Ni monatomic and Pd nanoparticle co-modified titanium dioxide photocatalyst as well as preparation and application thereof

Abstract

The invention discloses a TiO2 photocatalyst co-modified by Ni monatomic and Pd nanoparticles, a preparation method of the TiO2 photocatalyst and application of the TiO2 photocatalyst in preparation of olefin through photocatalysis of non-oxidative dehydrogenation of alkane. The preparation method comprises the following steps: firstly, preparing a monatomic photocatalyst with an organic ligand by using a surface organometallic chemical method, then calcining to obtain the monatomic photocatalyst, and then combining with a photodeposition method to prepare the photocatalyst simultaneously containing monatomic and nanoparticles. The Ni single atom in the obtained photocatalyst can enable the adjacent Pd nanoparticles to selectively photocatalyze alkane dehydrogenation to prepare olefin, so that the photocatalyst has excellent dehydrogenation activity, higher product selectivity and carbon deposition resistance in photocatalyze alkane non-oxidative dehydrogenation to prepare olefin.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalysis, and specifically relates to a method for co-modifying TiO 2 A photocatalyst, a preparation method thereof and application thereof in photocatalytic non-oxidative dehydrogenation of alkanes to olefins. Background Art

[0002] Ethylene and propylene are among the most productive and consumed basic organic chemical raw materials in the world. They are often widely referred to as the cornerstones of petrochemical industry, and the output of ethylene has been considered as one of the important indicators to measure the level of development of a country in petrochemical industry. With the rapid growth of my country's demand for olefins, the supply of olefins has become increasingly tight in recent years. At present, the main method for industrial production of olefins is through steam cracking of naphtha, but this requires high temperature and high pressure reaction conditions, and is accompanied by the generation of other by-products.

[0003] With the emergence of shale gas in recent years, its development and utilization have become a hot topic in the global energy field. Among them, ethane, as the second most abundant component in shale gas, has attracted widespread attention due to its low cost and low energy consumption for catalytic dehydrogenation to ethylene. At present, the reaction of ethane dehydrogenation to ethylene is generally divided into two categories: ethane oxidative dehydrogenation and ethane non-oxidative dehydrogenation. Although ethane oxidative dehydrogenation is more thermodynamically favorable, since the generated ethylene has a higher reactivity than the reactant ethane, over-oxidation often occurs, producing CO 2 and CO. Compared with ethane oxidative dehydrogenation, non-oxidative dehydrogenation of ethane has unique advantages in avoiding overoxidation and producing valuable ethylene and hydrogen fuels. However, whether it is industrial use of naphtha cracking to produce ethylene or ethane dehydrogenation to produce ethylene by thermal catalysis, high temperature reaction conditions are required. Such harsh high temperature conditions can cause metal sintering, resulting in rapid deactivation of the catalyst, poor stability, frequent regeneration, and reduced selectivity of the target product. The use of photocatalytic technology to dehydrogenate alkanes to olefins can greatly reduce the sintering of metals at high temperatures, thereby increasing the operating cycle of the catalyst. However, most of the current photocatalytic reactions of alkane to olefins are aerobic dehydrogenation, which greatly limits the selectivity of olefins. Summary of the invention

[0004] The present invention aims to provide a TiO2 co-modified with Ni single atom and Pd nanoparticles. 2 A photocatalyst and a preparation method thereof and application in photocatalytic non-oxidative dehydrogenation of alkanes to olefins. The photocatalyst has excellent activity and selectivity for olefins, and has strong stability and strong resistance to carbon deposition.

[0005] To achieve the above object, the present invention adopts the following technical solution: One of the purposes of the present invention is to protect a TiO2 co-modified with Ni single atom and Pd nanoparticles. 2 Photocatalyst, in which Ni in the form of single atoms and Pd in ​​the form of nanoparticles are uniformly distributed on TiO 2 surface, constituting the TiO 2 Photocatalyst.

[0006] Furthermore, in the photocatalyst, the content of Ni is 0.4wt%~1wt%, and the content of Pd is 0.2wt%~1.5wt%.

