Cerium oxide supported palladium catalyst as well as preparation method and application thereof

Abstract

The invention provides a cerium oxide supported palladium catalyst and a preparation method and application thereof.The preparation method comprises the following steps that 1, palladium salt and cerium salt are added into water to be evenly mixed, the pH value of the mixed solution is adjusted with an alkali solution, and mixed sediment is obtained; and (2) roasting the mixed precipitate in an air atmosphere and an inert gas in sequence to obtain the cerium oxide supported palladium catalyst. According to the scheme, palladium is loaded on the cerium oxide carrier through oxygen deficiency induced reduction, so that the cerium oxide loaded palladium catalyst is prepared, agglomeration of metal palladium in the high-temperature roasting process is avoided, flammable and explosive hydrogen is avoided, and the overall activity of the catalyst and the preparation safety are further enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a cerium oxide-supported palladium catalyst and a preparation method and application thereof. Background Art

[0002] Cerium oxide (CeO2) is widely used in various catalytic systems due to its high specific surface area, good thermal stability, and redox properties. Immobilizing active metals or compounds on a CeO2 support can significantly improve catalytic performance, particularly in environmental catalysis, energy conversion, and petrochemicals.

[0003] When metallic palladium is loaded on the surface of cerium oxide, the resulting Pd / CeO2 catalyst exhibits excellent performance in multiple catalytic reactions. However, related technologies typically use cerium oxide as a carrier to load palladium oxide, which is then further reduced using flammable and explosive hydrogen. This not only affects the overall activity of the catalyst, but also increases the safety risks of catalyst preparation.

[0004] Based on this, there is an urgent need to provide a cerium oxide-supported palladium catalyst and its preparation method and application. Summary of the Invention

[0005] The embodiments of the present invention provide a cerium oxide-supported palladium catalyst and a preparation method and application thereof, which can solve the problems of high safety risks and low overall activity in the preparation process of traditional cerium oxide-supported catalysts.

[0006] In a first aspect, the present invention provides a method for preparing a cerium oxide-supported palladium catalyst, the preparation method comprising the following steps:

[0007] (1) adding palladium salt and cerium salt into water and mixing them uniformly, and adjusting the pH value of the mixed solution with an alkaline solution to obtain a mixed precipitate;

[0008] (2) calcining the mixed precipitate in an air atmosphere and an inert gas atmosphere in turn to obtain the cerium oxide-supported palladium catalyst.

[0009] Preferably, in step (1), the palladium salt is palladium nitrate, palladium sulfate, palladium chloride or palladium acetate; and the cerium salt is cerium nitrate, cerium sulfate, cerium chloride or cerium acetate.

[0010] Preferably, the molar ratio of the palladium salt to the cerium salt is (0.015-0.085):1.

[0011] Preferably, in step (1), the alkaline solution is aqueous ammonia, urea, sodium carbonate or sodium hydroxide aqueous solution, the concentration of the alkaline solution is 0.5-1 mol / L, and the pH value of the mixed solution is 8.5-9.5.

[0012] Preferably, in step (2), under air atmosphere, the heating rate is 2-3°C / min, the calcination temperature is 300-500°C, and the calcination time is 4-6h.

[0013] Preferably, in step (2), the inert gas is one of nitrogen, argon or helium.

[0014] Preferably, under inert gas, the heating rate is 4-5°C / min, the calcination temperature is 700-800°C, and the calcination time is 2-4h.

[0015] In a second aspect, the present invention further provides a cerium oxide-supported palladium catalyst, which is prepared using any of the preparation methods described in the first aspect above.

[0016] In a third aspect, the present invention further provides a use of the cerium oxide-supported palladium catalyst described in the second aspect in catalyzing the oligomerization of ethylene to prepare α-olefins.

[0017] In a fourth aspect, the present invention also provides a method for preparing α-olefins using the cerium oxide-supported palladium catalyst described in the second aspect above, the method comprising: introducing the cerium oxide-supported palladium catalyst, a co-catalyst and an organic solvent into an ethylene gas reaction system to carry out a polymerization reaction to obtain the α-olefin.

[0018] Preferably, the co-catalyst is diethylaluminum monochloride, and the organic solvent is cyclohexane, n-hexane or toluene.

