Monatomic catalyst for polyolefin cracking as well as preparation method and application of monatomic catalyst

Abstract

The invention relates to a monatomic catalyst for polyolefin cracking as well as a preparation method and application thereof, and the preparation method of the monatomic catalyst comprises the following steps: placing an oxide carrier in a noble metal precursor solution for dipping, drying and roasting to obtain the monatomic catalyst. The obtained monatomic catalyst is applied to the polyolefin catalytic cracking reaction process, compared with a metal nano-catalyst, the monatomic catalyst shows better catalytic activity, the use amount of precious metal is effectively reduced, and the cost of the catalyst is reduced.

Description

Technical Field

[0001] This invention relates to the field of single-atom catalyst technology, and in particular to a single-atom catalyst for polyolefin cracking, its preparation method, and its application. Background Technology

[0002] Currently, polyolefin plastics are widely used in home furnishings, construction, automobiles, electronics, and packaging due to their lightweight, durability, ease of processing, and low cost. However, their relatively short service life and chemically stable properties make subsequent disposal difficult. Currently, less than 15% of plastic waste is recycled, with the majority ending up in the environment. Among various plastics, polyethylene (PE) has an annual production of approximately 83 million tons, accounting for nearly one-third of the total plastic production. Given the enormous volume of polyethylene, improper recycling will place a significant burden on the environment.

[0003] Currently, waste plastic treatment strategies mainly include incineration, landfill, mechanical recycling, and chemical treatment. Incineration and landfill have significant negative impacts on the surrounding environment, while mechanical recycling has limited application scope. In contrast, chemical treatment is an effective strategy to transform waste plastics into high-value-added products. To date, the most common method for chemically treating polyethylene waste plastics is pyrolysis, including high-temperature pyrolysis, catalytic pyrolysis, and catalytic hydrogenolysis. Catalysts play a crucial role in the pyrolysis of polyolefins, not only lowering the reaction temperature but also improving the selectivity of the target products. Among them, noble metal catalysts demonstrate significant advantages and potential in terms of catalytic activity and product selectivity.

[0004] Rorrer et al. used ruthenium nanoparticles loaded onto carbon (Ru / C) and reacted them at 200°C and 2 MPa hydrogen pressure for 16 hours to hydrogenoly decompose polyethylene into liquid alkanes with 8-45 carbon atoms. The mass yield of liquid alkanes was 45%, and the yield of gaseous products was >50%, with methane being the main product (JACS Au 2021, 1, 8-12). It is evident that the existing technology suffers from limitations in its application due to high metal loading and high yield of the low-value-added methane.

[0005] Therefore, given the problems of high metal loading and high methane yield (a low-value-added product) in existing technologies, developing a new single-atom catalyst for polyolefin cracking, its preparation method, and its application has become an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a single-atom catalyst for polyolefin cracking, its preparation method, and its application. The invention obtains the single-atom catalyst by impregnating an oxide support in a noble metal precursor solution, followed by drying and calcination. The single-atom catalyst comprises an oxide support and noble metal single atoms supported on the oxide support. When applied to the polyolefin cracking process, the single-atom catalyst exhibits superior catalytic activity compared to metal particles, effectively reducing the amount of noble metal used and lowering the catalyst cost.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a single-atom catalyst for polyolefin cracking, the method comprising: impregnating an oxide support in a noble metal precursor solution, drying it, and then calcining it to obtain the single-atom catalyst.

[0009] In this invention, an oxide support is mixed with a noble metal precursor solution, and the noble metal is dispersed at single atoms using an impregnation method. Metal ions are initially adsorbed / dispersed on the support through electrostatic interaction, ion exchange, or coordination with hydroxyl groups (-OH) on the support surface. After calcination in air, the precursor decomposes (e.g., nitrates, chlorides), and the metal ions form stronger chemical bonds with oxygen atoms or defect sites on the support surface (e.g., metal-O-support). The metal is anchored on the support in the form of isolated single atoms. This invention significantly improves the utilization rate of the active component, reduces the amount of noble metal used, and improves the reactivity of the catalyst, thereby effectively reducing the catalyst preparation cost.

[0010] As a preferred technical solution of the present invention, the oxide support includes a metal oxide support and / or a non-metal oxide support.