[0007] The second purpose of the present invention is to protect the TiO2 co-modified by the Ni single atom and Pd nanoparticles. 2 The preparation method of the photocatalyst comprises the following steps: 1) Anatase TiO 2 After being pressed, the tablet is placed in a quartz reaction tube and treated at 400°C in a flowing oxygen atmosphere for 10h~15h, then treated at 400°C for 2h~4h under dynamic vacuum conditions, and then cooled naturally to room temperature; 2) dissolving the organic transition metal compound in n-hexane to form a supersaturated solution, and then injecting the solution into the quartz reaction tube of step 1) in a liquid nitrogen cold trap environment, then removing the n-hexane under dynamic vacuum conditions, and then calcining under vacuum conditions, and then evacuating the solution again under dynamic vacuum after the calcination is completed; 3) calcining the sample obtained in step 2) in an oxygen atmosphere and then grinding it to obtain a solid powder; 4) Disperse the solid powder obtained in step 3) in deionized water and add H 2 PdCl 4 The solution was stirred at 300 mW·cm -2 The sample was irradiated with a xenon lamp for 5 min to 30 min, and then washed with deionized water and dried overnight to obtain the TiO 2 Photocatalyst.

[0008] Furthermore, the organic transition metal compound in step 2) is nickelocene.

[0009] Furthermore, in step 2), the calcination temperature is 100° C. to 200° C., and the calcination time is 12 h to 30 h.

[0010] Furthermore, the pressure range of the vacuum conditions used in the operation is 10 -2 ~10Pa.

[0011] Furthermore, in step 3), the calcination temperature is 300° C. to 400° C., and the calcination time is 10 h to 16 h.

[0012] Further, in step 4), H2 PdCl 4 The concentration of the solution was 1 mg / mL.

[0013] The third purpose of the present invention is to protect the TiO2 co-modified by the Ni single atom and Pd nanoparticles. 2 Application of photocatalysts in the photocatalytic nonoxidative dehydrogenation of alkanes to olefins.

[0014] Furthermore, the application method is to use a reactor with a volume of 200 mL, in an inert gas atmosphere, to use the TiO2 co-modified with the Ni single atom and Pd nanoparticles. 2 Photocatalyst (5~50mg) can be used for non-oxidative dehydrogenation of alkanes under light, normal temperature and pressure conditions.

[0015] Furthermore, the inert gas is argon, the alkane is one of ethane and propane, and the molar ratio of the inert gas to the alkane is 9-99:1.

[0016] Furthermore, the intensity of the light used was 300 mW·cm -2 .

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention prepares highly efficient and stable Ni single atom and Pd nanoparticle co-modified TiO by combining surface organometallic chemistry and photodeposition. 2 The photocatalyst has excellent activity and olefin selectivity compared with other photocatalysts.

[0018] (2) In the photocatalyst structure prepared by the present invention, the Ni single atom can regulate the adsorption and desorption ability of Pd nanoparticles to olefins, thereby further improving the selectivity of olefins and the stability of the catalyst.

[0019] (3) The preparation method of the present invention has low energy consumption, readily available raw materials, and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The T-Ni prepared in Example 1 0.6 Pd 0.24 Spherical aberration transmission electron microscopy image of the photocatalyst.

[0021] Figure 2 The T-Ni prepared in Example 1 0.6 Pd 0.24 Cyclic stability test diagram of photocatalyst.

[0022] Figure 3 This is a performance comparison chart of the photocatalysts prepared in Examples 1 to 4 for photocatalytic non-oxidative dehydrogenation of ethane to ethylene. DETAILED DESCRIPTION

[0023] A TiO2 co-modified with Ni single atoms and Pd nanoparticles 2 The photocatalyst, the preparation method thereof comprises the following steps: 1) Anatase TiO 2 After being pressed, the tablet is placed in a quartz reaction tube and treated at 400°C in a flowing oxygen atmosphere for 10h~15h, then treated at 400°C for 2h~4h under dynamic vacuum conditions, and then cooled naturally to room temperature; 2) dissolving nickelocene in n-hexane to form a supersaturated solution, and then injecting the solution into the quartz reaction tube of step 1) in a liquid nitrogen cold trap environment, then removing the n-hexane under dynamic vacuum conditions, and then calcining at 100°C~200°C for 12h~30h under vacuum conditions (heating rate of 1°C / min~5°C / min), and performing dynamic vacuum extraction again after calcination; 3) calcining the sample obtained in step 2) at 300° C. to 400° C. for 10 h to 16 h in an oxygen atmosphere, and then grinding to obtain a solid powder; 4) Disperse the solid powder obtained in step 3) in deionized water and add 1 mg / mL of H 2 PdCl 4 The solution was stirred at 300 mW·cm -2 The sample was irradiated with a xenon lamp for 5 min to 30 min, and then washed with deionized water and dried overnight to obtain the TiO 2 Photocatalyst.

