure 2 b-2d) of the Pt-Co / Al Figure 2 catalysts prepared in Examples 5-8 are as follows Figure 2 shown. It can be seen from Figure 2 that Pt-Co nanoparticles are uniformly distributed on the Al 2 O 3 support ( Figure 2 the brighter part in a), and the Pt element Figure 2 d) is highly dispersed throughout the Pt-Co / Al 2 O 3 catalyst.

[0084] Performance test:

[0085] The products (gaseous products and liquid products) obtained in Examples 1-5 and Example 9 were analyzed by gas chromatography. The results of the hydrocracking reaction are shown in Table 1; meanwhile, the results of the PP conversion rate and the phase product selectivity are shown in Table 2; in Examples 5-8, the results of the conversion rate and the phase product selectivity of the Pt-Co / Al 2 O 3 catalyst for cracking different plastics are shown in Table 3.

[0086] Table 1 Product analysis results of PP hydrocracking

[0087]

[0088]

[0089] - indicates solvent and is not included in the product distribution.

[0090] Both the gaseous products and the liquid products were normalized.

[0091] As can be seen from Table 1, the Co / Al prepared in Examples 1-5 and Example 9 2 O 3 catalyst, X-Co / Al 2 O 3 catalyst and Pt-Co / C-Al 2 O 3 catalyst can all crack PP. The Co / Al without noble metal modification prepared in Example 1 2 O 3 catalyst and the Pt-Co / C-Al prepared in Example 9 using commercial alumina support 2 O 3 catalyst have irregular product distributions and show random distributions. The X-Co / Al prepared in Examples 2-5 2 O 3 catalyst has similar catalytic performance for the hydrocracking of PP, with similar product distributions and following the same cracking mechanism.

[0092] Results of PP conversion and phase product selectivity in Table 2

[0093]

[0094] As can be seen from the conversion and phase product selectivity results in Table 2, the PP conversion and liquid phase product selectivity in Examples 2-5 are significantly improved compared to Example 1, indicating that the catalytic performance of the X-Co / Al 2 O 3 catalyst modified with trace noble metals is significantly improved, and among them, the Pt-Co / Al 2 O 3 catalyst has the highest PP conversion and liquid phase product selectivity. In addition, from Example 9, it is known that when Pt-Co nanoparticles are loaded on a commercial alumina support, its catalytic performance decreases. It is speculated that the main reason is that the commercial alumina contains impurities and is not as pure as the alumina provided in the present invention. Therefore, the X-Co / Al 2 O 3 catalyst designed by this method not only has good catalytic performance but also can significantly reduce the catalyst cost.

[0095] Table 3 Results of conversion and phase product selectivity of Pt-Co / Al 2 O 3 catalyst for cracking different plastics

[0096]

[0097] Performance evaluation of the Pt-Co / Al 2 O 3 catalyst prepared in Example 5 for the hydrocracking reaction of different polyolefin plastics:

[0098] From the results of the conversion rates and the selectivities of the phase products of different plastics in Table 3, it can be seen that the Pt-Co / Al 2 O 3 catalyst has excellent performance and high catalytic activity for different plastics, with the conversion rates of plastic pyrolysis all above 95%, which is suitable for the economic recycling of waste plastics.

[0099] From the performance test results of the above various embodiments, it can be seen that the Co / Al 2 O 3 catalyst modified with trace precious metals provided by the present invention has good catalytic performance for the pyrolysis of polyolefin plastics, can promote the hydrocracking of waste plastics to prepare liquid fuels under mild conditions, and this preparation method can significantly reduce the economic cost of the catalyst, which is a potential solution to improve the economic competitiveness of plastic chemical recycling.

[0100] The above is only the preferred embodiment of the present invention. It should be noted that for those skilled in the art of this technology, within the scope of the principle of the present invention, several improvements and modifications made should also be regarded as the protection scope of the present invention.

Claims

1. A Co / Al2O3 catalyst modified with trace amounts of precious metals, characterized in that: The catalyst uses Al2O3 as a carrier, Co as an active component, and precious metal X as a secondary active component that exerts a synergistic effect; Its composition is expressed as X-Co / Al2O3, the noble metal X is one or more elements selected from Pt, Ru, Rh, Pd and Ir, the content of Co in the catalyst is 10-15wt.%, and the atomic ratio of the noble metal to Co is 1:(300-600).

2. The method for preparing the catalyst according to claim 1, characterized in that: The method comprises the following steps: 1) preparing an isopropanol solution of aluminum isopropoxide, adding a sulfuric acid solution to the solution, aging at 260° C., filtering, washing, drying and calcining in sequence to obtain a nano γ-Al2O3 carrier; 2) preparing an aqueous solution of precious metal X, then loading the precious metal X onto Co3O4 nanoparticles, and finally drying and calcining to obtain X-Co nanoparticles; 3) The nano-γ-Al2O3 carrier of step 1) and the X-Co nanoparticles of step 2) are mixed, ethanol is added, and the mixture is uniformly mixed by ultrasound, and finally dried to obtain the X-Co / Al2O3 catalyst.

3. The method for preparing the catalyst according to claim 2, characterized in that: In the step 1), the mass percentage concentration of the sulfuric acid solution is 0.5-1wt.%.

4. The method for preparing the catalyst according to claim 2 or 3, characterized in that: In the step 1), the calcination temperature is 500-800° C. and the calcination time is 3-5 hours.

5. The method for preparing the catalyst according to claim 2 or 3, characterized in that: In the step 2), the drying temperature is 80-110° C. and the drying time is 10-15 hours.

6. The method for preparing the catalyst according to claim 2 or 3, characterized in that: In the step 2), the calcination temperature is 100-300° C. and the calcination time is 1-3 hours.

7. The method for preparing the catalyst according to claim 2 or 3, characterized in that: In the step 2), the atomic ratio of the noble metal to Co is 1:(400-600).

8. The method for preparing the catalyst according to claim 2 or 3, characterized in that: In the step 3), the ultrasonic time is 30-60 min.

9. Application of the catalyst according to claim 1 in the hydrocracking of polyolefin plastics.

10. Application of the catalyst according to claim 9 in hydrocracking of polyolefin plastics, characterized in that: The waste plastics are one or more of LDPE, HDPE, PP and GPPS.

Images