[0011] Preferably, the metal oxide support comprises any one or a combination of at least two of cerium oxide, titanium oxide, or aluminum oxide, wherein typical but non-limiting combinations include: a combination of cerium oxide and titanium oxide, a combination of cerium oxide and aluminum oxide, a combination of titanium oxide and aluminum oxide, and preferably cerium oxide.

[0012] In this invention, when the metal oxide support is cerium oxide, the catalytic activity of the single-atom catalyst is higher. This is because cerium oxide is easier to finely control the anchoring point of a single atom, and its variable valence characteristics make it easier to produce the MSI effect.

[0013] Preferably, the non-metallic oxide carrier comprises silicon dioxide.

[0014] Preferably, the noble metal precursor comprises any one or a combination of at least two of tetraammineplatinum nitrate, chloroplatinic acid, palladium chloride, tetraaminopalladium nitrate, ruthenium chloride, or nitrosylruthenium nitrate. Typical but non-limiting combinations include combinations of tetraammineplatinum nitrate and chloroplatinic acid, combinations of tetraammineplatinum nitrate and palladium chloride, combinations of tetraammineplatinum nitrate and tetraaminopalladium nitrate, combinations of tetraammineplatinum nitrate and ruthenium chloride, combinations of tetraammineplatinum nitrate and nitrosylruthenium nitrate, combinations of chloroplatinic acid and palladium chloride, combinations of chloroplatinic acid and tetraaminopalladium nitrate, combinations of chloroplatinic acid and ruthenium chloride, combinations of chloroplatinic acid and nitrosylruthenium nitrate, combinations of palladium chloride and tetraaminopalladium nitrate, combinations of palladium chloride and ruthenium chloride, combinations of palladium chloride and nitrosylruthenium nitrate, combinations of tetraaminopalladium nitrate and ruthenium chloride, combinations of tetraaminopalladium nitrate and nitrosylruthenium nitrate, combinations of ruthenium chloride and nitrosylruthenium nitrate, preferably ruthenium chloride and / or nitrosylruthenium nitrate.

[0015] As a preferred embodiment of the present invention, the loading of the single atom is 0.01-2% based on the mass of the oxide support being 100%, for example, it can be 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1.0%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, 1.55%, 1.6%, 1.65%, 1.7%, 1.75%, 1.8%, 1.85%, 1.9%, 1.95%, or 2%, but is not limited to the listed values; other unlisted values ​​within the above range are also applicable.

[0016] As a preferred technical solution of the present invention, the soaking time is 10-24h, for example, it can be 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0017] Preferably, the roasting process further includes a grinding process before the roasting process.

[0018] Preferably, the drying temperature is 100-140℃, for example, it can be 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃ or 140℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0019] Preferably, the drying time is ≥10h, for example, it can be 10h, 11h, 12h, 13h, 14h, 15h, 20h, 24h or 30h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0020] As a preferred technical solution of the present invention, the calcination temperature is 300-600℃, for example, it can be 300℃, 350℃, 400℃, 450℃, 500℃, 550℃ or 600℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0021] When the calcination temperature of this invention is too low, the precursor decomposes incompletely, and the residual anions will contaminate the catalyst, hinder reduction, and may poison the active sites. When the calcination temperature is too high, the support is severely sintered, the specific surface area drops sharply, the number of active sites decreases, metal species undergo bulk diffusion or surface migration, agglomerate into large particles, and the catalytic activity decreases.

[0022] Preferably, the calcination time is 30-400 min, for example, it can be 30 min, 50 min, 100 min, 150 min, 200 min, 250 min, 300 min, 350 min or 400 min, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0023] Preferably, the roasting process further includes reduction treatment and passivation treatment.

[0024] In this invention, the reduction process enables stronger electronic interactions between metal atoms and support defects (such as oxygen vacancies) to form M-support bonds. This bonding may be more effective in stabilizing single metal atoms. By passivating, these atoms are kept stable in air, facilitating storage, transportation, and subsequent characterization.

[0025] Preferably, the atmosphere for the reduction treatment is H2 and / or a mixture of H2 and N2.

