Hydrotalcite-derived platinum-based catalyst as well as preparation method and application thereof

Abstract

The invention discloses a hydrotalcite-derived platinum-based catalyst as well as a preparation method and application thereof. The chemical formula of the hydrotalcite derived platinum-based catalyst is PtO2 / ZnO-Al2O3. The invention further discloses a preparation method of the hydrotalcite derived platinum-based catalyst. The hydrotalcite-derived platinum-based catalyst has an efficient catalytic effect in the process of preparing propylene by photocatalytic propane dehydrogenation, and the photocatalytic reaction has a relatively high production rate and selectivity of the product propylene.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and more specifically to a hydrotalcite-derived platinum-based catalyst, a preparation method thereof, and applications thereof. Background Art

[0002] Propylene is an important chemical raw material with a wide range of uses in the global chemical industry. Propylene can be used to produce a variety of chemical products, including polypropylene, acrylonitrile, and propylene oxide, and its demand has surged year by year. In recent decades, the discovery and exploitation of shale gas has led to widespread attention in the production of propylene through propane dehydrogenation. The C-H bond energy of propane is 401.3 kJ·mol -1 As the rate-determining step in propane dehydrogenation, its activation and dissociation requires a large amount of energy. Pt species have been demonstrated to be active sites for catalyzing the activation and dissociation of C-H bonds in alkanes. However, the Pt-based propane dehydrogenation catalysts commonly used in current thermal catalysis typically operate at temperatures above 500°C, requiring the combustion of large amounts of fossil fuels annually to provide heat, resulting in significant carbon emissions. This conflicts with the principles of resource conservation and environmental sustainability. Therefore, there is an urgent need to develop catalysts that can drive the activation and dissociation of propane C-H bonds under mild conditions and efficiently catalyze the dehydrogenation of propane to propylene. Photocatalysis is a "zero-energy" technology in which semiconductor photocatalysts are excited by light to generate photogenerated electrons and holes, which drive the reduction and oxidation ends of the chemical reaction, respectively. In recent years, a large number of photocatalysts have been applied to methane coupling, cyclohexane dehydrogenation, and certain homogeneous organic reactions involving C-H bond activation and dissociation, achieving efficient activation of C-H bonds in alkanes or alkyl groups and high product selectivity under mild conditions.

[0003] Hydrotalcite is a unique layered anionic compound with a main layer structure similar to that of brucite Mg(OH)2. The layers are octahedral MO6 with shared edges, and metal ions occupy the center of the octahedron. Due to the adjustable elemental composition of the main layer, the controllable interlayer guests and the thermally induced topological transition characteristics, hydrotalcite has many applications in catalysis, carriers and functional materials. Summary of the Invention

[0004] In response to the above challenges, the present invention aims to provide a hydrotalcite-derived platinum-based catalyst, its preparation method, and its application. This hydrotalcite-derived platinum-based catalyst exhibits high catalytic efficiency in the photocatalytic dehydrogenation of propane to propylene, and the photocatalytic reaction exhibits high propylene production rate and selectivity.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In one aspect, the present invention provides a hydrotalcite-derived platinum-based catalyst having a chemical formula of PtO2 / ZnO-Al2O3.

[0007] In another aspect, the present invention provides a method for preparing the hydrotalcite-derived platinum-based catalyst as described above, the preparation method comprising the following steps:

[0008] Dissolve zinc salt and aluminum salt in deionized water to obtain solution A;

[0009] Dissolve sodium hydroxide in deionized water to obtain solution B;

[0010] Solution A and solution B were mixed dropwise while controlling the pH to be 10.7-10.8 to obtain a crude product;

[0011] The crude product is washed and freeze-dried to obtain a precursor hydrotalcite material;

[0012] Heating and maintaining the temperature of the precursor hydrotalcite material, and then cooling it to room temperature to obtain a zinc-aluminum mixed oxide;

[0013] The zinc-aluminum mixed oxide and chloroplatinic acid hexahydrate are uniformly dispersed in deionized water and stirred to obtain a crude impregnation product;

[0014] washing and drying the impregnated crude product to obtain a platinum impregnated product;

[0015] The platinum-impregnated product is heated and then cooled to room temperature to obtain the hydrotalcite-derived platinum-based catalyst.