[0019] Preferably, the content of the cerium oxide-supported palladium catalyst is 1.5-3 μmol, the amount of cyclohexane added is 15-25 mL, and the molar ratio of the co-catalyst to the metal palladium in the cerium oxide-supported palladium catalyst is (400-600):1.

[0020] Preferably, the reaction temperature is 25-50°C, the reaction time is 30-90 min, and the pressure is 0.5-2.0 MPa. Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] In the present invention, palladium salt and cerium salt are first added to water and mixed, and the pH value of the mixed solution is adjusted to weak alkalinity using an alkaline solution to obtain a mixed precipitate of palladium salt and cerium salt. Subsequently, the mixed precipitate is first calcined under an air atmosphere to form palladium oxide and cerium oxide with oxygen defects. The mixed precipitate is further calcined under an inert gas. During the calcination process, the cerium oxide can reduce the palladium oxide to metallic palladium through its own oxygen defects, thereby forming a palladium catalyst with the cerium oxide as a carrier. In this way, not only is the agglomeration of metallic palladium avoided during the high-temperature calcination process, but the use of flammable and explosive hydrogen is also avoided, thereby enhancing the overall activity of the catalyst and the safety of the preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 3 is the XRD pattern of the cerium oxide-supported palladium catalyst prepared in Examples 1 to 3 of the present invention; in the figure, the black line corresponds to Example 1, the red line corresponds to Example 2, and the blue line corresponds to Example 3. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] An embodiment of the present invention provides a method for preparing a cerium oxide-supported palladium catalyst, the preparation method comprising the following steps:

[0026] (1) adding palladium salt and cerium salt into water and mixing them uniformly, and adjusting the pH value of the mixed solution with an alkaline solution to obtain a mixed precipitate;

[0027] (2) calcining the mixed precipitate in an air atmosphere and an inert gas atmosphere in turn to obtain the cerium oxide-supported palladium catalyst.

[0028] In an embodiment of the present invention, palladium salt and cerium salt are first added to water and mixed, and the pH value of the mixed solution is adjusted to a weak alkaline state using an alkaline solution to obtain a mixed precipitate of palladium salt and cerium salt. Thereafter, the mixed precipitate is first calcined in an air atmosphere to form palladium oxide and cerium oxide with oxygen defects. By further calcining under an inert gas, the cerium oxide can reduce the palladium oxide to metallic palladium through its own oxygen defects during the calcination process, thereby forming a palladium catalyst with cerium oxide as a carrier. In this way, not only is the agglomeration of metallic palladium avoided during the high-temperature calcination process, but the use of flammable and explosive hydrogen is also avoided, thereby enhancing the overall activity of the catalyst and the safety of the preparation.

[0029] According to some preferred embodiments, the palladium salt is palladium nitrate, palladium sulfate, palladium chloride or palladium acetate; the cerium salt is cerium nitrate, cerium sulfate, cerium chloride or cerium acetate; the molar ratio of the palladium salt to the cerium salt is (0.015-0.085):1 (for example, it can be 0.015:1, 0.02:1, 0.03:1, 0.05:1, 0.07:1, 0.08:1 or 0.085:1).

[0030] In the embodiment of the present invention, since the palladium salt and the cerium salt of the above-mentioned kind have good solubility, after being placed in water and stirred, the palladium salt and the cerium salt can be evenly dispersed in water to form a uniform mixed precipitate, thereby contributing to improving the uniformity of the catalyst. By further accurately controlling the molar ratio of palladium salt and cerium salt, not only can palladium oxide be completely reduced to metallic palladium alone, but also metallic palladium alone can be uniformly loaded on the surface of cerium oxide; For example, if the molar ratio of palladium salt to cerium salt is too low, the loading amount of metallic palladium alone in cerium oxide will be low, and the number of active sites will decrease, thereby being unfavorable for ensuring that the catalytic activity of cerium oxide-supported palladium catalyst is high, and if the molar ratio of palladium salt to cerium salt is too high, not only is it unfavorable for palladium oxide to be completely reduced to metallic palladium alone, but also is unfavorable for metallic palladium monomer to be evenly distributed in cerium oxide, thereby being equally unfavorable for ensuring that the catalytic activity of cerium oxide-supported palladium catalyst is high.