[0026] Preferably, the volume fraction of H2 in the atmosphere of the reduction treatment is 0.5-100%, for example, it can be 0.5%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0027] Preferably, the temperature of the reduction treatment is 50-600℃, for example, it can be 300℃, 350℃, 400℃, 450℃, 500℃, 550℃ or 600℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0028] When the reduction temperature of this invention is too low, the metal ions are not completely reduced, resulting in low catalyst activity. When the reduction temperature is too high, the metal atoms gain excessive kinetic energy, overcome the binding force of the anchoring points, and undergo thermal migration and aggregation, forming nanoparticles or even larger aggregates. The single-atom structure is destroyed, and the catalytic activity is reduced.

[0029] Preferably, the reduction process takes 1-300 min, for example, 1 min, 10 min, 50 min, 100 min, 150 min, 200 min, 250 min or 300 min, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0030] Preferably, the gas flow rate for the reduction treatment is 1-500 mL / min, for example, it can be 1 mL / min, 50 mL / min, 100 mL / min, 150 mL / min, 200 mL / min, 250 mL / min, 300 mL / min, 350 mL / min, 400 mL / min, 450 mL / min or 500 mL / min, but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0031] Preferably, the passivation treatment atmosphere is a mixture of N2 and O2.

[0032] Preferably, the volume fraction of O2 in the passivation treatment is 0.1-10%, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0033] Preferably, the passivation treatment temperature is 20-100℃, for example, it can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0034] Preferably, the passivation treatment time is 1-300 min, for example, it can be 1 min, 10 min, 50 min, 100 min, 150 min, 200 min, 250 min or 300 min, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0035] Preferably, the gas flow rate for the passivation treatment is 1-500 mL / min, for example, it can be 1 mL / min, 50 mL / min, 100 mL / min, 150 mL / min, 200 mL / min, 250 mL / min, 300 mL / min, 350 mL / min, 400 mL / min, 450 mL / min or 500 mL / min, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0036] As a preferred technical solution of the present invention, the preparation method specifically includes the following steps:

[0037] The oxide support was immersed in a solution of noble metal precursor for 10-24 h, dried at 100-140℃ for ≥10 h, then ground, and finally calcined at 300-600℃ for 30-400 min, reduced at 50-600℃ for 1-300 min, and passivated at 20-100℃ for 1-300 min to obtain a single-atom catalyst.

[0038] Wherein, based on the mass of the oxide support as 100%, the loading of the single atom is 0.01-2%, and the oxide support includes a metal oxide support and / or a non-metal oxide support; the metal oxide support includes any one or a combination of at least two of cerium oxide, titanium oxide, or aluminum oxide; the non-metal oxide support includes silicon dioxide; the noble metal precursor includes any one or a combination of at least two of tetraammineplatinum nitrate, chloroplatinic acid, palladium chloride, tetraaminopalladium nitrate, ruthenium chloride, or nitrosylruthenium nitrate; the atmosphere for the reduction treatment is H2 and / or a mixture of H2 and N2, the volume fraction of H2 in the atmosphere for the reduction treatment is 0.5-100%, and the gas flow rate for the reduction treatment is 1-500 mL / min; the atmosphere for the passivation treatment is a mixture of N2 and O2, the volume fraction of O2 in the passivation treatment is 0.1-10%, and the gas flow rate for the passivation treatment is 1-500 mL / min.

[0039] In a second aspect, the present invention provides a single-atom catalyst for polyolefin cracking prepared by the preparation method described in the first aspect, wherein the single-atom catalyst comprises an oxide support and a noble metal single atom supported on the oxide support;

[0040] The precious metal includes any one or a combination of at least two of Pt, Pd, or Ru.

[0041] This invention constructs a single-atom catalyst for polyolefin cracking, comprising an oxide support and noble metal single atoms supported on the oxide support. The noble metal is anchored on the support in the form of isolated single atoms, each atom being an active site, resulting in high atom utilization. Through the synergistic effect of the atomically dispersed noble metal sites and the oxide support, Lewis acid sites on the support surface can adsorb polyolefin chains, forming "bifunctional active centers" with the noble metal single atoms, synergistically breaking C-C bonds, thus achieving efficient and selective breaking of C-C bonds in polyolefins. When applied to the polyolefin cracking reaction, the single-atom catalyst exhibits superior catalytic activity compared to metal particles. The reaction products differ from those using ruthenium nanocatalyst particles, especially the yield of liquid-phase products, which is higher than that of nanocatalysts. Therefore, when the single-atom catalyst of this invention is used for polyolefin cracking, the yield of low-value-added methane and other substances is low, and the amount of noble metal used is effectively reduced, thus lowering the catalyst cost. Furthermore, the catalyst exhibits high stability and can be recycled and reused.