[0016] Furthermore, the conditions for heating and maintaining the temperature are: 5-6°C·min -1 The temperature is raised to 500°C at a rate of 0.5°C and maintained at this temperature for 2 to 2.5 hours.

[0017] Furthermore, the heating conditions are: 5-6°C·min -1 The temperature is raised to 500°C at a rate of 0.5°C and maintained at this temperature for 2 to 2.5 hours.

[0018] Furthermore, the heating is performed in an air atmosphere.

[0019] Furthermore, the method of cooling to room temperature is preferably natural cooling to room temperature.

[0020] Furthermore, in the solution A, the concentration of zinc salt is 1.2 to 1.6 mol·L -1 The concentration of aluminum salt is 0.6~0.8mol·L -1 .

[0021] Furthermore, the zinc salt is selected from zinc nitrate, and the aluminum salt is selected from aluminum nitrate.

[0022] Furthermore, in the solution B, the concentration of sodium hydroxide is 2.4 to 2.6 mol·L -1.

[0023] Furthermore, the volume ratio of solution A to solution B is (15-16):(25-40).

[0024] Furthermore, the chemical formula of the precursor hydrotalcite material is [Zn 2+ 2Al 3+ 1(OH)2] n+ ·(A x- ) n / x yH2O, where 0.2≤n≤0.33; x is the valence of the anion; y is the amount of crystal water, and the value of y ranges from 0.5 to 9; A x- It is NO3 - or CO3 2- .

[0025] Furthermore, the ratio of zinc, aluminum and chloroplatinic acid hexahydrate in the zinc-aluminum mixed oxide is 5 mmol: 2.5 mmol: (20-70) mg.

[0026] Furthermore, the crude product is washed and freeze-dried in the following manner:

[0027] The washing method is to wash with deionized water for 3 times; the freeze-drying temperature is -50 to -47°C, the pressure is 5 to 10 Pa, and the time is 24 hours.

[0028] Furthermore, the impregnated crude product is washed and then dried at a temperature of 60 to 70° C. for 24 hours.

[0029] Furthermore, in the above preparation method, the salts and precipitants used are all analytically pure.

[0030] In another aspect, the present invention provides use of the hydrotalcite-derived platinum-based catalyst described above in photocatalytic propane dehydrogenation to produce propylene.

[0031] Furthermore, the application includes the following steps:

[0032] Under the protection of inert gas, propane is introduced into a closed reactor with a light-transmitting quartz glass window and a hydrotalcite-derived platinum-based catalyst, and the reaction is carried out under light conditions.

[0033] Furthermore, the light-transmitting quartz glass window functions as a light-transmitting component, and the light from the light source shines through the quartz glass window onto the surface of the platinum-based catalyst to drive the photocatalytic propane dehydrogenation reaction.

[0034] Furthermore, the volume ratio of the propane to the inert gas is 5:95.

[0035] Furthermore, the inert gas is argon.

[0036] Furthermore, the gas pressure in the reactor is 0.1-0.121 MPa.

[0037] Furthermore, the light source of the illumination is ultraviolet light, preferably 365nm ultraviolet light.

[0038] Unless otherwise specified, the raw materials used in the present invention can be obtained commercially. Any range described in the present invention includes the end value and any numerical value between the end values ​​and any sub-range formed by the end value or any numerical value between the end values.

[0039] The beneficial effects of the present invention are as follows:

[0040] The hydrotalcite-derived platinum-based catalyst provided by the present invention is used to catalyze the production of propylene from propane, realizing for the first time the use of a platinum-based catalyst for the photocatalytic dehydrogenation of propane to produce propylene, with a propylene production rate of nearly 1 mmol g -1 h -1 The hydrotalcite-derived platinum-based catalyst of the present invention is expected to be applied in industrial production.

[0041] The preparation method of the hydrotalcite-derived platinum-based catalyst of the present invention is simple, has a simple process, and is easy to mass-produce. In this preparation method, layered hydrotalcite is used as a precursor, and its inherent lattice positioning effect and structural topological transformation effect are utilized to form a platinum-based catalyst with highly dispersed platinum active sites through equal volume impregnation and high-temperature calcination. In this preparation method, the activity of the resulting platinum-based catalyst in the photocatalytic propane dehydrogenation to propylene reaction can be further optimized by controlling the amount of chloroplatinic acid hexahydrate impregnated in the equal volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0043] Figure 1 The XRD spectra of the products obtained in Example 1 and Example 2 of the present invention are shown; curves a and b in the figure correspond to the XRD spectra of the platinum-based catalysts prepared in Example 1 and Example 2, respectively.