[0031] According to some preferred embodiments, in step (1), the alkaline solution is aqueous ammonia, urea, sodium carbonate or sodium hydroxide aqueous solution, the concentration of the alkaline solution is 0.5-1 mol / L (for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L), and the pH value of the mixed solution is 8.5-9.5 (for example, it can be 8.5, 8.8, 9.0 or 9.5).

[0032] In an embodiment of the present invention, the pH value of the mixed solution is adjusted by using an alkaline solution, so that the palladium salt and the cerium salt react with the alkaline solution to form a mixed precipitate of palladium salt and cerium salt, which is then centrifuged, dried and calcined to obtain a uniformly dispersed composite oxide.

[0033] It should be noted that, in the embodiment of the present invention, when the pH of the mixed solution is adjusted by an alkaline solution, the alkaline solution is added to the mixed solution and vigorously stirred and mixed until the pH value of the mixed solution reaches the above range, and then the mixed solution is allowed to stand for aging, centrifuged, and moved into a vacuum drying oven (60-120°C) and dried for 12-24 hours to obtain a mixed precipitate, and the mixed precipitate is first calcined in a muffle furnace to obtain a catalyst precursor (cerium oxide loaded palladium oxide), wherein the loading amount of palladium oxide is 0.1 to 0.3 wt%.

[0034] According to some preferred embodiments, in an air atmosphere, the heating rate is 2-3°C / min (for example, it can be 2°C / min, 2.2°C / min, 2.5°C / min, 2.8°C / min or 3°C / min), the calcination temperature is 300-500°C (for example, it can be 300°C, 350°C, 400°C, 450°C or 500°C), and the calcination time is 4-6h (for example, it can be 4h, 5h or 6h).

[0035] In an embodiment of the present invention, the obtained mixed precipitate of palladium salt and cerium salt is first calcined under an air atmosphere, and the calcination temperature is controlled so that the palladium salt and cerium salt in the mixed precipitate can be completely decomposed during the calcination process to form palladium oxide and cerium oxide with oxygen defects. It has been confirmed by experiments of the present invention that if the calcination temperature is too low, it is not conducive to the complete decomposition of the palladium salt and cerium salt precipitates, and if the calcination temperature is too high, the palladium salt and cerium salt precipitates will agglomerate during the calcination process, which is not conducive to the subsequent generation of cerium oxide-supported palladium catalyst.

[0036] According to some preferred embodiments, in step (2), the inert gas is one of nitrogen, argon or helium; under the inert gas, the heating rate is 4-5°C / min (for example, it can be 4°C / min, 4.2°C / min, 4.5°C / min, 4.8°C / min or 5°C / min), the calcination temperature is 700-800°C (for example, it can be 700°C, 720°C, 750°C, 780°C or 800°C), and the calcination time is 2-4h (for example, it can be 2h, 3h or 4h).

[0037] Unlike traditional cerium oxide-supported palladium catalysts, which often use flammable and explosive hydrogen as a reducing gas to promote the production of metallic palladium, in the embodiments of the present invention, inert gas is used instead of the traditional hazardous gas hydrogen during the roasting process, and the roasting temperature is further precisely controlled. This not only facilitates the loading of metallic palladium onto the cerium oxide support through oxygen deficiency-induced reduction, but also avoids the use of flammable and explosive hydrogen, making the preparation process safe and simple.

[0038] An embodiment of the present invention further provides a cerium oxide-supported palladium catalyst, which is prepared using any of the above-mentioned preparation methods.

[0039] The catalyst prepared in the embodiment of the present invention has abundant oxygen vacancies and produces more catalytic active sites when combined with metal palladium. At the same time, the use of transition metals as carriers reduces production costs. The prepared cerium oxide-supported palladium catalyst has both good catalytic activity and stability.

[0040] An embodiment of the present invention further provides a use of the above-mentioned cerium oxide-supported palladium catalyst in catalyzing the oligomerization of ethylene to prepare α-olefins.

[0041] An embodiment of the present invention also provides a method for preparing α-olefins using the above-mentioned cerium oxide-supported palladium catalyst, which comprises: introducing the cerium oxide-supported palladium catalyst, a co-catalyst and an organic solvent into an ethylene gas reaction system to carry out a polymerization reaction to obtain the α-olefin.