[0042] Thirdly, the present invention provides an application of the single-atom catalyst described in the second aspect, the application including polyolefin hydrogenolysis and / or polyolefin pyrolysis.

[0043] As a preferred technical solution of the present invention, the method for hydrogenolysis of polyolefins includes:

[0044] The polyolefin was mixed with the single-atom catalyst, and the mixture was subjected to gas exchange with H2. The hydrogenolysis reaction was carried out at 200-300°C and 0.1-4 MPa H2 atmosphere for 0.5-4 h. After the reaction was completed, the catalyst and the pyrolysis products were separated, and the single-atom catalyst was recovered.

[0045] The temperature of the hydrogenolysis reaction is 200-300℃, for example, 200℃, 220℃, 240℃, 260℃, 280℃ or 300℃; the pressure is 0.1-4MPa, for example, 0.1MPa, 0.5MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa, 3.5MPa or 4MPa, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0046] The hydrogenolysis reaction time is 0.5-4h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0047] Preferably, the method for pyrolyzing the polyolefin includes:

[0048] The polyolefin was mixed with the single-atom catalyst, and the mixture was subjected to gas exchange with N2. The mixture was then subjected to pyrolysis at 200-300°C and 0.1-4 MPa N2 atmosphere for 0.5-4 h. After the reaction was completed, the catalyst and pyrolysis products were separated, and the single-atom catalyst was recovered.

[0049] The temperature of the pyrolysis reaction is 200-300℃, for example, 200℃, 220℃, 240℃, 260℃, 280℃ or 300℃; the pressure is 0.1-4MPa, for example, 0.1MPa, 0.5MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa, 3.5MPa or 4MPa, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0050] The pyrolysis reaction time is 0.5-4h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0051] As a preferred embodiment of the present invention, the mass ratio of the noble metal single atom to the polyolefin is 1:(50-5000), for example, it can be 1:50, 1:100, 1:500, 1:1000, 1:1500, 1:2000, 1:2500, 1:3000, 1:3500, 1:4000, 1:4500 or 1:5000, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0052] Preferably, the polyolefin includes polyethylene and / or polypropylene.

[0053] Compared with the prior art, the present invention has at least the following beneficial effects:

[0054] This invention constructs a single-atom catalyst and applies it to the reaction process of polyolefin cracking. Compared with metal particles, the single-atom catalyst exhibits superior catalytic activity, with a polyolefin conversion rate of over 85%. The yield of low-value-added products such as methane is low, and the gas phase product yield is only 14% at most. Furthermore, it effectively reduces the amount of precious metals used and lowers the cost of the catalyst. Detailed Implementation

[0055] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0056] Example 1

[0057] This embodiment provides a method for preparing a single-atom catalyst, the method comprising:

[0058] After immersing the cerium oxide support in a solution of the noble metal precursor ruthenium chloride for 24 h, drying it at 120 °C for 24 h, grinding it, and finally calcining it at 500 °C for 240 min, reducing it at 550 °C for 240 min, and passivating it at 25 °C for 240 min, a single-atom catalyst with a noble metal single-atom Ru loading of 0.5% was obtained.

[0059] The reduction treatment atmosphere has a volume fraction of 100% H2 and a gas flow rate of 100 mL / min; the passivation treatment atmosphere is a mixture of O2 and N2, the passivation treatment atmosphere has a volume fraction of 0.5% O2 and a gas flow rate of 40 mL / min.

[0060] Example 2

[0061] This embodiment provides a method for preparing a single-atom catalyst, the method comprising:

[0062] After impregnating the titanium oxide support in a solution of the noble metal precursor chloroplatinic acid for 10 h, drying it at 140 °C for 10 h, grinding it, and finally calcining it at 600 °C for 30 min, reducing it at 50 °C for 300 min, and passivating it at 100 °C for 10 min, a single-atom catalyst with a noble metal single-atom Pt loading of 0.01% was obtained.