[0044] Figure 2A The Pt 4d XPS spectrum of the platinum-based catalyst obtained in Example 1 of the present invention is shown.

[0045] Figure 2B The Pt 4d XPS spectrum of the platinum-based catalyst obtained in Example 2 of the present invention is shown.

[0046] Figure 2C The transmission electron microscope image of the platinum-based catalyst obtained in Example 1 of the present invention is shown.

[0047] Figure 2D The transmission electron microscope image of the platinum-based catalyst obtained in Example 2 of the present invention is shown.

[0048] Figure 2E The XRD spectrum of the precursor hydrotalcite material (ZnAl-LDH) obtained in step 2) of Example 1 of the present invention is shown.

[0049] Figure 3 The performance diagram shows the cyclic stability of the photocatalytic dehydrogenation of propane to propylene reaction using the platinum-based catalyst obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the following detailed description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0051] In the following examples, the preparation methods are conventional methods unless otherwise specified. The raw materials used are all available from public commercial sources unless otherwise specified, and the percentages are by mass unless otherwise specified.

[0052] Example 1

[0053] A method for preparing a platinum-based catalyst for photocatalytic propane dehydrogenation to produce propylene comprises the following steps:

[0054] 1) Prepare a mixed metal salt solution and a sodium hydroxide solution: dissolve 20 mmol of zinc nitrate hexahydrate and 10 mmol of aluminum nitrate hexahydrate in 15 mL of deionized water; dissolve 60 mmol of sodium hydroxide in 25 mL of deionized water;

[0055] 2) Preparation of a hydrotalcite precursor material for the catalyst by coprecipitation: The mixed metal salt solution and sodium hydroxide solution prepared in step 1) were simultaneously added dropwise to a round-bottom flask containing 100 mL of deionized water, and the pH was controlled to 10.7, and the mixture was added until the mixed metal salt solution was completely added to obtain a crude product;

[0056] 3) washing the crude product obtained in step 2) with deionized water three times, and then drying it in a freeze dryer at a temperature of -50°C and a pressure of 5-10 Pa for 24 hours to obtain a precursor hydrotalcite material;

[0057] 4) Take 1 / 4 of the total mass of the precursor hydrotalcite material obtained in step 3) and heat it in air at 5℃·min -1 The temperature was raised to 500°C at a heating rate of 1000 °C, maintained for 2 h, and then naturally cooled to room temperature to obtain zinc-aluminum mixed oxide;

[0058] 5) The zinc-aluminum mixed oxide obtained in step 4) and 21.6 mg of chloroplatinic acid hexahydrate were uniformly dispersed in 30 mL of deionized water and stirred for 10 h to obtain a crude impregnation product;

[0059] 6) centrifuging the crude impregnation product obtained in step 5), and then drying it in an oven at 60° C. for 24 hours to obtain a platinum impregnation product;

[0060] 7) The platinum impregnated product obtained in step 6) was heated in air at 5°C·min -1 The temperature was raised to 500 °C at a heating rate of 100 °C, maintained for 2 h, and then naturally cooled to room temperature to obtain platinum-based catalyst 1 for photocatalytic propane dehydrogenation to propylene, which was recorded as LD-Pt n .

[0061] The platinum-based catalyst prepared by the above method is applied to the photocatalytic dehydrogenation of propane to produce propylene, which specifically includes the following steps:

[0062] In a 56 mL sealed reaction vessel with a light-transmitting quartz glass window, 5 mg of a platinum-based catalyst was added. A certain proportion of propane (propane:argon volume ratio of 5:95) was introduced. The pressure in the vessel was maintained at 0.121 MPa. The reaction was carried out under 365 nm ultraviolet light for 1 hour. The product was detected by gas chromatography. The catalyst activity was determined.

[0063] The catalyst prepared in this example was characterized:

[0064] Attachment Figure 1 Curve a in the middle is the XRD spectrum of the platinum-based catalyst prepared in Example 1, from which it can be seen that the ZnO phase appears.