[0042] In an embodiment of the present invention, when α-olefins are prepared using a cerium oxide-supported palladium catalyst, ethylene is first introduced into the reaction system to ensure that the system is free of water and oxygen. Thereafter, under an ethylene gas atmosphere, the cerium oxide-supported palladium catalyst, an organic solvent, and a co-catalyst are introduced into a reactor to catalyze the oligomerization reaction of ethylene. Under the combined action of the above-mentioned cerium oxide-supported palladium catalyst and the co-catalyst, α-olefins can be prepared.

[0043] According to some preferred embodiments, the co-catalyst is diethylaluminum monochloride, and the organic solvent is cyclohexane.

[0044] According to some preferred embodiments, the content of the cerium oxide-supported palladium catalyst is 1.5-3 μmol (for example, it can be 1.5 μmol, 2 μmol or 3 μmol), the molar ratio of the co-catalyst to the metallic palladium in the cerium oxide-supported palladium catalyst is (400-600):1 (for example, it can be 400:1, 500:1 or 600:1), and the content of the organic solvent is 15-25 mL (for example, it can be 15 mL, 18 mL, 20 mL, 23 mL or 25 mL).

[0045] Experiments of the present invention have confirmed that using a relatively low content of a cerium oxide-supported palladium catalyst and adding a certain content of a co-catalyst can better promote the polymerization of ethylene to form α-olefins. For example, if the content of the cerium oxide-supported palladium catalyst is too low, the catalytic activity will be low, while if the content of the cerium oxide-supported palladium catalyst is too high, not only will the reaction cost increase, but it may also promote the occurrence of side reactions, thereby reducing the yield and purity of the target product.

[0046] Meanwhile, in the embodiment of the present invention, it is found that the promotor of suitable content can not only activate the cerium oxide supported palladium catalyst to form an active center, but also can remove impurities such as water and oxygen in the catalytic system; If the promotor amount is too low, the active center will be less, resulting in low catalytic activity; and if the promotor amount is too high, the subsequent acidified ethanol that terminates the promotor dosage is more, and pollutants increase. Therefore, the mol ratio of the promotor and metal palladium in the embodiment of the present invention is (400-600): 1.

[0047] According to some preferred embodiments, the reaction temperature is 25-50°C (for example, 25°C, 28°C, 30°C, 35°C, 40°C, 45°C or 50°C), the reaction time is 30-90 min (for example, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min or 90 min), and the pressure is 0.5-2.0 MPa (for example, 0.5 MPa, 0.8 MPa, 1 MPa, 1.5 MPa or 2.0 MPa).

[0048] In the embodiments of the present invention, by controlling the reaction conditions such as the reaction temperature and pressure of the ethylene oligomerization process, it is beneficial to ensure the probability of collision between ethylene and the active center of the catalyst, so that the cerium oxide-supported palladium catalyst can fully exert its catalytic performance. Therefore, based on the catalytic ethylene oligomerization activity and the selectivity of α-olefins and economic considerations, the reaction conditions in the above range are adopted in the embodiments of the present invention.

[0049] In order to more clearly illustrate the technical solutions and advantages of the present invention, a cerium oxide-supported palladium catalyst and its preparation method and application are described in detail below through several embodiments.

[0050] Example 1:

[0051] (1) adding palladium salt (palladium nitrate) and cerium salt (cerium nitrate) in a molar ratio of 0.085:1 to 12 mL of deionized water and stirring to mix, and adjusting the pH value of the mixed solution to 9.0 with an alkaline solution (a sodium carbonate aqueous solution with a concentration of 0.5 mol / L), stirring vigorously for 30 min, and then standing for more than 1 h, centrifuging and washing for more than 5 times, and then transferring to a vacuum drying oven and drying at 65 ° C for 12 h to obtain a mixed precipitate;

[0052] (2) The mixed precipitate was first placed in a muffle furnace, heated to 450°C at a heating rate of 2°C / min in an air atmosphere, and calcined at a constant temperature for 4 hours. After that, it was placed in a tubular furnace, inert gas (nitrogen) was introduced at a rate of 10 mL / min, and heated to 800°C at a heating rate of 5°C / min, calcined at a constant temperature for 2 hours, and then cooled to room temperature (25°C) to obtain a cerium oxide-supported palladium catalyst.

[0053] Example 2:

[0054] Example 2 is substantially the same as Example 1, except that in step (1), the molar ratio of palladium salt (palladium nitrate) to cerium salt (cerium nitrate) is 0.05:1.