[0063] The reduction treatment atmosphere is a mixture of H2 and N2, with H2 having a volume fraction of 50% and a gas flow rate of 1-500 mL / min; the passivation treatment atmosphere is a mixture of O2 and N2, with O2 having a volume fraction of 5% and a gas flow rate of 200 mL / min.

[0064] Example 3

[0065] This embodiment provides a method for preparing a single-atom catalyst, the method comprising:

[0066] After impregnating the silica support in a solution of the noble metal precursor tetraaminopalladium nitrate for 15 h, drying it at 100 °C for 24 h, grinding it, and finally calcining it at 300 °C for 400 min, reducing it at 600 °C for 10 min, and passivating it at 70 °C for 30 min, a single-atom catalyst with a noble metal single-atom Pd loading of 2% was obtained.

[0067] The reduction treatment atmosphere is a mixture of H2 and N2, the volume fraction of H2 in the reduction treatment atmosphere is 0.5%, and the gas flow rate of the reduction treatment is 1-500 mL / min; the passivation treatment atmosphere is a mixture of O2 and N2, the volume fraction of O2 in the passivation treatment is 10%, and the gas flow rate of the passivation treatment is 500 mL / min.

[0068] Example 4

[0069] This embodiment provides a method for preparing a single-atom catalyst. The only difference from Example 1 is that the oxide support is replaced with a titanium oxide support, while the rest is the same as in Example 1.

[0070] Example 5

[0071] This embodiment provides a method for preparing a single-atom catalyst. The only difference from Example 1 is that the oxide support is replaced with an alumina support, while the rest is the same as in Example 1.

[0072] Example 6

[0073] This embodiment provides a method for preparing a single-atom catalyst. The only difference from Example 1 is that the oxide support is replaced with a silica support, while the rest is the same as in Example 1.

[0074] Example 7

[0075] This embodiment provides a method for preparing a single-atom catalyst. The only difference from Example 1 is that the noble metal precursor solution is replaced with ruthenium nitrite nitrite, while the rest is the same as in Example 1.

[0076] Example 8

[0077] This embodiment provides a method for preparing a single-atom catalyst. The only difference from Example 1 is that the noble metal precursor solution is replaced with chloroplatinic acid, and the noble metal in the obtained single-atom catalyst is changed from Ru to Pt. All other aspects are the same as in Example 1.

[0078] Example 9

[0079] This embodiment provides a method for preparing a single-atom catalyst. The only difference from Example 1 is that the noble metal precursor solution is replaced with palladium chloride, and the noble metal in the obtained single-atom catalyst is changed from Ru to Pd. All other aspects are the same as in Example 1.

[0080] Example 10

[0081] This embodiment provides a method for preparing a single-atom catalyst. The only difference from Example 1 is that the calcination temperature is 250°C, while the rest is the same as in Example 1.

[0082] Example 11

[0083] This embodiment provides a method for preparing a single-atom catalyst. The only difference from Example 1 is that the calcination temperature is 650°C, while the rest is the same as in Example 1.

[0084] Example 12

[0085] This embodiment provides a method for preparing a single-atom catalyst, which differs from Example 1 only in that the reduction treatment temperature is 45°C.

[0086] Example 13

[0087] This embodiment provides a method for preparing a single-atom catalyst, which differs from Example 1 only in that the reduction treatment temperature is 650°C.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing a single-atom catalyst, which differs from Example 1 only in that, except for the absence of calcination, all other aspects are the same as in Example 1.

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing a single-atom catalyst. The calcination treatment of the catalyst preparation method is as follows: the obtained catalyst precursor loaded with noble metal is ground and then calcined in a tube furnace. The temperature is controlled at 500°C, and pure hydrogen (H2) is maintained at a flow rate of 100 ml / min for 240 min to obtain a catalyst loaded with aggregated Ru. Except for the above, the other conditions are exactly the same as those in Example 1.