[0065] Figure 2A 4d XPS spectrum of Pt obtained in Example 1. Figure 2A From the above, we can see that the valence state of Pt in the catalyst is +4.

[0066] Figure 2C TEM image of the platinum-based catalyst obtained in Example 1. Figure 2C From the perspective of the catalyst, there are a large number of Pt clusters on the surface of the catalyst, which are dispersed on the ZnO and Al2O3 mixed oxide supports.

[0067] Table 1 shows its catalytic performance. The propylene production rate is 986.8 μmol g -1 h -1 , the selectivity of propylene is 99%.

[0068] Table 1 LD-Pt n Photocatalytic performance table

[0069]

[0070] Figure 3 This figure shows the cyclic stability of the photocatalytic propane dehydrogenation to propylene reaction using the platinum-based catalyst obtained in Example 1. The figure shows that under cyclic aeration conditions, the propylene production rate and propylene selectivity remain at relatively high levels over five cycles, demonstrating the excellent stability of the catalyst.

[0071] Example 2

[0072] A platinum-based catalyst, prepared by the same method as in Example 1, except that 21.6 mg of chloroplatinic acid hexahydrate in step 5) is replaced by 64.8 mg of chloroplatinic acid hexahydrate, and is denoted as LD-NP.

[0073] The platinum-based catalyst prepared by the above method is applied to the photocatalytic dehydrogenation of propane to produce propylene, which specifically includes the following steps:

[0074] In a 56 mL sealed reaction vessel with a light-transmitting quartz glass window, 5 mg of a platinum-based catalyst was added. A certain proportion of propane (propane:argon volume ratio of 5:95) was introduced. The pressure in the vessel was maintained at 0.121 MPa. The reaction was carried out under 365 nm ultraviolet light for 1 hour. The product was detected by gas chromatography. The catalyst activity was determined.

[0075] The catalyst prepared in this comparative example was characterized:

[0076] Attachment Figure 1 Curve b in the middle is the XRD spectrum of the platinum-based catalyst prepared in Example 2, from which it can be seen that the ZnO phase appears.

[0077] Figure 2B This is the Pt 4d XPS spectrum obtained in Example 2. Figure 2B From the above, we can see that the valence state of Pt in the catalyst is +4.

[0078] Figure 2D TEM image of the platinum-based catalyst obtained in Example 2. Figure 2D From the perspective of the catalyst, there are a large number of PtO2 particles on the surface of the catalyst, which are dispersed on the ZnO and Al2O3 mixed oxide support.

[0079] Table 2 shows its catalytic performance. The propylene production rate is 641.1 μmol g -1 h -1 , the selectivity of propylene is 98.8%.

[0080] Table 2 LD-NP photocatalytic performance

[0081]

[0082] Example 3

[0083] A platinum-based catalyst, prepared by the same method as in Example 1, except that the air atmosphere in step 7) is replaced by a hydrogen-argon mixed gas (10% H2, v / v) atmosphere, denoted as LD-Pt n 0 The obtained product was subjected to photocatalytic propane dehydrogenation to produce propylene, and the reaction steps were the same as in Example 1. The results are shown in Table 3:

[0084] Table 3 LD-Pt n 0 Photocatalytic performance table

[0085]

[0086] The results show that the photocatalytic dehydrogenation of propane to propylene by platinum-based catalysts calcined in air atmosphere is more active than that by platinum-based catalysts reduced in hydrogen-argon mixed atmosphere.

[0087] Comparative Examples 1-4

[0088] To examine the effect of the type of impregnated precious metal on catalyst performance, the preparation method was the same as in Example 1, except that the 21.6 mg of chloroplatinic acid hexahydrate in step 5) was replaced with chloroauric acid, silver nitrate, ruthenium trichloride, or potassium hexachloroiridate containing a precious metal equivalent in mass to the platinum in the catalyst. The resulting product was subjected to photocatalytic propane dehydrogenation to produce propylene, following the same reaction steps as in Example 1. The results are shown in Table 4:

[0089] Table 4 Catalytic performance of different precious metal-based catalysts

[0090]

[0091] The results show that the activity and selectivity of photocatalytic propane dehydrogenation to propylene of platinum-based catalysts are significantly better than those of other precious metal-based catalysts.