[0055] Example 3:

[0056] Example 3 is substantially the same as Example 1, except that in step (1), the molar ratio of palladium salt (palladium nitrate) to cerium salt (cerium nitrate) is 0.015:1.

[0057] The cerium oxide supported palladium catalysts prepared in Example 1 and Example 3 were subjected to XRD test, and the corresponding XRD spectra were as follows: Figure 1 As shown by Figure 1 It can be seen that in Examples 1 to 3, cerium oxide diffraction peaks appear at 2θ of 28.6°, 33.1°, 47.5°, 56.3°, 59.0°, 69.6°, 76.7° and 79.0°, and metal palladium diffraction peaks appear at 2θ of 40.1° and 46.7°, indicating that palladium oxide was successfully reduced to generate metal palladium element by oxygen deficiency induction and loaded onto cerium oxide.

[0058] Example 4:

[0059] Example 4 is basically the same as Example 1, except that in step (2), the calcination temperature is 700° C. under a nitrogen atmosphere.

[0060] Example 5:

[0061] Example 5 is basically the same as Example 1, except that in step (2), the calcination temperature is 720° C. under a nitrogen atmosphere.

[0062] Example 6:

[0063] Example 6 is basically the same as Example 1, except that in step (2), the calcination temperature is 750° C. under a nitrogen atmosphere.

[0064] Example 7:

[0065] Example 7 is basically the same as Example 1, except that in step (2), the calcination temperature is 780° C. under a nitrogen atmosphere.

[0066] Example 8:

[0067] Example 8 is basically the same as Example 1, except that in step (2), a tubular furnace is used to heat the mixture to 400°C at a heating rate of 5°C / min under H2 conditions, and the mixture is calcined at 400°C for 2h and then cooled to room temperature to obtain a cerium oxide-supported palladium catalyst.

[0068] Application Example 1:

[0069] Under anhydrous and oxygen-free conditions, a 100 mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure control system was dried and checked for airtightness. The reactor was replaced with ethylene three times to ensure the absence of oxygen and water, and then preheated at a predetermined temperature (60°C).

[0070] Under an ethylene gas atmosphere, 20 mL of a second organic solvent (cyclohexane), 2 μmol of a cerium oxide-supported palladium catalyst (Example 1), and a co-catalyst (diethylaluminum monochloride) were introduced into a reactor to conduct an ethylene oligomerization reaction. The autoclave was filled with ethylene to the desired pressure (0.5 MPa). After the reaction was completed at 25° C. for 30 minutes, the reactor was cooled to room temperature (25° C.), unreacted ethylene was discharged, and the reaction was quenched with a dilute 10% HCl ethanol solution. The liquid phase was separated from the catalyst, and the catalyst activator product distribution was calculated by gas chromatography using the area normalization method, and the catalyst activity was calculated based on the product. The molar ratio of the co-catalyst to the metal palladium was 500.

[0071] In the embodiment of the present invention, the selectivity of C4 in α-olefins was calculated to be 42.63%, the selectivity of C6 was 57.37%, and the catalytic activity reached 1.54×10 6 g / (molPb·h).

[0072] Application Example 2:

[0073] Application Example 2 is substantially the same as Application Example 1, except that 2 μmol of cerium oxide-supported palladium catalyst (Example 2) is used.

[0074] In the embodiment of the present invention, the selectivity of C4 in α-olefins was calculated to be 46.73%, the selectivity of C6 was 53.27%, and the catalytic activity reached 1.02×10 6 g / (molPb·h).

[0075] Application Example 3:

[0076] Application Example 3 is substantially the same as Application Example 1, except that 2 μmol of cerium oxide-supported palladium catalyst (Example 3) is used.

[0077] In the embodiment of the present invention, the selectivity of C4 in α-olefins was calculated to be 62.68%, the selectivity of C6 was 37.32%, and the catalytic activity reached 9.61×10 5 g / (molPb·h).

[0078] Application Example 4:

[0079] Under anhydrous and oxygen-free conditions, a 100 mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure control system was dried and checked for airtightness. The reactor was replaced with ethylene three times to ensure the absence of oxygen and water, and then preheated at a predetermined temperature (60°C).