[0092] Application Example 1

[0093] This application example provides the use of a single-atom catalyst in the hydrogenolysis of polyolefins, wherein the method for polyolefin pyrolysis includes:

[0094] 0.05 g of the catalyst obtained in Example 1 was placed into a batch reactor containing 1 g of LDPE (the mass ratio of noble metal single atoms to LDPE was 1:4000). The mixture was thoroughly mixed, and hydrogen gas was first introduced to replace the gas in the reaction system. After the air was purged, the gas pressure was maintained at 3 MPa. A programmed temperature controller was used for control. Once the set temperature of 250°C was reached, timing began. The reaction was carried out for 3 hours, and the reactor was quickly removed and cooled to room temperature in ice water. The gaseous products were collected using a gas sampling bag; the liquid products were extracted with toluene and then filtered to separate the solid and liquid phases.

[0095] Application Example 2-13

[0096] The difference from Application Example 1 is that the single-atom catalyst prepared in Example 1 is replaced with the single-atom catalyst prepared in Examples 2-13. Apart from the above, the other conditions are exactly the same as those in Application Example 1.

[0097] Application Example 14

[0098] The difference from Application Example 1 is that the amount of catalyst used in Application Example 1 is adjusted to 0.1g, while all other conditions are the same as in Application Example 1.

[0099] Application Example 15

[0100] The difference from Application Example 1 is that, except for changing the reaction system from 3 MPa hydrogen gas to 0.1 MPa nitrogen gas, all other conditions are the same as in Application Example 1.

[0101] Application Example 16

[0102] Four g of the catalyst obtained in Example 1 was placed into a batch reactor containing 1 g of LDPE (the mass ratio of noble metal single atoms to LDPE was 1:50). The mixture was thoroughly mixed, and hydrogen gas was first introduced to replace the gas in the reaction system. After the air was purged, the gas pressure was maintained at 0.1 MPa. A programmed temperature controller was used for control. Once the set temperature of 300°C was reached, timing was started, and the reaction was carried out for 0.5 hours. The reactor was then quickly removed and cooled to room temperature in ice water. The gaseous products were collected using a gas sampling bag; the liquid products were extracted with toluene and then filtered to separate the solid and liquid phases.

[0103] Application Example 17

[0104] 0.04 g of the catalyst obtained in Example 1 was placed into a batch reactor containing 1 g of LDPE (the mass ratio of noble metal single atoms to LDPE was 1:5000). The mixture was thoroughly mixed, and hydrogen gas was first introduced to replace the gas in the reaction system. After the air was purged, the gas pressure was maintained at 4 MPa. A programmed temperature controller was used for control. Once the set temperature of 300°C was reached, timing began. The reaction was carried out for 4 hours, and the reactor was quickly removed and cooled to room temperature in ice water. The gaseous products were collected using a gas sampling bag; the liquid products were extracted with toluene and then filtered to separate the solid and liquid phases.

[0105] Application Comparative Example 1-2

[0106] The difference from Application Example 1 is that the catalyst prepared in Example 1 is replaced with the catalyst prepared in Comparative Examples 1-2.

[0107] Application Comparative Example 3

[0108] The difference from Application Example 1 is that the catalyst used is ruthenium nanoparticle catalyst.

[0109] Performance testing:

[0110] The gaseous and liquid products from the polyolefin pyrolysis of Application Examples 1-17 and Comparative Examples 1-3 were collected. The gaseous products were collected using a gas bag; the liquid products were collected using toluene. The gaseous products were detected using an Al₂O₃ column and an FID detector; the liquid products were injected using an autosampler, and detected using an HP-5 column and an FID detector. The polyolefin conversion rate (%) = (1-m) / (2π) 产物 / m 残渣 ) × 100%, Liquid phase product yield (%) = (m 液相产物 / m 原料 ) × 100%, gas phase product yield (%) = (m 气相产物 / m 原料 The data of the pyrolysis products can be obtained by multiplying the product by 100%, and the results are shown in Table 1.

[0111] Table 1

[0112]

[0113] The test results show that:

[0114] (1) Analysis of the gaseous and liquid phase products after polyolefin pyrolysis in corresponding use cases 1-17 and application comparison examples 1-3 revealed that the liquid phase products are concentrated in C6-C6. 35 The gaseous products are concentrated in C1-C6, with methane and ethane being the main components.