[0024] The vacuum conditions used in the operation range from 10 -2 ~10Pa.

[0025] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0026] Example 1 1) 50 mg of anatase TiO 2 After being pressed, the pellets were placed in a quartz reaction tube with a sliding core and treated at 400°C in a flowing oxygen atmosphere for 12 h. -2 Pa dynamic vacuum condition at 400 °C for 3 h, and then naturally cooled to room temperature; 2) Dissolve nickelocene in n-hexane to form a supersaturated solution, then take 50 μL of the solution and inject it into the reaction tube in step 1) in a liquid nitrogen cold trap environment, then add n-hexane at 10 -2 Pa dynamic vacuum conditions, followed by calcination at 130 ° C for 30 h. -2Pumping under dynamic vacuum conditions for 3h; 3) calcining the sample obtained in step 2) at 400° C. in an oxygen atmosphere for 12 h, and then grinding to obtain a solid powder; 4) Disperse the solid powder obtained in step 3) in 50 mL of deionized water and add 0.35 mL of 1 mg / mL H 2 PdCl 4 The solution was stirred at 300 mW·cm -2 Xenon lamp irradiation for 10 minutes; 5) The sample obtained in step 4) was washed with deionized water for 5 times and dried at 80 °C overnight to obtain T-Ni 0.6 Pd 0.24 Photocatalyst.

[0027] Figure 1 The T-Ni prepared in this example 0.6 Pd 0.24 Spherical aberration transmission electron microscopy images of photocatalysts. As can be seen from Figure a, the Ni atoms in the prepared photocatalyst are dispersed in isolation on the catalyst surface; as can be seen from Figure b, Pd is distributed on the catalyst surface in the form of nanoparticles.

[0028] Figure 2 The T-Ni prepared in this example 0.6 Pd 0.24 Cyclic stability test diagram of the photocatalyst. It can be seen from the figure that the prepared photocatalyst has excellent performance, and its ethylene yield is 956.3 μmol·g -1 ·h -1 , and the production of nearly stoichiometric H 2 (890.6 μmol·g -1 ·h -1 ); and after ten cycles, the photocatalyst still maintains high activity, indicating that the photocatalyst has high activity, stability and anti-carbon deposition ability.

[0029] Example 2 The preparation method is the same as that of Example 1, except that 30 μL of the solution in step 2) is taken and injected into the reaction tube in step 1) in a liquid nitrogen cold trap environment to obtain T-Ni 0.4 Pd 0.24 Photocatalyst.

[0030] Example 3 The preparation method is the same as that in Example 1, except that 70 μL of the solution in step 2) is taken and injected into the reaction tube in step 1) in a liquid nitrogen cold trap environment to obtain T-Ni 0.8 Pd 0.24 Photocatalyst.

[0031] Example 4 The preparation method is the same as that of Example 1, except that 90 μL of the solution in step 2) is taken and injected into the reaction tube in step 1) in a liquid nitrogen cold trap environment to obtain T-Ni 1.0 Pd 0.24 Photocatalyst.

[0032] Figure 3 The performance diagram of the photocatalyst prepared in Examples 1 to 4 for the photocatalytic non-oxidative dehydrogenation of ethane to ethylene is shown in the figure. As can be seen from the figure, the performance is best when the Ni content in the photocatalyst is 0.6%.

[0033] Comparative Example 1 1) 50 mg of anatase TiO 2 After being pressed, the pellets were placed in a quartz reaction tube with a sliding core and treated at 400°C in a flowing oxygen atmosphere for 12 h. -2 Pa dynamic vacuum condition at 400 °C for 3 h, and then naturally cooled to room temperature; 2) Dissolve nickelocene in n-hexane to form a supersaturated solution, then take 50 μL of the solution and inject it into the reaction tube in step 1) in a liquid nitrogen cold trap environment, then add n-hexane at 10 -2 Pa dynamic vacuum conditions, followed by calcination at 130 ° C for 30 h. -2 Pumping under dynamic vacuum conditions for 3h; 3) The sample obtained in step 2) was calcined at 400°C in an oxygen atmosphere for 12 h, and then ground to obtain T-Ni 0.6 Photocatalyst.