[0092] Comparative Examples 5-7

[0093] To examine the effect of support type on catalyst performance, the preparation method was the same as in Example 1, with the following differences: for Comparative Example 5, the aluminum nitrate hexahydrate in step 1) was removed; for Comparative Example 6, the zinc nitrate hexahydrate in step 1) was removed, and the pH control in step 2) was changed from 10.7 to 8; and for Comparative Example 7, the zinc aluminum oxide in step 5) was replaced with titanium dioxide (P25). The resulting product was subjected to photocatalytic propane dehydrogenation to produce propylene, following the same reaction steps as in Example 1. The results are shown in Table 5:

[0094] Table 5 Photocatalytic performance of platinum-based catalysts loaded on different carriers

[0095]

[0096] The results show that the photocatalytic activity and propylene selectivity of the platinum-based catalyst obtained by using zinc-aluminum mixed oxides derived from zinc-aluminum hydrotalcite as a support are better than those of other supports in the photocatalytic dehydrogenation of propane to propylene.

[0097] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A platinum-based catalyst derived from hydrotalcite, characterized in that The chemical formula of the hydrotalcite-derived platinum-based catalyst is PtO2 / ZnO-Al2O3.

2. The method for preparing a hydrotalcite-derived platinum-based catalyst according to claim 1, wherein: The steps include: Dissolve zinc salt and aluminum salt in deionized water to obtain solution A; Dissolve sodium hydroxide in deionized water to obtain solution B; Solution A and solution B were mixed dropwise while controlling the pH to be 10.7-10.8 to obtain a crude product; The crude product is washed and freeze-dried to obtain a precursor hydrotalcite material; Heating and maintaining the temperature of the precursor hydrotalcite material, and then cooling it to room temperature to obtain a zinc-aluminum mixed oxide; The zinc-aluminum mixed oxide and chloroplatinic acid hexahydrate are uniformly dispersed in deionized water and stirred to obtain a crude impregnation product; washing and drying the impregnated crude product to obtain a platinum impregnated product; The platinum-impregnated product is heated and then cooled to room temperature to obtain the hydrotalcite-derived platinum-based catalyst.

3. The preparation method according to claim 2, characterized in that The conditions for heating and maintaining the temperature are: 5-6°C·min -1 The temperature is raised to 500°C at a rate of 0.5°C and maintained at this temperature for 2 to 2.5 hours.

4. The preparation method according to claim 2, characterized in that The heating conditions are: 5-6°C·min -1 The temperature is raised to 500°C at a rate of 0.5°C and maintained at this temperature for 2 to 2.5 hours; and / or The heating is performed in an air atmosphere.

5. The preparation method according to claim 2, characterized in that In the solution A, the concentration of zinc salt is 1.2-1.6 mol·L -1 The concentration of aluminum salt is 0.6~0.8mol·L -1 and / or The zinc salt is selected from zinc nitrate, and the aluminum salt is selected from aluminum nitrate; and / or In the solution B, the concentration of sodium hydroxide is 2.4-2.6 mol·L -1 and / or The volume ratio of solution A to solution B is (15-16):(25-40).

6. The preparation method according to claim 2, characterized in that The ratio of zinc, aluminum and hexahydrate chloroplatinic acid in the zinc-aluminum mixed oxide is 5 mmol: 2.5 mmol: (20-70) mg.

7. Use of the hydrotalcite-derived platinum-based catalyst according to claim 1 in photocatalytic propane dehydrogenation to produce propylene.

8. The use according to claim 7, characterized in that The application comprises the following steps: Under the protection of inert gas, propane is introduced into a closed reactor with a light-transmitting quartz glass window and a hydrotalcite-derived platinum-based catalyst, and the reaction is carried out under light conditions.

9. The use according to claim 8, characterized in that The light-transmitting quartz glass window functions as a light-transmitting component, and the light from the light source shines through the quartz glass window onto the surface of the platinum-based catalyst to drive the photocatalytic propane dehydrogenation reaction.

10. The use according to claim 8, characterized in that The volume ratio of propane to inert gas is 5:95; and / or The inert gas is argon; and / or The gas pressure in the reactor is 0.1 to 0.121 MPa; and / or The light source of the illumination is ultraviolet light, preferably 365nm ultraviolet light.

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