[0115] (2) As can be seen from Application Examples 1 to 3, by constructing the single-atom catalyst and applying it to the polyolefin cracking reaction process, the polyolefin conversion rate can reach up to 100%.

[0116] (3) As can be seen from Application Example 1 and Application Examples 4-6, by further regulating the type of oxide support, the present invention screens out the single-atom catalyst with cerium oxide support, which has the highest catalytic activity when applied to polyolefin cracking.

[0117] (4) As can be seen from Application Example 1 and Application Examples 7-9, by further selecting the noble metal precursor solution and the noble metal atom, the present invention screened out that when the noble metal precursor solution is ruthenium chloride and the noble metal atom is Ru, the single-atom catalyst has the highest catalytic activity when applied to polyolefin cracking.

[0118] (5) As can be seen from Application Example 1 and Application Examples 10-11, when the calcination temperature of the present invention is too low, the precursor decomposes incompletely, the residual anions will contaminate the catalyst, hinder the reduction, and may poison the active sites. When the calcination temperature is too high, the support is severely sintered, the specific surface area drops sharply, the number of active sites decreases, the metal species undergo bulk diffusion or surface migration, aggregate into large particles, and the catalytic activity decreases.

[0119] (6) As can be seen from Application Example 1 and Application Examples 12-13, when the reduction temperature of the present invention is too low, the metal ions are not completely reduced and the catalyst activity is low. When the reduction temperature is too high, the metal atoms gain too much kinetic energy, overcome the binding force of the anchoring point, undergo thermal migration and agglomeration, and form nanoparticles or even larger agglomerates. The single-atom structure will be destroyed and the catalytic activity will be reduced.

[0120] (7) As can be seen from Application Example 1 and Application Examples 14-17, the conversion rate of polyolefins is high when the amount of catalyst is adjusted or the reaction system is changed from hydrogen to nitrogen. It can be seen that the single-atom catalyst of the present invention can be successfully applied to the hydrogenolysis and / or pyrolysis of polyolefins.

[0121] (8) As can be seen from Application Example 1 and Application Comparative Example 1, when the present invention does not undergo calcination treatment, the metal-support interaction is weak, and the precursor is very easy to migrate and agglomerate into nanoparticles during reduction, which cannot form single atoms and the catalytic activity is significantly worse.

[0122] (9) As can be seen from Application Example 1 and Application Comparative Examples 2 and 3, the catalyst precursor loaded with noble metals obtained by the present invention is ground and then calcined in a tube furnace to obtain a catalyst loaded with aggregated Ru, and the catalytic activity is significantly reduced. The single-atom catalyst prepared by the present invention through one-step impregnation method shows better catalytic activity. In addition, compared with metal ruthenium particles, the single-atom catalyst provided by the present invention shows better catalytic activity. The reaction products are different from the reaction products using metal ruthenium nanocatalyst particles. In particular, the yield of liquid phase products is higher than that of nanocatalysts. It can be seen that when the single-atom catalyst of the present invention is used for polyolefin cracking, the yield of low-value-added methane and the like is low.

[0123] In summary, by applying the single-atom catalyst to the polyolefin cracking process, the present invention demonstrates superior catalytic activity compared to metal particles, while effectively reducing the amount of precious metals used and lowering the cost of the catalyst.

[0124] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a single-atom catalyst for polyolefin cracking, characterized in that, The preparation method includes: impregnating the oxide support in a noble metal precursor solution, drying it, and then calcining it to obtain the single-atom catalyst.

2. The preparation method according to claim 1, characterized in that, The oxide support includes a metal oxide support and / or a non-metal oxide support; Preferably, the metal oxide support comprises any one or a combination of at least two of cerium oxide, titanium oxide, or aluminum oxide, with cerium oxide being the most preferred. Preferably, the non-metallic oxide carrier comprises silicon dioxide; Preferably, the noble metal precursor includes any one or a combination of at least two of tetraammineplatinum nitrate, chloroplatinic acid, palladium chloride, tetraamminepalladium nitrate, ruthenium chloride, or nitrosylruthenium nitrate, preferably ruthenium chloride and / or nitrosylruthenium nitrate.