[0034] Comparative Example 2 1) 50 mg of anatase TiO 2 The powder was dispersed in 50 mL of deionized water and 0.35 mL of 1 mg / mL H 2 PdCl 4 The solution was stirred at 300 mW·cm -2 Xenon lamp irradiation for 10 minutes; 2) The sample obtained in step 1) was washed with deionized water for 5 times and dried at 80 °C overnight to obtain T-Pd 0.24 Photocatalyst.

[0035] Comparative Example 3 1) 50 mg of anatase TiO 2 After being pressed, the pellets were placed in a quartz reaction tube with a sliding core and treated at 400°C in a flowing oxygen atmosphere for 12 h. -2 Pa dynamic vacuum condition at 400 °C for 3 h, and then naturally cooled to room temperature; 2) Dissolve ruthenocene in n-hexane to form a supersaturated solution, then take 70 μL of the solution and inject it into the reaction tube in step 1) in a liquid nitrogen cold trap environment, then add n-hexane at 10 -2 Pa dynamic vacuum conditions, and then calcined at 150 ° C for 30 h under vacuum conditions. After calcination, -2 Pumping under dynamic vacuum conditions for 3h; 3) calcining the sample obtained in step 2) at 400° C. in an oxygen atmosphere for 12 h, and then grinding to obtain a solid powder; 4) Disperse the solid powder obtained in step 3) in 50 mL of deionized water and add 0.35 mL of 1 mg / mL H 2 PdCl 4 The solution was stirred at 300 mW·cm -2 Xenon lamp irradiation for 10 minutes; 5) The sample obtained in step 4) was washed with deionized water for 5 times and dried at 80°C overnight to obtain T-Ru 0.6 Pd 0.24 Photocatalyst.

[0036] Comparative Example 4 The preparation method is the same as that of Comparative Example 3, except that in step 2), cobaltocene is dissolved in n-hexane to form a supersaturated solution, and then 70 μL of the solution is taken and injected into the reaction tube of step 1) in a liquid nitrogen cold trap environment to obtain T-Co 0.6 Pd 0.24 Photocatalyst.

[0037] Performance test of photocatalytic non-oxidative dehydrogenation of alkanes to olefins The photocatalytic non-oxidative dehydrogenation of alkanes to olefins was carried out in a glass-enclosed batch reactor (volume 200 mL) with a quartz window on the top of the reactor to allow light irradiation. The specific operation was to disperse 5 mg of catalyst into 1 ml of H 2 O was added and ultrasonically treated for 5 min to obtain a slurry, which was then coated on a quartz plate and dried to form a catalyst film; the obtained catalyst film was then fixed in a reactor, and all experiments were performed at normal pressure (101 kPa). Before the reaction, the system was evacuated with a mechanical pump, and then filled with 101 kPa of high-purity Ar (>99.99%) for 30 min to make the O in the system 2 Then, use a syringe to inject 2 ml of C 2 H 6 or C 3 H 8 The system was then illuminated at room temperature using a 300 W xenon lamp (300 mW·cm -2) for 4 h, and 0.5 mL of gas was extracted every 1 h, and the product concentration was detected by gas chromatography (GC). The obtained alkanes were analyzed by flame ionization detector (FID) gas chromatography on Agilent 7890A, and the gas phase products were separated by HP-PLOT Q capillary column. Hydrogen was analyzed by thermal conductivity detector (TCD) gas chromatography on Agilent 7890B, and the product gas was separated by 5A molecular sieve packed column and Porapak q packed column.

[0038] Tables 1 and 2 are the comparisons of the photocatalytic activity of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 4 for the non-oxidative dehydrogenation of ethane and propane to olefins. It can be seen from the table that the photocatalyst prepared in Example 1 has the highest photocatalytic performance.