[0080] Under an ethylene gas atmosphere, 20 mL of a second organic solvent (cyclohexane), 2 μmol of a cerium oxide-supported palladium catalyst (Example 6), and a co-catalyst (diethylaluminum monochloride) were introduced into a reactor to conduct an ethylene oligomerization reaction. The autoclave was filled with ethylene to the desired pressure (0.5 MPa). After the reaction was completed at 60° C. for 30 minutes, the reactor was cooled to room temperature (25° C.), unreacted ethylene was discharged, and the reaction was quenched with a dilute 10% HCl ethanol solution. The liquid phase was separated from the catalyst, and the catalyst activator product distribution was calculated by gas chromatography using the area normalization method, and the catalyst activity was calculated based on the product. The molar ratio of the co-catalyst to the metallic palladium was 500.

[0081] In the embodiment of the present invention, the selectivity of C4 in α-olefins was calculated to be 36.51%, the selectivity of C6 was 63.49%, and the catalytic activity reached 3.39×10 6 g / (molPb·h).

[0082] Application Example 5:

[0083] Under anhydrous and oxygen-free conditions, a 100 mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure control system was dried and checked for airtightness. The reactor was replaced with ethylene three times to ensure the absence of oxygen and water, and then preheated at a predetermined temperature (60°C).

[0084] Under an ethylene gas atmosphere, 20 mL of a second organic solvent (cyclohexane), 2 μmol of a cerium oxide-supported palladium catalyst (Example 7), and a co-catalyst (diethylaluminum monochloride) were introduced into a reactor to carry out an ethylene oligomerization reaction. The autoclave was filled with ethylene to the desired pressure (0.5 MPa). After the reaction was completed at 60°C for 30 minutes, the reactor was cooled to room temperature (25°C), unreacted ethylene was discharged, and the reaction was quenched with a dilute 10% HCl ethanol solution. The liquid phase was separated from the catalyst, and the catalyst activator product distribution was calculated by gas chromatography using the area normalization method, and the catalyst activity was calculated based on the product; wherein, the molar ratio of the co-catalyst to the metal palladium element was 400.

[0085] In the embodiment of the present invention, the selectivity of C4 in α-olefins was calculated to be 37.88%, the selectivity of C6 was 62.12%, and the catalytic activity reached 2.71×10 6 g / (molPb·h).

[0086] Application Example 6:

[0087] Under anhydrous and oxygen-free conditions, a 100 mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure control system was dried and checked for airtightness. The reactor was replaced with ethylene three times to ensure the absence of oxygen and water, and then preheated at a predetermined temperature (60°C).

[0088] Under an ethylene gas atmosphere, 20 mL of a second organic solvent (cyclohexane), 2 μmol of a cerium oxide-supported palladium catalyst (Example 8), and a co-catalyst (diethylaluminum monochloride) were introduced into a reactor to carry out an ethylene oligomerization reaction. The autoclave was filled with ethylene to the desired pressure (0.5 MPa). After the reaction was completed at 60° C. for 30 minutes, the reactor was cooled to room temperature (25° C.), unreacted ethylene was discharged, and the reaction was quenched with a dilute 10% HCl ethanol solution. The liquid phase was separated from the catalyst, and the catalyst activator product distribution was calculated by gas chromatography using the area normalization method, and the catalyst activity was calculated based on the product; wherein, the molar ratio of the co-catalyst to the metal palladium element was 300.

[0089] In the embodiment of the present invention, the selectivity of C4 in α-olefins was calculated to be 61.09%, the selectivity of C6 was 38.11%, and the catalytic activity reached 1.30×10 5 g / (molPb·h).

[0090] Application Example 5:

[0091] Under anhydrous and oxygen-free conditions, a 100 mL stainless steel reactor equipped with a magnetic stirrer, temperature control system, and pressure control system was dried and checked for airtightness. The reactor was replaced with ethylene three times to ensure the absence of oxygen and water, and then preheated at a predetermined temperature (60°C).

[0092] Under an ethylene gas atmosphere, 20 mL of a second organic solvent (cyclohexane), 2 μmol of a cerium oxide-supported palladium catalyst, and a co-catalyst (diethylaluminum monochloride) were introduced into a reactor to conduct an ethylene oligomerization reaction. The autoclave was filled with ethylene to the desired pressure (0.5 MPa). After the reaction was completed at 60°C for 30 minutes, the reactor was cooled to room temperature (25°C), unreacted ethylene was discharged, and the reaction was quenched with a dilute 10% HCl ethanol solution. The liquid phase was separated from the catalyst, and the catalyst activity was calculated based on the product distribution using gas chromatography using the area normalization method. The molar ratio of the co-catalyst to the metal palladium was 500.