3. The preparation method according to claim 1 or 2, characterized in that, Based on the mass of the oxide support being 100%, the loading of the single atom is 0.01-2%.

4. The preparation method according to any one of claims 1-3, characterized in that, The soaking time is 10-24 hours; Preferably, the process further includes a grinding process before the roasting process; Preferably, the drying temperature is 100-140℃; Preferably, the drying time is ≥10h.

5. The preparation method according to any one of claims 1-4, characterized in that, The calcination temperature is 300-600℃; Preferably, the calcination time is 30-400 min; Preferably, the roasting treatment further includes a reduction treatment and a passivation treatment; Preferably, the atmosphere for the reduction treatment is H2 and / or a mixture of H2 and N2; Preferably, the volume fraction of H2 in the atmosphere of the reduction treatment is 0.5-100%; Preferably, the temperature of the reduction treatment is 50-600℃; Preferably, the reduction treatment time is 1-300 min; Preferably, the gas flow rate for the reduction treatment is 1-500 mL / min; Preferably, the passivation treatment atmosphere is a mixture of N2 and O2; Preferably, the volume fraction of O2 in the passivation treatment is 0.1-10%; Preferably, the passivation treatment temperature is 20-100℃; Preferably, the passivation treatment time is 1-300 min; Preferably, the gas flow rate for the passivation treatment is 1-500 mL / min.

6. The preparation method according to any one of claims 1-5, characterized in that, The preparation method specifically includes the following steps: The oxide support was immersed in a solution of noble metal precursor for 10-24 h, dried at 100-140℃ for ≥10 h, then ground, and finally calcined at 300-600℃ for 30-400 min, reduced at 50-600℃ for 1-300 min, and passivated at 20-100℃ for 1-300 min to obtain a single-atom catalyst. Wherein, based on the mass of the oxide support as 100%, the loading of the single atom is 0.01-2%, and the oxide support includes a metal oxide support and / or a non-metal oxide support; the metal oxide support includes any one or a combination of at least two of cerium oxide, titanium oxide, or aluminum oxide; the non-metal oxide support includes silicon dioxide; the noble metal precursor includes any one or a combination of at least two of tetraammineplatinum nitrate, chloroplatinic acid, palladium chloride, tetraaminopalladium nitrate, ruthenium chloride, or nitrosylruthenium nitrate; the atmosphere for the reduction treatment is H2 and / or a mixture of H2 and N2, the volume fraction of H2 in the atmosphere for the reduction treatment is 0.5-100%, and the gas flow rate for the reduction treatment is 1-500 mL / min; the atmosphere for the passivation treatment is a mixture of N2 and O2, the volume fraction of O2 in the passivation treatment is 0.1%-10%, and the gas flow rate for the passivation treatment is 1-500 mL / min.

7. A single-atom catalyst for polyolefin cracking prepared by the method according to any one of claims 1-6, characterized in that, The single-atom catalyst comprises an oxide support and a noble metal single atom supported on the oxide support; The precious metal includes any one or a combination of at least two of Pt, Pd, or Ru.

8. An application of the single-atom catalyst according to claim 7, characterized in that, The applications include polyolefin hydrogenolysis and / or polyolefin pyrolysis.

9. The application of the single-atom catalyst according to claim 8, characterized in that, The method for hydrogenolysis of polyolefins includes: The polyolefin was mixed with the single-atom catalyst, and the mixture was subjected to gas exchange with H2. The hydrogenolysis reaction was carried out at 200-300°C and 0.1-4 MPa H2 atmosphere for 0.5-4 h. After the reaction was completed, the catalyst and the pyrolysis products were separated, and the single-atom catalyst was recovered. Preferably, the method for pyrolyzing the polyolefin includes: The polyolefin was mixed with the single-atom catalyst, and the mixture was subjected to gas exchange with N2. The mixture was then subjected to pyrolysis at 200-300°C and 0.1-4 MPa N2 atmosphere for 0.5-4 h. After the reaction was completed, the catalyst and pyrolysis products were separated, and the single-atom catalyst was recovered.

10. The application of the single-atom catalyst according to claim 9, characterized in that, The mass ratio of the noble metal single atom to the polyolefin is 1:(50-5000); Preferably, the polyolefin includes polyethylene and / or polypropylene.

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