[0039] Table 1 Comparison of photocatalytic activity of different catalysts for non-oxidative dehydrogenation of ethane to ethylene

[0040] Table 2 Comparison of photocatalytic activity of different catalysts for non-oxidative dehydrogenation of propane to propylene

[0041] Comparative Example 5 50 mg of anatase TiO 2 NiCl containing 0.3 mg of metallic Ni 2 6H 2 O solution, then stirred and dried at 80 °C, and then calcined in a muffle furnace at 400 °C for 12 h to obtain a solid powder. The obtained solid powder was fully ground and dispersed in 50 mL of deionized water, and 0.35 mL of 1 mg / mL H 2 PdCl 4 The solution was stirred at 300 mW·cm -2 The sample was irradiated with xenon light for 10 min. The obtained sample was washed with deionized water 5 times and dried at 80 °C overnight to obtain iT-Ni 0.6 Pd 0.24 Photocatalyst.

[0042] Comparative Example 6 The preparation method is the same as that of Example 1, except that the obtained T-Ni 0.6 Pd 0.24 The photocatalyst was then calcined at 400 °C in an oxygen atmosphere for 12 h to obtain T-Ni 0.6 Pd 0.24 O photocatalyst.

[0043] Table 3 is a comparison of the photocatalytic activities of the photocatalysts prepared in Example 1 and Comparative Examples 5 to 6 for the photocatalytic non-oxidative dehydrogenation of ethane to ethylene. As can be seen from the table, the photocatalyst prepared in Example 1 has the best performance, which indicates that the synergistic effect of single-atom Ni and Pd nanoparticles is the best.

[0044] Table 3 Comparison of photocatalytic activity of different catalysts for non-oxidative dehydrogenation of ethane to ethylene

[0045] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles, characterized in that: Ni is evenly distributed on the surface of TiO2 in the form of single atoms and Pd is evenly distributed on the surface of TiO2 in the form of nanoparticles, forming the TiO2 photocatalyst.

2. The TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles according to claim 1, characterized in that: In the photocatalyst, the content of Ni is 0.4wt%~1wt%, and the content of Pd is 0.2wt%~1.5wt%.

3. A method for preparing the TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles as claimed in claim 1, characterized in that: The following steps are involved: 1) After pressing anatase TiO2 into a pellet, place it in a quartz reaction tube and treat it at 400℃ in a flowing oxygen atmosphere for 10h~15h, then treat it at 400℃ under dynamic vacuum conditions for 2h~4h, and then cool it naturally to room temperature; 2) dissolving the organic transition metal compound in n-hexane to form a supersaturated solution, and then injecting the solution into the quartz reaction tube of step 1) in a liquid nitrogen cold trap environment, then removing the n-hexane under dynamic vacuum conditions, and then calcining under vacuum conditions, and then evacuating the solution again under dynamic vacuum after the calcination is completed; 3) calcining the sample obtained in step 2) in an oxygen atmosphere and then grinding it to obtain a solid powder; 4) The solid powder obtained in step 3) was dispersed in deionized water, H2PdCl4 solution was added, and the mixture was heated at 300 mW·cm under stirring. -2 The sample was irradiated with xenon light for 5 min to 30 min, and then washed with deionized water and dried overnight to obtain the TiO2 photocatalyst.

4. The method for preparing the TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles according to claim 3, characterized in that: The organic transition metal compound in step 2) is nickelocene.

5. The method for preparing the TiO2 photocatalyst co-modified with Ni single atom and Pd nanoparticles according to claim 3, characterized in that: The calcination temperature in step 2) is 100°C to 200°C, and the calcination time is 12h to 30h.

6. The method for preparing the TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles according to claim 3, characterized in that: The vacuum conditions used in the operation range from 10 -2 ~10Pa.

7. The method for preparing the TiO2 photocatalyst co-modified with Ni single atom and Pd nanoparticles according to claim 3, characterized in that: The calcination temperature in step 3) is 300°C to 400°C, and the calcination time is 10h to 16h.

8. The method for preparing the TiO2 photocatalyst co-modified with Ni single atom and Pd nanoparticles according to claim 3, characterized in that: The concentration of the H2PdCl4 solution in step 4) is 1 mg / mL.

9. Use of the TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles as claimed in claim 1 in the photocatalytic non-oxidative dehydrogenation of alkanes to olefins.

10. The use according to claim 9, characterized in that: The application method is to use the Ni single atom and Pd nanoparticle co-modified TiO2 photocatalyst to perform non-oxidative dehydrogenation of alkanes under light, normal temperature and pressure conditions in an inert gas atmosphere; The inert gas is argon, the alkane is one of ethane and propane, and the molar ratio of the inert gas to the alkane is 9-99:1; the intensity of the light used is 300 mW·cm -2 .

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