[0093] Wherein, the cerium oxide supported palladium catalyst is prepared by the following method:

[0094] (1) Disperse the nanomaterial CeO2 in 8 mL of ethanol to prepare a 10 mg / mL CeO2 suspension, and ultrasonicate for 60 min to uniformly disperse the CeO2;

[0095] (2) adding 1 mL of NaBH4 (5 mg / mL) to the suspension obtained in step (1) to reduce CeO2 and ultrasonically reduce it for 10 min; centrifuging the reduced CeO2 to remove the supernatant, and drying the precipitate in a vacuum drying oven for 5 h;

[0096] (3) placing 10 mg of palladium dichloride solid and 30 mg of CeO2 reduced powder obtained in step (2) in a tube furnace and heating the mixture to 300° C. in a N2 atmosphere;

[0097] (4) NH3 was introduced into the tubular furnace in step (4) and reacted for 10 h to obtain a CeO2@Pd supported catalyst; wherein the Pd loading amount was 4.55 wt%.

[0098] In the embodiment of the present invention, due to the excessive loading of Pd, Pd agglomerates on the surface of cerium oxide, which is not conducive to ensuring good catalytic activity of the catalyst. Further calculations show that the selectivity of C4 in α-olefins is 86.15%, the selectivity of C6 is 13.85%, and the catalytic activity is 1.46×10 5 g / (mol Pd·h).

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a cerium oxide-supported palladium catalyst, characterized in that: The preparation method comprises the following steps: (1) adding palladium salt and cerium salt into water and mixing them uniformly, and adjusting the pH value of the mixed solution with an alkaline solution to obtain a mixed precipitate; (2) calcining the mixed precipitate in an air atmosphere and an inert gas atmosphere in turn to obtain the cerium oxide-supported palladium catalyst.

2. The preparation method according to claim 1, characterized in that In step (1), the palladium salt is palladium nitrate, palladium sulfate, palladium chloride or palladium acetate; the cerium salt is cerium nitrate, cerium sulfate, cerium chloride or cerium acetate; The molar ratio of the palladium salt to the cerium salt is (0.015-0.085):

1.

3. The preparation method according to claim 1, characterized in that In step (1), the alkaline solution is ammonia water, urea, sodium carbonate or sodium hydroxide aqueous solution, the concentration of the alkaline solution is 0.5-1 mol / L, and the pH value of the mixed solution is 8.5-9.

5.

4. The preparation method according to claim 1, characterized in that In step (2), under air atmosphere, the heating rate is 2-3°C / min, the calcination temperature is 300-500°C, and the calcination time is 4-6h.

5. The preparation method according to claim 1, characterized in that In step (2), the inert gas is one of nitrogen, argon or helium; Preferably, under inert gas, the heating rate is 4-5°C / min, the calcination temperature is 700-800°C, and the calcination time is 2-4h.

6. A cerium oxide supported palladium catalyst, characterized in that The preparation method according to any one of claims 1 to 5 is used.

7. Use of the cerium oxide-supported palladium catalyst according to claim 6 in catalyzing the oligomerization of ethylene to prepare α-olefins.

8. A method for preparing α-olefins using the cerium oxide-supported palladium catalyst according to claim 7, characterized in that: The method comprises: introducing a cerium oxide-supported palladium catalyst, a co-catalyst and an organic solvent into an ethylene gas reaction system to carry out a polymerization reaction to obtain the alpha-olefin.

9. The method according to claim 8, characterized in that The co-catalyst is diethylaluminum monochloride, and the organic solvent is cyclohexane, n-hexane or toluene; The addition amount of the cerium oxide supported palladium catalyst is 1.5-3 μmol, the addition amount of the cyclohexane is 15-25 mL, and the molar ratio of the co-catalyst to the metal palladium in the cerium oxide supported palladium catalyst is (400-600):

1.

10. The method according to claim 8, characterized in that The reaction temperature is 25-50° C., the reaction time is 30-90 min, and the pressure is 0.5-2.0 MPa.

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